Se ha denunciado esta presentación.
Se está descargando tu SlideShare. ×

Rigid pavement

Cargando en…3

Eche un vistazo a continuación

1 de 58
1 de 58

Más Contenido Relacionado

Audiolibros relacionados

Gratis con una prueba de 30 días de Scribd

Ver todo

Rigid pavement

  1. 1. M.Tech Assignment Report 1 | P a g e Civil engineering Department N.I.T Hamirpur 1. Introduction  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.  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) 1.1. 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. 1.2. What Is A Pavement? • A multi layer system that distributes the vehicular loads over a larger area. • 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. • It can also be defined as “structure which separates the tires of vehicles from the under lying foundation.”
  2. 2. M.Tech Assignment Report 2 | P a g e Civil engineering Department N.I.T Hamirpur • Pavement is the upper part of roadway, airport or parking area structure • It includes all layers resting on the original ground • It consists of all structural elements or layers, including shoulders Figure 1. Distribution of Wheel Load 1.3. Functions 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 .
  3. 3. M.Tech Assignment Report 3 | P a g e Civil engineering Department N.I.T Hamirpur 1.4. Requirements of 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 mat. shd be non-frost susceptible. • Pavement surface should be skid resistant. 2. History of Road Development 2.1. Ancient Roads 2.1.1. By foot • These human pathways would have been developed for purposes leading to camp sites, food, streams for drinking water etc. • The next major mode of transport was the use of animals 2.1.2. The invention of wheel • Led to the development of animal drawn vehicles. Then it became necessary that the road surface should be capable of carrying greater loads. Thus roads with harder surfaces emerged. • To provide adequate strength to carry the wheels, the new ways tended to follow the sunny drier side of a path. These have led to the development of foot-paths. After the invention of wheel, animal drawn vehicles were developed and the need for hard surface road emerged.
  4. 4. M.Tech Assignment Report 4 | P a g e Civil engineering Department N.I.T Hamirpur • Traces of such hard roads were obtained from various ancient civilization dated as old as 3500 BC 2.2. Roman roads • The earliest large scale road construction is attributed to Romans who constructed an extensive system of roads radiating in many directions from Rome. • Appian way which was build by Romans in 312 B.C. Figure 2. Roman Road 2.3. French roads or Tresaguet road • The next major development in the road construction occurred during the regime of Napoleon. • The signficant contributions were given by Tresaguet in 1764 . • He developed a cheaper method of construction than the locally unsuccessful revival of Roman practice. • The pavement used 200 mm pieces of stone of a more compact form and shaped such that they had at least one at side which was placed on a compact formation. • Smaller pieces of broken stones were then compacted into the spaces between larger stones to provide a level surface.
  5. 5. M.Tech Assignment Report 5 | P a g e Civil engineering Department N.I.T Hamirpur • Finally the running layer was made with a layer of 25 mm sized broken stone Figure 3. French Road 2.4. Telford Construction • The next development was done by Scottish engineer Thoms Telford (1757-1834). • The foundation was prepared for a road with width of 9 m and it was leveled. • Large size stones of width equal to 40 mm and depth 170 to 220 mm were then laid. • After filling the spaces between foundation stones, two layers of stones having compacted thickness of 100 and 50 mm respectively laid in the center of 5.4 m. of width. • The top layer of road was made of 40 mm thick binding layer of gravel.
  6. 6. M.Tech Assignment Report 6 | P a g e Civil engineering Department N.I.T Hamirpur Figure 4. Telford Road 2.5. British roads or Macadam Road • The British engineer John Macadam introduced what can be considered as the first scientific road construction method. • Stone size was an important element of Macadam road. By empirical observation of many roads, he came to realize that 250 mm layers of well compacted broken angular stone would provide the same strength and stiffness and a better running surface than an expensive pavement founded on large stone blocks. Figure 5. British Road
  7. 7. M.Tech Assignment Report 7 | P a g e Civil engineering Department N.I.T Hamirpur Figure 6. Composition Of Various Roads 2.6. Modern roads • The modern roads by and large follow Macadam's construction method. Use of bituminous concrete and cement. • Various advanced and cost- effective construction technologies are used. • Development of new equipment's help in the faster construction of roads. • Many easily and locally available materials are tested in the laboratories and then implemented on roads for making economical and durable pavements. Figure 7. Chronological arrangement of Types Of Roads
  8. 8. M.Tech Assignment Report 8 | P a g e Civil engineering Department N.I.T Hamirpur 3. Road/Pavement System 3.1. Typical Components • Several elements make up the roadway. • Each layer represents one of the elements of the pavement system. • All these elements work together to provide a quality durable pavement Figure 8. Typical Component of Pavement 3.1.1. Embankment  When roads are built higher than the surrounding ground, a structure of compacted earth called an embankment is built.  The embankment is built to support the other three layers of the pavement system.  Embankments can be made from almost any common type of deposit except topsoil. 3.1.2. Sub-grade  The sub-grade is made of soils that have been specially prepared to meet the requirements to support the other two layers.
