Applications of mortar with calcium carbide residue and high calcium fly ash: Mechanical properties and thermal performance

The present investigation evaluated the mechanical and thermal performance of cement mortar wall panels incorporating ground calcium carbide residue (CB) and as-received fly ash (FA) as partial replacements for ordinary Portland cement (OPC). The cementitious binder was modified by substituting 20% of OPC with either CB or FA, and by using a ternary blend consisting of 10% CB and 10% FA by weight. All mixtures were prepared with a constant water-to-binder ratio of 0.48, and a superplasticizer was incorporated to ensure adequate workability. The experimental results revealed that the ternary blend (10CB10FA) achieved compressive strengths of 21.1 MPa at 7 days and 34.9 MPa at 28 days, corresponding to 102.9% and 117.9% of the control mortar strength, respectively. This mixture also exhibited the highest flexural strength (5.5 MPa) and density (2185.5 kg/m³), together with reduced porosity compared to the binary and control mixes. In contrast, mortar wall panels incorporating 20% FA demonstrated superior thermal resistance relative to panels produced with OPC alone and other blends. Under simulated solar heat exposure, the 20FA panels recorded lower outer and inner surface temperatures of 35.20 °C and 34.28 °C, respectively, indicating improved thermal insulation performance. The CaO in CB and reactive silica in FA synergistically enhanced calcium silicate hydrate (C–S–H) formation, improving both strength and thermal insulation. These findings indicate that the CB–FA ternary system optimizes mechanical performance, while FA-rich mortars enhance thermal resistance for energy-efficient wall applications.