continuously reinforced concrete pavement

SEMINAR REPORT

J.N.E.C. Aurangabad Page 1

LET THE ROADS CRACK

PRESENTED BY:

S.A. QUADRI

ABSTRACT

CONTINUOUSLY REINFORCED CONCRETE PAVEMENT

SEMINAR REPORT


CONTINUOUSLY REINFORCED CONCRETE PAVEMENT as the title

suggests this type of pavement is reinforced throughout in longitudinal direction. This type of

pavement has no transverse joints unless and until there is end of pavement or the pavement

comes in contact with some other pavement or bridge. A longitudinal joint exists only if the

road is wider than 14 feet. Due to reduction of joints smooth and continuous riding is

possible resulting in fuel saving. Also CRCP roads are maintenance free if properly

constructed and care is taken while placement of steel. Once CRCP roads are constructed

they need not to be taken care of for the next 50-60 years.

The principal behind this roads is that Let the road crack, exactly opposite as in case

of other type of roads where we avoid crack formation at any cost. CRCP is aloud to crack

due to which stresses in the pavement are released. The cracks formed are held tightly by the

reinforcement, due to which widening and deepening of cracks is restricted. Hence we can

conclude that in CRCP controlled cracking is permitted.

The initial cost of CRCP is high, but as it is maintenance free, and lasts for decades,

overall cost of CRCP is less as compared to other type of reinforced concrete pavements.

Study and observations have shown that this type of roads are alarmingly successful, hence

CRCP is widely used in USA, GERMANY, BRITAN, and several other developed and

developing nations.

Use of CRCP will enhance the cement, and steel industries; it will reduce the fuel

consumption by vehicles, and will save lots of money required for frequent construction and

repairs of other type of pavements.

Considering all above aspects CRCP will surely boost the economy of any country.

SEMINAR REPORT


1. INTRODUCTION:

Transport is a vital infrastructure for rapid economic growth of the country. Speedy

transportation of natural resources (such as raw materials), finished goods and perishable

materials to all parts of the country including the points of export outlets are basic inputs to

economic growth. Recently there has been a major shift in transportation mode from

Railways towards the Road sector. Now a days about 60% of freight and 80% of passenger

transport is met by Road transport in India, which demonstrates the need for development of

a good road network.

In India flexible pavement (bitumen) is most common for both national and state highways.

Majority of roads under NHDP are also built with conventional bitumen pavements

considering its lower initial cost, though the life cycle cost of these pavements are very high

compared to rigid pavements due to frequent repairs and also need for complete resurfacing

at interval of 4-5 years.

Further fuel consumption of vehicles is much higher on this type of pavement than that on

rigid pavement. In advanced countries rigid pavement is increasingly being used due to large

number of benefits it offers. Considering durability of concrete pavements some portion

of Delhi - Mathura and Mumbai - Pune expressway was built with jointed concrete

pavement. But their performances are not very satisfied due to joint failure and

maintenance problems.

Continuously reinforced concrete pavement, (CRCP) eliminates the need for transverse joints

(other than at bridges and other structures) and keep cracks tight, resulting in a continuous,

smooth-riding surface that is virtually maintenance free. Life cycle cost of CRCP based on

study carried out by INSDAG2 for highways and expressways is much lower compared to

flexible pavement and also marginally cheaper compared to jointed plain cement concrete

(JPCP).

SEMINAR REPORT


What is CRCP?

Concrete pavement in which the longitudinal reinforcing steel is continuous

throughout the pavement length.

It is a joint less concrete pavement sufficiently reinforced to control cracking,

without the aid of weakened transverse joints such as are used in ordinary or

conventional type of jointed concrete pavement. Reinforced bars in the concrete

are lapped to form continuous reinforcement holding the pavement together in

all kinds of weather and preventing formation of large cracks that would

otherwise reduce the service life of the pavement. CRCP has all the good

features of concrete pavements such as durability, high structural strength,

nonskid surface and good visibility at night, wet or dryfeatures which make

concrete, and especially continuously reinforced concrete, a permanent road

surfacing material

Continuously

Reinforced

Concrete

Pavement -

Roads for this generation

and the next.

