Water-Cement Ratio Testing
The original water/cement ratio of a concrete mix affects a number of properties in the hardened concrete or in the concrete during curing.
Drying shrinkage - the higher the water/cement ratio the higher the potential shrinkage.
Permeability - High water cement ratio results in a higher permeability in the concrete.
Frost resistance - for reasons associated with compressive strength because the voidage left behind by uncombined water in the cement paste lowers the strength.
A test method for determining the original water/cement ratio is described in BS1881:Part 124:1988.
In essence this involves determining the volume of capillary pores and the weight of cement and combined water. The sum of the combined water and the pore water gives the original mixing water and the cement content is determined as previously described. Hence, the water/cement ratio can be calculated.
The test cannot be carried out on a poorly compacted concrete as this artificially inflates the value determined for capillary water.