Evaluation of Mix Time on Concrete Consistency and Consolidation

In an effort to look at ways to improve the quality of the finished concrete pavement product, the Iowa Department of Transportation and ISU conducted research on two existing highway projects in 1997. The objectives of that research included evaluation of two alternative types of central mixers, the effect of the type of hauling equipment, the mix design, and the mixing time employed to produce the mix on the consistency, consolidation and air matrix in the concrete pavement. The concrete was tested at the plant site and at the grade by standard methods employed in the testing of ready mixed concrete delivery. The results of that research have provided some insight into the consistency and consolidation of the concrete produced and placed. In addition, core analysis of the hardened concrete by the Scanning Electron Microscope (SEM) have given more information relative to the impact of the paving operation on the air matrix on the finished product. This paper will report some of those results and indicate how they may be shaping the future mix design and construction of concrete pavements.