Continuously Reinforced Concrete Pavement 2b2z6q

SEMINAR REPORT

CONTINUOUSLY REINFORCED CONCRETE PAVEMENT

“LET THE ROADS CRACK” PRESENTED BY: S.A. QUADRI

ABSTRACT J.N.E.C. Aurangabad

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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 ts unless and until there is end of pavement or the pavement comes in with some other pavement or bridge. A longitudinal t exists only if the road is wider than 14 feet. Due to reduction of ts smooth and continuous riding is possible resulting in fuel saving. Also CR roads are maintenance free if properly constructed and care is taken while placement of steel. Once CR 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. CR 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 CR controlled cracking is permitted. The initial cost of CR is high, but as it is maintenance free, and lasts for decades, overall cost of CR 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 CR is widely used in USA, , BRITAN, and several other developed and developing nations. Use of CR 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 CR will surely boost the economy of any country.

J.N.E.C. Aurangabad

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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 day’s about 60% of freight and 80% of enger 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 ted concrete pavement. But their performances are not very satisfied due to t failure and maintenance problems. Continuously reinforced concrete pavement, (CR) eliminates the need for transverse ts (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 CR based on study carried out by INSDAG2 for highways and expressways is much lower compared to flexible pavement and also marginally cheaper compared to ted plain cement concrete (JP).

J.N.E.C. Aurangabad

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SEMINAR REPORT

What is CR? Concrete pavement in which the longitudinal reinforcing steel is continuous throughout the pavement length. It is a t less concrete pavement sufficiently reinforced to control cracking, without the aid of weakened transverse ts such as are used in ordinary or conventional type of ted 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. CR has all the good features of concrete pavements such as durability, high structural strength, nonskid surface and good visibility at night, wet or dry—features 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.

J.N.E.C. Aurangabad

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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 ted concrete. Continuously reinforced concrete pavement (CR) can meet this challenge. CR 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 CR runway has been terrific‖3. In CR 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 year’s budget. The implementation of CR 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.

J.N.E.C. Aurangabad

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SEMINAR REPORT

2. DEFINITIONS AND CHARACTERISTICS OF CR: Continuously reinforced concrete pavement (CR) is concrete pavement reinforced with continuous steel bars throughout its length. Its design eliminates the need for transverse ts (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 CR is based essentially on the ―so-let-it-crack‖ philosophy rather than the difficult concept of avoiding cracks at any price6. The principle in CR 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 ted 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 CR: CR is an asset for today’s and tomorrows heavily traveled high-speed roadways. The excellent service of CRC pavements is reflected in the following significant operational features: 1. t less concrete pavement, CR offers excellent smooth riding surface for the vehicles that maximizes the comfort for the engers. 2. CR 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%

J.N.E.C. Aurangabad

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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. CR 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. There’s no need to worry about ruts, shoving effects common with asphalt pavement. 9. Concrete’s 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 manhour loss to the road s. 11. Use of CR 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, CR 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 today’s highways and expressways as they reach the end of their service lives.

J.N.E.C. Aurangabad

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SEMINAR REPORT

3. DESIGN CONSIDERATIONS, CRITERIAS, ASSUMPTIONS, AND METHOD OF DESIGN FOR CR: 3.1 DESIGN ASPECTS The volume changes stresses in CR 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. CR allows the concrete to develop very fine transverse cracks that seem to be uncontrolled and random. The spacings of transverse cracks that occur in CR 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 CR so that crack spacing lies between 1.1m to 2.4m, the crack width is less than 1.0mm and steel stress does J.N.E.C. Aurangabad

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SEMINAR REPORT not exceed 75% of the ultimate tensile strength. CR allows the use of slightly smaller load transfer co-efficient compared to JP. And hence the thickness requirement is less compared to JP. 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 CR as it affects transverse crack spacing and the width of the cracks. The longitudinal reinforcement in CR 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 CR. 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 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 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 t sawing, improper installation of longitudinal t inserts, and sub-base or subgrade irregularities.

