BACKGROUND OF INVENTION
A burgeoning population throughout the globe especially India as well as a huge
development of industry and infrastructure worldwide had made a demand for prodigious
quantities of concrete. In addition, the horizontal expansions are restricted hence vertical
growth has become faster that boosted its demand. This increase in demand of concrete, in
turn, resulted into a vigorous demand of Ordinary Portland Cement (OPC) - a primary
binder of concrete. Surprisingly, the data of production of OPC in 2014 was noted
approximately 275 million tons only in India! Unfortunately, the present process of
production of OPC is an expensive, user hostile and non-ecofriendly as it emits Carbon
Dioxide i.e. C02 - a primary greenhouse gas, into the atmosphere, due to decomposition of
Lime Stone and fossil fuels. The production of OPC by this process yields nearly the equal
amount of C02 due to Calcination of Limestone. Only C02 contributes about 65% of the
global warming and only the cement industry is responsible overall for about 6%.IMo energy
efficiency measures are effectively capable for its mitigation. The greenhouse effect is a
great factor responsible for global warming. This is a matter of great concern to
environmentalists and a red signal to the living communities across the planet. India is the
second largest country after China in population as well as in emission of C02 into the
atmosphere.
To simplify: 1 ton of OPC yield = 1 ton of C02 Emission into atmosphere.
The process of manufacturing OPC is not only a threat to environment but also
consumes a high energy in form of valuable Coal - a restricted natural resources
popularly known as black gold, for Calcination at vigorously elevated temperature.
Analogous to OPC, a tremendous increase in the demand of natural Sand also prevails
worldwide because of escalating demand of concrete. Once again, this is too, a great
concern to environment on account of its excessive exploitation against the restricted
natural resources. Not only transportation from faraway sources has made it expensive
but legislative restrictions have also made it more difficult to explore in some parts of
the universe.
OBJECT OF INVENTION
Fly ash has attracted researchers and engineers the most on account of its suitability as
well as profusion presence all over the globe as a discarded residue. It is a fine grained,
powdery, pulverized fuel ash produced from burning of pulverized coal in electric power
generating plants as a byproduct rich in Alumina and Silica.
Fortunately, Fly ash is relatively low cost to other materials. Though the global coal ash
production is more than 390 million per year but its utilization is only 15% resulting into
land filling. Only a systematic utilization of this by-product can solve the problem. Each
million ton of Fly ash which replaces OPC help to conserve one million ton of Limestone,
0.25 million ton of coal and more than 80 million units of power, notwithstanding the
abatement of 1.5 million tons of C02 into the atmosphere. In addition, the appropriate
usage of one ton of Fly ash earns one Carbon-credit that has a redemption value of
about 10 to 20 Euros. Therefore, a monetary benefits through Carbon-credit trade is also
possible to Indian economy.
A rubber tire is a composite of complex elastomeric formulations, fibres and steel or
fibred cord. They are made up of piles of reinforcing cords extending transversely from
bead to bead on top of which a belt is located below the thread. Their profusion
availability is also one of the reasons for selecting it as a second option for mixing. A
humongous amount of discarded rubber tires accumulate throughout the world each
year. A disposal of scrap tires also require shredding before land filling. The land filling is
becoming unacceptable due to fast depletion of land as well as an alarm to
environment. About 80 million tires from 33 million vehicles in India alone are on roads.
The amount is more than 303 million tires per year in only US and about 180 million in
European Union. About 6 lacs tonnes of scrap tires were reportedly dumped in the
landfills creating yet again a land filling problem similar to Fly ash. The stock piles of tires
create air, water, health and soil pollution problems. They are not only fire hazards but
also provide breeding grounds to rats, mice, vermin, mosquitoes, etc. The rubber tire
waste is of restricted use in recycling owing to its highly complex chemical structure. The
burning of tires is not only an impractical solution but also an expensive one and noneco
friendly. An enormous amount of dark smoke along with unacceptable smell
carrying some toxic type gaseous contents while burning creates health and
environmental problems. The figures are likely to increase as world traffic on roads
boosted abnormally. Consequently, the millions of tires are just buried all over the world
every year' but it could not serve the purpose as the waste is not bio-degradable in
ambient conditions. In order to save communities from air, water and soil pollutions,
dangerous health and fire hazards and aesthetic inconveniences, land filling, as well as
environmental problems, it is highly necessary to utilize the bulk rubber tire waste by
some another fruitful means. The aim of its application, at this juncture, is to build the
waste tires into a Geopolymeric matrix and thus, obtain technically valuable composite
material. This will prove to be most viable, sustainable, technically suitable, legally
sound, cost-effective, eco-friendly, publically welcomed, and systematic ultimate
solution to the dilemma.
Moreover, it is an eco and user friendly invention with multi benefits viz. self binder
for concrete, improved performance ,low cost, mitigated environmental impact, low
energy, eco and user friendly, nine times more cement for infrastructures and building
applications might be manufactured for the same emission of green house gas C02, to
minimise disposal problems of wastes i.e. land filling, plenty of availability of Fly ash
residues and health hazard rubber tire wastes as well as diminishing restricted natural
resources of Sand have motivated to invent a new type of sustainable, user and eco
friendly Fly ash based Geopolymer concrete incorporating waste rubber tire fibres as
partial replacement of natural Sand i.e. "A Rubberized Fly ash based Geopolymer
concrete ".
