INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING Volume 4, No 2, 2013

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1 INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING Volume 4, No 2, 2013 Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0 Research article ISSN Effect of molarity in geopolymer concrete Madheswaran C. K 1, Gnanasundar G 2, Gopalakrishnan. N 3 1- Principal Scientist, Advanced Seismic Testing and Research Laboratory, CSIR-Structural Engineering Research Centre, Taramani, Chennai. 2- M.E Student, Sree Sastha Institute of Engg and Technology, Chembarambakkam, Chennai 3- Senior Principal Scientist, Advanced Seismic Testing and Research Laboratory, CSIR- Structural Engineering Research Centre, Taramani, Chennai. ckm@serc.res.in doi: /ijcser ABSTRACT Geopolymer Concrete (GPCs) is a new class of concrete based on an inorganic aluminosilicate binder system compared to the hydrated calcium silicate binder system of concrete. It possesses the advantages of rapid strength gain, elimination of water curing, good mechanical and durability properties and are eco-friendly and sustainable alternative to Ordinary Portland Cement (OPC) based concrete. In the construction industry mainly the production of Portland cement causes the emission of air pollutants which results in environmental pollution. This paper presents the details of the studies carried out on development of strength for various grades of geopolymer concrete with varying molarity. The alkaline liquids used in this study for the geopolymerization are sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). Different molarities of sodium hydroxide solution (3M, 5M and 7M) are taken to prepare different mixtures. The test specimens were 150 x 150 x 150 mm cubes, 150 x 300mm cylinders prepared and ambient temperature curing conditions. The geopolymer concrete specimens are tested for their compressive strength at the age of 7 and 28 days. GPC mix formulations with compressive strength ranging from 15 to 52MPa have been developed. Experimental investigations have been carried out on workability, the various mechanical properties of GPCs. The test results indicate that the combination of fly ash and ground granulated furnace slag (GGBS) can be used for development of geopolymer concrete. Keywords: Geopolymer concrete, molarity, flyash, GGBS, Sodium hydroxide and Sodium silicate 1. Introduction The production of Portland cement worldwide is increasing 9% annually. Portland cement (PC) production is under critical review due to high amount of carbon dioxide gas released to the atmosphere and Portland cement is also one among the most energy-intensive construction material. The current contribution of green house gas emission from Portland cement production is about 1.5 billion tonnes annually or about 7% of the total greenhouse gas emissions to the earth s atmosphere. Geopolymer concrete is a new material that does not need the presence of Portland cement as a binder. Instead, the source of materials such as fly ash (FA) and ground granulated blast furnace slag (GGBS), that are rich in silicon(si) and aluminium(al),are activated by alkaline liquids to produce the geopolymeric binder. The major problem the world is facing today is the environmental pollution. But the production of cement means the production of pollution because of the emission of CO2 during its production. There are two different sources of CO2 during cement production. Received on July 2013 Published on November

