Volume 3, Issue 2 (February 2006)
Relationship Between Indentation Hardness and Water to Cement Ratio of Hardened Mortar and Concrete
Accurately estimating the water-to-cementitious materials ratio (w/cm) of hardened concrete is one of the most difficult tasks frequently requested of concrete petrographers. Different methods have been developed and implemented with varying degrees of success. To increase the reliability of estimated w/cm, the indentation hardness of laboratory prepared specimens of neat paste, mortar, and concrete was evaluated using a Buehler semi-automatic testing machine. Preliminary results indicate good correlations between the average indentation hardness measured on the Rockwell HRL scale and the w/cm of the specimens. The data demonstrate a potential for using these correlations to estimate the w/cm of hardened concrete. Testing protocols, sample preparation requirements, and the effects of aggregate and of the composition of concrete mixtures (portland cement and fly ash content) are illustrated. Directions for future work are also discussed.