STATEMENT OF INVENTION
1. It is a low energy product and is not only eliminates the binder like Ordinary Portland
Cement (i.e. OPC), but also eliminates water curing and consumes diminished
quantity (10 percent less) of natural Sand - a product of restricted natural resources.
2. The incorporation of waste rubber tire fibers resolves the problem of its disposal and
land filling to some extent analogous to Fly ash which too is a residual waste
profoundly accessible from coal based thermal power stations facing the same
dilemmas. The process emits nine times less Carbon Dioxide than Portland cement
which provides relief to the burning enigma of global warming.
6
SUMMARY OF INVENTION
An invention of "FLY ASH BASED GEOPOLYMER CONCRETE INCORPORATING RUBBER TIRE
FIBRES AS PARTIAL REPLACEMENT OF NATURAL SAND", a novel construction material in the
area of construction industry.
The present invention relates to develop a Fly ash based Geopolymer concrete
incorporating rubber tire fibers i.e. rubberized Fly ash based Geopolymer concrete, useful
for construction industry. The process to manufacture rubberized Fly ash based Geopolymer
concrete require low Calcium Fly ash, Sodium Hydroxide as activator, Sodium Silicate as
hardener, 10 percent rubber tire fibers preferably recycled rubber tires from automobiles
for partial replacement of natural Sand, aggregates and a very little quantity of distilled
water. Moreover, superplasticizer can also be admixed with the rubberized Geopolymer
concrete compositions to have desired workability of the Geopolymer concrete as an
additional material. The process can be carried out at room temperature but to obtain
earlier strength it has been carried out at 90°C and atmospheric pressure to obtain the best
results. This proves it to be a low energy product. This process is not only eliminates the
binder like Ordinary Portland Cement (i.e. OPC), but also eliminates water curing and
consumes diminished quantity (10 percent less) of natural Sand - a product of restricted
natural resources. Moreover, the incorporation of waste rubber tire fibers resolves the
problem of its disposal and land filling to some extent analogous to Fly ash which too is a
residual waste profoundly accessible from coal based thermal power stations facing the
same dilemmas. The process emits nine times less Carbon Dioxide than Portland cement
which provides relief to the burning enigma of global warming. Therefore, this invention is
an inexpensive, environmental and user friendly as well as it converts the wastes into the
best in its manufacturing. Furthermore, compressive strength of Fly ash based Geopolymer.
concrete remains almost similar even after incorporating ten percent rubber tire fibres.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1: SEM view of fly ash (50000x).
Figure 2: SEM view of fly ash (lOOOOx).
Figure 3: XRD analysis of fly ash.
Figure 4: EDS analysis of fly ash.
Table 1: Physical properties and chemical composition of fly ash.
Table 2: Properties of the Sodium Hydroxide.
Table 3 : Properties of the Sodium Silicate.
Figure 5: XRD analysis of sand.
Table 4 : Properties of the Fine aggregate and Coarse aggregate.
Figure 6: Rubber tyre fibres.
Figure 7: Particle size analysis of sand and rubber fibres.
Table 5: Properties of the Cement.
Table 6 : Mix design proportion (per m3).
Figure 8: Compressive strength of geopolymer concrete.
Figure 9: Compressive strength of OPC concrete.
Figure 10: Split tensile strength of geopolymer concrete.
Figure 11: Split tensile strength of OPC concrete.
Figure 12: Flexural strength of geopolymer concrete.
Figure 13: Flexural strength of OPC concrete.
Figure 14: Modulus of elasticity of OPC and geopolymer concrete.
Figure 15: Pull-off strength of OPC and geopolymer concrete.
8
Figure 16: Depth of wear for OPC and geopolymer concrete.
Figure 17: Water permeability of geopolymer and OPC concrete.
Figure 18: Sorptivity of geopolymer concrete.
Figure 19: Sorptivity of OPC concrete.
Figure 20: Physical appearance of geopolymer and OPC concrete.
Figure 21: Change in mass of geopolymer specimens after sodium sulfate exposure.
Figure 22: Change in mass of OPC specimens after sodium sulfate exposure.
Figure 23: Change in compressive strength of geopolymer concrete specimens after
sodium sulfate exposure.
Figure 24: Change in compressive strength of OPC concrete specimens after sodium
sulfate exposure.
Figure 25: Physical appearances of specimens after sulphuric acid exposure.
Figure 26: Change in mass of geopolymer specimen after sulfuric acid exposure.
Figure 27: Change in mass of OPC concrete specimen after sulfuric acid exposure.
Figure 28: Change in compressive strength of geopolymer specimens after exposure to 3%
sulfuric acid.
Figure 29: Change in compressive strength of geopolymer specimens after exposure to 5%
sulfuric acid.
Figure 30: Change in compressive strength of geopolymer specimens after exposure to 10%
sulfuric acid.
Figure 31: Change in compressive strength of OPC specimens after exposure to 3% sulfuric
acid.
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9
Figure 32: Change in compressive strength of OPC specimens after exposure to 5%sulfuric
acid.
Figure 33: Change in compressive strength of OPC specimens after exposure to 10% sulfuric
acid.
Figure 34: Chloride diffusion coefficient of geopolymer and OPC concrete.
