Highway Materials

8/11/2009

SE URBAN 2007-8 Class notes and slides on: Highway Materials Highway Construction and Highway Maintenance

Soil properties and Classification „ „ „ „ „

Highway Materials „ „ „

Soil Aggregates Bitumen

Soil Types

Soil Formation Soil Types Particle Size Analysis and Grading Characteristics Physical Properties of Soils Engineering classification of soils

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Particle Size Analysis

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PHYSICAL PROPERTIES OF SOIL

Classification

1.Soil Texture 2.Soil Structure 3.Bulk Density 4.Pore Space 5.Soil Temperature

Das, 1998

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Crushed stone (aggregate)

AGGREGATES „

Aggregate" is a collective term for the mineral materials such as sand, gravel and crushed stone that are used with a binding medium (such as water, water bitumen, bitumen portland cement, cement lime, etc.) to form compound materials (such as asphalt concrete and portland cement concrete). By volume, aggregate generally accounts for 92 to 96 percent of HMA and about 70 to 80 percent of portland cement concrete. Aggregate is also used for base and subbase courses for both flexible and rigid pavements

Aggregates Types - Gravel ƒ Naturally occurring, water born pieces of rock, in buried or current stream beds „ Normally rounded with smooth surfaces, other properties dependent on parent rock „ Crushed gravel is larger gravel particles that have been reduced in size by a crusher „ May be washed to remove undesirable material „ May be screened to divide into desired size groupings

Aggregates Types - Sands 9ƒ Naturally occurring, water or wind born pieces of rock in buried or current stream beds or dunes

9§ Often rounded with smooth surfaces, other properties dependent on parent rock 9§ May be washed to remove undesirable material 9§ May be screened to divide into desired size groupings

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Classification of Natural Aggregates „ „ „

In accordance with size In accordance with sources: In accordance with unit weight

In accordance with size „

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In accordance with sources 1. Natural Mineral Aggregates - Sand, gravel, and crushed rock derived from natural sources. (a) Igneous Rocks - Granite, basalt: hard, t tough, h strong t ®E Excellent ll t aggregates t (b) Sedimentary Rocks - about 80% of aggregates; Natural sand and gravel) Limestone, sandstone ® Excellent to poor (c) Metamorphic Rocks -. „ Marble, schist, slate ® Excellent to poor

Coarse aggregate: Aggregates predominately retained on the No. 4 (4.75 mm) sieve. For mass concrete, the maximum size can be as large as 150 mm. Fine aggregate (sand): Aggregates passing No.4 (4.75 mm) sieve and predominately retained on the No. 200 (75 mm) sieve.

Aggregate Production „

Aggregates are produced in a quarry or mine whose basic function is to convert in situ rock into aggregate with specified characteristics. h Usually ll the h rockk is blasted bl d or dug from the quarry walls then reduced in size using a series of screens and crushers. Some quarries are also capable of washing the finished aggregate.

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Sand and gravel excavation.

CRUSHING The first steps of processing begins after the extraction from quarry or pit. Many of these steps also are common to recycled materials, clay, and other manufactured aggregates. The first stage in most operations is the reduction and sizing by crushing. Some operations, however, provide a step prior to crushing called scalping.

Surge pile.

GRADATION CONTROL The best technique for gradation control is screening. Screening can be done wet or dry, depending on the kind of aggregate being processed and the degree of consistency needed for each product. Washing, for example, may be necessary to clean a concrete aggregate, but it may not be needed for hot mix asphalt products, which can contain more fines. For gradation control alone, however, a producer may come to realize that gradation consistency can only be maintained by using wet screening, especially for the hot mix asphalt products. Gradation consistency is usually an overriding factor for a hot mix asphalt customer. Water volume and flow direction are critical in wet screening.

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Screening. SAND PRODUCTION Sand plays a critical role as a construction aggregate and it deserves special attention when considering the means of process control. Unlike coarse aggregate where various types of crushers can be used to upgrade mineral quality quality, sand basically relies on the same techniques to address both mineral quality and sizing. These techniques are called particle exclusion.Whichever size the producer decides to eliminate for quality reasons obviously also will affect sizing.

