Comparative Investigation of the Effect of Recycled Fine Aggregate from New and Old Construction Wastes in C-25 Concrete in Ethiopia

Wherever there are construction activities, there is waste generation. In Ethiopia, the popular material for wall construction is a hollow concrete block that can be broken on the production site or the construction site during loading and unloading and is also found abundantly in demolished buildings. This research aimed at searching for alternative construction materials through recycling and examined the properties of recycled fine aggregate from demolished (old) and construction (new) hollow concrete block (HCB) wastes. The study examined the effect of the recycled HCB on fresh and hardened C-25 concrete properties and the possible replacement percentage of river sand by those recycled fine aggregates. The research also examined the comparative properties of the two recycled fine aggregates. The replacement percentage was in steps of 25%, starting from 25% up to 100%, and 0% represented the reference mix. In general, the recycled fine aggregate exhibited relatively lower physical properties than natural river sand but satisfied the American Society for Testing and Materials (ASTM) standard requirements. The demolished recycled fine aggregate (DRFA) had slightly lower physical properties than the construction recycled fine aggregate (CRFA). The properties of fresh and hardened concrete were decreased as percentage replacement of DRFA and CRFA increased. The optimum percentage replacement of river sand by recycled fine aggregate was between 50% to 75% but was much closer to 75% for that of recycled from construction (new) and closer to 50% for that of recycled from demolished (old) HCB. Recycling wastes can reduce environmental impact due to sand mining and waste disposal as well as partially conserve the natural resource depletion.