Analysis of the Toughness and Microstructural Mechanisms of Foam Concrete Reinforced with PP Fibers, FA, and HPMC

Foam concrete suffers from low intrinsic toughness originating from its porous microstructure, which restricts its engineering application. In this work, polypropylene fibers, fly ash, and hydroxypropyl methylcellulose were adopted to improve the toughness of A06-grade foam concrete. Response surface methodology was used to optimize additive dosages for flexural performance, and the optimal mixing proportions of the three additives were obtained. Drying-shrinkage tests, together with scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDS) microscopic characterizations, were performed to evaluate the compactness of the interfacial transition zone (ITZ) and reveal the underlying modification mechanism. The ternary composite system achieves superior performance compared with single-component modification. The synergistic effects, including fiber bridging, foam stabilization, and the pozzolanic-filling effect, jointly contribute to a denser ITZ, which effectively enhances the toughness of foam concrete. This study provides a reference for the performance optimization of lightweight functional foam concrete materials.