NATURAL SAND Good quality natural sand is readily available in many areas and may be easy to obtain and process. As with the gravels that they often accompany,the sand deposits may not have been laid uniformly uniformly, meaning a potential change in quality and size is possible. In some deposits, sand found below the water table differs in fines content and quality from that found above the water table. Subsurface drilling, sampling, and testing is necessary to know to what degree and where these differences occur.

PAVING ASPHALTS Origins, properties, manufacture and use

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Sources and Manufacture of Asphalt „

Sources „ „

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natural asphalt crude oil

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Asphalt manufacture „ „

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Composition and Structure of Asphalt

distillation extraction modification cracking processes

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- oxidation -

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Physical and chemical character of asphalt is determined by: „ composition of crude oil „ method of crude oil and asphalt processing Asphalt: complex, multicomponent, colloidal system Asphalt is composed of a multitude species which differ by: „ molecular mass, chemical structure, polarity Molecular mass between 400 - 3000 D Carbon skeleton: 25 - 150 atoms

Paving asphalt represents 3 ~ 4 % of the total annual crude oil throughput in USA and Canada

Composition and Structure of Asphalt (Cont’d) „

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Composition varies considerably among asphalts manufactured from different crude oils The largest portion of paving asphalts are produced as vacuum residues with the cut point between 425°C and 565°C

Specifications of Paving Asphalts „

The role of specifications: „

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specify properties that directly reflect asphalt behaviour express these properties in physical units provide limits for those properties to exclude poor performing f products provide information from which the service performance can be predicted

Important properties of asphalt: „ „ „

mechanical adhesive durability

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Classical Penetration- Based Specification

Specifications of Paving Asphalts (Cont’d) „ Conventional tests used for asphalt characterization: „

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Penetration Grade

Ageing characteristics: „

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REQUIREMENTS FOR ASPHALT CEMENT FOR USE IN PAVEMENT CONSTRUCTION ASTM D946

penetration, ductility, softening point R&B, flash point, spot test, Fraass breaking point….. Thin Film Oven Test, Rolling Thin Film Oven Test, Pressure Aging Vessel…

Rheological tests: „

Bending Beam Rheometer, Direct tension Test, Dynamic Shear Rheometer

Penetration @ 77°F(25°C) 100g, 5s

40-50

60-70

85-100

120-150

200-300

Min Max

Min Max

Min Max

Min Max

Min

Max

40

50

60

70

85

100

120

150

200

300

Flash Point, °F (Cleveland open cup)

450

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450

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450

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425

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350

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Ductility at 77°F (25°C) 5cm/min, cm

100

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100

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100

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100

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100A

Solubility in trichloroethylene, % Retained penetration after thin-film oven test, % Ductility at 77°F (25°C) 5cm/min, cm after thin-film oven test A

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99

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99

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99

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99

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99

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55+

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52+

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47+

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42+

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37+

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50

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75

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100

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100A

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If ductility at 77°F (25°C) is less than 100 cm, material will be accepted if ductility at 60°F (15.5°C) is 100 cm minimum at the pull rate of 5 cm/min

The Road Construction Process „

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Highway Construction

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The type of road construction used varies from one job to another. The type of construction adopted for a particular road depends on: the volume and nature of traffic to use the road, the nature of the materials available, the topography, foundation conditions, type and availability of construction equipment, and financing arrangements and timing.

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The Road Construction Process „

Any road construction job consists of number of basic steps, although the relevant importance and the interaction between these steps will vary from job to job. These steps can be summarized as: „ planning, programming and pre-construction activities; „ site clearance; „ setting out; „ earthworks; „ bridge construction; „ drainage structures; „ pavement construction; „ placement of road surfacing; „ placement of road furniture; and „ landscaping.

Sequence of Operations „

The normal sequence of operations in cut and fill work is: „ In Cut „ excavate to the depth necessary to reach formation level, „ transport away from the site undesirable material such as o ganic soils, organic soils „ haul suitable materials from cuts to fill areas, and „ suitably dispose of any excess cut material. „ In Fill „ drain water from depressions and dispose of any unsuitable underlying material, „ spread fill material in horizontal layers not more than 250 mm thick, and „ thoroughly compact these layers to required density.

