Ce 4G04 Midterm Review

Front 1

Pavement Types (5)

Back 1

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

Front 2

Flexible Layered Pavement System

Back 2

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

Front 3

Purpose of base/subbase

Back 3

1. Control drainage

2. Protect against frost action/volume change

3. Acts as working surface during construction

4. Increased structural capacity

Front 4

Purpose of AC/PCC Surface

Back 4

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

Front 5

Pros of Layered Pavement System

Back 5

-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)

Front 6

Perpetual Pavement

Back 6

Pros:

Durable, longer lasting

Less fatigue cracking

Less rutting

Smoother pavement

No major reconstruction required

Minimizing service disruption

Cons:

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

Front 7

Multi- (AC) Layer Design

Back 7

Layer 1: renewable surface layer

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

Layer 3: flexible, fatigue-resistant bottom layer

Front 8

Flexible Highway Pavements

Back 8

Surface Layer: thin, smooth, skid resistant

Binder Layer: Large aggregates, strong, rutting resistant

Front 9

Rigid Highway Pavements

Back 9

150-300mm Concrete slab thickness

100-300mm Subbase

Front 10

Types of Rigid Pavement

Back 10

Front 11

Load Transfer of Rigid Pavements

Back 11

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

Front 12

Differences between Flexible and Rigid Pavements

Back 12

Front 13

Interlocking Pavements

Back 13

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

Pros

Existing 'crack' structures, no new cracks

Cons

Slippery when wet

Front 14

Factors influencing pavement performance (5)

Back 14

1. Traffic

-Volume (AADT)

-Distribution (% trucks, aircraft, etc)

-Vehicle load and load distribution

2. Environment

-Precipitation, moisture

-Temperatures/gradients

-Freeze/thaw, wet/dry cycles

3. Material properties of each layer

4. Pavement structure details

5. Maintenance schedule

Front 15

Soil properties for pavement design

Back 15

1. Resilient Modulus

2. Poisson's Ratio

Deformation properties under high number of repeated loads

Front 16

Required soil tests (2)

Back 16

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

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

Front 17

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

Back 17

G - gravel

S - sand

M - silt

C - Clay

O - Organic

Pt - Peat

Front 18

Liquid limit symbols (2)

Back 18

H - high liquid limit (LL>50)

L - low liquid limit (LL<50)

Front 19

Fine Symbols (2)

Back 19

M - non-plastic fines

C - plastic fines

Front 20

Gradation symbols (2)

Back 20

W - well graded

P - poor graded

Front 21

Mechanical properties of soil

Back 21

Stiffness

Coefficient of subgrade reaction, k=p/delta

Poisson's Ratio, v

Resilient Modulus, Mr

CBR

Permanent Deformation Resistance

Front 22

Coefficient of subgrade reaction

Back 22

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

k=p/a=E/118R

**measured at p=6.9kPa OR 10 psi

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

Front 23

Resilient Modulus

Back 23

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

Front 24

Factors affecting resilient modulus (7)

Back 24

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

Front 25

CBR

Back 25

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

Front 26

General Ratings of Soil Quality

Back 26

Front 27

Relationship between CBR and Mr

Back 27

CBR > 10/20

17.6CBR^0.64

CBR < 10/20

10.3CBR

Front 28

Requirements of subgrade (5)

Back 28

1. Sufficient Bearing Capacity

2. Low Deformability

3. Time-independent Properties

4. Non-susceptibility to Environmental Change

5. Good Drainage

Front 29

Effects of Moisture Content on Subgrade

Back 29

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

Increased w/c

1) reduction of strength & stiffness

2) volume expansion

Front 30

Methods of moisture control (8)

Back 30

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

Front 31

Frost heace concequences

Back 31

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

Front 32

Depth of Frost Penetration in Ontario

Back 32

Hamilton: 2' OR 0.6m

Ottawa Valley: 4' OR 1.2m

Northern Ontario: 6/7' oR 2m

Front 33

Design considerations for frost heave (6)

Back 33

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

Front 34

Mud Pumping Required Conditions

Back 34

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

-Free water between slab and subgrade

-Frequent heavy wheel load

Front 35

Mud Pumping Design Consideration

Back 35

Introduce a subbase layer between the rigid slab and the subgrade

Front 36

Role of Granular Base Course (3)

Back 36

1.Provide support to surface layer

2.Drainage Layer

3. Frost Protection

Front 37

Properties of Granular Base Course (3)

Back 37

1. High internal friction angle

2. High permeability

3. Low fines content

Front 38

Unbound Granular Aggregate

Back 38

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

Front 39

RAP

Back 39

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

Front 40

Objectives of Soil Stabilization (8)

Back 40

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

Front 41

Mechanical Methods of Stabalization

Back 41

Front 42

Admixture Stabilization Methods

Back 42

Front 43

Cement Stabilization

Back 43

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

-Cannot be used in presence of sulphate or organic matter

Front 44

Bituminous Stabilization

Back 44

- 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

Front 45

Lime Stabilization

Back 45

- 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

Front 46

Effects of water on flexible pavement (4)

Back 46

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

Front 47

Effects of water on rigid pavement (3)

Back 47

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

2. Fatigue Cracking

3. Failure and collapsing

Front 48

Methods of controlling water in pavements (3)

Back 48

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

Front 49

Surface Prevention (Prevention)

Back 49

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

Front 50

Subsurface Drainage Methods (3) (Removal)

Back 50

Interception Drain

Keep water away

Subgrade Drainage

Hold ground water low

Base Drainage

prevent flooding of base

Through:

i)Drainage Blanket

ii)Longitudinal Drain

iii)Transverse Drain

Front 51

Pavement Distress Categories (5)

Back 51

1. Cracking

2. Potholes

3. Surface deformation

4. Surface Defects

5. Miscellaneous Distresses

Front 52

Flexible Pavement Distresses (

Back 52

1. Alligator/Fatigue Cracking

2. Transverse Cracking

3. Thermal Cracking

4. Joint Reflection Cracking

5. Longitudinal Cracking

6. Top Down Cracking (longitudinal)

Front 53

Alligator/Fatigue Cracking/Wheel Track Cracking

Back 53

- 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

Front 54

Transverse Cracking

Back 54

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

Front 55

Block Cracking (Thermal Cracking)

Back 55

- 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

Front 56

Joint Reflection Cracking

Back 56

- 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.

Front 57

Longitudinal Cracking

Back 57

-cracking occurs parallel to pavement centerline

- causes:

i) Load related (within wheel path)

ii) Poorly constructed pavement (non-wheel

path)

Front 58

Top Down Cracking Causation (longitudinal)

Back 58

-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)

Front 59

Rutting

Back 59

- 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

Front 60

Instability Rutting

Back 60

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

Front 61

Bleeding

Back 61

-excess asphalt binder on the surface of the pavement

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

- results in low skid resistance

Front 62

Slippage

Back 62

-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

Front 63

Shoving

Back 63

-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