Stabilization of extruded earth-based materials by adding hydrated cement powder from recycled concrete

Decarbonization policies in the construction and building sector have spurred the search for materials with a lower environmental impact. Traditional techniques, such as earth-based materials (EBMs), have inspired innovative solutions, although these materials often need enhancement to meet modern performance demands. Typically, this requires reinforcement or stabilization, which can increase both the carbon footprint and manufacturing costs. This study explores the feasibility of using powdered waste from concrete recycling (hydrated cement powder, HCP), which currently lacks effective utilization pathways. HCP, consisting mainly of hydrated cement and fines, has potential cementitious properties. We investigated the impact of incorporating HCP into EBMs by replacing soil with HCP at proportions of 20 %, 25 %, 30 %, 35 %, 40 %, and 60 %. The evaluation included tests for shrinkage, density, compression and flexural strength, thermal properties (thermal conductivity and specific heat capacity), and resistance to water (Swinburne's accelerated erosion test). Additionally, the microstructure of both the raw materials and the resulting EBMs was analyzed through the particle size distribution, scanning electron microscopy, X-ray diffraction, and X-ray fluorescence. The results show that HCP improves thermal resistance (e.g., from 0.86 to 0.4 W m⁻1 K⁻1 with 60 % HCP) while slightly reducing thermal capacity by approximately 30 %. Rainwater erosion is effectively mitigated from 35 % HCP. However, increased porosity from HCP leads to reduced compressive and flexural strength (e.g., from 3.4 to 1.5 MPa and from 1.2 to 0.5 MPa, respectively, with 60 % HCP). In conclusion, incorporating 35 % HCP is technically feasible, producing a lighter block with enhanced thermal resistance while meeting EN41410 standards.