Development of High-Strength Geopolymer Concrete

Journal of Construction Engineering, Technology and Management ISSN: 2249-4723 Volume 4, Issue 1 www.stmjournals.com

Development of High-Strength Geopolymer Concrete S. Kumaravel*, K. Girija Annamalai University, Annamalainagar-608002, Tamilnadu, India Abstract Pollution in cement production is a major environmental issue throughout the world. Geopolymer concrete is an alternate cement as well as environment-friendly material in construction field. It is also used as an alternative for ordinary Portland cement because of no emission of greenhouse gas CO2. The current limitation in geopolymer concrete has been applied in precast members. The geopolymer concrete is prepared by using fly ash, ground granulated blast furnace slag (GGBS) as base materials and combination of sodium hydroxide and sodium silicate as alkaline activators. The present study deals with alkaline solution ratio and compressive strength. SEM analysis shows bonding of metal with OPC and GPC, vibration frequency of metal with OPC and GPC for FT-IR spectra. The compressive strength of concrete is obtained and compared with cement concrete.

Keywords: Fly ash, GGBS, geopolymer concrete, alkaline solution, cubes, cylinders *Author for Correspondence E-mail: [email protected]

INTRODUCTION Ordinary Portland cement (OPC) is an important material in concrete. Cement industry is responsible for eco-pollution due to the emission of carbon dioxide [1]. Many efforts are being made to reduce the uses of cement in concrete. So fly ash, silica fume, ground granulated blast furnace slag (GGBS) and rice husk ash are used as alternative cementing material. In order to produce the binder, alkaline solution and fly ash are mixed with silicon (Si) and aluminum (Al). The chemical process taking place in the production of binder is called geopolymer [2]. The geopolymer technology shows considerable promise for application in

concrete industry as an alternative binder to cement [3]. In general, increasing of CaO content in the slag results as raised slag basicity and an increase in compressive strength. The main components of blast furnace slag are CaO (30–50%), SiO2 (28– 38%), Al2O3 (8–24%), and MgO (1–18%). Use of GGBS significantly reduces the risk of damage caused by alkali-silica reaction. The low-calcium-based fly ash and GGBS (Figure 1) are used at a level 50:50 in concrete. Instances of chloride attack occur in reinforced concrete as marine environments to protect against chloride attack. The use of GGBS in such instances will increase the life of the structure.

Fig. 1: Fly Ash and GGBS Powder Form.

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Development of Geopolymer Concrete Kumaravel and Girija __________________________________________________________________________________________

Fig. 2: SEM of Fly Ash

Fig. 3: SEM of GGBS. (Tamilnadu) was used for this study. The SEM analysis of fly ash (Figure 2) and its constituents is given in Table 1.

PREPARATION OF CONCRETE Fly ash Low-calcium (ASTM Class F) fly ash obtained from Mettur Thermal Power Station,

Table 1: Constituents of Fly Ash and GGBS. Fly ash Element Mg Al Si K Ca Total

GGBS

Weight (%) Atomic (%) Weight (%) Atomic (%) 1.36 27.57 66.61 3.14 1.32 100

Ground Granulated Blast Furnace Slag Ground granulated blast furnace slag (GGBS) from Toshaly Cements Pvt., Vishakhapatnam, (Andhra Pradesh) conforming to IS 120891987 was used. The SEM analysis of GGBS (Figure 3) and its constituents is given in Table 1. Alkaline Solution The mixture of sodium silicate and sodium hydroxide is called as alkaline solution (AS). Sodium hydroxide (NaOH) with sodium silicate solution (Na2SiO3) in the ratio 1:2.5 was used. The AS mixture was allowed to stand for a period of 24 h for the reaction of polymerization to take place [4, 5].Solids dissolved in water to make a solution with the required concentration. The 14 mole (14 M) solution was used. Since the molecular weight of sodium hydroxide is 40, in order to prepare 14-molar solution, sodium hydroxide was dissolved in 1000 mL of water. Aggregates The cement concrete industry generally uses coarse and fine aggregates which is suitable to

