01- Rigid pavement Manual

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Pavement Design Manual - 2002 ChapterErreur ! Style non dfini.Volume II - Rigid Pavements Erreur ! Style non dfini.

Ethiopian Roads Authority Page 1

1. INTRODUCTION

The purpose of this Pavement Design Manual - Volume II is to give specific guidance

and recommendations to the engineers responsible for the design of rigid pavements in

Ethiopia. It is one of the series of Design manuals, Standard Contract Documents andSpecifications The preparation of this rigid pavement design manual is part of the

framework initiated by ERA to upgrade the highway network in Ethiopia.

This volume contains :

o A description of rigid pavements : their characteristics, their components and

their function, the different types of slabs and joints, including drawing details.

o A description of the factors influencing the pavement type selection and the

design process.

o A design procedure for the different types of pavement, slab reinforcement, joint

details and joint layout.

The design method is a directly utilizable one, based mainly on empirical results and full

scale experiments. Although an analytical, comprehensive approach to the design is

possible, based on the stresses and strains induced in the pavement by an applied wheel

loading, it is very complicated, rarely used, leads to minor changes and as such is not

covered in these pages.


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2. RIGID PAVEMENTS

2.1 General Characteristics

Rigid pavements (also called concrete pavements), as the name implies, are rigid and

very strong in compression. The strength of the pavement is contributed mainly by a

concrete slab, unlike flexible pavements where successive layers of the pavement

contribute cumulatively. The rugose surface required for an adequate resistance to

skidding in wet conditions can be provided by dragging stiff brooms transversely across

the newly-laid concrete or by cutting shallow randomly spaced grooves in the surface of

the hardened concrete slab.

This constitution implies the following advantages :

o It is feasible to design rigid pavements for longer design lives, up to 60 years.

o Little maintenance is generally requiredo Rigid pavement do not deform under traffic

o A relatively thin pavement slab distributes the load over a wide area due to its

high rigidity. Localized low strength subgrade materials can be overcome due to

this wider distribution area.

o Concrete is very resistant to abrasion making the anti-skidding surface texture

last longer.

o In the absence of deleterious materials (either in the aggregate or entering the

concrete in solution from an external source), unlike with flexible pavements,

concrete does not suffer deterioration from weathering. Neither its strength nor

its stiffness are materially affected by temperature changes.

The main disadvantages compared to flexible pavements are as follows :

o The initial investment is often more costly.

o If badly designed or not properly constructed, they tend to be more troublesome

and reconstruction or repair is more difficult.

Until now, concrete pavements have not been extensively used in most tropical countries

and in Ethiopia in particular, mainly due to a lack of tradition and experience in their

design and construction. One characteristic of concrete pavements is that either they

prove to be extremely durable, lasting for many years with little attention andmaintenance, or they give troubles from the start, sometimes because of faults in design,

but more often because of mistakes in construction.

2.2 Types of Rigid Pavements

Depending on the level of reinforcement, the rigid pavements are categorized into three

basic types:

o Jointed Unreinforced Concrete Pavements (JUCP)

o Jointed Reinforced Concrete Pavements (JRCP)

o Continuously Reinforced Concrete Pavements (CRCP)


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2.2.1 JOINTEDUNREINFORCEDCONCRETEPAVEMENT

In Jointed Unreinforced Concrete Pavements (JUCP), the pavement consists in an

unreinforced concrete slab cast in place continuously and divided into bays of

predetermined dimensions by the construction of joints. The bays dimensions are made

sufficiently short so as to ensure that they do not crack. The bays are linked together by

tie bars, the main function of which is to prevent horizontal movement (i.e. the opening

of warping joints) and thus ensure load transfer through aggregate interlock.

2.2.2 JOINTEDREINFORCED CONCRETEPAVEMENT

In Jointed Reinforced Concrete Pavements (JRCP) the pavement consists generally in a

cast in place concrete slab divided in reinforced concrete bays separated by joints. The

reinforcement is made to prevent developing cracks from opening. This allows to design

much larger bays than with JUCP. The bays are linked together by tie bars to prevent

horizontal movement and thus ensure load transfer through aggregate interlock. The

longitudinal reinforcement is the main reinforcement. A transverse reinforcement though

not absolutely necessary in most cases is usually added to facilitate the placing of

longitudinal bars.