  9. 9. M.Tech Assignment Report 9 | P a g e Civil engineering Department N.I.T Hamirpur  The sub-grade is a selected soil material that is carefully compacted to provide uniform support to the pavement.  The sub-grade lies directly on either the embankment or the native soil. 3.1.3.Base  The base is a mixture of crushed rock.  The base layer provides uniform support to the pavement and allows water that penetrates any joints or cracks in the pavement to move quickly to the sub-drain without saturating and softening the sub-grade.  The base layer lies directly on top of the sub-grade and is built of clean sand or rock. 3.1.4. Pavement  The top layer is the pavement.  The pavement materials can either be Hot Mix Asphalt (HMA) and Portland Cement Concrete (PCC).  The pavement itself resists bending, and distributes vehicle weights over a large area.
  10. 10. M.Tech Assignment Report 10 | P a g e Civil engineering Department N.I.T Hamirpur 4.Types of Pavements (Modern) Typically Modern pavement is of two types as follows: 4.1. Flexible and Rigid Figure 9 . Modern Time Pavements
  11. 11. M.Tech Assignment Report 11 | P a g e Civil engineering Department N.I.T Hamirpur 4.2. Comparison Between Flexible And Rigid Pavements Figure 10. Comparison Between Flexible And Rigid Pavements Some other differences are as follows: 4.2.1. Flexible pavements: • Deep foundations / multi layer construction • Energy consumption due to transportation of materials • Increasing cost of asphalt due to high oil prices 4.2.2. Rigid pavements • Single layer. 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.
  12. 12. M.Tech Assignment Report 12 | P a g e Civil engineering Department N.I.T Hamirpur • Generally last longer. • May require asphalt topping due to noise / comfort issues . • Rigid pavements more economic when considering environmental / life-cycle costing • Heavy vehicles consume less fuel on rigid pavements Figure 11. Load Distribution In Flexible and Rigid Pavements. Figure 12. Load Distribution In Flexible and Rigid Pavements.
  13. 13. M.Tech Assignment Report 13 | P a g e Civil engineering Department N.I.T Hamirpur 5. Rigid pavement 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. Load is transmitted through beam action of slab in rigid pavements. Rigid pavements are those, which reduces the stress concentration and distributes the reduced stresses uniformly to the area under the slab.  Rigidity – does not deform under stress  Concrete – air entrained increases resistance to frost damage and salt corrosion  Reinforcement – may be bars or mesh. Continuous rigid pavements have heavy reinforcement  Joints – used in non-continuous pavements to allow for thermal movement. Includes a „filler‟ and surface sealant  Rigid pavements – laid as single layer by „concrete paver‟ 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
  14. 14. M.Tech Assignment Report 14 | P a g e Civil engineering Department N.I.T Hamirpur  Life span is more as compare to flexible (Low Maintenance Cost)  Rigid pavements are those pavements whose surface is hard  This pavement is not transferred the load from ground surface to lower surface.  Rigid Pavement has the capacity to transfer the wheel load from wider area of roads.  Rigid pavement is formed either of OPC slabs or cement concrete. 5.1. Distribution of load In rigid pavement, load is distributed by the slab action, and the pavement behaves like an elastic plate resting on a viscous medium The high modulus of elasticity and rigidity of concrete compared to other road making materials provides a concrete pavement with a reasonable degree of flexural or “beam” strength. This property leads to externally applied wheel loads being widely distributed. This in turn limits the pressures applied to the subgrade as illustrated in Figure . The major portion of the load carrying capacity of a concrete pavement is therefore provided by the concrete layer alone. Its thickness is primarily determined by the flexural strength of the concrete and by the magnitude of the wheel or axle loads. Subbases do not make a significant structural contribution to concrete pavements. The purpose of the subbase is to provide uniform support to the base concrete layer and to provide sufficient resistance to erosion of the subbase material under traffic and environmental conditions. Only lean mix concrete or bound subbases are recommended in the design guides. Although the strength of the subgrade does not significantly affect the thickness of the concrete pavement, unlike the situation with flexible pavements where the thickness is more sensitive to variations in the subgrade strength, the proper design and construction of the subgrade and subbase is still important to the performance and long term serviceability of a concrete pavement.
