Description:TECHNICAL FIELD
[0001] The present disclosure relates to geopolymer chemistry, in particular, the present disclosure relates to a geopolymer composition and a method for producing geopolymer with reduced efflorescence.
BACKGROUND
[0002] In the construction industry, there is a growing demand for sustainable alternatives to traditional cement-based materials due to increasing concerns over environmental degradation, carbon emissions, and resource depletion. The sustainable alternatives include geopolymers, which act as an eco-friendly alternative to the traditional cement-based materials. Moreover, the geopolymer has suitable compressive strength, enhanced chemical resistance, thermal stability, long-term durability, and a reduced carbon footprint compared to traditional cement-based materials. However, one of the challenges limiting the widespread use of the geopolymer is the phenomenon of efflorescence. Efflorescence is a white, powdery deposits that form on the surface of geopolymer materials. The efflorescence affects the durability of the geopolymer material. The efflorescence forms from the migration and crystallisation of free alkali ions, such as sodium, when exposed to moisture and carbon dioxide. Thus, there exists a technical problem of how to develop an efflorescence-free geopolymer for architectural applications.
[0003] Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks.
SUMMARY
[0004] The present disclosure provides a geopolymer composition, a method for producing geopolymer with reduced efflorescence. The present disclosure addresses the technical problem of how to develop an efflorescence-free geopolymer for architectural applications. An aim of the present disclosure is to provide a solution that overcomes at least partially the problems encountered in the prior art and provides an improved nanofiber composite and an improved method for preparing the nanofiber composite featuring a three-dimensional fibrous network for lead adsorption from water.
[0005] One or more objectives of the present disclosure is achieved by the solutions provided in the enclosed independent claims. Advantageous implementations of the present disclosure are further defined in the dependent claims.
[0006] In one aspect, the present disclosure provides a geopolymer composition with reduced efflorescence, comprising:
a geopolymer binder constituting 25-35% by weight of a total composition, the geopolymer binder comprising ground granulated blast furnace slag (GGBS) and fly ash (FA);
fine aggregate constituting 60-75% by weight of the total composition;
red mud in an amount of 5-15% by weight of the fine aggregate; and
an alkaline activator comprising sodium hydroxide;
wherein the red mud comprises alumina and silica compounds that react with unreacted sodium ions from the sodium hydroxide to form sodium-alumino-silicate minerals within the geopolymer binder which immobilize the sodium ions to prevent efflorescence.
[0007] By incorporating red mud in an amount of 5-15% by weight of the fine aggregate, the geopolymer composition provides a dual mechanism for efflorescence control. The dual mechanism includes chemical binding of sodium ions through the formation of sodium-alumino-silicate minerals, and optimisation of the pore structure to facilitate early leaching of excess free sodium. The 25-35% by weight proportion of geopolymer binder and 60-75% by weight proportion of fine aggregate ensures suitable workability with flow values between 130-139%, facilitating proper placement while maintaining cohesion. Additionally, the alumina and silica compounds in red mud enable a reduction in sodium hydroxide concentration from four molar to as low as two molars. Furthermore, the geopolymer composition transforms the red mud from an environmental liability into a valuable construction material component, promoting resource efficiency while delivering efflorescence resistance and adequate mechanical performance for non-load-bearing architectural applications.
[0008] In another aspect, the present disclosure provides a method for producing a geopolymer with reduced efflorescence, the method comprising:
preparing a dry mixture comprising ground granulated blast furnace slag (GGBS) and fly ash (FA), wherein the GGBS and the FA together constitute 25-35% by weight of a total composition;
adding fine aggregate to the dry mixture, wherein the fine aggregate constitutes 60-75% by weight of the total composition;
incorporating red mud in an amount of 5-15% by weight of the fine aggregate;
dry-mixing the GGBS, the FA, the fine aggregate, and the red mud to form a homogenous powder;
preparing a sodium hydroxide solution;
adding the sodium hydroxide solution to the homogenous powder and mixing to form a geopolymer mortar; and
curing the geopolymer mortar, wherein during curing, alumina and silica compounds in the red mud react with unreacted sodium ions from the sodium hydroxide to form sodium-alumino-silicate minerals which immobilize the sodium ions to prevent efflorescence.
[0009] The method for producing a geopolymer with reduced efflorescence achieves all the advantages and technical effects of the geopolymer composition with reduced efflorescence formed in the present disclosure.
[0010] Additional aspects of the present disclosure would be made apparent from the drawings and the detailed description of the illustrative implementations construed in conjunction with the appended claims that follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not to scale. Wherever possible, like elements have been indicated by identical numbers.
[0012] Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:
FIG.1 is a flowchart illustrating a method for producing a geopolymer with reduced efflorescence, in accordance with an embodiment of the present disclosure;
FIG. 2 is a graphical representation illustrating an X-ray diffraction (XRD) pattern of geopolymer samples, in accordance with an embodiment of the present disclosure;
FIG. 3 is a graphical representation illustrating an X-ray diffraction (XRD) pattern of geopolymer formulations with red mud and lime, in accordance with an embodiment of the present disclosure;
FIG. 4A is a graphical representation illustrating effect of red mud on water permeable porosity of geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 4B is a graphical representation illustrating effect of lime addition on water permeable porosity of geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 4C is a graphical representation illustrating effect of steam curing on water permeable porosity of geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 4D is a graphical representation illustrating effect of carbonation on water permeable porosity of geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 4E is a graphical representation illustrating pore volume distributions in geopolymer formulations subjected to different curing conditions, in accordance with an embodiment of the present disclosure;
FIG. 5A is a graphical representation illustrating effect of red mud on flexural strength of geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 5B is a graphical representation illustrating effect of lime on flexural strength of geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 5C is a graphical representation illustrating effect of steam curing on flexural strength of geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 5D is a graphical representation illustrating effect of carbon curing on flexural strength of geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 6A is a graphical representation illustrating effect of molarity on compressive strength development of geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 6B is a graphical representation illustrating effect of red mud on compressive strength development of geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 6C is a graphical representation illustrating effect of lime and quartz addition on compressive strength development of geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 6D is a graphical representation illustrating effect of carbon curing on compressive strength development of geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 6E is a graphical representation illustrating effect of steam curing on compressive strength development of geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 7A is a diagram illustrating a scanning electron microscope (SEM) image of an exemplary geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 7B is a graphical representation illustrating an energy dispersive spectroscopy (EDS) analysis of the exemplary geopolymer formulation, in accordance with an embodiment of present disclosure;
FIG. 8A is a diagram illustrating a scanning electron microscope (SEM) image of another geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 8B is a graphical representation illustrating an energy dispersive spectroscopy (EDS) analysis of another exemplary geopolymer formulation, in accordance with an embodiment of present disclosure;
FIG. 9A is a diagram illustrating a scanning electron microscope (SEM) image of yet another exemplary geopolymer formulation, in accordance with an embodiment of the present disclosure;
FIG. 9B is a graphical representation illustrating an energy dispersive spectroscopy (EDS) analysis of yet another exemplary geopolymer formulation, in accordance with an embodiment of present disclosure;
FIG. 10A is a graphical representation illustrating effect of red mud on total shrinkage of geopolymer formulation, in accordance with an embodiment of the present disclosure; and
FIG. 10B is a graphical representation illustrating effect of lime addition on total shrinkage of geopolymer formulation, in accordance with an embodiment of the present disclosure.
[0013] In the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing.
DETAILED DESCRIPTION OF EMBODIMENTS
[0014] The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognise that other embodiments for carrying out or practicing the present disclosure are also possible.
[0015] FIG.1 is a flowchart illustrating a method for producing a geopolymer with reduced efflorescence, in accordance with an embodiment of the present disclosure. With reference to FIG. 1, a method 100 includes steps 102 to 114.
[0016] At step 102, the method 100 (interchangeably referred to as “the batch method”) includes preparing a dry mixture comprising ground granulated blast furnace slag (GGBS) and fly ash (FA). GGBS is a fine, powdery material obtained by rapidly cooling molten slag. The molten slag is a by-product of iron production in blast furnaces using water or steam, followed by drying and grinding. The GGBS is a calcium-rich aluminosilicate material known for the latent hydraulic and pozzolanic reactivity in alkaline environments. The fly ash refers to the fine particulate residue collected from the flue gases of coal-fired power plants. In an implementation, the fly ash used is Class F fly ash, characterised by a high content of silicon dioxide (SiO₂), aluminium oxide (Al₂O₃), and iron oxide (Fe₂O₃), and a relatively low content of calcium oxide (CaO). The dry mixture is an aluminosilicate binder activated by alkaline activators, for example, potassium hydroxide (KOH), sodium hydroxide (NaOH), and silicates. In an implementation, the aluminosilicate binder includes ground granulated blast furnace slag (GGBS), fly ash (FA), metakaolin, and the like minerals rich in calcium, silicon, and aluminium.
[0017] In an implementation, the GGBS and the FA are combined in a ratio of 80-90:10-20 by weight. For example, the dry mixture is formed by weighing and combining 85 parts by weight of GGBS and 15 parts by weight of FA using an electronic precision balance to ensure formulation accuracy. The measured quantities of the GGBS and the FA are then transferred into a planetary mechanical mixer equipped with a stainless-steel mixing bowl and rotating blades configured for uniform blending of fine powders of the GGBS and the FA. In an implementation, the measured quantities of the GGBS and the FA are then transferred into a horizontal pan mixer for uniform blending. In another implementation, the dry mixing was carried out for 2 minutes to achieve a homogeneous dispersion of the particles and oxide phases. The mixing was periodically paused to manually scrape the sidewalls and bottom of the stainless-steel mixing bowl using a stainless-steel spatula to prevent material build-up and ensure complete blending. The mixing resulted in the aluminosilicate binder suitable for subsequent integration with alkaline activators during geopolymer formation. The GGBS and the FA together constitute 25-35% by weight of a total composition. The total composition of the geopolymer has 25-35% by weight GGBS and FA, indicating a balance between the aluminosilicate binder and the fine aggregate to ensure adequate mechanical strength, workability, and durability.
[0018] At step 104, the method 100 includes adding fine aggregate to the dry mixture. The fine aggregate refers to granular materials that pass through a 4.75 mm sieve and are configured to provide bulk, dimensional stability, and internal structure to the geopolymer material. In an implementation, the fine aggregate includes manufactured sand. The manufactured sand is processed by mechanically crushing hard granite stones and sieving to a uniform particle distribution.
[0019] In an implementation, the fine aggregate constitutes 60% to 75% by weight of the total composition. The fine aggregate is measured using an electronic balance and added to the dry mixture of GGBS and FA in a planetary mechanical mixer or a horizontal pan mixer. The mixing is continued for an additional 1 to 2 minutes, ensuring uniform dispersion of the fine aggregate throughout the dry mixer.
[0020] At step 106, the method 100 includes incorporating red mud in an amount of 5-15% by weight of the fine aggregate. The red mud is an alkaline industrial waste material rich in alumina (Al₂O₃), silica (SiO₂), and sodium oxide (Na₂O). In an implementation, the red mud is dried, pulverised, and sieved through a 75 µm mesh before being added to the dry mixture. The red mud contributes reactive aluminosilicate species that are configured to interact with free sodium ions during geopolymer curing. The reaction of the aluminosilicate species with free sodium ions reduces the availability of mobile sodium ions responsible for the formation of efflorescence. The red mud is added in an amount ranging from 5% to 15% by weight of the fine aggregate. In an example, red mud was incorporated at 5% by weight of the total fine aggregate.
[0021] The total quantity of fine aggregate used was 200 parts by weight. Accordingly, 10 parts by weight of red mud were used to replace an equivalent amount of manufactured sand. The final aggregate mix consisted of 190 parts of manufactured sand and 10 parts of red mud. In another example, 10% of the fine aggregate was replaced with the red mud. The total quantity of the fine aggregate used was 200 parts by weight. Accordingly, 20 parts by weight of red mud were added, replacing an equal mass of manufactured sand. As a result, the aggregate portion consisted of 180 parts of the manufactured sand and 20 parts of the red mud. In yet another example, 15% of the fine aggregate was replaced with the red mud. The total quantity of the fine aggregate used was 200 parts by weight. Accordingly, a quantity of 30 parts by weight of red mud was added, reducing the manufactured sand content to 170 parts by weight.
[0022] The amount of the red mud is selected based on the in-situ sodium oxide content of the red mud and the overall alkalinity required for the geopolymerization. For instance, if a higher amount of red mud with significant sodium oxide content is used, the external NaOH concentration can be reduced proportionally to avoid excessive free sodium ions in the geopolymer, which could otherwise lead to efflorescence. Conversely, if the red mud has low sodium oxide content, a higher sodium hydroxide molarity may be necessary to ensure sufficient dissolution of the aluminosilicate binder. Therefore, careful assessment and adjustment of the red mud dosage based on its sodium oxide content is vital for maintaining the alkaline equilibrium necessary for the formation of geopolymer gels for example, sodium-alumino-silicate hydrate (N-A-S-H), while also controlling the availability of unbound sodium ions that contribute to surface salt deposition.
