HIGHWAY CONSTRUCTION IRC: 58 - 2002, Guidelines for the design of Plain Jointed Rigid Pavements for Highways IRC: 15 - 2002, Code of practice for Construction of Cement Concrete Roads IRC: 44 - 2008, Guidelines for cement concrete mix design for pavements IRC:SP 62 – 2004, Guidelines for design of CC roads for Rural Roads
Types of Pavements
HIGHWAY CONSTRUCTIONS Pavement Design •
Pavement means surfacing layer only. • In terms of highway design, it means the total thickness of road including surfacing , base & subbase, if any. • Thus pavement includes all the structural layers of road structure lying on subgrade of the road
Parameters for Design of Pavements Design of pavements mainly consists of two aspects 1. Design mix of materials 2. pavement thickness
Factors for Design of Pavements • Following factors are responsible for pavement design 1. Climate : rainfall, Temp, Frost action 2. Environment : Ht of embankment, foundation cutting 3. Geometry: 4. Pavement materials: they have to resist climatic conditions ,durability, maintenance. 5. Subgrade Soil : decides thickness of pavement 6. Traffic : Repetitions, Speed, Wheel Loads , contact pressure, volume of traffic , no of vehicles/day .
Design Approach for rigid Pavements • 1. 2. 3. 4. 5. 6.
Variables for design Wheel Loads Traffic Climate Terrain Subgrade conditions Properties of Cement Concrete
Flexible
Rigid
Properties Design Principle
Material
Flexible Empirical method Based on load distribution characteristics of the components Granular material
Flexural Strength
Low or negligible flexible strength
Normal Loading Excessive Loading Stress
Elastic deformation
Made of Cement Concrete either plan, reinforced or prestressed concrete Associated with rigidity or flexural strength or slab action so the load is distributed over a wide area of subgrade soil. Acts as beam or cantilever
Local depression
Causes Cracks
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 Force of Friction
No stress is produced Less. Deformation in the sub grade is not transferred to the upper layers. Road can be used for traffic within 24 hours Rolling of the surfacing is needed
Stress is produced Friction force is High
Opening to Traffic Surfacing
Rigid Designed and analyzed by using the elastic theory
Road cannot be used until 14 days of curing Rolling of the surfacing in not needed.
Components of CC pavement
Types of Rigid Pavements 1. • 2. •
Jointed Plain Concrete Pavement (JPCP) – No temperature steel Jointed Reinforced Concrete Pavement (JRCP) – Temperature steel placed at mid height and discontinued at the joints 3. Continuously Reinforced Concrete Pavement (CRCP) • – Not popular in India – very costly 4. Prestressed Concrete Pavement (PCP) • – Not popular
Design Approach for rigid Pavements • Cement Concrete roads provides a highly rigid surface and hence for the success of such roads, following two conditions should be satisfied 1. They should rest on non- rigid surface having uniform bearing capacity. 2. The total thickness or depth of the concrete pavement & the non rigid base should be sufficient to distribute the wheel load on a sufficient area of subbase so that the pressure on unit area remains with the permissible SBC of the soil.
Design Approach for rigid Pavements • Concrete slab has high modulus of elasticity, high rigidity & flexural strength, so wheel loads are distributed over large areas of Subgrade . This leads to small deflections and also leads compressive stresses imposed on the Subgrade. • This leads to fatigue damage in concrete slab in form of development of micro cracks, due to repeated application of traffic loads. • This is arrested by limiting flexural stresses and increasing the Concrete mix grade.
Design Steps ( parameters ) 1.
2. 3. 4. 5. 6. 7. 8.
Traffic parameters : Design Wheel load, Traffic intensity Environmental parameters : temp differential ( CRRI table) Foundation strength k ( modulus of subgrade reaction ) Foundation surface characteristics ( As per IRC ) Concrete characteristics ( IRC :58-1988 ) Modulus of elasticity Coefficient of thermal expansion. Design slab thickness
Purpose of joints in Concrete Roads 1. To absorb expansion & contraction due to variation in temperature. ( horizontal movements of slabs) 2. To avoid warping of slab edges 3. To grant facility in construction .
