Reuse of engineering waste soil and recycled fine aggregate to manufacture eco-friendly unfired clay bricks: Experimental assessment, data-driven modeling and environmental friendliness evaluation

In order to explore the possible application of engineering waste soil (EWS) and recycled fine aggregate (RFA) in cement-based unfired clay bricks (CUCB), this paper utilizes the orthogonal experiment to investigate the combined utilization of EWS and RFA to fabricate eco-friendly CUCB. The study employs an L9 (34) orthogonal table with four factors and three levels for designing mix proportions. The factors include the ratios of water-to-cement (w/c), cement-to-EWS (c/e), RFA-to-EWS (r/e) and additive content. CUCB were tested for density, compressive strength, and flexural strength; and the impact of each factor on these properties was analyzed. The test results reveal that the eco-friendly CUCB exhibit lightweight characteristics and desirable mechanical properties. The ratio of flexural strength-to-compressive strength for eco-friendly CUCB ranges from 0.23 to 0.28, indicating that eco-friendly CUCB have good toughness. Data-driven models were developed to construct the relationships between target properties (i.e., density, compressive strength, and flexural strength) and four factors. The optimal mix proportion for physical and mechanical properties was determined to be w/c= 0.55, c/e = 0.3, r/e = 0.4 and additive content= 10%, with predicted compressive and flexural strengths of 19.68 MPa and 5.19 MPa, respectively. In addition, Scanning Electron Microscope (SEM) was performed to figure out the strength enhancement mechanism of eco-friendly CUCB with varying mix proportions. Environmental friendliness evaluation shows that the optimal mix pro-portion is more environ-mentally friendly to fabricate CUCB from the perspective of strength-normalized carbon footprint and energy consumption. Using large quantity of cement cannot increase the compressive strength and only acts as filler in the microstructure of eco-friendly CUCB.