Figure 35: Macrocell current of geopolymer concrete.
Figure 36: Macrocell current of OPC concrete.
Figure 37: Half-cell potential measurement of geopolymer concrete.
Figure 38: Half-cell potential mesurement of OPC concrete.
Figure 39: Drying shrinkage of geopolymer concrete specimen.
Figure 40: Drying shrinkage of OPC concrete specimen.
Figure 41: Carbonation depth of geopolymer concrete specimen.
Figure 42: Carbonation depth of OPC concrete specimen.
Figure 43: Salt Resistance of geopolymer concrete specimen.
Figure 44: Salt Resistance of OPC concrete specimen.
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DETAILED DESCRIPTION OF THE INVENTION
Materials used to develop rubberized Geopolymer concrete :
The two most important materials for producing geopolymer concrete are the source
material, such as fly ash, and the alkaline solution.
Fly ash
Class F low-calcium fly ash was used as the source material for making fly ash-based
geopolymer concrete. The chemical properties of fly ash are presented in Table 1. Silica,
magnesium oxide, sulfur trioxide, and sodium oxide are present in fly ash up to permissible
limits as per IS.3812 [1], It can be seen from the loss of ignition value (LOl) that the fly ash
contains a very small percentage of carbon. The total percentage of Si02 + AI203 + Fe203 is
92.26%, which is greater than the 70% limit prescribed in IS: 3812 [1].
The LOl value is very low because of the small amount of carbon present in the fly ash. The
fly ash contains less than 10% calcium. Hence, according to ASTM C618-03 [2], it is said to be
low calcium class F-type fly ash. The colour of the fly ash is dark grey, and its specific area is
428 m2/kg. The fineness of the fly ash can be described by stating that 95% passes through a
45 \xm sieve. Figures 1 and 2 show scanning electron microscopy (SEM) images of the y ash
at 50000x and lOOOOx. Fly ash is composed of spherical particles, as shown in Figure 1.
These small glass spheres improve the fluidity and workability of fresh geopolymer concrete.
The size of fly ash particles varies from 0.01 to 1000 jim. The fineness of fly ash particles
increase the surface area and improve the particle packing in the binder paste which in turn
contributes to its pozzolanie reactivity.
Figure 3 presents XRD images of fly ash at an angle of 28. The XRD analysis of fly ash reveals
the presence of mullite, magnetite, hematite, and quartz. Ca, Si, Al, and C are present in the
fly ash, as per the EDS analysis illustrated in Figure 4.
11
Alkaline Solution
An alkaline solution was prepared by mixing sodium hydroxide liquid and sodium silicate
solution.
Peculiarity of Sodium Hydroxide (NaOH)
Sodium Hydroxide (NaOH) is the most commonly used hydroxide activator in geopolymer
synthesis, as it is readily available and is cheaper than other alkali hydroxides. Its low
viscosity is an additional advantage as an activator. Therefore, NaOH flakes with 98% purity
and a laboratory-grade reagent were used in this study. The NaOH solution was prepared by
dissolving NaOH flakes into the water. The concentration of NaOH is expressed in terms of
molarity, M. A concentration of 14M was achieved by dissolving 404 g of NaOH flakes in 1 L
of water. The properties of the NaOH are given in Table 2.
Peculiarity of Sodium Silicate (Na2Si03)
A water glass form of sodium silicate was used for the current research. The properties of
sodium silicate are listed in Table 3.
Natural sand with a maximum particle size of 4.75 mm was used as a fine aggregate.
Crushed basalt rock of 20 mm and 10 mm diameter was used as a coarse aggregate. Tests
for fine and coarse aggregates were conducted as per the provisions of IS:2386-1963 [3] and
IS:383-1970 [4], respectively. The physical properties of the river sand, sand and coarse
aggregates are listed in Table 4. XRD analysis of the sand is illustrated in Figure 5. Potassium
aluminium silicate, sodium silicate, silicon oxide, and manganese rhodium silicon were
present in river sand, as shown in Figure 5.
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12
Rubber Tyre Fibres
Rubber tyre fibres obtained from the mechanical grinding of rubber tyre waste were used as
a partial replacement of the fine aggregates, as shown in Figure 6. These rubber tyre fibres
were approximately 2-4 mm wide and up to 22 mm long, with a specific gravity of 1.09.
Rubber fibres replaced 10%, 20% and 30% by weight of the fine aggregate. The particle size
of the rubber tyre fibres is within Zone II, as per IS:383-1970 [4], as shown in Figure 7.
Superplasticizer
It was observed that any increase in rubber fibre content in the geopolymer concrete mix
leads to a reduction in the slump value of the geopolymer concrete. Therefore, to achieve
the desired slump value, naphthalene sulfonate-based superplasticizer was used as an
admixture. This superplasticizer has a relative density of 1.26 ±0.02 at 25°C, pH>6, and a
chloride ion content of less than 0.2%.
Ordinary Portland cement
OPC 43 grade \Binani cement conforming to IS-4031-1989 [5] was used to prepare cement
concrete specimens. The properties of this cement are listed in Table 5.
