Drying Shrinkage of Cast-In-Situ Concrete in Half-Precast Concrete System Under Restraint Conditions

In half-precast concrete (PC) systems, the drying shrinkage of cast-in-place (CIP) concrete is significantly greater than that of PC slabs, which are typically manufactured in factories using well-controlled steam curing. In actual construction, however, the drying shrinkage of the CIP concrete is restrained by surrounding structural elements. Despite its importance, research involving field measurements of drying shrinkage in actual half-PC construction sites remains limited. Thus, in this study, field measurements were performed to investigate the effects of restraint by reinforcing bars in topping slab, PC slab, and PC column on drying shrinkage of CIP concrete. To this end, strain gauges for measuring drying shrinkage and thermocouples for recording temperature changes were embedded in a real construction site where the half-PC system was applied. Drying shrinkage was then measured over a period of 508 days. The results demonstrated that KDS 14 20 standard provided the most accurate predictions on the free shrinkage, and that the drying shrinkage of CIP concrete decreased by 30–67% compared to the free shrinkage. This indicates that drying shrinkage in actual construction environments can be reduced due to restraint provided by surrounding structural elements. Based on the measurement results, this study proposed a simple model capable of considering the effect of restraints, and its validity was investigated by comparing analysis and field measurement results. Consequently, it appeared that when the axial stiffness of the reinforcing bars was reflected, the closest prediction results were obtained with an average error of 30.7%. However, the applicable range of the proposed model should be limited to specific structural conditions due to modeling assumptions and insufficient field data. The model is suitable for one-way half-PC systems with simple reinforcement layout, where the reinforcement ratio of the CIP concrete ranges from 0.0017 to 0.002, the topping slab thickness is less than 100 mm, and the PC column dimensions are within 500 mm × 500 mm. Additionally, the top surface of the PC slab must be intentionally roughened to ensure full composite action with the topping concrete.