The addition of crystalline admixtures in the cementitious composite is instrumental in imparting water tightness, enhancing strength, and achieving self-healing abilities in various construction applications. In this work, the viability of using crystalline admixtures in heat-cured strain-hardening cementitious composites (SHCC) and their impact on specimens subjected to alkaline and aqueous environments are examined. In SHCC, lime stone-calcined clay cement (LC3) is used in the matrix and mineral-impregnated carbon yarns are used as reinforcement. The usefulness of heat curing for SHCC to water curing is initially assessed by analyzing the mechanical characteristics and connecting them to the microstructural components by SEM examination. Investigations reveal that the crystalline admixture increases compressive strength in water- and heat-cured specimens by 30–37%, respectively. Subsequently, a uniaxial tensile test is conducted on heat-cured SHCC specimens and on pre-damaged ones that are submerged in tap water and also in alkaline water. The impact of crystalline admixture on the SHCC's tensile response was examined, and the results were correlated with SEM examination. The maximal stress is increased by approximately 14% and 26% when pre-damaged SHCC specimens with crystalline admixture are submerged in water and an alkaline environment, respectively.