2 Combustion of fossil fuels to operate the rotary kiln is the largest source and other one is the chemical process of calcining limestone into lime in the cement kiln also produces CO2. Hendriks et al., carried out emission reduction of green house gases from the cement industry. Ernest Worerell and Lynn Price etal, have reported that CO2 emission from the global cement industry. In India about 2,069,738 thousands of metric tonnes of CO2 is emitted in the year And also, the cement is manufactured by using the raw materials such as lime stone, clay and other minerals. Quarrying of these raw materials is also causes environmental degradation. To produce 1 tonne of cement, about 1.6 tonnes of raw materials are required and the time taken to form the lime stone is much longer than the rate at which humans use it. On the other side the demand of concrete is increasing day by day for its ease of preparing and fabricating in all sorts of convenient shapes. So to overcome this problem, the concrete to be used should be environmental friendly. To produce environmental friendly concrete, it is necessary to replace the cement with the industrial by products such as fly ash, GGBS etc.,. Disposal of FA is a growing problem as only 15% of FA is currently used for high value addition applications like concrete and building blocks, the remaining being used for land filling. The FA increases the strength in case of hardened concrete. Another alternative but promising utility of FA in construction industry that has emerged in recent years is in Geopolymer concrete. Geopolymer technology can be appropriate process technology utilize all classes and grades of FA and therefore there is a great potential for reducing stockpiles of waste FA materials. The present study considers FA utilization in production of geopolymer concrete since it can accommodate a major portion of the ash produced. GGBS is a byproduct from the blast-furnaces used to make iron. The molten slag is rapidly chilled by quenching in water to form the sand like granulated material. GGBS is a glassy granular, non metallic material consisting essentially of silicates and aluminates of calcium and other bases. GGBS is also used as a binder component in geopolymer concrete. Geopolymer concretes (GPC) are a type of Inorganic polymer composites, to form a substantial element of an environmentally sustainable construction and building products industry by replacing/supplementing the conventional concretes. The term geopolymer was first introduced by Davidovits in 1970s to name the three-dimensional alumino-silicates material, which is a binder produced from the reaction of a source material or feedstock rich in silicon (Si) and aluminum (Al) with a concentrated alkaline solution. The source materials may be industry waste products such as fly ash, slag, red mud, rice-husk ash and silica fume may be used as feedstock for the synthesis of geopolymers. The alkaline liquids are concentrated aqueous alkali hydroxide or silicate solution, with soluble alkali metals, usually Sodium- (Na) or Potassium- (K) based. High alkaline liquids are used to induce the silicon and aluminium atoms in the source materials to dissolve and form the geopolymeric binder. Rajamane (2006), Ambily et.al (2011) and Ambily (2012) carried out experimental studies on structural behavior of reinforced geopolymer concrete beams. Effect of geopolymeric binders such as GGBS and FA by activating silicon dioxide and aluminium oxide present in the binders, to form inorganic polymer binder system. This binder system can be used to produce concretes containing river sand as fine aggregate and coarse aggregate in the form of either sintered FA aggregates (SFA) or crushed granite aggregates (CGA). It was concluded that the lightweight aggregate based geopolymer concrete have one day compressive strength of about 35 MPa and a 28 days strength greater than 50 MPa. CGA based geopolymer concretes produce higher compressive strength of about 45 MPa at one day and 65 MPa at 28 days. 107

3 Experimental results (Hardijito and rangan, 2005) have shown the following, higher the ratio of sodium silicate solution-to-sodium hydroxide solution ratio by mass, higher is the compressive strength of geopolymer concrete. The addition of naphthalene sulphonate-based super plasticizer, up to approximately 4% of fly ash by mass, improves the workability of the fresh geopolymer concrete, however, there is slight degradation in the compressive strength of hardened concrete when the super plasticizer dosage is greater than 2%. The principal objective of the research were 1. The development of structural grade geopolymer concrete with different combinations of FA and GGBS. 2. To study the influence of ground granulated blast furnace slag on geopolymer concrete. The types of geopolymer concrete mixes are (i) 10% GGBS and 90%FA, (ii) 15%GGBS and 85%FA, (iii) 20% GGBS and 80% FA,(iv) 50% GGBS and 50% FA. 3. To study the effect of concentration of alkaline activator solution in geopolymer concrete. The molar ratios considered are 3M, 5M and 7M Sodium Hydroxide Solutions are used. 2. Materials used Following materials are generally used to produce GPCs: 1. Fly ash 2. GGBS 3. Fine aggregates and 4. Coarse aggregates 5. Catalytic liquid system (CLS) 2.1 Ordinary Portland Cement (OPC) OPC conforming to IS 12269(1987) (with specific gravity of 3.15), fine aggregates, coarse aggregates and potable water were used for the control OPCC test specimens. The physical properties of the cement used are shown in the Table Fly ash and Ground Granulated Blast Furnace Slag (GGBS) FA conforming to grade 1 of IS 3812 and Ground granulated blast furnace slag) confirming to IS were used. River sand available in Chennai was used as fine aggregates. The GPCC was obtained by mixing calculated quantities of FA and GGBS, fine aggregates, coarse aggregates with Alkaline Activator Solution (AAS). FA obtained from Ennore Thermal Power Station and GGBS (Ground Granulated Blast Furnace Slag) obtained from Quality polytech, Mangalore conforming to IS were used. The physical properties of FA and GGBS are shown in table 1 and Chemical properties in Table Aggregates River sand available in Chennai was used as fine aggregates. They were tested as per IS 2386 standards. The specific gravity of river sand is 2.7. In this investigation locally available blue 108

