A CORROSION-RESISTANT CEMENTITIOUS MATERIAL FROM INDUSTRIAL WASTE
Field of the invention;
The present invention relates to a corrosion-resistant cementitious material from industrial.waste having iron content of more than 50%, resulting in comprehensive strength up to 95MPa, through alkali activation with low activator modulus and process of preparation thereof.
More particularly, the present invention relates to a corrosion-resistant cementitious material from industrial waste comprising 30 - 70% of red mud, haying more than 50% of iron content and 30 - 70% of ground granulated blast furnace slag (GGBS) as binder material combined with low concentration of activator solution of sodium hydroxide and sodium meta-silicate (Na2O)i.5(SiO2)n- XH2O (where n = number of mole in the range of 0 to 1.5 and x = water content of Na2O3Si), for obtaining the comprehensive strength of 25 - 95MPa. The disclosed corrosion-resistant cementitious material can also be obtained using ferrochrome slag with high chromium value and MgO (magnesium oxide) value with less than 10% of iron content, in place of red mud.
Background and prior art of the invention:
Cement industry is one of the highest generations of carbon dioxide and also requires vast amount of natural resources and energy for its production. The cement is also responsible for corrosion of steel in reinforced cement concrete. Early strength of cement and longevity of the present cement product with acid and alkali environment is an issue. Another problem with conventional cement is more water requirement both during mixing and curing over a period. The sustainability of different heavy industries like steel, aluminum and thermal power plants, lies in effective utilization of their wastes.
Previous studies on red mud based cement are mostly through calcination process, requiring more energy. Previous attempts with respect to development of alternate cementitious material using red mud with slag and red mud with fly ash uses high concentration of sodium hydroxide and sodium silicate solution. The previous attempt on alkali activation of red mud is mostly for high calcium-low iron content type red mud. Activation of low calcium and high iron content red mud is with high concentration of sodium silicate with clinker or other admixtures. The strength

tests of the cementitious material or concrete blocks are also limited to ambient and acid environment.
References may be mentioned to abstracts of Chinese patents disclosing methods of preparing cementitious materials, such as CN103739258A, CN103626469A, CN102491657A, CN103964710A, CN103964710A, CN101891406A, CN102249570A, CN1837121A, CN102849969A, CN1613809A, however none of the above disclose use of high iron content industrial waste as raw materials and alkali activator solution comprising SiO2/Na2O value less than equal to 1.0 on the said raw materials.
Yet another reference may be made to CN105174755 (A) disclosing red stucco finish prepared by red mud-based alkali-activated cementing material. The red mud-based alkali-activated cementing material is a powder material formed by 60 to 70 percent of red mud, 30 percent of slag powder and 0 to 10 percent of metakaolin; the powder material is activated by 3 to 5 percent of water glass (sodium silicate). This patent discloses the calcinated red mud added with metakaolinite as pozzolana, which is generally manufactured hence not cost effective. This patent discloses with high alkali concentration having activator modulus (SiO2/Na20) value varying from 1.6 to 2.2. Again the sodium silicate solution is used, which is not cost effective in comparison to sodium silicate powder.
Still another reference may be made to US20140429, disclosing a composition and a process for the preparation of chemical activated cold setting fly ash building construction materials. The chemical activator is an alkaline aqueous solution of 11.2 to 13.6 in pH and 1.25 to 1.40g/cc in density which contains admixtures of different concentrations of hydroxyl, sulfate, acetate and chloride bearing chemical salts of calcium, magnesium, sodium, potassium and aluminum in water medium. The reaction of chemical activator solution and the mineral constituents of fly ash mix develop binding property. The binding matrix of chemical activated fly. ash mix is mostly hydrous silica and silicate group of phases which on setting under atmospheric condition attains strength suitable for building construction application. Utilization of fly ash of any source by weight ranges from 80 to 99% in manufacture of building materials including heat and acid resistance and toxic waste disposal products. However, this patent discloses about the alkali activation of fly ash, which is more pozzolanic with higher content of SiO2+ AI2O3, unlike red

