Highway Engineering -II

Chapter 2

Types of PavementTypes of Joints in Rigid Pavement

2

Learning Outcome

� design road pavement structure using various design methods and computer software applications.

3

What is a Pavement ?

To transport people and goods smoothly, safely and in a most economical manner.

The thickness of each layer must be adequate to ensure that the applied loads will not lead to distress in the surface layer or the underlying layers

Highway: vehicles (car, truck, etc.)

Airport: aircrafts

4

Major Pavement Groups

� Pavement for Highways� Freeways and expressways (motorways)

� Rural highways

� Urban and suburban arterial streets

� Pavement for Airports� General aviation airports for short-haul flights not

exceeding 500 miles, such as pilot training, business and agricultural etc.

� Commercial airports for continental and international passengers and cargo flights

� Military airports

5

Roadway and Airport Cross Section

Shoulder varies

24’ pavement

24’ pavement

Median varies

Shoulder varies

DitchSubbase drain

Base through shoulderStrom

drain

Roadway

Strom drain

x x xTaxiway(20 to 100 ft.) Runway (50 to 200 ft.)

Airport

X : Clearance standards

6

Highway and Airports Pavements

� Weight: (truck: Approx wheel load 6,000 lbs; aircraft: wheel load in excess of 60,000 lbs)

� Number of highway repetitions are greater compared to airports

� Tire pressure of jet aircraft may be as high as 400 psi, whereas for trucks usually less than 120 psi

� Trucks on highways travel 2-3 ft from edge, whereas, traffic on the airfield in concentrated in the center

� Highways traffic more channelized compared to airfields; TW more channelized compared to RW

Types of Pavement

8

Definition of Pavement Types

Flexible

Rigid

Portland Cement Concrete

Base course may or may not be used

Base course

Subbase course

Compacted subgrade

Natural subgrade

Natural subgrade

Prime coat

Tack coatBinder courseSurface

courseSeal coat

9

Pavement Types

� Flexible pavements: called "flexible" since the total pavement structure bends (or flexes) to accommodate traffic loads. Generally surface is asphalt layer.

� Rigid pavements: PCC has a high modulus and rigidity and do not flex appreciably. Generally surface is Portland cement concrete.

� Composite pavement: Composite pavements are combination HMA and PCC pavements. They are usually result of pavement rehabilitation (e.g., HMA overlay of PCC pavement).

10

Load Distribution

11

Flexible Pavement Basics

� Total pavement structure deflects or flex under load.� Material layers are usually arranged in order of

descending load bearing capacity.� Load distribution between layers.

12

Surface Course

� Layer in contact with traffic loads and normally contains the highest quality materials.

� Provides friction, smoothness, noise control, rut and shoving resistance, and drainage

� Prevent the entrance of excessive quantities of surface water into the underlying base, subbase and subgrade.

� Also used as replaceable layer before damage transfer to lower layers.

Corrugation and shoving

13

Intermediate/Binder Course

� This layer provides the bulk of the HMA structure.� Main purpose is to distribute load.

14

Base Course

� Immediately beneath the surface course.� Provides additional load distribution and contributes

to drainage, and frost resistance.� Base courses are usually constructed out of:

� Aggregates can be either stabilized or un-stabilized.

� Durable aggregates that will not be damaged by moisture or frost action.

� Stabilized HMA or CTB (cement treated base) base course provide higher stiffness (required for heavy traffic areas and weak subgrade).

15

Subbase Course

� Its main functions are:

� Minimize the intrusion of fines from the subgrade

� Improve drainage

� Minimize frost action damage

� Provide a working platform for construction

� The subbase generally consists of lower quality materials than the base course

� Pavement constructed over a high quality, stiff subgrade may not need subbase course.

� For poor subgrade, subbase course may consist of high quality fill used to replace poor quality subgrade.

16

Subgrade

� Existing soil or natural ground level.� Mostly cohesive material have low permeability.� Pavement layered structure is provided to protect the

subgrade from excessive deformations that result in pavement distress (mainly rutting).

� Top 12 inches (30 cm) are usually compacted to provide a working platform for the pavement structure.

