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Swaagatham

Pavements

FLEXIBLE PAVEMENTS

APUSP - A project for the Urban Poor

● A GoAP Project funded by DFID of UK● Aims at reduction of vulnerability and poverty of

urban poor in Class I towns of Andhra Pradesh● Provides sustainable environmental infrastructure

in poor settlements under C2 component● Engineering related reforms under C1 component ● Community participation in infrastructure

planning & implementation

Civil Engineering Profession Engineering the natural resources and forces for

the welfare of mankindWhen we build

“Let us think that we build foreverLet it not be for the present delight

Nor for the present use alone

Let it be such work as our

descendants will thank us for”

John Ruskin

Flexible Pavement

● Flexible pavement is built up in several layers

● Load distributed through dispersion to layers below

● Resists very small tensile stresses due to low structural rigidity

● Deformation of sub-grade results in corresponding change in surface of pavement

Flexible pavement design● Design as per IRC:37-2001● Modeled as a three layer structure● Vertical compressive strain at top of sub

grade● Horizontal tensile strain at the bottom of

bituminous layer● Pavement deformation within the

bituminous layer

Flexible pavement- Design Parameters

● Design traffic at the end of design period in terms of cumulative standard axles depends on

– Initial traffic - No. of commercial vehicles/day– Traffic growth rate during design life - %/yr– Design life - No. of years– Vehicle Damage Factor (VDF)– Distribution of commercial traffic over carriage way

● CBR value of the sub-grade

CBR● CBR signifies California Bearing Ratio● CBR of a soil is the % of load required to

produce a defined penetration (1.25/2.5 mm) to that required for standard crushed rock specimen

● Normally, to simulate field conditions in monsoon, 4 day soaked (soil) CBR is obtained

● It has a relationship with the modulus of sub-grade reaction (k) given in IRC: 15-2002

Drainage measures● To prevent accumulation of moisture in the

pavement structure

● Reasonable cross fall facilitates quick runoff

● In low permeability sub grades, the GSB should be extended over entire formation width

● No gravelly soils in the drainage layer shall be allowed as it blocks the flow of water

Gravel and GSB● Gravel is that material between 80mm and 4.75 mm IS

sieves● Specification for Granular Sub Base● Material in mix passing 425 micron sieve shall have

Liquid limit < 25% (MORTH) 20% (APSS 138) Plasticity index < than 6%

● Material passing 75 micron sieve shall be less than 10%

● Extensive field studies documented by R&B dept. show that most of the gravels in the state are having liquid limit >25 and plasticity index >6

● They absorb moisture in the sub-grade, result in volume changes, reduce shear strength of the soil

Disadvantages of using gravelly soilsIn roads:▪ Undulations develop on low traffic roads▪ Continuous pot hole formation▪ Presence of moisture below BT layer results in loss

of bitumen▪ Sinking type failures due to gravel in sub base.▪ Damage of further treatments if gravel is present in

WBM or sub baseIn others:▪ Flooring damages in basement filling if proper compaction is not done▪ Lead to failure of retaining walls or structures if some loose spots are left over

Capillary cutoff● This is a layer of coarse/fine sand, graded

gravel/impermeable membrane to prevent rise of moisture into the sub-base

● In heavy clayey soils, a layer of course sand provided under sub base for full formation width to act as a blanket course/capillary cut-off

● Provided in water logged areas & where the sub-grade soil is impregnated with deleterious salts (excess of sulphates etc.)

Granular Sub Base (GSB) RequirementsIRC: 37-2001, MORT&H and APSS

❖ Minimum CBR required: 20% CBR If design traffic is less than 2 msa 30% CBR If design traffic is more than 2 msa

❖ Minimum sub base thickness: 150 mm If design traffic is less than 10 msa 200 mm If design traffic is more than 10 msa

❖ Material in the mix shall satisfy specified grading Material in mix shall have 10% fines value > 50 KN

❖ Layer thickness: 100 mm compacted with smooth wheeled roller 225 mm compacted with vibratory roller

preparation of samplefor LL and PL tests

IS: 2720 part 5

samplespassing 425micron

Liquid Limit: % of water content at

which the soil enters liquid state

Plastic Limit: % of water content at which the soil enters

plastic state

Plasticity Index: Liquid Limit - Plastic Limit

It indicates the water absorption and retention

capacity of the soil.It also indicates the presence

of negative charged clay minerals.

Specified Requirements of gravel or Moorum as per Standard Specifications

Standard Specification

As per APSS

As per MORT & H

Liquid Limit < 20 %< 25 % for GSB

< 20 % for WBM blindage

Plasticity Index < 6 % < 6 %

Percentage passing 75 micron sieve < 10 % < 10 %

Close graded granular sub-base- Grading 3

Size of IS sieve% by weight

passing the IS sieve

26.5 mm 1009.5 mm 65-954.75 mm 50-802.36 mm 40-650.425 mm 20-350.075 mm 3-10CBR (Minimum) 20

