Study on carbonation of construction joints through field tests on a 30-year-old bridge and accelerated carbonation tests

Construction joints accelerate concrete carbonation, which is one critical durability concern of concrete infrastructures. However, due to the lack of experimental data, it is still challenging to quantify its negative impact on concrete carbonation resistance. In this study, the carbonation depth of construction joints in the girder of Jinshan Bridge, which was exposed to an urban atmospheric condition in a metropolitan city for 30 years, were examined. Moreover, accelerated carbonation tests were conducted to investigate the effect of the water-cement ratio, compressive stress level, carbonation time, and the surface treatment of the joint on the concrete carbonation. The results showed that the joint influence factor, defined as the ratio between the depth at the joint section and the depth of monolithic concrete, ranged from 1.34 to 3.99 with a mean value of 2.26, and a lognormal distribution represented the random nature of the factor well. Furthermore, a function for predicting the distribution curve of carbonation depth for concrete with a construction joint was proposed, and methods to improve the carbonation resistance at the construction joint were suggested: reducing concrete’s water-cement ratio and applying silane impregnation on both sides of the joint within the range of 2.0 times of cover thickness.