2.2.3 CONTINUOUSLYREINFORCED CONCRETEPAVEMENT

Continuously Reinforced Concrete Pavements (CRCP) are made of a cast in place

reinforced concrete slab without joint. The expansion and contraction movements are

prevented by a high level of sub-base restraint. The frequent transverse cracks are held

tightly closed by a large amount of continuous high tensile steel longitudinal

reinforcement.


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3. PAVEMENT STRUCTURE

Rigid pavements generally consist of, as shown in Figure 1 below, a subbase, and aconcrete slab constructed above the subgrade. (With a capping layer if required)

Figure 1 Rigid Pavement structure

The capping layer consists of selected fill and is provided in cases of low strength

subgrade. It allows to increase the bearing capacity of the subgrade and thus enables a

lesser pavement thickness to be adopted.

The subbase of a rigid pavement structure consists of one or more compacted layers of

material placed between the subgrade and the concrete slab. In some cases the materialcan be cement stabilized to increase its quality. If the subgrade materials quality is

acceptable and if the design traffic is low (less than one million equivalent standard axles

(ESAs)), a subbase layer may not be necessary between the prepared subgrade and the

concrete slab.

A subbase is provided under a concrete pavement for the following reasons:

o to provide a stable working platform for the construction equipment;

o to prevent pumping at joints and slab edges.

The concrete slab consists of Portland cement concrete, reinforcing steel (When

required), load transfer devices and joint sealing materials.

Transverse reinforcement is provided to ensure that the longitudinal bars remain in the

correct position during the construction of the slab. It also helps to control any

longitudinal cracking that may develop.

The details regarding the design of the pavement slab thickness and the amount of

reinforcement required are discussed in Chapter 7.

Concrete Slab

Subbase

Capping Layer

( If required)

Natural ground or

embankment

Subgrade

Ri id Pavement


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4. JOINTS

Joints are placed in concrete pavements, whether reinforced or not to permit expansion,

contraction and warping of the slab, thereby relieving stresses due to environmental

changes (Temperature and moisture) and friction, and to facilitate construction. Jointsare classified according to their direction, either transverse or longitudinal and upon their

function. They are either contraction, expansion, warping or construction joints and in

most cases , they combine several of these functions.

Typical details of the different types of joints are presented in Appendix B (adapted from

Ref. 8).

4.1 Transverse Joints

Transverse Joints are the joints perpendicular to the centerline of the road. They are

designed to prevent contraction and expansion stresses which develop over long

distances. In some specific places like around in-pavement objects or at junctions,

transverse joints are also required to limit warping stresses.

4.1.1 CONTRACTIONJOINTS

Contraction joints are the main type of transverse joints. They are provided in JRCP and

JUCP to relieve the tensile stresses due to temperature or moisture changes and friction.

They provide weakened sections between bays to induce tension cracking at preferred

locations in the concrete after it has been placed. If contraction joints were not installed,

random and uncontrolled cracking would occur on the surface of the pavement. They

also contribute to the limitation of the warping stresses.

Load transfer between bays is provided by dowels.

Contraction joints shall consist of:

o a sawn joint groove

o dowel bars

o a sealing groove

The groove and sealant shall be as specified. The dowel bars shall be 20 mm in diameter

at 300 mm spacing, 400 mm long for slabs up to 239 mm thick, and 25 mm in diameter

for slabs 240 mm thick or more.

4.1.2 EXPANSIONJOINTS

The primary function of an expansion joint is to provide space for the expansion of the

slab, thereby preventing the development of compressive stresses, which may cause the

slab to buckle. Expansion joints are also contraction joints. Transverse expansion joints

are used at the limit between CRCP and other types of pavement or structures andsometimes at regular intervals in JUCP and JRCP.

The construction of this type of joints is relatively costly and they require high levels of

maintenance. If not well maintained and not functioning properly, they tend to stay

closed after expansion of the slab, which induces excessive opening of the adjacent

contraction joints, thus being a cause of failure. They are consequently avoided as far aspossible and it is often preferred to accept to maintain localized failures due to expansion

stresses than to run the risk of serious distress at the expansion joints.


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They are generally not required if the slab is cast during the hottest time of the year.

In expansion joints, complete separation between the two adjacent concrete bays is

required, and a compressible joint is used to fill the void.

Load transfer between bays is provided by dowels.

