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Rigid pavement


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theory and analysis of rigid pavement

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Rigid pavement

  2. 2. Transportation EngineeringTransportation Engineering THE RIGID PAVEMENTTHE RIGID PAVEMENT 2
  3. 3. INTRODUCTIONINTRODUCTION  Development of a country depends on the connectivity of various places with adequate road network.  Roads constitute the most important mode of communication in areas where railways have not developed much. 3
  4. 4.  India has one of the largest road networks in the world (over 3 million km at present).For the purpose of management and administration, roads in India are divided into the following five categories: • National Highways (NH) • State Highways (SH) • Major District Roads (MDR) • Other District Roads (ODR) • Village Roads (VR) 4
  5. 5. WHAT IS ROAD ?WHAT IS ROAD ?  Road is an open, generally public way for the passage of vehicles, people, and animals.  Finish with a hard smooth surface (pavement) helped make them durable and able to withstand traffic and the environment.  Roads have a life expectancy of between 20 - 30 years. 5
  6. 6. What is a Pavement?What is a Pavement? • A multi layer system that distributes the vehicular loads over a larger area 6
  7. 7. What is a Pavement?What is a Pavement? OR • Highway pavement is a structure consisting of superimposed layers of selected and processed materials whose primary function is to distribute the applied vehicle load to the sub grade. OR • It can also be defined as “structure which separates the tyres of vehicles from the under lying foundation.” • Pavement is the upper part of roadway, airport or parking area structure • It includes all layers resting on the original ground 7
  8. 8. Functions of the PavementFunctions of the Pavement • Reduce and distribute the traffic loading so as not to damage the subgrade. • Provide vehicle access between two points under all- weather conditions. • Provide safe, smooth and comfortable ride to road users without undue delays and excessive wear & tear. • Meet environmental and aesthetics requirement. • Limited noise and air pollution. • Reasonable economy. 8
  9. 9. RequirementRequirementss of pavement structureof pavement structure • Sufficient thickness to spread loading to a pressure intensity tolerable by subgade. • Sufficiently strong to carry imposed stress due to traffic load. • Sufficient thickness to prevent the effect of frost susceptible subgrade. • Pavement material should be impervious to penetration of surface water which could weaken subgrade and subsequently pavement. • Pavement surface should be skid resistant. 9
  10. 10. History of Road DevelopmentHistory of Road Development 10
  11. 11. Classification of PavementsClassification of Pavements 11
  12. 12. Types of PavementTypes of Pavement 12 Flexible Pavements PAVEMENTS Rigid Pavements
  13. 13. ComparisonComparison 13 Properties Flexible Rigid Design Principle Empirical method Based on load distribution characteristics of the components Designed and analyzed by using the elastic theory Material Granular material Made of Cement Concrete either plan, reinforced or prestressed concrete Flexural Strength Low or negligible flexible strength Associated with rigidity or flexural strength or slab action so the load is distributed over a wide area of subgrade soil. Normal Loading Elastic deformation Acts as beam or cantilever Excessive Loading Local depression Causes Cracks Stress Transmits vertical and compressive stresses to the lower layers Tensile Stress and Temperature Increases Design Practice Constructed in number of layers. Laid in slabs with steel reinforcement. Temperature No stress is produced Stress is produced Force of Friction Less. Deformation in the sub grade is not transferred to the upper layers. Friction force is High Opening to Traffic Road can be used for traffic within 24 hours Road cannot be used until 14 days of curing Surfacing Rolling of the surfacing is needed Rolling of the surfacing in not needed.
