Feasibility study of using recycled fresh concrete waste as coarse aggregates in concrete

In Hong Kong, a large amount of fresh concrete waste (FCW) is generated from ready mix concrete plants every day. Up to now, these wastes are usually delivered to landfills for disposal. The landfill areas in Hong Kong will be saturated in 6-8 years, as a result there is a need to develop a new technique for utilizing the FCW. In this study, FCW was crushed into coarse aggregate, and then it was used to replace natural coarse granite at percentages of 0%, 15%, 30% and 50%, in producing new concrete mixes. The concrete were produced with water/cement ratios of 0.35 and 0.50. The effect of using the normal mixing approach and the two-stage mixing approach on the properties of concrete was also compared. The results indicated that the density, strength and static modulus of elasticity of new concrete were decreased with an increase in FCW content. Due to the lower density and higher water absorption of FCW, the water absorption, chloride ion permeability and dry shrinkage of the new concrete was increased with the increase in FCW content. Moreover, the two-stage mixing approach (TSMA) only improved the strength of the FCW concrete when the concrete was prepared with a lower water-to-cement of 0.35. The results demonstrated that the FCW can be used to replace natural aggregates for the production of non-structural concrete.