The ABCs of POTHOLESPOTHOLES Producers Association Producers Ontario Hot MixOntario 2 The ABCs of Potholes conditions, thetoplayerdebonds andbreaks upunder the than 150mm),themechanism isslightlydifferent. spring With For majorarterialroads withtwoormore layersofasphalt(thicker potholes. orroads withalotoftrucktraffic are more prone to there is,themore damagethere will be.Heavilytravelled weakens, cracks,andthenfallsawayleavingapothole.Themore going overtheunsupportedpavementflexesasphalt,which subbase andunderminesthepavement.Theweightofvehicles roads, potholesstarttoform whenwaterseepsintothegravel For thinpavements(lessthan100mm),themajorityofmunicipal good sprinklingofwatertobringpotholeslife. water. Andjustliketheflowersthatbloominspring,ittakesa There are onlythree thingsthatcankillaroad –water, water, and The BirthofaPothole ten yearsearlier. created theproblem. Itwasthedecisionsmadefiveto It’s notthedecisionsthatwere madethisyearthat person. state oftheroads, they’re probably blamingthewrong motorist. Butwhendriverscallcityhalltobemoanthe pavement, ready toreach upandgrabtheunwary potholes cometolifeafterahard winter, lurkinginthe personal. Liketheflowersthatbloominspring, People putupwithalotofthingsbutpotholesare ABCs ofPotholes Compactthepatchwithahandheldvibratory Addtheasphaltinlayers • Usehotmix(ifavailable)forabetterbond • Useatackcoatontheedges • Square uptheedges • Cleanthehole • • Best Practice: truck tocompactthepatch. “Throw androll” –sameasabovebutusingtheutility mix andthenheadtothenextone. “Throw andgo”–atemporaryfixinwhichyouthrow in How toPatchPotholes: Maintaintheroad bysealingcracks. Step 2: Buildadurableroad withgooddrainage, Step 1: Stop watergettinginunderthepavement. How toPrevent Potholes: pothole. cavity. Theunsupportedpavementfallsawaycreating a Water getsintothepavementbase,creating asmall How PotholesForm: Potholes compactor adequate pavementthicknessandtightjoints

be installedforadditionaldrainage. structural support.Insomesituations,subsurfacedrainsshould granular subbaseprovides gooddrainageaswellsolid sheds watertogutters,drainsandditches.Awell-designed drainage isessentialforgoodroads. Aproperly crowned pothole seasonahead. heavy snoworrainandrepeated freeze-thaw cyclesmeansabig air pocketsthatleavethepavementunsupported.Awinterof temperatures warmthecoldpavement,meltingice,creating pushing upthepavementandfurtherweakeningit.Spring penetrate. Whenthewaterinsubbasefreezes, itexpands, cycles openupthecracksinasphalt,allowingmore waterto Potholes bloominthespringbecausewinterfreeze thaw even inthewinter, iscritical. of timetodevelop,timelyfillingpotholesinthesurfacelayer, pavement andultimatelyintothesubbase.Sincethistakesabit ponds inthehole,leadingtofurtherinfiltrationofwaterinto thesurfaceliftgone,water lower layerofpavement.With repeated loadingofthetraffic leavingapotholeandexposingthe can makeitswaythrough thepavementintounderlyingbase. alongthewheelpath,itbecomes moreworn porous andwater asphalt pavementistoothin,inadequatelycompacted,orbadly asphalt isrelatively impermeableandwatertight.However, ifthe special typesofasphaltthatare designedtobeporous, most theexceptionofsome water canstillgetintothesubbase.With Even ifthere are nocracksordiscontinuitiesinthepavement, create discontinuitiesinthemat. Utility cutsinthepavementforunderground cablesandpipesalso a matoffresh hot-mixisplacedalongsideanexistingcoolermat. mat, thelongitudinaljoints,whichare formedbetweenlaneswhen Cracks canalsoformalonganothertypeofdiscontinuityinthe rain, andice,cracksstarttoappear. trucks, thescrapingofsnowplows,andweatheringfrom thesun, but timetakesitstoll.Inevitablywiththepoundingfrom carsand Asphalt pavementstartsoutlifeasasmoothcontinuoussurface porous pavements. – through breaks intheasphaltmatorbypenetratingthrough There areapavement twowaysthatwatercangetunderneath Where There’s aCrack,There’s aWay Good Thickness: Good Drainage: prevents waterfrom underminingthepavementin firstplace. built road lastslonger, hasfewercracksanddiscontinuities, decisions neededtobemadeyearsearlier. Awell-designed, well- You cannotprevent potholesbymakingdecisionsthisyear. The Build ItRightintheFirstPlace deformation andcracking. surface courses,toprovide thestrength neededtoresist nominal aggregate size,typically50millimetres formostroad The thicknessoftheasphaltpavement shouldbe3to4timesthe and more prone tocracking. a muchhigherairvoidcontentandasresult willbemore porous in asphaltpavementsbutapoorlycompactedpavementwillhave compact itproperly. Airvoids(typically5to6percent) are normal pavement needstobethickenoughsothatthecontractorcan The Ontario HotMix Producers Association Everypavementengineerwilltellyouthatgood Donotskimpontheasphaltpavement.The 3 The ABCs of Potholes

requires shutting down the road completely for a day or two. shutting down the road requires construction If echelon paving is not practical, then proper techniques, joint overlap and rolling techniques, such as correct durable more tighter, joint heating, and joint adhesives, can create seams. Crack Sealing: The Best Defence main- inevitable, preventive Since cracks in the pavement are the cracks and keep the water out of the tenance to repair is the best defence against potholes. pavement structure maintenance after about will need some preventive Most roads years of service. three You don’t want to fill the cracks. You want to seal them so that want to seal them so want to fill the cracks. You don’t You Cracks water cannot penetrate into the pavement structure. and then cleaned with a jet of hot air to get rid should be routed that it the asphalt sealer to ensure of any dust or debris. Warm bonds well to the sides of the crack. diagram courtesy of Virginia Department of Transportation