  15. 15. M.Tech Assignment Report 15 | P a g e Civil engineering Department N.I.T Hamirpur Figure 13 . Distribution of Wheel Loads under Concrete Pavements 5.2. Basic component of concrete pavements Figure 14. Basic component of concrete pavements
  16. 16. M.Tech Assignment Report 16 | P a g e Civil engineering Department N.I.T Hamirpur 6. Types of Concrete Pavements Figure 15 .Flow Chart of Types of concrete Pavements 6.1. Un-Reinforced Concrete Pavement (URCP) /PCP  PCPs contain no reinforcement, except at special situations where irregularly shaped slabs or mismatching joints are involved.  PCP is the most common pavement for highways Worldwide.  Transverse contraction joints are induced by saw cuts and their spacing is determined by limiting the maximum shrinkage movement in the joint to 2 mm.  This results in an average spacing of about 4.2 m (For longer lengths of up to 5 m, dowels have to be used).  Longitudinal joints are either induced by saw cuts or formed. These have a maximum spacing of 4.3 m and are held together by suitably spaced 12 mm Ø deformed tie bars Types of concrete pavement UN-Reinforced concrete pavement (URCP) Jointed dowelled concrete pavements (JDCP or JPCP) Jointed un – dowelled concrete pavements (JUCDP) Reinforced Concrete pavement (RCP) Jointed Reinforced concrete pavements (JRCP) Continousl y reinforced concrete pavements (CRCP)
  17. 17. M.Tech Assignment Report 17 | P a g e Civil engineering Department N.I.T Hamirpur  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. Figure 16.. PCP And JDCP 6.2. Reinforced Concrete pavement -RCP • 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. 6.2.1. Reinforced Concrete Pavement – JRCP • 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. • JRCPs are typically reinforced with welded steel fabric, usually (8mm Ø bars at 200 mm centres)
  18. 18. M.Tech Assignment Report 18 | P a g e Civil engineering Department N.I.T Hamirpur • Transverse contraction joints are induced by saw cuts providing slab lengths of 8 m – 12 m. (Slab lengths are varied depending on the length of the mesh sheets available) • JRCP joints are always dowelled. • The criteria for longitudinal joints is the same as for PCP Figure 17. JRCP 6.2.2. Continuously Reinforced Concrete Pavements -CRCP • CRCP has continuous longitudinal reinforcement of N16 Ø deformed bars to induce transverse cracking at random spaces of 0.5 – 2.5m. • Nowadays the preferred location is central. • No contraction joints are provided. • Transverse reinforcement bars are provided to support the longitudinal steel and as a means of holding together any unplanned longitudinal cracks. • The criteria for longitudinal joints are the same as for PCP. • Worldwide there is no universal agreement on the percentage of the longitudinal steel required. • 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.
  19. 19. M.Tech Assignment Report 19 | P a g e Civil engineering Department N.I.T Hamirpur • CRCP preferred in (i) main heavy traffic corridors (expressways) (ii) Adverse climatic conditions (iii) Weak sub grades. Figure 18. CRCP 6.3. Steel Fiber Concrete Pavement – SFCP • SFCP is used in situations where there is a need to provide increased resistance to cracking in both odd shaped and acute cornered slabs and is ideally suited for areas with high proportion of slabs of irregular shape, e.g.round abouts. • Transverse and longitudinal contraction joints in SFCPs are un dowelled and at a maximum spacing of 6 m • Steel fiber is usually mixed at ~70 kg/m3 and the characteristic compressive strength of concrete is 40 – 45 MPa, giving a flexural strength of 5 MPa. • Slabs are generally thinner than those of conventional concrete and have a minimum thickness of 180 mm. 6.4. Prestressed Concrete Pavement - PSCP • PSCP is generally used for prefabrication of base slabs for replacement of damaged slabs in all types of concrete pavements.