mud which contains less amount of SiO2+ AI2O3. This patent also discloses about the use of high concentration of activator.
The inventors of the present invention, have come up with a suitable alternative to the existing construction material, which is corrosion resistant and durable under acid and alkali environment, cost effective thus obviating the drawbacks of the prior art.
Objectives of the present invention:
The main object of the present invention is to provide a corrosion-resistant cementitious material from industrial waste having iron content of more than 50%, resulting in comprehensive strength up to 95MPa, through alkali activation with low modulus.
Another object of the present invention is to provide a method for the preparation of the said corrosion-resistant cementitious material.
Yet another object of the present invention is to provide the mentioned corrosion-resistant cementitious material from industrial waste comprising 30 - 70% of red mud, having more than 50% of iron content and 30 - 70% of ground granulated blast furnace slag (GGBS) as binder material combined with low concentration of activator solution of sodium hydroxide and sodium meta-silicate (Na2O)i.5(SiO2)n. xH2O (where n = number of mole in the range of 0 to 1.5 and x = water content of Na2O3Si), for obtaining the comprehensive strength of 25 - 95MPa.
Still another object of the present invention is to provide alternative choice to produce the corrosion-resistant cementitious material containing ferrochrome slag with high chromium value and MgO (magnesium oxide) value with less than 10% iron content in place of red mud.
Summary of the present invention:
The present invention provides a corrosion-resistant cementitious material from industrial waste, which is durable under both acid and alkali environment also cost effective.

Accordingly, A corrosion-resistant cementitious material from industrial waste comprising 30¬70% of red mud having more than 50% of iron content and 30 - 70% of ground granulated blast furnace slag (GGBS) as binder material combined with activator solution of sodium hydroxide and sodium metasillicate (Na2O)1.5(SiO2) n. XH2O (where n = number of mole in the range of 0.0 to 1.5 and x = water content of Na2O3Si), for obtaining the comprehensive strength value of 25 -95MPa.
In an embodiment, alternative choice has been made to obtain the corrosion-resistant cementitious material from industrial waste comprising 30 - 70% of ferrochrome slag having iron content less than 10% and 30 - 70% of ground granulated blast furnace slag (GGBS) as binder material combined with activator solution of sodium hydroxide and sodium metasillicate (Na2O) 15(SiO2) n- XH2O (where n = number of mole in the range of 0.0 to 1.5 and x - water content of Na2O3Si), for obtaining the comprehensive strength value of 25 - 95MPa
In another embodiment of the present invention, the said cementitious material is obtained from industrial wastes, which include (i) red mud containing less than wt. 2% of CaO and more than 50%o of iron content; (ii) ferrochrome slag with more than 25% of MgO content; with blast furnace slag containing more than 35% of CaO content (and/or fly ash) mixture acting as binder.
In another embodiment of the present invention, the activator solution contains silica to sodium oxide molar ratio (SiO2/Na2O) lower than equal to 1 with pH between 12.1 to 13.3, at temperature range of 27 to 35°C with varying concentration of SiO2 (0-1.5 mole) with fixed concentration of Na2O.
In yet another embodiment of the present invention, the comprehensive strength of the said cementitious material is tested up to 28 days under four different curing conditions, viz. for ambient water, acid and alkali as 25 - 80, 25 - 60, 25 - 90 and 35 - 95MPa, respectively, which are obtained by casting the mold without adding water externally, followed by thermal curing at 60°C for 24 hours in an oven.
In yet another embodiment of the present invention, the said blocks obtained under varied range of ambient, water, acidic and alkaline conditions, result in manufacturing artificial ceramic stone

chips, tiles, concrete blocks and paver blocks having compressive strength up to 50MPa having characteristics of resistance to chloride attack and corrosion cracking for longer period of time in compared to Portland slag cement concrete, as per accelerated corrosion monitoring tests and physical and microstructure properties such as compressive strength, morphology and mercury intrusion porosimetry test.
Further, in another embodiment of the present invention, a process for preparation of the said corrosion-resistant cementitious material, comprising the following steps of:
(a) preparing a solution by combining sodium hydroxide pellets and sodium metasillicate powder with chemical formula: (Na2O) 1.5 (SiO2) n- XH2O (where, n = number of mole varying from 0.0 to 1.5 and x = water content of Na2O3Si);
(b) The industrial wastes and granulated blast furnace slag (GGBS) are grinded separately in ball mill to have particles finer than 150um, the solution of step (a) added with the mixture of industrial waste with the GGBS as the binding material varies as weight percentages 30 to 70%, keeping the solution-solid ratio varying in the range of 0.2 to 0.5.
(c) Adjusting the setting time of the paste as obtained from step (b) by adding measured percentage amount of phosphogypsum.
(d) Preparing the sample of the paste obtained from step (b) through table vibration and
• demoulding the sample after 12 hours.
(e) thermal curing for 24h maintain at 60° C in an oven after demolding as obtained from step (d), for all the proposed products with cling film as wrapper to avoid moisture loss;
(f) exposing the paste/product obtained from step (e) for curing under different conditions, i.e., ambient, water, acid and alkali conditions till testing age;
In yet another embodiment of the present invention, prepared mortar blocks made of fine aggregate comprises three graded Indian standard sand including: (a) Grade I: 2mm to 1 mm; (b) Grade II: 1mm to 500 mm; (c) Grade III: 500mm to 90um and coarse aggregate passing through 10mm, retained in 4.75 mm and prepared concrete blocks consists of river sand fine aggregate (less than 2 mm) and hard granite coarse aggregate (10mm - 4.75 urn).

