Experimental study on the mechanical and microstructural properties of lightweight hybrid fibre reinforced concrete

The utilisation of lightweight materials to reduce building weight results in cost savings, enhanced efficiency, and energy conservation. It also mitigates damage from natural hazards such as earthquakes and reduces problems associated with structural overload. This research aims to develop sustainable lightweight aggregate concrete (LWAC) incorporating hybrid fibres and two lightweight aggregates (Lytag and Leca). Two fibres type were used: basalt fibres (BF) with lengths of 48 mm and two types of polypropylene fibres with lengths of 20 mm (PPX fibre) and 40 mm (PPD fibre). The performance of LWAC was experimentally evaluated in terms of modulus of elasticity, compressive strength, splitting tensile strength, flexural strength, fracture toughness, and microstructural characteristics. Ten distinct mixtures were designed, and 150 LWAC samples (cubes, cylinders, and prisms) were tested. The results showed that all oven-dried densities are below 1930 kg/m3, meeting the definition of LWAC as outlined by the BS EN 206. Specimens made with Lytag aggregate significantly outperformed those with Leca aggregate, exhibiting enhancements in modulus of elasticity, compressive strength, splitting tensile strength, and flexural strength of 31.1%, 61%, 47.2%, and 23.6%, respectively. Fibres inclusion had little effect on compressive strength, but significantly enhanced splitting tensile strength (up to 37.9%), flexural strength (up to 34.3%), and energy absorption capacity (up to 71.8%). Mixtures containing 0.5% BF + 1.0% PPD (regardless of the aggregate type) demonstrated the best performance among the fibre-reinforced LWAC specimens.