Resistance of Concrete Containing Waste Glass Powder Against MgSO4 Attack
Most soils contain some sulphate in the form of calcium, sodium, potassium and magnesium. They occur in soil or ground water. Because of solubility of calcium sulphate is low, ground water contain more of other sulphates and less of calcium sulphate. Ammonium sulphate is frequently present in agricultural soil and water from the use of fertilizers or from sewage and industrial effluents. This study presents investigation on the effect of sulphate attack on the properties of concrete. Decomposing of waste glass possesses major problem because glass is non-biodegradable, remains in our environment and do not decompose easily by itself therefore do not have significant environmental and social impact could result in serious impact after disposal. Concrete produced by replacing cement with waste glass powder (GP) in different proportion has been studied. Higher resistance to sulphate attack was obtained when 20% cement was replaced by waste glass.
M. N. Bajad, Research Scholar, S.V.N.I.T, Surat, C. D. Modhera, Professor, S.V.N.I.T, Surat and A. K. Desai, Associate Professor, S.V.N.I.T, Surat.
Table 1 and Figure 1,2 shows the chemical composition of the cementing materials. The particle size distribution of the glass powder and cement are shown in figure 3
Figure 1: Chemical composition of cement
Figure 2: Chemical composition of glass powder
Figure 3: Particle Size Distributions of Cementitious Materials
Figure 4: Mechanism of sulfate attack
Sulphates reacts chemically with the product of hydration (hydrated lime and hydrated calcium aluminates in the cement paste to form calcium sulphate and calcium sulfo aluminates) are called ettringite. These new crystals occupy empty space (Figure 4) and as they continue to form, they cause expansion, disruption, loss of bond between the cement paste and aggregate because paste expansion produces a small gap around small aggregate particles and a bigger gap around larger particles as shown in figure 5, which result in micro cracks and these cracks may be responsible for reduction in strength or damaging the concrete (Figure 6) by changing the chemical nature of the cement paste and of the mechanical properties of the concrete.
It can be summerarised that at a concentration of about 0.2% sulphate content in the ground water, concrete may suffer sulphate attack; that magnesium sulphate can be more aggressive than sodium; and that there are three key chemical reactions between sulphate ions and hardened cement pastes. The reactions are: recrystallisation of ettringite; formation of gypsum; and decalcification of the main cementitious phase (C-S-H).
In the presence of the calcium hydroxide formed in cement paste, when the latter comes in contact with sulphate ions, the alumina containing hydrates are converted to the high sulphate from ettringite. These etteringte crystals grow, expand, or swell by mechanisms, which are still the subject of controversy among researchers. While there is agreement that most (but not all) ettringites will expand in this formation, the exact cause are not agreed.
The formation of gypsum as a result of cat ion exchange reactions is also capable of causing expansion but is normally linked to loss of mass and strength. The decalcification of the C-S-H has not received as much discussion as the other two types of sulphate attack, but can be just as important, particularly where the sulphate solution is lower in PH (i.e. more acidic. This particular reaction, with more gypsum formation, leads to both strength loss and expansion. This is a particular situation in which blended cements with lower initial calcium/silica (C/S) ratios in the C-S-H gel are shown to be less susceptible to this type of attack.
C3A.Cs.H18 + 2CH +2s+12H = C3A.3Cs.H32
C3A.CH.H18 + 2CH +3s + 11H = C3A.3Cs.H32
The sulphate ion + hydrated calcium aluminates and/or the calcium hydroxide components of hardened cement paste + water = gypsum (calcium sulphate hydrate)
Na2SO4+Ca(OH)2 +2H2O = CaSO4.2H2O +2NaOH
MgSO4 + Ca(OH)2 + 2H2O = CaSO4.2H2O + MgOH
when concrete contain waste glass powder it gives higher percentage of C2S,Low C3A,C4AF,C3S/C2S Content which result in production of less heat of hydration and offers greater resistance to the attack.
It has been estimated that several million tons of waste glass is generated annually worldwide due to rapid growth of population, improvement in the standard of living, industrialization and urbanization. Hence utilization of waste glass has become a critical issue worldwide. The key sources of waste glasses are waste containers, window glasses, and windscreen, medicinal bottles, liquor bottles, tube lights, bulbs, electronic equipment, etc.