In still another embodiment of the present invention, the binder is mixed with alkali activator keeping the solution-solid ratio varying in the range of 0.2 to 0.5, depending upon the type of blocks required to be developed, such as, 0.2 - 0.3 for paste block with block size 50x50x50 mm3, 0.4 - 0.5 for mortar block having block size 50x50x50 mm3 and 0.4 for concrete blocks with block size 70x70x70 mm..
In yet another embodiment of the present invention, the cementitious material can be precast and factory-made, with low energy consumption, durable under both acidic and alkaline environment and effective in corrosion resistance of steel reinforcement, helping in conservation of natural resources with utilization of industrial wastes.
Brief description of the drawings:
Figure 1 illustrates the process of the developing product materials followed by process. Product materials include as - paste, mortar and concrete block. The process of preparing the industrial wastes, preparation of the alkali solution and preparation process is shown in the figure. The exposure of the prepared sample i.e. paste, mortar and concrete to curing temperature and days of curing is also shown in this diagram. Figure 1 also shows the physical and microstructure properties of the cement and concrete like consistency, compressive strength, morphology and mineralogy.
Figure 2 illustrates a typical comparative compressive strength corresponds to alkali activated red mud slag (GGBS) composite pastes (30:70) (SR30) (30% of red mud with 70% of slag) activated with different solution with the number of mole of SiO2 of 0.0 (So), 0.5 (S0.5), 1.0 (S1.0) and 1.5(Si.5) with activator modulus (SiO2/Na20) value as 0.0, 0.33, 0.67 and 1.0, respectively, under ambient curing condition for testing ages up to 3 and 28 days. It shows that the strength of paste increased with age for both alkali and acid conditions.
Figure 3 illustrates a typical compressive strength of alkali activated ferrochrome slag with blast furnace slag (GGBS) composite (30:70) (SR30) under ambient conditions with activator modulus

value varying from 0.0 to 1.0. It shows higher compressive strength was obtained with activator modulus value of 1.0 (S i .5).
Figure 4 illustrates a typical compressive strength of alkali activated red mud slag composite (50:50) (SR50) under different curing conditions with activator modulus as 1.0 (S1.5). It shows in comparison to other curing conditions, higher strength was observed under alkali condition.
Figure 5 illustrates a typical mortar compressive strength of alkali activated red mud slag composite (30:70) (SR30) under different curing conditions with activator modulus as 1.0 and solution solid ratio as 0.45. The 28 days mortar compressive strength is more than 30 MPa for all curing conditions.
Figure 6 illustrates a typical compressive strength of alkali activated red mud slag (30:70) (SR30) concrete composite under ambient, water and acid curing conditions with activator modulus as 0.67 (Si o)and solution solid ratio as 0.4. The 28 days mortar compressive strength is more than 30 MPa for all curing conditions.
Figures 7(a) - 7(d) illustrate the morphology of alkali activated red mud slag composite under different conditions - (a) ambient; (b) water; (c) alkali and (d) acid, respectively. The hexagonal plate shape conforms to calcium silicate hydrate and found more in quantities in both alkali and acidic curing conditions.
Figures 8(a) and 8(b) illustrate the x-ray diffraction (XRD) plots of alkali activated red mud slag composite under (a) ambient and (b) alkali conditions of curing respectively. The calcium silicate hydrate are observed in both ambient and alkali conditions.
Figure 9 illustrates the FTIR of alkali activated red mud slag composite under different curing conditions showing the chemical compounds responsible for development of strength.
Figures 10(a) and 10(b) illustrate the corrosion effect on reinforced concrete related to cement and alkali activated red mud slag under sodium chloride solution, respectively, thus explaining the corrosion-resistance characteristics of reinforced cement concrete (Figures 10a); as compared to the reinforced concrete with cementitious material developed in present invention (Figures 10b).

