Effects of the increased fibre surface wettability on the polypropylene fibre-concrete interfacial bonding and the properties of the polypropylene fibre reinforced concrete

In this investigation, both the fluorination and the oxyfluorination process were used to treat the surface of PP fibres. It was found that the Lewis acid, base components (gamma (circle plus), gamma-) of the surface free energies are increased by fluorination and oxyfluorination, with the increment of gamma (circle plus) ranging from 6 to 20 times. The interfacial bond strength can be increased by maximum of 2.5 times after the PP fibres were fluorinated or oxyfluorinated. The mechanism of the increment in interfacial bonding was proposed using the Lewis acid-base interfacial interaction concept. The effect of the increased PP fibre surface wettability, as well as the enhanced interfacial bonding, on the properties of PP fibre reinforced concrete was examined by comparing the physical and mechanical properties of the oxyfluorinated PP fibre reinforced concrete to the concrete reinforced by unmodified PP fibre. It was found that the oxyfluorinated PP fibres in concrete could more effectively reduce the concrete bleeding, reduce the water absorption and apparent porosity, reduce the setting time of concrete and increase the plastic and drying shrinkage cracking control capability. The impact resistance and the toughness of the PP fibre reinforced concrete subjected to flexural loading are also increased.