Celebrating Over 30 Years of Paving Excellence Celebrating Over 30 Years Good Joints: for Since a longitudinal joint is the most vulnerable point of failure avoid durable road, strong asphalt pavements, if you want a really only one is, however, longitudinal joints in the first place. There way to do that and that is by paving in echelon – paving multiple pavers – which usually side-by-side with two or three Good Bond: Cutting back from, say, 50 millimetres of hot mix to 40 millimetres of hot mix to 40 millimetres 50 millimetres say, Cutting back from, cost of a few The incremental will not cut costs by 20 percent. of asphalt is minimal. extra millimetres A tack coat is a light application of asphalt emulsion between hot maintain the mix asphalt layers that helps bond them together, penetrating structural integrity and helps keep water from road’s coat is inexpensive insurance against the pavement. Tack through early de-bonding of the layers. If you want to cut down on road construction costs, eliminating the tack coat is one way to do it your maintenance costs in a few to increase but be prepared years time. 4

Crack sealing should be done either in the spring or the fall. In the For “throw and go”, the most basic of repairs, the crew throws summer, the pavement expands, closing up the crack, so less some asphalt in the leaving it slightly higher than the crack sealant is used. When the winter arrives, the crack opens pavement and lets the traffic compact the material. It is a up pulling the crack sealant apart. Conversely, if you fill cracks in temporary solution at best but useful for emergency repairs. the winter when they are at their widest, they close up in the With “throw and roll”, the crew drives the utility truck back and summer and the sealant is pushed out. forth over the patch to provide some initial compaction. Some A good crack seal should last for about seven years. crews will come back later, soften the patch with infrared heaters and then do another roll for more compaction. Seals and Overlays: There are two types of patches that can be used: a cold mix Seals and overlays can provide a new surface for roads with a asphalt, which is kept pliable with solvents and emulsions, and the large number of surface cracks. A new thin surface for the traditional hot mix asphalt. Hot mix is preferable because it bonds pavement will restore the surface with a continuous layer and fill better to the existing pavement but unless you have enough and seal most small cracks. Overlays will not correct deep volume (Toronto, for example, keeps a hot mix plant open all year), structural cracks. Deep cracks will simply reflect through the new hot mix may be difficult to obtain in the winter and really shouldn’t surface. be used when temperatures are below freezing. There are a number of treatments such as chip seals, Using a hot box, a small trailer hauled behind the utility truck, is a microsurfacing, and slurry seals that can restore the surface of the practical way to get small quantities of hot mix from the yard to pavement, seal small cracks, and prevent water getting into the the road, without having to constantly go back to reload. The crew pavement. A surface treatment will extend the life of the road by loads the hot box with previously prepared plugs of asphalt. Some about five years. A hot mix overlay, known as shave and pave, municipalities are using reclaimed asphalt pavement (better should be used for roads with severe cracks and surface distress known as RAP). However, since RAP is stiff, it takes a lot of but are still structurally adequate. In this technique the surface is heating and only results in a temporary patch. A propane heater removed and re-profiled by milling equipment and then paved with in the box maintains the temperature of the hot mix, which can a new hot mix overlay. This treatment is much more permanent then be used to fill the potholes. and should last from 14 to 20 years depending on the traffic and thickness of the overlay. Microsurfacing, a thin cold mix, can be High performance cold mix is best used as a temporary patch in used to seal longitudinal joints. the winter. It should be warmed before use. Care must be taken not to overheat the cold mix which will result in a loss of solvents Manholes and Catchbasins: making the cold mix stiff and unusable. Sealing around “ironwork” is difficult and often requires handwork. Regardless of which type of material is used, the best way to If there is not good compaction at the edges, the asphalt can sink ensure a good patch is to do the necessary preparatory work first, leaving standing water that can eventually work its way into the rather like a dentist filling a cavity. pavement. Clean out the water, ice and debris first (a leaf blower is cheap, A well sealed compacted edge to the pavement around manholes quick, and surprisingly efficient). For large pothole repairs in the and catchbasins is essential to prevent deterioration. One summer, square up the hole using a jackhammer to make a more technique is to use a core rig that is larger than the cover to vertical edge. Use a bonding compound or tack coat on the remove the asphalt around the perimeter and then fill it with a edges for a tighter seal. Add the asphalt in layers. Finish the job preformed resilient rubber ring gasket that resists shock loading. with a hand held vibratory compactor or small steel wheeled roller Patches to get good compaction. The time-honoured practice of patching potholes has developed Avoid rushing. Try to ignore the outcries demanding that every its own unique vocabulary. pothole should be fixed within hours after it has formed. Do the worst first and make sure they are repaired properly.

The Ontario Hot Mix Producers Association 365 Brunel Road, Unit 4, Mississauga, ON L4Z 1Z5 Phone: 905.507.3707 • Fax: 905.507.3709 web site: www.ohmpa.org • email: [email protected]

The Fine Print: This brochure is designed as a general guide only. It is not a design manual. Professional engineers should be consulted to ensure that pavements are not only designed functionally but also economically to fit your budget requirements.

Issue 1.0, November 2009