Mix Design Proportioning
OPC Concrete Mix Design
The proportions for the OPC concrete mix were calculated based on IS 10262-2009 [6]. The
volume of aggregate used in the OPC concrete was in the range 75-80% by mass. The fine
aggregate was taken as 35% of the total aggregate. The mixture proportion of OPC concrete
is listed in Table 6. Waste rubber tyre fibres were used in concrete as a partial replacement
for the fine aggregate (0%, 10%,20%,30%). The mixture proportions of OPC concrete are
similar to those of the geopolymer concrete mixture, except for the water content (see
Table 6).
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13
Geopolymer Concrete Mix Design
The geopolymer concrete mix design was finalized, according to the past studies of Rangan
[7], by considering parameters such as NaOH concentration, alkaline liquid ratio, alkaline
liquid to fly ash ratio, aggregate content, and water content The main difference between
geopolymer concrete mix design and OPC concrete mix design is the binding material. In
geopolymer concrete, a source material such as fly ash, which is rich in silica and alumina,
reacts with an alkaline liquid to form geopolymeric bonds between the aggregates,
geopolymer paste, and other unreacted materials that make up geopolymer concrete [8]. In
geopolymer concrete, the aggregate was taken as 75-78% of the entire mix by mass. This
value is similar to that used in OPC concrete. Fine aggregate constituted 35% of the total
aggregate. The average density of the geopolymer concrete was similar to that of OPC
concrete, i.e. 2500 kg/m3 [9].
Concrete Mix Proportioning for Geopolymer Concrete
The following constituents for mix design of each mix:
• Ratio of alkaline liquid to fly ash by mass: 0.4
• Ratio of sodium silicate to sodium hydroxide: 2.5
• Concentration of sodium hydroxide solution: 14 M
• Admixture dosage: 2%
• Additional water content: 5%
• Curing-temperature: 90°C
• Curing time: 48 h
• Rest period: Iday
14
Results and Discussion:
Compressive Strength Test
The compressive strength of geopolymer concrete measured at 3, 7, 28, 90, and 365 days is
shown in Figure 8. It can be seen that, as the percentage of waste rubber tyre increases
from 0-30%, the compressive strength decreases at all ages. In geopolymer concrete, a fast
geopolymerization process takes place due to a chemical reaction between the alkaline
solution and source material, resulting in 95% compressive strength gain in only 7 days [10-
12]. After 28 days, the compressive strength of geopolymer concrete varies from 30-54 MPa
depending on the rubber fibre content. The compressive strength depends on the
gqopolymeric mechanism developed in the geopolymer paste. After 365 days, the
compressive strength had only increased marginally because of the speed of the
polymerization process. This is because of the chemical reaction of the geopolymer gel with
age and the development of a crystalline structure [8,13]. The compressive strength of
geopolymer concrete depends on factors such as NaOH concentration, alkaline liquid ratio,
curing temperature, and aggregate content. From past studies, it is clear that increasing
each of these factors will increase the compressive strength of the geopolymer concrete
[13/14]. Figure 9 shows the compressive strength of OPC concrete measured at 28, 90, and
365 days. The compressive strength of OPC concrete depends on the hydration mechanism
of cement paste [15]. The hydration process is a long, continuous process whereby the
pores of the concrete gradually fill, resulting in strength gains over the course of a year [16].
The compressive strength of OPC concrete is decreases when waste rubber fibres are
introduced. The compressive strength of OPC concrete is less than that of geopolymer
concrete.
Split Tensile Strength Test
Figures 10 and 11 show the split tensile strength of geopolymer concrete and OPC concrete
after 28, 90, and 365 days. The split tensile strength of all mixes is ranges from 5.34-5.49
MPa after 365 days. The geopolymer concrete exhibits higher tensile strength than OPC
15
concrete because of the good bonding between the geopolymer paste and aggregate.
Similar observations have been reported in past studies [17-19]. The highest split tensile
strength was found in the 30% rubber fibre mix after 365 days, and the lowest tensile
strength was found in the control geopolymer concrete after 28 days. A gradual increase in
split tensile strength can be observed as the rubber fibre content increases from 0-30%.
Similar results have been reported in previous study [20]. In geopolymer concrete, there is a
high level of geopolymeric bonding between the geopolymer paste and aggregate;
therefore, during testing, when the cylinder was broken in half, none of the aggregate was
pulled out, unlike for the OPC concrete. This is a result of the chemical bonding between the
alkaline liquid and aggregate [21].
Flexural Strength Test
Figures 12 and 13 show the average flexural strength of the geopolymer concrete and OPC
concrete. The flexural strength of the geopolymer concrete varies from 6.45-9.97 MPa,
whereas that for OPC concrete varies from 5.35-6.86 MPa. The flexural strength increases
with age in all mixtures. This proves that the flexural strength of geopolymer concrete is
higher than that of OPC concrete. Similar evidence has been reported in previous research
[13, 22]. The tension properties of geopolymer concrete, such as flexural and tensile
strength, are superior to those of OPC concrete because of the better bonding between the
geopolymeric paste and aggregate. The
flexural strength also increases with percentage of rubber fibres for both OPC and
geopolymer concrete.
