Development of high-strength lightweight concrete by utilizing food waste digestate based biochar aggregate

Abstract

The application of carbon-negative biochar in cement composites can effectively reduce carbon emissions of construction materials. In this study, low-carbon composites were tailored with high volume of food waste digestate (FWD) biochar aggregate. The biochar was customized at different temperatures with the goal of enhancing the properties of cement-based composites. Backscattered electron microscopy (BSEM) images show that FWD biochar with a grey circle shape exhibited strong bonding with the cement matrix. Nano-indentation results indicate that the two statuses of FWD biochar showed visco-elastic and elastic-plastic modes of deformation, respectively. The FWD biochar aggregate prepared at higher pyrolysis temperatures (i.e., 650 °C and 750 °C) has higher elastic modulus (up to 11.4 GPa), which can be applied to make biochar blocks with higher strength and lower density compared to the biochar pyrolyzed at 550 °C. As a result, FWD 750BC blocks could reach 28-d compressive strength of 57.8 MPa and density of 1.77 g cm−3, which fulfilled the requirements of high-strength lightweight aggregate concrete. Hence, this study established a foundation to utilize FWD biochar as an aggregate in high-strength biochar construction materials.