Presentation on theme: "Engr. Muhammad Uzair, Executive Engineer C&W Department"— Presentation transcript:
1Engr. Muhammad Uzair, Executive Engineer C&W Department CPD SEMINAR ONCAUSES OF PREMATURE ROAD FAILURE AND STRATEGIES ADOPTED FOR REPAIR AND RE-HABILITATIONByEngr. Muhammad Uzair, Executive Engineer C&W DepartmentNovember 7, 2012
3SEQUENCE OF PRESENTATION IMPORTANCE OF THE SUBJECTCAUSES OF PREMATURE ROAD FAILURESTATEGIES FOR RE-HABILITATIONQUESTION & ANSWER SESSION
4IMPORTANCE OF THE SUBJECT The Seminar on the subject will help:TO SENSITIZE THE ROAD ENGINEERS AGAINST THEPOTENTIAL CAUSES OF ROAD FAILURE AND TO ACQUAINTTHEM WITH APPROPRIATE REMEDIAL TOOLSTO IMPART AWARNESS REGARDING THE MENACE OFOVER- LOADING AND AXLE CONTROL REGIMETO CONCENTRATE MORE ON DESIGN & QUALITY ISSUESFOR PRESERVATION OF PRECIOUS ROAD NETWORK
6MAJOR CAUSES OF PREMATURE ROAD FAILURE Following are the major causes of Premature road failure:IN-ADEQUATE PAVEMENT DESIGNFAULTY CONSTRUCTIONIMPEDED DRAINAGEOVER-LOADINGLACK OF PROPER & TIMELY REPAIR
7IN-ADEQUATE PAVEMENT DESIGN Under-estimation or carelessness in design parameters leads to in-adequate pavement design which results into premature road failure much before the predicted design life.It may be due to :Incorrect traffic count or traffic analysis.Incorrect assessment of Subgrade materialIncorrect selection of design parameters likeserviceability indices, Reliability, and drainagecoefficient etc.
8FAULTY CONSTRUCTION It may be due to: Effective Quality control at the time of construction is the essence of good quality work. The design specification, if not followed in construction as well as in selection of materials, will obviously lead to some type of distress resulting into premature road failure.It may be due to:Use of Sub-standard materialsPoor workmanship.In-adequate Compaction of various pavement layersDeviation from specified construction methodology
9IMPEDED DRAINAGESurface drainage is the most important factor affecting the performance and serviceability of flexible pavement. A well-designed and well-constructed road with poor drainage system will fail much ahead of its design life.Water damage is initially caused by hydraulic pressure.This pressure pushes the water down into the roadfabrics and break it up.Freezing & Thawing phenomena during winter seasonfurther aggravate the situation.Eventually, the water descends into the Subgrade layer,lowers its CBR and results into the deep seated roadfailure.
10OVER-LOADINGThe most dangerous cause of premature road failure is the overloaded vehicles carrying load much heavier than the legal weight anticipated in the pavement design.The failure on this account is usually very fast as thedamaging factor used in the pavement design has a 4thdegree exponential effect.This phenomenon results into severe rutting under thewheel track particularly during hot weather.The over-loading needs to be checked through aneffective Axle control regime as this menace itself issufficient for destruction of an ideal road
13LACK OF PROPER & TIMELY MAINTENANCE One of the basic factors of premature road failure is the lack of proper and timely maintenance. Any distress if not taken care of at initial stage with proper approach will certainly multiply and increase till such time that it will result into complete road failure.The following distresses need timely repair before causing major road failure :Cracking (Alligator, Longitudinal, Transverse & Block cracks)RuttingShovingRavelingBleedingPotholes & Patches
15SRATEGIES FOR REPAIR & REHABILITATION Once the distress is noticed in the road pavement, the same should be repaired immediately with appropriate technique otherwise the damages will multiply with the passage of traffic and subsequent rainy spills.While selecting an appropriate mode of repair or re-habilitation, the following factors should be kept in mind:Type of roadType and volume of trafficMaterial availabilityEconomic considerationsBefore discussing various repair techniques, lets through some light on the types of Distresses.
16TYPES OF ROAD FAILUREThe following distresses usually develop in flexible pavements due to premature road failure :Cracking (Alligator, Longitudinal and Transverse cracks)RuttingSettlementShovingRavelingFrettingBleedingPotholes & PatchesDetails of these failures and their repair/ re-habilitation are mentioned in the next slides:-
17CRACKING Alligator Cracking Longitudinal Cracking Transverse Cracking CRACKING is the most significant distress causing roughness and leading to water infiltration deep into the underlying pavement layers. Cracks should be sealed as soon as possible with appropriate Crack seals, Fog seals or Slurry seals according to their intensity, nature and locations. Cracks are further sub divided into the following categories:Alligator CrackingThese are series of interconnected cracks formed due to fatigue failure of Asphalt surface generally caused by repeated traffic loading. These may be “Bottom –up” or “Top-Down” cracking depending upon the thickness of Asphalt concrete. The cracked area should be cold milled and re-filled with fresh HMA layers.Longitudinal CrackingThese cracks are formed parallel to the road centerline; caused usually due to fatigue action or faulty construction joint.Transverse CrackingThese cracks are formed perpendicular to the road centerline; caused due to shrinkage of Asphalt in low temperatures. Longitudinal and transverse cracks when interconnect, become Block cracking.