  20. 20. M.Tech Assignment Report 20 | P a g e Civil engineering Department N.I.T Hamirpur 7. Factors Governing Design Of Pavements • Design wheel load  Static load on wheels.  Contact Pressure.  Load Repetition. • Subgrade soil  Thickness of pavement required.  Stress- strain behavior under load.  Moisture variation. • Design Period . • Design commercial traffic volume. • 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. • Traffic consideration
  21. 21. M.Tech Assignment Report 21 | P a g e Civil engineering Department N.I.T Hamirpur 7.1. 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. 7.2. 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. 7.3. 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. 7.4.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. 7.5. Static Load On Wheels This factor is used to design the thickness of slab because the load of the axle is ultimately transfers to wheel. 7.6. 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
  22. 22. M.Tech Assignment Report 22 | P a g e Civil engineering Department N.I.T Hamirpur design period . 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 for fatigue damage analysis are : Single axle-10 kN Tandem axle -20 kN Tridem axle -30 kN 7.7. 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. Axle load configurations Figure 19 . Axle Load Configurations
  23. 23. M.Tech Assignment Report 23 | P a g e Civil engineering Department N.I.T Hamirpur 7.8. Design Period The design period is defined in terms of cumulative numbers of standard axles that can be carried out before strengthening of the pavement is necessary .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. 7.9. Design Commercial Traffic Volume. 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 (in general whose weight is more than 3 tonne) and LMVT 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. The forecast can be done with reference to on-site traffic count data, traffic census or other available traffic studies and planning data . The average daily traffic should normally be based on seven day 24-hrs count . The traffic growth rate of commercial vehicle shall be taken to be minimum 5 percent however for typical design 7.5 percent value has been considered ) ) Where, C= Commercial Vehicles r = Traffic Growth Rate Composition of commercial traffic in terms of single , tridem , tandem
  24. 24. M.Tech Assignment Report 24 | P a g e Civil engineering Department N.I.T Hamirpur This factor governing the design of pavement for top down fatigue cracking or bottom up fatigue cracking and base on the other factors. The edge flexural stress caused by axle load for bottom up cracking is the maximum when the tyre imprint both the outer wheel touches the longitudinal edge . when the tyre position is away even by 150 mm from the longitudinal edge , stress in the edge region reduced substantially . The edge stress is small when the wheel are close to transverse joint. 7.10. 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. 7.11. Lateral placement characteristics. Taking into consideration above factors 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 bottom up cracking. 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 traffic flow will be the portion of BUC analysis only those vehicles with the spacing between the front axles and front rear axles less than the spacing between transverse joint. 7.12. 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.
  25. 25. M.Tech Assignment Report 25 | P a g e Civil engineering Department N.I.T Hamirpur The variation of temperature with depth is non linear during the day time and linearly during the night time hours. the maximum temperature differential during the night is nearly half of the day time maximum temperature differential. Temperature differentials are positive when the slab has the tendency to have convex shape during the day hours and negative with concave shape during the night. 7.13. Subgrade 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 .
  26. 26. M.Tech Assignment Report 26 | P a g e Civil engineering Department N.I.T Hamirpur 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. Figure 20 . Winkler‟s Model 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) Where: Φ= plate diameter in metres kΦ= modulus of subgrade reaction ( MPa/m) with plate diameter Φ K750= modulus of subgrade reaction (Mpa/m) with plate diameter of 750 mm. The above test performed is known as Plate load test. 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 )
  27. 27. M.Tech Assignment Report 27 | P a g e Civil engineering Department N.I.T Hamirpur Definition: California bearing ratio is the ratio of the force per unit area required to penetrate in to a soil mass with a standard circular piston at the rate of 1.25mm/min to that required for the corresponding penetration of a standard material. CBR = *100 Subgrade Performance A subgrade‟s performance generally depends on two interrelated characteristics: Load bearing capacity. The subgrade must be able to support loads transmitted from the pavement structure. This load bearing capacity is often affected by degree of compaction, moisture content, and soil type. A subgrade that can support a high amount of loading without excessive deformation is considered good. Volume changes. Most soils undergo some amount of volume change when exposed to excessive moisture or freezing conditions. Some clay soils shrink and swell depending upon their moisture content, while soils with excessive fines may be susceptible to frost heave in freezing areas . Poor subgrade should be avoided if possible, but when it is necessary to build over weak soils there are several methods used to improved subgrade performance: Removal and replacement (overexcavation).Poor subgrade soil can simply be removed and replaced with higher qualityfill. Although this is simple in concept, it can be expensive. Stabilization with a cementitious or asphaltic binder. The addition of an appropriate binder (such as lime, portland cementor emulsified asphalt) can increase subgrade stiffness and/or reduce swelling tendencies.
  28. 28. M.Tech Assignment Report 28 | P a g e Civil engineering Department N.I.T Hamirpur Additional base layers. Marginally poor subgrade soils may be made acceptable by using additional base layers. These layers spread pavement loads over a larger subgrade area. This option is rather perilous; when designing pavements for poor subgrades the temptation may be to just design a thicker section with more base material because the thicker section will satisfy most design equations. However, these equations are at least in part empirical and were usually not intended to be used in extreme cases. In short, a thick pavement structure over a poor subgrade may not make a good pavement. Subgrade Physical Properties Subgrade materials are typically characterized by (1) their resistance to deformation under load, in other words, their stiffness or (2) their bearing capacity, in other words, their strength. In general, the more resistant to deformation a subgrade is, the more load it can support before reaching a critical deformation value. Although there are other factors involved when evaluating subgrade materials (such as shrink/swell in the case of certain clays and ash), stiffness is the most common characterization. 7.14. 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.
