Development of high strength recycled aggregate concrete-composite effects of fly ash, silica fume and rice husk ash as pozzolans

The world today has started facing bigger problems related to the concrete industry, especially with concrete becoming the most extensively used construction material in the world. At a time like this, where more eco-friendly substitutions are stringent, it calls for a more comprehensive approach in producing recycled concrete from recycled concrete aggregates (RCA). This study is an extension to previous studies involving composite utilization of pozzolans in treating RCA. It investigates on the possibility of using rice husk ash (RHA) along with other pozzolans as a cement replacement, in both stages of aggregate treatment and concrete production. It was observed that through this treatment, aggregate specific gravity was increased to a value of 2.37 which was earlier 2.18 for untreated RCA, 26% and 59% reductions were obtained for water absorption and porosity of aggregates, respectively. Further the concrete which contained RHA in both stages, attained a high strength of 55.4 MPa, even surpassing the control mix containing natural aggregates. The same mix resulted a 12% increase in its surface resistivity. Rapid Chloride Permeability Test (RCPT) and water permeability results also showed substantial improvements when compared to the reference RCA mix. Similar to previous studies involving composite use of pozzolans, improvements in the microstructure of both the aggregates and concrete through the use of RHA resulted in the amelioration of both mechanical and durability properties of concrete. This evidently indicates the possibility of achieving high strengths, even with the use of RCA derived from parent concretes of lower grades.