Determination of water-to-cement ratio in freshly mixed rapid-setting calcium sulfoaluminate concrete using 2.45 GHz microwave radiation

Abstract

This paper describes how 2.45 GHz microwave radiation can be conveniently and accurately used for the on-site determination of the water-to-cement (w/c) ratio in a batch of fresh rapid-setting concrete. Calcium sulfoaluminate cements are attracting attention because of their superior properties compared to traditional Portland cements. While w/c is an important factor in process control of Portland cement, it is a factor of crucial importance in rapid-setting cements containing calcium sulfoaluminate (C 4A 3S̄). A main advantage of such concretes, in addition to their low permeability and high sulfate resistance, is their very early strengths. But because of these very early strengths, the traditional microwave tests approved by AASHTO for w/c control cannot be used. We describe a test allowing determination of w/c in a rapid-setting concrete. We present results on the accuracy of the technique in the laboratory and in the field during trial batches. In all cases, the accuracy of the microwave technique was excellent. The accuracy of the test has been shown to be (w/c) measured=(w/c) theoretical±0.03 in the field, with an even higher accuracy of 0.01 in the laboratory. Therefore, it would be reasonable to set an upper quality limit of (w/c) +0.05 for onsite quality control using microwave testing.