  14. 14. 14 Pavements ComparisonPavements Comparison Flexible pavements: • Deep foundations / multi layer construction • Energy consumption due to transportation of materials • Increasing cost of asphalt due to high oil prices Rigid pavements • Single layer • Generally last longer • May require asphalt topping due to noise / comfort issues
  15. 15. 15 Pavements ComparisonPavements Comparison • Heavy vehicles consume less fuel on rigid pavements • Rigid pavements more economic when considering environmental / life-cycle costing
  16. 16. Types Of PavementsTypes Of Pavements 16
  17. 17. Flexible Rigid
  18. 18. 18
  19. 19. RIGID PAVEMENTRIGID PAVEMENT 19 Rigid pavements are those, which contain sufficient beam strength to be able to bridge over the localized sub-grade failures and areas of in adequate support. OR Load is transmitted through beam action of slab in rigid pavements. OR Rigid pavements are those, which reduces the stress concentration and distributes the reduced stresses uniformly to the area under the slab.
  20. 20. RIGID PAVEMENTRIGID PAVEMENT 20 Deflection is very small hence the name rigid pavement. The high flexural strength is predominant and the subgrade strength does not have much importance as in case of flexible pavement.  usually finite slab with joints.  continously slab can be provided without jointed.
  21. 21. RIGID PAVEMENTRIGID PAVEMENT 21 Rigid pavements, though costly in initial investment, are cheap in long run because of low maintenance costs, The cost of construction of single lane rigid pavement varies from 35 to 50 lakhs per km in plain area, •Rigid pavement have deformation in the sub grade is not transferred to subsequent layers. •Design is based on flexural strength or slab action,Have high flexural strength. •No such phenomenon of grain to grain load transfer exists •Have low repairing cost but completion cost is high •Life span is more as compare to flexible (Low Maintenance Cost)
  22. 22. Basic Components of Concrete PavementBasic Components of Concrete Pavement 22
  23. 23. 23 Rigid PavementsRigid Pavements
  24. 24. Types of Concrete PavementsTypes of Concrete Pavements 24
  25. 25. Un Reinforced Concrete PavementsUn Reinforced Concrete Pavements 25 •These are plain cement concrete pavements (PCCP) constructed with closely spaced. •In almost all jointed pavements , load transfer mechanism is implemented using dowel bars placed in transverse joints. Such pavements are called JDCP/JPCP. •When The traffic intensity is very low in that case dowel bars are not provided such pavements are termed as JUDCP.
  26. 26. JPCPJPCP 26
  27. 27. Jointed Plain Concrete Pavement (JCPC)Jointed Plain Concrete Pavement (JCPC)
  28. 28. Reinforced Concrete PavementReinforced Concrete Pavement 28 •Occurrence of cracks in concrete slabs is inevitable due to repeated applications of axle loads and weathering action in different seasons. • Steel reinforcement in slab is provided to inhibit widening of cracks and known as RCP. •In JRCP steel mesh or mat is placed at the middle of each slab . It is not meant for structural strength but to provide control the crack width.
  29. 29. JRCPJRCP 29
  30. 30. Continuous Reinforced Concrete Pavement:Continuous Reinforced Concrete Pavement: 30 •Complete elimination of joints are achieved by reinforcement. •Bars are distributed continuously in the longitudinal direction so that the construction of transverse joints can be eliminated. • CRCP preferred in (i) main heavy traffic corridors (expressways) (ii) Adverse climatic conditions (iii) Weak sub grades.