Recycling, disposal and decomposing of waste glass possesses major problems for municipalities everywhere, and this problem can be greatly eliminated by re-using waste glass as a cement replacement in concrete. Moreover, there is a limit on the availability of natural aggregate and minerals used for making cement, and it is necessary to reduce energy consumption and emission of carbon dioxide resulting from construction processes, solution of this problem are sought thought usages of waste glass as partial replacement of Portland cement. Replacing cement by pozzolanic material like waste glass powder in concrete, not only increases the strength but also reduces the unit weight.
Recycling of waste glass may affect respiratory system if breath in pollutants. Case-local residents at merceds Arumbula claimed that the neighborhood and kids have developed asthma once the plant was built in their community
Disposal of waste glass degrade communities living condition and harmful to human health because lactates and gas releases from the landfill site
Sulphate reacts with product of hydration causes expansion. Therefore an experimental investigation in developing concrete containing waste glass powder is very important
The purpose of this investigation was to evaluate the effect of partial replacement of cement by waste glass powder (GP) on strength of concrete specimens. The experimental parameters and their levels were chosen according. Experimental programme plan is shown in Figure 7.
Figure 7: Plan of Experimental programme
Constituent Materials
Cement
Ordinary Portland Cement (OPC) 43 grade confirming to IS 8112
Aggregate
Locally available sand and coarse aggregates were used in this experiment. The sand used was Zone II, with specific gravity of 2.62. Specific gravity of coarse aggregate was 2.93. Coarse aggregate used 20 mm and down size.
Admixture
To impart workability to the mix, a superplasticiser from a reputed company was used with the dosage of 2% by weight of cement
Supplementary Cementitious Materials
The glass powder was obtained by crushing waste glass pieces in a cone crusher mill. The 600-micron passing fraction was used for the experimentation
Mix Proportions and experimental factors
Mix design carried out to form M20 grade of concrete by IS 10262: 2009 yielded a mix proportion of 1:2.35:4.47 with water cement ratio of 0.50. Nine different mixes (M1,M2,M3,M4,M5,M6,M7,M8,M9)were prepared using cement replaced by waste glass powder (GP) at varying percentages of 0, 5, 10, 15, 20, 25, 30, 35 and 40.
Casting
Fifty four number of Specimens size 150 x 150 x 150 mm and Twenty seven number of specimens of dimensions 150 x150x 700 mm were cast according to the mix proportion and by replacing cement with glass powder (GP) in different proportion
Preparation of Solution and Caution
A 5% MgSO4 solution has five grams of magnesium sulphate dissolved in 100 ml solution.
Procedure Weigh 5 gram of magnesium sulphate & pour it into a graduated cylinder or volumetric flask containing about 80 ml of water. Once the magnesium sulphate has dissolved completely add water to bring the volume up to final 100 ml.
Caution-Do not simply measure 100 ml of water and add 5 gram of magnesium sulphate. This will introduce error because adding the solid will change the final volume of the solution and change the final percentage.
Curing of Specimens
To find out the effect of water (concrete without subjected to attack), the specimens were immersed in a 100% H2O solution (water) for 7, 28, and 90 days
To find out the effect of Sulphate attack, the specimens were immersed in a 5% MgSo4 solution for 7, 28, and 90 days.
Testing
To find out the strength, specimens were tested at 7, 28 and 90 days using a compression testing machine (CTM) of capacity 2000KN in accordance with the provisions of the Indian Standard specification IS 516:1959
Workability
Table 2 and Figure 8 shows the results of workability of concrete with cement replacement by glass powder in various percentages ranging from 5% to 40% in increments of 5% (0%, 5%, 10%, 15%, 20%,25%, 30%,35% and 40%). It seems workability of concrete decreases as the glass content increases.
Figure 8: Variation of slump of concrete with cement replacement by glass powder
Density
Table 3 and Figure 9 shows the results of density of concrete at 28 days with cement replacement by glass powder in various percentages. It seems unit weight of concrete decreases as the glass content increases.
Figure 9: Variation of density of concrete with cement replacement by glass powder
Strength
(a) Compressive Strength
As expected, the compressive strength increased with increasing curing time as shown in table 4,8 and in figure 10,14. Table 5,6,7 and Figure 11,12,13 shows overall results of compressive strength with and without subjecting to sulphate attack with cement replacement by glass powder for 7 days, 28 days, and 90 days.
