Abrams law, air and high water-to-cement ratios

Abrams law linearly relates the logarithm of strength to the water to cement ratio. This article shows that between water to cement ratios of 0.30 and 1.20 significant improvements to the linear regression correlation coefficient can be made by the inclusion of the volume of entrained air, but not entrapped air, in the mix to the water content. However, the inclusion of higher water and air to cement ratios above 1.20 in the analysis produced unreliable regression coefficients. Further investigation showed an independent, second linear relationship existed at high water plus air cement ratios with a different slope and intercept. This change of slope coincides with a turning point predicted by the Dewar method of mix design. Comparison is also made of the logarithm of strength and porosity, as a fundamental relationship. The augmented Abrams law was found in all cases to improve the accuracy of regression analysis