  29. 29. M.Tech Assignment Report 29 | P a g e Civil engineering Department N.I.T Hamirpur 7.15. Concrete 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 7.16. Modulus Of Elasticity And Poisson Ratio Of Concrete 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 7.17. 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. 7.18. Fatigue Behavior Of Cement Concrete Due to repeated application of flexural stresses by the traffic load , progressive fatigue damage takes place in the cement concrete slab in the form of gradual development 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. N=unlimited for SR < 0.45 N= ]3.268 when .45 ≤ SR ≤.55 log 10N= ] when SR > 0.55
  30. 30. M.Tech Assignment Report 30 | P a g e Civil engineering Department N.I.T Hamirpur 7.19.Environmental Factors Environmental factors affect the performance of the pavement materials and cause various damages. 7.19.1 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 . 7.19.2. 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. 7.20. 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.
  31. 31. M.Tech Assignment Report 31 | P a g e Civil engineering Department N.I.T Hamirpur 8. RIGID PAVEMENT DESIGN 8.1. Failure criteria of rigid pavements Traditionally fatigue cracking has been considered as the major, or only criterion for rigid pavement design. The allowable number of load repetitions to cause fatigue cracking depends on the stress ratio between flexural tensile stress and concrete modulus of rupture. Of late, pumping is identified as an important failure criterion. Pumping is the ejection of soil slurry through the joints and cracks of cement concrete pavement, caused during the downward movement of slab under the heavy wheel loads. Other major types of distress in rigid pavements include faulting, spalling, and deterioration. 8.1.1. Design Stresses 8.1.1a. Traffic-induced Stresses Bending of a concrete slab due to traffic loading will generate both compressive and tensile stresses within the slab. In general, the thickness of the slab will be governed by maximum tensile stress within the slab.The critical loading point is along the slab edges in both longitudinal and transverse directions. The stresses can be reduced by providing an effective mechanism, such as dowels or tie bars, to transfer part of the loads to the adjacent slabs. 8.1.1b. Thermal Stresses Thermal stresses consist of two components, i.e. uniform longitudinal stresses over the cross- section of the concrete due to seasonal temperature variations and warping stresses due to daily temperature gradient change .Longitudinal tensile stresses develop when the concrete cools and its contraction is prevented by the friction between the concrete slab and sub-base. Stresses are greatest in the centre of the slab and increase with longer slabs. Warping stresses are the result of an uneven temperature distribution over the cross-section of the slab. If the top surface of a slab is warmer than the bottom surface, the slab becomes convex but its own gravity opposes such stress-free distortion, resulting in compressive stresses at the top and tensile stresses at the bottom of the slab.
  32. 32. M.Tech Assignment Report 32 | P a g e Civil engineering Department N.I.T Hamirpur 8.1.1c. Fatigue Failure Concrete is subject to the effects of fatigue which are induced by repeated traffic loading and temperature variations. The fatigue behavior of concrete depends on the stress ratio. 8.1.2. Design Criteria 8.2. Modulus of Sub-Grade Reaction As already discussed in section 7.13 ,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. 8.3. Relative 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 . l= √( ) ) Where, l=radius of relative stiffness(cm) E= modulus of elasticity of cement concrete kg/cm2 µ=Poisson‟s ratio for concrete =.015 h= slab thickness, cm k= subgrade modulus or modulus of subgrade reaction kg/cm3
  33. 33. M.Tech Assignment Report 33 | P a g e Civil engineering Department N.I.T Hamirpur 8.4. Equivalent 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. b= {√{ 8.5. Critical 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. 8.6. Wheel Load Stresses - Westergaard's Stress Equation The cement concrete slab is assumed to be homogeneous and to have uniform elastic properties with vertical sub-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 8.6.1. Interior – Load in the interior and away from all the edges and is given by in kg/cm2 8.6.2. Edge – Load applied on the edge away from the corners is given by in kg/cm2
  34. 34. M.Tech Assignment Report 34 | P a g e Civil engineering Department N.I.T Hamirpur 8.6.3. Corner – Load located on the bisector of the corner angle is given by in kg/cm2 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 is the radius of the relative stiffness in cm and b is the radius of the resisting section in cm Figure 21. Crirical Stress Location , 8.7. Temperature Stresses Temperature stresses are developed in cement concrete pavement due to variation in slab temperature. This is caused by (i) daily variation resulting in a temperature gradient across the thickness of the slab and (ii) seasonal variation resulting in overall change in the slab temperature. The former results in warping stresses and the later in frictional stresses.
