USING CEMENT PASTE RHEOLOGY TO PREDICT CONCRETE MIX DESIGN PROBLEMS: TECHNICAL REPORT

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 setting time, workability, and curing-related issues, which sometimes lead to severe early-age cracking especially in severe weather conditions. The objective of the present study was to examine the applicability of the Superpave Dynamic Shear Rheometer (DSR) to measure cement paste rheology on the one hand and identify cement and mineral/chemical admixtures incompatibilities based on cement paste rheological behavior on the other hand. Based on the extensive laboratory investigation, it is observed that DSR in modified form can measure cement paste rheology with permissible repeatability and sensitivity and has a great potential to identify cement and mineral/chemical admixture incompatibilities. The heat of hydration data from isothermal calorimeter test and setting time results for the studied mixtures have strongly supported the rheology-based observations. A procedure to formulate rheology-based acceptance criteria has been developed based on the available test results. Further refinement of these acceptance criteria based on detailed work covering a wide range of incompatibilities and validation through implementation efforts is warranted. This will ultimately help concrete producers and district laboratories detect problematic combinations of concrete ingredients during the mixture design process. The researchers also investigated the feasibility of the mini slump cone test as an alternative or supporting tool for the rheology test.