6.2 : Factors Affecting Workability

The workability of concrete is a critical characteristic that influences the ease of mixing, handling, and finishing the concrete. It is affected by several factors including water content, aggregate properties, and admixtures like air entrainment. Water plays a fundamental role as it lubricates the concrete mix, facilitating easier movement and placement. However, the water requirement varies depending on the texture and shape of aggregates. Finer particles and angular, rough-textured aggregates demand more water compared to smooth, rounded ones due to their greater surface area and texture, which inhibit movement.

The porosity of aggregates also impacts water consumption as porous materials absorb more water, reducing the amount available for lubrication, thus affecting workability. During the curing process, water may evaporate or participate in chemical reactions, increasing the temperature and reducing workability. Moreover, the ratio of coarse-to-fine aggregates can influence the texture and consistency of the mix; a high coarse-to-fine ratio may lead to segregation and decreased workability, producing a rougher texture in the final concrete.

In terms of aggregate distribution, the use of semi-lightweight aggregates instead of standard ones can also affect workability. These aggregates have a lower specific gravity, which causes them to occupy more volume, thereby reducing workability. Lastly, air entrainment is a technique that incorporates small air bubbles into the concrete, reducing the water required to achieve desired workability, and helping to improve the mix's overall performance and durability.