Study on the rheology, mechanical properties and microstructure of polypropylene fibers in different binder systems

To explore the effects of polypropylene fiber (PPF) on the properties of different binder materials, the effects of PPF on the rheology, shrinkage, mechanical properties and microstructure of alkaliactivated mortar (AAM) and ordinary Portland cement mortar (PCM) were studied. The results showed that the addition of PPF reduced the fluidity of the mortar, and the lower the initial yield stress and plastic viscosity of the paste were, the more obvious the increase. PPF reduced the drying shrinkage of both the AAMs and PCMs by 7.63-12.85 %. The inclusion of PPF to the mortar had a limited effect on enhancing the mortar compressive and flexural strength, but it notably improved the mortar toughness. At a fiber content of 0.5 %, the samples from the cement and slagsteel slag systems exhibited a more compact of the interfacial transition zone (ITZ) between the fiber and paste. Conversely, the slag-steel slag-fly ash and slag-fly ash systems showed poorer compact of the ITZ, which was attributed to increased unreacted precursors and shrinkage cracks. This phenomenon primarily accounted for the superior residual stresses observed in the cement and slag-steel slag systems. This study provides an avenue for analysis the effect of the same fiber on different binder systems.