Distribution of Voids in Field Concrete

About the report:

This study was intended to evaluate the air void characteristics of concrete in an attempt to identify, quantitatively or semi-quantitatively, different types of voids and to predict their influence on strength and durability. At the outset, it was anticipated that total air contents and water-- cement ratios of concrete mixtures would reflect the presence of excess water or air voids. However, because it is difficult to determine the water-cement ratio of hardened concrete, an attempt was made to relate the water-cement ratio and the air content, taken as independent variables, to the parameters of the void system that are .readily determined from the hardened concrete. The parameters of the void system considered were 1. The specific surface and the spacing factor calculated from linear traverse data. 2. The constants of a continuous chord frequency distribution curve derived from a probability density function. 3. The mean diameters and the number of bubbles per unit volume determined by a graphical method. The concrete samples were prepared in the laboratory, and the variables included the amount of air entrainment, the water cement ratio, the mixing time, and the mixture temperature. The data on the void system were obtained by utilizing the chord lengths of voids determined by the linear traverse analysis of concrete specimens. Within the framework of the study it was not possible to correlate the combined effect of water and air content with the above mentioned void parameters. A good correlation was obtained between the air contents of fresh and hardened concretes that were properly measured. Satisfactory relationships were established between the measures of resistance to freezing and thawing (weight loss, relative dynamic modulus of elasticity, and the surface rating), and certain parameters-of the void system (the spacing factor, the specific surface, and the diameter of the bubbles).

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