Hydration, Soundness, and Strength of Low Carbon LC Mortar Using Waste Brick Powder as a Source of Calcined Clay.

The construction industry is responsible for 39% of global CO emissions related to energy use, with cement responsible for 5-8% of it. Limestone calcined clay cement (LC), a ternary blended binder system, offers a low-carbon alternative by partially substituting clinker with calcined clay and limestone. This study investigated the use of waste clay brick powder (WBP), a waste material, as a source of calcined clay in LC formulations, addressing both environmental concerns and SCM scarcity. Two LC mixtures containing 15% limestone, 5% gypsum, and either 15% or 30% WBP, corresponding to clinker contents of 65% (LC-65) or 50% (LC-50), were evaluated against general purpose (GP) cement mortar. Tests included setting time, flowability, soundness, compressive and flexural strengths, drying shrinkage, isothermal calorimetry, and scanning electron microscopy (SEM). Isothermal calorimetry showed peak heat flow reductions of 26% and 49% for LC-65 and LC-50, respectively, indicating a slower reactivity of LC. The initial and final setting times of the LC mixtures were 10-30 min and 30-60 min longer, respectively, due to the slower hydration kinetics caused by the reduced clinker content. Flowability increased in LC-50, which is attributed to the lower clinker content and higher water availability. At 7 days, LC-65 retained 98% of the control's compressive strength, while LC-50 showed a 47% reduction. At 28 days, the compressive strengths of mixtures LC-65 and LC-50 were 7% and 46% lower than the control, with flexural strength reductions being 8% and 40%, respectively. The porosity calculated from the SEM images was found to be 7%, 11%, and 15% in the control, LC-65, and LC-50, respectively. Thus, the reduction in strength is attributed to the slower reaction rate and increased porosity associated with the reduced clinker content in LC mixtures. However, the results indicate that the performance of LC-65 was close to that of the control mix, supporting the viability of WBP as a low-carbon partial replacement of clinker in LC.