Waste-Based Precipitated Calcium Carbonate as a Partial Cement Replacement in Cementitious Composites Subjected to Geothermal-Related Thermal Cycling

Geothermal energy production requires durable well-cementing materials capable of withstanding extreme thermal fluctuations, yet the high carbon footprint and cost of Ordinary Portland Cement (OPC) necessitate sustainable alternatives such as fillers and supplementary cementitious materials. This study investigates whether waste-based Precipitated Calcium Carbonate (PCC), a sugar beet industry by-product, is feasible for use as a sustainable partial replacement/filler material in OPC-based concrete mixtures considered for geothermal-related cementitious applications. The experimental program was conducted in two distinct phases. Initially, PCC replaced OPC at 5%, 10%, 15%, 20%, and 25% by weight to evaluate mechanical performance. In the second phase, optimized mixes with 0%, 5%, and 10% PCC were subjected to thermal cycling between 10 °C and 250 °C for up to 30 cycles to simulate harsh geothermal conditions. Results showed that 5% PCC increased compressive strength by 9.47% (34.3 MPa) and tensile strength by 2.93% (3.0 MPa) relative to the control mixture. During thermal cycling, the 5% PCC mix demonstrated superior stability, maintaining 32.1 MPa after 10 cycles, while higher PCC contents led to significant degradation. Within the limits of the laboratory tests conducted, the study concludes that a low PCC replacement level, particularly 5%, is an optimal threshold, offering improved thermal resilience and mechanical strength while reducing OPC consumption and carbon emissions. Further slurry-level, chemical durability, and field-representative testing are required before broader geothermal well cementing validation.