  35. 35. M.Tech Assignment Report 35 | P a g e Civil engineering Department N.I.T Hamirpur Figure 22. Types of Temperature Stresses 8.7.1. Warping 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 Figure 23 ..Warping stress in concrete slab when curling is restrained at different times
  36. 36. M.Tech Assignment Report 36 | P a g e Civil engineering Department N.I.T Hamirpur . 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. Warping stress in concrete slab when curling is restrained at different times 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 Table No-4 Bradbury‟s coefficients lx /l or ly/l 1 2 3 4 5 6 7 8 8.5 9 10 11 >12 Cx or Cy 0.00 0 0.040 0.175 0.440 0.720 0.92 1.03 1.07 1.084 1.08 1.075 1.050 1.000
  37. 37. M.Tech Assignment Report 37 | P a g e Civil engineering Department N.I.T Hamirpur 8.7.2. Frictional 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 . Figure 24. Frictional stress in the slab Where, σf = tensile stress in concrete slab due to friction W= Unit weight of concrete. h= Thickness of slab. L= Length of slab. f = Average coefficient of friction. 8.8. Critical 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.
  38. 38. M.Tech Assignment Report 38 | P a g e Civil engineering Department N.I.T Hamirpur • Mid-nights: The critical combination of stress is for the corner region given By σcritical = σc + σtc. Figure 25. Critical Combinations due to Load and warping.
  39. 39. M.Tech Assignment Report 39 | P a g e Civil engineering Department N.I.T Hamirpur 9. Design Of Slab Thickness 9.1. 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 . Figure 26. Bottom Up Cracking. This condition is likely to produce Bottom- Up cracking(BUC).  Location of the points of maximum flexural 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.
  40. 40. M.Tech Assignment Report 40 | P a g e Civil engineering Department N.I.T Hamirpur Figure 27. Placement of Axles In Case of BUC  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 ny the self weight of concrete and by the dowel connections, temperature tensile stresses are caused at top Figure 28. Top Down Cracking. • 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)
  41. 41. M.Tech Assignment Report 41 | P a g e Civil engineering Department N.I.T Hamirpur Figure 29. Placement of Axles In Case of BUC 9.2. Calculation 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. Analysis 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
  42. 42. M.Tech Assignment Report 42 | P a g e Civil engineering Department N.I.T Hamirpur 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. 9.3. Cumulative Fatigue Damage Analysis 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 Similarly for assessing the TDC fatigue damage 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) Figure 30. Sample graphs for Flexural stress Calculations.
  43. 43. M.Tech Assignment Report 43 | P a g e Civil engineering Department N.I.T Hamirpur Figure 31. Sample Equations for Flexural stress Calculations.
  44. 44. M.Tech Assignment Report 44 | P a g e Civil engineering Department N.I.T Hamirpur 9.4.Recommended 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 • 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. • 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 .
  45. 45. M.Tech Assignment Report 45 | P a g e Civil engineering Department N.I.T Hamirpur 10. Conventional Pavement Joints Joints are defined Break in continuity of pavement . Conventional pavements (JPCP, JRCP, and CRCP) make use of several types of transverse and longitudinal joints. Transverse contraction joints are used in JPCP and JRCP, usually with dowels. At the end of each daily paving operation, or for a significant delay in paving, transverse construction joints are placed, generally at the location of a planned contraction joint for JPCP or JRCP. Transverse expansion or isolation joints are placed where expansion of the pavement would damage adjacent bridges or other drainage structures. Longitudinal contraction joints are created where two or more lane widths or shoulders are paved at the same time. In contrast ,longitudinal construction joints are used between lanes or shoulders paved at different times . The performance of concrete pavements depends to a large extent upon the satisfactory performance of the joints. Most jointed concrete pavement failures can be attributed to failures at the joint, as opposed to inadequate structural capacity. Distresses that may result from joint failure include faulting, pumping, spalling, corner breaks, blowups, and mid-panel cracking. 10.1. Types of joints Figure 32. Flow Charts Of Types Of Joints Types of joints Transverse joints Expansion Joints Contraction joints Warping joints Construction joints Longitudinal joints
  46. 46. M.Tech Assignment Report 46 | P a g e Civil engineering Department N.I.T Hamirpur Figure 33. Various types of joints 10.1.1. Expansion Joints An expansion joint is defined as “a joint placed at a specific location to allow the pavement to expand without damaging adjacent structures or the pavement itself” . Smooth dowels are the most widely used method of transferring load across expansion joints. 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. Figure 34. Expansion Joint 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
  47. 47. M.Tech Assignment Report 47 | P a g e Civil engineering Department N.I.T Hamirpur 10.1.2. Contraction Joints These are provided to permit the contraction of slabs. These joints are spaced closer than the expansion joints. Load transfer at this joint is by aggregate physical interlocking at the joint face. The maximum spacing of contraction joints is 4.5 m.Since it is recommended to provide contraction joints at close spacing , there seems to be no need of providing any load transference, as mainly this will be done by the aggregate interlocking for added safety some agencies recommended to use of dowel bars which are fully bounded in concrete. Figure 35. Contraction Joint 10.1.3. Warping Joints These are provide to relieve stresses induced due to warping known as hinged joints. These joints are rarely provided 10.1.4. Construction Joints A construction joint is defined as “a joint between slabs that results when concrete is placed at different times. This type of joint can be further broken down into transverse and longitudinal joints”. A header and dowel basket for a transverse construction joint are shown .
