Size of Aggregates:

For the given quantity of water and aggregates the other way to improve the lubrication is to reduce the total surface area of the aggregate (which is mainly responsible for causing internal friction between the particles). For the given volume of aggregate, bigger the size of aggregates, lesser is the surface area of aggregates and more water will be available for the lubrication thus, better will be the workability and vice-versa. So, large size of aggregates provides better workability as compared to smaller size aggregates so far as the W/C ratio and the total volume of aggregate are constant.

Shape of Aggregates:

By keeping other parameters constant, the rounded aggregates provide better workability as compared to the angular aggregates because rounded aggregates provide less surface area and less internal friction as compared to angular aggregates hence more water will be available for lubrication. But, by using the rounded aggregates the bond strength between the aggregate and cement paste is reduced because, angular aggregate and aggregate with rough surface provides better bond due to more surface area hence gives better strength to concrete.