Figure 11 shows the mass loss of the reinforced bar after the accelerated corrosion monitoring test for red mud slag and ferrochrome slag with ground granulated blast furnace slag (GGBS) and conventional cement concrete, respectively. It shows that more mass loss due to corrosion was observed with conventional cement.
Detailed description of the present invention:
The present invention describes a corrosion-resistant cementitious material from industrial wastes with different combinations (red mud + blast furnace slag; ferrochrome slag + blast furnace slag) as the basic material, which are activated by low activator modulus (SiO2/Na2O) (< 1.0). The cementitious material developed here are resistant to both acidic and alkali environment. Hence, building blocks made from this cement is less susceptible to acid and alkali degradation.
The utilization of red mud, ferrochrome slag and fly ash helps the industry in relieving the burden of wastes. The developed cement is more corrosion resistant than conventional cement. In present invention, 0 to 1 activator modulus (SiO2/Na2O) based solution is used to activate the solid wastes i.e. red mud, red mud-fly ash, ferrochrome slag, with common addition of blast furnace slag. In the present invention, the activator modulus is adjusted by mole of SiO2 and Na2O of both sodium metasilicate powder and sodium hydroxide pellets to develop cement alternation of binder material.
The present invention also uses industrial wastes like red mud, ferrochrome slag and fly ash in different combinations with GGBS as the basic material, which are activated by alkali solutions of low activator modulus (SiO2/Na2O) (< 1.0). Product inventions are based on test on composites blocks of paste, mortar and concrete. The samples are made with above composites in different proportion between 30 to 70%. The chemical activators are prepared in combination of sodium hydroxide and sodium silicate that varies as 0 to 1.5 mole proportion.
The paste samples are prepared as solution to solid ratio of 0.2 to 0.3 with composites as the solid and prepared activator as solution. The prepared paste blocks are kept in mold for 10 to 12hours. The de-molded samples are wrapped by cling film and kept in oven for 24h maintained

at 40 to 60°C temperature. After that samples are kept for different condition i.e. - ambient, water, acid and alkali. For ambient and water condition samples are kept at normal room temperature. For acid condition, samples are kept in closed container filled with 0.1N HC1 solution. For alkali condition samples are kept in closed container filled with 1M NaOH solution and exposed to oven maintained at 80°C temperature up to testing ages.
For mortar the solution solid ratio varies as 0.4 to 0.5 and Indian standard sand (IS 650: 1991) is used for preparation of the mortar with sand binder proportion as per Indian standard (IS 4031 (Part - 7): 1988) following the procedure as per ASTM standard (ASTM C109/C 109M-13). For concrete, solution solid ratio varies as 0.35 to 0.40 and river sand is used as fine aggregate and hard igneous rock as coarse aggregate. Similar to paste samples, mortar and concrete samples are exposed to curing conditions; ambient, water, acid and alkali. Mechanical strength of paste, mortar and concrete are determined as per Indian and ASTM standards. For extending the setting time, phosphogypsum may be added as admixture whose percentage varies as 2 to 4% depending on the design consistency. The corrosion resistance test was conducted using accelerated corrosion monitoring test of alkali activated reinforced concrete and compared to conventional reinforced cement concrete. The chemistry, morphology and mineralogy of the raw materials and products are also determined using X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) fitted with Energy dispersive X-ray (EDX), and X-ray diffraction (XRD) to correlate the physical properties with the micro-properties.
The investigation on the sample in terms of paste, mortar and concrete were prepared in order to use the same as cementitious material, as a binder (mortar) for masonry works, stucco and also in concrete replacing conventional cement.
The present invention is advantageous for being cost effective as well as less hazardous due to consumption of low concentration of sodium hydroxide. The proportion of the alkali (NaOH and Na2O3Si) is unique for development of high strength of the cementitious material. The alkali

activation of ferrochrome slag with blast furnace slag and low activator modulus (SiO2/Na2O) in combination with blast furnace slag are yet to be reported elsewhere.
The setting time of the cementitious is also maintained using another- industrial waste, phospogypsum.
The following examples are given by the way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention.
Example:
Red mud, ferrochrome slag and fly ash all those materials were passed under 150um sieve after grinded by ball mill. Paste of different proportions were prepared by activating with different solutions consisting of SiO2-Na2O that varying as 0 to 1.5 moles and prepared prior to the test. For preparation of paste block - solution solid ratio was kept as 0.2 or 0.30; for mortar block solution solid ratio is kept as 0.4 to 0.5; and for concrete block- solution: solid ratio was kept as 0.4. All those products were thermally cured in oven for 24h, covered by cling film to avoid moisture loss. After thermal curing, cling films were removed and samples were exposed to further different conditions i.e. -ambient, water, acid and alkali. For acid curing, samples were exposed to 0.1N HC1 and for alkali curing; samples were exposed to 1M NaOH solution that heated with closed container maintaining temperature as 80°C in oven. Then, all the samples were tested for physical and other tests as mentioned in Fig. 1. The chemistry, morphology and mineralogy of the sampled used for compressive strength were also determined to correlate the physical properties with the micro-properties.