TYPES OF JOINTS • Concrete pavements are provided with Joints in Transverse & Longitudinal directions which are classified as • a) CONTRACTION JOINTS • b) EXPANSION JOINTS • d) CONSTRUCTION JOINTS
CONTRACTION JOINTS • These are purposely made weakened planes which relieve the tensile stresses in the concrete • Caused due to changes in the moisture content (Drying shrinkage) and/or temperature and • Prevent the formation of irregular cracks due to restraint in free contraction of concrete . • They are also provided to 1) )Relieve stresses due to warping 2) To permit the contraction of the slab
Details of the contraction joints are given in IRC:SP 62 • They are formed initially by sawing a groove of 3-5 mm with up to about one-fourth to one-third the slab Details of the contraction joints are given in IRC:SP 62. They are formed initially by sawing a groove of 3-5 mm with up to about one-fourth to one-third the slab thicknesses. This facilitates the formation of a natural crack at this location extending to the full depth. • In order to seal the joint, the top 10-20 mm of this groove is widened to 610 mm. • Spacing of contraction joints may be kept at 2.50m to 3.75m. • Length of panel shall not be more than width of panel.
LONGITUDINAL JOINTS • Lanes are jointed together by joint known as Longitudinal joint • Longitudinal joints are provided in multilane pavements and also when the pavement is more than 4.5 m wide. • They are provided normally at 3.5m c/c to • 1) Relieve stresses due to warping. • 2) To allow differential shrinkage & swelling due to changes of sub grade moisture
• 3) To prevent longitudinal cracking Procedure of construction • Initially joint is cut to a depth 1/3rd slab Initially joint is cut to a depth 1/3rd slab thick ± 5mm. Tie bars are provided at the joints not for load transference but for keeping the adjoining slabs together. The details of such joints are given in IRC:SP 62. • The top 15-20 mm of the joint is sawn to a width of 6-8 mm for sealing
Expansion joints • There are full-depth joints provided transversely into which pavement can expand, thus relieving compressive stresses due to expansion of concrete slabs, and preventing any tendency towards distortion, buckling, blow-up and spalling. • The current practice is to provide these joints only when concrete slab abuts with bridge or culvert. • They allow expansion of slabs due to temperature • They permit contraction of slabs Normal Details of these joints are given in IRC:SP62. • They are about 20 mm in width • A joint filler board of compressible material conforming to IRC:SP:62 is used to fill the gap between the adjacent slabs at the • joint. • The height of the filler board is such that its top is 23-25mm below the surface of the pavement. • The joint groove is filled by a sealant .
Construction joints The need for such joint arises when construction work is required to be stopped at a place other than the location of contraction or an expansion joint, due to some breakdown of the machinery or any other reason. Such joints are of butt type and extend to the full depth of the pavement. The sealing of such joints shall be done in the same manner as for contraction joints, by cutting a groove 10-12 mm wide and 20-25 mm deep. Generally, such joints are avoided in highways. The work is normally terminated at a contraction or expansion joint
JOINT FILLER • Joint spaces are first filled with compressible filler materials and top of the joints are sealed using sealer • Joint filler should possess following properties o Compressibility o Elasticity i.e they should be capable of regaining their shape when compression is released o Durability
Load Transfer at Transverse Joints • IRC:58-2001 had adopted equations developed by Friberg for analyzing long beam on elastic foundation (bar embedded in concrete) , for computation of maximum bending stress in the dowel bar & max bearing stress in concrete . • High bearing stress on the concrete surrounding the dowel bar can fracture the same, leading to the looseness of the dowel bar and the deterioration of the transfer system leading to faulting of the slab. • The dowel bars are installed at a suitable spacing across the joints and the system is assumed to transfer 40% of the wheel load.
