Field measurement of water-cement ratio for Portland cement concrete. Phase II, Field evaluation and development

Abstract

The water-cementitious material ratio (w-cm) is defined as the ratio by mass of free water to cementitious material in a concrete mix. The microwave oven method (AASHTO provisional standard TP23-93) and the nuclear water-cement gauge were evaluated in actual field trials at seven different concrete paving sites as potential methods to rapidly determine the water-cementitious material ratio during construction. Two standard Grade A-FA Wisconsin Department of Transportation mix designs with 19% and 30% fly ash replacement were used at these sites. The coarse and fine aggregates were either igneous-based or limestone depending on the project location. Separate laboratory evaluations were conducted on mixtures using the same materials to provide calibration points. Using known batch quantities as the basis, the microwave oven method will generally result in standard errors in w-cm of at least 0.023. The performance of the nuclear gauge depended on aggregate type despite attempts to remove this dependency with calibration. Standard errors in w-cm associated with the nuclear gauge ranged from a minimum 0.018 when using limestone aggregates to 0.072 when using igneous aggregates.