Earthworks „

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The eventual aim of the earthworks phase of the construction is to position the subgrade underlying the pavement layers in the right location and at the correct level, and to provide drainage. The operations to be performed are: „ formation f ti off cuttings tti b by excavating ti th through h hi high h ground, d „ formation of embankments by filling over low ground, „ shaping the finished surface to design levels, and „ excavating for drainage works. The earthworks is often the largest task in the road building process and therefore careful planning and organisation are essential. Speed and efficiency depend very much upon the quantity and types of earthmoving plant available.

NED roadwork-11 Aug 2009

Subgrade prepared

Base course materials stacked

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Pavement Construction „

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Gravel and Crushed Rock Pavements „ Source: pits,quarries. „ Haulage: trucks. „ Spreading: grader or paver. „ Compaction: higher compaction standard than subgrade; different roller types used. „ Accuracy of levels important. Asphalt Pavements „ Manufacture: fixed plants (up to 400 tonnes per hour), or large mobile plants. „ Haulage: trucks. „ Placement: paving machine. „ Compaction: rollers - smooth vibrating drum and pneumatictyred. „ Usually final layer thin to achieve good riding surface.

Placement of Road Surfacing May be gravel, sprayed bituminous seal, asphalt or cement concrete. Construction of Sprayed Bituminous Surfacing „ Pavement must be sound. For new work: compaction and trimming of underlying gravel or crushed rock pavement. For existing bituminous surface: patching. Steps: „ Sweep surface - drawn rotary broom + hand sweeping. „ Prepare binder - transport to job by road or rail tanker, or in drums. „ Flux and/or cutback binder. „ Incorporate adhesion agent. „ Prepare aggregate - stockpiles, precoating

Pavement Construction „

Cement Concrete Pavements „ Manufacture: ready-mixed batching plant. „ Haulage: agitator truck. „ Large quantities: site manufacture + normal trucks. „ Placement: slip-form paver. „ Compaction: internal vibrators + external screeds screeds.

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Spray binder - air temperature should be > 15 C; no rain should be threatening; mark out spray runalignment and start and finish. Apply aggregate - quick incorporation into hot bitumen before excessive cooling; spreaders required; drag broom to correct spreading inconsistencies. Roll surface - to bed stone; pneumatic-tyred or static steel drum rollers. D Drag b broom Record work - quantities bitumen sprayed, aggregate spread, etc. Traffic control - throughout steps 1 to 10; minimise traffic delays.

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Preparation for a Sprayed Bituminous Surfacing Left: Sweeping a gravel pavement prior to the application of a prime. Sweeping is usually carried

out with drawn mechanical brooms, although some hand sweeping is often required as well.

Construction of HMA Road

Preparation for a Sprayed Bituminous Surfacing Right: Damping the pavement. It is found that a

prime or seal will adhere better to an underlying gravel pavement if the pavement is slightly damp.

Left: A bitumen road tanker. Transport of bitumen to the job site will usually be by rail tanker or road tanker.

Asphalt Production Right: Batching Plant, Toowoomba. The mix falls through a series of inclined vibrating screens and the various size fractions are stored in hot storage bins. The plant operator then weighs out the correct proportions of each size for a single batch. The sizes are mixed and then the required amount of hot bitumen is added and mixing continued. The batch is then discharged from the mixer into a waiting truck, and the batching process repeated. Left: Hot Storage Bins, Brisbane Plant. In the Brisbane plant, the batches of hot mix are stored in insulated storage bins, and this means that arriving trucks can be filled more rapidly.

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Asphalt Paving.

Left: Paving Machine, Front View.

This is a view of the front of a typical self-propelled, floating screed, paving machine. Tip trucks discharge the hot asphalt into the front hopper and it is then conveyed to the rear of the machine by a chain and slat conveyor.

Right: Paving Machine, Rear View.

This picture shows a truck with its tray tipped, discharging mix into the paver. The operator sits on top and steers the machine to the required alignment.