  31. 31. CRCPCRCP 31
  32. 32. Precast Prestressed PavementPrecast Prestressed Pavement 32
  33. 33. Factors Governing Design of PavementsFactors Governing Design of Pavements • Design wheel load Static load on wheels. Contact Pressure. Load Repetition. • Subgrade soil Thickness of pavement required. Stress- strain behaviour under load. Moisture variation. • Design Period . • Design commercial traffic volume. 33
  34. 34. • Composition of commercial traffic in terms of single , tridem , tandem. • Axle load spectrum. • Tyre pressure. • Lateral placement characteristics. • Pavement component materials. • Climatic factors. • Required Cross sectional elements of the alignment. 34
  35. 35. Axle load • The total weight of the vehicle is carried by its axles. The load on the axles is transfers to the wheels and this load is ultimately transferred to the surface of the pavement in contact with the tyres . therefore more number of axles more load is to be transferred on wider area. Wheel load • The next important factor is the wheel load which determines the depth of the pavement required to ensure that the subgrade soil is not failed. Wheel configuration affect the stress distribution and deflection within a pavement. Many commercial vehicles have dual rear wheels which ensure that the contact pressure is within the limits. 35
  36. 36. Contact Pressure • For most of the commercial vehicles the commonly used tyre inflation pressures range about .7 Mpa to1.0 Mpa it is found that stress in concrete pavements having thickness of 200 mm or higher are not affected significantly by the variation of tyre pressure . a tyre pressure of 0.8 Mpa is adopted .The imprint area is generally taken as circular area for design purpose. Load Repletion • This factor govern the that the type of axles repeated throughout the design life that is how much repletion of single , tandem and tridem axles are taking place , and this factor considered for TDC and BUC. 36
  37. 37. Static Load On WheelsStatic Load On Wheels • This factor is used to design the thickness of slab because the load of the axle is ultimately transfers to wheel. • Axle Load Characteristics Though the legal limits in India are 10.2 tonnes , 19.0 tonnes, 24.0 tonnes for single , tandem , tridem axle respectively but a large number of axles operating on national highways carry much heavier loads than the legal limits. Data on load spectrum of the commercial vehicles is required to estimate the repetitions of single ,tandem , tridem axles in each direction expected during the design period 37
  38. 38. • Minimum percentage of vehicle to be weighed should be 10 percent if Commercial vehicles per day (cvpd) exceeding 6000 , 15 percent for cpvd for 3000 to 6000 and 20 percent for cpvd for less than 3000 . Axle load survey may be conducted at least for 48 hrs and data on axle load spectrum of the commercial vehicles is required to estimate the repletion of single , tandem , tridem axles . If the spacing of consecutive vehicle is greater than 2.4 meters then the each vehicle may be considered as single axle.The interval at which axle load group should be classified : • Single axle-10 kN • Tandem axle -20 kN • Tridem axle -30 kN 38
  39. 39. Wheel Base Characteristics • Information on typical spacing between successive axles of commercial vehicle is necessary to identify the proportion of axles that should be considered for estimating Top- Down fatigue cracking caused by axle load during night period when the slab has tendency of curling up due to negative temperature differential. The axles spacing of more than 4.5 m are not expected to contribute Top-Down fatigue cracking. 39
  40. 40. 2 Axle Truck 3 Axle Truck Truck ConfigurationTruck Configuration 4 Axle Semi Articulated 5 Axle Truck LCV
  41. 41. Axle ConfigurationsAxle Configurations Single Axle With Single Wheel Single Axle With Dual Wheel Tandem Axle Tridem Axle An axle is a central shaft for a rotating wheel or gear
  42. 42. Standard AxleStandard Axle Single axle with dual wheels carrying a load of 10.2 tonnes is defined as standard axle. 10.2 Tonnes Standard Axle
  43. 43. DESIGN LIFEDESIGN LIFE • To achieve a design of low life cycle cost and in respect of the high social cost for full depth reconstruction, • The design life for rigid pavement is generally recommended as 30 years. • Within this life span, it is expected that no extensive rehabilitation is required under normal circumstances . • The service life of the pavement structure can be sustained by minor repairs. • It is anticipated that the service life can be further extended upon ‘expiry’ of the original ‘design life’ by timely maintenance and localized bay replacement. 43