17

Rigid Pavement Basics

� Structure deflects very little because of High Modulus of Elasticity

� Composed of PCC layer with or without base layer� Load is distributed over a wide area with one or two

structural layers� Basic structural elements:

� Surface course

� Base course

� Subbase course

18

PCC – Surface Course

� Layer in contact with traffic loads and is made of PCC� Provides characteristics such as friction, smoothness,

noise control and drainage� Serves as a waterproofing layer to the underlying

base, subbase and subgrade� Vary in thickness but is usually between 6 inches for

light loading and 12 inches for heavy loads and high traffic

19

PCC – Base Course

� It provides:� Additional load distribution

� Contributes to drainage and frost resistance

� Uniform support to the pavement and for construction

� Prevent slab pumping phenomena

� Constructed out of:� Aggregate base/Stabilized aggregate, soil, HMA

� Permeable HMA (high stiffness and good drainage)

� Lean concrete

20

PCC – Subbase Course

� It provides:� Minimize the intrusion of fines from the subgrade into

the pavement structure

� Improve drainage

� Minimize frost action damage

� Provide a working platform for construction.

� Generally consists of lower quality materials than the base course

� Not always needed or used

21

Control of Pumping� Pumping is defined as ejection of water and subgrade soil through joints,

cracks, and the edges of pavement. � Pumping leads to creation of void space.� Corrective measures

� Joint sealing

� Undersealing with asphalt cement

� Muck jacking with soil cement

� Factors responsible for pumping

� Material under slab saturated with free water with poor drainage

� Heavy load repetitions

� Material under slab must be erodible. Erodibility of material depends upon the hydro-dynamic force.

22

Faulting and Pumping Phenomena

� Pumping is defined as ejection of water and subgrade soilthrough joints, cracks, and the edges of pavement. As theweight and volume of traffic increased, pumping began tooccur and the use of granular base course became quitepopular.

� Heavily traveled pavements, use of cement-treated andasphalt-treated base course is common practice.

� The sequence of events leading to pumping includes thecreation of void space under the pavement caused by thetemperature curling of the slab and the plastic deformationof the subgrade, the entrance of water, the ejection of muddywater, enlargement of void space and finally the faulting andcracking.

23

Frost Action

Cap

illar

y Z

one

24

Frost Action

� Frost heave is caused by formation and continuing expansion of ice lenses

� Freezing causes water deficiency and increases capillary tension. Small voids with unfrozen water act as conduits

� Factors for frost action� Soil must be frost susceptible (3% finer than 0.02 mm;

uniform fine sand more than 10% finer than 0.02 mm)

� Supply of water (water table)

� Freezing for a sufficient period of time

25

Frost Action

Fatigue cracking from frost action

Frost susceptible: silt is more frost susceptible than clay because ii has both high capillarity and high permeability. Clay has high capillarity but low permeability.

26

Factors Affecting the Pavement Design

� Design life� Time period for which initially designed pavement structure will

last before any rehabilitation is needed.

� Level of serviceability (LoS) criterion• The design life is the time elapsed as a new, reconstructed or

rehabilitated pavement structure deteriorates from its initial LoS to its terminal level serviceability.

� Reliability� Stands for the probability that any particular type of distress or

their combination will remain below or within the permissible level during the design life.

27

Factors Affecting the Pavement Design� Traffic load

� Wheel load and Repetition of wheel load

� Impact of load

� Position of wheel load (causes localized distress)

� Iron-tyred vehicles

� Climate factors

� Rainfall

� Frost action

� Temperature

� Road geometry

� Horizontal (additional stresses at curved sections)

� Vertical curves

28

Factors Affecting the Pavement Design� Subgrade Properties

� Subgrade strength

� Drainage

� Material Properties for Structural Design

� Coarse aggregates

� Fine aggregates

� Cement (for rigid pavement)

� Properties of cement concrete

� Asphalt binder (typically for flexible pavements)

� Additives such as polymers for asphalt binder modification

29

PCC - Joints

� Joints are purposefully placed discontinuities in a rigid pavement surface course

� Type of joints� Contraction joints

� Expansion joints

� Longitudinal joints

� Construction joints

30

PCC - Joints

31

PCC – Contraction Joints

� Contraction joint is a sawed, formed, or tooled groove in a concrete slab that creates a weakened vertical plane.

