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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 an environmentally friendly alternative to ordinary Portland cement. AAMs reinforced with carbon fibers enable the piezoresistivity of materials that can sense its own strain, resistivity and damage. However, the high cost of carbon fiber limits the wide application in construction. In this study, a novel type of conductive aggregates is prepared by using porous ceramsites impregnated with modified agar and carbon black. Conductive alkali-activated fly ash/slag (AAFS) is prepared using carbon fibers and conductive ceramsites. Orthogonal experiment is applied to assess the effect of different parameters on the piezoresistivity and early age properties of AAFS mortars. The results reveal that with the combination of carbon fibers and conductive ceramsite, the electrical resistivity and piezoresistivity of AAFS are significantly improved. The good binding of ceramsites with AAFS matrix and carbon fibers ensured a high piezoresistivity of AAFS samples. A synergistic effect exists between the carbon fibers and ceramsites in view of the piezoresistivity. However, the workability and mechanical strength reduced with the addition of conductive ceramsites. AAFS mortar with 0.3% carbon fiber content, 25%–30% ceramsite content and 70% slag content is proposed as the optimal mixture in view of its mechanical properties and piezoresistivity. [ABSTRACT FROM AUTHOR]