Title: New Formulas for the Prediction of the Effect of Porosity on Concrete Strength
Author(s): Sandor Popovics
Publication: Journal Proceedings
Appears on pages(s): 136-146
Keywords: air entrainment; capillarity; compressive strength; concretes; flex-ural
strength; porosity; water-cement ratio.
After a review of the published predictive methods for the estimation of the effect of air content on the concrete strength, new formulas are introduced. The formulas are based on a novel combination of water- cement ratio, w/c, and air content, a, forming the porosity factor (w/c + 0.03a). It is shown that these formulas are (a) conceptually simple; (b) applicable at various ages both for compressive strength, as demonstrated by Eq. (12) through (IS), and flexural strength, as demonstrated by Eq. (16); and (c) better supported by experimental data than the earlier formulas. The new formulas also show that effect of the capillary porosity on the concrete differs, in general, from the effect of the same volume of air voids. The nature of these differences is such that the minimum acceptable entrained air is recommended for concretes of high cement contents and the practical maxima for concretes of low ce-ment contents.