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63 Cards in this Set

  • Front
  • Back

Pavement Types (5)

1. Flexible

Asphalt Concrete (AC)

2. Rigid

Portland Cement Concrete (PCC)

3. Composite

Asphalt + Portland Cement Concrete

Stabilized base/subbase

AC overlay on PCC

4. Interlocking Brick Pavements

5. Unpaved Roads

Flexible Layered Pavement System

1. Surface

Very strong, durable, impermeable manufactured, expensive [75-200mm]

2. Base

Strong, free-draining, manufactured, less expensive USE GRANULAR A, [150-500mm]

3. Subbase

Moderate Strength, free-draining, natural material, inexpensive USE GRANULAR B[150-500mm]

4. Subgrade

Relatively weak, moisture sensitive, in-situ soil

Purpose of base/subbase

1. Control drainage

2. Protect against frost action/volume change

3. Acts as working surface during construction

4. Increased structural capacity

Purpose of AC/PCC Surface

1. To provide a tough, smooth, skid-resistant surface

Pros of Layered Pavement System

-Stronger surface layers sheild weaker base layers.

-Stress at point of loading is very high, as depth increases the stresses decrease (think 2:1 triangle rule)

Perpetual Pavement


Durable, longer lasting

Less fatigue cracking

Less rutting

Smoother pavement

No major reconstruction required

Minimizing service disruption


Higher initial cost - 250-350mm thick HMA vs. traditional <150mm

Multi- (AC) Layer Design

Layer 1: renewable surface layer

Layer 2: strong, rut-resistant, durable intermediate layer

Layer 3: flexible, fatigue-resistant bottom layer

Flexible Highway Pavements

Surface Layer: thin, smooth, skid resistant

Binder Layer: Large aggregates, strong, rutting resistant

Rigid Highway Pavements

150-300mm Concrete slab thickness

100-300mm Subbase

Types of Rigid Pavement

Load Transfer of Rigid Pavements

Due to the rigidity of the concrete, the stress is spread over the surface area of the slab. Whereas in flexible pavement the stress is concentrated at the application point

Differences between Flexible and Rigid Pavements

Interlocking Pavements

Layers: soil subgrade, aggregate base, sand bedding layer, concree paver wearing surface, edge restriants, and drainage structures

Performs as flexible pavement when load is applied


Existing 'crack' structures, no new cracks


Slippery when wet

Factors influencing pavement performance (5)

1. Traffic

-Volume (AADT)

-Distribution (% trucks, aircraft, etc)

-Vehicle load and load distribution

2. Environment

-Precipitation, moisture


-Freeze/thaw, wet/dry cycles

3. Material properties of each layer

4. Pavement structure details

5. Maintenance schedule

Soil properties for pavement design

1. Resilient Modulus

2. Poisson's Ratio

Deformation properties under high number of repeated loads

Required soil tests (2)

1. Sieve Analysis - for coarse grained material, classified by GSD

2. Hydrometer Analysis - fine grained soils, classified by Atterberg Limits

Soil symbols used for unified soil classification system (USCS) [G, S, M, C, O, Pt]

G - gravel

S - sand

M - silt

C - Clay

O - Organic

Pt - Peat

Liquid limit symbols (2)

H - high liquid limit (LL>50)

L - low liquid limit (LL<50)

Fine Symbols (2)

M - non-plastic fines

C - plastic fines

Gradation symbols (2)

W - well graded

P - poor graded

Mechanical properties of soil


Coefficient of subgrade reaction, k=p/delta

Poisson's Ratio, v

Resilient Modulus, Mr


Permanent Deformation Resistance

Coefficient of subgrade reaction

Not a material property, as the coefficient is dependant on the size of the plate


**measured at p=6.9kPa OR 10 psi

**30" (762mm) diameter plate used in test

Resilient Modulus

Measures the elastic modulus of subgrade OR granular base/subbase material

Mr is sensitive to w/c when % of fines increase

Mr=Cyclic Stess/Resilient Strain

Factors affecting resilient modulus (7)

