Gypsum as a Bloating Agent for Expanded Concrete Waste Fines LWA

Concrete waste fines (CWF) are a major by-product of concrete recycling. Recycled coarse aggregates have already been introduced into the construction industry. However, little has been done on the utilization of the fine fraction of concrete waste. This research investigated a method of recycling CWF to produce expanded lightweight aggregate (LWA) using gypsum as a foaming agent. Further, the effects of quartz and bauxite addition on the bloating characteristics of LWA were studied by utilizing the CWF by different ratios of 25, 36, 72, and 100%. This was done to modify the chemical composition of the mixture in accordance with Riley’s ternary diagram. A physical and chemical analysis of the raw materials was conducted initially using X-ray diffraction, and inductively coupled plasma spectroscopy. A series of tests were conducted with the burning temperatures and gypsum content as experimental variables. A detailed analysis of the apparent density, water absorption, and bloating index was conducted and the microstructure of LWA particles and pore sizes were studied using optical fluorescence microscopy. The experimental results demonstrated that adding 15% of gypsum by weight to the 25% CWF mixture and a maximum heating temperature of 1200 ℃, resulted in a bloating index of 155%, an apparent density of 573 kg/m³, and a water absorption of 128 wt. %. This expansion of LWA was achieved primarily due to the gypsum acting as a bloating agent. The research confirmed the feasibility of producing high-quality LWAs by combining fine concrete waste with gypsum.