J.N.E.C. Aurangabad

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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 ts is necessary. A variety of methods have been used through the years to install the steel reinforcing bars in CR 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 CR: 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 CR with JP and flexible pavement options. INSDAG’s 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 = 21°C (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 = 30°C (Assuming 35°C at the time of construction and 5°C at coldest period)  TOTAL REINFORCEMENT REQUIRED FOR 1 KM LENGTH 18M WIDE CR = 241.50 TONNES J.N.E.C. Aurangabad

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

Item

Flexible

JP

CR

Pavement Design Code

IRC-37

IRC-58

British-HD 26 / 94,

Total pavement

AASHTO’93 (Design thickness

Part-3,vol. 7,

adjusted as

section 2

UTCA report)

800

675

625

610

-

M40

M40

M40

-

4.25 m

-

-

PQC-Thk.mm

-

300

250

230

Steel

-

Only at ts

0.69%

0.57%

long - 16mm @

long – 16 mm @

140mm c/c

140

Trans – 12

mm c/c

thickness (mm) Grade of concrete Spacing of contraction ts

reinforcement

occasionally thin mesh in top surface

mm@ 600 mm c/c

Trans – 12 mm @ 600 mm c/c

J.N.E.C. Aurangabad

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SEMINAR REPORT

Durability

Poor (5-6 years)

Long (>30

Long (>30 years)

years) Saving in Fuel

-

10-20%

10-20%

Maintenance

High

Less

Very less

World

Poor

Good reports

Very good reports. 4500 km in

experience

performance

USA; all states have started using CR

Construction

Easy

Special care is

More special care needed

needed Expertise in the

Very large

Yes

Yes

No

Reinforcement

ts are practically eliminated.

at ts needs

Cracks do not propagate due to

periodic

reinforcement. No corrosion

protection

problem.

country Corrosion problem

J.N.E.C. Aurangabad

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SEMINAR REPORT Table No.2 COST COMPARISON OF VARIOUS TYPES OF PAVEMENT2 (RS. IN -LAC) Item of Cost

PAVEMENT TYPE Flexible

JP

CR

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%

-

36.86

42.59

Saving in VOC over Flexible

409.99

-

-

Maintenance cost

109.08

25.30

1.30

-

(-) 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%

382.18

301.87

283.60

Extra in Direct Initial Cost over Flexible

Revenue due to early Completion

LCC without considering fuel saving

J.N.E.C. Aurangabad

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SEMINAR REPORT

4. TS IN CR: 4.1 LONGITUDINAL T: Longitudinal ts 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 t 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 ts‖.

4.2 TRANSVERSE CONSTRUCTION T: (a) A construction t is formed by placing a slotted header board across the pavement to allow the longitudinal steel to through the t. The longitudinal steel through the construction t 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 t. 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 T: 4.3.1 TERMINAL TREATMENTS: CR can extend to any level till bridge structures or any other pavement obstructs them. The free end of the CR, 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 t; the most widely used system of restraint involves the use of anchoring lugs. J.N.E.C. Aurangabad

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SEMINAR REPORT What are terminal ts, and why are they needed in continuously- reinforced concrete pavements (CR)? A terminal t is used in continuously reinforced concrete pavement (see CR) 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 CR so that excessive movement does not occur. Terminal ts 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 ts, care should be taken in their design. 4.3.2 DESIGN OF TERMINAL T: There are a number of terminal t designs in service today. The performance of some designs has been better than others. The following figures illustrate the recommended and possible terminal t designs

Figure1. Recommended Terminal t Design J.N.E.C. Aurangabad

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SEMINAR REPORT (a) The WF beam t 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)

CR

Embedment

thickness

in

WF Beam

"Sleeper‖

Size

(in )

slab - in.

8

6

9

5

10

6

11

J.N.E.C. Aurangabad

Flange

Web Thickness

Width Thickness

(in. )

14 x 61

10

5/8

3/8

16 x 58

8-1/2

5/8

7/16

5

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FIGURE 2-

SEMINAR REPORT

J.N.E.C. Aurangabad

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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 t 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 ive resistance of the soil, it is not effective where cohesionless soils are encountered. Figure 3 shows a typical lug anchor terminal treatment

J.N.E.C. Aurangabad

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FIGURE 4-

SEMINAR REPORT

J.N.E.C. Aurangabad

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SEMINAR REPORT

CONCLUSIONS: 1. Continuously reinforced concrete pavement, CR, 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 of well – established fuel saving. 3. Compared to flexible pavement, CR 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 CR it is desirable to construct all these concrete roads with CR. 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 CR pavement. Corrosion resistant TMT bars may be used in corrosion prone areas. 7. The demerit of CR is its high initial cost & difficulty in repair works required to be done if not constructed properly.

J.N.E.C. Aurangabad

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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

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