Measuring the Change in Water-to-Cement Ratio in Fresh and Hardened Concrete

Abstract

A key parameter in concrete is the water-to-cementitious ratio (w/cm). Unfortunately, it can be difficult to ensure the w/cm of a concrete mixture is within the specified limit(s) in either fresh or hardened concrete. An increase in w/cm will cause a decrease in strength and durability for the concrete structure. This work compares how the w/cm impacts fresh and hardened property measurements from the slump, unit weight, surface resistivity, compressive strength, and emerging test method called the Phoenix. The Phoenix test method determines the w/cm of concrete by utilizing heat to evaporate water from fresh concrete and the volumetric relationship of the sample to the concrete mixture. Fresh and hardened property testing is completed for eight trucks that were retempered with known amounts of water to investigate 31 different mixtures with w/cm from 0.28 to 0.54. The results show that only the Phoenix and the 28-day surface resistivity measurements are able to detect changes in the w/cm. However, the Phoenix shows great promise to be a new method to help producers develop consistent concrete with reliable hardened properties.