Expansion joints shall consist of :

o a joint filler board

o dowel bars

o a sealing groove

The joint filler board and sealing groove shall be as per the Specifications. The dowel

bars shall be 25 mm in diameter at 300 mm spacing, 600 mm long for slabs up to 239

mm thick, and 32 mm in diameter for slabs 240 mm thick or more.

Warping Joints

Warping joints allow a slight relative rotation of the bays and reduce the stresses due to

warping.

Transverse warping joints are used for special cases, such as extra joints at manhole

positions, or when unreinforced slabs are alongside reinforced slabs, or in long and

narrow or tapered (odd-shaped) JUCP slabs between normal joint positions, to reduce the

length/width ratio of the bays to 2 or less, and in other similar situations.

Warping joints shall consist of:

o a sawn groove

o tie barso a sealing groove

The sealant shall be as per the Specifications. The tie bars shall be 12 mm in diameter at

300 mm spacing, and 1000 mm long.

4.2 Longitudinal Joints

Longitudinal joints are warping joints, allowing a slight relative rotation of the slab

portions and reducing the stresses due to warping. They are required at such a spacing

that they will reduce the combination of thermal warping stresses and loading stresses to

a minimum, they also reduce the risk of longitudinal random cracking, and often serve atthe same time as construction joints. These joints allow a slight rotation, but differential

lateral displacements between adjacent bays are prevented by tie bars provided at mid-

depth of the slab.

These tie bars also prevent the opening of the cracks and thus the Load transfer is

achieved through aggregate interlock.

Longitudinal joints shall consist of :

o bottom crack inducer

o a sawn groove

o tie barso a sealing groove


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The sealant shall be as per the Specifications. The tie bars for all longitudinal joints,

except where transverse reinforcement is permitted in lieu, shall be 12 mm in diameter at

600 mm spacing, and 1000 mm long.

4.3 Construction Joints

Construction joints are required to facilitate construction, especially when concreting is

stopped.

In JUCP and JRCP, they shall be coupled with other joints

Additional reinforcement shall be placed when dealing with transverse construction

joints for CRCP. This can be achieved by providing for each longitudinal bar, a 700mm

long reinforcement bar (Dia. 20mm ) centered on the joint as shown in Figure 2 below.

Figure 2 Transverse construction joint for CRCP slabs


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5. SELECTION OF THE PAVEMENT TYPE

The highway engineer or administrator does not have at his disposal an absolute or

indisputable method for determining the type of pavement which should be selected for a

given set of conditions.

First a judgment must be made on many varying factors such as traffic, soil, weather,

materials, construction, maintenance and environment. In some cases overriding factors

can dictate pavement type. For instance, for heavily traveled facilities in congested

locations, the need to minimize the disruptions and hazard to traffic may dictate the

selection of CRCP.

When there is no overriding factor, which may often be the case, it is standard practice to

design typical sections of the road using each of the available options and then to

compare them on an economical point of view.

Unavoidably, there will be instances where financial circumstances are such to make firstcost the dominate factor in selection, even though higher maintenance or repair costs may

be involved at a later date.

Where circumstances permit, a more realistic economical evaluation has to take into

account all expected costs including the initial cost of construction, the cost of

subsequent stages or corrective works, anticipated life, maintenance cost and salvage

value. Costs to road users during periods of reconstruction or maintenance operations are

also appropriate for consideration.

Although pavement structures are based on an initial design period, few are abandoned at

the end of this period and continue to serve as part of the future pavement structure. For

this reason, the analysis period should be of sufficient duration to include a representativereconstruction of all pavement types.

Figure 3 Pavement type selection process


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If the analysis of the above given factors does not show a far higher interest of one option

rather than another, a second set of factors can be considered such as the performance of

similar pavements in the area or the skills of contractors.

Basically, the use of the different types of rigid pavement is as follows:

o JUCP is suitable for all levels of traffic, whenever the risk of subgrade

movement is low.

o JRCP is suitable for all levels of traffic and is used when the risk of settlements

of the subgrade can not be neglected.

o CRCP shall basically be considered only for rather high design traffic (>30

msa). They can also be included for less heavily trafficked schemes where the

advantage of lower maintenance throughout the design life may be worthwhile.

they are particularly suitable were settlement of the sub-soil is expected.


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6. STRESS DEVELOPMENT AND DESIGN CRITERIA

6.1 Stress Development

The concrete slabs in concrete pavement are subjected to two main types of stresses :

o The stresses developed because of changes of the environment (moisture and

temperature) and closely depending upon the intrinsic properties of the concrete.

