Effect of Alkali Activated Slag on Punching Shear

The need to meet a sustainable development is now an important challenge to the cement industry. The production of OPC is responsible for about 7% of the world?s CO2 emission, a major contributor to the green house effect which is implicated in global warming and climatic changes, lead to the search for more environmentally viable alternative to cement. One of those alternative material is alkali activated slag (AAS) where ground granulated blast furnace slag is used not as partial replacement to cement but also as a sole binder in the production of concrete. The overall aim of the study was to investigate the potential of alkali activated slag as a sole binder in producing concrete. The performance of alkali-activated slag concrete with sodium silicate, sodium hydroxide, sodium carbonate as activator are used at 4% Na2O(by weight of slag) and 4% of hydrated lime by total weight of solid binder content if used as a retarder. The scope of the work covered four mixes: - Normal OPC mix and three alkali activated slag mixes of the same binder content and the same water binder ratio. The fresh concrete properties studied were setting time and workability and the Engineering properties studied are compressive strength was measured in 1, 7, 28 days, split tensile strength was measured in 7, 28 days and flexure, punching shear strength was compared in 12 days only. The AAS concrete with different activators investigated was found to achieve good workability comparable with that of OPC. Sodium silicate, sodium hydroxide activated slag mixes sets very quickly. AAS concrete is much more sensitive to curing where if there is no addition of retarder (hydrated lime) to the mix. Among AAS mix sodium silicate was the best; sodium carbonate was the second; and sodium hydroxide was third in terms of compressive, split tensile strengths and in terms of flexure strength and punching shear strength sodium hydroxide was best; sodium carbonate was second; sodium silicate (water glass) was third.