AbstractUnderstanding the biaxial mechanical behavior of polypropylene fiber–reinforced expansive self-consolidating concrete (PPESCC) is of critical significance for predicting the response of a structure under multiaxial compression or multiaxial compression and tension. To study the combined effects of polypropylene fiber and expansive agent on strength, the addition of an expansive agent (8% by cementitious material mass) and the volume fraction of polypropylene fiber (0%, 0.05%, and 0.1% by concrete volume) were designed as experimental variables. A series of biaxial compression-compression (C-C) and biaxial compression-tension (C-T) tests on cubic specimens with a side length of 100 mm was conducted. The observed failure mode showed that there was no significant difference in the crack patterns regardless of the addition of expansive agent and fiber content. The experimental results also indicated that although the biaxial compressive strength was affected by the polypropylene fiber content and the incorporation of expansive agent, the normalized failure envelops under biaxial compression are approximately the same for both normal self-consolidating concrete (SCC) and expansive SCC with different fiber contents. Based on previous investigations in the literature, a strength criterion and constitutive model were developed for PPESCC under biaxial compression. Through comparison, the error between the strength criterion model and experimental results is less than 10%. Meanwhile, it was demonstrated that the biaxial C-T strength decreased by 77% on average due to the exertion of tension. The proposed strength formulas for biaxial C-T loading were in good agreement with the experimental data for PPESCC.