Investigating the effect of recycled concrete aggregates and cow dung ash on the physical and mechanical properties of concrete.

Abstract

Recently, environmentally friendly building is becoming a crucial issue in the construction industry. The course towards sustainable concrete involves mainly minimizing the environmental impact of concrete production by substituting virgin mineral materials with recycled ones as well as reducing the global carbon dioxide (CO2) emission. The approach adopted here included a large substitution of Natural coarse aggregates (NCA) with Recycled coarse aggregates (RCA) obtained from crushed concrete debris as well as the use of Cow dung ash (CDA) as a partial replacement for Portland cement for concrete production. Previous studies revealed the potential of using RCA to produce concrete with a similar 28-day design strength to that obtained when using natural aggregates. Similarly, the chemical properties and pozzolanic effects of partial replacements (5%,10% and 15%) of cement with cow dung ash (CDA) in concrete were investigated. This research discusses the effect of using both recycled concrete aggregates (RCAs) and cow dung ash (CDA) as partial replacements for natural coarse aggregates and cement in concrete respectively. Physical and mechanical properties have been examined for both Normal concrete and concrete with CDA and RCAs for mixes designed with various proportions of CDA (5%,10%,15%) and RCAs (20%,30%,40%) by mass. Results obtained showed that while embedding high amounts of CDA could lower the compressive strength of concrete, a smaller percentage of 5% enhanced the concrete strength beyond that of normal concrete by 8%. High amounts of RCA had an insignificant effect on the compressive strength. The concrete mix with 5% CDA and 30% RCA had a compressive strength of 28.6 N/mm2 and 36.5N/mm2 at 7 and 28 days respectively with the control experiment having 28.1 N/mm2 and 33.9 N/mm2 at 7 and 28 Days respectively. A high-water absorption was observed in concrete containing CDA and RCAs compared to that of the normal concrete. A decrease in density of concrete was observed with increase in percentages of both CDA and RCA compared to the normal concrete. The use of CDA and RCAs in concrete is economical in terms of cost and eliminates the problem of landfills, reducing the environmental risk, maintaining the ecological balance, which is very much required for our nation.