[0023] At step 108, the method 100 includes dry mixing the ground granulated blast furnace slag (GGBS), fly ash (FA), fine aggregate, and red mud to form a homogeneous powder blend. This step ensures that the GGBS, FA, fine aggregate and red mud of the geopolymer composition are uniformly distributed before the addition of the alkaline activator. The dry mixing is carried out in a planetary mechanical mixer or a horizontal pan mixer. In an implementation, the mixing duration is in the range of 2 to 3 minutes, sufficient to eliminate agglomerates and achieve a homogenous powder. In an example, during dry mixing, the planetary mechanical mixer is periodically paused, and the inner walls and bottom of the mixing bowl are scraped manually using a stainless-steel spatula to avoid material build-up and ensure consistent blending. The homogeneous powder comprises reactive aluminosilicate binder from the dry mixture comprising GGBS and FA, inert and reactive silica-containing particles from the fine aggregate, and sodium- and alumina-rich components from the red mud.
[0024] At step 110, the method 100 includes preparing a sodium hydroxide solution. The sodium hydroxide solution is used as the alkaline activator in the geopolymer composition. The sodium hydroxide functions as a chemical reagent that dissolves the reactive aluminosilicate binder and initiates the geopolymerization reaction, leading to the formation of a three-dimensional alumino-silicate network.
[0025] In an example, solid sodium hydroxide pellets are measured using an electronic analytical balance and dissolved in 100 mL of distilled water under continuous stirring to form a homogeneous alkaline solution. The dissolution process is exothermic and results in a significant rise in temperature. Therefore, the homogeneous alkaline solution is allowed to cool to ambient temperature, approximately ranging between 23-27 degrees Celsius.
[0026] The total amount of sodium hydroxide solution prepared is determined based on the required solution-to-binder (S/B) ratio, falling within the range of 0.70 to 0.80 by weight, as claimed in claim 5. This ratio ensures optimal workability, consistency, and reaction kinetics. A higher S/B ratio may improve flow characteristics but can increase porosity, while a lower ratio may result in insufficient activation of binder phases. The prepared alkaline solution is held in a sealed polypropylene container until ready for use to prevent contamination and carbon dioxide absorption from the ambient atmosphere.
[0027] In an implementation, the sodium hydroxide solution has a concentration of 2-4 molar (M). In an example, to prepare a 2M sodium hydroxide (NaOH) solution, 8 grams of solid sodium hydroxide pellets are measured using the electronic analytical balance and dissolved in 100 millilitres of distilled water under continuous stirring until a clear and homogeneous solution is formed. In another example, to prepare a 3M sodium hydroxide solution, 12 grams of solid NaOH pellets are weighed and added to 100 millilitres of distilled water. The mixture of solid sodium hydroxide and distilled water is stirred continuously to ensure complete dissolution and uniformity. In yet another example, to prepare a 4M sodium hydroxide solution, 16 grams of solid NaOH pellets are measured and gradually added to 100 millilitres of distilled water while stirring.
[0028] At step 112, the method 100 includes adding the sodium hydroxide solution to the homogenous powder and mixing to form a geopolymer mortar. The sodium hydroxide solution is introduced to the homogenous powder mixture comprising GGBS, FA, fine aggregate, and red mud. In an implementation, the sodium hydroxide solution is added to the homogenous powder at a solution-to-binder ratio of 0.70-0.80 by weight. The sodium hydroxide solution is added to the homogenous powder over 30 seconds, followed by 3 minutes of continuous mechanical mixing in a planetary mixer. Further, after scraping the sides and bottom of the planetary mixer, an additional 2 minutes of mixing is performed to achieve complete homogeneity. The solution-to-binder ratio below 0.70 would result in insufficient workability, making the geopolymer mortar difficult to cast and causing inadequate consolidation and increased porosity. Conversely, a ratio exceeding 0.80 would introduce excess water to the geopolymer mortar, diluting the concentration of the sodium hydroxide solution and creating additional pathways for efflorescence formation.
[0029] In an implementation, the geopolymer mortar has a flowability of 130-140%. The flowability is useful for ensuring proper placement of the geopolymer mortar in various applications for example, masonry joints, formwork filling, and surface overlays, while maintaining cohesion and minimising segregation.
[0030] At step 114, the method 100 includes curing the geopolymer mortar. During the curing, alumina and silica compounds in the red mud react with unreacted sodium ions from the sodium hydroxide to form sodium-alumino-silicate minerals, which immobilise the sodium ions to prevent efflorescence. In an implementation, the curing includes moist curing under wet burlap at ambient temperature. The geopolymer mortar is cast into appropriate moulds and covered with wet burlap sheets. The burlap sheets refer to coarse woven fabric sheets made from natural jute or hemp fibres. The burlap sheets are kept moist during curing to help retain surface moisture, regulate temperature, and prevent premature drying or cracking of the geopolymer mortar, thereby promoting proper hydration and strength development. The burlap sheets are maintained in a saturated condition by periodic water spraying to ensure a relative humidity of at least 90%. The saturated condition is maintained for 22-24 hours at a temperature approximately ranging between 25-30 degrees Celsius. The high humidity environment prevents premature water loss from the geopolymer mortar, promoting continued dissolution and polycondensation reactions for strength development of the geopolymer.
[0031] In another implementation, the curing includes exposure to 3-7% carbon dioxide for 1-3 hours, followed by curing under wet burlap. The geopolymer mortar is placed in a carbon dioxide incubator maintained at 5% carbon dioxide concentration for 2 hours. The controlled exposure to elevated carbon dioxide levels accelerates the carbonation of free sodium ions at the surface of the geopolymer, thereby reducing the ability of the free sodium ions to migrate and form efflorescence deposits. Following the carbon dioxide exposure, the specimens are wrapped in wet burlap for an additional 22 hours to ensure continued hydration and geopolymerization reactions.
[0032] In yet another implementation, the curing includes steam curing at 45-55 degrees Celsius for 1-3 hours, followed by wet burlap curing. The geopolymer mortar is exposed to steam curing at 50 degrees Celsius for 2 hours in a controlled steam chamber. The temperature in the steam chamber accelerates the dissolution of alumina and silica from the aluminosilicate binder and red mud, enhancing the formation of N-A-S-H gels and zeolite-like phases that can effectively bind sodium ions. Experimental results demonstrate that steam-cured specimens exhibit significantly reduced efflorescence compared to ambient-cured specimens, particularly for formulations containing 5% red mud (3M-5R). Following the steam curing, the geopolymer mortar is wrapped in wet burlap for an additional 22 hours to prevent moisture loss and ensure continued reaction progression.
[0033] In an implementation, the method 100 further includes immersing the geopolymer mortar after curing in water for 18-30 hours to remove excess free sodium ions. The immersion of the geopolymer mortar in water serves as a leaching process that removes residual soluble sodium ions from the geopolymer matrix before they can contribute to efflorescence. In an example, the geopolymer matrix is immersed in distilled water maintained at a temperature approximately ranging between 20-24 degrees Celsius for 24 hours. The water to geopolymer mortar volume ratio is maintained at 3:1 to ensure sufficient dilution of leached sodium ions.
[0034] In another implementation, the concentration of the sodium hydroxide solution is reduced by 0.5-1 molar relative to a baseline concentration in consideration of the in-situ sodium hydroxide content of the red mud. The red mud contains 5-10% sodium oxide by weight. For instance, when incorporating 10% red mud as a replacement for fine aggregate, the sodium hydroxide concentration can be reduced from 3M to 2M without compromising the geopolymerization process. The reduction in external alkaline activator (sodium hydroxide minimises the risk of efflorescence by reducing the total sodium content in the geopolymer while maintaining adequate alkalinity for dissolution and polycondensation reactions.
[0035] The steps 102 to 114 are only illustrative, and other alternatives can also be provided where one or more steps are added, one or more steps are removed, or one or more steps are provided in a different sequence without departing from the scope of the claims herein.
[0036] The geopolymer composition with reduced efflorescence includes the geopolymer binder, constituting 25-35% by weight of the total composition. The geopolymer binder includes ground granulated blast furnace slag (GGBS) and fly ash (FA). The GGBS and FA together function as the primary reactive aluminosilicate binder. In an example, in the 3M-10R geopolymer formulation, the combined GGBS and FA constitute 33.3% by weight of the total composition (85g GGBS and 15g FA in a total mix of 300g), providing suitable aluminosilicate species for geopolymerization. The precise control of the content of the geopolymer binder enables the formation of a three-dimensional network structure of a geopolymer with sufficient strength for masonry applications while minimising material costs.
[0037] In an implementation, the geopolymer binder comprises 80-90% by weight GGBS and 10-20% by weight FA. For example, when the geopolymer binder contains 85% GGBS and 15% FA (as used in the exemplary 3M-10R formulation), the calcium from GGBS promotes the formation of calcium-alumino-silicate-hydrate (C-A-S-H) gels that contribute to early strength development, while the FA supplies additional reactive silica and alumina to produce sodium-alumino-silicate-hydrate (N-A-S-H) gels that can incorporate free sodium ions. In another example, when 80% GGBS and 20% FA are used (as in the 3M-5R-0Q-5L formulation with 5% lime replacement), the higher proportion of FA provides more reactive silica for binding with the calcium from both GGBS and lime, resulting in a more complex gel structure with enhanced mechanical properties. The balanced ratio of the GGBS and the FA ensures that calcium-rich and sodium-rich gel phases coexist, creating a dense microstructure that physically restricts ion mobility while chemically binding sodium ions into stable mineral structures to control efflorescence effectively.
[0038] The geopolymer composition includes fine aggregate, constituting 60-75% by weight of the total composition. The fine aggregate, consisting primarily of manufactured sand (M-sand) with a particle size distribution conforming to ASTM C33, provides dimensional stability, reduces shrinkage, and contributes to the mechanical strength of the geopolymer. For instance, in the 3M-10R formulation, the fine aggregate (including red mud as partial replacement) constitutes 66.7% by weight of the total composition (180g M-sand and 20g red mud in a total mix of 300g). The fine aggregate creates a granular skeleton within the geopolymer that resists deformation and cracking during setting and hardening, while the spaces between aggregate particles are filled with the geopolymer binder that binds the components together. The optimised aggregate content ensures sufficient particle packing density to minimise voids and porosity, thereby reducing pathways for moisture and ion transport that could lead to efflorescence.
[0039] In an implementation, the red mud is present in an amount of 8-12% by weight of the fine aggregate. For example, when red mud is incorporated at 10% by weight of fine aggregate (as in the 3M-10R formulation), it results in complete elimination of efflorescence while maintaining a compressive strength of approximately 22 MPa at 28 days. Further, the optimal amount of reactive alumina and silica provided by the red mud is sufficient to bind free sodium ions without significantly disrupting the geopolymer network structure. In another example, the 2M-10R formulation also incorporates red mud at 10% (20g of the total 200g fine aggregate), achieving excellent efflorescence resistance while enabling a reduction in sodium hydroxide concentration from 3M to 2M due to the contribution of inherent alkalinity from the red mud.
[0040] In an implementation, the total weight of red mud comprises 15-25% alumina, 8-15% silica, and 5-10% sodium oxide by weight. For example, the red mud used in the experimental formulations contains 20.1% alumina, 12.5% silica, and 8.67% sodium oxide, falling within these optimal ranges. The alumina content provides reactive sites for sodium incorporation into alumino-silicate networks, as evidenced by the formation of zeolite-A crystals observed in the SEM images (FIG. 8A and FIG. 9A). In another example, the energy dispersive X-ray analysis of the 3M-10R-0Q-5L formulation (FIG. 9B) confirms the presence of aluminium at 7.21% by weight and silicon at 11.01% by weight in the final geopolymer, reflecting the contribution of these elements from the red mud. The inherent sodium oxide content contributes to the overall alkalinity of the system while already being partially bound within the red mud structure, allowing for a reduction in external alkaline activator concentration as demonstrated in the 2M-10R formulation.
[0041] The red mud includes alumina and silica compounds that react with unreacted sodium ions from the sodium hydroxide to form sodium-alumino-silicate minerals within the geopolymer binder, which immobilise the sodium ions to prevent efflorescence. The reaction of the sodium ions occurs during the curing process, where alumina (Al₂O₃) and silica (SiO₂) from the red mud dissolve in the alkaline environment and then reconstitute with free sodium ions to form stable mineral phases.
[0042] In an implementation, the sodium-alumino-silicate minerals include zeolite-A crystals. Zeolite-A is a sodium-alumino-silicate mineral with the approximate formula Na₁₂[(AlO₂)₁₂(SiO₂)₁₂]·27H₂O, characterised by a three-dimensional framework structure with cavities that can incorporate sodium ions. The formation of zeolite-A is useful for efflorescence control as it incorporates sodium ions into the crystal structure, removing them from the pore solution where they would otherwise be available for migration and efflorescence formation.
[0043] In an implementation, by mixing 10% red mud by weight of the manufactured sand, the workable time of geopolymer may be increased by at least 119 minutes compared to 93 minutes for the geopolymer formulation containing no red mud.
[0044] FIG. 2 is a graphical representation illustrating an X-ray diffraction (XRD) pattern of geopolymer samples, in accordance with an embodiment of the present disclosure. FIG. 2 is described in conjunction with elements of FIG. 1. With reference to FIG. 2, there is shown a graphical representation 200 including a first XRD pattern 202 of a 4M-0R geopolymer formulation. The 4M-0R geopolymer formulation indicates that the geopolymer composition includes zero grams of red mud and four molarity of sodium hydroxide. Further, the graphical representation 200 includes a second XRD pattern 204 of a 3M-0R geopolymer formulation. The 3M-0R geopolymer formulation indicates that the geopolymer composition includes zero grams of red mud and three molarity of sodium hydroxide.
