AbstractThis study investigates the effects of raw sugarcane bagasse ash (SCBA) used as a partial or complete replacement for silica sand in engineered cementitious composites (ECCs). ECC mixtures with five different replacement levels of sand with SCBA were produced (i.e., 0%, 25%, 50%, 75%, and 100% by volume). The SCBA utilized in this study was comprehensively characterized. Furthermore, the fresh and hardened properties of the produced ECC materials were thoroughly evaluated. The characterization of SCBA revealed that raw SCBA consisted mainly of small (i.e., 256 μm average particle size), porous, and irregularly shaped particles with carbon and silica as the main constituents. Furthermore, the SCBA met the pozzolanic component requirement for Class C pozzolans; however, it did not meet the minimum strength activity index requirement to be classified as a pozzolan; however, it did not meet the minimum strength activity index requirement to be classified as a pozzolan. In terms of ECC fresh properties, the incorporation of SCBA produced an important loss in workability, which was mitigated with increasing dosages of high-range water reducer for increasing amounts of SCBA, which also resulted in a substantial increase in the air content. In the case of hardened material properties, the incorporation of SCBA as sand replacement produced a slight decrease (up to 11%) of the compressive strength of ECCs. However, the tensile strength and especially the tensile ductility of the composites were substantially enhanced (up to 22.3% and 311%, respectively). The tensile strength improvements were credited to the pozzolanic and/or filler effect of SCBA. On the other hand, enhancements in the tensile ductility were associated to the combined effect of the reduction of crack-tip matrix toughness (credited to the decrease in aggregate particle size), reduction in ECC cracking strength (due to increase in air content), and increase in the complementary energy (attributed to the potential decrease in the chemical bond of the fiber/matrix interface and an enhanced fiber dispersion). The surface resistivity of ECC materials was negatively affected by the addition of SCBA. Furthermore, the length change of all SCBA-ECC materials, at all ages of curing, was higher in comparison with that of the control mixture, except for the mixture with 25% replacement at 28 days of curing.