High volume of slag and polypropylene fibres in engineered cementitious composites: microstructure and mechanical properties

The use of engineered cementitious composite (ECC) is increasing owing to its high tensile strength and ductility; however, little attention has been paid to substitutes for its ingredients. Blast furnace slag instead of fly ash and polypropylene (PP) fibres instead of polyvinyl alcohol (PVA) fibres may be considered to be appropriate alternative substitutes. Therefore, the present study aimed to produce an ECC with a large proportion of slag and PP fibres that would achieve high strength and ductility characteristics and create controlled microcracking behaviour under tensile stresses (i.e. strain-hardening behaviour). The specimens made from ECC thus prepared were subjected to compressive, four-point bending, X-ray diffraction (XRD) and scanning electron microscope (SEM) tests. The results showed that a slag/cement ratio of 0.5 in ECC led to the highest compressive strength (55.6 MPa) and modulus of rupture (MOR) (7.0 MPa), while the corresponding energy absorption was fairly high. The results of XRD and SEM analyses indicated that applying the slag/cement ratio of 0.5 led to a homogenous cement matrix and produced the highest calcium-silicate-hydrate (C-S-H) in the ECC microstructure. Finally, to predict the load-deflection of specimens, a three-part model was proposed and verified with other available data.