Properties and improvement of ultra-high performance concrete with coarse aggregates and polypropylene fibers after high-temperature damage

Ultra-high performance concrete containing coarse aggregates (UHPC-CA) is more cost-effective, with its low cost and easy access to materials, but its high-temperature performance and self-healing capability after post-fire curing remain to be further explored. In this paper, after high temperature, the compressive strength increases by approximately 20 MPa within 400 degrees C, and the micro-characteristics reveal that this is mainly because the temperature promotes the cement hydration reaction and pozzolanic reaction, which plays the role of secondary accelerated curing. Due to the continuous decomposition of substances, the flexural strength and ultrasonic pulse velocity gradually decrease; the mass loss, total porosity, and the amount of absorbed water increase, especially the sorptivity coefficient, which increases by more than 100 times after 800 degrees C. The residual values of all properties of UHPC-CA are best maintained by adding all of the finer PP fibers. Relying on many unhydrated gelling materials, UHPC has a more significant self-healing potential, improving its mechanical properties and permeability in all three post-fire curing environments. The most significant effect is seen in the water environment, where its recovery rate of strength exceeds 50 % in all cases. The self-healing enhancement of UHPC does not come from a single source, but from multiple combinations of physical and chemical reaction processes.

Automated summary

Ultra-high performance concrete containing coarse aggregates (UHPC-CA) is cost-effective and easily accessible, but its high-temperature performance and self-healing capability after post-fire curing need further exploration. High temperature enhances cement hydration and pozzolanic reactions, increasing compressive strength by approximately 20 MPa at 400 degrees C. However, flexural strength and ultrasonic pulse velocity gradually decrease, while mass loss, porosity, and absorbed water increase. Adding finer PP fibers helps maintain residual values of all properties. UHPC has significant self-healing potential, particularly in water environments, where strength recovery exceeds 50% in all cases, relying on multiple physical and chemical reaction processes.