Properties of Green Concrete with Various Alternative Alkali Binders

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 materials is alkali activated slag (AAS). Where alkali activated slag is used not as partial replacement to cement but 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 the sole binder in producing concrete. The performance of alkali-activated slag concrete with sodium silicate, sodium hydroxide, sodium carbonate, potassium hydroxide as activator are used at 4% Na2O & K2O (by weight of slag) and 4% of hydrated lime by weight of slag if used as retarder. The scope of the work covered four mixes: a normal OPC mix, four AAS slag mixes of the same binder content and the same water binder ratio, the coarse aggregates are replaced by the 10% recycled aggregates. The fresh concrete properties studied were setting time and workability in terms of slump. The Engineering properties studied were compressive, split tensile strength and flexure strength measured in 1, 3, 7, 14, 28, 56 and 90days. 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 (Na2SiO3), 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, NaOH was the best; KOH was the second; Na2SiO3 was third; and Na2CO3 was the fourth in terms of compressive strength. Na2SiO3was best; KOH was the second; Na2CO3 was third; and NaOH was the fourth in terms of split tensile strength. KOH was the best; NaOH was the second; Na2CO3 was third; Na2SiO3 was fourth in terms of flexure strength.