Eco-efficient foam concrete with waste tire aggregates: Effects of slag and polypropylene fibers

The development of foam concrete incorporating recycled and industrial by-product materials as partial replacements for cement and conventional aggregates has attracted considerable research interest. Among these alternatives, waste tire aggregates (WTA) offer low density, favorable thermal insulation properties, and an effective solution for recycling end-of-life tires. Although WTA, granulated blast-furnace slag (GBFS), and polypropylene fibers (PPF) have been individually investigated in cementitious materials, their combined and synergistic effects in foam concrete systems have not yet been comprehensively evaluated. This study investigates the influence of GBFS and PPF on the fresh, physical, mechanical, thermal, and durability properties of WTA-based foam concretes. A series of mixtures containing different GBFS replacement levels and PPF dosages were produced and experimentally evaluated using a comprehensive testing program. The results indicate that moderate GBFS incorporation significantly improves matrix densification through hydraulic and pozzolanic reactions, leading to enhanced strength, durability, and overall performance. PPF contributed to crack control and thermal insulation; however, excessive fiber contents adversely affected workability and mechanical properties due to increased pore connectivity and air entrainment. An optimum combination of GBFS and PPF provided a favorable balance between mechanical performance, durability, and thermal efficiency. The improved behavior was primarily associated with a refined pore structure, enhanced matrix continuity, and stronger interfacial bonding within the foam concrete system. The results demonstrate that the combined use of GBFS and PPF can improve the performance of WTA-based foam concretes and support the utilization of industrial by-products and tire waste in lightweight construction materials.