TYPES OF SEALANTS • Hot poured rubberized (Thermoplastic type) • Cold applied poly sulphide sealants • Cold silicone Sealants
Asphalts
Cleaning of Longitudinal Joint
Fixing of Back up Rod after Initial Cut
Widened Groove after 14 days
Finished PQC surface with Sealed Joints
Desirable Properties of Soil as Subgrade Material
• • • •
Stability Incompressibility Permanency of strength Minimum changes in volume and stability under adverse condition of weather and ground water • Good drainage • Ease of compaction
Cements that can be used as per IRC: 44-2008 Any of the following types of cements capable of achieving the design strength and durability may be used with the prior approval of the Engineer. 1. Ordinary Portland Cement, 33 grade, IS: 269 2. Ordinary Portland Cement, 43 grade, IS: 8112 3. Ordinary Portland Cement, 53 grade, IS: 12269 4. Portland Pozzalona Cement (fly ash based, IS: 1489, part1 5. Portland Slag Cement, IS: 455
Fly ash can be as a partial replacement of cement (OPC) up to an extent of 35%. Fly ash for blending shall satisfy the following Properties conforming to IS:3812-2004
Advantages in adding Fly Ash a) Increases CSH ( Calcium Silicate Hydrate) volume b) Denser CSH formed by secondary reaction c) Better Pore structure and composition d) Low heat of hydration e) Resistance to adverse exposure conditions Reaction when Fly Ash is added: CS + H CSH + CaOH
CaOH + Fly AshCSH (cementing gel)
Design Approach for Flexible Pavements • Traffic is considered in terms of the cumulative number of standard axles (8160 kg) to be carried by the pavement during the design life • For estimating the design traffic, the following Information is needed: 1. Initial traffic after construction (CVPD) 2. Traffic growth rate during the design life 3. By studying the past trends of traffic growth 4. As per the econometric procedure outlined in IRC:108
Design Approach for Flexible Pavements Bituminous paving mixes. • Following factors are involved in design of bituminous paving mixes 1. Durability 2. fatigue resistance 3. flexibility 4. fracture or tensile strength 5. permeability 6. Skid resistance 7. Thermal characteristics
Design Approach for Flexible Pavements Mix Design Methods 1. Marshall method of Mix Design 2. Hveem method of Mix design
Design Approach for Flexible Pavements Marshall method of Mix Design Stability Flow Test
• Max load resistance that a Std specimen will develop at 60 Deg C
Flow is measured as a deformation or total amount in units of 0.25 mm between no of load & maximum during the stability test expressed as 0.10 mm
Design Approach for Flexible Pavements • Marshall method of Mix Design criteria Test Property
Category of traffic Heavy
Medium
Light
Stability kg Min
340
230
230
Flow value (0.25 mm)
8 to 16
8 to 16
8 to 20
a) For surfacing
3 to 5
3 to 5
3 to 5
b) For base course
3 to 5
3 to 8
3 to 8
% Voids
Design Approach for Flexible Pavements Hveem method of Mix design This method of mix design starts with obtaining an estimate of optimum bitumen content by use of Centrifuge Kerosene equivalent ( C.K.E) The % of kerosene retained in the aggregate after being soaked and centrifuged as a specified is called C.K.E value & charts are available to find out the optimum bitumen content from C.K.E value
Design Approach for Flexible Pavements Hveem method of Mix design • • 1. 2. 3. • • • •
It consists of 3 tests on bituminous samples of 100 mm diameter & 63.50 mm ht. Each specimen is tested for subsequent tests Following tests are conducted Swell Test 100 mm dia Stabilometer Test Cohesive meter Test Swell should not be < 0.76 mm 63.50 mm Stabilometer values for light, medium, heavy should be 30,35 & 67 respectively Cohesive meter value should not be more than 50 Air voids % should have minimum value of 4%
Design Approach for Flexible Pavements
Methods of Design
Group Index Method ( G I )
California Bearing ratio ( C B R ) Method
