Applicability of Dynamic Shear Rheometer to Measure Cement Paste Rheology for Identifying Cement–Admixture Incompatibilities

The complex interaction between cement and chemical / mineral admixtures in concrete mixture sometimes leads to unpredictable concrete performance in the field which is generally defined as concrete incompatibilities. Cement paste rheology measurements instead of traditional workability tests can have a great potential to detect those incompatibilities in concrete before the concrete is placed to avoid related workability problem and setting time and heat evolution abnormalities. The objective of the present study was to examine the applicability of Dynamic Shear Rheometer (DSR, originally designed to measure asphalt rheology) using Bingham model to measure cement paste rheology in one hand and identifying cement – admixtures incompatibilities based on the determined rheological parameters on the other hand. Rheological parameters were determined by modified DSR for both normal and incompatible mixtures using five different plate gaps. DSR with 1 mm plate gap is the most representative to distinguish the studied mixtures based on their rheology with best reproducibility and sensitivity. In order to validate the DSR as a standard rheometer, the DSR test results were verified by another advanced rheometer (AR 2000). The heat of hydration data from isothermal calorimeter test and setting time results for the studied mixtures have strongly supported the rheology based observations as supporting tools. Cement paste rheology measurement technique using the modified DSR has a great potential to identify cement - admixture incompatibilities. This will ultimately help material suppliers, concrete producers, and other users to detect problematic combination of concrete ingredients before the concrete is placed.