Modulus of Elasticity Test
The average modulus of elasticity of the geopolymer concrete and OPC concrete was
measured after 28 days. The modulus of elasticity of the geopolymer concrete varied from
16
20-31.5 GPa, and that for OPC concrete ranged from 18-27.5 GPa (see Figure 14). It can be
seen that, in all the mixes, the modulus of elasticity decreases as the rubber fibre content
increases. The modulus of elasticity of geopolymer concrete depends on the geopolymeric
microstructure, and is independent of the aggregate and source materials. An increase in
the rubber fibre content decreases the homogeneity of the geopolymer and OPC concrete,
resulting in a decrease in the modulus of elasticity. Similar observations have been made in
previous studies [20]. The modulus of elasticity of the geopolymer concrete and OPC
concrete decrease by 36.34% and
34.54%, respectively, as the rubber fibre content increases from 0-30%.
Pull-off Test
The average pull-off strength was measured after 28 days, and the results are shown in
Figure 15. As the compressive strength increases, the pull-off strength increases. It can be
seen that the pull-off strength decreases when rubber fibres are introduced to the mix. The
results show geopolymer concrete has better pull-off strength than OPC concrete; Both
rubber fibre geopolymer and OPC concrete exhibit poor pull-off strength performance,
because there is less bonding between the paste and aggregate, which results in a weaker
surface layer than in the control geopolymer and control OPC concrete. The pull-off strength
of geopolymer concrete decreases from 13.46% to 21.15% and then by 32.69% as the
rubber fibre content increases to 10%, 20%, and 30%, respectively; the pull-off strength of
the OPC concrete reduces from 2.38% to 21.42% and then 26.19%, respectively.
Abrasion Resistance Test
The abrasion resistance test was carried out at 28 days age according to IS 1237-2009 [23].
Abrasion resistance was measured in terms of depth of wear. Figure 16 shows that the
abrasion resistance increases as more rubber fibres are added to the mix. As per IS 1237-
17
2009 [23], the permissible depth of wear for general purpose tiles and heavy-duty floor tiles
is 4.0 mm and 2.5 mm, respectively. From the figure, it is evident that the maximum depth
of wear occurs when there are no rubber fibres in the mix. In all mixes, the depth of wear is
within permissible limits. It can be concluded that rubber tyre fibres could be used with fly
ash or cement to make general purpose and heavy-duty floor tiles.
Water Permeability Test
The water permeability test was carried out according to DIN-1048 [24]. Permeability was
evaluated in terms of the depth of water penetration. Figure 17 shows the variation in
water penetration depth with respect to rubber fibre content. The water penetration depth
increases as the rubber fibre content is increased. The water penetration is lower in
geopolymer concrete than in OPC concrete. Similar results have been reported in previous
study [24]. The continuous chemical reaction between fly ash and alkaline solution results in
a change in porosity and creates denser pores in geopolymer concrete [25,26]. However, a
detailed examination found that the variations were very small in the case of geopolymer
concrete. Minimum and maximum water penetration values of 31.2 mm and 35.7 mm occur
in the geopolymer concrete. The increase in penetration depth can be attributed to the
increase in porosity of the concrete, which is evident at higher replacement levels of rubber
fibres. In OPC concrete, the minimum and maximum water penetration is 38.03 mm and
42.8 mm, respectively. It is evident that the development of pores is dependent on the
alkaline solution, aggregate, and source materials. Unlike the OPC concrete, which
undergoes a hydration process, the pores in the geopolymer are filled by alumino-silicates.
This lower permeability of geopolymer concrete has led to it being referred to as "excellent"
concrete [13,27].
Sorptivity Test
Sorptivity measures the transport properties of concrete by which water passes through
capillary pores into the concrete. Figures 18 and 19 illustrate the sorptivity index of
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18
geopolymer concrete and OPC concrete. From Figure 18, it can be concluded that the
geopolymer concrete has lower sorptivity (0.09-0.164 mm/min0"5) than OPC concrete
(0.113-0.203 mm/min0,5) after 28 days. A similar observation was recorded in previous
research [28]. The limit of the sorptivity index is below 0.200 mm/min0,5, which is the
recommended value for concrete according to previous research [28]. The control
geopolymer concrete has a sorptivity index of 0.09 mm/min0,5 after 28 days.
This fact indicates that few capillary pores exist following the effective reaction between the
alkaline solution and source material, whereas capillary pores persist in the OPC concrete to
enable the hydration of the cement. Also as the percentage of rubber fiber is increased, the
sorptivity index is also increased for both the concrete (geopolymer and OPC). Hence,
geopolymer concrete has fewer capillary pores than OPC concrete. This results in a slower
rate of sorptivity into the geopolymer concrete compared with OPC concrete.
Sulfate Resistance Test
The sulfate resistance test was conducted on the geopolymer concrete and OPC concrete.
The test was performed by soaking the specimen in 5% Na2S04 (sodium sulfate) solution.
The sulfate resistance was evaluated based on changes in physical appearance, mass,
length, and compressive strength after exposure periods of 7, 28, 84,162 and 365 days. For
comparison, specimens were also soaked in distilled water.
The physical appearance of the geopolymer specimens after one year exposure is shown in
Figure 20. After exposure to sodium sulfate for up to one year, no changes were observed in
the geopolymer specimens. These specimens did not exhibit any change in shape, and no
cracking or spading; in contrast, the OPC concrete specimen had expanded and suffered
from frequent random cracking. Figure 20 shows that the physical appearance of the
geopolymer specimen soaked in 5% sodium sulfate solution was also unchanged. Similar
observations have been reported in previous research [29].
