Development of Ultra-High Performance Concrete (UHPC) matrix based on recycled concrete fines subjected to coupling curing of microwave and wet carbonation

The energy consumption of the wet carbonation method is increased by water bath heating, which is not conducive to the sustainable development of wet carbonation for Recycled Concrete Fines (RCF) treatment. In this study, a microwave wet carbonation method targeting low energy consumption and high carbonation rate is developed. Microwave heating is used instead of water bath heating to reduce the energy consumption of wet carbonation and prepare microwave carbonation recycled concrete fines (MCRCF). The results show that under the reaction condition of 80 degrees C, microwave reduces the activation energy of wet carbonation reaction through nonthermal effect and promotes the formation of aragonite and calcite grains. When preparing 50 g MCRCF and heating to 80 degrees C, microwave heating can reduce energy consumption by 26.6 %. At the same time, the CO2 absorption rates of microwave wet carbonation and pressured carbonation are 19.4 and 6.4 g/(min & sdot; kg), respectively. Therefore, microwave wet carbonation has stronger energy efficiency advantages. Additionally, the effect of MCRCF on the properties of UHPC matrix is studied. The results show that when the replacement rate of MCRCF is about 50 %, the 28d average compressive strength of the UHPC matrix increases slightly, and the development of the interface transition zone and the hydration process are promoted. This study provides a new idea for clean and efficient treatment method of RCF and verifies the feasibility of using microwaves for wet carbonation.