Mechanical characterization of Engineered Cement-based Composites prepared with hybrid fibres and expansive agent

In this work fifteen Engineered Cement-based Composites (ECCs) were studied, in which CaO-based expansive agent was added. First of all, the effectiveness of three different dosages of expansive agent on the mechanical properties of ECCs reinforced with ribbon-shaped amorphous metallic fibres was studied. Then, twelve mixtures were prepared with 40 kg/m3 of expansive agent, by using three different polymeric fibres, in combination with the metallic ones, in order to obtained hybrid reinforcement systems. Five combinations were tried: 100-0%, 75-25%, 50-50%, 25-75%, 0-100% metallic-polymeric, respectively. The three plastic fibres alternatively employed were: hooked polyethylene terephthalate (PET), corrugated polypropylene (PP), and smooth polyvinyl alcohol (PVA) fibres. All the mixtures were characterized by recording fresh consistency, compressive and flexural strength. The microstructure of the mixtures reinforced with metallic fibres was investigated by means of Mercury Intrusion Porosimetry (MIP). Results obtained showed an improved flexural strength if high dosage of CaO-based expansive agent is used with metallic fibres. The reason could be an increased adhesion between fibre and cement-based matrix, due to its pore refinement promoted by the addition of CaO-based expansive agent. Optimum percentage of combination among metallic and polymeric fibres was sought, in terms of peak strength and ductile post-cracking behaviour.