AbstractThis paper presents the results of the experimental study on the thermal cracking of the wall of rectangular reinforced concrete (RC) tank. The tank is located in the sewage treatment plant in Żywiec, Poland, and has capacity of 27,500 m3. Since the tank was designed without the expansion joints, it was constructed using the lean concrete mixture and low-heat cement to minimize the potential for thermal cracking. The temperature sensors were installed in both the primary and the complementary segments of the wall. In addition to the temperature data, the paper also presents the results of measurements of longitudinal concrete deformation, of crack development, and crack width on both surfaces of the complementary segment. The results of measurement of concrete strains and crack width development in vertical construction joints are also discussed. The current paper is the first one in a two-part series, and it contains the data collected from the actual RC rectangular tank. The second paper of thi...