Figure 10: Variation of compressive strength development in concrete without subjecting to chloride attack with age
Figure 11: Variation of compressive strength of concrete with cement replacement by glass powder and when subjected to Sulphate attack for 7 days
Figure 12: Variation of compressive strength of concrete with cement replacement by glass powder and when subjected to Sulphate attack for 28 day
Figure 13: Variation of compressive strength of concrete with cement replacement by glass powder and when subjected to Sulphate attack for 90 days
Figure 14: Variation of compressive strength development in concrete subjected to sulphate attack with age
Sulphate attack lowered the compressive strength of concrete between 2 to 4 % in 7 days, 3 to 6% in 28 days and 11 to 17% in 90 days
Compressive strength of concrete with 20% cement replacement by glass powder in the sulphate attack experiment showed a higher value by 30%, 25%, 27% compared to control concrete for 7 days, 28 days and 90 days respectively.
(b) Flexural Strength
Table 9, 10 and figure 15, 16 shows the result of Variation of flexural strength of concrete with cement replacement by glass powder for 7, 28 and 90 days. It seems flexural strength of concrete with 20% cement replacement by glass powder showed a higher value by 22%, 20%, 17% compared to control concrete for 7 days, 28 days and 90 days respectively
Figure 15: Variation of flexural strength of concrete with cement replacement by glass powder for 7, 28 and 90 days
Figure 16: Variation of flexural strength development in concrete with age
Workability decreases as the glass content increased (i.e. cement content decreased) due to reduction of fineness modulus of cementatious material, less quantity of cement paste is available for providing lubricating effect per unit surface area of aggregate, and hence mobility of aggregate is restrained.
Density
Unit weight of concrete without waste glass is higher than with waste glass. Such a difference was attributive to the fact that the specific gravity of waste glass i.e. 2.58 is much lower than specific gravity of cement i.e. 3.15
Strength
An increasing trend in strength was observed with increasing replacement of cement with glass powder up to 20%. The highest percentage increase in the compr- essive strength was about 30% and flexural strength was about 22% at 20% replacement level. When the cement replacement level was increased beyond 20%, the compressive strength decreased.
The increase in strength up to 20% replacement of cement by glass powder may be due to the pozzolanic reaction of glass powder. Waste glass when ground to a very fine powder, SiO2 react chemically with alkalis in cement and form cementitious product that help contribute to the strength development. Also it may be due to the glass powder effectively filling the voids and giving rise to a dense concrete microstructure as a result waste glass powder offers resistance against expansive forces caused by sulphates and penetration of sulphates ion into the concrete mass. However, beyond 20%, the dilution effect takes over and the strength starts to drop. Thus it can be concluded that 20% was the optimum level for replacement of cement with glass powder.
The strength improvement at early curing ages was slow due to pore filling effect. Waste glass powder(GP) initially acts like a pore filler and only later, after 7-10 days, its hydration liberates sufficient amount of lime for starting the secondary pozzolanic reaction.This reaction leads to more quantity of C-S-H gel getting formed.
M. N. Bajad, Research Scholar, S.V.N.I.T, Surat, C. D. Modhera, Professor, S.V.N.I.T, Surat and A. K. Desai, Associate Professor, S.V.N.I.T, Surat.
