The Free Water/Cement Ratio is defined as the ratio by weight of the free water content to the cement content. It has been long been accepted that a low free water/cement ratio in a concrete mix is essential for the concrete’s subsequent strength and durability. It appears that an excessive free water content leads to the formation of capillary pores, which seriously affect the concrete strength and the concrete durability.
The DOE method determines the Free Water/Cement Ratio, which will provide a particular concrete strength for different cement properties and coarse aggregate types, using the results of numerous tests.
If Pozzolan is included in a mix, Firstmix, following the DOE Method, employs a Pozzolan Cementing Efficiency Factor to obtain a Free Water/Equivalent Cement Ratio, which is used instead of the Free Water/Cement Ratio to estimate the concrete strength.
Firstmix also allows the user to specify a Maximum Free water/Cement Ratio for durability purposes. The smaller of these two ratios is used to obtain the cement content for the mix from the required free water content. However for concrete made with a Pozzolan, since the presence of a Pozzolan generally reduces the heat of hydration and improves the durability of a mix, in Firstmix the Free Water/Cement and Pozzolan Ratio, rather than the Free Water/Cement Ratio, is checked against the Maximum Free water/Cement Ratio.
Range: 0.3 - 0.9.