Thermal Stress Distribution and Evolution of Concrete Particles under Microwave Irradiation

Abstract

Microwave heating could increase the efficiency of eliminating mortar in recycled concrete aggregate and improving recycled concrete aggregate quality. A 2D finite element model of microwave oven and concrete particles was established to study the distribution and evolution law of thermal stress field in concrete particles. In this model, influences of power, time, aggregate radius, and mortar thickness were considered. Results showed that the temperature and stress of concrete particles in a microwave field are in approximately symmetric distribution. The maximum stress of mortar is on the interface between mortar and the recycled concrete aggregate. The maximum tensile stress of mortar and recycled concrete aggregate was proportional to microwave power and irradiation time but inversely proportional to aggregate radius. The maximum tensile stress of mortar and recycled concrete aggregate initially increased and then decreased with increased mortar thickness. Given the same energy consumption, higher microwave power led to stronger tensile stress of concrete particles and higher energy use. With reasonable irradiation time, the mortar produced cracks, whereas the recycled concrete aggregate remained integral.

Quality Improvement Techniques for Recycled Concrete Aggregate: A review

“…The original aggregate will cool down slowly and its contraction will be hindered by the external layer of mortar surrounding the aggregate particles which will induce tension and encourage the separation of the external mortar (De Juan and Gutiérrez 2009). (2) Microwave heating The microwave heating technique benefits from the differences in the electromagnetic properties between the original aggregate and the adhered mortar (Like et al 2016). Microwave heating results in fracturing and separates the adhered mortar without harming the original aggregate, and consequently reduces the content of adhered mortar in the RCA (Akbarnezhad et al 2011;Akbarnezhad and Ong, 2010).…”

Mechanical properties of the concrete with recycled coarse aggregate surface treated by microbes

“…The quality of RCA was enhanced either through removal of adhered mortar or strengthening of adhered mortar. Various techniques such presoaking in water (Katz, 2004; Pepe et al , 2015), mechanical treatment (Revathi et al , 2014; Kothari et al , 2016), thermal treatment (Like et al , 2016; Al-bayati et al , 2016), thermo-mechanical treatment (Pawluczuk et al , 2019), acid immersion (Saravanakumar et al , 2016; Kim et al , 2016), etc. have been developed to eliminate the adhered mortar on the surface of RCA.…”