1.57 28.68 66.57 2.25 0.92

5.05 16.87 42.24 1.69 34.15 100

5.24 17.11 43.15 1.13 33.36

manufacture the geopolymer concrete. The aggregate grading curves currently used in concrete practice are applicable in the case of geopolymer concrete [6]. Natural river sand available in Thiruppanadaal, (Tamilnadu) was used as fine aggregate. They were tested as per IS 2386-1997. In this investigation, locally available blue granite crushed stone aggregate of size 12.5 mm and less than that was used and characterization tests were carried out as per IS 2386-1997. The properties of aggregate used were specific gravity of fine and coarse aggregate –2.66 and 2.70 and fineness modulus of fine and coarse aggregate –2.43 and 6.71.

EXPERIMENTAL PROGRAM Geopolymer Concrete (GPC) The compressive strength of concrete to be used for construction is M-60 grade as heavy load and long span structure. The mix ratio for M-60 grade 1:1.15:2.30 was used in this study. The constituents of geopolymer concrete of 14 mole sodium hydroxide for M-60 grade concrete is shown in Table 2 and Figure 4.


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Journal of Construction Engineering, Technology and Management Volume 4, Issue 1, ISSN: 2249-4723 __________________________________________________________________________________________

Table 2: Constituents of Geopolymer Concrete. Description Quantity Fly ash (50%) + GGBS (50%) 528 kg/m3 Na2SiO3/NaOH 2.5 (Na2SiO3 + NaOH)/Fly ash 0.45 NaOH solid 38.02 kg/m3 Water (added with NaOH solid) 29.87 kg/m3 Na2SiO3 solution 169.71 kg/m3 Fine aggregate 607.20 kg/m3 Coarse aggregate 1214.40 kg/m3 Super plaster 5.18 kg/m3 24 h (hot air ) curing 75°C

Fig. 4: Materials for GPC. Mixing and Casting Geopolymer concrete was manufactured by adopting the conventional techniques used in the manufacturing of Portland cement concrete. The conventional concrete was made as an admixture of microsilica fume to increase the compressive strength. To increase the workability of OPC and GPC, sulfonated napthalene polymer-based super plasticizer, conplast SP430 was used. Fly ash, GGBS and the fine aggregate which were dry were mixed

Fig. 5: Pan-mixer.

in a 100 L capacity Pan-mixer for 3 min (Figure 5). The saturated surface coarse aggregate was added and mixed with fly ash, GGBS and fine aggregate until the coarse aggregate was uniformly distributed throughout the batch. The chemical solution (AS) was added in the entire batch mix for 4 min to form fresh concrete [7]. The workability of fresh concrete measured by slump was 100 mm for GPC as shown in Figure 6. It was cast and compacted by the usual methods used in the case of Portland cement concrete. The prepared concrete was kept in mold of specimen cubes and cylinders; size of cube 100 × 100 × 100 mm and cylinder as 100 mm diameter, 200 mm height as shown in Figure 7. It was observed that geopolymer concrete stuck hard to the mold, so oiling the molds is very important to release each cube specimen, while cast in three layers by compacting manually. Each layer received 25 strokes of compaction by standard compaction rod for concrete.

Fig. 6: Measuring of Slump.


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Fig.7: Casting of Specimens. Curing Geopolymer concrete specimens after casting were kept in the rest period in room temperature for one day and kept in hot air curing at an elevated temperature of 75 °C in an autoclave for 24 h [8]. The cubes and cylinders were kept for curing in a room temperature for about the test period.