Construction of RCC Road

Asphalt Paving. Right: Screed Unit. The screed unit consists of levelling arms, a screed plate which vibrates to act as a tamper, and thickness controls. It is supported d by b the h mix i which hi h gives i it i a floating action. Left: Reference Beam Attached to Paver. A long moving reference

beam, mounted on shoes (or skis) can be used to ensure the screed follows a smooth line regardless of irregularities in the surface being paved.

Construction of RCC Road

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Construction of RCC Road

Dowel bars location

Placement of dowels and tie bars

PCC thickness

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Roofing paper

Tie bars

Roofing paper-1

Dowel basket

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Placement of reinforcement

Forms, Steel form

Dowels images

Wooden Form

Figure 7.113: Steel Forms

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Removal of Form

Vibrator

75% Time 40% Quality Drop

Highway Maintenance Surface Distresses

40% Quality Drop

Each Rs.1000 of R Renovation ti Cost C t Here… Will Cost Rs.4000 to Rs.5000 if Delayed to Here

17% Time Years

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Surface Distress „

According to the HAPI Pavement Guide start with „ „ „

Fracture (e.g., cracking, spalling) Distortion (e.g., deformations) Disintegration (e.g., stripping, raveling)

Surface Distress ASTM E1778 Standard Terminology Relating to Pavement Distress „ „ „ „ „

Alligator cracking Bleeding Block cracking Corrugations Edge cracking

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Oil spillage Polished aggregate Potholes Raveling Reflection cracking Rutting

Surface distress „

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2.

3.

Surface distress is "Any indication of poor or unfavorable pavement performance or signs of impending failure; any unsatisfactory performance of a pavement short of failure" (Highway Research Board, 1970). Surface distress modes can be broadly classified into the following three groups: Fracture. This could be in the form of cracking or spalling resulting from f such things as excessive loading, fatigue, thermal changes, stripping, slippage or contraction. Distortion. This is in the form of deformation, which can result from such things as excessive loading, creep, densification, consolidation, swelling, or frost action. Disintegration. This is in the form of stripping or raveling, which can result from such things as loss of bonding, chemical reactivity, traffic abrasion, aggregate degradation or binder aging.

Alligator cracks are interconnected cracks, forming a series of small blocks resembling an alligator’s skin. This occurs when the sub-base gravel fails to provide adequate support for the asphalt pavement. It is also known as fatigue cracking, and repeated heavy loads and moisture create excess flexing of the surface. NO Defects

Low

Med

High

Low

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Med

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High

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Alligator Cracking „

Potholes arise when the wearing surface disintegrates under traffic, due to inadequate structural strength in one or more layers of the pavement. They are bowl-shaped voids and are often located in areas of poor drainage. Patches are portions of pavement that have been removed and replaced, usually to repair defects in the pavement. Problems occur when the patches crack, settle, or distort. NO

Defects

GOOD

(0)

FAIR

(2)

POOR

(5)

Alligator/Fatigue

ALLIGATOR Cracking „

Problem: Roughness, indicator of structural failure, cracks allow moisture infiltration into the base and subgrade, eventually results in potholes and pavement disintegration if not treated.

A series of interconnected cracks caused by fatigue failure of the HMA surface under repeated traffic loading. As the number and magnitude of loads becomes too great, longitudinal cracks begin to form (usually in the wheelpaths). h l th ) After Aft repeated loading, these longitudinal cracks connect forming many-sided sharpangled pieces that develop into a pattern resembling the back of an alligator or crocodile.

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Possible Causes: Inadequate structural support for the given loading, which can be caused by a myriad of things. A few of the more common ones are: Decrease in pavement load supporting characteristics Probably the most common reason is a loss of base, subbase or subgrade support from things like poor drainage or spring thaw. Water under a pavement will generally cause the underlying materials to become weak. Stripping on the bottom of the HMA layer. The stripped depth contributes little to pavement strength so the effective HMA thickness decreases. Increase in loading (i.e., the pavement is being loaded more heavily than anticipated in design) Inadequate structural design (i.e., the pavement was designed too thin for the anticipated loads) Poor construction (i.e., inadequate compaction)

