Exploring the synthesis effects of glazed hollow beads and polypropylene fibers on the strength retention of ultra-high performance concrete after fire exposure using X-Ray computed tomography

Ultra-high performance concrete (UHPC) is a cementitious composite characterized by its ultra-high durability attributes and mechanical properties. It is primarily used in large-span and ultra-high-rise structures for control of deflections. However, its mechanical properties decrease significantly after exposure to fire or high temperatures, limiting its applicability. In this paper, the exceptional characteristics of glazed hollow beads (GHBs), including their lightweight, high strength, and thermal insulating properties, were utilized to develop a novel fire-resistant UHPC. UHPC specimens with varying GHB content were prepared, and the corresponding mass loss, thermal performance degradation, and compressive strength after exposure to high temperatures were evaluated. The test results demonstrate that adding GHBs can improve the fire resistance of UHPC. With 40 % (by volume) GHB addition, the resulting UHPC could retain 47 % of its original compressive strength even after exposed to 800°C. The effects of temperature on the UHPC microstructure were analyzed using scanning electron microscopy and X-ray computed tomography. It was found that the combination of polypropylene fibers and GHBs created a release channel for vapor pressure within the concrete, thereby enhancing its high-temperature resistance. This study proposes a practical solution to enhance the high-temperature resistance of UHPC. • Study shows GHBs reduces fire-induced spalling in UHPC. • Performance of UHPC containing GHBs was studied. • Microstructural analysis revealed GHBs’ role in UHPC. • An effective prediction model about compressive strength and cracking parameters of UHPC was established.