When concrete is exposed to high temperatures during initial hydration, delayed ettringite formation (DEF) may occur and cause expansion, with consequences similar to that of the alkali-silica reaction (ASR). This study investigated the structural performance of prestressed concrete (PC) beams exhibiting expansion owing to DEF and the combined effects of DEF and ASR. In both cases, concrete cylinders were cast to determine the expansion, compressive strength, and dynamic elastic modulus at different expansion levels. The compressive strength and Young’s modulus of the plain concrete specimens were significantly reduced with large free expansion, which caused map cracking on the surface. Because of the restraining effects of the reinforcement and prestressing load, the expansion of the PC beams was anisotropic, with more longitudinal cracks. The Young’s modulus determined from stiffness of the cross-section of the DEF and ASR–DEF-affected beams at a low load level without bending cracking decreased moderately (22 % for DEF and 30 % for ASR–DEF beams) as compared to that of the non-reactive companion beam. The load capacities of DEF and ASR–DEF-damaged beams, even with many cracks, were reduced by 16 % and 23 %, respectively, compared to those of the non-reactive beam. Though the compressive strength of deteriorated plain concrete decreased significantly, less compressive strength reduction in concrete of DEF and ASR–DEF-damaged beams owing to confinement resulted in the lesser load capacity reduction in beams.