Expanded vermiculite acting as artificial flaws to enhance the tensile properties of high-strength engineered cementitious composites

In this study, an expanded vermiculite (EV) was proposed to substitute silica sand, and act as artificial flaws in high-strength engineered cementitious composites (ECC) to improve its ductility. Experimental and analytical investigations were conducted on the mechanical behavior, micromechanical analysis and microstructural analysis of ECC from macro-, meso-, and micro-scales. The results demonstrated that the inclusion of EV reduced the compressive strength of ECC composites from 77.6 MPa to 60.2 MPa, although this does not hinder its role as a constituent of high-strength concrete (60 MPa). However, compared with that of 2.56 % in reference ECC mixture, due to the EV addings, the strain capacity of ECC mixtures was increased up to 8.22 %. On the other hand, incorporating fine EV particles (0.15 mm, 0.42 mm, and 2 mm) was positive to the tensile strength of ECC mixtures with a 23 % improvement, while the addition of coarser EV (1–3 mm and 3–5 mm) led to an 8 % reduction. At microscale, the incorporation of EV reduced the critical flaw size and increased the flaw size, significantly increased the number of active flaws, as a result, more micro-cracks were initiated, and thus greatly improving ductility of ECC. • Expanded vermiculite (EV) was used to act artificial flaws in ECC. • The inclusion of EV significantly improved the ductility of ECC. • The incorporation of EV effectively increased the number of active flaws for initiating micro-cracks in ECC.