  48. 48. M.Tech Assignment Report 48 | P a g e Civil engineering Department N.I.T Hamirpur 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.. Figure 36. Transverse Construction Joint 10.1.5. Longitudinal 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. Figure 37. Tie Bar Basket Assembly 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.
  49. 49. M.Tech Assignment Report 49 | P a g e Civil engineering Department N.I.T Hamirpur 11. Distress In Rigid Pavement Concrete pavement engineering is the selection of design, materials, and construction practices to ensure satisfactory performance over the projected life of the pavement. Pavement users are sensitive to the functional performance of pavements – smoothness and skid resistance – rather than structural performance. Pavements, as a general rule, develop distresses gradually over time under traffic loading and environmental effects. An exception is when poor material choices or construction practices cause defects before or shortly after the pavement is put into service. 11.1. ≥ Distress Types For JPCP And JRCP: 11.1.1. Cracking – divided into corner breaks, durability (“D”) cracking, longitudinal cracking, and transverse cracking. 11.1.2. Joint Deficiencies – joint seal damage (transverse or longitudinal), and joint spalling (transverse or longitudinal). 11.1.3. Surface Defects – divided into map cracking, scaling, polished aggregates, and popouts. 11.1.4. 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. 11.2 .≥ Distress Types For CRCP: 11.2.1. Cracking – as above, except CRCP cannot have corner breaks. 11.2.2. Surface defects – as above describe. 11.2.3. 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.
  50. 50. M.Tech Assignment Report 50 | P a g e Civil engineering Department N.I.T Hamirpur 11.3. Corner Breaks Corner breaks only occur at corners of JPCP or JRCP. A triangular piece of concrete, from 0.3 m to half the width of the slab, breaks off These are more likely with longer slabs,because as the slabs warp or curl upward the slab corners may become unsupported and break off when heavy vehicles travel across them. Figure 38. Corner Breaking 11.4.Cracking Cracks may form in concrete pavements due to a one time overload or due to repeated fatigue loading. The exception is tight, closely spaced transverse cracks formed intentionally in CRCP. Figure 39. Cracking
  51. 51. M.Tech Assignment Report 51 | P a g e Civil engineering Department N.I.T Hamirpur 11.4.1. Longitudinal Cracking Longitudinal cracks are defined as those parallel to the pavement centerline. longitudinal cracks are caused by a combination of heavy load repetitions, loss of foundation support, and curling and warping stresses, or by improper construction of longitudinal joints. If longitudinal cracks are not in vehicle wheel paths and do not fault appreciably, the effect on pavement performance may not be significant Figure 40. Longitudinal Crack 11.4.2. Transverse Cracking Transverse cracks are defined as those perpendicular to the pavement centerline. Once a transverse crack forms its faulting and deterioration leads to severe roughness. JPCP does not have steel across the crack to hold it together. The cracking can progress and lead to a shattered Slab. Figure 41. Transverse Cracking
  52. 52. M.Tech Assignment Report 52 | P a g e Civil engineering Department N.I.T Hamirpur 11.5. Joint Deficiencies As only JPCP and JRCP have joints, these pavement types alone can have joint deficiencies. These are classified as seal damage or spalling. 11.5.1 .≥ Joint Seal Damage (Transverse Or Longitudinal) Joint seals are used to keep incompressible materials and water from penetrating joints. Incompressible materials can lead to stress concentrations when open pavement joints close, causing some of the concrete to spall off. Water leads to deterioration in the pavement and underlying layers.Typical types of joint seal damage include extrusion (seal coming up outof joint), hardening, adhesive failure (loss of bond), cohesive failure (splitting),complete loss of sealant, intrusion of foreign material, or weed growth in the joint. 11.5.2 .≥ Joint Spalling (Transverse Or Longitudinal) Joint spalling is defined as “cracking, breaking, chipping, or fraying of slab edges within 0.3 m (1 foot) from the face of the joint” . Spalls are a surface phenomenon and are generally caused by incompressible materials creating stress concentrations in joints as they close due to slab expansion or traffic loading. They may also be caused by “poorly designed or constructed load transfer devices”. Therefore, the best way to avoid spalls is to properly maintain joints. Figure 42. Joint Spalling
