Effect of Concrete Curing Conditions and Testing Variability on The Formation Factor

Abstract

AASHTO R 101 uses formation factor (FF) as one of the main properties related to transport properties and the freeze-thaw critical saturation, however, FF depends on the determination of the pore solution electrical resistivity, a very complex process. Thus, alternative indirect methods have been proposed, such as the conditioning method used in ASTM C1876, and in AASHTO R 101, which bypasses the need of directly measuring the pore solution by immersing specimens in a soaking solution of known resistivity and assuming equilibrium between the soaking solution and the pore solution.  Nevertheless, the industry has shown the following concerns regarding this type of conditioning: 1) the degree of equilibrium that can be achieved between the pore solution and the soaking solution, and its effect on the formation factor, 2) time needed to achieve this equilibrium, 3) the requirement to condition different batches of concrete in separate containers containing a specific volume of concrete to volume of solution ratio and consequently requiring a large laboratory footprint, 4) logistics and costs of large quantities of solution, since soaking solutions cannot be reused, and 5) Disposal of large quantities of the high pH soaking solution.

This paper will present a compilation of studies on the effect of specimens conditioning on the formation factor, as well as other means to determine formation factor, including laboratory testing, mathematical modelling, Monte Carlo simulation, and a large interlaboratory study conducted to determine the variability of ASTM C1876.