High-strength flowing-concretes, having variable water-cement ratio, unit amount of water, type of cement and type of admixture, were subjected to air current drying at early ages, and propagation of cracks at early ages and their evaluation method were examined. Major findings are as follows, 1) The propagation of cracks at early ages was influenced firstly by the water-cement ratio, secondly by the unit amount of water and slightly by the other mixture parameters. 2) Crack initiation at early ages was not observed or was generally slight when it was observed for specimens with water-cement ratio of 0.45 and 0.60, while that with lower water-cement ratio of 0.27 and 0.30 showed considerable cracks. 3) Evaluation of cracks at early ages can be made by three methods: the average crack area, the number of cracks per unit area and the total crack area per unit area. Correlation between the average crack area and the water-cement ratio was particularly recognized.