  53. 53. M.Tech Assignment Report 53 | P a g e Civil engineering Department N.I.T Hamirpur 11.6. Surface Defects Unlike cracking and joint deficiencies, surface defects are usually unrelated to design. They are due to either poor materials selection or poor construction practices, or both. 11.7. Map Cracking Map cracking is defined as “a series of cracks that extend only into the upper surface of the slab.Larger cracks frequently are oriented in the longitudinal direction of the pavement and are interconnected by finer transverse or random cracks” . it is usually caused by overfinishing of concrete. Figure 43. Map Cracking 11.8. Scaling Scaling is defined as “the deterioration of the upper concrete slab surface, normally 3–13 mm (1/8-1/2 inch), and may occur anywhere over the pavement”. Scaling may progress from map cracking .Scaling may also occur with repeated application of deicing salts. This type of scaling may be prevented by using an adequately air entrained low permeability concrete with a low water/cement (w/c) ratio. Figure 44. Scaling
  54. 54. M.Tech Assignment Report 54 | P a g e Civil engineering Department N.I.T Hamirpur 11.9. Polished Aggregates Polished aggregate problems refer to “surface mortar and texturing worn away to expose coarse aggregate” . This typically leads to a reduction in surface friction. The reduction in surface friction can make pavements unsafe, particularly in wet weather. Because cement paste does not have good abrasion resistance, the wear resistance of concrete depends on the hardness of aggregates used. Poor finishing practices may also lead to a weak surface layer and lower abrasion resistance. Skid resistance may be restored. Figure 45. Polished Aggregate Surface 11.10. Popouts Popouts are “small pieces of pavement broken loose from the surface, normally ranging in diameter from 25–100 mm (1–4 inches), and depth from 13–50 mm (1/2–2 inches)”. Popouts may be caused by “expansive, nondurable, or unsound aggregates or by freeze and thaw action” 11.11. Miscellaneous Distresses 11.11.1. Blowups Blowups are “localized upward movement of the pavement surface at transverse joints or cracks, often accompanied by shattering of the concrete in that area” 11.11.2.Faulting Of Transverse Joints Faulting is defined as a “difference in elevation across a joint or crack”. It represents a failure of the load-transfer
  55. 55. M.Tech Assignment Report 55 | P a g e Civil engineering Department N.I.T Hamirpur Figure 46. Blow Up Figure 47. Faulted Transverse Joint 11.11.3. Water Bleeding And Pumping Water bleeding and pumping is “seeping or ejection of water from beneath the pavement through cracks. In some cases, detectable by deposits of fine material left on the pavement surface, which were eroded (pumped) from the support layers and have stained the surface”. Water bleeding and pumping may occur at joints, cracks, and pavement edges.
  56. 56. M.Tech Assignment Report 56 | P a g e Civil engineering Department N.I.T Hamirpur Figure 48. Water Bleeding And Pumping 11.11.4. Punchouts Punchouts, which only occur with CRCP, are rectangular chunks of concrete broken loose and punched down below the surface of the adjacent pavement. “the area enclosed by two closely spaced (usually <0_6 m [2 foot]) transverse cracks, a short longitudinal crack, and the edge of the pavement or a longitudinal joint. Figure 49. High Severity Punch Out
  57. 57. M.Tech Assignment Report 57 | P a g e Civil engineering Department N.I.T Hamirpur 12. Advantages Of Concrete Pavement The beneficial attributes of concrete pavements can be summarised as :  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.  Can be constructed over poor subgrades.  Thinner overall pavement thickness = lower consumption of raw materials.  Resistant to abrasion from turning actions.  Not susceptible to high or low temperatures.  No affected by weather, inert to spills and fire.  Completely recyclable.  High abrasion durability.  Profile durability.  Safer because it maintains its shape, no deformation, resistance to rutting and potholes and excellent skid resistance.  High sustainability rating through use of local materials.  Use of waste products like flyash and slag.  Riding quality does not deteriorate.  Can be slip formed up to 13 m.  Saving of fuel costs of at least 1.1% over asphalt .  Light colour enhances night visibility.  Less energy for street lighting (up to 30%).
  58. 58. M.Tech Assignment Report 58 | P a g e Civil engineering Department N.I.T Hamirpur 13. Disadvantages of Concrete Pavements  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  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. 14. References [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.