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Alligator Cracking „

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Alligator Cracking

Repair: A fatigue cracked pavement should be investigated to determine the root cause of failure. Any investigation should involve digging a pit or coring the pavement to determine the pavement's structural makeup as well as determining whether or not subsurface moisture is a contributing factor. Once the characteristic alligator pattern is apparent, repair by crack sealing is generally ineffective. Fatigue crack repair generally falls into one of two categories:

Small, localized fatigue cracking indicative of a loss of subgrade support. Remove the cracked pavement

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Large fatigue cracked areas indicative of general structural failure. Place an HMA

overlay over the entire pavement surface. This overlay must be strong enough structurallyy to carryy the anticipated p loading g because the underlying fatigue cracked pavement most likely contributes little or no strength (Roberts et. al., 1996).

area then dig out and replace the area of poor subgrade and improve the drainage of that area if necessary. Patch over the repaired subgrade.

Block Cracking Edge cracks are approximately 1ft from the road edge. Normally they are caused by lack of shoulder support, or by the settlement of the material under the edge. This can indicate poor drainage, frost heaves, or shrinkage of the surrounding earth.

NO Defects

Low

Med

High

Low

1

2

3

Med

4

5

6

High

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8

9

Description: Interconnected cracks that divide the pavement up into rectangular pieces. Blocks range in size from approximately 1 ft2 to 100 ft2. Larger blocks are generally classified as longitudinal and transverse cracking. g Block cracking g normally occurs over a large portion of pavement area but sometimes will occur only in non-traffic areas. Problem: Allows moisture infiltration, roughness Possible Causes: HMA shrinkage and daily temperature cycling. Typically caused by an inability of asphalt binder to expand and contract with temperature cycles because of: Asphalt binder aging Poor choice of asphalt binder in the mix design

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Corrugation and Shoving

Block Cracking „

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Repair: Strategies depend upon the severity and extent of the block cracking: Low severity cracks (< 1/2 inch wide). Crack seal to prevent (1) entry of moisture into the subgrade through the cracks and (2) further raveling of the crack edges. HMA can provide years of satisfactory service after developing small cracks if they are kept sealed (Roberts et. al., 1996).

High severity cracks (> 1/2 inch wide and cracks with raveled edges). Remove and replace the cracked pavement layer with an overlay.

Description: A form of plastic movement typified by ripples (corrugation) or an abrupt wave (shoving) across the pavement surface. The distortion is perpendicular to the traffic direction. Usually occurs at points where traffic starts and stops ((corrugation) g ) or areas where HMA abuts a rigid object (shoving). Problem: Roughness Possible Causes: Usually caused by traffic action (starting and stopping) combined with: An unstable (i.e. low stiffness) HMA layer (caused by mix contamination, poor mix design, poor HMA manufacturing, or lack of aeration of liquid asphalt emulsions) Excessive moisture in the subgrade

Depression

Corrugation and Shoving „

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Repair: A heavily corrugated or shoved pavement should be investigated to determine the root cause of failure. Repair strategies generally fall into one of two categories:

Small, localized areas of corrugation or shoving. Remove the distorted pavement

and patch. „

Large corrugated or shoved areas indicative of general HMA failure. Remove the

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Description: Localized pavement surface areas with slightly lower elevations than the surrounding pavement. Depressions are very noticeable after a rain when they fill with water. Problem: Roughness, depressions filled with substantial water can cause vehicle hydroplaning

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Possible Causes: Frost heave or subgrade settlement resulting from inadequate compaction during construction. construction Repair: By definition, depressions are small localized areas. A pavement depression should be investigated to determine the root cause of failure (i.e., subgrade settlement or frost heave). Depressions should be repaired by removing the affected pavement then digging out and replacing the area of poor subgrade. Patch over the repaired subgrade.

damaged pavement and overlay.

