Effects of Fine Recycled Aggregate as Sand Replacement in Concrete

Although fine recycled aggregate (RA) constitutes a significant amount of C&D wastes after crushing, the current specification in Hong Kong momentarily does not allow the use of fine RA in ready-mixed concrete production due to its high water absorbability, which is believed to have a negative impact on the workability and durability performances of the resulting concrete. Nevertheless, few studies have quantified the detrimental effects of fine RA on the properties of concrete. This paper, therefore, presents a research study for accessing the influences of fine RA on the properties of concrete prepared with coarse natural aggregate. In order to tackle the high water absorption of the fine RA in the mixing stage, a double mixing method was adopted in lieu of the traditional mixing method. The results indicated that the mechanical properties and some of the durability parameters were debilitated by the incorporation of the fine RA. However, these drawbacks could be adequately compensated by the use of fly ash and a sufficient curing time.