Effect of molarity of NaOH and alkalinity ratio on compressive strength of geo-polymer concrete

Abstract

Concrete is the most copious man-made material in the planet. One of the main ingredients in a normal concrete mixture is Portland cement. However, the production of cement emits approximately 5% of the world’s carbon dioxide (Greenhouse gas). On the other hand, the climate change due to global warming and environmental protection has become major concerns. The production of Portland cement involves the emission of carbon dioxide, thus replacing of the Portland cement with industrial waste can be one of the solutions for reduction of the carbon dioxide emission. At the same time, thermal power plants produce fly ash in a very large amount and it creates a huge problem for its disposal. Disposal of this fly ash requires approximately 40,000 ha of land every year. In order to avoid the above environmental issues as well as the disposal problem, researchers have employed fly ash an alternative of cement in making of concrete exploiting the binding property of fly ash thereby it led to make attempt to carry out more research on the replacement of cement by fly ash in the concrete. Therefore, the focus to work in this direction acquainting with the idea that the replacement of cement is possible with 100% fly ash and this alternative to regular concrete is known as Geo Polymer Concrete (GPC). The theme of the present work is fully replacement of cement with fly ash to produce the GPC. To produce the GPC, the main constituent materials used are Fly Ash (which is a by-product obtained from thermal power plants) and the alkaline activators in addition to aggregates and water. The alkaline activators used in this study for the polymerization are sodium hydroxide (NaOH) in flakes form and sodium meta -silicate (Na2SiO3) in gel form. The objective of the present work is to study the effect of NaOH molarity and alkaline activator ratios on the compressive strength (3, 7 and 28 days) of GPC at a constant curing period and curing temperature and compare with controlled concrete prepared using ordinary Portland cement (OPC). In the present work 5 and 10 M of NaOH and 1:1, 1:1.5 and 1:2 alkaline ratios were considered with constant curing temperature of 90° C and 24 h curing time. M20 grade of concrete mix design was carried out as per BIS (IS: 10262–2009) for control concrete and the same mix proportion was adopted for GPC also. From the experimental results, it was found that the both NaOH molarity and alkaline solution ratio effecting the compressive strength at 3, 7 and 28 days and maximum compressive strength was obtained at higher NaOH molarity (10 M) and medium alkaline solution ratio (1:1.5). Further, it was found that the compressive strength of GPC was higher than the controlled concrete prepared using OPC.