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Longitudinal Cracking Depression

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Description: Cracks parallel to the pavement's centerline or laydown direction. Usually a type of fatigue cracking. Problem: Allows moisture infiltration, roughness, indicates possible onset of fatigue cracking and structural failure. Possible Causes: „ Poor joint construction or location. Joints are generally the least dense areas of a pavement. Therefore, they should be constructed outside of the wheelpath so that they are only infrequently loaded. Joints in the wheelpath like those shown in third through fifth figures above, will general fail prematurely. „ A reflective crack from an underlying layer (not including joint reflection cracking) „ HMA fatigue (indicates the onset of future fatigue cracking) „ top-down cracking

Longitudinal Cracking „

Longitudinal Cracking

Repair: Strategies depend upon the severity and extent of the cracking: „

Low severity cracks (< 1/2 inch wide and q cracks)). Crack seal to p prevent (1) ( ) infrequent

entry of moisture into the subgrade through the cracks and (2) further raveling of the crack edges. HMA can provide years of satisfactory service after developing small cracks if they are kept sealed (Roberts et. al., 1996).

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High severity cracks (> 1/2 inch wide and numerous cracks). Remove and replace the cracked pavement layer with an overlay.

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Patching „

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Description: An area of pavement that has been replaced with new material to repair the existing pavement. A patch is considered a defect no matter how well it performs.

Patching

Problem: Roughness Possible Causes: Previous localized pavement deterioration that has been removed and patched Utility cuts Repair: Patches are themselves a repair action. The only way they can be removed from a pavement's surface is by either a structural or non-structural overlay

Polished Aggregate „

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Description: Areas of HMA pavement where the portion of aggregate extending above the asphalt binder is either very small or there are no rough or angular aggregate particles.

Polished Aggregate

Problem: Decreased skid resistance Possible Causes: Repeated traffic applications. Generally, as a pavement ages the protruding rough, angular particles become polished. This can occur quicker if the aggregate is susceptible to abrasion or subject to excessive studded tire wear. Repair: Apply a skid-resistant slurry seal or BST or overlay.

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Potholes

Potholes Description: Small, bowl-shaped depressions in the pavement surface that penetrate all the way through the HMA layer down to the base course. They generally have sharp edges and vertical sides near the top of the hole. Potholes are most likely to occur on roads with thin HMA surfaces (1 to 2 inches) and seldom occur on roads with 4 inch or deeper HMA surfaces (Roberts et al., 1996).

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Problem: Roughness (serious vehicular damage can result from driving across potholes at higher speeds), moisture infiltration Possible Causes: Generally, potholes are the end result of fatigue cracking. As fatigue cracking becomes severe, the interconnected cracks create small chunks of pavement, which can be dislodged as vehicles drive over them. The remaining hole after the pavement chunk is dislodged is called a pothole. Repair: In accordance with patching techniques

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Raveling „

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Description: The progressive disintegration of an HMA layer from the surface downward as a result of the dislodgement of aggregate particles. Problem: Loose debris on the pavement, roughness, water collecting in the raveled locations resulting in vehicle hydroplaning, loss of skid resistance Possible Causes: Loss of bond between aggregate particles and the asphalt binder as a result of: A dust coating on the aggregate particles that forces the asphalt binder to bond with the dust rather than the aggregate Aggregate segregation. If fine particles are missing from the aggregate matrix, then the asphalt binder is only able to bind the remaining coarse particles at their relatively few contact points. Inadequate compaction during construction. High density is required to develop sufficient cohesion within the HMA. Mechanical dislodging by certain types of traffic (studded tires, snowplow blades or tracked vehicles).

Raveling „

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Repair: A raveled pavement should be investigated to determine the root cause of failure. Repair strategies generally fall into one of two categories: Small, localized areas of raveling. Remove the raveled pavement and patch. Large raveled areas indicative of general HMA failure. Remove the damaged pavement and overlay

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Rutting

Description: Surface depression in the wheel path. Pavement uplift (shearing) may occur along the sides of the rut. Ruts are particularly evident after a rain when they are filled with water. There are two basic types of rutting: mix rutting and subgrade rutting. Mix rutting occurs when the subgrade does not rut yet the pavement surface exhibits wheel path depressions as a result of compaction/mix design problems. Subgrade rutting occurs when the subgrade exhibits wheel path depressions due to loading. loading In this case case, the pavement settles into the subgrade ruts causing surface depressions in the wheel path. Problem: Ruts filled with water can cause vehicle hydroplaning, can be hazardous because ruts tend to pull a vehicle towards the rut path as it is steered across the rut.

