Effects of cold joints on concrete mechanical properties and tunnel service performance

Abstract Cold joints are weak areas of tunnel lining structure, which form due to the discontinuous pouring of concrete. To reveal their impacts on tunnel service performance, indoor tests and theoretical analysis are used to assess the mechanical properties of concrete with cold joints, including elastic modulus, tensile strength, and compressive strength. Additionally, the numerical model is established to investigate their influence on the damage of tunnel lining concrete, considering factors such as pouring intervals, steel bar degradation, bedding coefficients, and cold joint location. Research findings indicate that the elastic modulus and splitting tensile strength of concrete decrease linearly and exponentially, respectively, as the pouring interval increases. Compared to intact concrete, specimens with cold joints formed due to a 12.9‐h pouring interval exhibit reductions of 41.2% in splitting tensile strength and 11.6% in elastic modulus. When there are cold joints formed due to a 10‐h pouring interval, the compressive strength of concrete in cold joint areas can decrease by as much as 80.5%. Cold joints affect tunnel service performance by influencing the damage extent and cracking of lining concrete. Reductions in steel bar diameter and bedding coefficients exacerbate the damage extent of concrete within cold joint areas. Under the researched conditions, cold joints at the arch foot have the greatest impact on tunnel service performance, followed by joints at the side wall and bottom sections.