The GWT measures the permeation of water into the test surface under an applied pressure. A pressure chamber containing a watertight gasket is secured tightly to the surface by two anchored clamping pliers or by means of a suction plate.
The chamber is filled with water and the top cap of the chamber is turned until a desired water pressure is displayed on the gauge. As water permeates into the concrete, the selected pressure is maintained by means of a micrometer gauge pushing a piston into the chamber. The piston movement compensates for the volume of water penetrating into the material.
The travel of the piston as a function time is recorded and the speed the piston travel in µm/s is used to characterize the permeation of the test surface in different ways.
Water Permeability Test.