  44. 44. Commercial Vehicle ForecastCommercial Vehicle Forecast The definition of commercial vehicle follows the one given in the Annual Traffic Census published by Transport Department, which includes medium /heavy goods vehicle and bus, other light vehicles, for examples, motor cycle ,private car and public light bus, are normally ignored as their induced structural damage on pavements is minimal. The annual flow of commercial vehicles at the time of road opening is obtained by multiplying the daily flow by 365 days/year. The cumulative number of commercial vehicles using a road during its design life is obtained by summing up the annual traffic of each year taking into consideration the predicted growth rate. 44
  45. 45. The forecast can be done with reference to on-site traffic count data, traffic census or other available traffic studies and planning data . C=(365*A{(1+r) n -1})/r˄ 45
  46. 46. Traffic considerationTraffic consideration Design lane The lane carrying the maximum number of heavy commercial vehicle is termed as design lane . each lane of the two way lane highways are the outer lane of multi lane highways can be considered as design lane . • Lateral placement characteristics. It is recommended that 25 percent of the total two –way commercial traffic may be considered as design traffic for two- lane two – way roads for the analysis of BUC. In case four lanes and other multi lane divided highways 25 percent of the total traffic in the direction of predominant traffic may be considered for design of pavement for bottom up cracking. For TDC those vehicles with the spacing between transverse joint. 46
  47. 47. Temperature Consideration • Temperature differential between the top and the bottom fibers of concrete pavements causes the concrete slab to curl giving rise to the stress and this is a function of solar radiation received by the pavements surface , wind velocity , latitude etc . As far as possible actual temperature differential should be considered. In the absence of data code has given the maximum temperature differential. 47
  48. 48. Concrete strengthConcrete strength Flexural strength of the concrete is required for the purpose of design of concrete slab and this flexural strength is taken for 90 days insist of 28 days because initial repletion a are very low and it can be obtained by multiplying factor 1.1 fcr= 1.1 * 0.7√fck 48
  49. 49. Modulus of elasticity and poission ratio ofModulus of elasticity and poission ratio of concreteconcrete • The modulus of elasticity and poisson ratio are known to vary with the concrete materials and strength. • The elastic modulus increase with the increase in strength and poisson ratio decrease with increase in modulus of elasticity • E=30000Mpa • µ=0.15 • Coefficient of Thermal Expansion • The coefficient of thermal expansion of concrete is dependent to a great extent on the types of aggregate used in concrete. However for design purpose a value of α=10*10-6˚C is adopted. 49
  50. 50. Fatigue behavior of cement concreteFatigue behavior of cement concrete • Due to repeated application of flexural streesse by the traffic load , progressive fatigue damage takes place in the cement concrete slab in the form of gradual devlopement of micro cracks especially when the ratio between the flexure stress and flexure strength of concrete is high this ratio is termed as stress ratio (SR) and following relation is given. 50
  51. 51. Environmental factorsEnvironmental factors • Environmental factors affect the performance of the pavement materials and cause various damages. Temperature: • In rigid pavements, due to difference in temperatures of top and bottom of slab, temperature stresses or frictional stresses are developed. When there is variation in temperature due to which curling of slab with different temperature will be different and hence TDC and BUC factors has to be considered . 51
  52. 52. Precipitation : The precipitation from rain and snow affects the quantity of surface water infiltrating into the subgrade and the depth of ground water table. Poor drainage may bring lack of shear strength, pumping, loss of support, etc. •Material characteristics Pavement material consists of different types of sub grade soil , fine aggregates, granular materials , binders, , etc . physical and engineering properties of different material used for constructing any kind of pavement plays an important role in thickness design of pavement. 52
  54. 54. SubgradeSubgrade • In winkler model it is assumed that the foundation is made up of springs supporting the concrete slabs the strength of subgrade is expressed in terms of modulus of subgrade reaction K . • Which is defined as the pressure per unit deflection of the foundations as determined by plate load test The modulus of subgrade reaction (k) is used as a primary input for rigid pavement design. It estimates the support of the layers below a rigid pavement surface course (the PCC slab). The k value can be determined by field tests or by correlation with other tests. There is no direct laboratory procedure for determining k value. 54
