The flow table is a standardized test that is widely used to qualify a mortar to be tested for compressive strength and air content. It is also the only standard test to quantify a mortar workability property. Therefore, the calibration of this device is paramount and it is done today by preparing a reference material that consists of a mixture of silica powder and oil. Once the two materials are selected, they are mixed and tests are performed using the flow table at the Cement and Concrete Reference Laboratory (CCRL). This flow table is identical to commercial versions used in practice, and the values obtained with this flow table are considered the reference values that are used to calibrate all the flow tables in the United States (US). This procedure is an empirical procedure and relies heavily on one device that could break or, through mechanical wear have a result that drifts over time. This study will review the production process of the reference material, provide historical data and then propose a more scientifically-based approach to developing a improved reference material. It was found that the flow table results are more sensitive to the particle size distribution of the powder than the viscosity of the oil. Fundamental rheological properties were determined using a rheometer and some correlations were drawn. A new method to produce the silica powder is proposed that would make the process more reliable, safe, and clean.
Report to TRANSPORTATION RESEARCH BOARD
Rheology, flow table, reference material