Special Design Paths for Achieving UHPC Fire Resistance

The fire resistance of UHPC requires systematic improvement through material modification and structural design. Based on fire protection standard requirements, Qinglong Group has summarized a four-dimensional fire resistance enhancement strategy covering fiber optimization, aggregate selection, admixture design, and cover thickness.

The fiber system is key to fire resistance. Ordinary steel fibers lose strength sharply above 300℃, so stainless steel fibers (304 or 316) or blended polypropylene fibers should be used. Qinglong Group incorporates 0.1% polypropylene fibers into the mix; these melt at high temperatures to form pores, releasing steam pressure and preventing spalling. Tests show that this design keeps UHPC intact for up to 2 hours at 800℃.

Aggregate selection affects thermal stability. Quartz sand undergoes phase transformation and volume expansion at 573℃, so basalt (heat-resistant up to 1000℃) or corundum aggregates are preferable. Qinglong Group uses calcined bauxite aggregates in high-temperature projects; their thermal expansion coefficient matches the cement matrix, reducing thermal stress. Optimized aggregate grading improves density and reduces permeability at high temperatures.

Admixture design enhances high-temperature resistance. Active admixtures such as silica fume and slag reduce Ca(OH)₂ content, improving stability at high temperatures. By adding 20% silica fume, Qinglong Group raises the material's residual strength after 400℃ exposure from 40% to 60%. Meanwhile, adding nano clay (2%-3%) forms a more stable gel structure.

Cover thickness and structural design. Increasing the cover thickness to above 25mm delays heat transfer. Thermal buffer layers, such as ceramic fiber boards, are incorporated into the structure. Through systematic design, Qinglong UHPC achieves a fire resistance rating of up to 4 hours, meeting the highest fire protection class requirements.