  55. 55. • Westergaard considered the rigid pavement slab as a thin elastic plate resting on soil subgrade,which is assumed as a dense liquid. The upward reaction is assumed to be proportional to the deflection. Base on this assumption, Westergaard defined a modulus of subgrade reaction in kg/cm given by where is the displacement level taken as 0.125 cm and is the pressure sustained by the rigid plate of 75 cm diameter at a deflection of 0.125 cm. • If the diameter of plate is not 75 cm then even then we can find the value of k by using the following equations K750=kΦ(1.21Φ+.078) 55
  56. 56. • In case the plate bearing test could not be conducted, the approximate k- value corresponding to CBR values can be obtained from its soaked CBR value using Table 2 (IRC:58-2011 ) 56
  57. 57. 57
  58. 58. Sub Base The main purpose of the sub base is to provide the uniform ,stable,and the permanent support to the concrete slab laid over it .It should have sufficient strength so that it is not subjected to disintegration and erosion under heavy traffic and adverse environment conditions. For these sub base of Dry lean concrete having 7 day strength of 10 Mpa determined is recommended. The effective k value of different combinations of subgrade and sub base can be estimated from table 3. 58
  59. 59. Drainage layer /Filtration layerDrainage layer /Filtration layer • Entrapped water in the subgrade and granular sub base may cause erosion of the foundation material since pore water pressure generated by the tandem and tridem is substantially high. • To facilitate quick disposal of water that is likely to enter subgarde, a drainage layer together with filter/ separation layer may be provided beneath the subbase throughout the road width. The filtration layer also prevents fines from pumping up from the subgrade to the drainage layer. 59
  60. 60. Debonding layerDebonding layer • To reduce the friction between concrete slab and DLC. • Generally 125 micron thin sheet .(polythene). 60
  62. 62. Modulus of sub-grade reactionModulus of sub-grade reaction Westergaard considered the rigid pavement slab as a thin elastic plate resting on soil sub-grade, which is assumed as a dense liquid. The upward reaction is assumed to be proportional to the deflection. Base on this assumption, Westergaard defined a modulus of sub-grade reaction K in kg/cm3 given by ΔK = p where Δ is the displacement level taken as 0.125 cm and p is the pressure sustained by the rigid plate of 75 cm diameter at a deflection of 0.125 cm. 62
  63. 63. Relative stiffness of slab to sub-gradeRelative stiffness of slab to sub-grade A certain degree of resistance to slab deflection is offered by the sub-grade. The sub-grade deformation is same as the slab deflection. Hence the slab deflection is direct measurement of the magnitude of the sub-grade pressure. This pressure deformation characteristics of rigid pavement lead Westergaard to the define the term radius of relative stiffness l in cm is given by the below equation 63
  64. 64. Equivalent radius of resisting sectionEquivalent radius of resisting section When the interior point is loaded, only a small area of the pavement is resisting the bending moment of the plate. Westergaard's gives a relation for equivalent radius of the resisting section in cm in the below equation where a is the radius of the wheel load distribution in cm and h is the slab thickness in cm. 64
  65. 65. Critical load positionsCritical load positions Since the pavement slab has finite length and width, either the character or the intensity of maximum stress induced by the application of a given traffic load is dependent on the location of the load on the pavement surface. There are three typical locations namely the interior, edge and corner, where differing conditions of slab continuity exist. These locations are termed as critical load positions. 65
  66. 66. where h is the slab thickness in cm, P is the wheel load in kg, a is the radius of the wheel load distribution in cm, l the radius of the relative stffiness in cm and b is the radius of the resisting section in cm 66
  67. 67. Wheel load stresses - Westergaard's stressWheel load stresses - Westergaard's stress equationequation • The cement concrete slab is assumed to be homogeneous and to have uniform elastic properties with verticalsub-grade reaction being proportional to the deflection. • Westergaard (1926) developed equations for solution of load stresses at three critical regions of the slab – interior, corner and edge • Interior -Load in the interior and away from all the edges • Edge – Load applied on the edge away from the corners 67
  68. 68. 68 Corner – Load located on the bisector of the corner angle Westergaard developed relationships for the stress at interior, edge and corner regions, in kg/cm2