Built continuously

reinforced concrete

pavement today, and forget

it for next 50-60 years.

SEMINAR REPORT


Airports pavements are generally thicker than highway pavements and require better

surfacing materials because the loading and tire pressure of aircraft are much greater than

those of highway vehicles. Airports will have to upgrade their runways with stronger, longer

lasting materials than asphalt or even conventional jointed concrete. Continuously

reinforced concrete pavement (CRCP) can meet this challenge. CRCP offers greater

durability, structural strength, a smoother surface, and better visibility characteristics

.According to Mr. Peter Mok, Chief Engineer, Air Force Plant 42

Military aircraft are notorious for being pavement destroyers. Despite the heavy loads and

continual use, the performance of CRCP runway has been terrific3.

In CRCP reinforcement steel is an important element and it offers the following functions:

1. Holds crack tight

2. Facilitates load transfer across cracks

3. Provides stiffness by restraining end movement

About 250 tonnes of reinforcement steel and approximately 2000 tonnes of cement

will be consumed for building 1 Km length 18 m wide 4-lane carriageway CRC pavement.

The total requirement for converting 25% of the proposed 36000 Km highway pavement will

be in the order of 2.25 million tones of reinforcement steel. The requirement of reinforcement

of steel may exceed 3.0 million tones for highway development alone if we also consider 48

new road projects approved in this years budget. The implementation of CRCP will not only

benefit the steel and cement industry but the nation will also gain a lot because it reduces the

transportation costs drastically and minimizes the accidents on highways.

SEMINAR REPORT


2. DEFINITIONS AND CHARACTERISTICS OF CRCP:

Continuously reinforced concrete pavement (CRCP) is concrete pavement reinforced

with continuous steel bars throughout its length. Its design eliminates the need for transverse

joints (other than at bridges and other structures) and keep cracks tight, resulting in a

continuous, smooth-riding surface that is virtually maintenance-free. The whole idea of

CRCP is based essentially on the so-let-it-crack philosophy rather than the difficult concept

of avoiding cracks at any price6. The principle in CRCP is to confine random cracking to

acceptable spacings and crack widths so that the slab performs the same as if no crack exists,

i.e. equal deflection at cracks and the midspan of the slab. In an unreinforced slab, cracks

which occur will normally widen and get progressively worse under the effects of traffic and

climatic conditions. During the contraction of the concrete fine dirt enters the wide cracks ,

leading to faulting , spalling and cracking and blow-ups develop , requiring extensive repairs

and early surfacing to restore the smooth surface. The amount of reinforcement required to

control the cracking is relatively smaller for shorter spans. As length of the slab increases

amount of steel needed also increases. However, the steel is not directly proportional to the

slab length, as is usually assumed in the design of conventional jointed reinforced pavement.

The steel requirement vs. the amount of steel at a progressively decreasing rate as the slab

length increases and reaching a maximum at slab length of 180 to 240 meters. Beyond this

the steel requirement does not increase.

2.1 ADVANTAGES OF CRCP:

CRCP is an asset for todays and tomorrows heavily traveled high-speed roadways.

The excellent service of CRC pavements is reflected in the following significant operational

features:

1. Joint less concrete pavement, CRCP offers excellent smooth

riding surface for the vehicles that maximizes the comfort for the passengers.

2. CRCP is more durable, which can last 40-50 yrs without much

maintenance problem during the life of the pavement. Concrete actually hardens over

time. After its first month in place, concrete continues to slowly gain about 20%

SEMINAR REPORT


Strength in first 12 months.

3. It needs minimal cost of maintenance and rehabilitation.

4. It minimizes the detrimental dynamic loads that are applied to the vehicles and

pavement.

5. It offers best visibility. Concrete reflects light, which increases

visibility and can save on street lighting costs. During summer riding over flexible

pavement causes difficulties due to bitumen sticking to the tires. Visibility also gets

affected due to shining appearance of flexible pavement.

6. CRCP provides best traction grip there by leading to reduction in accidents CRC

pavements are easily roughed up during construction to create a surface that

provides superior traction and reduced accidents. Ease in driving with reduced mental

tension and overall improvement in quality of driving.

