What Are UHPC's Biggest Performance Weaknesses?

Although UHPC possesses the outstanding "three highs and one low" properties, no material is perfect. A clear understanding of its relative weaknesses or challenges is essential for proper design, application, and maintenance. Based on years of R&D and engineering experience, Qinglong Group believes that UHPC's current main performance weaknesses or points requiring special attention are concentrated in "economics, certain aspects of fire resistance, volume stability control, and adaptability to on-site construction."

Economic cost is currently one of the main factors restricting the wider application of UHPC. Because it uses high-grade cement, large amounts of silica fume, steel fibers, and high-range water-reducing agents, and requires refined preparation processes and curing control, its raw material and manufacturing costs are far higher than those of ordinary concrete and even high-performance concrete. As a result, UHPC is typically applied to critical parts or landmark projects with extremely high requirements for performance, durability, or architectural effect, such as the Shanghai Century Plaza and the Shenzhen Yirui Biotechnology Building projects that Qinglong participated in, and it is still difficult to fully promote in ordinary buildings.

In terms of fire resistance, UHPC also has characteristics that require attention. The dense structure of UHPC is prone to explosive spalling risk at high temperatures, mainly because internal free water and chemically bound water vaporize under high temperature, and the steam pressure cannot escape in time from the low-permeability matrix. Although incorporating polypropylene fibers (which melt at high temperatures to form channels for steam escape) can effectively mitigate the explosive spalling risk, this needs to be considered in advance during material design. In addition, the bond performance between steel fibers and the matrix degrades at high temperatures, leading to a significant reduction in toughness.

Volume stability, especially early autogenous shrinkage, is another challenge requiring fine control. The extremely low water-binder ratio causes a significant self-desiccation effect in UHPC, producing considerable autogenous shrinkage; if curing measures are improper, early cracking is likely to occur. Qinglong effectively controls shrinkage through measures such as optimizing mix proportions (e.g., using shrinkage-reducing agents) and strengthening early moist curing. Finally, UHPC is currently more suitable for prefabricated assembled structures; its flexibility in on-site casting and construction adjustment is relatively lower than that of traditional concrete, placing higher demands on the precision of construction organization. Recognizing these weaknesses helps us better leverage strengths and avoid weaknesses to ensure the success of UHPC projects.