� It regulates the location of the cracking caused by dimensional changes in the slab.

� Sawing depth 1/4 - 1/3 of slab � Skewed joints for improved

load transfer

32

PCC - Expansion Joints

� Expansion joint is placed at a specific location to allow the pavement to expand without damaging adjacent structures

� Expansion joint are not typically used today because their progressive closure tends to cause contraction joints to progressively open

� Progressive or even large seasonal contraction joint openings cause a loss of load transfer — particularly for joints without dowel bars

33

PCC – Construction Joint

� Construction joint is a joint between slabs that results when concrete is placed at different times

� They can be transverse and longitudinal construction joints

� Longitudinal constructionjoints also allow slab warping without appreciable separation or cracking of the slabs

34

PCC - Joints

Expansion Joint

Longitudinal Joint

Contraction Joint

35

Load Transfer Across PCC Pavement Joint

http://www.pavementinteractive.org/article/load-transfer/

36

Load Transfer

� "Load transfer" is a term used to describe the transfer (or distribution) load across discontinuities such as joints or cracks.

� Load transfer devices (aggregate interlock, dowel bars, and reinforcing steel).

� Poor load transfer creates high slab deflections, resulting in faulting, pumping and corner breaks.

37

Load Transfer – cont’d

� Efficiency of load transfer depends on:� Temperature (which affects joint opening)

� Joint spacing

� Number and magnitude of load applications

� Foundation support

� Aggregate particle angularity

� Presence of mechanical load transfer devices

38

Aggregate Interlock

� Mechanical interlocking across fractured surfaces along saw cut

� Mainly used for low-volume and secondary road systems

� Inadequate for high traffic(and especially truck)

� Generally, ineffective in cracks wider than about 0.035 inches

39

Dowels Bars

� Steel bars for load transfer without restricting horizontal joint movement (slip at one end).

� Reduces joint deflection (1.25 to 1.5 inches in dia., 18 inches long and spaced 12 inches apart).

� Dowel bars are usually inserted at mid-slab depth

40

Reinforcing Steel

� Reinforcing steel can be used to provide load transfer.� In CRCP (no joints), PCC cracks on its own and the

reinforcing steel provides load transfer across cracks.� Steel is bonded to the PCC on either side of the crack

in order to hold the crack tightly together.� Typically, rigid pavement reinforcing steel consists of

grade 60 (yield stress of 60 ksi.) No. 5 or No. 6 bars.� Steel is about 0.6-0.7% of the pavement x-sect. area.� Placed at slab mid-depth or shallower (at least 2.5

inches of PCC cover for preventing steel corrosion).

41

Tie Bars

� Tie bars are deformed steel bars to hold two slabs together.

� They may provide some minimal amount of load transfer, they are not designed to act as load transfer devices

� Used at longitudinal joints or edge joint and a curb or shoulder.

� Typically, tie bars are about 0.5 inches in diameter and between 24 and 40 inches long.

42

Pavement Types

� Rigid pavements� Jointed plain concrete pavements

� Jointed reinforced concrete pavements

� Continuous reinforced concrete pavements

� Pre-stressed concrete pavements

43

Rigid Pavement Types

� Jointed plain concrete pavement (JPCP)� Most common type of rigid pavement.

� Controls cracks by dividing the pavement up into slabs separated by contraction joints.

� Typically slab length is between 12 ft. and 20 ft. long.

� Does not use any reinforcing steel but does use dowel bars and tie bars.

44

Rigid Pavement Types – cont’d

� Jointed reinforced concrete pavement (JRCP)� Slabs are much longer (as long as 50 ft.) than JPCP slabs.

� Uses reinforcing steel control cracking.

� Continuously reinforced concrete pavement (CRCP)� Uses reinforcing steel for crack control (no contraction

joints)

� Cracks typically appear ever 3.5 - 8 ft. are held tightly together by the underlying reinforcing steel.

45

Jointed Plain Concrete Pavement (JPCP)

46

Jointed Reinforced Concrete Pavement (JRCP)

47

Continuously Reinforced Concrete Pavement (CRCP)

48

Pavement Distress Measure of Performance

Fatigue Cracking

Low temperature cracking

Polished aggregates

Bleeding

Raveling