7. Air and noise environment improve along the thickly populated existing corridor.

Concentrations of CO and NOX are expected to reduce by around 70 % and 45%

respectively. The noise level would reduce substantially.

8. Concrete can withstand even the heaviest traffic loads. Theres no need to worry

about ruts, shoving effects common with asphalt pavement.

9. Concretes hard surface makes it easier for rolling wheels. Studies have even shown

that this can increase truck fuel efficiency. Savings in fuel to the extent of 20%, may

be considered ultimately reducing the vehicle operating cost.

10. Concrete roads facilitate increased speed and thereby savings in time and money.

Almost maintenance free service reduces traffic disturbances and thus reduces man-

hour loss to the road users.

11. Use of CRCP drastically can reduce import of bitumen there by leading to saving of

foreign currency.

With the potential to accommodate any level of traffic, under climatic extremes,

CRCP has a longer service life than roads made of other materials. This longevity is

advantageous to road owners and drivers and can be the long-term answer to revitalizing

todays highways and expressways as they reach the end of their service lives.

SEMINAR REPORT


3. DESIGN CONSIDERATIONS, CRITERIAS, ASSUMPTIONS, AND

METHOD OF DESIGN FOR CRCP:

3.1 DESIGN ASPECTS

The volume changes stresses in CRCP will be taken care by providing sufficient

reinforcement to keep the cracks tightly closed while maintaining adequate pavement

thickness to counteract the stresses produced by wheel loads. CRCP allows the concrete to

develop very fine transverse cracks that seem to be uncontrolled and random.

The spacings of transverse cracks that occur in CRCP is an important variable that

directly affect the behaviour of the pavement. Relatively large distances between cracks

result in high steel stresses at the crack and in excessive crack widths. A decrease in crack

spacing reduces the steel stresses and crack widths.

3.2 CRACK SPACING:

The limits on crack spacing are based on the possibility of spalling and punchouts.

Based on experience, the maximum spacing between consecutive cracks should be limited to

2.4m to minimize spalling. To minimize the potential of punchouts, the minimum desirable

crack spacing is about 1.1m.

3.3 CRACK WIDTH:

The limit on crack width is based on a consideration of spalling and water infiltration.

The crack width should be reduced as much as possible through the selection of higher steel

percentage or smaller diameter reinforcing bars. As per AASHTO stipulation the allowable

crack width should not exceed 1.0mm.

3.4 STEEL STRESS:

The limiting stress of 75% of the ultimate tensile strength is recommended. AASHTO

Design Nomographs and Equation are available for determining the percentage of

longitudinal reinforcement to satisfy the criteria of crack spacing, crack width and steel stress

respectively.

The optimum amount of steel reinforcement is selected in CRCP so that crack

spacing lies between 1.1m to 2.4m, the crack width is less than 1.0mm and steel stress does

SEMINAR REPORT


not exceed 75% of the ultimate tensile strength. CRCP allows the use of slightly smaller load

transfer co-efficient compared to JPCP. And hence the thickness requirement is less

compared to JPCP. The maximum desirable crack spacing is derived from a correlation

between crack spacing and incidence of spalling. Maximum crack spacing is derived from

consideration of effect of slab length on the formation of punchouts.

3.5 STEEL REINFORCEMENT:

The amount and depth of longitudinal reinforcing steel are the most important aspects

of steel reinforcement in CRCP as it affects transverse crack spacing and the width of the

cracks. The longitudinal reinforcement in CRCP is used to control the fine transverse cracks

that form due to volume changes in the concrete. The function of steel is to hold the random

cracks tightly closed, to provide structural continuity and to minimize the penetration of

potentially damaging surface water and incompressible.

3.6 LONGITUDINAL REINFORCING BARS:

These are the main reinforcement in CRCP. The total area of longitudinal reinforcing

bars required usually is stated as a percentage of the cross-sectional area of the pavement.

The amount of longitudinal reinforcing bars is generally between 0.5% and 0.7% and it may

be more where weather conditions are severe and also the temperature differentials are more.

