High volume of slag and PP fibres in engineered cementitious composites (ECC): Microstructure and mechanical properties

The use of engineered cementitious composite (ECC) is increasing due 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. However, scanty research has examined the effect of using high levels of slag and PP fibres on the mechanical properties and microstructure of ECC. Therefore, the present study aimed to produce an engineered cementitious composite with a large proportion of slag and PP fibres for achieving high strength and ductility characteristics and creating a controlled microcracking behavior under tensile stresses (i.e., strain-hardening behavior). The specimens made from the ECC thus prepared were subjected to compressive, four-point flexural, X-ray diffraction assessment (XRD), and scanning electron microscope (SEM) tests. The results showed that the slag-to-cement ratio of 0.5 in ECC led to the highest compressive strength (55.6 MPa) and modulus of rupture (7.0 MPa), while the corresponding energy absorption was fairly high. The results of XRD and SEM analyses indicated that applying the slag-to-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.