PERFORMANCE OF RECYCLED ALKALI ACTIVATED SLAG PLAIN AND REINFORCED CONCRETE IN TERMS OF MECHANICAL PROPERTIES WITH EMPHASIS ON SIZE EFFECT OF PUNCHING SHEAR

structural engineering

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 as a a sole binder in the production of concrete. The overall aim of the study was to investigate the potential of alkali activated slag as the sole binder in producing concrete. The performance of alkali-activated slag concrete with sodium silicate, with hydrated lime, sodium hydroxide, sodium carbonate as activator are used at 4% Na2o(by weight of slag) and 4% of hydrated lime by weight of solid binder content if used as retarder. The scope of the work covered four mixes: a normal OPC mix, three AAS slag mixes of the same binder content and the same water binder ratio. The fresh concrete properties studied were setting time and workability in terms of slump. The engineering properties studied were compressive, split tensile strength was measured in 7,12,28 days and flexure and punching shear strength was compared in 12 days only. The AAS concrete with different activators investigated was found to achieve very good workability which was higher or comparable with that of OPC. The addition of hydrated lime to AAS mix was resulted in decrease in workability. Water-glass(Solid powder form), NaoH 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. L.S.S. was the best; Na2co3 was the second; and NaOH was third in terms of compressive, tensile strengths and NaOH was best; Na2co3 was second; and Na2sio3(Solid powder form) was third in terms of flexure and punching shear strength.

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