Engr. Muhammad Uzair, Executive Engineer C&W Department CPD SEMINAR ON CAUSES OF PREMATURE ROAD FAILURE AND STRATEGIES ADOPTED FOR REPAIR AND RE-HABILITATION By Engr. Muhammad Uzair, Executive Engineer C&W Department November 7, 2012

SEQUENCE OF PRESENTATION IMPORTANCE OF THE SUBJECT CAUSES OF PREMATURE ROAD FAILURE STATEGIES FOR RE-HABILITATION QUESTION & ANSWER SESSION

IMPORTANCE OF THE SUBJECT The Seminar on the subject will help: TO SENSITIZE THE ROAD ENGINEERS AGAINST THE POTENTIAL CAUSES OF ROAD FAILURE AND TO ACQUAINT THEM WITH APPROPRIATE REMEDIAL TOOLS TO IMPART AWARNESS REGARDING THE MENACE OF OVER- LOADING AND AXLE CONTROL REGIME TO CONCENTRATE MORE ON DESIGN & QUALITY ISSUES FOR PRESERVATION OF PRECIOUS ROAD NETWORK

CAUSES OF PREMATURE ROAD FAILURE

MAJOR CAUSES OF PREMATURE ROAD FAILURE Following are the major causes of Premature road failure: IN-ADEQUATE PAVEMENT DESIGN FAULTY CONSTRUCTION IMPEDED DRAINAGE OVER-LOADING LACK OF PROPER & TIMELY REPAIR

IN-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 material Incorrect selection of design parameters like serviceability indices, Reliability, and drainage coefficient etc.

FAULTY 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 materials Poor workmanship. In-adequate Compaction of various pavement layers Deviation from specified construction methodology

IMPEDED DRAINAGE Surface 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 road fabrics and break it up. Freezing & Thawing phenomena during winter season further aggravate the situation. Eventually, the water descends into the Subgrade layer, lowers its CBR and results into the deep seated road failure.

OVER-LOADING The 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 the damaging factor used in the pavement design has a 4th degree exponential effect. This phenomenon results into severe rutting under the wheel track particularly during hot weather. The over-loading needs to be checked through an effective Axle control regime as this menace itself is sufficient for destruction of an ideal road

LACK 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) Rutting Shoving Raveling Bleeding Potholes & Patches

SRATEGIES FOR REPAIR & REHABILITATION

SRATEGIES 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 road Type and volume of traffic Material availability Economic considerations Before discussing various repair techniques, lets through some light on the types of Distresses.

TYPES OF ROAD FAILURE The following distresses usually develop in flexible pavements due to premature road failure : Cracking (Alligator, Longitudinal and Transverse cracks) Rutting Settlement Shoving Raveling Fretting Bleeding Potholes & Patches Details of these failures and their repair/ re-habilitation are mentioned in the next slides:-

CRACKING 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 Cracking These 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 Cracking These cracks are formed parallel to the road centerline; caused usually due to fatigue action or faulty construction joint. Transverse Cracking These 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.

Longitudinal Crack

Transverse Crack

Alligator Crack

Alligator Cracking

Block Cracking

RUTTING Rutting is of two types: Rutting is caused due to: Rutting usually occurs under the wheel track during hot weather when the Asphalt concrete in the wheel path softens and displaces to both sides forming longitudinal humps and depressions along the traffic flow. The rutted area should be removed and reconstructed with the required pavement layers according to its severity. Rutting is of two types: Mix Rutting Subgrade Rutting Rutting is caused due to: Over loading Excessive mineral filler High Asphalt content Deficiency of angular aggregate in the mix Insufficient compaction of HMA layers during construction.

QUESTIONS ?

SETTLEMENT This 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. SHOVING It 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.

SHOVING

COLD MILLING

COLD MILLING

COLD MILLING ON MARDAN –SWABI ROAD

TACK COAT APPLIED TO MILLED SURFACE

FILLING OF MILLED SURFACE WITH ASPHALT CONCRETE

RAVELING This 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) BLEEDING It 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.

FRETTING 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 & PATCHES Small 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.

Extensive Cracking and potholes

CRACK SEALS Crack 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 SEALS A 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.

SLURRY SEALS A 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 the addition of polymers for specialized cases; the process being called Micro surfacing.

BITUMINOUS 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 increased reflective 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.

BITUMINOUS SURFACE TREATMENT (BST)

SUMMARY OF FAILURES, CAUSES AND CURES S.No Type of Failure Causes Cures 1 Cracking Fatigue 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. 2 Rutting In-adequate pavement design, Excessive mineral filler, high asphalt content, in-adequate compaction and over-loading Cold milling and relaying of fresh HMA layers OR Bituminous Surface Treatment (BST) 3 Settlement Faulty pavement design, Sub-standard materials, impeded drainage and in-adequate compaction Removal of damaged layers and reconstruction as per fresh pavement design 4 Shoving Traffic action and faulty JMF 5 Raveling Dust coating on aggregate, segregation of aggregate, Sub standard asphalt binder and in-adequate compaction Bituminous Surface Treatment (BST) with single or double coats as per surface condition 6 Fretting Dust coating on aggregate, Sub standard asphalt binder and in-adequate compaction 7 Bleeding Excessive Asphalt content in HMA, excessive application of binder in BST or low HMA air voids Sand blotting OR in severe cases the excessive Asphalt is removed through motor grader and surface rectified through BSTs. 8 Potholes & Patches Final result of Alligator cracking or sometimes due to utility cuts. Filling of potholes with Base and Asphalt as needed.   40

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