Introduction
Glass is a rigid liquid i.e. super cooled liquid, static, not solid, not a gas but does not change molecularly between melting and solidification in to a desired shape. Glass is one of the most versatile substances on earth used in many applications and in a wide variety of forms. Glass occurs naturally when rock high in silicates melt at high temperature and cool before they can form a crystalline structure. Obsidian or volcanic glass is a well known example of naturally occurring glass. When manufactured by human's the glass is a mixture of silica, sand, lime and other materials. The elements of glass are heated to 9820 Celsius. Heat can return the glass to a liquid and workable form, making it easy to reuse and recycle.Table 1 and Figure 1,2 shows the chemical composition of the cementing materials. The particle size distribution of the glass powder and cement are shown in figure 3
| Table 1: Chemical composition of cementing materials | ||
| Composition (% by mass)/ property | Cement | Glass powder |
| Silica (SiO2) | 20.2 | 72.5 |
| Alumina (Al2O3) | 4.7 | 0.4 |
| Iron oxide (Fe2O3) | 3.0 | 0.2 |
| Calcium oxide (CaO) | 61.9 | 9.7 |
| Magnesium oxide (MgO) | 2.6 | 3.3 |
| Sodium oxide (Na2O) | 0.19 | 13.7 |
| Potassium oxide (K2O) | 0.82 | 0.1 |
| Sulphur trioxide (SO3) | 3.9 | - |
| Loss of ignition | 1.9 | 0.36 |
| Fineness % passing (sieve size) | 97.4(45 µm) | 80 (45 µm) |
| Unit weight,Kg/m3 | 3150 | 2579 |
| Specific gravity | 3.15 | 2.58 |
Figure 1: Chemical composition of cement
Figure 2: Chemical composition of glass powder
Figure 3: Particle Size Distributions of Cementitious Materials
Figure 4: Mechanism of sulfate attack
 Figure 5: Paste expansion produces a small gap around small aggregate particles and a bigger gap around larger particle |
 |
|
| Figure 6: Cracking of concrete due to sulphate attack |
The Chemistry of Sulphate Attack
The end result of sulphate attack can be excessive expansion, delaminating, cracking, and loss of strength. The degree to which this attack can occur depends on water penetration, the sulphate salt and its concentration and type (e.g. .sodium or magnesium), the means by which the salt develops in the concrete (e.g. is it rising and drying causing crystallization), and the chemistry of the binder present in the concrete. These processes and factors have been the subject of intense study across the world in recent years and outcomes are reported widely.It can be summerarised that at a concentration of about 0.2% sulphate content in the ground water, concrete may suffer sulphate attack; that magnesium sulphate can be more aggressive than sodium; and that there are three key chemical reactions between sulphate ions and hardened cement pastes. The reactions are: recrystallisation of ettringite; formation of gypsum; and decalcification of the main cementitious phase (C-S-H).
In the presence of the calcium hydroxide formed in cement paste, when the latter comes in contact with sulphate ions, the alumina containing hydrates are converted to the high sulphate from ettringite. These etteringte crystals grow, expand, or swell by mechanisms, which are still the subject of controversy among researchers. While there is agreement that most (but not all) ettringites will expand in this formation, the exact cause are not agreed.
The formation of gypsum as a result of cat ion exchange reactions is also capable of causing expansion but is normally linked to loss of mass and strength. The decalcification of the C-S-H has not received as much discussion as the other two types of sulphate attack, but can be just as important, particularly where the sulphate solution is lower in PH (i.e. more acidic. This particular reaction, with more gypsum formation, leads to both strength loss and expansion. This is a particular situation in which blended cements with lower initial calcium/silica (C/S) ratios in the C-S-H gel are shown to be less susceptible to this type of attack.
Chemical process
The sulphate ion + hydrated calcium aluminates and/or the calcium hydroxide components of hardened cement paste + water = ettringite (calcium sulphoaluminate hydrate)C3A.Cs.H18 + 2CH +2s+12H = C3A.3Cs.H32
C3A.CH.H18 + 2CH +3s + 11H = C3A.3Cs.H32
The sulphate ion + hydrated calcium aluminates and/or the calcium hydroxide components of hardened cement paste + water = gypsum (calcium sulphate hydrate)
Na2SO4+Ca(OH)2 +2H2O = CaSO4.2H2O +2NaOH
MgSO4 + Ca(OH)2 + 2H2O = CaSO4.2H2O + MgOH
Research Significance
waste glass contain high silica (SiO2) i.e.72%. Waste glass when ground to a very fine powder (600 micron) SiO2 react with alkalis in cement (pozzolanic reaction) and form cementitious product that help contribute to the strength development and durability.when concrete contain waste glass powder it gives higher percentage of C2S,Low C3A,C4AF,C3S/C2S Content which result in production of less heat of hydration and offers greater resistance to the attack.
It has been estimated that several million tons of waste glass is generated annually worldwide due to rapid growth of population, improvement in the standard of living, industrialization and urbanization. Hence utilization of waste glass has become a critical issue worldwide. The key sources of waste glasses are waste containers, window glasses, and windscreen, medicinal bottles, liquor bottles, tube lights, bulbs, electronic equipment, etc.
Recycling, disposal and decomposing of waste glass possesses major problems for municipalities everywhere, and this problem can be greatly eliminated by re-using waste glass as a cement replacement in concrete. Moreover, there is a limit on the availability of natural aggregate and minerals used for making cement, and it is necessary to reduce energy consumption and emission of carbon dioxide resulting from construction processes, solution of this problem are sought thought usages of waste glass as partial replacement of Portland cement. Replacing cement by pozzolanic material like waste glass powder in concrete, not only increases the strength but also reduces the unit weight.
