The effects of the aggregates characteristics on the performance of Portland cement concrete

Aggregate shape, texture, and grading have a significant effect on the performance of fresh concrete. Aggregates blends with well-shaped, rounded, and smooth particles require less paste for a given slump than blends with flat, elongated, angular, and rough particles. At the same time, uniform gradings with proper amounts of each size result in aggregate blends with high packing and in concrete with low water demand. Optimized aggregate blends have high packing, requiring low amounts of paste. As a result, they are less expensive and will have less durability problems caused by the paste such as head generation, porosity, and drying shrinkage. The effect of shape, texture and grading of aggregates on fresh concrete was evaluated experimentally, quantified by means a proportioning method based on packing density concepts, the Compressible Packing Model (CPM), and analyzed by an empirical tool suggested by Shilstone. The effect of different types and amounts of microfines was evaluated simultaneously as well as the impact of chemical admixtures and some supplementary cementing materials can be used to improve the workability of concrete with high microfines without negatively affecting hardened concrete. Guidelines for portioning and optimizing aggregate blends were made based on Shilstone's Coarseness Chart and the 0.45 Power Chart and CPM equations and procedures.