POTHOLES: - CSIR

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CHAPTER 3CLASSIFICATION ANDMANAGEMENT3.1 ClassificationPrior to any successful pothole repair, it isessential to have identified and classified thecause of the problem. The surficial repair ofpotholes, without attending to the fundamentalcauses, is normally a complete waste of timeand resources – incorrectly repaired potholes arelikely to fail again soon after repair (Figure 19).To assist with the identification of the causesof potholes, the decision key process shown inTable 1 can be used. Table 1 shows that theclassification process is purely visual, exceptfor Key point 10, where it is necessary todetermine whether the top of a cementitiouslystabilisedbase has carbonated. This requiresthe application of a small quantity of dilute(5N) hydrochloric acid. If the acid effervesces(or fizzes) vigorously, this is a strong indicationof excessive carbonation. The use ofphenolphthalein to confirm the absence of severecarbonation may also be necessary.Similarly, the determination of whether thesubgrade is excessively wet requires somejudgement, which is gained with experience.An assessment of whether water-loving vegetationor evidence of ponding is present in the area(see Figure 1) will usually be an initial guideto whether excessive moisture (not necessarilyseasonal moisture fluctuations) is the cause ofproblems. Seasonal moisture fluctuations in theouter zone of the road adjacent to unsealedshoulders are a necessary and expected partof road performance. Failure in this zone isusually attributed to marginal or poor materialquality, resulting in excessive moisture sensitivityof the material strength. This key is followednumerically with reference to various correctionor repair techniques described in Section 4.It is important to classify asphalt pavements withcare. If the asphalt has been resealed with a thinbituminous surfacing (slurry and chip seals arecommon applications over asphalt), the potholeshould be classified as an asphalt pothole forrepair-identification purposes. The applicationof asphalt overlays on top of old surfacingseals is rare, but could occur. In these cases,the surfacing would be classified as asphalt forpothole cause-identification purposes. It is alsocommonly seen on older roads that numerouschip seals have been applied over the years,resulting in an effective seal of 25 mm thicknessor greater. These seals should still be classifiedas thin bituminous seals and not as asphalt forrepair purposes described in Section 4.Potholes are seldom deeper than 150 or200 mm, as they then become serious safetyhazards and are generally repaired or filledwith local materials at that stage. The failureof layers beneath (or even within) the subbaseis thus very seldom visible from thesurface. Potholes associated with failures ofdeeper materials tend to be manifested byvisible surface deformation (rutting, shearing,mounding, depressions, etc.). Evidence of thisindicates the need for deep repairs, as discussedin the following sections.24
Table 1: Key to the decision process for the repair of potholesKey Defect Repair action Go to1Surfacing is asphalt 2Surfacing is thin bituminous seal 42Pothole is deeper than asphalt wearingcourseBottom of pothole is within asphalt wearingcourseShallow asphalt (HMA or cold mix)33Pothole caused by cracking due to fatigue ofasphaltPothole caused by localised surface wateringress with no associated crocodile crackingDeep repair after sub-soil drainageinstallationMedium-depth asphalt repair45678Pothole has exposed an unstabilised base 5Pothole has exposed a stabilised base 10Pothole is not associated with cracks 6Pothole is associated with cracks 8Pothole affects seal and top of baseonly (< 50 mm)Shallow surface repairPothole extends > 50 mm into base 7Pothole affects only the baseMedium-depth repairPothole extends below the base 8Pothole does not affect entire pavementstructure (only base and sub-base)Medium-depth or deep repairPothole affects entire pavement structure 99Pothole is the result of saturated subgrade orsupportPothole is the result of poor material – noevidence of excessive subsoil waterDeep repair after sub-soil drainageinstallationDeep repair10Top of base has carbonated and is weak 11Top of base has not carbonated excessivelyand is still strongShallow surface repair11Pothole is associated with crocodile crackingPothole is not associated with crocodilecrackingDeep repairMedium-depth repair25
Page 1 and 2: POTHOLES:Technical guide to their c
Page 3 and 4: forewordWe have great pleasure in p
Page 5 and 6: TABLE OF FIGURESFigure 1:Localised
Page 8 and 9: CHAPTER 2CAUSES OF POTHOLESAlthough
Page 10 and 11: Figure 3: Cracking of asphalt resul
Page 12 and 13: Figure 6: Initiation of potholes as
Page 14 and 15: Figure 8: A typical pothole formed
Page 16 and 17: 14Figure 12: Fatigue cracking of a
Page 18 and 19: 16Figure 14: A typical pothole form
Page 20 and 21: Figure 19: Failure of a patch withi
Page 22 and 23: 2.6 Mechanisms of pothole developme
Page 24 and 25: Figure 24: Moisture/traffic-associa
Page 28 and 29: 3.2 ManagementFor effective managem
Page 30: 4.3 Preliminary treatmentThe area t
Page 34 and 35: of compaction after placement). To
Page 36 and 37: MethodOnce the area to be patched h
Page 38 and 39: 4.5.5 Medium-depth repair (thin bit
Page 41 and 42: CHAPTER 5QUALITY CONTROL5.1 General
Page 43 and 44: 5.2.3 HMA compaction temperatures m
Page 46 and 47: APPENDIX A - Standard form for the
Page 48 and 49: APPENDIX BKey to THE identification
Page 50 and 51: Notes
Page 52: www.csir.co.zaSee www.csir.co.za/po

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