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Continuously reinforced concrete pavement is a jointless concrete pavement continuously reinforced throughout the pavement length in the longitudinal direction to control cracking without the aid of weekend transverse joint.
CRCP has all the good features of concrete pavement such as high structural strength, durability, non-skid surface and good visibility at night, wet or dry features which make concrete and especially continuously reinforced concrete is a permanent road surfacing material.
The major functions of continuously reinforced concrete pavement are :
- Facilitates load transfer across cracks.
- Holds cracks tightly
- Provides stiffness by restraining and movement.
Design Characteristics of Continuously Reinforced Concrete Pavement
1. Design Aspect
The continuous reinforcement provided in the CRCP undertakes the stress produced by wheel loads, the volume changes stress successfully and keep the cracks tightly closed while maintaining adequate pavement thickness.
The important variable in CRCP is that it affects the behavior of the pavement is the spacing of transverse cracks. Excessive crack width and high Steel stress occur due to the relatively large distance between the cracks. A decrease in crack spacing reduces the steel stress and crack width.
2. Crack Spacing
The limit on crack spacing is dependent on spalling and punch functions. The maximum spacing between two consecutive cracks should be limited to 2.4 meters to minimize spalling. The minimum desirable crack spacing is 1.1 meters to minimize the potential of punch outs.
3. Crack Width
The selection of higher steel percentage or smaller dia reinforcement bar, the crack width can be reduced as much as possible. The allowable crack width should not exceed 1 mm as per AASHTO.
4. Steel Stress
The recommended limiting stress of +5% of the ultimate tensile strength. The determination of the percentage of longitudinal reinforcement to satisfy the criteria of crack spacing, crack width and steel stress is calculated using AASHTO design monograph and equations.
5. Steel Reinforcement
The steel reinforcement in CRCP is the amount and depth of longitudinal reinforcement as it affects the width of the crack and transverse crack spacing.
The function of steel is to hold a random crack tightly closed to provide structural continuity and to minimize the penetration of potential damaging surface water.
6. Longitudinal Reinforcement
The longitudinal reinforcement is the main reinforcement CRCP whose total area of longitudinal reinforcing bars required is stated as the percentage of the cross-sectional area of the pavement.
The amount of longitudinal reinforcement bar is generally between 0.5% to 0.7% and it may be more where weather conditions are severe and also the temperature differential is more.
7. Transverse reinforcement
The function of transverse reinforcement in CRCP are :
- Hold unplanned longitudinal cracks that may occur close.
- To support longitudinal bars and hold them at the specified spacing.
Construction Tips for CRCP
- The base must be finished with a uniform roadbed for the reinforcement support and construction equipment as well as to provide a uniform slab thickness.
- The base must ensure proper drainage to the slab.
- Slab base interface should be non-erodible to limit the potential of punch out.
- The design must be in accordance with the concrete cover specifications.
- Longitudinal reinforcement bars must be placed on the transverse ones and then tied to the latter.
- To limit crack openings, it is recommended that longitudinal reinforcement be placed on the upper third section of the slab.
- To prevent any corrosion, a sufficient amount of concrete cover above the reinforcement is necessary.
- The longitudinal bars to be welded to one another or tied. If tied, the recommended overlap is 25 to 35 bar’s Dia.
- To ensure they are not in the same cross-section the overlap is usually from one lane to the next.
- Fibers should be placed in longitudinal construction joints to keep the slab edges together on either side of the joint.
- Special attention must be paid when forming the transverse construction joint.
Comparison of Different Types of Pavements for Highways with CRCP
Table 1: Comparison of Different Types of Pavements for Highways with CRCP
|Item||Design Manual for Roads and Bridges (DMRB)||Flexible Pavement||Jointed Plain Concrete Pavement (JPCP)||Continuously Reinforced Concrete Pavement (CRCP)|
|Design Code||British-HD 26/94,Part-3,vol.7,section 2||IRC-37||IRC-58||AASHTO’93|
|Total pavement thickness (mm)||625||800||675||610|
|Grade of concrete||M40||–||M40||M40|
|Spacing of contraction joints||–||–||4.25 m||–|
|Steel reinforcement||0.69% long – 16mm @ 140mm c/c Trans – 12 [email protected] 600 mm c/c||–||Only at joints occasionally thin mesh in top surface||0.57% long – 16 mm @ 140mm c/c Trans – 12 mm @ 600mm c/c|
|Durability||Long (>30 years)||Poor (5-6 years)||Long (>30 years)||Long (>30 years)|
|Saving in Fuel||10-20%||–||10-20%||10-20%|
|Maintenance||Very less||High||Less||Very less|
|World experience||Very good reports. 4500 km in USA; all states have started using CRCP||Poor performance||Good reports||Very good reports. 4500 km in USA; all states have started using CRCP|
|Construction||More special care needed||Easy||Special care is needed||More special care needed|
|Expertise in the country||Yes||Very large||Yes||Yes|
|Corrosion problem||No corrosion problem.||No||R/F at joints needs protection||No corrosion problem.|
1. Types of Concrete Pavements -Their Construction Details and Applications
2. Types of Distresses in Concrete Pavements and their Causes