2018 Volume 72 Issue 1 Pages 158-165
Air voids are an important phase that provides concrete with frost resistance. To evaluate the air-void systems, the spacing factor has been used for long. However, the procedure to evaluate it is quite time-consuming and tedious. The authors have proposed a new method which is based on spatial point process statistics. In the proposed method, the air voids present in concrete are evaluated as a 2D spatial point process. The characteristic distance between the points is defined using the nearest neighbor distance function. In this study, concretes with different air contents were produced. Their air-void systems were evaluated by ASTM C457 linear traverse procedure and the proposed method. Two characteristic distance parameters obtained by the two methods were compared for the concretes with different air contents. There was quite good correlation between the spacing factor and the characteristic distance defined in the proposed method. In particular, the characteristic distances were almost the same as the spacing factors when the spacing factor was calculated using image analysis. A random nature evaluated by line proves in the linear traverse procedure was consistent with that expressed by the point intensity. The similarity between the spacing factor and the characteristic distance was also observed when low magnification images of air voids were used. Hence, the characteristic distance could be used as a quality parameter instead of the spacing factor and the point process statistics is a useful evaluating method for air-void distribution in concrete. However, when the air-void systems were observed at different magnifications, linear relationship of the characteristic distances between the magnifications was not observed. Further study is needed to clarify the effect of uncounted air voids on the relationship between the two characteristic distances, especially in concretes with small air content.