In Ethiopia, though the annual range of temperature is small, the daily range of

temperature is high, varying from 20C to 40 C (Ref. 1), and hence thermal

stresses deserve special attention.

o The stresses coming from the traffic loads.

Both types of stresses can not be prevented from developing, but the design of concrete

pavement shall take them into account in order to keep them in acceptable ranges of

values. Analytical methods have been developed aiming at computing accurately the

stresses developed in concrete pavements for a theoretical design. But they are rather

complicated and necessitate strong hypothesis on the quality and the evolution of the

different layers composing the subgrade. That is why the approach of this manual is

limited to a qualitative description of the phenomena which justify the pragmatic design

procedure exposed in section 7.

6.1.1 HORIZONTAL TENSILE STRESSES

While hardening and later depending on external humidity, the moisture rate of the

concrete decreases, thus inducing tensile stresses in the material.

When the temperature drops after hardening, thermal tensile stresses are also induced,

depending on the thermal coefficient of the concrete.

Since the movements of the lower face of the pavement are limited by the friction with

the subbase, cracks appear as soon as the sum of these tensile stresses exceed the

concrete tensile strength. When cracks become too wide, they enable water infiltration or

slabs and subgrade vertical movements thus accelerating the degradation of the

pavement.

Depending on the type of slab this issue is coped with differently:

In JUCP

The development of cracks is controlled by placing joints at regular intervals and a

separation membrane between the slab and the subbase. The limited lengths of the bays

and the increased possibility of horizontal movements limit the tensile stresses and thus

prevent the slabs from cracking between joints.

In JRCP

The transverse cracks which are expected to develop between transverse joints are held

tightly closed by the longitudinal reinforcement that is incorporated into the slab.


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In CRCP:

The continuous reinforcement causes the cracking to occur at regular and little spaced

locations thus limiting the opening of cracks to acceptable values.

6.1.2 HORIZONTAL COMPRESSIVE STRESSES

If the temperature rises after hardening, thermal compressive stresses are induced,

depending on the thermal coefficient of the concrete. If they become too high, this may

cause the slab to buckle.

According to the type of slab, this issue is treated as follows:

In JUCP and JRCP:

The placing of expansion joints and the increased possibility of movement through the

use of the separation membrane permit the expansion of the concrete and the dissipation

of compressive stresses. Nevertheless, the issue is avoided as far as possible in casting

the concrete at the hottest period of the year.

In CRCP:

The continuous reinforcement increases the resistance of slabs but the compressive

strength remain limited and the slab is prone to expansion failure. It is thus preferable to

cast CRCP slabs during the hottest time of the year to limit the potential of thermal

expansion.

6.1.3 WARPING STRESSES

Warping stresses occur in rigid pavement slabs when variations in moisture contentand/or temperature from the top to the bottom of the slab occur.

In dry climate, or dry periods, the top of the slab is drier than the bottom, causing the

edges of the slab to tend to heave as represented in Figure 4 below and inducing tensilestresses at the top of the slab and compressive stresses at the bottom. Permanent warping

stresses also generally occur because the top of the slab cures faster and shrinks more

than the bottom.

Figure 4 Curling of concrete slab due to moisture gradients

During daytime, the top of the slab tends to be warmer than the bottom, causing the

middle of the slab to tend to heave and inducing tensile stresses at the bottom of the slaband compressive stresses at its top as represented in Figure 5 below.During nighttime, the opposite phenomenon occur.

Drier

Wettertension

Base

Concrete slab self

weight and traffic loads


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Figure 5 Curling of concrete slab due to temperature gradients

Warping stresses are limited in providing joints, either warping or contraction joints

which allow a slight relative rotation of the bays.

6.1.4 SHEAR AND BENDING STRESSES

With a minimum concrete thickness of 150 mm and a theoretical continuous support on

the subbase shear and bending stresses developed by the traffic loads are not prejudicial

to rigid pavement except in case of punctual loss of support due to movements of thesubbase or of the subgrade. The continuous transmission of vertical loads along the

pavement is essential because relative vertical movements of the bays create pumping

mechanisms which accelerate dramatically the deterioration of the subbase.