Transverse reinforcements are useful to support the longitudinal steel when the steel is preset

prior to concrete placement. Transverse reinforcement may be lesser grade.

3.7 TRANSVERSE REINFORCING BARS:

The function of the bars is as follows:

1. To support the longitudinal bars and hold them at the specified spacing. When used for

this purpose, the longitudinal bars are tied or clipped to the transverse steel at specified

locations.

2. To hold unplanned longitudinal cracks that may occur tightly closed. Causes of

unplanned longitudinal cracking include late or shallow longitudinal joint sawing, improper

installation of longitudinal joint inserts, and sub-base or subgrade irregularities.

SEMINAR REPORT


In order to ensure the quality of construction proper care has to be taken for checking the

grade and size of reinforcement bars. The identification marks on steel reinforcement

facilitate field checking to assure incorporation of the specified reinforcement in the

constructed pavement. Close inspection of reinforcing bar splice details and construction

joints is necessary.

A variety of methods have been used through the years to install the steel reinforcing

bars in CRCP with varying degrees of success. Of these methods, manual presetting of the

steel prior to concrete placement, and mechanized feeding of the longitudinal bars through

parallel tubes contained within the concrete spreader during concrete placement, have

predominated.

3.8 TYPICAL DESIGN OF CRCP:

Brief details of design and cost estimation of a typical 4 Lane (18m wide)

carriageway pavement has been presented below along with cost comparison of CRCP with

JPCP and flexible pavement options. INSDAGs publication Life Cycle Cost Analysis and

Techno-Economic Study for the use of Reinforced Concrete Roads for National Highways

and Expressways may be referred for detail design calculations for various traffic data.

The following parameters are considered for design2:

1. Design Life (a) 20 years for Flexible pavement

(b) 30 years for Rigid pavements.

2. Traffic Density (a) 5000 Vehicles/day on 4-lane road

FOR RIGID PAVEMENTS

1. Concrete grade: M40

2. Grade of steel: Fe 415

3. Maximum temperature differential between top and bottom of Slab = 21C (The

maximum value for India as per IRC 58)

4. Difference between mean temperatures of the slab at the time of construction and

coldest period = 30C (Assuming 35C at the time of construction and 5C at coldest

period)

TOTAL REINFORCEMENT REQUIRED FOR 1 KM LENGTH 18M WIDE

CRCP = 241.50 TONNES

SEMINAR REPORT


Table No. 1 COMPARISON OF DIFFERENT TYPES OF PAVEMENTS FOR HIGHWAYS2.

Item Flexible

Pavement

JPCP CRCP

Design Code IRC-37 IRC-58 British-HD

26 / 94,

Part-3,vol. 7,

section 2

AASHTO93

(Design

thickness

adjusted as

UTCA report)

Total pavement

thickness (mm)

800 675 625 610

Grade of

concrete

- M40 M40 M40

Spacing of

contraction

joints

- 4.25 m - -

PQC-Thk.mm - 300 250 230

Steel

reinforcement

- Only at joints

occasionally thin

mesh in top

surface

0.69%

long - 16mm @

140mm c/c

Trans 12

mm@ 600 mm

c/c

0.57%

long 16 mm @

140

mm c/c

Trans 12 mm

@ 600

mm c/c

SEMINAR REPORT


Durability Poor (5-6 years) Long (>30

years)

Long (>30 years)

Saving in Fuel - 10-20% 10-20%

Maintenance High Less Very less

World

experience

Poor

performance

Good reports Very good reports. 4500 km in

USA; all states have started using

CRCP

Construction Easy Special care is

needed

More special care needed

Expertise in the

country

Very large Yes Yes

Corrosion

problem

No Reinforcement

at joints needs

periodic

protection

Joints are practically eliminated.

Cracks do not propagate due to

reinforcement. No corrosion

problem.