[0045] XRD is used to identify the crystallographic structure, composition, and physical properties of materials. Peaks in the XRD pattern correspond to atomic planes in a crystal lattice, and their intensities relate to the number of such atomic planes and the orientation of the crystals. The diffraction angle denoted by 2θ is measured in degrees in an abscissa axis. The intensity is expressed in arbitrary units (A.U.) on an ordinate axis. Peaks at specific 2θ degrees values indicate the presence of specific crystallographic planes. Higher peaks indicate more atoms arranged in the corresponding crystallographic plane. The graphical representation 200 illustrating the XRD pattern includes peaks at 2θ values corresponding to specific crystallographic planes of the zinc oxide films.
[0046] The first XRD pattern 202 exhibits a first peak 206, approximately ranging between 26-30 degrees. The first peak 206 is associated with quartz from the fine aggregate. The quartz remains largely unreacted during geopolymerisation. The first XRD pattern 202 further includes a dominant peak 208, approximately ranging between 28-32 degrees. The dominant peak 208 is associated with the sodium carbonate (Na₂CO₃). The sodium carbonate is the product of efflorescence formed when free sodium ions react with atmospheric carbon dioxide. The first XRD pattern 202 further includes a second peak 210 approximately ranging between 34-36 degrees. The second peak 210, associates with the sodium carbonate, indicating availability of efflorescence forming compounds on the surface of the geopolymer. The first XRD pattern 202 further includes a few minor peaks between the dominant peak 208 and the first peak 206. Such minor peaks are associated with the hydrosoladite (Na₆Al₆Si₆O₂₄·8H₂O). Hydrosodalite is a zeolitic formed during geopolymerization and indicates the transformation of amorphous aluminosilicates into a crystalline form. The presence of hydrosodalite indicates that the alkaline activation with sodium hydroxide was sufficient to promote zeolite crystallisation. The first XRD pattern 202 further includes a third peak 212 associated with the sodium carbonate, approximately ranging from 36-40 degrees. The third peak 212 further exhibits the presence of efflorescence.
[0047] Furthermore, the first XRD pattern 202 includes a fourth peak 214 associated with the hydrosodalite. The presence of hydrosodalite indicates further sodium hydroxide activation to form zeolite crystals. The prominence of multiple sodium carbonate peaks in the first XRD pattern 202 indicates that the high concentration of sodium hydroxide, as compared to the sodium hydroxide used in the geopolymer formulation, results in free sodium ions that are not fully incorporated into the geopolymer structure, leading to extensive efflorescence formation.
[0048] The second XRD pattern 304 exhibits a first peak 216, approximately ranging between 26-30 degrees. The first peak 216 is associated with quartz from the fine aggregate, which remains unreacted during the geopolymerization process. The second XRD pattern 204 further includes a dominant peak 218, approximately ranging between 28-32 degrees. The dominant peak 218 is associated with sodium carbonate (Na₂CO₃), which is the primary efflorescence product. Compared to the dominant peak 208 in the first XRD pattern 202, the dominant peak 218 in the second XRD pattern 204 shows slightly lower intensity, indicating a slight reduction in efflorescence formation when the sodium hydroxide concentration is reduced from 4M to 3M. The second XRD pattern 204 further includes a second peak 220, approximately ranging between 34-36 degrees. The second peak 220 is also associated with sodium carbonate, further confirming the presence of efflorescence-forming compounds, with slightly reduced intensity compared to the second peak 210. Between the dominant peak 218 and the second peak 220, the second XRD pattern 204 exhibits minor peaks associated with hydrosodalite (Na₆Al₆Si₆O₂₄·8H₂O), like those observed in the first XRD pattern 202. The second XRD pattern 204 further includes a third peak 222 associated with sodium carbonate, approximately ranging from 36-40 degrees. Additionally, the second XRD pattern 204 includes a fourth peak 224 associated with hydrosodalite, indicating the formation of zeolitic phases during geopolymerization.
[0049] FIG. 3 is a graphical representation illustrating an X-ray diffraction (XRD) pattern of geopolymer formulations with red mud and lime, in accordance with an embodiment of the present disclosure. FIG. 3 is described in conjunction with elements from FIGs. 1 to 2. With reference to FIG. 3, there is shown a graphical representation 300 including a first XRD pattern 302 representing red mud, a second XRD pattern 304 representing 3M-0R-5L geopolymer formulation, a third XRD pattern 306 representing 3M-5R-5L geopolymer formulation, a fourth XRD pattern 308 representing 3M-10R-5L geopolymer formulation, a fifth XRD pattern 310 representing 3M-0R geopolymer formulation, and a sixth XRD pattern 312 representing 3M-5R geopolymer formulation. The diffraction angle denoted by 2θ is measured in degrees in the abscissa axis. The intensity is expressed in arbitrary units in the ordinate axis.
[0050] The first XRD pattern 302 has an amorphous structure indicating a non-crystalline nature. The amorphous character of the red mud contributes to the reactivity of red mud with the geopolymer. As non-crystalline phases are more readily dissolved in the alkaline activator (for example, sodium hydroxide). The minor peaks in the red mud pattern correspond primarily to iron oxide phases.
[0051] The second XRD pattern 304 has a peak 330 at approximately 10 degrees corresponds to Goethite (FeOOH), which has minimal intensity due to the absence of red mud. The peak 332 at approximately 29 degrees has calcium-silicate-hydrate (C-S-H) gel phases, intensity due to the reaction between lime and the aluminosilicate binder.
[0052] The third XRD pattern 306 has a peak 326 at approximately 10 degrees corresponds to Goethite (FeOOH), with increased intensity compared to the second XRD pattern 304 due to the iron content contributed by the 5% red mud. The peak 328 at approximately 29 degrees has calcium-silicate-hydrate (C-S-H) gel phases, similar to the second XRD pattern 304 but with slightly reduced intensity.
[0053] The fourth XRD pattern 308 has a peak 322 at approximately 10 degrees corresponds to Goethite (FeOOH), indicating further increased intensity compared to the third XRD pattern 306 due to the higher iron content from 10% red mud. The peak 324 at approximately 32 degrees has Zeolite-A, indicating the highest intensity among all lime-containing formulations. The presence of Zeolite-A confirms the formation of sodium-alumino-silicate minerals that immobilize sodium ions and prevent efflorescence.
[0054] The fifth XRD pattern 310 has a peak 318 at approximately 10 degrees shows minimal intensity, indicating the absence of iron-rich phases. The peak 320 at approximately 29 degrees has calcium-alumino-silicate-hydrate (C-A-S-H) gel phases derived from GGBS.
[0055] The sixth XRD pattern 312 has a peak 314 at approximately 10 degrees corresponds to Goethite (FeOOH), with intensity comparable to the third XRD pattern 306 due to the same 5% red mud content. The peak 316 at approximately 29 degrees has calcium-alumino-silicate-hydrate (C-A-S-H) gel phases from GGBS, with reduced intensity compared to the fifth XRD pattern 310, indicating that red mud addition modifies the gel formation process.
[0056] FIG. 4A is a graphical representation illustrating effect of red mud on water permeable porosity of geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 4A is described in conjunction with elements from FIGs. 1 to 3. With reference to FIG. 4A, there is shown a graphical representation 400A illustrating water permeable porosity of various geopolymer formulations. The water permeable porosity measured in percentage (%) is represented on the ordinate axis. The different geopolymer formulations are labelled along the abscissa axis. The graphical representation 400A includes a bar 402A representing a 4M-0R geopolymer formulation. The 4M-0R geopolymer formulation indicates that the geopolymer composition includes zero grams of red mud and four molarity of sodium hydroxide. Further, the graphical representation 400A includes a bar 404A representing a 3M-0R geopolymer formulation indicating that the geopolymer composition includes zero grams of red mud and three molarity of sodium hydroxide, a bar 406A representing 3M-5R geopolymer formulation. The 3M-5R geopolymer formulation indicates that the geopolymer composition includes five grams of red mud three molarity of sodium hydroxide. The graphical representation 400A further includes a bar 408A representing 2M-10R geopolymer formulation and a bar 410A representing 3M-10R geopolymer formulation.
[0057] Water permeable porosity (WPP) influences both efflorescence formation and mechanical properties of the geopolymer. The value of WPP quantifies the volume percentage of interconnected pores accessible to water within the geopolymer. Higher WPP values indicate a more porous geopolymer with increased pathways for moisture migration and ion transport, facilitating efflorescence formation in the geopolymer.
[0058] The bar 402A exhibits a WPP value of approximately 32%. The sodium hydroxide increases the dissolution of the aluminosilicate binder and creates an open pore structure of the geopolymer due to the formation of hydrogen gas during the reaction between the sodium hydroxide and the aluminosilicate binder. The 4M-0R geopolymer formulation does not have red mud as a reactive additive and relies solely on GGBS and FA for the aluminosilicate binder.
[0059] The bar 404A indicates a WPP value of approximately 29%. The reduction in porosity compared to the bar 402A is consistent with the decrease in molarity of sodium hydroxide (from 4M to 3M), which decreases the intensity of the geopolymerization reaction. However, the decrease in WPP is relatively minor approximately 3% as compared to the bar 402A. Therefore, the geopolymer formulation 3M-0R still exhibits efflorescence.
[0060] The bar 406A indicates the lowest WPP value of approximately 28% as compared to the bar 402A, the bar 404A, the bar 408A and the bar 410A. The bar 406A has reduction in porosity due to the incorporation of red mud as a partial replacement for fine aggregate. The reduction in porosity indicates the delayed onset of efflorescence.
[0061] The bar 408A indicates the highest WPP value of approximately 36% as compared to the bar 402A, the bar 404A, the bar 406A and the bar 410A. The WPP value facilitates the early leaching of free sodium ions from the geopolymer during the curing. The early leaching of free sodium ions removes the efflorescence. Simultaneously, the red mud provides abundant reactive sites for binding the remaining free sodium ions into stable sodium-alumino-silicate minerals.
[0062] The bar 410A has a WPP value of approximately 33%. The WPP of bar 410A is higher than that of the bar 404A. The high WPP value of the bar 410A is due to an increased quality of the red mud from 0% to 10%. The increased quantity of the red mud while keeping the concentration of sodium hydroxide same (i.e. 3M) facilitates to the high specific surface area and pore volume of red mud, which increases the water demand of the geopolymer formulation.
[0063] FIG. 4B is a graphical representation illustrating effect of lime addition on water permeable porosity of geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 4B is described in conjunction with elements from FIGs. 1 to 4A. With reference to FIG. 4B, there is shown a graphical representation 400B illustrating water permeable porosity of various geopolymer formulations. The water permeable porosity measured in percentage (%) is represented on the ordinate axis. The different geopolymer formulations are labelled along the abscissa axis. The graphical representation 400B includes a bar 402B representing a 3M-5R-0Q-5L geopolymer formulation. The 3M-5R-0Q-5L geopolymer formulation indicates that the geopolymer composition includes zero grams of quartz, five grams of red mud, five grams of lime and 3 molarity of sodium hydroxide. Further, the graphical representation 400B includes a bar 404B representing a 3M-5R-10Q-5L geopolymer formulation, a bar 406B representing 3M-10R-0Q-5L geopolymer formulation. The graphical representation 400B further includes a bar 408B representing 3M-10R-10Q-5L geopolymer formulation, a bar 410B representing 3M-0R-0Q-5L geopolymer formulation and a bar 412B representing 3M-0R-10Q-5L geopolymer formulation.
[0064] The bar 402B exhibits a WPP value of approximately 33%. The WPP value of the bar 402B is higher compared to the WPP value of the bar 406A approximately 28%. The higher WPP value indicates that lime addition increases the water permeable porosity of the geopolymer matrix. The increase in WPP is attributed to the reaction between lime (Ca(OH)₂) and the aluminosilicate components, which alters the geopolymerization kinetics. The Ca²⁺ ions from lime compete with Na⁺ ions during gel formation, resulting in mixed calcium-sodium-alumino-silicate-hydrate gels with different morphological characteristics.
[0065] The bar 404B exhibits a WPP value of approximately 35%. The WPP value of the bar 404B is higher compared to the WPP value of the bar 402B. The higher WPP value of the bar 404B is attributed to the incorporation of quartz powder. The quartz powder functions primarily as an inert filler in the geopolymer matrix and does not participate significantly in the geopolymerization reaction. The presence of these unreactive quartz particles disrupts the continuity of the geopolymer gel, creating interfaces and interstitial spaces that contribute to increased porosity.
[0066] The bar 406B exhibits a WPP value of approximately 37%. The WPP value of the bar 406B is the highest among all tested lime-containing samples. The significant increase in porosity is attributed to the high content of red mud. The high specific surface area of red mud (18.41 m²/g) increases water demand during mixing, potentially leading to higher initial water content in the fresh mixture. Additionally, the interaction between the inherent sodium oxide in red mud (measured at 8.67%) and the calcium hydroxide from lime affects the pH balance and reaction kinetics during geopolymerization, resulting in a more porous structure.
