Road Pavement Crack Sealing: Experiences in the Republic of ...

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8 th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICAThe slurry consisted of the following mix by volume:• Rubber crumbs 60%• Stable grade bitumen emulsion 35%• Revertex 3%• Cement 2%Also acceptable is that the previously described warm bitumen rubber sealant (or alternative) bestruck off with the surface leaving a bandage thicker than 3mm and 50mm wide. This bandagewill also serve as a stress absorbing membrane interlayer.A cold applied crack sealant (e.g. Petroseal) can also be used as a standby product as it is notcost-effective to keep a specialised machine, such as for hot sealants, on site for the fullduration of the contract. The cold-applied crack sealant is of a medium thick consistency whichmakes it pourable and spreadable.The cold sealant consists of a rubber polymer and filler which imparts toughness and elasticproperties to the product. Undiluted the product sets within an hour or two depending onweather conditions. Cracks wider than 3mm can be sealed by applying the product through apurpose designed applicator with suitable nozzle or pouring the product into the crack andspreading the excess by squeegee. Fine cracks may be sealed by spreading the product overthe cracked area with squeegees and finally gritting the area (if required).The cold-applied crack sealant can also be mixed on site by using an anionic emulsion andlatex. The latex must contain 65% styrene butadiene rubber. The sealant (Petroseal) had thefollowing characteristics:Table 4. Properties of Petroseal.Property Min Max Test methodRing and ball softening point ( o C) 53 63 ASTM D36Penetration value 25 o C 100g (0.1mm) 55 75 ASTM D5Elasticity @ 10 o C 1 000 - ASTM D5Recovery (%) 50 - ASTM D113Wide cracks:Cracks wider than 15mm, such as when clays shrink are too expensive to fill with infill materials.A mixture of 1 part washed river sand, plus 1 part slaked lime and water to make a wet slurrymust be poured into the crack until 20mm below the surrounding surface. Allow a period for thismixture to settle and dry, refill if necessary, and then prime using MSP 1 or equivalent and fill tothe level of the surrounding surface using a rubber crumb/crusher dust slurry.3. TOP CLOSED CRACKS (3MM OR NARROWER)The top closed cracks caused by fatique etc. are normally witnessed as fine cracks andnumerous, it represents a crazed area. Because of the tightness of these cracks and the manylinear metres of cracks in these crazed areas are they invariable treated by applying a sheettype surface sealant (or the road be reworked if too severe).3.1 AimSurface seals such as bitumen rubber single seals and geotextile fabrics are prime examples ofthis group. Normally applied as a surface dressing covering a wide area, if not the total roadwidth.Paper 016
8 th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICAA proper surface seal should provide for:• prevention of surface water ingress• reduce the stress on the crack tip (SAMI)• bridge the crack opening• retard reflective cracking• tolerate large deflections• stabilise pavement moisture content• prolong fatigue lifeThere have been a number of attempts to examine the problem of minimising reflection crackingin asphalt overlays. One such study has been concerned with the influence of rubber-bitumeninterlayers (SAMI’s). In this study the finite element procedure was used to examine thedistribution of stress in an overlay in the vicinity of a crack for situations with and without theSAMI at the interface. Figures 2 and 3 illustrate the effective stress distribution for a specificsituation with and without the interlayer. Comparing these figures it is apparent that there is alarge reduction in stress levels when the crack sealing is finished off in such a way that it acts asa SAMI underneath the proposed layer.Figure 2. Effective stress distribution inasphalt overlay (in psi) with stress absorbingmembrane interlayers (SAMI).Figure 3. Effective stress distribution inasphalt overlay (in psi) without stressabsorbing membrane interlayers (SAMI).3.2 Geotextile FabricsThe use of geotextiles (e.g. Sealmac) has become standard practice over the last couple ofyears. This system is easily applied by hand with a team of say 5 workers which can lay 2km ofseal in a day.The method consists of properly cleaning and sweeping the road to be geotextile sealed.Generally the strips are 200mm wide but full sheets of 2,1m is also available. Where discreetcracks are to be covered, sheets measuring 0.5-1.0m wide are used to seal areas of cracking orpotholes. A typical specification for the geotextile appears in table 4. The geotextiles are gluedto the road using a tack coat such as cationic 60 or anionic 60-grade emulsion.Paper 016
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Road Pavement Crack Sealing: Experiences in the Republic of ...

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