An increase in ________ would result in:

Bulk Stress - Major Increase

Shear Stress - Major Decrease

Broader Grading - Minor Increase

Fines - Decrease

Larger Size - Increase

Density - Increase

Moisture Content - Major Decrease


Provides a measure of a soil's strength/ductility and moisture susceptibility

CBR = Unit load carried by specimen @ 2.5mm /

Load carried by standard crushed rock

CBR = Unit Load (kPa)/6900kPa

General Ratings of Soil Quality

Relationship between CBR and Mr

CBR > 10/20


CBR < 10/20


Requirements of subgrade (5)

1. Sufficient Bearing Capacity

2. Low Deformability

3. Time-independent Properties

4. Non-susceptibility to Environmental Change

5. Good Drainage

Effects of Moisture Content on Subgrade

Expansive soils can cause severe distress on the surface of the pavement

Increased w/c

1) reduction of strength & stiffness

2) volume expansion

Methods of moisture control (8)

Compaction Control Methods

Compact wet of optimum

Maintain material uniformity

Maintain uniform moisture content and compaction

Grading Control Methods

Excavate deep cuts first

Place expansive soils at the bottom of fill

Cross haul less expansive soils for top of subgrade

Cross haul to get uniform subgrade

Stabilize expansive soil with cement/lime

Frost heace concequences

1. heaving of pavement surface caused by formation of Ice Lense

2. Loss of strength with thawing of excess pore water

3. loss of performance due to heaving or weakening of the structure

Depth of Frost Penetration in Ontario

Hamilton: 2' OR 0.6m

Ottawa Valley: 4' OR 1.2m

Northern Ontario: 6/7' oR 2m

Design considerations for frost heave (6)

1. removal of frost susceptible soils (high % silt)

2. Install subdrains to lower water table

3. excavation of soil to frost line & place impermeable seal

4. Install insulating layer to prevent frost penetration

5. Increase void volume/size, via chemical action, to inhibit soil suction

6. Provision of insulating layer

Mud Pumping Required Conditions

-Soils have >45% passing 0.075mm sieve, PL > 6

-Free water between slab and subgrade

-Frequent heavy wheel load

Mud Pumping Design Consideration

Introduce a subbase layer between the rigid slab and the subgrade

Role of Granular Base Course (3)

1.Provide support to surface layer

2.Drainage Layer

3. Frost Protection

Properties of Granular Base Course (3)

1. High internal friction angle

2. High permeability

3. Low fines content

Unbound Granular Aggregate

New Aggregates

Crushed rock, gravel, etc

Recycled material

RAP [Recycled Asphalt Pavement]

RBM [Recycled Bituminous Material]

RAC [Recycled Aggregate Concrete]

Other Materials

Blast furnace slag


Can compose mix of up to 50% if pulverized, usually 20-30% of granular material

Reduces CBR value significantly, however Mr values remain similar

Increasing RAP content will induce large accumulative deformation and rutting

Objectives of Soil Stabilization (8)

1. Increase soil strength

2. Reduce compressibility

3. Reduce moisture susceptibility of fine grained soils

4. Improve properties of borderline materials

Temporary Construction Measures

5. Dust Control

6. Moisture Control

7. Salvage Old Road

8. Construction of superior bases

Mechanical Methods of Stabalization

Admixture Stabilization Methods

Cement Stabilization

- Improve strength, compressibility, expansive characteristics, and reduce frost susceptibility

-Cannot be used in presence of sulphate or organic matter

Bituminous Stabilization

- Used for granular material, not for fines

- Reduces water absorption of soil

- Provides strength and cementation

- Can be used as membrane to control moisure in subgrade or subbase

Lime Stabilization

- Used for fine grained material

- avoid use in claw with low Pl, causes loss of cohesion

- Slow strength gain with time

- Decreases soil density, increases soil strength, and change Pl

Effects of water on flexible pavement (4)

1. Fatigue Cracking

2. Subgrde Rutting

3. Continuous contact with water causes stripping of AC mix and durability cracking of concrete

4. Failure and collapsing

Effects of water on rigid pavement (3)

