Vacuum Dewatering

Summary

Vacuum Dewatering - Method used to increase the strength of concrete.

Technical Information

Because fresh concrete contains a system of water filled channels, the application of a vacuum to the surface results in water being extracted from a certain depth of the concrete, this water is sometimes referred to as ‘water of workability’.

The final water / cement ratio at the surface is thus reduced and as this ratio largely controls the strength of the concrete and a higher strength will be obtained. However it must be noted that some of the water extracted leaves voids and as such the theoretical advantage of removing the water may not be fully achieved in practice.

It is safe to say that the increase in strength gained with the vacuum dewatering (VDW) system is proportional to the amount of water removed. However, this is dependent on the depth of the concrete and the mix proportions. The VDW process, if carried out over a 25 minute period, can reduce the water content by 20% but is only really effective at depths of 100 – 150mm.