Shrinkage deformation and impact performance of high‐strength high‐performance concrete with fibers based on steam curing and its microscopic mechanism

Abstract This study aims to evaluate the synergistic effects of polypropylene (PP) and polyoxymethylene (POM) fibers on the performance of high‐strength high‐performance concrete (HSHPC) under steam curing, and to identify the optimal hybrid fiber combination. A C90‐grade HSHPC matrix was used, with single additions of PP fibers (0.1%, 0.3%, and 0.5%) and POM fibers (0.1%, 0.25%, and 0.4%), followed by hybrid fiber mixtures designed by the Box–Behnken response surface methodology. Two curing regimes—standard curing and steam curing—were compared. The evaluated properties included drying shrinkage, impact resistance, compressive strength, splitting tensile strength, axial compressive strength, and elastic modulus. Microstructural analyses (x‐ray diffraction, scanning electron microscopy, MIP) were also conducted. Key results show that steam curing significantly accelerates early strength development, with the highest compressive strength of 89.4 MPa in the hybrid group. POM fibers are more effective than PP fibers in enhancing splitting tensile strength and impact resistance while reducing drying shrinkage. A pronounced positive hybrid effect is observed: the optimal hybrid combination (0.3% PP + 0.25% POM) achieves a 28‐day compressive strength of 97.5 MPa and a final impact energy exceeding 8967 J under standard curing, representing more than a 100% improvement over the plain matrix. Under steam curing, the same hybrid mixture exhibits excellent early performance with a compressive strength of 89.4 MPa and final impact energy of 9512 J. Response surface optimization predicts the optimal hybrid ratio as 0.26% PP + 0.26% POM. Microstructural evidence reveals that steam curing accelerates hydration, while the hybrid fibers form a three‐dimensional bridging network that effectively arrests cracks and toughens the matrix, even though porosity increases. The study demonstrates that the combination of PP and POM fibers, together with optimized steam curing, enables a balanced achievement of high strength, high toughness, and superior impact resistance, providing a practical basis for the design of fiber‐reinforced HSHPC in precast applications.