Determination of Thermal Properties of Pavement Materials and Unbound Aggregates by Transient Heat Conduction

A laboratory procedure for determining the thermal conductivity (k) and diffusivity (a) of pavement materials and unbounded aggregate beds by means of a transient heat conduction experiment is described. It is first established that the plane-wall theory of heat conduction can be applied to a finite-slab problem provided that the thickness-to-width ratio is kept within 0.2. The procedure is to obtain the k and α values that would match the theoretical temperature-time history response with the measured response. An analytical curve-fitting technique is used to match the inflection points of the measured to the theoretical temperature- √t curves. The heat experiment is conducted in a controlled convection oven with parallel air flow at constant velocity over a horizontal test specimen bed. This allows for the testing of unbounded aggregate beds made into a slab by placement of aggregates in an insulated polystyrene box that fits into the base of the oven. The test method is first validated by comparing steady-state heat conduction results with the transient test predictions of k for a solid acrylic slab, two bituminous slabs, and four concrete slabs, with good agreement in the values of k determined by both methods. For the unbounded aggregates, it is observed that there is trend of decreasing values of k and α, with increase in particle size. Also, wet aggregates exhibit higher thermal conductive properties than dry aggregate beds. The test method will be useful for obtaining thermal properties of pavement materials to allow for thermal analysis in pavement layers subjected to solar heating.