1. Mud pumping of PCC pavements leading to faulting, cracking and general shoulder deterioration

2. Fatigue Cracking

3. Failure and collapsing

Methods of controlling water in pavements (3)

1. Prevention

sealing the pavement surface

surface drainage

2. Removal

drainage layer of blanket

longitudinal drain

transverse drain

3. Strong pavement section

Use thicker HMA or PCC slab

appropriate improvement of subgrade

soil, granular base/subbase material

Surface Prevention (Prevention)

Pavement & Shoulders

for full width, impervious surface with sealed shoulder

the pavement should be maintained without cracks or holes

Special Mixes

Open graded hot mix can adequately

drain water to the side. Then a transverse

pipe can drain the water away.

Curbs & Dykes

Storm sewers in areas where open channels are not appropriate

Subsurface Drainage Methods (3) (Removal)

Interception Drain

Keep water away

Subgrade Drainage

Hold ground water low

Base Drainage

prevent flooding of base


i)Drainage Blanket

ii)Longitudinal Drain

iii)Transverse Drain

Pavement Distress Categories (5)

1. Cracking

2. Potholes

3. Surface deformation

4. Surface Defects

5. Miscellaneous Distresses

Flexible Pavement Distresses (

1. Alligator/Fatigue Cracking

2. Transverse Cracking

3. Thermal Cracking

4. Joint Reflection Cracking

5. Longitudinal Cracking

6. Top Down Cracking (longitudinal)

Alligator/Fatigue Cracking/Wheel Track Cracking

- caused by fatigue failure of asphalt under repeated traffic loading

- typically occurs in wheel path, but may present itself elsewhere due to vehicle wandering

- begins at bottom of asphalt concrete and propagates to road surface

- caused by fatigue failure of asphalt under repeated traffic loading

- typically occurs in wheel path, but may present itself elsewhere due to vehicle wandering

- begins at bottom of asphalt concrete and propagates to road surface

Transverse Cracking

- perpendicular to pavement centerline, may extend part or fully across travel lane

Block Cracking (Thermal Cracking)

- divides pavement into large rectangular pieces (blocks)

- caused by thermal shrinkage of asphalt binder

- binder age hardening is also related to these cracking types

- not caused by fatigue

Joint Reflection Cracking

- occurs on pavement that have asphalt surfaces over concrete slabs

- cracks occur over transverse and longitudinal joints where pavement was widened

- caused by slab movement beneath asphalt due to thermal and moisture changes

- knowing the dimensions beneath the asphalt concrete surface help identify cracks at joints.

Longitudinal Cracking

-cracking occurs parallel to pavement centerline

- causes:

i) Load related (within wheel path)

ii) Poorly constructed pavement (non-wheel


Top Down Cracking Causation (longitudinal)

-non-uniform vertical loading (contact pressures) resulting in higher surface tensile/shear stresses

-poor/inconsistent hot-mix asphalt quality, production, placement, and compaction

-interlayer slippage or delamination

-thermal stresses

-stiffness gradients within the surface course and between asphalt concrete courses

-premature AC age hardening (binder stiffening)


- characterized by depressions that form in the wheel paths

-stems from deformations occuring in any layer of the pavement/subbgrade

- caused by:

i) compression or lateral movement of materials due to traffic loading

ii) plastic movement of asphalt in hot weather, or poor compaction during construction

Instability Rutting

- failure attributed to mix properties and occurs withing 50mm of the top AC layer


-excess asphalt binder on the surface of the pavement

- caused by high asphalt content, or low air void content

- results in low skid resistance


-characterized by half-moon shaped cracks, pointed into the direction of traffic

- causes:

i) lack of bond between surface layer and underlying layers

ii) excessive deflection of pavement structure

-found in area's of acceleration and decceleration


-longitudinal displacement of a localized area of pavement surface.

-caused by braking or accelerating of vehicles

-seen on hills, curves, at intersections, may result in vertical displacement