CHANNELING.— Channeling, also referred to as“grooving” or “rutting,” is channelized depressions thatdevelop in the wheel tracks of flexible pavements (fig.16-16). Channeling may result by consolidation orlateral movement under traffic in one or more of theunderlying courses or by displacement in the bituminoussurface itself. It may develop under traffic in newflexible pavements that had too little compaction duringconstruction or from plastic movement in a mix thatdoes not have enough stability to support traffic.CORRUGATIONS AND SHOVING.— Corru-gation, or washboarding, are a form of plastic movementtypified by ripples across the flexible pavement surface(fig. 16-17). Shoving is the plastic movement of thepavement, resulting in localized bulging of the pavement(fig. 16-18). Both corrugations and shoving normallyoccur at points where traffic starts and stops or on hillswhere vehicles brake on the downgrade.Corrugations and shoving usually occur in flexiblepavement mixtures that lack stability. This may be theresult of too much binder, too much fine aggregate, orround- or smooth-textured coarse aggregate. In the caseFigure 16-17.-Corrugations.Figure 16-18.–Shoving.of emulsified and cutback asphalt mixes, it maybe dueto a lack of aeration.DEPRESSIONS.— Depressions are localizedareas of limited size that may or may not beaccompanied by cracking (fig. 16-19). Water collects indepressions that then become not a source of pavementdeterioration but a hazard to motorists. Depressions arecaused by traffic heavier than that for which thepavement was designed, by poor construction methods,or by consolidation deep within the subgrade.UPHEAVAL.— Upheaval is the localized upwarddisplacement of the pavement due to swelling of thesubgrade or some portion of the pavement structure (fig.16-20). It is commonly caused by ice expansion in thegranular courses beneath the pavement or in theFigure 16-19.—Depression.Figure 16-20.—Upheaval.16-19
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