Cement degree of hydration in mortar and concrete

Properties of concrete depend on the cement degree of hydration. Standard test methods proposed for quantifying cement degree of hydration employ thermogravimetric (TG) analysis which can be problematic when aggregates are added. This study aims to quantify the variances in the cement degree of hydration in mortar and concrete by comparing TG results to isothermal calorimetry. For the TG, 3 hydration models were considered; model A uses experimentally determined values for ultimate amount of chemically bound water, model B employs a constant value for this parameter, and model C employs an equation to determine the change in non-evaporable water content. Four mortar mixes containing CSA type GUL cement with and without silica fume and/or ground granulated blast-furnace slag were evaluated using TG and isothermal calorimetry at 220 h. The cement degree of hydration in 16 concrete mixes with varying composition was also measured using TG at 84 days. Maximum COV for cement degree of hydration is 2% and 6% for isothermal calorimetry and TG, respectively, revealing a slightly higher accuracy of the former. The cement degree of hydration’s standard error in mortar for models A, B and C is 0.047, 0.018, and 0.017, respectively, with a mean value of 0.704. The corresponding COV is 2% for models B and C and 7% for model A. Difference between the three models for estimating the amount of bound water is not statistically significant. For the concrete mixes, models A and B results have the same precision and accuracy.