Effects of recycled micro-powders mixing methods on the properties of recycled concrete

Recycled micro-powders were introduced into recycled concrete by adhering them to the surface of recycled aggregate, and a systematic comparison was conducted with recycled concrete prepared with the recycled micro-powder admixture to examine the effects of the mixing modes of recycled micro-powders on the workability and mechanical properties of recycled concrete. In addition, the microhardness test, the hydration products, and the hydrated microstructure were used to investigate its mechanism. The results indicated that recycled micro-powders as a cement admixture decreased the fluidity and compressive strength of recycled concrete. However, the incorporation of recycled micro-powders attached to recycled aggregates improved the fluidity of recycled concrete and obtained a higher compressive strength; in particular, the 28d and 56d compressive strengths increased by 3.66 % and 7.28 %, respectively, compared to those of ordinary recycled concrete. When the incorporation amounts of recycled micro-powders into recycled concrete were identical, the recycled concrete exhibited a denser microstructure and higher microhardness in the interface transition zone when the recycled micro-powders were adhered to the recycled aggregate.