What Special Designs Are Required to Achieve UHPC Fire Resistance?

Optimizing the fire resistance of UHPC is a systematic engineering task, achieved through special designs such as "material composition design, fiber selection, protective layer construction, and latent phase-change heat absorption technology." Although the UHPC matrix is a non-combustible material, its mechanical properties degrade at high temperatures, and steel fibers may soften and fail. Qinglong Group's fire resistance testing and engineering practice demonstrate that by incorporating polypropylene fibers (which melt at high temperatures to form pressure-relief channels), using high-alumina cement or adding fine calcined bauxite to enhance high-temperature stability, and designing an appropriate protective layer thickness, the fire resistance rating of UHPC components can exceed 180 minutes. In the core tube protection design of a super high-rise building in Shenzhen, our fire-resistant UHPC solution successfully passed the R180 standard test, providing solid protection for building safety.

Material Composition Optimization to Resist High-Temperature Degradation

Ordinary Portland cement-based UHPC suffers significant strength loss above 400°C. Qinglong adopts two strategies: first, partially replacing it with high-alumina cement or sulfoaluminate cement, whose hydration products are more stable at high temperatures; second, externally adding fine calcined bauxite or quartz powder to the Portland cement system, so that at high temperatures they react with Ca(OH)₂ to form aluminosilicate phases with greater thermal stability, effectively delaying explosive spalling and strength decline.

Strategic Selection of the Fiber System

Steel fibers gradually soften above 300°C and lose their reinforcing effect. To address this, we adopt a hybrid system of "steel fiber + polypropylene fiber." Steel fibers ensure room-temperature toughness, while low-melting-point polypropylene fibers (melting point around 160°C) melt in the early stages of a fire, forming interconnected micro-channels within the matrix that release the pressure generated by water vapor at high temperatures, fundamentally preventing explosive spalling. This is one of the key technologies for improving fire resistance.

Structural Design and Protective Layer Application

For load-bearing UHPC components, increasing the protective layer thickness or applying external fire-resistant boards can delay heat transfer to the core zone and maintain component stability during a fire. In large UHPC curtain wall systems, we design cavity structures and install fire-stopping seals to effectively block the spread of flames and high-temperature smoke, ensuring the system's fire integrity.

Through the above special designs, UHPC can be upgraded from a high-performance structural material to a safety material with excellent fire resistance. Qinglong Group's fire-resistant UHPC solutions are now widely used in various buildings with stringent fire protection requirements.