  69. 69. Temperature stressesTemperature stresses Temperature stresses are developed in cement concrete pavement due to variation in slab temperature. This iscaused by (i) daily variation resulting in a temperature gradient across the thickness of the slab and (ii) seasonalvariation resulting in overall change in the slab temperature. The former results in warping stresses and the later in frictional stresses. 69
  70. 70. 70
  71. 71. Warping stressWarping stress •Temperature differential between the top and the bottom surfaces of a cement concrete slab is a common phenomenon whether its day or night. Expansion and contraction of the slab as a result of temperature difference causing geometric deformation – either curling up or down. Warping or temperature stresses will produced in the slab when geometric deformations are completely restrained by its self weight. Two critical conditions of warping stresses in a cement concrete slab are presented in figure (next slide). Due to curling of the slab , tensile and compressive stresses are produced in its bottom fibers during the day and night respectively . maximum warping stress is observed at the interior of the slab than towards its edges since the interior part of the slab is more restrained against curling than the edges. 71
  72. 72. Warping stress in concrete slab when curlingWarping stress in concrete slab when curling is restrained at different timesis restrained at different times 72
  73. 73. • Based on the plate theory, westergaard (1926) developed formula for calculating the warping stresses in the concrete slab . In 1938 , Bradbury modifies his formulae and developed the following equations for calculating the maximum warping stress at the interior and edge of the slab having finite dimensions 73
  74. 74. Frictional stressesFrictional stresses Slab movement are restrained by its self weight caused by the inter surface frictional forces between the slab and the supporting layer ( sub – base layer ). For example when the slab contracts its movement are restrained by frictional forces and tensile stresses are developed 74
  75. 75. Critical Combination of StressesCritical Combination of Stresses The cumulative effect of the different stress give rise to the following three critical cases. • Summer, mid-day: The critical stress is for edge region given by σcritical =σe + σte -σ f. • Winter, mid-day: The critical combination of stress is for the edge region given by σcritical = σe+σte +σf. • Mid-nights: The critical combination of stress is for the corner region given by σcritical = σc + σtc. 75
  76. 76. Design of slab thicknessDesign of slab thickness Critical stress condition The severest combination that induce the maximum stress in the pavement will give the critical combinations . The flexural stress due to the combined action of traffic loads and temperature differential between the top and the bottom fibers of the concrete slab is considered for the design of pavement thickness The flexural stress at the bottom layer of the concrete slab is maximum during the day hours when the axle load act mid ways on the pavement slab while there is positive temperature gradient . as shown . This condition is likely to produce Bottom- Up cracking(BUC). 76
  77. 77. 77 •Location of the points of maximum flexureal stresses at the bottom of the pavement slab without tied concrete shoulder for single , tandem , tridem axle as shown . the tyre imprints the longitudinal to the edges. For tied shoulder same stress will be produced at same location. Single axle cause highest stress followed by tandem and tridem axles respectively.
  78. 78. 78
  79. 79. During the night hours the top surface is cooler than the bottom surface and the ends of the slab curl up resulting in loss of support for the slab as shown . Due to the restrained provide by the self weight of concrete and by the dowel connections, temperature tensile. stresses are caused at top 79
  80. 80. • Figure shows the placement of axles load close to transverse joint when there is negative temperature gradient during night period causing high flexural stress at the top of the slab leading to the Top – down cracking (TDC) 80
  81. 81. Calculation of flexural stressCalculation of flexural stress • For bottom up cracking case the combination of load and positive non linear temperature differential has been considered . for BUC single /tandem has been placed on the slab in the position . in BUC single axle load causes the largest edge stress followed by tandem and tridem axles . since the stress due to tridem axles are small they were not considered for stresses analysis For BUC. • For TDC only one axle of single/ tandem / tridem axles units has been considered for analysis in combination with front front axle . front axle weight has been assumed to be 50 percent of the rear axle unit. 81
