What Special Designs Are Required to Achieve the Fire Resistance of UHPC?

UHPC's weakness in high-temperature performance stems from fiber failure at elevated temperatures and matrix dehydration cracking. Conventional UHPC has a fire resistance limit of only 0.5-1 hours, making it difficult to meet the fire protection requirements of public buildings. As an enterprise deeply engaged in high-end construction projects, Qinglong Group has developed multi-dimensional special design solutions through material modification, structural design, and process optimization, raising UHPC's fire resistance limit to 1.5-3 hours to suit the needs of various scenarios.

Fire-resistant aggregate substitution and mix ratio optimization enhance the matrix's high-temperature resistance. Conventional UHPC uses quartz sand aggregate, which is prone to crystal phase transformation at high temperatures (≥600℃), causing volume expansion and cracking. Qinglong selects fire-resistant aggregates such as mullite sand and basalt sand (fire resistance temperature ≥1500℃) to replace 30%-50% of the quartz sand, while adjusting the cementitious material ratio and increasing the high-alumina cement content (10%-15%), leveraging the calcium aluminate gel it forms at high temperatures to improve the matrix's high-temperature stability. In laboratory high-temperature tests, after the optimized UHPC was held at 800℃ for 1 hour, its strength loss rate dropped from the conventional 60% to below 30%, with a volume deformation rate ≤0.5%. In the UHPC decorative components project for the Wuhan Hanxiu Theater, this design enabled the components to pass fire inspection with a fire resistance limit of 1.5 hours, meeting the fire protection requirements of performance venues.

Fiber type optimization and protective layer design delay fiber failure. Steel fibers soften and fail above 500℃. To address fire protection needs, Qinglong selects basalt fiber (fire resistance temperature ≥1200℃) or hybrid fiber (steel fiber + basalt fiber = 2:1) at a dosage of 3%-4%, which ensures toughness at room temperature while improving crack resistance at high temperatures. Meanwhile, the fire protection layer thickness of components is increased: for load-bearing components, the protective layer thickness is ≥25mm; for non-load-bearing decorative components, ≥15mm, to prevent fibers from being directly exposed to high-temperature environments. In the Shenzhen Pingshan High-tech Zone Comprehensive Service Center (Luban Award project), Qinglong's UHPC curtain wall components adopted a "basalt fiber + 20mm fire protection layer" design. In fire simulation tests, the components maintained their integrity for 2 hours with no collapse or detachment.

Composite fire protection system construction extends the fire resistance limit. For scenarios with extremely high fire resistance requirements (≥2.5 hours), Qinglong adopts a "UHPC + fire-retardant coating/fire board" composite design: applying a high-temperature-resistant fire-retardant coating (3-5mm thick) to the surface of UHPC components, or laminating calcium silicate fire boards, leveraging the coating's heat-absorbing expansion properties and the fire board's thermal insulation to delay heat transfer to the interior. In a UHPC ceiling project at a convention and exhibition center, the composite fire protection system raised the components' fire resistance limit to 3 hours, far exceeding the 2-hour design requirement. In addition, fire-resistant sealant is filled at component joints to prevent flames from spreading through gaps, forming fully enclosed fire protection. Qinglong adopted this design at the joints of hyperbolic curved components in the Guangxi New Media Center, and it passed fire inspection.

Hydration heat and porosity control reduce the risk of high-temperature cracking. UHPC's dense structure is prone to internal stress cracking at high temperatures due to rapid moisture evaporation. Qinglong controls the hydration heat peak (≤60℃) by adding retarders to avoid internal thermal stress; meanwhile, an appropriate amount of closed micropores is introduced (porosity controlled at 1%-1.2%) to provide buffer space for volume expansion at high temperatures. In the public art sculpture project at the Shanghai Astronomy Museum, this design ensured the sculpture showed no obvious cracking in high-temperature tests and maintained structural integrity. In addition, Qinglong's precast UHPC components have expansion joints reserved during production at 2-3 meter intervals, further releasing volume stress at high temperatures and reducing the risk of cracking.

UHPC's fire resistance must be achieved through multi-dimensional special designs in materials, structure, and process. Qinglong Group's solutions both preserve UHPC's original performance advantages and significantly improve the fire resistance limit, making it suitable for public buildings, industrial plants, and various other scenarios. For projects with high fire protection requirements, customers are advised to communicate fire protection design needs with the manufacturer in advance to avoid rework caused by conventional products failing to meet fire code requirements, and to choose suppliers with specialized fire protection design capabilities and proven project cases.