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Rutting „

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Rutting „

Possible Causes: Permanent deformation in any of a pavement's layers or subgrade usually caused by consolidation or lateral movement of the materials due to traffic loading. Specific causes of rutting can be: Insufficient compaction of HMA layers during construction. If it is not compacted enough initially, HMA pavement may continue to densify under traffic loads. Subgrade rutting (e.g., as a result of inadequate pavement structure) Improper mix design or manufacture (e.g., excessively high asphalt content, excessive mineral filler, insufficient amount of angular aggregate particles) Ruts caused by studded tire wear present the same problem as the ruts described here, but they are actually a result of mechanical dislodging due to wear and not pavement deformation.

RUTTING

Repair: A heavily rutted pavement should be investigated to determine the root cause of failure (e.g. insufficient compaction, subgrade rutting, poor mix design or studded tire wear). Slight ruts (< 1/3 inch deep) can generally be left untreated. Pavement with deeper ruts should be leveled and overlayed.

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Rutting

Slippage Cracking „

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Description: Crescent or half-moon shaped cracks generally having two ends pointed into the direction of traffic. Problem: Allows moisture infiltration, roughness Possible Causes: Braking or turning wheels cause the pavement surface to slide and deform. The resulting sliding and deformation is caused by a low-strength surface mix or poor bonding between the surface HMA layer and the next underlying layer in the pavement structure. Repair: Removal and replacement of affected area.

Transverse (Thermal) Cracking

Slippage Cracking „

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Description: Cracks perpendicular to the pavement's centerline or laydown direction. Usually a type of thermal cracking. Problem: P bl All Allows moisture i infiltration, i fil i roughness h Possible Causes: Shrinkage of the HMA surface due to low temperatures or asphalt binder hardening. Reflective crack caused by cracks beneath the surface HMA layer top-down cracking Repair: Strategies depend upon the severity and extent of the cracking:

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Transverse (Thermal) Cracking „

Transverse (Thermal) Cracking

Low severity cracks (< 1/2 inch wide and infrequent cracks). Crack seal to prevent (1)

entry of moisture into the subgrade through the cracks and (2) further raveling of the crack edges. HMA can provide years of satisfactory service after developing small cracks if they are kept sealed (Roberts et. al., 1996). „

High severity cracks (> 1/2 inch wide and numerous cracks). Remove and replace the cracked pavement layer with an overlay

Water Bleeding and Pumping Description: Water bleeding (left two photos) occurs when water seeps out of joints or cracks or through an excessively porous HMA layer. Pumping (rightmost photo) occurs when water and fine material is ejected from underlying layers through cracks in the HMA layer or out the sides of the HMA layer under moving loads. loads Problem: Decreased skid resistance, an indication of high pavement porosity (water bleeding), decreased structural support (pumping) Possible Causes: •Porous pavement as a result of inadequate compaction during construction or poor mix design •High water table •Poor drainage

Water Bleeding and Pumping Repair: Water bleeding or pumping should be investigated to determine the root cause. If the problem is a high water table or poor drainage, subgrade drainage should be improved. If the problem is a porous mix (in the case of water bleeding) a fog seal or slurry seal may be applied to limit water infiltration

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Water Bleeding and Pumping

Joint Reflection Cracking Description: Cracks in a flexible overlay of a rigid pavement. The cracks occur directly over the underlying rigid pavement joints. Joint reflection cracking does not include reflection cracks that occur away from f an underlying d l i joint j i or from f any other h type of base (e.g., cement or lime stabilized). Problem: Allows moisture infiltration, roughness Possible Causes: Movement of the rigid pavement slab beneath the HMA surface because of thermal and moisture changes. Generally not load initiated, however loading can hasten deterioration.

Joint Reflection Cracking „

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Repair: Strategies depend upon the severity and extent of the cracking:

Joint Reflection Cracking

Low severity cracks (< 1/2 inch wide and infrequent cracks). Crack seal to prevent (1)

entry of moisture into the subgrade through the cracks and (2) further raveling of the crack edges. In general, rigid pavement joints will eventually reflect through an HMA overlay without proper surface preparation. „

High severity cracks (> 1/2 inch wide and numerous cracks). Remove and replace the cracked pavement layer with an overlay.

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