A study on how to improve the physical properties of recycled coarse aggregates with the use of rice husk ash- cement slurry

This paper discusses about a surface enhancement method for recycled coarse aggregates (RCA) in order to reduce the water absorption capacity. The main aim of the research was to apply a surface coating technique by using different slurry ratios (i.e., Liquid: Solid) containing varying amounts of rice husk ash (RHA) and cement. The slurry ratios used in the study were 0.625, 0.75, 0.875, 1.0, 1.25, 1.5 and 2.0. The solid compositions in the slurry were varied by varying the RHA: cement ratio as follows: 0%:100%, 20%:80%, 40%:60%, 50%:50%, 60%:40% and 80%:20%. The treated recycled coarse aggregate (TRCA) had been then cured for 3 days, 7 days, 14 days and 28 days and the water absorption of the TRCA were analyzed. When analyzing the results it could be clearly seen that with the increase of RHA in the solid composition of the slurry, the water absorption of the TRCA increases and furthermore, the strength of the coating decreases. Therefore it is not recommended to replace cement beyond 40% with RHA in any slurry used to treat RCA. When RCA was treated with slurry containing only cement, the best slurry ratio that gave the minimum water absorption was 1.5. But when a mixture of RHA and cement was used in the slurry, the best slurry ratio was 0.875. The lowest water absorption capacity of TRCA was obtained at a curing age of 7 days. Grade 30 concrete was made with three selected scenarios of TRCA, RCA and NCA. The concrete scenarios made with the TRCA and NCA obtained strengths greater than 30 N/mm2 after 28 days of curing, except that made with RCA