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Alkali-activated materials (AAMs) have gained increasing attention as potential candidates for conductive and self-sensing concretes. This study investigated the effect of fly ash microspheres and quartz sands on the piezoelectric properties of carbon fiber-reinforced alkali-activated fly ash/slag (AAFS) mortars. The rheological property, mechanical property, resistivity, and piezoelectric properties of different AAFS mortars were investigated. Our findings demonstrated that the use of fly ash microspheres (FAM) significantly reduced the yield stress and plastic viscosity of the mortars due to the "ball bearings" effect. In addition, the finer particles of FAM led to a dense gel pore structure of AAFS. The use of FAM improved carbon fiber dispersion and formed a stable conductive network. Therefore, AAFS mortars with FAM exhibited superior conductivity and piezoelectricity. The use of quartz sands exhibited adverse effects on the self-sensing properties of AAFS mortars. The incorporation of quartz sands predominantly hindered the conductive network formation of carbon fibers, resulting in a significantly higher resistivity and piezoresistivity with low strain sensitivity. • The use of FAM in carbon fiber reinforced-AAFS results in superior conductivity and piezoresistivity. • FAM improved the rheology of AAFS, facilitating the dispersion of carbon fibers. • The use of quartz sands led to a higher resistivity and poor piezoresistivity. [ABSTRACT FROM AUTHOR]

Alkali-activated materials (AAMs) are regarded as promising alternatives to Portland cement. However, the significant high shrinkage of AAMs, particularly in alkali-activated slag system, is a critical issue that hinders their wide application. This study investigated the effect of expansive admixture, i.e. CaO on the autogenous shrinkage and drying shrinkage of alkali-activated slag/ fly ash microsphere (AASFAM). The effect of CaO content on heat evolution, reaction products, microstructure development and compressive strength was systematically investigated. The results revealed that the addition of CaO can effectively reduce both the autogenous and drying shrinkage of AASFAM. Mixture with 3% and 5% CaO exhibited expansion within the first 24 hours after casting, while the drying shrinkage was reduced by 72% and 82%, respectively. The addition of CaO promoted the formation of crystalline phases including Ca(OH) 2 , hydrotalcite and calcite, leading to a lower free water content and coarser pore structure, which in turn reduced the capillary stress during the drying process. The results demonstrated the promising potential of CaO in effectively mitigating the high autogenous shrinkage and drying shrinkage of AAMs without compromising its mechanical properties. • The addition of CaO can effectively reduce both the autogenous and drying shrinkage of AASFAM. • The addition of CaO facilitates the crystalline phases in AASFAM including Ca(OH) 2 , hydrotalcite and calcite. • The formation of Ca (OH) 2 led to a larger pore size distribution. [ABSTRACT FROM AUTHOR]