Mechanical behaviour of wollastonite-based cement composites incorporating fibres and recycled rubber aggregates

Calcium phosphate cement (CPC) is a wollastonite-based inorganic cement that hardens at room temperature to a brittle cementitious material with low fracture behaviour. Recycled rubber aggregates from end-of-life tyres were incorporated up to 17.5 wt% into the CPC matrix to produce high-strength composites with improved strain capacities for structural repair purposes. Furthermore, the effects of 0.75% and 1.5% volume fibre content (Vf) of macro polypropylene, amorphous metallic and recycled carbon fibres on the flexural behaviour of CPC were studied. The synergy between the rubber aggregates and the selected corrosion-resistant fibres in improving the fracture properties of the plain CPC was investigated. The changes in other mechanical properties of CPC such as modulus of rupture, compressive and splitting tensile strength due to the inert inclusions (i.e. rubber aggregates and/or fibres) were determined. It was found that increasing the quantity of inert inclusions in the cement matrix improved the fracture energy of the plain CPC. Incorporating 1.5% Vf of macro polypropylene, amorphous metallic, and recycled carbon fibres into the CPC matrix produced cementitious composites with fracture energies that were 11.8 times, 63.4 times, and 75.8 times that of plain cement, respectively. For the rubberised fibre-reinforced CPC composites, a positive synergistic relationship was observed between rubber aggregates and macro polypropylene fibres while a negative synergistic relationship was found between rubber aggregates and the other fibres (amorphous metallic and recycled carbon fibres). The rubber aggregates decreased the flexural, compressive and splitting tensile strengths of the plain CPC, while the fibre inclusions improved these properties.