Design Approach for Flexible Pavements Group Index Method •
GI is a arbitrary index given to the type of soil and is based on % of fines ,liquid limit, and plasticity index of the soils • GI values range from 0 to 20 • Greater GI value, poorer the soil
Design Approach for Flexible Pavements Group Index Method Volume of traffic is divided as below Very light
Less than 50 vehicles per day
Light
50-250 vehicles per day
Medium
250-500 vehicles per day
Heavy
500-750 vehicles per day
Very heavy
750-1000 vehicles per day
Design Approach for Flexible Pavements Group Index Method • Depending upon G I grading of soil , daily volume of the traffic, thickness of surface, base, & subbase are designed as per the chart below
Design Approach for Flexible Pavements
Design Approach for Flexible Pavements California Bearing Ratio Method GI method does not take in account characteristics of the pavement material , So I.R.C has recommended CBR method for design of flexible pavements
Design Approach for Flexible Pavements California Bearing Ratio Method CBR test : It is a property of a grade soil which is measured by an test designed by California State highways USA. It has been standardized by IS also. • • • • • •
It is made on the sample of subgrade soil in a standard loading device which measures the load required to cause 2.5 mm penetration of the plunger having cross section area 1690 Sq.mm The plunger is made to penetrate the sample, at a rate of 1.25mm/min unit a penetration of 2.5 mm is obtained. This pressure at 2.5 mm penetration is worked out and it is expressed as a % of unit standard pressure. This % is known as CBR The test is repeated for 5 mm penetration & the CBR is worked out. Generally 2.5 mm value is higher Standard loads 2.5 mm 70 kg/cm2 5 mm 105 kg/cm2
CBR Test
Load Penetration Curve ( CBR Test )
Relation Between CBR and E • • • • • • • • •
Subgrade E (MPa) = 10 * CBR if CBR<5% and = 176 *(CBR)0.64 for CBR > 5% Granular subbase and base E2 = E3*0.2*h0.45 E2 = Composite modulus of sub-base and base (MPa) E3 = Modulus of subgrade (MPa) h = Thickness of granular layers (mm)
Typical pavement section
Steps in design of flexible pavements • The following steps are used in design of flexible pavements for stage construction. i) Provide design thicknesses of subbase and base courses for 20 years. ii) Provide bituminous surfacing course for traffic of msa. iii) Provide a shoulder of thickness equal to that of the sum of the layers in steps (i) and (ii) on both sides. iv) Provide bituminous surfacing course for traffic of msa after 10 years. v) Provide shoulder thickness equal to the thickness calculated in step (iv) at the same time
Modulus values for Bituminous materials
Penetration value Penetration value is a measure of hardness or consistency of bituminous material. It is the vertical distance traversed or penetrated by the point of a standard needle in to the bituminous material under specific conditions of load, time and temperature. This distance is measured in one tenths of a millimeter. AIM: (i) To determine the consistency of bituminous material (ii) To assess the suitability of bitumen for use under different climatic conditions and various types of construction. This test is used for evaluating consistency of bitumen.
Penetration value • Penetration test is a commonly adopted test on bitumen to grade the material in terms of its hardness. • A 80/100 grade bitumen indicates that its penetration value lies between 80 & 100. • Grading of bitumen helps to assess its suitability in different climatic conditions and types of construction. • For bituminous macadam and penetration macadam, IRC suggests bitumen grades 30/40, 60/70, 80/100. • In warmer regions, lower penetration grades are preferred to avoid softening whereas higher penetration grades like 180/200 are used in colder regions to prevent the occurrence of excessive brittleness. High penetration grade is used in spray application works.
