Evaluation of Reducing Cement Content in NDOR Class R Combined Aggregate Gradations

To encourage the more use of locally available aggregates, Nebraska Department of Roads (NDOR) Materials and Research recently introduced a new blend aggregate band named 47B Revised (47BR). While results showed that mixes with this new blend can satisfy NDOR requirements, there is a fairly large amount of voids in the aggregate particle skeleton. As a result, a relatively high amount of cement (approximately 600pcy) is currently used in these mixes to compensate the high void content, which increase the cost of these mixes. A further study is needed to improve the cost effectiveness of the current 47BR mixes by allowing contractors and ready-mixed concrete producers to apply mixture designs with lower cement content. The reduced cement content can be achieved by reducing the void content in the aggregate granular skeleton through the change of aggregate proportion and/or the introduction of a third kind of aggregate (e.g., intermediate size aggregate) to optimize the gradation.