6.2 Design Criteria

As above explained, the factors which shall intervene in the design of rigid pavements

are as follows:

o the subgrade quality

o the quality of the steel and concrete composing the slabs

o the traffic

o the environment (Moisture and temperature)

o the notional design life

For the simplified experience-based design procedure exposed in this manual, the

assumption is made that the materials used for construction meets the standard

requirements as defined in section 3. Which means mainly a yield strength of 500 MPa

for the steel reinforcement bars and a 28 day characteristic compressive strength of 40

MPa for the concrete.

As stated in the previous section, the accurate computation of the stresses in the concrete

is not in the scope of this manual and thus, the proposed thickness design procedure and

Cooler

hottertension

Base

Concrete Slab self

weight and traffic loadsNighttime

hotter

Cooler

tension

Base

Concrete Slab self

weight and traffic loadsDaytime


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joint layout for rigid pavement is suitable for the usual natural ranges of temperature and

moisture rates.

Consequently, the two parameters to be accounted for in the design procedure are the

traffic data and the bearing capacity of the subgrade.


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7. DESIGN OF RIGID PAVEMENTS

A general methodology of rigid pavement design is presented in Figure 9, page 20.

7.1 Design life

Due to the structural properties of concrete slabs, their durability is very good and they

can be designed for periods of up to 60 years. If properly constructed, the pavement will

last long with a good level of serviceability and low maintenance requirements.

It is common practice to design concrete pavements for 40 years or more. Given that the

required slab thickness varies linearly with the logarithm of the cumulated number of

ESAs, designing for longer periods generally requires marginal additional slab thickness

and reinforcement and proves to be more economical.

This possibility to design rigid pavements for more than twice the maximum design lifeof flexible pavements and the lower associated maintenance costs make them generally

more economical in the long term.

7.2 Design Traffic Loading

The method for computing Cumulative Equivalent Axle Load over the design life is

described in in ERA Pavement Design Manual 2002, volume 1, Chapter 2. The same

method is used for rigid pavement but the equivalency factors to be used are those given

in table 1.

Table 1

Equivalency Factors for Different Axle Loads(Rigid Pavements)

Wheel load (103

kg)

(single and dual)

Axle load

(103

kg)

Equivalency

factor

1.5 3.0 0.02

2.0 4.0 0.05

2.5 5.0 0.13

3.0 6.0 0.28

3.5 7.0 0.53

4.0 8.0 0.934.5 9.0 1.53

5.0 10.0 2.40

5.5 11.0 3.63

6.0 12.0 5.25

6.5 13.0 7.33

7.0 14.0 9.92

7.5 15.0 13.1

8.0 16.0 17.0

8.5 17.0 21.6

9.0 18.0 27.1

9.5 19.0 33.7

10.0 20.0 41.4


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These factors are marginally higher, when compared with the corresponding values from

Table 2.3 of ERA Pavement Design Manual Volume 1, for loads up to the standard axle

load. However, for heavier loads, the equivalency factors for rigid pavements are lower

and the difference increases exponentially. This reflects the facts that rigid pavements are

more resistant to heavy loads because of the capacity of the concrete slab to spread loads

over a large surface of subbase.

7.3 Thickness Design

7.3.1 CAPPING AND SUBBASE

A capping layer is required only if the CBR of the subgrade is 15% or less. The required

thickness of a capping layer for a CBR value inferior to 15% can be obtained from Figure10, page 21.

The subbase layer is required when the subgrade material doesnt comply with the

requirement for a subbase (CBR is less than 30%) but it is almost always used tofacilitate the obtaining of surface levels with the tolerances required. Generally, the

thickness of the subbase provided will be a constant 15 cm and can be cement stabilized.

For subgrade CBR values inferior to 2%, the subgrade material needs to be treated either

by replacement or in-situ stabilization. These methods of soil improvement are described

in section 7 of the Pavement design manual- Vol. I2002.

A separation membrane (such as a polythene sheet) is required between subbase and

concrete slab, mainly in order to reduce the friction between the slab and the subbase in

JUCP and JRCP pavements, and thus inhibits the formation of mid-bay cracks. It also

reduces the loss of water from the fresh concrete. For CRCP pavements, a bituminousspray should be used on the subbase, instead of polythene, because a high degree of

restraint is required.

7.3.2 CONCRETESLAB THICKNESS ANDREINFORCEMENT

Based on the design traffic volume expressed in Equivalent Standard Axle determined as

per sub section 7.2 and project-specific characteristics, the thickness of pavement isdetermined.