Recycling of waste glass may affect respiratory system if breath in pollutants. Case-local residents at merceds Arumbula claimed that the neighborhood and kids have developed asthma once the plant was built in their community
Disposal of waste glass degrade communities living condition and harmful to human health because lactates and gas releases from the landfill site
Sulphate reacts with product of hydration causes expansion. Therefore an experimental investigation in developing concrete containing waste glass powder is very important
The Methodology and Investigations
Experimental ProgrammeThe purpose of this investigation was to evaluate the effect of partial replacement of cement by waste glass powder (GP) on strength of concrete specimens. The experimental parameters and their levels were chosen according. Experimental programme plan is shown in Figure 7.
Figure 7: Plan of Experimental programme
Constituent Materials
Cement
Ordinary Portland Cement (OPC) 43 grade confirming to IS 8112
Aggregate
Locally available sand and coarse aggregates were used in this experiment. The sand used was Zone II, with specific gravity of 2.62. Specific gravity of coarse aggregate was 2.93. Coarse aggregate used 20 mm and down size.
Admixture
To impart workability to the mix, a superplasticiser from a reputed company was used with the dosage of 2% by weight of cement
Supplementary Cementitious Materials
The glass powder was obtained by crushing waste glass pieces in a cone crusher mill. The 600-micron passing fraction was used for the experimentation
Mix Proportions and experimental factors
Mix design carried out to form M20 grade of concrete by IS 10262: 2009 yielded a mix proportion of 1:2.35:4.47 with water cement ratio of 0.50. Nine different mixes (M1,M2,M3,M4,M5,M6,M7,M8,M9)were prepared using cement replaced by waste glass powder (GP) at varying percentages of 0, 5, 10, 15, 20, 25, 30, 35 and 40.
Casting
Fifty four number of Specimens size 150 x 150 x 150 mm and Twenty seven number of specimens of dimensions 150 x150x 700 mm were cast according to the mix proportion and by replacing cement with glass powder (GP) in different proportion
Preparation of Solution and Caution
A 5% MgSO4 solution has five grams of magnesium sulphate dissolved in 100 ml solution.
Procedure Weigh 5 gram of magnesium sulphate & pour it into a graduated cylinder or volumetric flask containing about 80 ml of water. Once the magnesium sulphate has dissolved completely add water to bring the volume up to final 100 ml.
Caution-Do not simply measure 100 ml of water and add 5 gram of magnesium sulphate. This will introduce error because adding the solid will change the final volume of the solution and change the final percentage.
Curing of Specimens
To find out the effect of water (concrete without subjected to attack), the specimens were immersed in a 100% H2O solution (water) for 7, 28, and 90 days
To find out the effect of Sulphate attack, the specimens were immersed in a 5% MgSo4 solution for 7, 28, and 90 days.
Testing
To find out the strength, specimens were tested at 7, 28 and 90 days using a compression testing machine (CTM) of capacity 2000KN in accordance with the provisions of the Indian Standard specification IS 516:1959
Test Results
Test results are presented graphically and in tubular forms and have been discussed under different categories.Workability
Table 2 and Figure 8 shows the results of workability of concrete with cement replacement by glass powder in various percentages ranging from 5% to 40% in increments of 5% (0%, 5%, 10%, 15%, 20%,25%, 30%,35% and 40%). It seems workability of concrete decreases as the glass content increases.
| Table 2: Overall result of slump of concrete | |||
| Mix Designation | Percentage replacement of cement by glass powder | Slump (mm) |
Percentage increase or decrease with respect to reference mix |
| M1 | 0(Ref.mix) | 100 | - |
| M2 | 05 | 94 | -6 |
| M3 | 10 | 91 | -9 |
| M4 | 15 | 88 | -12 |
| M5 | 20 | 82 | -18 |
| M6 | 25 | 76 | -24 |
| M7 | 30 | 73 | -27 |
| M8 | 35 | 72 | -28 |
| M9 | 40 | 66 | -34 |
Figure 8: Variation of slump of concrete with cement replacement by glass powder
Table 3 and Figure 9 shows the results of density of concrete at 28 days with cement replacement by glass powder in various percentages. It seems unit weight of concrete decreases as the glass content increases.
