Hydration, microstructure and mechanical properties of cement-based materials with heat-modified autoclaved aerated concrete waste

As a typical construction and demolition waste (C&DW), autoclaved aerated concrete waste (AACW) can be utilized as a cementitious component of cement-based materials, but its low activity limits its application. In this work, heat-modified technique was proposed as a potential approach to stimulate the activity of AACW. The influence of AACW with different heat-modified temperatures ranging from 500 to 900 degrees C in increments of 100 degrees C on the phase change was studied. The effect of heat-modified autoclaved aerated concrete waste (HM-AACW) on the workability, hydration kinetics, microstructure development and mechanical properties of cement-based materials were investigated. The results showed that heat-modification in a proper temperature range (500-700 degrees C) changed the phase structure of AACW, and allows them to gain activity. The incorporation of HM-AACW at the level of 20% cement replacement can enrich the amount of hydration products in the cement paste to varying degrees and the HM-AACW treated at 700 degrees C improved 28 d compressive strength and flexural strength by up to 31.0% and 13.0% compared to original AACW. It was proved that the inert AACW can be effectively activated by heat-modified technique, with the heat-modified temperature much lower than the calcination temperature of cement clinker (1350 degrees C), resulting in environmental and economic benefits.