[0067] The bar 408B exhibits a WPP value of approximately 36.5%. The WPP value of the bar 408B is slightly lower than the WPP value of the bar 406B. The reduction in porosity suggests that quartz powder, when combined with high levels of red mud, provides some pore-filling effect. However, the overall porosity remains significantly higher than that of formulations without lime. The high porosity is attributed to the cumulative effects of the water demand of red mud, the inert nature of quartz powder disrupting the gel structure, and the lime-induced alterations to geopolymerization kinetics.
[0068] The bar 410B exhibits a WPP value of approximately 24%. The WPP value of the bar 410B is the lowest among all tested lime-containing samples. The dramatic reduction in porosity compared to other lime-containing formulations indicates that lime, when used as the sole additive, significantly densifies the geopolymer microstructure. This effect is attributed to the reaction between calcium hydroxide and the soluble silica and alumina from GGBS and FA, forming calcium-silicate-hydrate (C-S-H) and calcium-alumino-silicate-hydrate (C-A-S-H) gels that have pore-filling characteristics.
[0069] The bar 412B exhibits a WPP value of approximately 26%. The WPP value of the bar 412B is slightly higher than the WPP value of the bar 410B. The increase in porosity confirms the pore-disrupting effect of quartz powder observed in other formulations. However, the porosity remains relatively low compared to red mud-containing samples, suggesting that the absence of high-surface-area red mud significantly reduces water demand and resulting porosity.
[0070] FIG. 4C is a graphical representation illustrating effect of steam curing on water permeable porosity of geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 4C is described in conjunction with elements from FIGs. 1 to 4B. With reference to FIG. 4C, there is shown a graphical representation 400C illustrating water permeable porosity of various geopolymer formulations. The water permeable porosity measured in percentage (%) is represented on the ordinate axis. The different geopolymer formulations are labelled along the abscissa axis. The graphical representation 400C includes a bar 402C representing a 4M-0R geopolymer formulation. The 4M-0R geopolymer formulation indicates that the geopolymer composition includes zero grams of red mud and four molarity of sodium hydroxide. Further, the graphical representation 400C includes a bar 404C representing a 3M-0R geopolymer formulation, a bar 406C representing 2M-10R geopolymer formulation. The graphical representation 400C further includes a bar 408B representing 3M-5R geopolymer formulation, a bar 410C representing 3M-0R-10Q geopolymer formulation and a bar 412C representing 3M-5R-10Q geopolymer formulation.
[0071] The bar 402C exhibits a WPP value of approximately 30%. The WPP value of the bar 402C is lower than the WPP value of the bar 402A approximately 32%. The reduction in porosity is attributed to the accelerated dissolution of aluminosilicate species from GGBS and FA under elevated temperature conditions, leading to more rapid gel formation and densification of the microstructure. The elevated temperature enhances ion mobility and reaction rates, promoting more complete geopolymerization within the initial curing period.
[0072] The bar 404C exhibits a WPP value of approximately 32%. The WPP value of the bar 404C is higher than the WPP value of the bar 402C. The WPP value of the bar 404C is also higher than the WPP value of the bar 404A approximately 29%. The increase in porosity is attributed to differential thermal expansion effects during steam curing, which introduce microcracks in the geopolymer matrix. The lower alkalinity of 3M NaOH results in less complete dissolution of silica and alumina species during the early stages of reaction, creating a heterogeneous microstructure that responds differently to elevated temperature exposure.
[0073] The bar 406C exhibits a WPP value of approximately 38%. The WPP value of the bar 406C is the highest among all tested formulations. The WPP value of the bar 406C is higher than the WPP value of the bar 408A i.e., approximately 36%). The substantial increase in porosity is attributed to the combined effects of two molarity concentration of NaOH and 10% red mud content. The steam curing regime accelerates the leaching of soluble components from the red mud while simultaneously enhancing the geopolymerization reaction, creating a more open pore structure.
[0074] The bar 408C exhibits a WPP value of approximately 34%. The WPP value of the bar 408C is significantly higher than the WPP value of the bar 406A approximately 28%. The substantial increase in porosity indicates that the combination of three molarity concentration of NaOH and 5% red mud content responds differently to elevated temperature exposure during steam curing. The steam curing accelerates the reaction between sodium hydroxide and the alumina and silica components in red mud, creating a more heterogeneous microstructure with regions of varying density.
[0075] The bar 410C exhibits a WPP value of approximately 31%. The WPP value of the bar 410C is higher than the WPP value of the bar 404A approximately 29%, but lower than other steam-cured formulations containing red mud. The moderate increase in porosity suggests that the inert quartz powder is less affected by the steam curing conditions than reactive components for example, red mud. The quartz particles function primarily as fillers in the geopolymer and do not participate significantly in the geopolymerization reaction at 50 degrees Celsius of temperature used in steam curing.
[0076] The bar 412C exhibits a WPP value of approximately 32%. The WPP value of the bar 412C is intermediate between the WPP value of the bar 408C i.e. approximately 34% and the WPP value of the bar 410C i.e. approximately 31%. The moderation in porosity compared to the 3M-5R formulation suggests that the inert quartz powder provides some physical filling effect that partially counteracts the porosity-increasing effect of red mud under steam curing conditions.
[0077] FIG. 4D is a graphical representation illustrating effect of carbonation on water permeable porosity of geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 4D is described in conjunction with elements from FIGs. 1 to 4C. With reference to FIG. 4D, there is shown a graphical representation 400D illustrating water permeable porosity of various geopolymer formulations. The water permeable porosity measured in percentage (%) is represented on the ordinate axis. The different geopolymer formulations are labelled along the abscissa axis. The graphical representation 400D includes a bar 402C representing a 4M-0R geopolymer formulation. The 4M-0R geopolymer formulation indicates that the geopolymer composition includes zero grams of red mud and 4 molarity of sodium hydroxide. Further, the graphical representation 400D includes a bar 404D representing a 3M-0R geopolymer formulation, and a bar 406D representing 2M-10R geopolymer formulation.
[0078] The bar 402D exhibits a WPP value of approximately 30%. The WPP value of the bar 402D is lower than the WPP value of the bar 402A i.e. approximately 32%. The reduction in porosity is attributed to the formation of sodium carbonate precipitates within the pore network during the early carbonation curing. The sodium carbonate has a larger molar volume than the reactants, potentially filling some of the pore spaces and reducing the overall water-accessible porosity.
[0079] The bar 404D exhibits a WPP value of approximately 29.5%. The WPP value of the bar 404D is similar to the WPP value of the bar 404A i.e. approximately 29%. The carbonation of free alkalis reduces porosity through precipitation of sodium carbonate in pore spaces, while the associated slight expansion creates microcracks that provide new pathways for water penetration. The standard deviation for this formulation is notably smaller than for other samples, suggesting high consistency between test specimens.
[0080] The bar 406D exhibits a WPP value of approximately 39%. The WPP value of the bar 406D is higher than the WPP value of the bar 408A i.e. approximately 36%. The substantial increase in porosity is attributed to the interaction between the two molar concentration of sodium hydroxide, 10% red mud content, and the carbonation curing. The carbonation reaction consumes the limited free sodium hydroxide available in this low-molarity formulation, potentially disrupting the ongoing geopolymerization process and creating a heterogeneous microstructure of the geopolymer.
[0081] FIG. 4E is a graphical representation illustrating pore volume distributions in geopolymer formulations subjected to different curing conditions, in accordance with an embodiment of the present disclosure. FIG. 4E is described in conjunction with elements from FIGs. 1 to 4D. With reference to FIG. 4E, there is shown a graphical representation 400E illustrating the pore volume distribution categorised into two size ranges i.e. pores smaller than 10 nm represented by white bars and pores in the range of 10-100 nm represented by patterned bars. The graphical representation includes a section 402E representing 3M-0R geopolymer formulation, a section 404E representing 4M-0R geopolymer formulation, a section 406E representing 3M-5R geopolymer formulation, and a section 408E representing 2M-10R geopolymer formulation. For each geopolymer formulation, three curing conditions are shown i.e. normal curing (N), carbonation curing (CC), and steam curing (STC). The steam curing is configured to reduce the volume of small and medium capillary porosity in the pores in the range of 10-100 nm.
[0082] The pore volume is expressed in cubic centimetres per gram (cm³/g) × 10⁻³ and is represented on the ordinate axis. The pore volume distribution provides insights into the microstructural characteristics of the geopolymer formulations and how they are affected by different curing conditions. The pore volumes are determined using the gas adsorption method with nitrogen as the adsorbate. The geopolymer formulation is degassed at 70°C for 8 hours prior to analysis to remove moisture and adsorbed gases from the pore surfaces.
[0083] The section 402E has a pore volume of approximately 2 × 10⁻³ cm³/g for pores smaller than 10 nm and 40 × 10⁻³ cm³/g for pores in the 10-100 nm range under normal curing (N). The pore volume of pores in the 10-100 nm range increases to approximately 60 × 10⁻³ cm³/g under carbonation curing (CC), while the volume of pores smaller than 10 nm remains relatively unchanged. Under steam curing (STC), the pore volume is approximately 3 × 10⁻³ cm³/g for pores smaller than 10 nm and 46 × 10⁻³ cm³/g for pores in the 10-100 nm range.
[0084] The section 404E has a pore volume of approximately 6 × 10⁻³ cm³/g for pores smaller than 10 nm and 55 × 10⁻³ cm³/g for pores in the 10-100 nm range under normal curing (N). The pore volume of pores in the 10-100 nm range increases to approximately 65 × 10⁻³ cm³/g under carbonation curing (CC). Under steam curing (STC), the pore volume is approximately 4 × 10⁻³ cm³/g for pores smaller than 10 nm and 43 × 10⁻³ cm³/g for pores in the 10-100 nm range.
[0085] The section 406E has a pore volume of approximately 5 × 10⁻³ cm³/g for pores smaller than 10 nm and 56 × 10⁻³ cm³/g for pores in the 10-100 nm range under normal curing (N). The pore volume increases to approximately 7 × 10⁻³ cm³/g for pores smaller than 10 nm and 68 × 10⁻³ cm³/g for pores in the 10-100 nm range under carbonation curing (CC). Under steam curing (STC), the pore volume of pores smaller than 10 nm increases to approximately 8 × 10⁻³ cm³/g and the volume of pores in the 10-100 nm range increases to 69 × 10⁻³ cm³/g.
[0086] The section 408E has a pore volume of approximately 5 × 10⁻³ cm³/g for pores smaller than 10 nm and 69 × 10⁻³ cm³/g for pores in the 10-100 nm range under normal curing (N). The pore volume increases gradually to approximately 7 × 10⁻³ cm³/g for pores smaller than 10 nm and 79 × 10⁻³ cm³/g for pores in the 10-100 nm range under carbonation curing (CC). Under steam curing (STC), the pore volume is approximately 8 × 10⁻³ cm³/g for pores smaller than 10 nm and 53 × 10⁻³ cm³/g for pores in the 10-100 nm range. The steam curing eliminates efflorescence of the geopolymer formulation containing 10% of red mud by weight of the sand i.e. 2M-10R
[0087] FIG. 5A is a graphical representation illustrating effect of red mud on flexural strength of geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 5A is described in conjunction with elements from FIGs. 1 to 4E. With reference to FIG. 5A, there is shown a graphical representation 500A illustrating 28 days flexural strength of geopolymer formulations. The flexural strength measured in megapascals (MPa) is represented on the ordinate axis. The geopolymer formulations are labelled along the abscissa axis. The graphical representation 500A includes a bar 502A representing a 4M-0R geopolymer formulation. The 4M-0R geopolymer formulation indicates that the geopolymer composition includes zero grams of red mud and four molarity of sodium hydroxide. Further, the graphical representation 500A includes a bar 504A representing a 3M-0R geopolymer formulation, a bar 506A representing 3M-5R geopolymer formulation. The graphical representation 500A further includes a bar 508A representing 2M-10R geopolymer formulation and a bar 510A representing 3M-10R geopolymer formulation.
[0088] The bar 502A exhibits a flexural strength approximately ranging between 6 to 8 MPa. The 4M-0R geopolymer formulation has flexural strength due to the aluminosilicate binder that contributes in the formation of sodium-alumino-silicate-hydrate (N-A-S-H) and calcium-alumino-silicate-hydrate (C-A-S-H) gels. The sodium hydroxide provides alkalinity for the dissolution of silica and alumina from the aluminosilicate binder. The flexural strength obtained in the bar 502A exceeds the minimum requirement for non-load-bearing masonry applications.
[0089] The bar 504A exhibits a flexural strength approximately ranging between 4 to 6 MPa. The flexural strength of the bar 504A is lower than the flexural strength of the bar 502A. The reduction in flexural strength is attributed to the lower molarity of sodium hydroxide as compared to the bar 502A. The lower molarity of sodium hydroxide reduces the dissolution rate of the aluminosilicate binder and results in a less developed geopolymer network.
[0090] The bar 506A has a flexural strength approximately ranging between 5 to 7 MPa. The flexural strength of the bar 506A is comparable to the flexural strength of the bar 504A but lower than the flexural strength of the bar 502A. The incorporation of 5% red mud as a partial replacement for fine aggregate introduces additional reactive alumina and silica to the geopolymer formulation. However, the 5% red mud appears insufficient to enhance the binding capacity of the geopolymer.