| Table 3: Overall, result of density of concrete | |||
| Mix Designation | Percentage replacement of cement by glass powder | Density (at 28 Day in kg/m3) |
Percentage decrease in density with respect to reference mix |
| M1 | 0(Ref.Mix) | 2408 | ---------- |
| M2 | 05 | 2396 | 0.49 |
| M3 | 10 | 2379 | 1.2 |
| M4 | 15 | 2369 | 1.61 |
| M5 | 20 | 2354 | 2.24 |
| M6 | 25 | 2335 | 3.03 |
| M7 | 30 | 2315 | 3.86 |
| M8 | 35 | 2303 | 4.36 |
| M9 | 40 | 2283 | 5.19 |
Figure 9: Variation of density of concrete with cement replacement by glass powder
(a) Compressive Strength
As expected, the compressive strength increased with increasing curing time as shown in table 4,8 and in figure 10,14. Table 5,6,7 and Figure 11,12,13 shows overall results of compressive strength with and without subjecting to sulphate attack with cement replacement by glass powder for 7 days, 28 days, and 90 days.
| Table 4:Overall results ofdevelopment of compressive strength in concrete without subjecting to attack with age | |||||||||
| Age, days | Compressive strength, MPa | ||||||||
| 0% GP |
5% GP | 10% GP | 15% GP | 20% GP | 25% GP | 30% GP | 35% GP | 40% GP | |
| 7 | 21.05 | 22.28 | 23.27 | 24.86 | 27.30 | 23.72 | 17.62 | 16.04 | 12.93 |
| 28 | 27.05 | 28.58 | 29.77 | 31.56 | 33.50 | 30.52 | 24.22 | 22.44 | 19.03 |
| 90 | 27.33 | 28.87 | 30.08 | 31.85 | 33.86 | 30.82 | 24.44 | 22.72 | 19.25 |
Figure 10: Variation of compressive strength development in concrete without subjecting to chloride attack with age
| Table 5:Overall results of compressive strength with and without subjecting to sulphate attack for 07 days. | ||||||
| Mix Designation | Percentage replacement of cement by glass powder (%) |
Concrete without subjecting to Sulphate attack | Concrete subjected to Sulphate attack for 07days | Percentage decrease of compressive strength when subjected to Sulphate attack | ||
| Compressive Strength (MPa) | Percentage increase or decrease in compressive strength w.r t. ref.mix. | Compressive Strength (MPa) | Percentage increase or decrease in compressive strength w.r t. ref.mix. | |||
| M1 | 0(Ref.mix) | 21.05 | ------- | 20.62 | -------- | 2.04 |
| M2 | 05 | 22.28 | +6 | 21.83 | +6 | 2.01 |
| M3 | 10 | 23.27 | +11 | 22.57 | +9 | 3.00 |
| M4 | 15 | 24.86 | +18 | 24.36 | +18 | 2.01 |
| M5 | 20 | 27.3 | +30 | 26.75 | +30 | 2.01 |
| M6 | 25 | 23.72 | +13 | 23.00 | +12 | 3.03 |
| M7 | 30 | 17.62 | -17 | 17.09 | -17 | 3.00 |
| M8 | 35 | 16.04 | -24 | 15.71 | -24 | 2.05 |
| M9 | 40 | 12.93 | -39 | 12.67 | -39 | 2.01 |
Figure 11: Variation of compressive strength of concrete with cement replacement by glass powder and when subjected to Sulphate attack for 7 days
| Table 6: Overall results of compressive strength with and without subjecting to sulphate attack for 28 days. | ||||||