SPECIFICATION OF PENETRATION GRADE BITUMEN
Default Values of Poisson’s Ratio (μ) (as suggested in IRC:37-2001)
Subgrade and unbound granular layers
Default value of μ = 0.4 Bituminous Layers Default value of μ at 35/45 degree C = 0.5 Default value of μ at 20 - 30 degree C = 0.35 μ: Poisson's ratio
Traffic 1. Design life in number of years • NH & SH – 15 years • Expressways & Urban Roads – 20 years • Other roads – 10 to 15 years 2.Vehicle damage factor (VDF) • Need to be worked out from axle load survey 3.Distribution of commercial traffic over the • carriageway. (D & L Factors)
Computation of design traffic
Computation of design traffic • • • •
D = Lane distribution factor F = Vehicle damage factor n= Design life in years R= Annual growth rate of commercial vehicles
Traffic in the year of completion x
A= P(1+r)
P = Number of commercial vehicles as per day last count x = Number of years between the last count and the year of the completion of construction
Subgrade • The subgrade should be compacted to 97% of the dry density achieved with heavy compaction (modified proctor density) a per IS:2720 (Part 8). • For Expressways, National Highways and State Highways, the material used for subgrade construction should have the dry density of not less than 1.75 gm/cc.
Subgrade • For determining the CBR value, the standard test procedure described in IS:2720 (Part 16) should be strictly adhered to. • The test must always be performed on remoulded samples of soils in the laboratory • It is recommended that the samples be soaked in water for four days prior to testing • In situ CBR test is not recommended
Pavement Composition (Sub-base course) • Granular Sub-base (GSB) materials conforming to clause 401 of MORT&H specifications for road and bridge works is recommended • The sub-base material should have minimum CBR of 20% for cumulative traffic up to 2 msa and 30% for traffic exceeding 2 msa. • The thickness of sub-base should not be less than 150 mm for design traffic less than 10 msa and 200 mm for design traffic of 10 msa and above.
Pavement Composition (Sub-base course) • Preferably the subgrade soil should have a CBR of 2% • If the CBR<2%, the design should be based on a CBR of 2% and a capping layer of 150 mm thickness of material with a minimum CBR of 10% shall be provided in addition to the subbase • Where stage construction is adopted, the thickness of sub-base shall be provided for ultimate pavement section for the full design life
Pavement Composition (Base course) • The recommended minimum thickness of granular base is 225 mm for traffic up to 2 msa and 250 mm for traffic exceeding 2 msa. • For heavily trafficked roads, use of WMM base laid by paver finisher or motor grader is recommended. • Where WBM construction should be adopted in the base course for roads carrying traffic more than 10 msa, the thickness of WBM shall be increased from 250 mm to 300 mm.
Bituminous Surfacing • Shall consists of either a wearing course or a binder course with a wearing course depending upon the traffic to be carried. • The selection criteria for the grade of bitumen to be used for bituminous courses are given in the table shown • Where the wearing course adopted is premix carpet of thickness up to 25 mm, the thickness of surfacing should not be counted towards the total thickness of the pavement
Criteria for selection of Grade of Bitumen for Bituminous courses
Pavement Thickness Design Chart for Traffic 1-10 msa
Pavement Composition
Pavement Thickness Design Chart for Traffic 10-150 msa
Life Cycle Cost Analysis of rigid & Flexible Pavements • According to a rough estimate ,the physical & financial needs of highway sector for the next 20 years indicates an average annual outlay of Rs 250000 Crores in the next 10 years & Rs 37500 Crores in the next subsequent period. • In addition to this, Rs 10000 Crores per year would be required for maintenance with a steady increase of 5 to 6 %
Comparative Study of Rigid & flexible pavements
• Flexible pavements are widely used despite some doubts regarding their economics under different conditions • Two most important parameters that govern the pavement design are soil sub-grade and traffic loading • The Indian guidelines for the design of flexible pavements use soil sub-grade strength in terms of California Bearing Ratio (CBR) and traffic loading in terms of million standard axles (msa).
Comparative Study of Rigid & flexible pavements
