Statistical Analysis of the Impact of Cold Joint on the Compressive Strength of Concrete Made by the National Method for Concrete Mix Design

One of the common problems in the implementation of concrete structures is seam or cold joint. The discontinuity in concrete body can cause structural weakness, increased permeability, reduced durability, corrosion of the rebar, and bad appearance of concrete. In this study, in order to evaluate the effect of cold joint on compressive strength of concrete, 192 cubic samples by national method of mix design in 4 modes, in which 48 samples without cold joint, 48 samples with horizontal cold joint, 48 samples with vertical cold joint, and 48 samples with diagonal cold joints were concreted in a 24-hour time interval. After 28 days of treatment with standard conditions by pressure cylinder device, the compressive strength of the samples was evaluated. After evaluating the results of the experiments, the values of the effect of cold joint on the compressive strength of the samples, the uncertainty and the probability of failure of the samples have been investigated. The results of analyzes indicate that, generally, the creation of a cold joint in concrete reduces the compressive strength of concrete. However, the reduction in compressive strength depends on the degree of cold joint to its angle. Also, the size of surface angle of the cold joint is also affected by the probability of failure.