Uniaxial Compressive Properties and Constitutive Model of Foamed Concrete Modified by Polymer and Fiber

As a new building material with an internal porous structure, foamed concrete has the problems of high brittleness, low strength, and poor toughness. In this paper, polymer and fiber are used to modify foamed concrete, in which the polymer is polyvinyl alcohol and redispersible latex powder, and the fibers are basalt fiber and polypropylene fiber. The influence of polymer and fiber content on the compressive properties of foamed concrete and its stress–strain constitutive relationship were studied through uniaxial compression tests. The hydration products were analyzed by X-ray diffraction and scanning electron microscope, revealing the modification mechanism of polymer and fiber on foam concrete. The results showed that when the volume fractions of redispersible latex powder and polypropylene fiber were 7.5% and 0.6% respectively, the modification effect was the best. Compared with P-1, the compressive strength, total energy absorption, specific energy absorption, and energy absorption rate increased by 149.8%, 234.2%, 224.3%, and 53.8%, respectively. The modification mechanism is that after polymer hydration, new hydration products are generated, which polymerize on the surface of the foam to form a network structure, and through diffusion and adsorption, they converge to form a continuous and complete membrane structure to cover the surface of the foam. Fibers form a three-dimensional random grid system inside the matrix as secondary reinforcement, supporting the internal structure and limiting the generation and development of cracks; on the other hand, some hydration product particles adhere to the surface of the fibers, improving the physical adhesion between the fibers and the matrix. Based on the Avalle model, a multiparameter polymer and fiber foamed concrete compression constitutive model was established considering the polymer volume fraction and fiber characteristic parameters.