SEMINAR REPORT


Table No.2 COST COMPARISON OF VARIOUS TYPES OF PAVEMENT2

(RS. IN

-LAC)

Item of Cost PAVEMENT TYPE

Flexible JPCP CRCP

Material & labour 252.38 298.04 303.55

Interest during Construction 20.73 11.92 12.14

Initial Direct cost 273.10 309.96 315.69

Percentage of initial direct cost 100% 113.5% 115.6%

Extra in Direct Initial Cost over

Flexible

- 36.86 42.59

Saving in VOC over Flexible 409.99 - -

Maintenance cost 109.08 25.30 1.30

Revenue due to early Completion - (-) 33.39 (-) 33.39

Total Life Cycle Cost 792.17 301.87 283.60

Percentage of total LCC cost 100% 38.10% 35.8%

Saving in LCC w.r.t. Flexible - 490.30 508.57

Saving in LCC w.r.t. Flexible (%) - 61.9% 64.2%

LCC without considering fuel saving 382.18 301.87 283.60

SEMINAR REPORT


4. JOINTS IN CRCP:

4.1 LONGITUDINAL JOINT:

Longitudinal joints are necessary to relieve stresses caused by concrete shrinkage and

temperature differentials in a controlled manner and should be included when pavement

widths are greater than 14 feet. Pavements greater than 14 feet wide are susceptible to

longitudinal cracking. The joint should be constructed by sawing to a depth of one-third the

pavement thickness. Adjacent slabs should be tied together by tie bars or transverse steel to

prevent lane separation. Tie bar design is discussed in the FHWA Technical Advisory

entitled "Concrete Pavement Joints.

4.2 TRANSVERSE CONSTRUCTION JOINT:

(a) A construction joint is formed by placing a slotted header board across the pavement to

allow the longitudinal steel to pass through the joint. The longitudinal steel through the

construction joint is increased a minimum of one-third by placing 3-foot long shear bars

of the same nominal size between every other pair of longitudinal bars. No longitudinal

steel splice should fall within 3 feet of the stopping side or closer than 8 feet from the

starting side of a construction joint. Refer to paragraph 4b(1) (e) for recommended

splicing patterns. If it becomes necessary to splice within the above limits, each splice

should be reinforced with a 6-foot bar of equal size.

(b) Special provisions for the protection of the headerboard and adjacent rebar during

construction may be nice.

4.3 TERMINAL JOINT:

4.3.1 TERMINAL TREATMENTS:

CRCP can extend to any level till bridge structures or any other pavement obstructs

them. The free end of the CRCP, unless restrained, can be expected to undergo outward

movements of up to and sometimes exceeding 50mm. Annual movements of up to 25mm to

50mm also can be expected. These movements can be either accommodated or restrained for

protection of abutting installations. The most widely used system of accommodation in

current application involves the use of a wide-flange beam joint; the most widely used

system of restraint involves the use of anchoring lugs.

SEMINAR REPORT


What are terminal joints, and why are they needed in continuously- reinforced

concrete pavements (CRCP)?

A terminal joint is used in continuously reinforced concrete pavement (see CRCP) to

transition to another pavement type or to a bridge structure. They are found at the beginning

and end of a CRC paving job, as well as spaced periodically in between, depending on the

length of the job. Their function is to (1) isolate adjacent pavement types or structures, and

(2) anchor the CRCP so that excessive movement does not occur. Terminal joints

accomodate differential horizontal movements and prevent damage between a pavement and

another pavement or structure. Because pavement performance can be significantly affected

by the planned use and location of terminal joints, care should be taken in their design.

4.3.2 DESIGN OF TERMINAL JOINT:

There are a number of terminal joint designs in service today. The performance of

some designs has been better than others. The following figures illustrate the recommended

and possible terminal joint designs

Figure1. Recommended Terminal Joint Design

SEMINAR REPORT


(a) The WF beam joint consists of a WF beam partially set into a reinforced concrete sleeper

slab approximately 10 feet long and 10 inches thick. The top flange of the beam is flush with

the pavement surface. Expansion material, sized to accommodate end movements, is placed

on one side of the beam along with a bond-breaker between the pavement and the sleeper

slab. In highly corrosive areas the beam should be treated with a corrosion inhibitor. Several

States have reported premature failures of WF beams where the top flange separated from the

beam web. Stud connectors should be welded to the top flange, as shown in Figure 1, to

prevent this type of failure. Table 4 and Figure 1 contain recommended design features

WIDE FLANGE Beam (weight and dimensions)

CRCP

thickness

(in )

Embedment

in

"Sleeper

slab - in.

