Ultra-high performance concrete (UHPC) has been recently developed as an innovative cementitious-based material, which exhibits excellent tensile and compressive strengths, as well as long-term durability. However, information regarding shrinkage-induced stress development in a composite system of UHPC-reinforced concrete (RC) is limited. The objective of the present research is to identify the restrained shrinkage of reinforced UHPC layer restrained by the RC substrate in UHPC-RC composites for 150 days. Free shrinkage of the UHPC layer was also measured for comparison. The UHPC layers were cured under normal laboratory (NC) temperature (5$°C$–35$°C$) and high-temperature steam (HC) at a temperature of 100$°C$ for 48 h. Shrinkage-induced restrained stresses composite members have been evaluated based on a preexisting model used for conventional concrete. As UHPC shows different properties such as strength, shrinkage, and viscous behavior compared to conventional concrete, the development of elastic modulus of UHPC was included in the model for verification of cracking potential. A parametric study was conducted to investigate the influence of creep coefficients of UHPC and NSC on the restrained stresses. Results showed that restrained shrinkage in UHPC overlay was decreased by 57% and 80% compared to free shrinkage under NC and HC, respectively. The five stages of UHPC shrinkage development under NC during the first three days were observed while UHPC shrinkage under HC continually and rapidly increased during the curing period. On the other hand, the same shrinkage value was obtained for both NC and HC of UHPC at the age of 150 days. The preexisting model could calculate the restrained stresses, which was compared with tensile strengths of the different ages. The parametric study indicated that increasing creep coefficients of UHPC and NSC decreased the magnitude of shrinkage-induced restrained stresses in UHPC-RC composite structures.

最近，超高性能混凝土（UHPC）被开发为一种创新的水泥基材料，具有出色的拉伸和压缩强度以及长期耐久性。但是，有关UHPC增强混凝土（RC）复合系统中收缩引起的应力发展的信息有限。本研究的目的是确定UHPC-RC复合材料中受RC基材约束的增强UHPC层在150天内的收缩率。还测量了UHPC层的自由收缩以进行比较。UHPC层在常规实验室（NC）温度下固化（5$°C$–35$°C$）和温度为100的高温蒸汽（HC）$°C$持续48小时。收缩引起的约束应力复合构件已经基于用于传统混凝土的预先存在的模型进行了评估。由于UHPC与常规混凝土相比具有不同的性能，例如强度，收缩率和粘滞特性，因此在模型中包括了UHPC弹性模量的发展，以验证开裂的可能性。进行了参数研究，以研究UHPC和NSC的蠕变系数对约束应力的影响。结果表明，与NC和HC下的自由收缩相比，UHPC覆盖层中的约束收缩分别减少了57％和80％。在前三天观察到在NC下UHPC收缩发展的五个阶段，而在HC下，UHPC收缩在固化期间持续且迅速地增加。另一方面，在150天时，UHPC的NC和HC均获得相同的收缩值。预先存在的模型可以计算约束应力，并将其与不同年龄的拉伸强度进行比较。参数研究表明，UHPC和NSC蠕变系数的增加降低了UHPC-RC复合结构中收缩诱导的约束应力的大小。