18 RUTTING AND SHOVING Rutting and shoving are permanent vertical or longitudinal displacements of the asphalt. Rutting is the permanent depression of asphalt in the wheel path. It results from heavy traffic loading and insufficient strength of the pavement section, resulting in deformation of the asphalt surface or underlying layers. Weak asphalt mixtures, insufficient pavement section thickness, or inadequate compaction can lead to rutting. Rutting can also occur when there is too much asphalt binder in the HMA mix, signifying a problem with the mix design. Shoving is the formation of ripples or small mounds in the asphalt surface. Shoving is also known as washboarding. Shoving can be caused by excess asphalt, too much fine aggregate, rounded aggregate, too soft an asphalt or a weak granular base. Shoving is most likely to occur where heavy vehicles frequently decelerate rapidly. To prevent rutting and shoving, you can: • Follow design and construction best practices. • Include polymeric additives in the binder. • Use a stiffer binder to increase resilience of the asphalt layer. Tips on responding to rutting and shoving: • If rutting is caused by failure below the asphalt layer, surface repairs won’t address the underlying cause and will not be a permanent solution to the problem. • When replacing asphalt experiencing shoving with a mix having a stiffer binder, be aware that mixes with stiffer binders are more susceptible to cracking.
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