19
Figure 21 illustrates the change in mass of geopolymer concrete specimens after exposure
to sodium sulfate for up to one year. It can be seen that there has been no significant
change in mass in the geopolymer specimen, whereas the mass of the OPC concrete
specimen has increase intially due to absorption of sodium sulphate solution and
degradation of mass observed due to effect of sodium sulphate solution shown in Figure 22.
A significant increase in mass was observed in the geopolymer specimen as a result of the
absorption of liquid through geopolymer specimens. The absorption of liquid by the
geopolymer specimens increased their mass by 1.3%, compared with an increase in mass of
3.0-3.5% in the OPC specimens.
The change in compressive strength of the geopolymer concrete and OPC concrete
specimens after exposure to sodium sulfate is illustrated in Figures 23 and 24. The
compressive strength of each specimen was measured under the SSD condition after
exposure. A significant change in compressive strength was observed in the geopolymer
specimens with exposure, whereas the OPC concrete specimens show reduced compressive
Strength. The reduced compressive strength in OPC concrete is due to the formation of
ettringite and expansive gypsum, which result in cracking, expansion, and spalling. Similar
results have been observed in past research [29-31]. In geopolymer concrete, the
geopolymerization process occurs in place of hydration, meaning that there is generally no
formation of gypsum and ettringite. The high alkali content improves the resistance of
geopolymers against sulfate exposure, as confirmed by previous research [29]. These test
results clearly show the superior resistance of geopolymer concrete against sulfates over
that of OPC concrete.
Acid Resistance Test
The acid resistance test was conducted on the geopolymer concrete and OPC concrete
specimens by soaking them in 3%, 5%, and 10% concentrations of sulfuric acid for 7, 28, 84,
20
162, and 365 days. This test demonstrates the behaviour of geopolymer concrete and OPC
concrete in terms of physical appearance, change in mass, and change in compressive
strength after exposure to sulfuric acid.
Figure 25 shows the physical appearance of the geopolymer specimens after one year
exposure period. It is evident that the specimens of all mixtures undergo erosion after
exposure to acid. The damage to the concrete surface increases as the sulphuric acid
becomes stronger. The erosion of the QPC concrete specimens is greater than that of the
geopolymer concrete.
Figures 26 and 27 show the change in mass of both types of concrete after 5% acid exposure
for up to 365 days. It can be seen that the geopolymer concrete specimens gain some
weight during the first week of exposure, because they absorb the liquid over this period.
From this point on, the mass of all specimens decreases as a result of acid exposure. It can
be seen that the percentage of mass loss increases with the exposure period. In geopolymer
concrete, the results for the first week show that the mass of the specimens increased by
0.98-1.15% for all concentrations, then decreased over the remaining exposure period. In
the OPC concrete, the mass of the specimen increased by 1.8-2.5% in the first week, and
then decreased. The OPC concrete specimens lost more mass than the geopolymer concrete
specimens. This result agrees with previous research [29, 32-35].
Figures 28-33 show the change in compressive strength of the geopolymer concrete and
OPC concrete specimens after each exposure period. These results can be compared with
the compressive strength of specimens that were not subjected to acid exposure. From
Figures 28-33, it can be seen that the compressive strength is reduced on exposure to
sulfuric acid. The change in compressive strength depends on the concentration of sulfuric
acid and the period of exppsure. Increases in the period of exposure and concentration of
sulfuric acid enhance the degradation in compressive strength of all.mixes. The rate of
21
reduction of compressive strength is highest following the one year exposure period. In the
control geopolymer concrete, the 3%, 5%, and 10% concentrations of sulfuric acid result in
compressive strengths of 32.14, 30.78, and 17.65 MPa, respectively, after 365 days, whereas
for the control OPC concrete, the respective strengths are 29.23, 26.00, and 13.89 MPa. This
shows that the geopolymer concrete is more resistant to sulfuric acid than OPC concrete. In
geopolymer concrete, the source material contains relatively little calcium, which is the
major factor in increasing resistance against acid [29,34,35]. In all mixes, it was found that
higher concentrations of sulfuric acid result in greater deterioration, resulting in greater loss
of strength. In the geopolymer specimens, this deterioration is due to the formation of
zeolite and the depolymerization of alumino-silicate. Similar results have been confirmed by
previous research [29,35]. These results also prove that geopolymer and OPC concrete
containing rubber fibres increase the porosity of the concrete, which causes a greater
reduction in compressive strength.
Chloride Diffusion Test
The steady state chloride ion migration test was performed for the geopolymer and OPC
concrete specimens, and the coefficients of chloride diffusion are presented in Figure 34.
From this Figure, it can be seen that the geopolymer concrete has lower chloride diffusion
coefficients than the OPC concrete. The chloride diffusion coefficients increase with the
rubber fibre content in both types of concrete. The minimum chloride diffusion coefficients
for geopolymer concrete and OPC concrete are 1.0 x 10"12 and 1-5 x 10"12, respectively, and
the maximum chloride diffusion coefficients are 1.2 x 1012 and 1.7 x 10"12, respectively.
These values are similar to those reported in a previous study [20].
