A fundamental parameter that characterises the water movement in pavements is the water content. This provides information on the condition of the road layers regarding the moisture saturation stage, which controls the main parameters in the governing equations for water flow (see Chapter 2, Section 2.8). A number of methods are available for measuring water content. They can be divided into destructive methods (gravimetric methods) and non-destructive methods that provide indirect measurements of the water content.
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The simplest and most widely used method to measure the soil water content is the gravimetric method where a soil sample is taken and weighed, dried in an oven at 105 °C for 24 h and then reweighed. To shorten the drying period a microwave oven can be used as an alternative, although this method introduces the possibility of removing chemically bonded water which would lead to an over-estimation of water content. The gravimetric water content, w, is the mass of water per mass of dry soil (see Eq. 2.10) or
where Wb is the total (or “bulk”) weight of the soil and Wd is the dry weight of the soil.
This method has two major drawbacks: the sampling is destructive for the road and the method can not be used to make in-situ measurements in real time. However it is an accurate method and is often used to calibrate other measurement techniques.