4 granite crushed stone aggregates of maximum size 12.5mm and down size were used and characterization tests were carried out as per IS The specific gravity is S. No. Descriptions Physical Properties Table 1: Properties of Cement, Fly Ash and GGBS OPC Fly ash 1 Fineness (Sq.m/kg) Normal Consistency (%) Setting Time (minutes) a) Initial b) Final Specific gravity GGBS Table 2: Chemical analysis of fly ash and GGBS Parameters % by mass Fly Ash GGBS LOI 0.76 SiO Al 2O Fe 2O CaO MgO Na 2O K 2O TiO Mn2O Insoluble Residue SO Free Lime - - Chlorides Catalytic Liquid System (CLS) The term CLS is used to represent the alkaline activator solution (AAS) in GPC concrete. The CLS is a combination of sodium silicate solution, sodium hydroxide solution and distilled water. The role of AAS is to activate the source materials Si and Al present in fly ash and GGBS. The sodium hydroxide was taken in the form of pellets. The sodium hydroxide (NaOH) solution was prepared by dissolving the pellets in distilled water. Therefore, it was decided prepare the AAS separately and mix them at the time of casting. Since lot of heat is generated when sodium hydroxide pellets react with water, the sodium hydroxide solution was prepared a day earlier to casting. It should be noted here that water is the medium for dissolution and polymerization of Al and Si precursors to take place appropriately and is essential to achieve the desired degree of workability of the GPC concrete mix. However, 109

5 excess water can result in formation of pore network, which could be the source of low strength and low durability In this paper the compressive strength of geopolymer concrete is examined for the mix of varying molarities of sodium hydroxide (3M, 5M, and 7M). The molecular weight of sodium hydroxide is 40. To prepare 3M sodium hydroxide solution, 120g of sodium hydroxide pellets were weighed and they more dissolved in distilled water to form 1 liter solution. After the pellets dissolved fully in the water, then remaining water was added to make 1liter solution. The weights of pellets added for other molarity of solutions are as given in Table-3. Table 3: Molarity of alkaline activator solutions Required Molarity Weight in g. of Sodium Hydroxide pellets 3M 120 5M 200 7M Mix Design The primary difference between geopolymer concrete and Portland cement concrete is the binder. The silicon and aluminium oxides in the low-calcium flyash and GGBS reacts with the alkaline liquid to form the geopolymer paste that binds the loose coarse aggregates, fine aggregates, and other un-reacted materials together to form the geopolymer concrete. As in the case of Portland cement concrete, the coarse and fine aggregates occupy about 75% to 80% of the mass of geopolymer concrete. This component of geopolymer concrete mixtures can be designed using the tools currently available for Portland cement concrete. The compressive strength and the workability of geopolymer concrete are influenced by the proportions and properties of the constituent materials that make the geopolymer paste. The role and the influence of aggregates are considered to be the same as in the case of Portland cement concrete. The mass of combined aggregates may be taken to be between 75% and 80% of the mass of the geopolymer concrete. The performance criteria of a geopolymer concrete mixture depend on the application. For simplicity, the compressive strength of hardened concrete and the workability of fresh concrete are selected as the performance criteria. In order to meet these performance criteria, the alkaline liquid-to-fly ash ratio by mass, water-to binder ratio by mass, water to geopolymer solids ratio by mass, the wet-mixing time, the heat-curing temperature, and the heat-curing time are selected as parameters. 4. Mixing and Casting of Geopolymer Concrete Geopolymer concrete can be produced by adopting the conventional techniques used in the manufacture of Portland puzzolana cement concrete. In the laboratory, the fly ash, GGBS and the aggregates were mixed together dry in a pan mixer for about three minutes. The aggregates were prepared in saturated-surface dry (SSD) condition. The alkaline liquids used in this study for the polymerization are sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). Different molarities of sodium hydroxide solution 3M, 5M and 7M are taken to prepare different mixtures. The sodium hydroxide is available in the form of pellets and mixed with the distilled water and prepared alkaline solution one day before casting. The Sodium silicate is added just before casting. The AAS is added to the dry 110