[0091] The bar 508A exhibits a flexural strength approximately ranging between 8.0 to 9.0 MPa. The flexural strength of the bar 508A is higher than the flexural strengths of the bar 504A and the bar 506A, and comparable to the bar 502A. Despite the reduced molarity of sodium hydroxide to two molars, the geopolymer formulation achieves suitable flexural performance due to the incorporation of 10% red mud. The red mud provides reactive alumina and silica content for the formation of additional binding phases within the geopolymer. In an implementation, the steam curing may be used to improve the 28-day flexural strength of the geopolymer formulation containing 10% red mud and mitigates efflorescence.
[0092] The bar 510A has a flexural strength approximately ranging between 8.5 to 9.5 MPa. The combination of three molar sodium hydroxide and 10% red mud creates suitable conditions for geopolymerization and the development of a strong binding matrix. The sodium hydroxide concentration of three molarity compared to the bar 508A with sodium hydroxide concentration of ten molarity provides additional alkalinity for dissolution of the aluminosilicate binder, while the red mud contributes reactive alumina and silica.
[0093] FIG. 5B is a graphical representation illustrating effect of lime on flexural strength of geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 5B is described in conjunction with elements from FIGs. 1 to 5A. With reference to FIG. 5B, there is shown a graphical representation 500B illustrating 28 days flexural strength of geopolymer formulations. The flexural strength measured in megapascals (MPa) is represented on the ordinate axis. The geopolymer formulations are labelled along the abscissa axis. The graphical representation 500B includes a bar 502B representing a 3M-5R-0Q-5L geopolymer formulation. The 3M-5R-0Q-5L geopolymer formulation indicates that the geopolymer composition includes zero grams of quartz, five grams of red mud, five grams of lime and three molarity of sodium hydroxide. Further, the graphical representation 500B includes a bar 504B representing a 3M-5R-10Q-5L geopolymer formulation, a bar 506B representing 3M-10R-0Q-5L geopolymer formulation. The graphical representation 500B further includes a bar 508B representing 3M-10R-10Q-5L geopolymer formulation, a bar 510B representing 3M-0R-0Q-5L geopolymer formulation and a bar 512B representing 3M-0R-10Q-5L geopolymer formulation.
[0094] The bar 502B exhibits a flexural strength approximately ranging between 5 to 6 MPa. The 3M-5R-0Q-5L geopolymer formulation has flexural strength due to the partial replacement of GGBS with 5% lime. The lime reacts with the aluminosilicate binder to form calcium-silicate-hydrate (C-S-H) and calcium-alumino-silicate-hydrate (C-A-S-H) gels. The flexural strength of the bar 502B is comparable to the flexural strength of 3M-5R formulation represented by the bar 506A, indicating that the 5% lime replacement does not significantly alter the flexural performance of the 5% red mud geopolymer formulation.
[0095] The bar 504B has a flexural strength approximately ranging between 8 to 9 MPa. The flexural strength of the bar 504B is higher than the flexural strength of the bar 502B. The increased flexural strength is attributed to the incorporation of 10% quartz powder in addition to 5% red mud and 5% lime. The quartz powder contributes to the development of a more refined microstructure by providing nucleation sites for gel formation and enhancing the packing density of the matrix. The combination of lime and quartz powder with red mud creates synergistic effects that significantly improve the flexural performance of the geopolymer formulation.
[0096] The bar 506B has a flexural strength approximately ranging between 8 to 9 MPa. The flexural strength of the bar 506B is similar to the flexural strength of the bar 504B but higher than the flexural strength of the bar 502B. The incorporation of 10% red mud with 5% lime creates suitable conditions for geopolymerization and the development of a strong binding matrix resulting in a strong geopolymer. The red mud provides reactive alumina and silica while the lime contributes calcium for the formation of gel phases within the geopolymer. The flexural strength is comparable to the 3M-10R formulation represented by the bar 510A. The comparable flexural strength between the bar 510A and 504B indicates that lime replacement does not significantly impact the flexural strength when 10% red mud is present.
[0097] The bar 508B has a flexural strength approximately ranging between 5 to 6 MPa. The flexural strength of the bar 508B is lower than the flexural strength of the bar 506B. The reduction in flexural strength is attributed to the combined effect of 10% red mud, 10% quartz powder, and 5% lime. Further, 20% by weight of fine aggregate and 5% by weight GGBS content can disrupt the reactive balance required for optimal geopolymerization, leading to a weaker structure of the aluminosilicate binder. Additionally, quartz powder, being inert at ambient curing temperatures, may create weak interfaces that reduce flexural strength.
[0098] The bar 510B has a flexural strength approximately ranging between 4.5 to 5.5 MPa. The absence of red mud and quartz powder limits the development of additional binding phases that could enhance flexural performance. Although lime contributes calcium for the formation of C-S-H and C-A-S-H gels, the 5% lime appears insufficient to improve the flexural strength of the 3M-0R geopolymer formulation.
[0099] The bar 512B has a flexural strength approximately ranging between 5 to 6 MPa. The flexural strength of the bar 512B is slightly higher than the flexural strength of the bar 510B. The incorporation of 10% quartz powder with 5% lime produces an improvement in flexural strength of the geopolymer formulation. The quartz powder enhances the packing density of the geopolymer, reducing porosity.
[0100] FIG. 5C is a graphical representation illustrating effect of steam curing on flexural strength of geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 5C is described in conjunction with elements from FIGs. 1 to 5B. With reference to FIG. 5C, there is shown a graphical representation 500C illustrating 28 days flexural strength of geopolymer formulations subjected to steam curing. The flexural strength measured in megapascals (MPa) is represented on the ordinate axis. The geopolymer formulations are labelled along the abscissa axis. The graphical representation 500C includes a bar 502C representing a 4M-0R geopolymer formulation, a bar 504C representing a 3M-0R geopolymer formulation, a bar 506C representing 2M-10R geopolymer formulation. The graphical representation 500C further includes a bar 508C representing 3M-5R geopolymer formulation, a bar 510C representing 3M-0R-10Q geopolymer formulation and a bar 512C representing 3M-5R-10Q geopolymer formulation.
[0101] The bar 502C exhibits a flexural strength approximately ranging between 4 to 5 MPa. The steam-cured 4M-0R geopolymer formulation has lower flexural strength compared to the 4M-0R geopolymer formulation represented by the bar 502A. The reduction in flexural strength is attributed to thermal expansion during steam curing, which may introduce microcracks in the geopolymer.
[0102] The bar 504C has a flexural strength approximately ranging between 6 to 7 MPa. The flexural strength of the bar 504C is higher than the flexural strength of the bar 502C. The three-molar concentration of sodium hydroxide is more compatible with steam curing, allowing for accelerated reaction kinetics without brittleness in the geopolymer. The elevated temperature due to steam curing promotes enhanced geopolymerization resulting in enhanced flexural strength of the geopolymer formulation.
[0103] The bar 506C has a flexural strength approximately ranging between 9 to 10 MPa. The combination of 2 molar sodium hydroxide molarity and 10% red mud content is responsive to steam curing. The elevated temperature due to steam curing improves the dissolution of alumina and silica components from red mud and promotes the formation of sodium-alumino-silicate minerals. The formation of sodium-alumino-silicate minerals results in geopolymer formulation with suitable flexural capacity.
[0104] The bar 508C has a flexural strength approximately ranging between 6 to 7 MPa. The flexural strength of the bar 508C is lower than the flexural strength of the bar 506C. The 5% red mud appears insufficient to provide improvement in flexural strength under steam curing conditions, although there is a slight improvement.
[0105] The bar 510C has a flexural strength approximately ranging between 4 to 5 MPa. The quartz powder, being relatively inert at the moderate temperatures used in steam curing, does not contribute to the formation of additional binding phases. The bar 512C has a flexural strength approximately ranging between 5 to 6 MPa. The flexural strength of the bar 512C is slightly higher than the flexural strength of the bar 510C. The combination of 5% red mud and 10% quartz powder creates a balanced geopolymer formulation that responds moderately well to steam curing. The red mud provides reactive silica and alumina components for accelerated gel formation. The addition of red mud provides a slight improvement in the flexural strength of the geopolymer.
[0106] FIG. 5D is a graphical representation illustrating effect of carbon curing on flexural strength of geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 5D is described in conjunction with elements from FIGs. 1 to 5C. With reference to FIG. 5D, there is shown a graphical representation 500D illustrating 28 days flexural strength of geopolymer formulations subjected to carbonation curing. The flexural strength measured in megapascals (MPa) is represented on the ordinate axis. The geopolymer formulations are labelled along the abscissa axis. The graphical representation 500D includes a bar 502D representing a 4M-0R geopolymer formulation, a bar 504D representing a 3M-0R geopolymer formulation, and a bar 506D representing 2M-10R geopolymer formulation.
[0107] The bar 502D has a flexural strength approximately ranging between 7 to 8 MPa. The carbon curing involves the reaction between atmospheric carbon dioxide and free sodium ions. The carbonation of free sodium hydroxide to form sodium carbonate may densify the surface layer of the geopolymer formulation. The carbonation of free sodium hydroxide does not improve the flexural strength of the geopolymer formulation.
[0108] The bar 504D has a flexural strength approximately ranging between 5 to 6 MPa. The flexural strength of the bar 504D is lower than the flexural strength of the bar 502D. The three molarity of sodium hydroxide results in less free alkali available for carbonation curing, limiting the impact of the carbonation curing on the microstructure and mechanical properties of the geopolymer formulation. The bar 506D has a flexural strength approximately ranging between 7 to 8 MPa. The flexural strength of the bar 506D is higher than the flexural strength of the bar 504D and approximately 34% higher as compared to the flexural strength of the bar 502D. The binding phases formed in the structure of the geopolymer through the interaction of red mud with the alkaline activator are not affected by the carbonation curing.
[0109] FIG. 6A is a graphical representation illustrating effect of molarity on compressive strength development of geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 6A is described in conjunction with elements from FIGs. 1 to 5D. With reference to FIG. 6A, there is shown a graphical representation 600A illustrating compressive strength development of geopolymer formulations at 3 day curing age, 7 day curing age, 28 day curing age, and 120 day curing age. The compressive strength measured in megapascals (MPa) is represented on the ordinate axis. The curing ages are labelled along the abscissa axis. The graphical representation 600A includes a bar 602A, a bar 606A, a bar 610A, a bar 614A representing a 4M-0R geopolymer formulation and a bar 604A, a bar 608A, a bar 612A, a bar 616A representing a 3M-0R geopolymer formulation. The 4M-0R geopolymer formulation indicates that the geopolymer composition includes zero grams of red mud and four molarity of sodium hydroxide, while the 3M-0R geopolymer formulation indicates that the geopolymer composition includes zero grams of red mud and three molarity of sodium hydroxide. At the 3-day curing age, the bar 602A has a compressive strength approximately ranging between 10 to 12 MPa, while the bar 604A exhibits a compressive strength approximately ranging between 14 to 15 MPa. The higher compressive strength of the bar 604A is attributed to a lower solution-to-binder ratio of approximately 0.72 compared to the bar 602A with solution-to-binder ratio of approximately 0.75. The lower solution-to-binder ratio results in a denser initial microstructure of the geopolymer with fewer pores. Additionally, the reaction kinetics associated with three molarity of sodium hydroxide may reduce the formation of microcracks during the 3 day curing age, contributing to a higher initial strength of the geopolymer formulation associated with the bar 604A.
[0110] At the 7-day curing age, the bar 606A has a compressive strength approximately ranging between 16 to 18 MPa, while the bar 608A exhibits a compressive strength approximately ranging between 20 to 21 MPa. The bar 606A and the bar 608A indicate significant strength development between 3 and 7 days of the curing age. The strength development indicates that the geopolymerization reaction continues at a suitable rate between 3 days and 7 days of hydration age. The bar 608A maintains a strength advantage over the bar 606A, indicating that lower porosity and controlled reaction kinetics provide better compressive strength as compared to the bar 606A. At the 28-day curing age, the bar 610A has a compressive strength approximately ranging between 19 to 21 MPa, while the bar 612A exhibits a compressive strength approximately ranging between 24 to 26 MPa. The bar 612A achieves approximately 25% higher strength than the bar 610A at 28 day curing age. In addition, the higher porosity of the bar 610A creates more stress concentration points and reduces the effective load-bearing cross-section, resulting in lower compressive strength of the geopolymer formulation.
[0111] At the 120-day curing age, the bar 614A has a compressive strength approximately ranging between 23 to 25 MPa, while the bar 616A has a compressive strength approximately ranging between 24 to 26 MPa. The strength gap between the bar 614A and the bar 616A narrows at the 120-day curing age. The bar 614A shows continued strength development while the bar 616A appears to be stable and reaching towards a no further improvement. The continued strength development of the bar 614A suggests that although higher molarity leads to slower initial strength development, the higher molarity of sodium hydroxide may provide longer-term reactivity as the higher concentration of sodium hydroxide continues to facilitate the dissolution of unreacted aluminosilicate binder over extended periods. Further, the bar 616A shows minimal strength gain between 28 and 120 days, indicating that the majority of the geopolymerization reaction is completed within the first month when three molarity of sodium hydroxide is used.