EXPERIMENTAL INVESTIGATION Scanning Electron Microscopy (SEM) Analysis Chemical reaction of goepolymer concrete and cement concrete of microstructure is as follows. Process of geopolymerization of hardening material is different from the process of hydration of inorganic binders in Porland cement. The part of fly ash and GGBS are initially dissolved in strong alkali solution; the Si/Al ratio of synthesized geopolymer are

present in the range of 1.75–2.60 [9]. This SiO-Al structure is classified as a polysialate with Si/Al composition of 1.0–2.0. Increasing the silicate concentration in the activating solution (SiO2/Na2O) and to a decrease in Al substition around Si is geopolymer gel. The bond structure for geopolymer concrete (GPC) and cement concrete (OPC) corresponing to Si-O and Al-O by penetration of Al4+ atoms into the original arrangement of the Si-O-Si skeletal structure [10] is shown in Figure 8. For conventional concrete, C-S-H phase formed is shown in Figure 9. Fourier Transform Infrared (FT-IR) Spectral Analysis The FT-IR investigation is carried out on the powdered samples of M-60 GPC and OPC by KBr pellet technique. The peak obtained at GPC 3450.65 cm−1 is shifted to 3431.36 cm−1 in OPC and this could be due to O-H stretching and the peak is broad in both due to intra-molecular hydrogen bonding. The alkaline action of GPC and hydration of OPC are found in the FT-IR spectra, the band at 1072.42 cm−1 and 1028.06 cm−1 of GPC specimen (Figure 10) are compared to 1078.21 cm−1 and 1024.20 cm−1 in OPC specimen (Figure 11). Al incorporation into the original structure of Si-O-Si skeleton (chain) in GPC specimen shows the peak value due to higher amount of Al incorporation GPC specimen.

Fig. 8: SEM of GPC.


Fig. 9: SEM of OPC.

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Journal of Construction Engineering, Technology and Management Volume 4, Issue 1, ISSN: 2249-4723 __________________________________________________________________________________________

Fig. 10: FT-IR for GPC.

Fig. 11: FT-IR for OPC.

Test Setup A compressive strength machine of 2000 kN capacity was used to apply the axial force of compression. The hot-cured geopolymer

concrete cubes and cylinders were kept in room temperature for 28 days. Their compressive strength is given in Table 3.

Table 3: Compressive Strength of Geopolymer Concrete at 28 days. Weight Ultimate load Compressive Avg. compressive Specimens (g) (kN) strength (N/mm2) strength (N/mm2) Cube 1 2285 66.55 66.50 Cube 2 2324 68.00 68.00 66.67 Cube 3 2297 65.50 65.50

RESULTS AND DISSCUSSIONS Geopolymer concrete of mix ratio of 1:1.15:2.30 was used with fly ash and GGBS with alkaline solution and the compressive strength of concrete was obtained. The density of geopolymer concrete was found to be 2330 kg/m3 which is less than that of cement

Compressive Strength in N/mm2

80 66.67

70 60 50

62.25

58.5

concrete. The alkaline binder ratio of 1:2.5, 7 and 28 days average compressive strength of ordinary Portland cement concrete and geopolymer concrete are shown in Figure 12. These results obtained in geopolymer concrete are suited for structural applications with a concrete strength of 60 N/mm2. GPC-7 days

GPC-28 days

OPC-7 days

OPC-28 days 56.17

48.75

52.85

49.25 41.3

40 30 20 10 0 Cube

Cylinder

Fig. 12: Compressive Strength of Concrete at 7 and 28 days.


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CONCLUSIONS The compressive strength of GPC specimens obtained for cube is 66.67 N/mm2 and for cylinder it is 56.17 N/mm2. Geopolymer concrete possesses good compressive strength and is well-suited to manufacture precast concrete products. It is evident from the obtained results that geopolymer concrete is encouraging alkaline solution ratio 2.5. It can be increased by properly selecting the influencing parameters such as to make concrete for 7 and 28 days. Low calcium fly ash and GGBS-based geopolymer concrete has an excellent compressive strength and is quite suitable for structural applications.

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