6 materials and mixing continued for another four minutes. The fresh geopolymer concrete was cast and compacted by the usual methods in the case of Portland cement concrete (Hardijito and Rangan, 2006, Sumajouw and Rangan, 2006). The ratio of the composition of FA+GGBS was varied suitably. The primary objective for performing the trial and error procedure was to obtain desired compressive strength. The secondary objective was to obtain a good cohesive mix with good workability (slump of 75 to 100mm). The proportions of GPS and AAS were so decided that the test specimens cast were demouldable after 24 hours of in-mould curing and as the required strength could be realized. Table 4 presents the mixes formulated for the study of geopolymer concrete. Table 4: The mixes formulated for the study of geopolymer concrete MIX ID MOLAR RATIO Binder Composition Mix proportion (BINDER:S AND:CA) CLS/ GPS Com press ive stren gth(7 days) MPa Com pres sive stre ngth (28 days ) MPa Split tensi le stre ngth (MP a) GPCAs GPCAs GPCAs GPCBs GPCBs GPCBs GPCCs GPCCs GPCCs 3M(120) 50%GGBS,50% Fly ash 1:1.31: M(200) 50%GGBS,50% Fly ash 1:1.31: M(280) 50%GGBS,50% Fly ash 1:1.31: M(120) 75%GGBS,25% Fly ash 1:1.31: M(200) 75%GGBS,25% Fly ash 1:1.31: M(280) 75%GGBS,25% Fly ash 1:1.31: M(120) 100%GGBS 1:1.31: M(200) 100%GGBS 1:1.31: M(280) 100%GGBS 1:1.31: PPCs 100% CEMENT 1:2.48: Note:GPCAs=GPCA series GPCBs=GPCB series,gpccs=gpcc series The dry mixture consisting of GPC solids and the coarse and fine aggregates were swiveled in the pan mixer for about 3 minutes before the addition of the AAS. After the addition of the AAS, the mixture was mixed for duration of 5 minutes for obtaining good homogeneity. It was found that the fresh geopolymer was slightly darker in colour compared NGPC, and was also more cohesive due to higher paste volume. Photo.1 shows the view of pan mixer used for mixing of aggregates in concrete. All the GPCC specimens were air cured, for a period of 7 days and 28days respectively. 111

7 4.1 Discussion of results Figure 1: Pan mixer used for mixing concrete A Compression testing Machine (CTM) of 200 T capacity was used to measure the compressive strength of concrete cubes at 7 and 28 days of curing time as shown in photo 3. Concrete cubes were cast with 150 mm cube mould. Specimens cured in ambient Laboratory condition. Compressive strength for the concrete cubes were measured by applying load of 5.3 kg/cm 2 /sec. 4.2 Effect of molarity in geopolymer concrete The effect of molarity on the compressive strength of GPC and the stress strain characteristics of GPC and PPCC concrete are discussed. The test specimens were 150 x 150 x 150 mm cubes, 150 x 300mm cylinders and ambient temperature curing were carried out. The important property of concrete is its strength in compression. The strength in compression has definite relationship with all other properties of concrete i.e., these properties are improved with the improvement in compressive strength. The test specimens were cured for periods of 7 days and 28 days. Longer curing time improved the polymerization process resulting in higher compressive strength. This might be due to relatively fast chemical reaction process in the geopolymer concrete. The cubes were tested in compressive testing machine to determine their compressive strength at the age of 7 and 28 days of curing. Table 4 shows the Compressive strength of the cube specimens at 7 days, 28 days age of concrete. Fig 1 shows the variations in Compressive strength increment with molarity of NaOH (3M, 5M, 7M) for the GPC specimens. The compressive strength obtained was in the range of 25MPa to 60MPa. Higher concentration of sodium hydroxide solution yielded higher compressive strength. The mix 3 (7M) gives the maximum compressive strength among other mixes. 4.3 Stress-strain characteristics of GPC Figure 2 shows the Stress-strain characteristics of GPC mixes with 50% GGBS and 50% Flyash and 5M Alkaline Activator Solutions. A 250 kn Servo hydraulic controlled Universal Testing Machine was used for compression testing of Geopolymer cylinders. The measured modulus of elasticity of GPC was in the range of 13,500 to 14,140MPa. 112

8 4.4 Influence of Ground granulated blast furnace slag on geopolymer concrete Figure 1 shows the compressive strength of geopolymer concrete at the end of 7th day and 28 day curing in ambient laboratory conditions. The percentage of GGBS is varied from 50%, 75% and 100%. It was observed that as percentage of GGBS increases the Compressive strength is also increases. Compressive Strength(MPa) M 5M 7M 0 GPCA series GPCB series MIX ID GPCC series Figure 1: Variation of Compressive strengths at the end of 28 th day Es = 14,142MPa 4.5 Split tensile test (a ) GPCA series (50% GGBS, 50% FA) Figure 2: Stress-strain characteristics of GPC Geopolymer and PPC Concrete cylinders of size 150mm diameter and 300mm long were cast with 5M NaOH concentration. The CTM machine of 200 T capacity was used to measure the Split Tensile test.the rate of Loading is 0.7 kg/cm 2 /sec. The test was carried out at 28 days 113