[0112] FIG. 6B is a graphical representation illustrating effect of red mud on compressive strength development of geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 6B is described in conjunction with elements from FIGs. 1 to 6A. With reference to FIG. 6B, there is shown a graphical representation 600B illustrating compressive strength development of geopolymer formulations at 3 day curing age, 7 day curing age, 28 day curing age, and 120 day curing age. The compressive strength measured in megapascals (MPa) is represented on the ordinate axis. The curing ages are labelled along the abscissa axis. The graphical representation 600B includes a bar 602B, a bar 608B, a bar 614B, a bar 620B representing 3M-5R, a bar 604B, a bar 610B, a bar 616B, a bar 622B representing 2M-10R, and a bar 606B, a bar 612B, a bar 618B, a bar 624B representing 3M-10R geopolymer formulations. The 3M-5R geopolymer formulation indicates that the geopolymer composition includes five grams of red mud and three molarity of sodium hydroxide. The 2M-10R geopolymer formulation indicates that the geopolymer composition includes ten grams of red mud and two molarity of sodium hydroxide. The 3M-10R geopolymer formulation indicates that the geopolymer composition includes ten grams of red mud and three molarity of sodium hydroxide. At the 3-day curing age, the bar 602B geopolymer formulation has a compressive strength approximately ranging between 15 to 17 MPa, while the bar 604B exhibits a compressive strength approximately ranging between 14 to 16 MPa, and the bar 606B has a compressive strength approximately ranging between 14 to 16 MPa. The 3-day curing age compressive strength of the bar 602B, the bar 604B and the bar 606B indicates that the incorporation of red mud provides early strength development regardless of the specific red mud content or sodium hydroxide molarity. The compressive strength values at 3 days curing age for the bar 602B, the bar 604B and the bar 606B are comparable to or higher than the 3M-0R formulation represented by the bar 604A in FIG. 6A, indicating that red mud contributes positively to early strength development through the reactive alumina and silica present in the red mud.
[0113] At the 7-day curing age, the bar 608B has a compressive strength approximately ranging between 21 to 23 MPa, while the bar 610B exhibits a compressive strength approximately ranging between 15 to 17 MPa, and the bar 612B has a compressive strength approximately ranging between 18 to 20 MPa. The bar 608B has the most significant strength development between 3 and 7 days, achieving the highest 7-day strength as compared to the bar 608B, the bar 610B and the bar 612B. The gain in strength at the 7-day curing age is attributed to the combination of five percent red mud content and three molar concentration of sodium hydroxide, which promotes efficient dissolution and recombination of reactive species. The bar 610B has the least strength development during the 7-day curing age, indicating that the two-molar concentration of sodium hydroxide may be insufficient for fully activating the 10% red mud content at the 7-day curing age.
[0114] At the 28-day curing age, the bar 614B has a compressive strength approximately ranging between 24 to 26 MPa, while the bar 616B has a compressive strength approximately ranging between 15 to 17 MPa, and the bar 618B has a compressive strength approximately ranging between 21 to 23 MPa. The bar 614B maintains the strength advantage over the bar 616B and the bar 618B. The bar 614B has a compressive strength comparable to the bar 612A in FIG. 6A. The comparison between the bar 614B and the bar 612A indicates that the 5% red mud replacement does not compromise the mechanical properties of the geopolymer while providing significant benefits in terms of efflorescence reduction. The lower strength of the bar 616B indicates that the two-molar concentration of sodium hydroxide limits the complete activation of the geopolymer binder, forming a less developed geopolymer despite the higher red mud content.
[0115] At the 120-day curing age, the bar 620B has a compressive strength approximately ranging between 22 to 24 MPa, while the bar 622B has a compressive strength approximately ranging between 12 to 14 MPa, and the bar 624B has a compressive strength approximately ranging between 20 to 22 MPa. The bar 620B and the bar 624B has a slight strength reduction between 28- and 120-days curing age. The slight strength reduction may be attributed to microstructural changes associated with prolonged ambient curing. The bar 622B has a strength reduction as compared to the bar 616B, indicating that the combination of the 10% red mud content and two molar concentration of sodium hydroxide may lead to increased porosity and potential microcracking. However, the bar 622B still maintains compressive strength well above the minimum requirement of 3.50 MPa for masonry applications while providing efflorescence resistance.
[0116] FIG. 6C is a graphical representation illustrating effect of lime and quartz addition on compressive strength development of geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 6C is described in conjunction with elements from FIGs. 1 to 6B. With reference to FIG. 6C, there is shown a graphical representation 600C illustrating compressive strength development of geopolymer formulations at 3 day curing age, 7 day curing age, 28 day curing age, and 120 day curing age. The compressive strength measured in megapascals (MPa) is represented on the ordinate axis. The curing ages are labelled along the abscissa axis. The graphical representation 600C includes a diagonal pattern bar representing 3M-5R-0Q-5L geopolymer formulation, a honeycomb pattern bar representing 3M-5R-10Q-5L geopolymer formulation, a dense diagonal lines pattern bar representing 3M-10R-0Q-5L geopolymer formulation, a checkboard pattern bar representing 3M-10R-10Q-5L geopolymer formulation, a dotted pattern bar representing 3M-0R-0Q-5L geopolymer formulation, and a vertical lines pattern bar representing 3M-10Q-5L geopolymer formulation.
[0117] At the 3-day curing age, the diagonal pattern bar, the honeycomb pattern bar, the dense diagonal lines pattern bar, the checkboard pattern bar, the dotted pattern bar, and the vertical lines pattern bar have a similar compressive strength approximately ranging between 14 to 17 MPa. The similar compressive strength at 3 day curing age indicates that the incorporation of 5% lime provides consistent early strength development regardless of the specific red mud content or quartz powder addition. The calcium hydroxide in lime reacts rapidly with the aluminosilicate components of the geopolymer binder, forming calcium-silicate-hydrate (C-S-H) and calcium-alumino-silicate-hydrate (C-A-S-H) gels that contribute to compressive strength development. The dotted pattern bar containing only lime without red mud or quartz powder, has comparable compressive strength to the diagonal pattern bar, the honeycomb pattern bar, the dense diagonal lines pattern bar, the checkboard pattern bar geopolymer formulation containing red mud, indicating that lime alone is useful for strength development for 3 day curing age.
[0118] At the 7-day curing age, the diagonal pattern bar has a compressive strength approximately ranging between 23 to 25 MPa, while the dense diagonal lines pattern bar, and the honeycomb pattern bar have compressive strengths approximately ranging between 22 to 24 MPa. The checkboard pattern bar, the dotted pattern bar, and the vertical lines pattern bar have compressive strengths approximately ranging between 18 to 20 MPa. The higher content of the red mud-containing formulations without quartz powder or with 10% quartz powder indicates that the combination of red mud and lime improves strength development during 3 to 7 day curing age. The alumina and silica components in red mud enhance the formation of calcium-silicate-hydrate and calcium-alumino-silicate-hydrate gels, while the lime contributes calcium ions that improve the microstructure of the geopolymer.
[0119] At the 28-day curing age, the diagonal pattern bar, and the honeycomb pattern bar have compressive strengths approximately ranging between 27 to 29 MPa, while the dense diagonal lines pattern bar, and the checkboard pattern bar, have compressive strengths approximately ranging between 24 to 26 MPa. The dotted pattern bar, and the vertical lines pattern bar, have compressive strengths approximately ranging between 22 to 24 MPa. The higher compressive strength of the geopolymer formulations containing 5% red mud compared to those with 10% red mud indicates a suitable amount of red mud for strength development when combined with lime. The 5% red mud provides sufficient alumina and silica components for enhancing the formation of calcium-alumino-silicate gels without disrupting the overall structure of the geopolymer. The continued strength development between 7 and 28 days of curing age indicates ongoing geopolymerization and calcium gel formation.
[0120] At the 120-day curing age, the diagonal pattern bar has a compressive strength approximately ranging between 35 to 37 MPa, showing the most significant long-term strength development among the diagonal pattern bar, the honeycomb pattern bar, the dense diagonal lines pattern bar, the checkboard pattern bar. The honeycomb pattern bar, and the dense diagonal lines pattern bar have compressive strengths approximately ranging between 28 to 30 MPa, while the checkboard pattern bar, the dotted pattern bar, and the vertical lines pattern bar have compressive strengths approximately ranging between 26 to 28 MPa. The compressive strength gains in the 3M-5R-0Q-5L formulation between 28 and 120 days of curing age indicates that the combination of 5% red mud content and 5% lime without quartz powder creates a geopolymer for long-term strength development. The absence of the inert quartz powder allows for a more homogeneous distribution of alumina and silica components, while the red mud provides additional silica and alumina for continued gel formation without excess porosity.
[0121] FIG. 6D is a graphical representation illustrating effect of carbon curing on compressive strength development of geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 6D is described in conjunction with elements from FIGs. 1 to 6C. With reference to FIG. 6D, there is shown a graphical representation 600D illustrating compressive strength development of geopolymer formulations subjected to carbonation curing at 3 day curing age, 7 day curing age, 28 day curing age, and 120 day curing age. The compressive strength measured in megapascals (MPa) is represented on the ordinate axis. The curing ages are labelled along the abscissa axis. The graphical representation 600D includes a bar 602D, a bar 608D, a bar 614D, a bar 620D representing 4M-0R geopolymer formulation, a bar 604D, a bar 610D, a bar 616D, a bar 622D representing 3M-0R geopolymer formulation, and a bar 606D, a bar 612D, a bar 618D, a bar 624D representing 2M-10R geopolymer formulation. A horizontal dashed line 626D at approximately 18 MPa indicates a reference strength value for comparison purposes.
[0122] At the 3-day curing age, the bar 602D has a compressive strength approximately ranging between 9 to 11 MPa, while the bar 604D has a compressive strength approximately ranging between 13 to 15 MPa, and the bar 606D has a compressive strength approximately ranging between 8 to 10 MPa. The carbonation curing involves exposure to 5% carbon dioxide for 2 hours followed by normal curing. The carbonation curing does not significantly alter the compressive strength development for 3 days curing age in geopolymer formulations. The relatively low early strength of the 2M-10R formulation indicates that the carbonation process may temporarily retard the initial geopolymerization reactions in formulations with low alkalinity and high red mud content.
[0123] At the 7-day curing age, the bar 608D has a compressive strength approximately ranging between 11 to 13 MPa, while the bar 610D has a compressive strength approximately ranging between 18 to 20 MPa, and the bar 612D has a compressive strength approximately ranging between 10 to 12 MPa. The 3M-0R formulation demonstrates significant strength development between 3 days and 7 days curing age, surpassing the reference strength line 626D, while the bar 608D and the bar 612D have relatively low compressive strength. The accelerated strength development of the 3M-0R formulation indicates that three molar concentration of sodium hydroxide provides suitable conditions for the combined effects of carbonation and geopolymerization, with the carbonation of excess free sodium ions densifying the microstructure without disrupting the ongoing formation of aluminosilicate gels in the geopolymer.
[0124] At the 28-day curing age, the bar 614D has a compressive strength approximately ranging between 17 to 19 MPa, while the bar 616D has a compressive strength approximately ranging between 20 to 22 MPa, and the bar 618D has a compressive strength approximately ranging between 10 to 12 MPa. The bar 614D approaches the reference strength line 626D. The bar 618D has minimal strength development between 7- and 28-days curing age, indicating that the combination of two molar concentration of sodium hydroxide, 10% red mud content, and carbonation curing may not be favourable for continued compressive strength development.
[0125] At the 120-day curing age, the bar 620D has a compressive strength approximately ranging between 19 to 21 MPa, while the bar 622D has a compressive strength approximately ranging between 24 to 26 MPa, and the bar 624D has a compressive strength approximately ranging between 7 to 9 MPa. The bar 622D exhibits continued compressive strength development over the 120 days curing age, while the bar 620D has relatively lower compressive strength gain. The bar 624D exhibits a reduction in compressive strength between 28- and 120-days curing age, indicating a long-term instability in the formulation.
[0126] FIG. 6E is a graphical representation illustrating effect of steam curing on compressive strength development of geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 6E is described in conjunction with elements from FIGs. 1 to 6D. With reference to FIG. 6E, there is shown a graphical representation 600E illustrating compressive strength development of geopolymer formulations subjected to steam curing at 3 day curing age, 7 day curing age, 28 day curing age, and 120 day curing age. The compressive strength measured in megapascals (MPa) is represented on the ordinate axis. The curing ages are labelled along the abscissa axis. The graphical representation 600E includes a dotted pattern bar representing 4M-0R, a dense diagonal pattern bar representing 3M-0R geopolymer formulation, a vertical pattern bar representing 2M-10R geopolymer formulation, a stipple pattern bar representing 3M-5R geopolymer formulation, a dashed vertical pattern bar representing 3M-0R-10Q geopolymer formulation, and a grid pattern bar representing 3M-5R-10Q geopolymer formulation.
[0127] At the 3-day curing age, the dotted pattern bar, the dense diagonal pattern bar, the vertical pattern bar, the stipple pattern bar, the dashed vertical pattern bar, and the grid pattern bar have compressive strengths approximately ranging between 12 to 16 MPa. The compressive strength of the geopolymer formulations indicates that steam curing, which involves exposure to 50 degrees Celsius steam for 2 hours followed by normal curing, accelerates the initial geopolymerization reactions. The steam curing creates uniform compressive strength development during 3 days of curing age. The elevated temperature during steam curing enhances the dissolution of silica and alumina from the geopolymer binder and accelerates the condensation reactions that form the geopolymer. The grid pattern bar has slightly higher compressive strength compared to the dotted pattern bar, the dense diagonal pattern bar, the vertical pattern bar, the stipple pattern bar, and the dashed vertical pattern bar. The higher compressive strength may be achieved due to the combined effects of 5% red mud providing additional reactive components and 10% of quartz powder enhancing the packing density of the structure of the geopolymer.
