Is the Shrinkage Rate of UHPC High? A Comprehensive Analysis of the Volume Stability of Ultra-High Performance Concrete

The shrinkage characteristics of UHPC are a key indicator affecting its engineering applications. Compared with ordinary concrete, the shrinkage behavior of UHPC follows its own unique patterns. Research shows that the total shrinkage of UHPC typically falls between 300-600μɛ, comparable to high-strength concrete, but its shrinkage development rate and final value are influenced by multiple factors such as mix proportion and curing conditions. Properly understanding and controlling the shrinkage behavior of UHPC is essential to ensuring engineering quality.

The shrinkage of UHPC mainly consists of three parts: autogenous shrinkage, drying shrinkage, and carbonation shrinkage. Among these, autogenous shrinkage accounts for the major portion of total shrinkage, which is determined by the low water-binder ratio of UHPC. Due to insufficient moisture, the internal self-desiccation effect of UHPC is significant, resulting in higher autogenous shrinkage. Experimental data show that the 7-day autogenous shrinkage of UHPC can reach 200-400μɛ, while ordinary concrete is usually less than 100μɛ. If this early shrinkage is not properly controlled, it may cause cracking of components and affect durability.

UHPC shrinkage can be effectively controlled by optimizing mix design. Research and development by Qinglong Group shows that appropriately increasing the steel fiber content (2-3% by volume) can reduce the restrained shrinkage of UHPC by 20-30%; introducing high-performance expansion agents can produce moderate early expansion, compensating for part of the autogenous shrinkage; and using special admixtures such as calcined limestone powder can optimize the hydration process and reduce shrinkage. In the Yangshengtang Pharmaceutical Hangzhou Industrial Park project, through mix proportion optimization, the 28-day shrinkage of UHPC cladding panels was controlled within 350μɛ, effectively avoiding cracking problems.

The curing regime is particularly critical for UHPC shrinkage control. Steam curing not only promotes strength development but also effectively reduces long-term shrinkage. Research shows that appropriate steam curing (temperature 80-90°C, duration 48-72 hours) can reduce the total shrinkage of UHPC by 30-50%. For the UHPC perforated panels used by Qinglong Group in the Ouargla Hotel project in Algeria, an optimized curing regime kept the 28-day drying shrinkage within 200μɛ, ensuring the dimensional stability of the components.

It is worth noting that the shrinkage development pattern of UHPC differs significantly from that of ordinary concrete. The early shrinkage of UHPC develops rapidly, with 50-70% of the final shrinkage completed within 24 hours, whereas ordinary concrete requires 7-14 days. This characteristic demands special attention to early curing during construction and timely moisture-retention measures. Qinglong Group's engineering practice shows that spraying a curing agent immediately after demolding can reduce the 7-day shrinkage of UHPC panels by 15-20%.

Long-term monitoring data reveal the time-dependent nature of UHPC shrinkage. The shrinkage of UHPC mainly occurs within the first 3 months, accounting for approximately 80% of the total shrinkage; after 1 year, shrinkage is essentially stable, with the final shrinkage value typically ranging from 500-800μɛ. The industry standard that Qinglong Group participated in developing requires the 28-day drying shrinkage of UHPC components not to exceed 400μɛ, an indicator that can be fully achieved through reasonable mix design and curing measures. Through scientific material design and construction control, the volume stability of UHPC can fully meet the requirements of precision engineering, providing a reliable guarantee for its applications in architectural decoration, bridge engineering, and other fields.