Observations of thermal shoving failures in pavements:

Recent blogs have concentrated upon the cracking failures occurring in asphalt as a result of thermal stresses. But generally if a change in temperature causes tensile cracking failure then a temperature change in the opposite sense is likely to induce compression and a number of associated shoving forms of failure mode. Here are just a few examples where pavements exhibit signs of compression related shoving failures.  

Figure 4(a) shows paving slabs on a footpath in Camden Town, London. Over a period of time the staggered longitudinal cracks between adjacent slabs have been widened due to the opening up of these cracks during cooling, followed by an infill of detritus preventing the cracks from closing. Having started with a few mm of spacing between adjacent slabs many have a year or so later reached widths of more than 25 mm. Temperature increases have resulted in a gradual outward motion of the concrete paving slabs. The outward motion of the slabs would have been even greater were it not for the adjacent asphalt section of the pavement partially preventing this motion. In Figure 4(b) can be seen a ridge of asphalt that has been pushed up by the outward expansion forces from the concrete slabs.

There are situations where the shear transfers between paving slabs are sufficient to induce tensile stresses within alternating slabs great enough to cause a tensile fracture of the slabs. In these cases it is quite common for the cracking to follow a generally straight rather than staggered path.  

 

 

(a)

 

(b)

Figure 4 : Compression related failures as a result of expansion, (a) outward movement of pavement slabs and associated widening of inter-slab cracks, and (b) the shoving-up of adjacent asphalt to form an asphalt ridge. 

I am currently writing this blog while waiting a decent weather window to allow my sailing on the south coats of Italy to continue. In this part of Calabria there are extremes of temperature. Sadly I do not have a camera to record some of the effects on the railway station platforms. Many of the stations have beautifully tiled surfaces - well they were beautiful before recent increases in temperature forced rows of tiles to pop-up to form rather unsightly ridges – in much the same way as laminate floors are heaved up by temperature or moisture changes inducing compression.