  82. 82. Analysis has been done for the following casesAnalysis has been done for the following cases BOTTOM – UP CRACKING • Pavement with tied concrete shoulder for single rear axle • Pavement without tied concrete shoulder for single rear axle • Pavement with tied concrete shoulder for tandem axle • Pavement without tied concrete shoulder for tandem axle TOP – DOWN CRACKING • Paving with and without dowel bars having front steering axles with the single tyres and the first axles of the rear unit placed on the same panel. 82
  83. 83. CUMULATIVE FATIGUE DAMAGECUMULATIVE FATIGUE DAMAGE ANALYSISANALYSIS • For a given slab thickness and other parameter the pavement will be checked for cumulative bottom up and top down fatigue damage. For bottom up cracking the flexural stress at the edge due to combined action of single or tandem rear axle load and positive temperature differential cycles are considered. • The stress can be either selected from the stress charts ( as shown some sample figures) or by using the equation ( shown some sample equations.. chart explain clearly the interplay of thickness , modulus of subgrade reaction, axle load and temperature differential 83
  84. 84. • Similarly for assessing the TDC fatigue damagef caused by repeated cycles of axle load and negative temperature , flexural stress can be estimated in same manner. • The flexural stress is divided by the design flexural strength of the cement to obtain the stress ratio ( SR) 84
  85. 85. 85
  86. 86. Recommended procedure for slab designRecommended procedure for slab design The following steps may be followed for design. • Step-1: Stipulate design values for the various parameters. • Step-2: select a trial design thickness of pavement slab . • Step-3: Compute the repetitions of axles load of different magnitude and different categories during the design life . • Step-4: Find the proportions of axle load repetitions operating during the day and night periods 86
  87. 87. • Step-5: Estimate the axle load repetitions in the specified six hours period during the day time . the maximum temperature differential is assumed to be remain constant during the 6 hrs for analysis of bottom Up cracking. • Step-6: Estimate the axle load repetitions in the specified six hours period during the night time . • The maximum negative temperature differential during night is taken as half of day time maximum temperature differential. Built in negative temperature differential of 50 ˚c developed during the setting of the concrete to be added to the temperature differential for the analysis of top – down cracking . only those vehicle whose front and first rear axle come between transverse joints are considered. 87
  88. 88. • Step-7: compute the flexural stresses at the edge due to single and tandem axle load for the combined effect of axle load and positive temperature differential during ay time determine the stress ratio and evaluate the CFD for single and tandem axle loads. Sum of the two CFD should be less than 1.0 for the slab to be safe against bottom up cracking. • Step-8: compute the flexural stresses at the centre area of transverse joint and the rear axle close to the following joint in the same panel under negative temperature differential. determine the stress ratio and evaluate the CFD for single and tandem axle loads. Sum of the two CFD should be less than 1.0 for the slab to be safe against bottom up cracking . 88
  90. 90. Load Transfer At The JointsLoad Transfer At The Joints 90 •It is important that the load applied on the slab is shared by adjacent slab also for better performance of pavement. •If load transfer across the slab is poor, distress such as faulting pumping, and corner break occur. •Load transfer occurs through different mechanism. •The ability of the pavement to transfer load at joint is called “load transfer efficiency”. •Granular interlocking is expected along the cracks that form at transverse joints. •For low volume road the load transfer is expected to be provided by interlocking. •For higher traffic volume thicker higher dowel bars are provided.
  91. 91. 91
  92. 92. Types Of JointsTypes Of Joints
  93. 93. 93
  94. 94. Expansion JointsExpansion Joints • Joints are provided to allow for expansion of the slabs due to rise in slab temperature above the construction temperature . It also permits the contraction of slabs it is provided in India in the interval of 50 to 60 cm for smooth interface in winter and 90-120 cm for smooth interface in summer . • Maximum spacing is 140 m • Expansion joint dowels are specially fabricated with a cap on one end of each dowel that creates a void in the slab to accommodate the dowel as the adjacent slab closes the expansion joint.
  95. 95. Contraction jointsContraction joints • These are provided to permit the contraction of slabs. These joints are spaced closer than the expansion joints. • Load tranfer at this joint is by aggregate interlocking at the joint face. • The maximum spacing of contraction joints is 4.5 m.
