Comparison of Thermally Measured Setting of Cement Paste and Penetrometer Measured Setting of Ready Mixed Concrete

Abstract

Abstract Expedient materials and proportions screening methods are needed prior to trial concrete mix design as ingredient complexities continue to increase. Cement paste thermal measurements (e.g., the recently published ASTM C1753, Standard Practice for Evaluating Early Hydration of Hydraulic Cementitious Mixtures Using Thermal Measurements [Superseded]) are a minimal labor screening tool in which the temperature of a hydrating specimen is recorded over time but no attempt is made to quantify heat evolution (i.e., thermal methods as used herein are not calorimetry). Thermal methods have promise to reduce the combinations evaluated in trial concrete. This article evaluates setting tendencies because they are of first order concern for many projects. Although ongoing work in ASTM may soon produce a Standard Test Method for thermal measurement–derived setting indications of mortar or concrete, the use of laboratory paste mixtures to better understand and predict setting trends of concrete using the same or similar materials and proportions has not been widely studied. The specific emphasis of this article was to compare ASTM C403 (Standard Test Method for Time of Setting of Concrete Mixtures by Penetration Resistance) penetrometer measured setting on sieved concrete to thermally measured setting on cement paste in general accordance with ASTM C1753 and to provide guidance on aspects of thermally measured setting that have not been fully studied. Two of this article’s findings validated statements already present in ASTM C1753: that thermal methods are a within laboratory method and that thermal measured setting is not sensitive to a specimen’s water to cementitious ratio. Additional findings showed there is not a single factor that relates setting times between penetrometer and thermal methods, and that one adjustment factor is unrealistic for a wide range of conditions. Cement source and fly ash class meaningfully affected thermal to penetrometer relationships. Correlations were reasonable for thermal and penetrometer setting if there were 50 % or less supplementary cementitious materials present.