What Are UHPC's Biggest Performance Weaknesses?

Although UHPC possesses outstanding mechanical properties and durability, it still has performance weaknesses such as "high autogenous shrinkage, temperature sensitivity, and cost pressure". Through 28 years of engineering practice, Qinglong Group has gained a deep understanding of these weaknesses and developed corresponding improvement technologies. In the Wuhan Han Show Theatre project, by incorporating expansion agents and optimizing curing regimes, the autogenous shrinkage of UHPC was successfully reduced from 1000μɛ to below 600μɛ; however, its cost being 5-8 times higher than ordinary concrete remains the main obstacle restricting its widespread application. Objectively understanding these weaknesses is the prerequisite for the scientific selection of UHPC.

High autogenous shrinkage is the most notable technical weakness of UHPC. Due to its low water-binder ratio and high cementitious material content, the autogenous shrinkage of UHPC can reach 800-1200μɛ, more than 10 times that of ordinary concrete. This early shrinkage tends to cause cracking, especially in large-area thin panel components. Through internal curing technology, incorporation of MgO expansion agents, and other methods, Qinglong can control the shrinkage rate within 600μɛ, achieving good results in the large-area roof application at the Hainan Convention and Exhibition Center.

Temperature sensitivity is another important weakness. UHPC uses a large amount of cementitious materials and generates high hydration heat, and its thermal conductivity is 1.5 times that of ordinary concrete, making it sensitive to temperature changes. In environments with large temperature differences, thermal stress tends to cause cracking. Qinglong successfully applied technologies in projects in Northwest China by incorporating phase change materials and optimizing mix proportions to reduce hydration heat. However, such technologies increase costs and process complexity.

Cost pressure is the main obstacle to the market promotion of UHPC. Its material cost is 5-10 times that of ordinary C50 concrete and 3-5 times that of C80 concrete. Although the whole-life cycle cost may be lower, the higher initial investment affects owner decisions. Qinglong reduces costs by developing a gradient utilization scheme (using UHPC in critical areas and ordinary concrete in secondary areas), reducing total cost by 30% in a project in Shenzhen.

In addition, although the fire resistance of UHPC is superior to that of ordinary concrete, the fibers may melt or soften at high temperatures, causing a sharp drop in toughness; the interface bonding with ordinary concrete also requires special treatment. These weaknesses need to be overcome through material innovation and design optimization, and Qinglong is committed to enhancing the comprehensive performance of UHPC through technologies such as nano-modification and hybrid fibers.