A proposed method and monitoring system for evaluating workability of Portland cement concrete during mixing

The objective of this study is to address the problem that the traditional quality control method of fresh Portland cement concrete cannot allow the workability to be evaluated during the mixing process. Based on the rheological theory and observed linear relationship between the shear force and flow deformation of concrete mixtures, a mathematical model was established to characterize the workability of concrete using the stirring power of concrete mixers. In this study, a laboratory-scale two-shaft mixer with a rotation speed control system and a power monitoring system was designed and tested. A LabVIEW program was also developed to process and analyze changes of the stirring power data. Laboratory test results show that the optimal workability of fresh concrete with very different mix designs is usually obtained when the second wave trough of stirring power appears. The test results are also compared to the conventional slump test, which indicate the proposed approach and developed system can be used to evaluate the workability of fresh concrete during mixing and identify the optimal mixing time length.