Effect of Waste Concrete Powder Content and Microwave Heating Parameters on the Properties of Porous Alkali-Activated Materials from Coal Gangue.

The objective of this research is to fabricate waste-based alkali-activated foams with better properties in a quick time by using energy-efficient techniques such as microwave irradiation. The present study reports the effect of microwave heating parameters, including heating time and output power, on the properties of porous alkali-activated materials (AAMs) that use coal gangue (CG) as a precursor. The effects of concrete waste (CW) content (0-20 wt %) on the performance and microstructure of CG-based AAMs were investigated. Mechanical, thermal, and microstructural investigations were conducted to characterize the obtained materials. The experimental results indicate that the best characteristics of CG-based alkali-activated foams were achieved when microwave power and microwave heating time were 800 W and 10 min, respectively. The foams prepared by adding the waste concrete powder increased stability and showed lower bulk density and thermal conductivity. When the waste concrete powder content was 10 wt %, the CG-based alkali-activated foams showed the best overall performance. At the same time, the mechanical properties of the alkali-activated foams declined only slightly (~9%). The findings of this work provide a basis for further studies on improving the characteristics of CG-based alkali-activated foams due to the physical effect of a microwave field on fresh mortar without the use of a chemical foaming agent while reducing energy consumption in the production process.