The following represents procedures for determining the thickness and reinforcement for

each of the pavement types.

Jointed Unreinforced Concrete Pavement (JUCP)

For a given traffic volume in terms of ESAs, the thickness of JUCP concrete slab can be

determined using Figure 12, page 22.Figure 4 assumes the presence of an effective lateral support to the edge of the most

heavily-trafficked lane (i.e., the right lane), such as a shoulder with a pavement structure

able to carry occasional loads. In the absence of such a shoulder adjacent to the most

heavily trafficked lane, an additional slab thickness is required, and this additional

thickness can be determined using Figure 14, page 23.JUCP pavements have no reinforcement. However, the longitudinal and transverse jointsare provided with dowels or tie bars depending upon the type of joint. The joint details

are described in section 4.


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Jointed Reinforced Concrete Pavement (JRCP)

For a given traffic volume in terms of ESAs, the thickness of a JRCP concrete slab can

be determined using Figure 12, page 22. The figure can also be used to determine thelongitudinal reinforcement in terms of mm

2/m for a given concrete slab thickness. Thus,

several alternate combinations of thickness of concrete slab and amount of reinforcement

can be compared.

In the absence of an effective lateral support provided by the shoulder adjacent to the

most heavily trafficked lane, an additional slab thickness is required and can be

determined using Figure 14.In addition to the longitudinal reinforcement, JRCP pavements shall be provided with

transverse reinforcement, consisting of 12 mm diameter steel bars at 600 mm spacing.

Continuously Reinforced Concrete Pavement (CRCP)

CRCP pavement can withstand severe stresses induced by differential movements. For a

given traffic volume, in terms of ESAs, the thickness of CRCP concrete slab can be

obtained from Figure 13.Longitudinal reinforcement in CRCP pavements shall be 0.6% of the concrete slab cross-

sectional area, consisting of 16 mm diameter deformed steel bars. Transverse

reinforcement shall be provided at 600 mm spacing, consisting of 12 mm diameter

deformed steel bars, to prevent the opening of any longitudinal cracks which may form.

Transverse reinforcement is required for ease of construction.

Similarly to JUCP and JRCP pavements, in the absence of effective shoulder support

adjacent to the most heavily trafficked lane, the additional slab thickness required can be

determined using Figure 14.As is evident from Figure 12 and Figure 13, the minimum thickness of concretepavement for JUCP and JRCP pavement is 150 mm and that for CRCP pavement is 200

mm. Hence, the designer should carefully assess the necessity and requirements for such

pavements, depending on the design traffic volume, and shall include flexible pavement

as an alternate.

A design example of rigid pavement design is presented in Appendix A.

7.4 Design for Movement

Joints shall be designed according to the general considerations of sub section 4 and

using Drawings B2 to B8.

The general layout of joints shall account for construction consideration and the

following limitations concerning joint spacing and bays dimensions:

7.4.1 TRANSVERSEJOINTSPACING

Maximum transverse joint spacing for JUCP pavements is 4 m for slab thickness up to

230 mm and is 5 m for slab thickness over 230 mm.

For JRCP, contraction joints are generally at a standard distance of 25m.


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Expansion joint are required at the limit with other pavement types or with structures like

bridges.

In the current section, expansion joints shall be avoided in casting the concrete slab at the

hottest period of the year. If required, expansion joints should replace every third

contraction joint.

7.4.2 LONGITUDINAL JOINT SPACING

Longitudinal joints shall be placed at the edge of each traffic lanes.

7.5 Design detailing

7.5.1 BAY-LAYOUT

In the current sections of the road, the longitudinal and transverse joints placed as

described in the previous sub-sections divide the slabs in even rectangular bays. Atspecial locations, like crossings or junctions or when manholes or gulleys are fund,

adapted layouts fitting the road geometry must be adopted, in order to prevent the

development of warping stresses. The main principles for designing the joints layout at

special locations are :

o to avoid long, narrows bays with a length/width ratio greater than 2.

o to avoid bays with acute angled corners.

o to avoid bays with re-entrant angles.

The sketches in Figure 6 below present a possible layout for bays at crossing andjunctions illustrating these principles.

Intersection oftransverse joints

Longitudinal joints Transverse joints

Figure 6 Joints layout at junctions and crossings

7.5.2 GULLIES AND MANHOLES

When gullies, manholes and other in-pavement objects are found, it is essential to

prevent the concrete slab from been supported by the structure. This shall be achieved in


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boxing out around the object, which means providing an expansion joint without load

transfer device.

