Experimental study on the properties and shear toughness of strain-hardening cementitious composite of the combined use of polypropylene fiber and clinoptilolite

This study is aimed at the utilization of domestic polypropylene (PP) fiber with special dispersion treatment and natural clinoptilolite as the prospective type of supplementary cementitious materials (SCMs) of strain hardening cementitious composite (SHCC) in connection with proposing a sustainable and economical SHCC to reduce cement consumption and engineering costs. The mechanical properties and microstructures of PP fiber-reinforced cementitious composite modified with fly ash or clinoptilolite powder have been investigated by compressive test, flexural test, tensile test, direct shear test, X-ray diffraction (XRD) and scanning electron microscope (SEM). Results show that polypropylene fiber reinforced cementitious composite shows the characteristics of strain hardening and ductile fracture in tensile and direct shear test, and clinoptilolite has superior and better performances than fly ash as 15% cement replacement (by mass) in polypropylene fiber reinforced cementitious composite. When fiber mass fraction increases from 0‰ to 2‰, the cubic compressive, axial compressive, flexural, tensile and direct shear performances of specimens have an increasing trend. Clinoptilolite with a high specific surface area and fine fineness, exhibits higher pozzolanic reactivity than fly ash in cementitious composite and promotes the secondary hydration with cement hydration product portlandite to form calcium silicate hydrate. XRD peak of calcium silicate hydrate in specimens with 15% clinoptilolite powder is stronger, and fiber is more effective in enhancing the mechanical properties other than the flexural property of specimens with clinoptilolite powder than those of specimens with fly ash. Besides, a new evaluation method of shear toughness is also proposed referring to the Japanese JSCE-SF4 and German DVB method, and a polynomial relationship model between fiber mass fraction and the proposed shear energy dissipation coefficient parameters is established.