Free Water Content

The water, which is available to react with the cement, is termed the free water content of the concrete and influences the strength, durability and workability of the concrete critically. It is the sum of

• the mix water
• the surface water of the aggregates
• the water content of admixtures

less

• the water absorbed by the aggregate in the time between the mixing and the setting of the concrete.

The free water content is generally determined by a compromise between workability requirements and strength and durability needs.

The Specify Free Water Content Tick Box lets you select between specifying a value for the free water content and accepting the content calculated by Firstmix from the DOE method. If the free water content is specified, the corresponding estimated slump or Vebe time is displayed on the Mix Design Form.

The DOE Method first determines the minimum Free Water Content, which will provide the required workability, for the given fine and coarse aggregate types and the maximum aggregate size.

The cement content is then made the minimum, which will give a free water/cement ratio, that is low enough to provide the desired strength and durability.

Range: 50-500 kg/m³.or 85-850 lb/yd³.