Prediction of restrained stress for UHPC: Considering relationship between long-term and in-situ creep

The accurate calculation of restrained stress is crucial for assessing the cracking risk in concrete structures. However, existing methods often lack precision in accounting for in-situ creep during the cracking process, thereby affecting the reliability of stress predictions. This paper introduces methods for calculating the restrained stress of Ultra-High Performance Concrete (UHPC) considering in-situ creep measurements. Firstly, novel molds, loading devices, and test methods are proposed to efficiently acquire long-term creep data of UHPC. In addition, the compressive and tensile in-situ creep behavior during the cracking process were characterized using an improved Temperature Stress Testing Machine (TSTM) with a dual-feedback method. Then the mapping relationship between long-term creep and in-situ creep was established based on a modified Double Power Law (DPL) model. The in-situ creep model for UHPC can be established by determining parameters through fitting long-term creep data. Finally, the restrained stress of UHPC can be calculated based on the compressive and tensile in-situ creep models. Compared to the traditional creep models, DPL in-situ creep models can enhance the accuracy of predicting in-situ creep of UHPC under varying conditions, including the presence of Expansive Agents (EA) and Superabsorbent Polymers (SAP). Comparative analysis demonstrates that the proposed method enables more precise calculation of restrained stress for different types of UHPC by considering the relationship between long-term and in-situ creep, as well as the difference between compressive and tensile creep. • An efficient long-term tensile creep test method was provided. • Compressive and tensile in-situ creep during the cracking process was obtained based on modified TSTM. • The mapping relationship between long-term creep and in-situ creep was established. • A restrained stress calculation method considering in-situ creep was proposed.