Firstly, the water/cement ratio is lowered to a maximum of 0.5 reducing the volume of capillary pores in the concrete matrix. This increases the density of the mix and minimises the size of pores.

Secondly, a pore blocking admixture is used to create a hydrophobic layer within the remaining pores, thus blocking the passage of water through the remaining capillary pores.

The minimum requirements for watertight concrete are:

• A minimum cement content of 360kg/m³
• A maximum water cement ratio of 0.5
• The use of a pore blocker

Depending on the location and the scale of the project Roadstone can use one of two pore blocking admixtures. At larger locations or for the supply of larger projects, a liquid pore blocking admixture is typically used. For smaller projects a powdered pore blocker is commonly used which allows for the production process to be simplified.

In conjunction with the watertight concrete admixture, a plasticising admixture is commonly used to allow for high water reduction which in turn results in low water/cement ratio concrete being achieved with high density and reduced permeability. In addition, the effect of plasticisers results in improved placing and compaction characteristics of the concrete.