| Mix Designation | Percentage replacement of cement by glass powder | Concrete without subjecting to Sulphate attack | Concrete subjected to Sulphate attack for 28 days | Percentage decrease of compressive strength when subjected to Sulphate attack | ||
| Compressive Strength (MPa) | Percentage increase or decrease in compressive strength w.r t. ref.mix. | Compressive Strength (MPa) | Percentage increase or decrease in compressive strength w.r t. ref.mix. | |||
| M1 | 0(Ref.mix) | 27.05 | ------ | 25.45 | -------- | 5.91 |
| M2 | 05 | 28.58 | +6 | 27.15 | +7 | 5.00 |
| M3 | 10 | 29.77 | +10 | 28.10 | +10 | 5.61 |
| M4 | 15 | 31.56 | +17 | 30.00 | +18 | 4.94 |
| M5 | 20 | 33.50 | +24 | 31.85 | +25 | 4.92 |
| M6 | 25 | 30.52 | +13 | 29.01 | +14 | 4.94 |
| M7 | 30 | 24.22 | -10 | 23.20 | -9 | 4.21 |
| M8 | 35 | 22.44 | -17 | 21.55 | -15 | 3.96 |
| M9 | 40 | 19.03 | -30 | 18.25 | -28 | 4.1 |
Figure 12: Variation of compressive strength of concrete with cement replacement by glass powder and when subjected to Sulphate attack for 28 day
| Table 7:Overall results of compressive strength with and without subjecting to sulphate attack for 90 days | ||||||
| Mix Designation | Percentage replacement of cement by glass powder | Concrete without subjecting to sulphate attack | Concrete subjected to sulphate attack | Percentage decrease of compressive strength when subjected to sulphate attack | ||
| Compressive Strength (MPa) | Percentage increase or decrease in compressive strength w.r t. ref.mix. | Compressive Strength (MPa) | Percentage increase or decrease in compressive strength w.r t. ref.mix. | |||
| M1 | 0(Ref.mix) | 27.33 | ------ | 22.80 | ------- | 16.57 |
| M2 | 05 | 28.87 | +6 | 24.22 | +6 | 16.10 |
| M3 | 10 | 30.08 | +10 | 25.65 | +11 | 14.72 |
| M4 | 15 | 31.85 | +17 | 27.18 | +19 | 14.66 |
| M5 | 20 | 33.86 | +24 | 28.86 | +27 | 14.76 |
| M6 | 25 | 30.82 | +13 | 26.30 | +15 | 14.66 |
| M7 | 30 | 24.44 | -11 | 21.60 | -5 | 11.62 |
| M8 | 35 | 22.72 | -17 | 19.70 | -14 | 13.29 |
| M9 | 40 | 19.25 | -30 | 16.88 | -26 | 12.31 |
Figure 13: Variation of compressive strength of concrete with cement replacement by glass powder and when subjected to Sulphate attack for 90 days
| Table 8: Overall results of development of compressive strength in concrete subjected to sulphate attack with age | |||||||||
| Age, days | Compressive strength, MPa | ||||||||
| 0% GP |
5% GP | 10% GP | 15% GP | 20% GP | 25% GP | 30% GP | 35% GP | 40% GP | |
| 7 | 20.62 | 21.83 | 22.57 | 24.36 | 26.75 | 23.00 | 17.09 | 15.71 | 12.67 |
| 28 | 25.45 | 27.15 | 28.10 | 30.00 | 31.85 | 29.01 | 23.20 | 21.55 | 18.25 |
| 90 | 22.80 | 24.22 | 25.65 | 27.18 | 28.86 | 26.30 | 21.60 | 19.70 | 16.88 |
Figure 14: Variation of compressive strength development in concrete subjected to sulphate attack with age
Compressive strength of concrete with 20% cement replacement by glass powder in the sulphate attack experiment showed a higher value by 30%, 25%, 27% compared to control concrete for 7 days, 28 days and 90 days respectively.