Corrosion Resistance Test
Macrocell current mesurements
ELBE 3a-©?-2;©I&- 1? : 41
22
The Macrocell current was measured according to ASTM G109 [36] with the 100 Ohm
resistance. The positive macrocell current indicate that corrosion is in progress. A minimum
value of IOJIA is considered to ensure the presence of sufficient corrosion. Figure 35 shows
that, the macrocell current of geopolymer concrete specimen was less than 10 jiA, up to the
age of 9 months for control as well as rubberized geopolymer concrete. Whereas, more than
IO^IA macrocell current was recorded at 10th, 11th and 12th month for all mixes.
The variation of macrocell current with time for geopolymer concrete and OPC concrete is
shown in Figures 35 and 36. The macrocell current for rubberized concrete mixes was more
than that for the control concrete at all the ages. For OPC concrete, current exceeded 10 nA
at 8th month to 12th month for all mixes. The maximum anodic current for control mix was
measured as 11.2 \JA, 13.4 \xA, 17.1 \xA and 19.3 \JK at 12th month for geopolymer concrete
whereas the maximum current for OPC concrete was measured as 15.3 \xA, 18.9 \xA , 15.8
\xA and 22.1 \xA . From the above results, it can be shown that the inclusion of waste rubber
fiber increases the probability of early initiation of corrosion in both type of concrete.
Half-cell potential measurements
The half-cell potential was measured as according to ASTM C876 [37] between top bar and
reference electrode. The results of half-cell potential readings for geopolymer concrete and
OPC concrete are shown in Figures 37 and 38. According to ASTM standard, when potentials
are more negative than -350 mV, there is more than 90% probability that corrosion in
reinforcing steel bars will occur. For geopolymer concrete, the potential was less negative
than -350 mV up to 9th months shown whereas for OPC concrete, the potential was less
negative than -350 mV up to 8th months as shown in Figures 37 and 38.
The variation of half-cell potential for geopolymer and OPC concrete is shown in Figure 38.
The half cell potential of waste rubber fiber concrete was higher than that for the control
23
mix at the ages. More negative than -350 mV potential was recorded at 10 month to 12
month in geopolymer concrete whereas, OPC concrete the potential became more negative
than -350 mV at 9th month to 12th month.
The maximum potential was measured as -360mV, -400 mV and -420, and -460 mV for
geopolymer concrete at 12th month whereas the maximum potential for OPC concrete at
12th month was measured as -400 mV, -455 mV, -432 mV and -500 mV, It is observed from
the above results that the geopolymer concrete decreases the probability of early initiation
of corrosion compare than OPC concrete.
Drying Shrinkage Test
The drying shrinkage with time for geopolymer concrete and OPC concrete is shown in
Figures 39 and 40 From the Figure it can be seen that geopolymer concrete undergoes low
drying shrinkage compare with OPC concrete. The low drying shrinkage associated with its
finer pore structure leads to low diffusibility and considerably slows down rate of drying
shrinkage. In the geopolymerization process water is expelled which results less amount of
water present in the micro pores of geopolymer concrete. This Results in low drying
shrinkage. The shrinkage strain is fluctuating with time due to moisture movement from the
environment to concrete and vice versa which develops reversible shrinkage and swelling of
concrete. It can be observed that the drying shrinkage increased with the increase in the
rubber fiber content as well as increase in time for both the cases. The increase in porosity
due to rubber particles leads to increase in the rate of shrinkage.
24
Carbonation Resistance Test
The depth of carbonation measured for geopolymer and OPC concrete is shown in Figures
41 and 42 for 14, 21, 28, 35, 42, 56 and 90 days duration (5% C02 exposure). It can be
observed that the carbonation depth increased with the increase of C02 exposure duration
and replacement level for all the mixes. It is observed from the present study that the
carbonation depth for large replacement level (30%) and high C02 concentration (5% for 90
days) was less than the minimum cover required (15 mm) for both the concrete. The
carbonation depth for any replacement level of fine aggregate by rubber fiber decreased
with increase in rubber content. The increase in carbonation depth may be due to increase
in water absorption and water permeability as earlier observed in the present research. A
maximum carbonation depth of 8.0 mm was observed for geopolymer concrete with 30%
replacement level of fine aggregate whereas at the same replacement level, carbonation
depth of 9,0 mm was observed for OPC concrete at 90 days exposure.
Salt Resistance Test
Salt resistance test was conducted on geopolymer concrete and OPC concrete. The test was
performed by soaking the specimen in 5% NaCI (Sodium chloride) solution. The salt
resistance was evaluated based on change in compressive strength after exposure of 7, 28,
84, 162, and 365 days. Compressive strength of geopolymer concrete and OPC concrete
after exposure to sodium chloride is shown in Figures 43 and 44, respectively. Compressive
strength of specimens was taken under saturated surface dry condition after exposure and
results compared with the specimens with no exposure. No significant change was observed
in the compressive strength of geopolymer concrete on exposure to salty solution. There
was however some reduction in the compressive strength of the rubberized geopolymer
concrete on exposure to salt after replacement of more than 10%. There was significant
reduction in the compressive strength on exposure to salty solution for controi OPC
concrete as well as rubberized concrete. The results clearly show the excellent resistance of
25
geopolymer concrete (both control as well as rubberized) against the OPC concrete (both
rubberized as well as geopolymer).
Conclusion
From the results reported in this chapter, the following conclusions can be drawn:
1. As the percentage of waste rubber fibers increases, the compressive strength decreases
at all ages. Geopolymer concrete gain 95% compressive strength only in 7 days. The
compressive strength of OPC concrete is less than that of geopolymer concrete.