WF Beam

Size

Flange Web

Thickness

(in. ) Width Thickness

8 6

14 x 61 10 5/8 3/8

9 5

10 6

16 x 58 8-1/2 5/8 7/16

11 5

SEMINAR REPORT


F

IGU

RE

2-

SEMINAR REPORT


Figure 3. Typical Lug Anchor Terminal Treatment

(b) The lug anchor terminal treatment generally consists of three to five heavily reinforced

rectangularly shaped transverse concrete lugs placed in the subgrade to a depth below frost

penetration prior to the placement of the pavement. They are tied to the pavement with

reinforcing steel. Since lug anchors restrict approximately 50 percent of the end movement of

the pavement an expansion joint is usually needed at a bridge approach. A slight undulation

of the pavement surface is sometimes induced by the torsional forces at the lug. Since this

treatment relies on the passive resistance of the soil, it is not effective where cohesionless

soils are encountered. Figure 3 shows a typical lug anchor terminal treatment

SEMINAR REPORT


FIG

UR

E 4

-

SEMINAR REPORT


CONCLUSIONS:

1. Continuously reinforced concrete pavement, CRCP, is the most economical option for

highways as its LCC is much lower, by about Rs 5crore/Km (4-lane carriageway; 18 m

wide) compared to that of flexible pavement and compared to plain concrete, its LCC is

lower by Rs 18.27 lac for the assumed rates based on Mumbai - Pune Expressway

experience. These savings will be much higher for 6 and 8 lane carriageway.

2. The major part of the benefit (about 80%) in respect of rigid pavement over flexible is on

account of well established fuel saving.

3. Compared to flexible pavement, CRCP gives additional design life of at least 10 years.

Further, it offers much better riding quality, less dislocations to traffic movement and

substantial saving in vehicle operating cost comprising reduced consumption of fuel,

lubricants etc.

4. In view of long term economy and potential saving in precious foreign exchange

Government has announced that atleast 25% of the proposed 48 new roads of

approximate budget of Rs. 40,000 crore will be made of concrete roads. Considering

durability and maintenance free service of CRCP it is desirable to construct all these

concrete roads with CRCP.

5. The reinforcement requirement will be in the order of 3.0 million tones for highway

development alone, which will be consumed in next 5-6 years. The reinforcement

requirement will be much higher when construction of others associated structures is also

considered.

6. Thermo mechanically treated, TMT, bars are desirable for CRCP pavement. Corrosion

resistant TMT bars may be used in corrosion prone areas.

7. The demerit of CRCP is its high initial cost & difficulty in repair works required to be

done if not constructed properly.

SEMINAR REPORT


REFERENCES:

1. NHAI website.

2. Life Cycle Cost Analysis and Techno-Economic Study for the Use of Reinforced

Cement Concrete Roads in National Highways and Expressways; INSDAG

Publication.(No.INS/Pub/035)

3. Reinforced Concrete Airports web site of Cement Reinforcing Steel Institute

(CRSI)

4. Raymond Sharp, 1997, Cement Concrete Roads, National Seminar on Concrete

Roads and Pavements, Kolkata.

5. Handbook on Cement Concrete Roads,2000,CMA, New Delhi.

6. Continuously Reinforced Concrete Pavement Design and Construction Practices in

USA, Web Site of Cement Reinforcing Steel Institute (CRSI).

7. HD 29/94, Volume 7, section 2, part 3 Pavement Design and Maintenance- Design

Manual for Roads and Bridges, British Standard.

8. Concrete Pavement Performance in the Southeastern United States,University

Transportation Center for Alabama, Tuscaloosa, UTCA Project Number 99247,

September 2000

9. E J Yoder Concrete Roads Alternate Construction Methods, Brajendra Singh,

Principles of Pavement Design, National Seminar on Concrete Roads & pavements,

CMA

continuously reinforced concrete pavement

Documents

crcp roads

type of roads

type of pavements

roads crack

initial cost of crcp

overall cost of crcp

aspects crcp

rigid pavements