| Summary: | Although potholes are a perennial problem in UK roads, the mechanisms of their formation are poorly understood. There is no established experimental method to characterise the pothole resistance of an asphalt mixture or means of specification directly related to this phenomenon. Inspired by recent progress in geophysics, this research models the potential mechanisms of crack propagation in asphalt, under the conditions considered to increase the likelihood of this form of deterioration and develops a novel experimental framework to validate these models.
Asphalt is a complex viscoelastic multiphase material and is known to deteriorate in a number of ways, which are dependent on various environmental and loading conditions. Most commonly, the frequency of potholes is observed to increase more during the winter than in any other time of the year, which is the stimulus of the research. There are several peculiarities of the winter months potentially responsible for this e.g., higher snowfall, lower temperatures, higher precipitation, etc. However, one possibly key factor that has received little attention is the presence of detritus on the road surface. The novelty of this research is to introduce this road detritus into the modelling and experimental environment. The hypothesis is that this will lead to accelerated crack propagation by a ratchet mechanism caused by the prevention of crack closure.
Modelling this type of phenomenon has received recent attention because a similar mechanism occurs in the fracking process, where hard particles are forced under pressure into fissures in rock to keep them open permitting shale gas release. This will be exploited by applying fracking models to pothole formation, calibrating model results using the experimental data.
From the experimentation, it is concluded that the coarse-grained detritus does prevent the closure of cracks in freezing and thawing as well as in simulated tyre loading, which in turn triggers the crack to propagate faster.
It is also concluded that the presence of fine-grained detritus causes failure to occur quicker when the crack propagation is entirely fluid-driven.
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