I claim:
1. A corrosion-resistant cementitious material from industrial waste comprising 30 - 70% of red mud having more than 50% of iron content and 30 - 70% of ground granulated blast furnace slag (GGBS) as binder material combined with activator solution of sodium hydroxide and sodium metasillicate (Na2O) 1.5(SiO2) n. XH2O (where n = number of mole in the range of 0.0 to 1.5 and x = water content of Na2O3Si), for obtaining the comprehensive strength value of 25 - 95MPa.
2. A corrosion-resistant cementitious material from industrial waste comprising 30 - 70% of ferrochrome slag having iron content less than 10% and 30 - 70% of ground granulated blast furnace slag (GGBS) as binder material combined with activator solution of sodium hydroxide and sodium metasillicate (Na20) 1 s(Si02) „. xHbO (where n = number of mole in the range of 0.0 to 1.5 and x = water content of Na2O3Si), for obtaining the comprehensive strength value of 25 - 95MPa.
3. A corrosion-resistant cementitious material as claimed in claim 1 and claim 2, cementitious material obtained from industrial wastes including (i) red mud containing less than wt. 2% of CaO and more than 50% of iron content; (ii) ferrochrome slag with more than 25%) of MgO content; with blast furnace slag containing more than 35% of CaO content (and/or fly ash) mixture acting as binder.
4. A corrosion-resistant cementitious material as claimed in claim 1, wherein the comprehensive strength of the said cementitious material, being tested up to 28 days under four different conditions, viz. for ambient, water, acid and alkali as 35 - 90, 35 -75, 40 - 90 and 60 - 95MPa respectively, as obtained by casting the mold without adding water externally, followed by thermal curing at 60 C for 24 hours in an oven.
5. A process for preparation of the said corrosion-resistant cementitious material of claim 1, wherein the said process comprising the following steps of:
(a) preparing a solution by combining sodium hydroxide pellets and sodium metasillicate powder with chemical formula: (Na2O) 15 (SiO2) n- XH2O (where, n = number of mole varying from 0.0 to 1.5 and x = water content of Na2O3Si);

(b) The industrial wastes and granulated blast furnace slag (GGBS) are grinded separately in ball mill to have particles finer than 150um, the solution of step (a) added with the mixture of industrial waste with the GGBS as the binding material varies as weight percentages 30 to 70%, keeping the solution-solid ratio varying in the range of 0.2 to 0.5.
(c) adjusting the setting time of the paste as obtained from step (b) by adding measured percentage amount of phosphogypsum;
(d) preparing the sample of the paste obtained from step (b) through table vibration and demoulding the sample after 12 hours;
(e) thermal curing for 24h maintain at 60° C in an oven after demolding as obtained from step (d), for all the proposed products with cling film as wrapper to avoid moisture loss;
(f) exposing the paste/product obtained from step (e) for curing under different conditions, i.e., ambient, water, acid and alkali conditions till testing age.

6. A process for preparing corrosion-resistant cementitious material as claimed in claim 5, wherein the said blocks obtained under varied range of ambient, water, acidic and alkaline conditions, resulting in manufacturing artificial ceramic stone chips, tiles and concrete blocks, having compressive strength of at least up to 48MPa, having characteristics of resistance to chloride attack and corrosion cracking for longer period of time in compared to Portland slag cement concrete, as defined by the physical and microstructure properties such as, compressive strength, morphology, mineralogy.
7. A process for preparing corrosion-resistant cementitious material as claimed in claim 5, wherein the binder GGBS mixing with alkali activator keeping the solution-solid ratio varying in the range of 0.2 to 0.5, depending upon the type of blocks required to be developed, such as, 0.2 - 0.3 for paste block, 0.4 - 0.5 for mortar block and 0.4 for concrete blocks.
8. A process of preparing corrosion-resistant cementitious material as claimed in claim 7, wherein the prepared mortar blocks made of fine aggregate comprises three graded Indian standard sand including: (a) Grade I: 2mm to 1 mm; (b) Grade II: 1mm to 500 mm; (c) Grade III: 500mm to 90um and coarse aggregate passing through 10mm, retained in 4.75

mm and prepared concrete blocks consists of river sand fine aggregate (less than 425 um) and hard granite coarse aggregate (10mm - 4.75 um). 9. A process of preparing corrosion-resistant cementitious materialas claimed in claim 5, wherein the said construction material as obtained from the said process, can be precast and factory-made, with low energy consumption, durable under acid and alkali environment and effective in corrosion resistance of steel reinforcement, helping in conservation of natural resources with utilization of industrial wastes.