Since the opening in the slab structure is likely to create a weakened section prone to

cracking, it is necessary to locate it at the crossing of normal joints or with additional

warping joints as shown in Figure 7 below.

Figure 7 Box-out around in-pavement objects : layout of joints

7.5.3 I NTEGRALCURBS

Where sidewalks are required. Integral curbs shall be used and linked to the carriageway

slab by a longitudinal joint.

All transverse joints shall extend continuously through the pavement and curb.

Figure 8 below shows typical dimensions and construction provisions for rigid pavementintegral curbs.

Figure 8 Typical Integral Curb


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7.5.4 ENDANCHORAGE FOR CONTINUOUSLYREINFORCEDPAVEMENTSLABS

At CRCP slabs ends (connection with flexible pavements, other concrete pavement types

or structures) anchorage devices are required because the surface of friction is not

sufficient to counterbalance the contraction and expansion stresses, which could provoke

the formation of wide openings.

This can be achieved in providing a succession of reinforced concrete lugs which anchor

the slab in the soil. The lugs are typically bout 1 m deep, they cover the all width of the

slab and are placed every 5 meters over the 30 last meters of the continuous reinforced

pavement. Refer to drawing B6 in appendix B for the design details.


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Figure 9 Design Methodology flow diagram

Check forRequirement ofCapping Layer

No

DetermineCappingLayer Thicknessfrom Figure 3.2

DetermineConcrete SlabThickness and

Reinforcement from Figure3.3.

Determineslab thicknessfrom Figure 3.3.

Check for Site Constraints,if any.

Determine pavement type.

Determine Concrete SlabThickness from Figure

3.4.

CRCP

Check for requirement of

transverse reinforcement (cf. 3.2).

Determine joint type

Determine additional slabthickness from Figure 3.5.

Yes

JRCP

JUCPDetermine longitudinal

reinforcement (cf. 3.2)

Determine

Design CBR

Design ESAs


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Figure 10 Capping Layer and Subbase Thickness design(Adapted from Ref.5)

Figure 11 Joint spacing for JUCP and JRCP Slabs

18

19

20

21

22

23

24

25

26

1 10 100 1000

Design Traffic (millions of ESAs)

3

4

5

6

7

8

9

10

11

JUCP

Type of

Pavement2

JRCP

4

5

400

Spacing of transverse

Joints (m)

-200

-100

0

100

200

300

400

500

0 5 10 15 20 25 30150

ImproveSubgrade

2

Capping Layer

Thickness

Subbase Thickness

Subgrade CBR ( %)

CappingLayer and

Subbase Thickness


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Figure 12 Design Thickness for JUCP and JRCP Slabs(Adapted from Ref. 5)

Figure 13 Design Thickness for CRCP Pavement

100

150

200

250

300

350

400

1 10 100 1000

Design Traffic (millions of ESAs)

0 JUCP500

600

700

800

JRCP

Longitudinal

Reinforcement

(mm2/m)

0

50

100

150

200

250

300

1 10 100 1000

Design Traffic (Millions of ESAs)

DesignThickn

essofconcrete(mm)


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Figure 14 Additional Concrete Slab Thickness for Rigid Pavements WithoutLateral Support


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REFERENCES

1. ETHIOPIAN MAPPING AUTHORITY (1988). National Atlas of Ethiopia.

2. ETHIOPIAN ROADS AUTHORITY (2000). Pavement Design Manual, Volume

1, Flexible Pavements and Gravel Roads.

3. TRANSPORT RESEARCH LABORATORY (1993). Road Building in the

Tropics. State-of-the- Art Review, No. 9.

4. AMERICAN ASSOCIATION OF STATE HIGHWAY and

TRANSPORTATION OFFICIALS (1993). AASHTO Guide for Design of

Pavement Structures.

5. THE DEPARTMENT OF TRANSPORT, London (1997). Design Manual for

Roads and Bridges.

6. HIGHWAYS AGENCY, UK (1998). Manual of Contract Documents for

Highway Works, Vol. 1: Specification for Highway Works.


Highway Works, Vol. 2: Notes for Guidance on the Specification for Highway

Works.


Highway Works, Vol. 3: Highway Construction Details.

01- Rigid pavement Manual

Documents

Transcript of 01- Rigid pavement Manual