[0128] At the 7-day curing age, the dashed vertical pattern bar and the grid pattern bar have compressive strengths approximately ranging between 16 to 18 MPa, while the dotted pattern bar, the dense diagonal pattern bar, the vertical pattern bar, and the stipple pattern bar have compressive strengths approximately ranging between 13 to 15 MPa. The higher strength of the stipple pattern bar and the grid pattern bar indicates that the combination of steam curing and quartz powder may improve the compressive strength between 3 to 7 days of curing age. The steam curing may enhance the interfacial bond between the quartz particles and the geopolymer gel, creating a more cohesive structure of the geopolymer.
[0129] At the 28-day curing age, the dashed vertical pattern bar, has a compressive strength approximately ranging between 22 to 24 MPa. The grid pattern bar and the vertical pattern bar have compressive strengths approximately ranging between 20 to 22 MPa, while the dotted pattern bar, the dense diagonal pattern bar, and the stipple pattern bar have compressive strengths approximately ranging between 17 to 19 MPa. The compressive strength of the stipple pattern bar indicates that the combination of three molar concentration of sodium hydroxide, 10% quartz powder, and steam curing creates useful conditions for compressive strength development at the 28-day curing age. The quartz powder likely contributes to a more refined microstructure, while the three-molar concentration of sodium hydroxide ensures sufficient activation without excessive free sodium ions that could lead to microcracking in the structure of the geopolymer. The 2M-10R formulation has strength development between 7 and 28 days, indicating that steam curing compensates for the lower alkalinity in the red mud-containing formulation.
[0130] At the 120-day curing age, the dashed vertical pattern bar has a compressive strength approximately ranging between 23 to 25 MPa. The grid pattern bar has a compressive strength approximately ranging between 22 to 24 MPa, while the dotted pattern bar, the dense diagonal pattern bar, the vertical pattern bar, and the stipple pattern bar have compressive strengths approximately ranging between 18 to 22 MPa. The compressive strength for 120 days curing age indicates that steam curing accelerates the chemical reactions to such an extent that most of the compressive strength development is achieved within the first month i.e. upto 28 days curing age. The 3M-0R-10Q formulation maintains strength advantage over the curing age of 120 days indicates good long-term stability of the microstructure developed through the combination of three molar concentration of sodium hydroxide, 10% quartz powder, and steam curing.
[0131] FIG. 7A is a diagram illustrating a scanning electron microscope (SEM) image of an exemplary geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 7A is described in conjunction with elements from FIGs. 1 to 6E. With reference to FIG. 7A, the diagram 700A provides insight into the morphological characteristics and surface topology of the 3M-0R-0Q-5L geopolymer formulation. The 3M-0R-0Q-5L indicates that the geopolymer formulation includes three molar concentration of sodium hydroxide, zero percent red mud, zero percent quart and five percent lime. The SEM image reveals a heterogeneous microstructure characterized by a matrix of geopolymer gel interspersed with unreacted or partially reacted particles.
[0132] The diagram 700A indicates a region 702A indicating the presence of lime in the geopolymer. The lime particles appear as bright, angular formations within the geopolymer, ranging in size from approximately 5 to 15 micrometres. The presence of the lime particles suggests that some of the calcium hydroxide added as a partial replacement for GGBS remains unreacted or has formed calcium-rich phases that are distinguishable from the surrounding geopolymer gel.
[0133] FIG. 7B is a graphical representation illustrating an energy dispersive spectroscopy (EDS) analysis of an exemplary geopolymer formulation, in accordance with an embodiment of present disclosure. FIG. 7B is described in conjunction with FIGs. 1 to 7A. With reference to FIG. 7B, there is shown a graphical representation 700B depicting an energy dispersive spectroscopy (EDS) analysis of the network of interwoven nanofibers. Specifically, the graphical representation 700B depicts the absorption of high energy electron beam by the 3M-0R-0Q-5L geopolymer formulation. The 3M-0R-0Q-5L indicates that the geopolymer formulation includes three molar concentration of sodium hydroxide, zero percent red mud, zero percent quart and five percent lime. The high energy electron beam is measured in kilo electron volt (keV) in an abscissa axis. The intensity is expressed in arbitrary units in an ordinate axis.
[0134] The first peak 702B corresponds to oxygen (O) and reflects a high relative content, with oxygen accounting for approximately 43.86% by weight of the total composition. The second peak 704B represents magnesium (Mg) with an abundance of approximately 5.98% by weight. The third peak 706B indicates the presence of aluminium (Al) at approximately 9.50% by weight, while the fourth peak 708B corresponds to silicon (Si) at 13.53% by weight. The fifth peak 710B signifies the presence of calcium (Ca) with a relative weight percentage of 18.23%. The presence and relative intensities of the peaks for oxygen, magnesium, aluminium, silicon, and calcium confirm the successful formation of the 3M-0R-0Q-5L geopolymer formulation.
[0135] FIG. 8A is a diagram illustrating a scanning electron microscope (SEM) image of another exemplary geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 8A is described in conjunction with elements from FIGs. 1 to 7B. With reference to FIG. 8A, the diagram 800A provides insight into the morphological characteristics and surface topology of the 3M-5R-0Q-5L geopolymer formulation. The 3M-5R-0Q-5L indicates that the geopolymer formulation includes three molar concentration of sodium hydroxide, five percent red mud, zero percent quart and five percent lime. The SEM image reveals a heterogeneous microstructure characterised by a matrix of geopolymer gel with distinct crystalline formations. The diagram 800A indicates a region 802A highlighting grain-like zeolite products in the geopolymer. The zeolite products appear as clustered crystalline formations with a granular texture, distinguished from the surrounding amorphous gel phase. The zeolitic formations, enclosed within the dashed rectangle, range in size from approximately 2 to 8 micrometres and exhibit a characteristic morphology consistent with zeolite-A crystals.
[0136] FIG. 8B is a graphical representation illustrating an energy dispersive spectroscopy (EDS) analysis of another geopolymer formulation, in accordance with an embodiment of present disclosure. FIG. 8B is described in conjunction with FIGs. 1 to 8A. With reference to FIG. 8B, there is shown a graphical representation 800B depicting an energy dispersive spectroscopy (EDS) analysis of the network of interwoven nanofibers. Specifically, the graphical representation 800B depicts the absorption of high energy electron beam by the 3M-5R-0Q-5L geopolymer formulation. The 3M-5R-0Q-5L indicates that the geopolymer formulation includes three molar concentration of sodium hydroxide, five percent red mud, zero percent quart and five percent lime. The high energy electron beam is measured in kilo electron volts (keV) in an abscissa axis. The intensity is expressed in arbitrary units in an ordinate axis.
[0137] The first peak 802B corresponds to carbon (C) and reflects a relative content, with carbon accounting for approximately 5.90% by weight and 9.91% by atomic percentage of the total composition. The second peak 804B represents oxygen (O) with a dominant abundance of approximately 44.60% by weight and 56.26% by atomic percentage. The third peak 806B indicates the presence of sodium (Na) at approximately 4.58% by weight and 4.02% by atomic percentage, while the fourth peak 808B corresponds to magnesium (Mg) at 4.24% by weight and 3.52% by atomic percentage. The fifth peak 810B signifies the presence of aluminium (Al) with a relative weight percentage of 9.35% and an atomic percentage of 6.99%. The sixth peak 812B indicates silicon (Si) at 16.08% by weight and 11.55% by atomic percentage, representing one of the major elemental components of the geopolymer matrix. The seventh peak 814B corresponds to sulfur (S) with a relative weight percentage of 2.49% and atomic percentage of 1.57%. The eighth peak 816B represents potassium (K) at 1.06% by weight and 0.55% by atomic percentage. The ninth peak 818B shows calcium (Ca) at 9.78% by weight and 4.93% by atomic percentage, which is significant for the formation of calcium-based gel phases. The tenth peak 820B indicates manganese (Mn) at 0.44% by weight and 0.16% by atomic percentage, while the eleventh peak 822B represents iron (Fe) at 1.48% by weight and 0.54% by atomic percentage. The presence and relative intensities explained above confirm the successful incorporation of red mud into the 3M-0R-0Q-5L geopolymer formulation.
[0138] FIG. 9A is a diagram illustrating a scanning electron microscope (SEM) image of yet another geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 9A is described in conjunction with elements from FIGs. 1 to 8B. With reference to FIG. 9A, the diagram 900A provides insight into the morphological characteristics and surface topology of the 3M-10R-0Q-5L geopolymer formulation. The 3M-10R-0Q-5L indicates that the geopolymer formulation includes three molar concentration of sodium hydroxide, ten percent red mud, zero percent quart and five percent lime. The SEM image reveals a more developed crystalline microstructure.
[0139] The diagram 900A includes a region 902A highlighting zeolitic products in the geopolymer. The zeolitic formations appear more abundant and well-defined than in the 3M-5R-0Q-5L formulation, reflecting the 10% red mud content as compared to the 5% red mud content, which provides additional reactive alumina and silica for zeolite formation. The region 904A indicates areas where the zeolite crystals have formed interconnected networks, creating a more cohesive microstructure. The zeolitic products indicates a characteristic morphology with sizes ranging from approximately 1 to 5 micrometres.
[0140] FIG. 9B is a graphical representation illustrating an energy dispersive spectroscopy (EDS) analysis of yet another geopolymer formulation, in accordance with an embodiment of present disclosure. FIG. 9B is described in conjunction with FIGs. 1 to 9A. With reference to FIG. 9B, there is shown a graphical representation 900B depicting an energy dispersive spectroscopy (EDS) analysis of the network of interwoven nanofibers. Specifically, the graphical representation 900B depicts the absorption of high energy electron beam by the 3M-10R-0Q-5L geopolymer formulation. The 3M-0R-0Q-5L indicates that the geopolymer formulation includes three molar concentration of sodium hydroxide, ten percent red mud, zero percent quart and five percent lime. The high energy electron beam is measured in kilo electron volt (keV) in an abscissa axis. The intensity is expressed in arbitrary units in an ordinate axis.
[0141] The first peak 902B corresponds to carbon (C) and reflects a substantial relative content, with carbon accounting for approximately 15.19% by weight and 24.29% by atomic percentage of the total composition. The second peak 904B represents oxygen (O) with a dominant abundance of approximately 39.71% by weight and 47.69% by atomic percentage. The third peak 906B indicates the presence of sodium (Na) at approximately 5.12% by weight and 4.28% by atomic percentage, showing an increase compared to the 5% red mud formulation due to the 10% red mud content. The fourth peak 908B corresponds to magnesium (Mg) at 1.98% by weight and 1.56% by atomic percentage. The fifth peak 910B signifies the presence of aluminium (Al) with a relative weight percentage of 7.21% and atomic percentage of 5.13%. The sixth peak 912B indicates silicon (Si) at 11.01% by weight and 7.53% by atomic percentage. The seventh peak 914B corresponds to sulfur (S) with a relative weight percentage of 4.10% and atomic percentage of 2.46%. The eighth peak 916B represents potassium (K) at 0.95% by weight and 0.47% by atomic percentage. The ninth peak 918B shows calcium (Ca) at 11.20% by weight and 5.37% by atomic percentage, which is higher than in the 5% red mud formulation, suggesting potential interaction between calcium from lime and components in the red mud. The tenth peak 920B indicates manganese (Mn) at 0.85% by weight and 0.30% by atomic percentage, while the eleventh peak 922B represents iron (Fe) at 2.69% by weight and 0.93% by atomic percentage, showing a significant increase compared to the 5% red mud formulation. The higher iron and manganese content in the 3M-10R-0Q-5L geopolymer formulation indicates the increased red mud incorporation of 10% as compared to the 3M-5R-0Q-5L geopolymer formulation with red mud incorporation of 5%.
[0142] FIG. 10A is a graphical representation illustrating effect of red mud on total shrinkage of geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 10A is described in conjunction with elements from FIGs. 1 to 9B. With reference to FIG. 10A, there is shown a graphical representation 1000A illustrating change in length (total shrinkage) of geopolymer formulations over hydration age of 60 days. The change in length measured in micro-strain (μƐ) is represented on the ordinate axis, with negative values indicating shrinkage. The hydration age in days is labelled along the abscissa axis. The graphical representation 1000A includes a curve 1002A representing 3M-0R, a curve 1004A representing 3M-5R, a curve 1006A representing 3M-10R, and a curve 1008A representing 2M-10R geopolymer formulation.
[0143] The curve 1002A representing the 3M-0R geopolymer formulation exhibits a more gradual shrinkage profile compared to the curve 1004A, the curve 1006A and the curve 1008A. The total shrinkage of the 3M-0R formulation reaches approximately -3300 micro-strain after 60 days of hydration. The more controlled shrinkage behaviour is attributed to the absence of red mud. The absence of red mud results in a more homogeneous microstructure with fewer regions of differential shrinkage. The curve 1002A indicates a relatively steady rate of shrinkage throughout the hydration age, with the rate gradually decreasing after approximately 30 days as the geopolymerization reaction approaches completion and the microstructure stabilises.
