The effects of the properties of coarse aggregates on the workability of concrete

Abstract

Summary It is well known that different types of aggregate produce different degrees of workability when used in concrete of given mix proportions and water/cement ratio. A rounded aggregate will, for example, give concrete of higher workability than all angular aggregate. Thirteen coarse aggregates were investigated to determine the effects of their shape, surface texture and water absorptive capacity on the workability of concrete. An attempt has also been made to assess these effects quantitatively. The main conclusions were as follows. (1) Changes in the angularity of coarse aggregates have a greater effect on the workability of concrete than changes in the flakiness of the aggregates. Increased angularity and/or flakiness leads to a reduction in the workability of concrete. (2) Although there was a wide variation in the surface textures of the aggregates, no correlation was found between this property and the workability of concrete. (3) The differences in the capacities of the aggregates to absorb water were insufficient to produce significant changes in the compacting factor. No correlation was, therefore, found between this property and concrete workability. This does not rule out the possibility that highly porous aggregates when used in a dry condition will affect the workability of concrete.