  96. 96. Warping jointsWarping joints • These are provide to relieve stresses induced due to warping known as hinged joints. • These joints are rarely provided
  97. 97. Construction JointsConstruction Joints • A construction joint is defined as “a joint between slabs that results when concrete is placed at different times. A header and dowel basket for a transverse construction joint are shown . After paving up to the header, the header will be removed. The next paving day will start with new concrete butted up against the old concrete.. 97
  98. 98. Longitudinal jointsLongitudinal joints • A longitudinal joint is defined as a joint between two slabs which allows slab warping without appreciable separation or cracking of the slabs . • Longitudinal joints are used to relieve warping stresses and are generally needed when slab widths exceed [4.5m] . • To aid load transfer, tie bars are often used across longitudinal joints. Tie bars are thinner than dowels, and use deformed reinforcing bars rather than smooth dowel bars. • On soil subgrade of clay , such joints are provided to allow differential shrinkage and swelling due to rapid changes in subgrade moisture under the edges than the under the centre of road.
  99. 99. • In these joints tie bars are provided to hold the adjacent slab . 99
  100. 100. Distress In Rigid PavementDistress In Rigid Pavement • Distress Types For JPCP And JRCP: • Cracking – divided into corner breaks, durability (“D”) cracking, longitudinal cracking, and transverse cracking. • Joint Deficiencies – joint seal damage (transverse or longitudinal), and joint spalling (transverse or longitudinal). • Surface Defects – divided into map cracking, scaling, polished aggregates, and popouts. • Miscellaneous Distresses – classified as blowups, faulting of transverse joints and cracks, lane-to- shoulder drop off, lane-to-shoulder separation, patch deterioration, and water bleeding and pumping.
  101. 101. Distress Types For CRCP: • Cracking – as described, except CRCP cannot have corner breaks. • Surface defects – as described. • Miscellaneous Distresses – as above, with the addition of punchouts, transverse construction joint deterioration, and longitudinal joint seal damage. Also, CRCP does not have joints, so joint faulting does not occur. 101
  102. 102. cracking Transverse cracking
  103. 103. Longitudinal cracking
  104. 104. Advantages of Concrete PavementAdvantages of Concrete Pavement • Longer lasting – 40 year Design Life . • Heavy duty Pavements have generally the lowest cost. • Pavement maintenance costs are up to 10 times cheaper than the same for flexible pavements. • Minimum maintenance requirements result in less traffic disruption, minimum congestion time and as a result Work zone safety. • Lowest Life Cycle Cost of all Heavy Duty pavements and highest salvage value. 105
  105. 105. • Can be constructed over poor subgrades. • Thinner overall pavement thickness = lower consumption of raw materials. • Resistant to abrasion from turning actions. • No affected by weather, inert to spills and fire. • High abrasion durability. • Profile durability. • Use of waste products like flyash and slag. • Riding quality does not deteriorate. • Saving of fuel costs of at least 1.1% over asphalt . • Light colour enhances night visibility 106
  106. 106. Disadvantages of Rigid PavementDisadvantages of Rigid Pavement • To provide economics and quality, it requires larger projects. • Set-up costs are significant. • On-site batch plant is essential for slip forming. • Slip forming requires minimum 200 m runs. • Concrete must achieve a certain strength before it can be placed under traffic • Repairs take longer = traffic disruption and work site safety. • Unless longitudinal grooving is used, tyre/road noise can become a nuisance
  107. 107. • Issue in urban areas after 80/90 km/h speeds. • May lose non-skid surface with time. • Needs even sub-grade with uniform settling. • May fault at transverse joints. • Requires frequent joint maintenance. 108
  108. 108. REFRENCESREFRENCES 109 [1] IRC-58-2011 Guidelines for the design of plain jointed rigid pavements for highways . [2] IRC-9-1972 Traffic census on Non- urban road. [3] S.K. Khanna –C.E.G Justo , book of highway engineering . [4] R Srinivas Kumar , Book of Highway engineering . [5] Chakroborty Book Of highway engineering.
  109. 109. 110