9 of curing. The split tensile strength of GPC in the range of 3.96MPa to 5.39MPa and PPC cylinder is 6.71MPa. The split tensile strength of GPC and PPC are shown in the Table.4. It was observed that the quantity of GGBS increases and split tensile strength of GPC increases. 5. Conclusions Based on the experimental investigations carried out on geopolymer concretes, it can be concluded that 1. The compressive strength of the geopolymer concrete is increased with the increasing concentration of NaOH. The geopolymer concretes produced with different combination of FA and GGBS are able to produce structural concretes of high grades (much more than M40MPa) by self curing mechanisms only. 2. The GPC mixes were produced easily using equipment similar to those used for production of conventional cement concretes. 3. The influences of GGBS on strength of geopolymer concrete mixes were studied. It has been observed that the increasing the quantity of GGBS and Compressive strength of geopolymer increases. The measured compressive strength of geoploymer mix is in the range from 45 MPa to 60 MPa and maximum of 60 MPa for 100% GGBS. 4. Apart from less energy intensiveness, the GPCs utilize the industrial wastes for producing the binding system in concrete. There are both environmental and economical benefits of using flyash and GGBS. Acknowledgements This paper is being published with the permission of the Director, CSIR-Structural Engineering Research Centre, Chennai. The cooperation and guidance received from Dr K. Muthumani Advanced Seismic Testing and Research laboratory and the technical staff of Advanced Materials Laboratory of CSIR-SERC are gratefully acknowledged. 6. References 1. Ambily P.S, Madheswaran C.K., Sharmila.S and Muthiah.S., (2011), Experimental and analytical investigations on shear behavior of reinforced geopolymer concrete beams, International journal of civil and structural engineering, India, 2(2), pp Ambily P.S, Madheswaran C.K., Lakshmanan.N, Dattatreya.J.K and Bhuvaneswari (2012), Experimental studies on shear behavior of reinforced geopolymer concrete thin webbed tee beams with and without steel fibre, International journal of civil and structural engineering, India, 3(1). 3. Dattatreya.J.K, Madheswaran C.K., Ambily P.S, Sabitha.D and Annie Peter.J., (2011), Development of advanced composite construction materials and methodologies for assessment of durability related parameters, CSIR-structural engineering research centre, India, September 2011, R& D 05-OLP13941-RR Ernst Worerell, Lynn Price et.al. Co2 emission from the global cement industry Annual review of energy and the environment, 26, pp

10 5. Nurudin M.F, Sobia Quzi, N. Shafiq and A. Kusbiantoro, (2010), Compressive strength & Micro structure of polymeric concrete incorpating fly ash and silica fume, Canadian journal on civil engineering, 1(1. 6. Sumajouw D.M.J, Hardijito, D, Wallah, S, and B.V. Rangan, Behaviour of geopolymer concrete columns under Equal load eccentricities. Research report GC-3, Faculty of Engineering, Curtin University of Technology, Perth, Australia. 7. Davidovits. J., (1991), Geopolymers: inorganic polymeric new materials, Journal of thermal analysis, 37, pp IS : 2770 ( Part I ) 1967, Indian Standard Methods Of Testing Bond in Reinforced Concrete Part I Pull-Out Test, Reaffirmed 1997, BIS, New Delhi. 9. IS: 456:2000, Indian Standard Code for Plain and reinforced concrete-code of practice, 4 th Revision, BIS, New Delhi. 10. IS: 3812:1981, Specification for fly ash for use as pozzolana and admixtures 3812(part1): IS: 2386: Part I-1963 Methods of tests for aggregates for concrete. 12. IS: 12089:1987, Specification for granulated slag for the manufacture of Portland slag cement. 13. IS516:1959 Method of test for strength of concrete. 14. Rangan. B. V, Hardjito, D., (2005), Development and properties of low calcium fly ash based geopolymer concrete. Research report GC-1, Faculty of Engineering, Curtin University of Technology, Perth, Australia. 15. Rangan. B.V, Wallah. S.E., (2006), Low-calcium fly ash based geopolymer concrete: Long term properties. Research report GC-2, Faculty of Engineering, Curtin University of Technology, Perth, Australia. 16. Rajamane N.P, Sabitha D., (2005), Studies on geo-polymer mortars using fly ash and blast furnace slag powder, International Congress on fly ash, Fly ash India, Chapter 6, pp 0019, pp