(b) Flexural Strength
Table 9, 10 and figure 15, 16 shows the result of Variation of flexural strength of concrete with cement replacement by glass powder for 7, 28 and 90 days. It seems flexural strength of concrete with 20% cement replacement by glass powder showed a higher value by 22%, 20%, 17% compared to control concrete for 7 days, 28 days and 90 days respectively
| Table 9: Overall results of flexural strength of concrete with cement replacement by glass powder | |||||||
| Mix Designation | Percentage replacement of cement by glass powder | Flexural strength (N/mm2) [07days] |
Percentage increase or decrease in flexural strength with respect to reference mix | Flexural strength (N/mm2) [28 days] |
Percentage increase or decrease in flexural strength with respect to reference mix | Flexural strength (N/mm2) [90 days] |
Percentage increase or decrease in flexural strength with respect to reference mix |
| M1 | 0(Ref.mix) | 2.40 | - | 3.50 | - | 3.60 | ------ |
| M2 | 05 | 2.45 | +2 | 3.62 | +4 | 3.64 | +2 |
| M3 | 10 | 2.78 | +16 | 3.78 | +8 | 3.82 | +7 |
| M4 | 15 | 2.85 | +19 | 3.95 | +13 | 4.00 | +12 |
| M5 | 20 | 3.05 | +22 | 4.17 | +20 | 4.21 | +17 |
| M6 | 25 | 2.90 | +21 | 4.00 | +15 | 4.05 | +13 |
| M7 | 30 | 2.82 | +18 | 3.90 | +12 | 3.92 | +9 |
| M8 | 35 | 2.42 | +1 | 3.57 | +2 | 3.60 | 0 |
| M9 | 40 | 2.32 | -4 | 3.41 | -3 | 3.45 | -5 |
Figure 15: Variation of flexural strength of concrete with cement replacement by glass powder for 7, 28 and 90 days
| Table 10: Overall results of development of flexural strength in concrete with age. | |||||||||
| Age, days | Flexural strength, MPa | ||||||||
| 0% GP |
5% GP | 10% GP | 15% GP | 20% GP | 25% GP | 30% GP | 35% GP | 40% GP | |
| 7 | 2.40 | 2.45 | 2.78 | 2.85 | 3.05 | 2.90 | 2.82 | 2.42 | 2.32 |
| 28 | 3.50 | 3.62 | 3.78 | 3.95 | 4.17 | 4.00 | 3.90 | 3.57 | 3.41 |
| 90 | 3.60 | 3.64 | 3.82 | 4.00 | 4.21 | 4.05 | 3.92 | 3.60 | 3.45 |
Figure 16: Variation of flexural strength development in concrete with age
Discussion on Test Results
WorkabilityWorkability decreases as the glass content increased (i.e. cement content decreased) due to reduction of fineness modulus of cementatious material, less quantity of cement paste is available for providing lubricating effect per unit surface area of aggregate, and hence mobility of aggregate is restrained.
Density
Unit weight of concrete without waste glass is higher than with waste glass. Such a difference was attributive to the fact that the specific gravity of waste glass i.e. 2.58 is much lower than specific gravity of cement i.e. 3.15
Strength
An increasing trend in strength was observed with increasing replacement of cement with glass powder up to 20%. The highest percentage increase in the compr- essive strength was about 30% and flexural strength was about 22% at 20% replacement level. When the cement replacement level was increased beyond 20%, the compressive strength decreased.
The increase in strength up to 20% replacement of cement by glass powder may be due to the pozzolanic reaction of glass powder. Waste glass when ground to a very fine powder, SiO2 react chemically with alkalis in cement and form cementitious product that help contribute to the strength development. Also it may be due to the glass powder effectively filling the voids and giving rise to a dense concrete microstructure as a result waste glass powder offers resistance against expansive forces caused by sulphates and penetration of sulphates ion into the concrete mass. However, beyond 20%, the dilution effect takes over and the strength starts to drop. Thus it can be concluded that 20% was the optimum level for replacement of cement with glass powder.
The strength improvement at early curing ages was slow due to pore filling effect. Waste glass powder(GP) initially acts like a pore filler and only later, after 7-10 days, its hydration liberates sufficient amount of lime for starting the secondary pozzolanic reaction.This reaction leads to more quantity of C-S-H gel getting formed.
Conclusions
Based on experimental observa- tions, the following conclusions are drawn:- Higher strength was achieved when 20% cement was replaced by glass powder in concrete.
- The density of concrete reduces with the increase in the percentage of replacement of cement by glass powder.
- The workability decreased as the glass content increasedvUse of super plasticizer was found to be necessary to maintain workability with restricted water cement ratio.
- Considering the strength criteria, the replacement of cement by glass powder is feasible.
- It is recommended that the utilization of waste glass powder in concrete as cement replacement is possible.
- Strength properties were affected when concrete produced by replacing cement by glass powder was subjected to attack.
- Waste glass powder in appropriate proportions could be used to resist sach attack.
Acknowledgements
The authors would like to thank the authorities of S.V.N.I.T. Surat for their kind support. The valuable suggestions, efforts and timely help extended by one and all in concrete discipline are gratefully acknowledged. Sincere gratitude is extended to all the authors whose publications provided us directional information from time to time. The cooperation and help received from the scientific and technical staff of advanced materials laboratory in the preparation of this paper are gratefully acknowledged.References
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NBM&CW May 2012