[0144] The curve 1004A representing the 3M-5R geopolymer formulation shows an increased rate of shrinkage compared to the curve 1002A. The total shrinkage of the 3M-5R formulation reaches approximately -3300 micro-strain after 60 days of hydration, similar to the curve 1002A but achieved through a different shrinkage progression. The incorporation of 5% red mud increases the early rate of shrinkage, which can be attributed to the higher pore volume in the size range of 10-100 nm. The tensile capillary stress around the pores increases with the increase in pore volume, leading to higher early shrinkage.
[0145] The curve 1006A representing the 3M-10R geopolymer formulation has the highest rate of shrinkage among the curve 1002A, the curve 1004A and the curve 1008A. The total shrinkage of the 3M-10R formulation reaches approximately -3400 micro-strain after 60 days of hydration. The significant increase in shrinkage rate and final shrinkage value at hydration age of 60 days is attributed to the increase in red mud content to 10%. The increase in red mud content further increases the volume of pores in the size range of 10-100 nm contributing to shrinkage.
[0146] The curve 1008A representing the 2M-10R geopolymer formulation has a high rate of shrinkage similar to the 3M-10R formulation, the shrinkage stabilizes at approximately -2700 micro-strain after about 35 days of hydration. The curve 1008A indicates a change in length by 14% compared to the curve 1002A containing no red mud. The shrinkage can be attributed to the lower sodium hydroxide concentration. The two molar concentrations of sodium hydroxide result in less extensive dissolution of silica and alumina from the aluminosilicate binder, creating a different gel structure with higher resistance to long-term shrinkage.
[0147] FIG. 10B is a graphical representation illustrating effect of lime addition on total shrinkage of geopolymer formulation, in accordance with an embodiment of the present disclosure. FIG. 10B is described in conjunction with elements from FIGs. 1 to 10A. With reference to FIG. 10B, there is shown a graphical representation 1000B illustrating change in length (total shrinkage) of various lime-containing geopolymer formulations over hydration age of 60 days. The change in length measured in micro-strain (μƐ) is represented on the ordinate axis, with negative values indicating shrinkage. The hydration age in days is labelled along the abscissa axis. The graphical representation 1000B includes a curve 1002B representing 3M-0R-0Q-5L, a curve 1004B representing 3M-5R-0Q-5L, and a curve 1006B representing 3M-10R-0Q-5L geopolymer formulation.
[0148] The curve 1002B representing the 3M-0R-0Q-5L geopolymer formulation exhibits the most gradual shrinkage profile among the lime-containing formulations. The total shrinkage of the 3M-0R-0Q-5L formulation reaches approximately -3400 micro-strain after 60 days of hydration. The addition of 5% lime without red mud results in a controlled shrinkage rate during the initial 20 days, followed by an accelerated shrinkage period between 20 and 50 days, before stabilising at the ultimate value. The accelerated shrinkage period between 20 and 50 days can be attributed to the formation of calcium-silicate-hydrate (C-S-H) and calcium-alumino-silicate-hydrate (C-A-S-H) gels, which have different shrinkage characteristics compared to the sodium-based gels in geopolymer. The lime contributes to the formation of the calcium-rich gels (calcium-silicate-hydrate (C-S-H) and calcium-alumino-silicate-hydrate (C-A-S-H) gels).
[0149] The curve 1004B representing the 3M-5R-0Q-5L geopolymer formulation shows an increased rate of shrinkage compared to the 3M-0R-0Q-5L formulation, particularly during the first 30 days of hydration. The total shrinkage of the 3M-5R-0Q-5L formulation reaches approximately -3500 micro-strain after 60 days of hydration, which is slightly higher than the lime-only formulation. The incorporation of 5% red mud along with 5% lime creates a more complex reaction environment with potential synergistic effects on shrinkage behaviour. The red mud provides additional reactive alumina and silica that can participate in the formation of both sodium-based and calcium-based gel phases, resulting in a more rapid early shrinkage as these reactions proceed simultaneously. The stabilisation of shrinkage occurs earlier than in the curve 1002B, at approximately 40 days, suggesting that the presence of red mud accelerates the overall reaction kinetics of the geopolymer formulation.
[0150] The curve 1006B representing the 3M-10R-0Q-5L geopolymer formulation has the highest rate of shrinkage among the curve 1002B, the curve 1004B and the curve 1008B. The total shrinkage of the 3M-10R-0Q-5L formulation reaches approximately -3800 micro-strain after 60 days of hydration, which is significantly higher than both the 3M-0R-0Q-5L and 3M-5R-0Q-5L formulations. The increase in shrinkage rate and shrinkage value is attributed to the 10% red mud content, which, when combined with lime, creates a highly reactive system with increased gel formation. The interaction between the sodium oxide in red mud and the calcium hydroxide from lime may generate unique gel phases with different shrinkage characteristics. The curve 1006B has a slight expansion after 45 days, which may indicate a late-stage reaction or recrystallisation process that counteracts the overall shrinkage.
EXPERIMENTAL DATA
Table 1
Geopolymer Formulation 1-day 7-day 14-day 28-day 56-day Efflorescence
4M-0R Uniform surface Dark stain begins Surface crystallization visible Dense surface efflorescence Severe efflorescence Similar efflorescence
3M-0R Smooth surface No visible deposit Slight surface deposit Moderate surface deposit Patchy surface deposit Reduced efflorescence
2M-10R Clean surface Clean surface Clean surface No visible salt No visible salt No efflorescence
The effect of steam curing was evaluated for three geopolymer formulations as summarised in table 1. The three geopolymer formulations comprises four molar concentration sodium hydroxide and zero grams of red mud formulation (4M-0R), three molar concentration sodium hydroxide and zero grams of red mud formulation (3M-0R), and two molar concentration sodium hydroxide and ten grams of red mud formulation (2M-10R). The three geopolymer formulations are evaluated over multiple curing ages 1, 7, 14, 28, and 56 days. The 4M-0R formulation exhibited noticeable surface degradation and progressive efflorescence formation, with severe white salt deposits observed by 28 day curing age and persisting through 56 day curing age. The 3M-0R formulation has a moderate reduction in surface efflorescence as compared to the 4M-0R formulation., The 3M-0R formulation has patchy salt deposits appearing during 56 days curing age. In contrast to the 4M-0R formulation and the 3M-0R formulation, the 2M-10R formulation has a clean surface with no observable efflorescence at any curing age. The results in table 1, indicates the effectiveness of red mud in chemically binding free sodium ions and reducing surface salt migration, thereby confirming the functional role in suppressing efflorescence within the geopolymer.
Table 2
Geopolymer Formulation 1-day 7-day 14-day 28-day 56-day Efflorescence
3M-0R-10Q Clean surface Clean surface Uniform texture Minor surface salt Patchy salt Reduced efflorescence
3M-5R-0Q Clean surface Clean surface Clean surface Moderate salt High surface salt Reduced efflorescence
3M-5R-10Q Clean surface Clean surface Patchy salt Visible efflorescence Dense salt Similar efflorescence
The effect of steam curing on efflorescence formation was further evaluated for three additional geopolymer formulations, as summarised in table 2. The formulations include three molar concentration sodium hydroxide with zero grams of red mud and ten grams of quartz powder (3M-0R-10Q), three molar concentration sodium hydroxide with five grams of red mud and zero grams of quartz powder (3M-5R-0Q), and three molar concentration sodium hydroxide with five grams of red mud and ten grams of quartz powder (3M-5R-10Q). The performance of the geopolymer formulations was evaluated at curing ages of 1, 7, 14, 28, and 56 days. The 3M-0R-10Q formulation exhibited minor surface salt deposition for 28 day curing age, indicating reduced efflorescence. The 3M-5R-0Q formulation has stability, but moderate to severe efflorescence appeared by the 56-day curing age. In contrast, the 3M-5R-10Q formulation has visible surface salt accumulation from day 14 onwards, with salt deposits persisting through 56 days, indicating similar efflorescence levels as indicated in table 1. The results in table 2 indicates that while red mud contributes to sodium binding, the addition of quartz powder in high proportions may reduce the overall efficiency of efflorescence control due to the inert nature of quartz.
Table 3
Geopolymer Formulation 1-day 7-day 14-day 28-day 56-day Efflorescence
4M-0R Clean surface Clean surface Salt formation Moderate salt Heavy salt Increased efflorescence
3M-0R Clean surface Clean surface Salt patches Dense salt Severe efflorescence Increased efflorescence
2M-10R Clean surface Clean surface Clean surface Light patches Mild salt Mild efflorescence
The impact of carbonation curing was evaluated for three geopolymer formulations, as detailed in table 3. The formulations include four molar sodium hydroxide with zero grams of red mud (4M-0R); three molar sodium hydroxide with zero grams of red mud (3M-0R); and two molar sodium hydroxide with ten grams of red mud (2M-10R). Each formulation was evaluated at curing ages of 1, 7, 14, 28, and 56 days. The 4M-0R formulation has surface salt formation, with moderate efflorescence visible from day 14 and increasing significantly by day 56. Similarly, the 3M-0R formulation exhibited dense surface salt deposits during 28 days curing age resulting in increased efflorescence. In contrast, the 2M-10R formulation maintained a clean surface with only mild efflorescence observed at the 56-day curing age. The results confirm that red mud, in conjunction with a lower alkali concentration, enhances sodium ion immobilization and reduces reactivity with atmospheric carbon dioxide, thus mitigating efflorescence even under carbonation exposure conditions.
[0151] Modifications to embodiments of the present disclosure described in the foregoing are possible without departing from the scope of the present disclosure as defined by the accompanying claims. Expressions such as "including", "comprising", "incorporating", "have", "is" used to describe and claim the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. The word "exemplary" is used herein to mean "serving as an example, instance or illustration". Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments. The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments". It is appreciated that certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the present disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable combination or as suitable in any other described embodiment of the disclosure.
, Claims:CLAIMS
We claim:
1. A geopolymer composition with reduced efflorescence comprising:
a geopolymer binder constituting 25-35% by weight of a total composition, the geopolymer binder comprising ground granulated blast furnace slag (GGBS) and fly ash (FA);
fine aggregate constituting 60-75% by weight of the total composition;
red mud in an amount of 5-15% by weight of the fine aggregate; and
an alkaline activator comprising sodium hydroxide;
wherein the red mud comprises alumina and silica compounds that react with unreacted sodium ions from the sodium hydroxide to form sodium-alumino-silicate minerals within the geopolymer binder which immobilize the sodium ions to prevent efflorescence.
2. The geopolymer composition as claimed in claim 1, wherein the geopolymer binder comprises 80-90% by weight GGBS and 10-20% by weight FA.
3. The geopolymer composition as claimed in claim 1, wherein the red mud comprises 15-25% alumina, 8-15% silica, and 5-10% sodium oxide by weight of red mud.
4. The geopolymer composition as claimed in claim 1, wherein the sodium hydroxide has a concentration of 2-4 molar.
5. The geopolymer composition as claimed in claim 1, wherein the alkaline activator is present at a solution-to-binder ratio of 0.70-0.80 by weight.
6. The geopolymer composition as claimed in claim 1, wherein the red mud is present in an amount of 8-12% by weight of the fine aggregate.
7. The geopolymer composition as claimed in claim 1, wherein the sodium-alumino-silicate minerals comprise zeolite-A crystals.
8. A method for producing a geopolymer with reduced efflorescence, the method comprising:
preparing a dry mixture comprising ground granulated blast furnace slag (GGBS) and fly ash (FA), wherein the GGBS and the FA together constitute 25-35% by weight of a total composition;
adding fine aggregate to the dry mixture, wherein the fine aggregate constitutes 60-75% by weight of the total composition;
incorporating red mud in an amount of 5-15% by weight of the fine aggregate;
dry-mixing the GGBS, the FA, the fine aggregate, and the red mud to form a homogenous powder;
preparing a sodium hydroxide solution;
adding the sodium hydroxide solution to the homogenous powder and mixing to form a geopolymer mortar; and
curing the geopolymer mortar, wherein during curing, alumina and silica compounds in the red mud react with unreacted sodium ions from the sodium hydroxide to form sodium-alumino-silicate minerals, which immobilize the sodium ions to prevent efflorescence.
9. The method as claimed in claim 8, wherein the GGBS and the FA are combined in a ratio of 80-90:10-20 by weight.
10. The method as claimed in claim 8, wherein the sodium hydroxide solution has a concentration of 2-4 molar.
11. The method as claimed in claim 8, wherein the sodium hydroxide solution is added to the homogenous powder at a solution-to-binder ratio of 0.70-0.80 by weight.
12. The method as claimed in claim 8, wherein the geopolymer mortar has a flowability of 130-140%.
13. The method as claimed in claim 8, wherein the curing comprises at least one of
moist curing under wet burlap at ambient temperature;
exposure to 3-7% CO2 for 1-3 hours followed by wet burlap curing; and
steam curing at 45-55°C for 1-3 hours followed by wet burlap curing.
14. The method as claimed in claim 8, further comprising immersing the geopolymer mortar after curing in water for 18-30 hours to remove excess free sodium ions.
15. The method as claimed in claim 8, wherein the concentration of the sodium hydroxide solution is reduced by 0.5-1 molar relative to a baseline concentration in consideration of in-situ sodium hydroxide content of the red mud.