2. The geopolymer concrete exhibits higher tensile strength than OPC concrete because of
the good bonding between the geopolymer paste and aggregate.
3. The tension properties of rubberized geopolymer concrete, such as exural and tensile
strength/are increased as the percentage of rubber fibers increased. The maximum Flexural
strength was observed in 30% replacement of sand by fibers. This is because of the fibers
which provide a better bridge between propagated cracks.
4. It can be seen that, in all the mixes, the modulus of elasticity decreases as the rubber
fibre content increases. The moduius of eiasticity of the geopdiymer concrete and OPC
concrete decreased by 3634% and 34.54%, respectively, as the rubber fibre content
increases from 0-30%.
5. it can be seen that the pull off strength decreases when rubber fibres are introduced to
the mix. The results show geopolymer concrete has better pull off strength than OPC
concrete.
6. It is evident that the maximum depth of wear occurs when there are no rubber fibres in
the mix. In all mixes, the depth of wear is within permissible limits. It can be concluded that
rubber tyre fibres could be used with fly ash or cement to make general purpose and heavyduty
floor tiles.
7. The water penetration depth increases as the rubber fibre content is increased. The water
penetration depth is lower in geopolymer concrete than in OPC concrete. The increase in
26
penetration depth can be attributed to the increase in porosity of the concrete, which is
evident at higher replacement levels of rubber fibres.
8. After exposure to sodium sulfate for up to one year, no physical changes were observed
in the geopolymer specimens. These specimens did not exhibit any change in shape, and no
cracking or spalling, in contrast, the OPC concrete specimen had expanded and suffered
from frequent random cracking. A significant change in compressive strength was observed
in the geopolymer specimens after exposure, whereas the OPC concrete specimens show
reduced compressive strength.
9. The specimens of all mixtures undergo erosion after exposure to acid. The damage to the
concrete surface increases as the sulfuric acid becomes stronger, it was found that higher
concentrations of sulfuric acid result in greater deterioration, resulting in greater loss of
strength,
10. It can be seen that the geopolymer concrete has lower chloride diffusion coefficients
than the OPC concrete. The chloride diffusion coefficients increase with the rubber fibre
content in both types of concrete.
11. The macrocell current for rubberized concrete mixes was more than that for the control
concrete at all the ages. For OPC concrete, current exceeded 10 \xA at 8th month to 12th
month for ail mixes. It can be stated that the inclusion of waste rubber fiber increases the
probability of early initiation of corrosion in both type of concrete.
12. The half cell potential of waste rubber fiber geopolymer and OPC concrete was higher
than that for the control geopolymer and OPC concrete mix. More negative than -350 mV
potential was recorded at 10th month to 1.2th month in rubberized geopolymer concrete
whereas, rubberized OPC concrete the potential became more negative than -350 mV at 9th
month to 12th month.
13. The drying shrinkage increased with the increase in the rubber fiber content as well as
increase in time for both the cases. The increase in porosity due to rubber particles which
lead to decrease the rate of shrinkage.
27
14. The carbonation depth for any replacement level of fine aggregate by rubber fiber
decreased with increase in rubber content A maximum carbonation depth of 8.0 mm was
observed for geopoiymer concrete with 30% replacement level of fine aggregate whereas at
the same replacement level, carbonation depth of 9.0 mm was observed for OPC concrete
at 90 days exposure.
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I/We claim
1. A fly ash based geopolymer concrete incorporating rubber tire fibres consisting low
Calcium Fly ash, Sodium Hydroxide as activator. Sodium Silicate as hardener, 10
percent rubber tire fibers and a very little quantity of distilled water.
2. As claimed in claim 1, the process is carried out at 90°C and atmospheric pressure to
obtain earlier strength.
3. As the percentage of waste rubber fibers increases, the compressive strength
decreases at all ages whereas Geopolymer concrete gain 95% compressive strength
only in 7 days as claimed in claim 2.
4. The process as claimed in claim 3, the maximum Flexural strength was observed in
30% replacement of sand by fibers.
5. As claimed in claim 4, the modulus of elasticity of the geopolymer concrete and OPC
concrete decreased by 36.34% and 34.54%, respectively, as the rubber fibre content
increases from 0-30%.
6. After exposure to sodium sulfate for up to one year, no physical changes were
observed in the geopolymer specimens wherein a significant change in compressive
strength was observed in the geopolymer specimens after exposure, whereas the
OPC concrete specimens show reduced compressive strength as claimed in claim 5.7. For OPC concrete, current exceeded 10 [iA at 8 month to 12 month for all mixes.
8. As claimed in claim 7, more negative than -350 mV potential was recorded at 10th
month to 12th month in rubberized geopolymer concrete whereas rubberized OPC
concrete the potential became more negative than -350 mV at 9th month to 12th
month.
9. The carbonation depth for any replacement level of fine aggregate by rubber fiber
decreased with increase in rubber content.
10. The process as claimed in claim 1 and claim 2, a maximum carbonation depth of 8.0
mm was observed for geopolymer concrete with 30% replacement level of fine
aggregate whereas at the same replacement level carbonation depth of 9.0 mm was
observed for OPC concrete at 90 days exposure.
l>obsPB=