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

The fire resistance of UHPC is achieved through three special design approaches: adjustment of material composition, optimization of structural configuration, and surface protection treatment. Through patented technology, Qinglong achieves a fire resistance rating of 1.5-2.0 hours for UHPC, meeting the strict fire protection requirements of high-rise and public buildings and solving the pain point of spalling at high temperatures.

1. Material Composition Adjustment: Enhancing High-Temperature Stability

Material-level optimization is the core guarantee of fire resistance. Selecting refractory aggregates: replace part of the quartz sand with corundum sand and refractory clay sand (refractoriness ≥1770°C) with excellent fire resistance, at a dosage of 30%-40%, reducing aggregate expansion and cracking at high temperatures; Qinglong's fire-resistant UHPC uses a composite aggregate of corundum sand and quartz sand. Optimizing the cementitious system: add 20%-25% mineral admixtures such as fly ash and slag powder to reduce cement content and minimize hydration heat and shrinkage cracking at high temperatures; mineral admixtures account for 22% of Qinglong's cementitious system, significantly improving high-temperature stability. Fiber selection and dosage: use high-temperature-resistant steel fibers (melting point ≥1538°C) at a dosage of 2.5%-3% to partially replace alkali-resistant glass fibers (which soften easily at high temperatures); steel fibers can bridge high-temperature cracks and prevent spalling. The steel fibers in Qinglong's fire-resistant UHPC have an aspect ratio of 80 and retain their reinforcing effect at high temperatures. Adding fireproof admixtures: incorporate 5%-8% intumescent fireproofing agent, which generates an expansion layer at high temperatures to block heat transfer; Qinglong's fireproofing agent enables UHPC to achieve a volume expansion rate of 3%-5% at high temperatures, forming an effective protective layer.

2. Structural Configuration Optimization: Delaying Heat Transfer

Structural design can further improve the fire resistance rating. Controlling member thickness: for load-bearing members, thickness ≥50mm; for non-load-bearing members, ≥30mm, forming a sufficient heat conduction path. Qinglong's fire-resistant UHPC curtain wall panels, at 35mm thick, achieve a fire resistance rating of 1.5 hours. Setting up cavities or insulation layers: create cavities inside UHPC members filled with insulation materials such as rock wool and ceramic fiber to delay heat transfer. In a Qinglong high-rise project, the UHPC fire partition wall, internally filled with 50mm rock wool, achieved a fire resistance rating of 2.0 hours. Optimizing reinforcement design: if reinforcement is required, the rebar cover thickness should be ≥25mm to avoid rapid heating of the steel bars at high temperatures leading to strength loss. The rebar cover thickness of Qinglong's reinforced UHPC members is ≥30mm, complying with fire codes.

3. Surface Protection Treatment: Forming a Fire Barrier

Surface protection is the last line of fire defense. Applying fireproof coatings: use cement-based fireproof coatings (5-10mm thick) or intumescent fireproof coatings (3-5mm thick), which form a dense carbonized layer or expansion layer at high temperatures to block oxygen and heat. Qinglong recommends cement-based fireproof coatings, which have good compatibility with UHPC and are not prone to peeling. Cladding with fireproof boards: cover the surface of UHPC members with fireproof boards (such as calcium silicate boards or fiber cement boards), 10-15mm thick, forming a composite fireproof structure, suitable for scenarios where surface decoration requirements are not high. Surface carbonation treatment: apply light carbonation treatment to the UHPC surface to form a dense calcium carbonate surface layer, improving spalling resistance at high temperatures. Qinglong laboratory data show that carbonation treatment reduces the high-temperature spalling area of UHPC by 60%.