Experimental Analysis of Fly Ash Based Geopolymer Concrete and its Applicability in Highway Construction

Abstract

The rising threat of global warming and the high cost of raw materials for the production of cement, which is widely regarded as the second most used material in the world after water, have prompted many construction industry leaders to ponder upon finding newer environmentally friendly (green) and cost-effective ways to produce concrete. One such method is the use of Geopolymer concrete, which is quickly becoming a popular material among academics, and as a result, there has been a great deal of worldwide and Pakistani research on this topic. But one aspect which has been found wanting is the comparison of two similar mixture designs i.e., one mixture of standard concrete (OPC) based and one mixture of fly ash geopolymer concrete (FGPC). From literature review it was found that fly ash geopolymer concrete (FGPC) showed optimum mechanical properties when sodium hydroxide (NAOH) had a range of 8 molar – 14 molar concentration in the mix, when sodium silicate and sodium hydroxide had a ratio of 2.5 and when it was cured at high temperature or with an added admixture for ambient curing. In this research three batches of ordinary Portland cement concrete (OPCC) as (control mix), fly ash geopolymer concrete (FGPC) and FGPC with 5 % cement as an admixture were prepared respectively with similar mix proportions and then to check their mechanical properties some elementary tests like compression strength test and splitting test were performed to compare their behaviour in normal conditions prevalent in Pakistan. Three-point flexural test were also performed to investigate the behaviour of FGPC on rigid pavements. It was found out that FGPC concrete cured at higher temperatures of 60 C showed an increase of 9 % compressive strength at 7 days when compared with that of control mix at 28 days, whereas FGPC with 5% cement admixture showed an increase of 4 % in 28 days compressive strength form the control mix. Similarly, the 7 days flexural strength of FGPC was slightly higher that that control at 28 days but FGPC with 5 % cement as an admixture at ambient curing showed a significant increase of up to 15 % in flexural strength with that of control mix after 28 days. Thickness of a standard rigid pavement lane (1 km long and 3.65 m wide), calculated from the data collected showed that FGPC and OPCC rigid pavement had similar thickness but FGPC with 5 % cement showed a decrease of 8 % in pavement thickness compared with OPCC pavement. Finally, a cost analysis was carried out, it was found out that FGPC pavement costs would reduce by 22 % and FGPC with 5 % cement as admixture pavement cost would reduce by 18.8 % respectively when compared with the costs of OPCC rigid pavements.