partial replacement of sand in concrete with recycled fine aggregates from construction and demolition wastes

Abstract

Concrete is one of the most widely used construction material in the world. Concrete is a composite material that consists of binding materials, sand, and gravel. Extraction of sand from the river has socio-economic, cultural and even political consequences. Construction and demolition waste is generated whenever any construction and demolition activities take places. These construction and demolition waste disposals are released in huge quantities as landfills and cause environmental pollution. An attempt has been made to recycle these waste materials into usable material for the production of concrete to sustain limited natural resources and as well as to reduce environmental hazards. The main objective of this research is to find alternative construction material sources from construction and demolition waste to conserve limited natural resources and prevent environmental hazards due to these waste disposals. It includes extraction of fine aggregate from construction and demolition wastes of hollow concrete block (HCB) found in Ethiopia, investigate physical and chemical properties of recycled fine aggregate. Finally, the replacement amount of river sand by recycled fine aggregate in the production of concrete was determined. The study was carried out through experimental investigation of basic properties of recycled fine aggregate from HCB wastes and also compare these properties with river sand. The comparative result of the experiments of fresh and hardened concrete with different replacement ratios of natural sand with recycled fine aggregate is presented in this paper. Three types of concrete mixtures were tested: concrete made completely with natural river sand as a control concrete and two others types of concrete made with demolished recycled fine aggregate (DRFA) and construction recycled fine aggregate (CRFA). For both types of concrete, the basic concrete properties like workability, density, and compressive strength of concrete was studied with 25 %, 50 %, 75 %, and 100 % replacement of natural sand with the recycled fine aggregate. 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 DRFA has slightly lower physical properties than CRFA. The properties of fresh and hardened concrete were decreased as percentage replacement of LUCY F. VI DRFA and CRFA increased. The optimum percentage replacement of river sand by recycled fine aggregate was lay between 50% to 75% but very 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 which can conserve the natural resource depletion problem partially.