Utilisation of dewatered extracted soil in concrete blocks produced with Portland cement or alkali-activated slag: Engineering properties and sustainability

Abstract

Disposal of soil from foundation excavation in the construction industry has been recognised as a critical challenge for environmental protection. This study investigates the feasibility of incorporating dewatered extracted soil (DES) in concrete blocks manufactured with ordinary Portland cement (OPC) or alkali-activated slag (AAS). The physical and engineering properties, including bulk density, water absorption, compressive strength and flexural strength, of the concrete blocks with different contents of DES were investigated. Scanning electron microscope (SEM) analysis was also conducted to investigate the microstructure of the blocks. The results indicate that replacing sand by DES can enhance the physical and mechanical properties of the concrete blocks. The optimal replacement ratios are 30% for the OPC concrete blocks (OPCCB) and 20% for the AAS concrete blocks (AASCB). At the optimal replacement ratios, the densities of OPCCB and AASCB are 10.5% and 19.6% higher than those without DES, respectively, while the water absorption ratios are 38.0% and 48.7% lower than those without DES, respectively. Consequently, the 28-day compressive and flexural strengths for both blocks were increased by over 100%. The SEM photographs indicate that the improvements are attributed to the densification of the structure. However, further increasing the incorporation ratio of DES increases the surface area of total aggregates and requires more OPC or AAS to bind them, which consequently weakens the properties of concrete blocks. Besides, the strength of concrete blocks with AAS is around 2 times that with the same amount of OPC, indicating that AAS is more effective in improving the strength of concrete blocks. Moreover, a cradle-to-gate life cycle assessment (LCA) was performed to analyse the energy consumption and embodied carbon of the concrete blocks. The results indicate that AASCBs exhibits superior environmental sustainability over both conventional fired clay bricks and OPCCBs. Results in this study can help promote the application of DES in producing green concrete blocks.