Inert particles enhance strength-ductility relationship for Engineered Cementitious Composites based on PVA fibers

Engineered Cementitious Composites (ECC) is recognized as a durable and resilient infrastructure material for its ultrahigh tensile ductility and autogenous crack width control. However, simultaneously enhancing its compressive strength and tensile ductility presents an intrinsic challenge. In this study, we examine the strength-ductility relationship for PVA-ECC with varied densities attained by tailoring the volume of inert particles. The goal is to improve the composite compressive strength by reducing porosity while maintaining a low fracture toughness in the cementitious matrix. The latter is intended to amplify the composite multiple cracking in favor of high tensile ductility. We adopted ground quartz and slag as inert and reactive particles, and investigated the properties of the matrix, composite, and fiber/matrix interface. Results show that incorporating ground quartz weakened the positive correlation between compressive strength and fracture toughness, thereby producing a dense matrix prone to flat cracking. When combined with the hydrophilic PVA fibers, ground quartz had a minimal influence on the fiber/matrix interface, forming a stark contrast to slag, which resulted in a twice-high chemical and frictional bond. The strong interface in the slag-modified composites increased the resistance against fiber slippage and lowered the composite complimentary energy. As such, the quartz-modified ECC manifested a simultaneous gain in strength and ductility for a rising density, while the slag-modified group exhibited a contradictory strength-ductility relationship as conventionally observed in the literature. The optimal quartz content was determined to be 25 %, resulting in a 40 % increase in compressive strength besides slight improvement in the composite tensile ductility. These findings offer a fresh perspective for tuning the properties of ECC and facilitate more efficient use of low-reactivity mineral fines in value-added infrastructure applications. • Inert particles decouple matrix fracture toughness and compressive strength for ECC. • Inert particles maintain favorable fiber/matrix interfacial bond. • Composite compressive strength can be improved without reducing ductility. • Multiple cracking is improved by incorporating inert particles.