Abstract
The objective of this research is (1) to develop an easy-to-use Superpave dynamic shear rheometer (DSR)–based device that could measure cement paste rheology with permissible repeatability and sensitivity, and (2) to investigate whether potential cement-admixtures (mineral and chemical) incompatibilities can clearly be identified through direct measurement of cement paste rheology. The DSR was modified to make it suitable for measuring cement paste rheology and a DSR-based rheology test procedure with optimum parameters and test conditions was subsequently developed. An extensive laboratory investigation using the modified and optimized DSR-based rheology test procedure with varieties of cements, supplementary cementitious materials, and different types and dosages of commonly used chemical admixtures under different temperature conditions was conducted. The heat of hydration (HOH) and setting time tests were also performed for all of the studied mixtures as supporting tools. The rheology tests were conducted using both static and dynamic mode of operations. The rate of change of plastic viscosity and yield stress was found to be the most sensitive parameter to identify the studied incompatible mixtures in the static mode and used to develop acceptance criteria. Similarly, monitoring storage modulus over time followed by determining ultimate storage modulus was used to detect the same incompatible mixtures in the dynamic mode. The rheology-based test results are strongly supported by the HOH and setting time results. The test results show that DSR in modified form is capable of measuring cement paste rheology with permissible reproducibility and sensitivity and detecting incompatible mixtures. The modified DSR-based procedure has a great potential to detect problematic combinations of concrete ingredients during the mixture-design process and thereby avoid concrete cracking and other durability issues resulting from incompatibilities.
