Title: Instantaneous In-Situ Determination of Water-Cement Ratio of Fresh Concrete
Author(s): M. Mancio, J. R. Moore, Z. Brooks, P. J. M. Monteiro, and S. D. Glaser
Publication: Materials Journal
Appears on pages(s): 587-593
Keywords: durability; electrical resistivity; fresh concrete; nondestructive testing; quality assurance; quality control; strength; water-cement ratio
The water-cement ratio (w/c) is one of the most important parameters determining the quality of cement-based materials. Currently, there is no practical way to accurately determine this ratio after all the ingredients of concrete have been mixed, posing a significant quality-control problem for the construction industry. A new method has been developed to address this challenge whereby an electrical resistivity probe is immersed in fresh concrete, providing an instantaneous and accurate measure of a concrete’s w/c. Experiments were conducted on eight concrete mixtures designed according to the ACI 211.1 procedure, with varying w/c (0.30, 0.40, 0.50, and 0.60) and fly ash percentages (0 and 25%). The results demonstrate a strong direct correlation between the resistivity of fresh concrete and the w/c. Average w/c estimates based on measurements using the resistivity probe were within ±0.01 of the actual values for all mixtures tested.