23RUTTING Rutting is of two types: Rutting is caused due to: Rutting usually occurs under the wheel track during hot weather whenthe Asphalt concrete in the wheel path softens and displaces to bothsides forming longitudinal humps and depressions along the trafficflow. The rutted area should be removed and reconstructed with therequired pavement layers according to its severity.Rutting is of two types:Mix RuttingSubgrade RuttingRutting is caused due to:Over loadingExcessive mineral fillerHigh Asphalt contentDeficiency of angular aggregate in the mixInsufficient compaction of HMA layers duringconstruction.
26SETTLEMENTThis is the most serious road failure caused due to faulty design, sub-standard construction, poor drainage or excessive over-loading.In this type of failure, the damage extends down to the subgrade bottom. It can be rehabilitated through complete reconstruction only.SHOVINGIt is a form of plastic movement typified by ripples or corrugations visible as an abrupt wave across the pavement surface. The distortion is usually perpendicular to the traffic direction and occurs at points where traffic starts or stops. It is caused by traffic action coupled with poor JMF or mix contamination. It is corrected through cold milling and re-laying of Fresh HMA or resurfacing.
33RAVELINGThis is the progressive disintegration of Bituminous layers as a result of the dislodgement of aggregate particles. It leads to surface roughness due to loose debris on the pavement and loss of skid resistance. Raveling may be treated with appropriate Bituminous Surface Treatment(BST)BLEEDINGIt is the formation of a thin film of Asphalt binder due high Asphalt content commonly observed in hot weather. It usually creates a shiny surface that can become quite sticky. Minor bleeding can often be corrected by applying coarse sand to blot up the excess asphalt binder.Major bleeding can be treated by cutting off excessive asphalt with motor grader. If the resulting surface become excessively rough, resurfacing may be necessary.
34FRETTING POTHOLES & PATCHES This is a phenomenon in which the surface material gradually loose its control with the surface due to ageing or overheated mixture causing premature ageing. It not only causes undulated surface but also invite ponding of water in the fretted out surface. Such type of damage can economically be restored with single or double coat of surface dressing according to its severity.POTHOLES & PATCHESSmall Bowl-shaped depressions in the pavement surface that penetrate all the way through the HMA layers down to the base course are called potholes. They generally have sharp edges and vertical sides near the top. Serious vehicular damage can result from driving across potholes at higher speeds. Potholes are the end result of alligator cracking. For repair, the potholes should be trimmed to geometrical shape and filled with base and/or Asphalt concrete. Interconnected potholes can be combined to form a patch and treated in the same way as that of individual pothole.
36CRACK SEALSCrack seal products are used to fill individual pavement cracks to prevent entry of water or non-compressible substance such as sand, dirt or weeds. Crack sealant is typically used on early stage longitudinal cracks ,transverse cracks ,reflection cracks and block cracks. Alligator cracks are most often too extensive to warrant filling with crack sealer; they usually require an area treatment such as MILL & FILL or reconstruction. Crack filler material is typically some form of rubberized asphalt or sand slurry.FOG SEALSA fog seal is a light application of a diluted slow-setting asphalt emulsion to the surface of an aged(oxidized) pavement surface. Fog seals are low-cost and are used to restore flexibility to an existing HMA pavement surface. They may be able to temporarily postpone the need for a surface treatment or non-structural overlay for an year or two.
37SLURRY SEALSA slurry seal is a homogeneous mixture of emulsified asphalt, water, well-graded fine aggregate and mineral filler that has a creamy fluid-like appearance when applied. Slurry seals are used to fill existing pavement surface defects as either a preparatory treatment for other maintenance treatments or as a wearing course. There are three basic aggregate gradations used in slurry seals:Type I : Fine Slurry Seals (with aggregate size upto 0.25 in)Type II : General Slurry Seals(with aggregate size upto 0.25 in)Type III: Coarse Slurry Seals(with aggregate size upto 0.25 in)The performance of Slurry seals can further be improved with theaddition of polymers for specialized cases; the process being calledMicro surfacing.
38BITUMINOUS SURFACE TREATMENT (BST) Bituminous surface treatment, also known as a seal coat or chip seal, is a thin protective wearing surface that is applied to a pavement or base course. BSTs can provide the following functions:A waterproof layer to protect the underlying pavement.Increased skid resistance.A fill for existing cracks or raveled surfaces.A anti-glare surface during wet weather and an increasedreflective surface for night driving.BST can be Single Surface Treatment (SST), Double Surface Treatment(DST) or Triple Surface Treatment (TST) depending upon the number of coats needed to restore a worn out surface.
40SUMMARY OF FAILURES, CAUSES AND CURES S.NoType of FailureCausesCures1CrackingFatigue failure of HMA, Loss of pavement supporting characteristics and Temperature cycling.Crack seals, Fog seals, Slurry seals or ultimately “MILL & FILL” for severe alligator cracking.2RuttingIn-adequate pavement design, Excessive mineral filler, high asphalt content, in-adequate compaction and over-loadingCold milling and relaying of fresh HMA layers OR Bituminous Surface Treatment (BST)3SettlementFaulty pavement design, Sub-standard materials, impeded drainage and in-adequate compactionRemoval of damaged layers and reconstruction as per fresh pavement design4ShovingTraffic action and faulty JMF5RavelingDust coating on aggregate, segregation of aggregate, Sub standard asphalt binder and in-adequate compactionBituminous Surface Treatment (BST) with single or double coats as per surface condition6FrettingDust coating on aggregate, Sub standard asphalt binder and in-adequate compaction7BleedingExcessive Asphalt content in HMA, excessive application of binder in BST or low HMA air voidsSand blotting OR in severe cases the excessive Asphalt is removed through motor grader and surface rectified through BSTs.8Potholes & PatchesFinal result of Alligator cracking or sometimes due to utility cuts.Filling of potholes with Base and Asphalt as needed.40