Close graded granular sub-base- Grading

IS sieve size % of material considered in data

9.5-11.2 mm 35%

Crusher stone dust 65%

Coarse graded granular sub-base- Grading 3

Size of IS sieve % by weight passing the IS sieve

26.5 mm 1009.5 mm 4.75 mm 25-452.36 mm0.425 mm0.075 mm <10CBR (Minimum) 20

Coarse graded granular sub-base- Grading 3

IS sieve size % of material considered in data

9.5-11.2 mm 33%

5-7 mm 33%

Crusher stone dust

34%

IS Sieve Cumulativ %passing

specified

125mm 100 100

90mm 92 90 - 100

63mm 45 25 - 60

45mm 8 0 - 15

22.4mm 3 0 - 15

Grade I HBG metal

IS SieveCumulativ

%passing

specified

90mm 100 100

63mm 94 90 - 100

53mm 50 25 - 75

45mm 7 0 - 15

22.4mm 3 0 - 15

Grade II HBG metal

IS SieveCumulativ

%passing

specified

63mm 100 100

53mm 97 95 - 100

45mm 80 65 - 90

22.4mm 8 0 - 15

11.2mm 2 0 - 15

Grade III HBG metal

Type of screenings IS Sieve % passing

Type A 13.2mm(6mm & 10mm chips)

13.2mm 10011.2mm 95-1005.6mm 15-35

180 micron 0-5

Type B 11.2mm(stone dust)

11.2mm 1005.6mm 90-100

180 micron 15-35

Type B screenings or binder

Type A screenings

WBMStone screenings Binder

per 10SqMtype quantity/10Sqm

Gr I - 133/100mm type A 0.27 to 0.3 cum 0.08 to 0.10 cum

Gr II – 100/75mm type A 0.12 to 0.15 cum0.06 to 0.09 cum-do- type B 0.20 to 0.22 cum

Gr III 100/75mm type B 0.18 to 0.21 cum

Quantities of aggregates, stone screenings and binder per 10 Sqm for WBM as per MORT&H (above) and as as per MORT&H data 2003(below)

ItemCoarse

Aggregates

Type A screenings

(6mm)

Type B screenings

(dust)

Binder(dust)

Grad I WBM 1.21 cum 0.27 cum nil 0.08 cumGrade II WBM with

type A screenings 0.91 cum 0.12 cum nil 0.06 cum

Grade II WBM with type B screenings 0.91 cum nil 0.20 cum 0.06 cum

Grade III WBM 0.91 cum nil 0.18 cum 0.06 cum

GSB with gravel, stone dust and metal also caused problems when executed during rainy season

Gravel associated GSB (mixture of gravel, metal and sand etc.,) is creating lot of problems during rains.

It is preferable to opt for GSB without any gravel

Mud pumping

Quality of rubbish in WBMLL=45%, PI=25%

Observe surface undulations a day after WBM is done

Plight of a WBM road with red earth ( presuming it as gravel) blindage in West Godavari district during R&B Minister’s visit

After dry rolling, spreading of screenings is in progress to fill voids in the coarse aggregates.

Brooming with handbrooms , to fill voids in the coarse aggregates

Sprinkling of water is in progress

Rolling after sprinkling of water

Application of binding material successively in two or more

thin layers.

Due to application of stone dust as screenings and binderInternal friction between coarse aggregates is not getting

reduced

GR III WBM with stone screeningsas per clause 404 of MORT & H

RIGID PAVEMENTS

Rigid Pavement● Concrete slab has significant flexural

strength and E value. They enable the slab to spread load over larger area of sub-grade

● Slab can carry loads and bridge small depressions in the sub grade due to structural rigidity of slab

● Resists high tensile stresses compared to flexible pavement

Why rigid pavement?● Preferred in poor settlements as they provide sustainable

access to them; place for doing domestic chores & social functions; for relaxation and rest; give them social status

● Longer life of ~ 30-40 years● Better riding quality, skid resistance & serviceability● For rural roads, 6% lower life cycle costs than BT roads,

though initial costs are 25% higher ● Savings in fuel compared to flexible pavements● Preferred over poor sub-grade and in water logged areas● About 50% of C2 funding goes to roads sector

Modulus of sub grade reaction (k)

‘k’ is defined as the pressure per unit deflection of the sub-grade as determined by plate bearing tests

k = p /Δ (in kN/cm2/cm)p = pressure in kN/ sq.cmΔ = deformation in cm

(Limiting Deflection for CC pavements is 1.25 mm)

Sub base

● Forms a working surface for slab on clays & silts● Prevents mud-pumping ● Provides stable and uniform support for the slab

on roughly shaped formations● Ensures sub-surface drainage for the pavement● Protects the foundation from frost penetration● Reduces bending stresses & deflections in slab● Improves load transfer at joints and helps reduce

cracks

“k” corresponding to CBR

CBR Values % 2 3 5 7 10 15 20 50 100

K-Value Kg/cm3 2.1 2.8 4.2 4.8 5.5 6.2 6.9 14 22.2

Increase in ‘k’ values of sub grade due to granular sub base

K-values of sub-gradeKg/cm3

Effective k-values (kg/cm3) over un- treated granular sub-base thickness in cm15cm 22.5cm 30cm

Minimum value of ‘k’: 6Kg/cm3

2.8 3.9 4.4 5.3

5.6 6.3 7.5 8.8

8.4 9.2 10.2 11.9

K - values over Dry Lean Concrete sub-base

K-value of sub gradeKg/cm2/cm

2.1 2.8 4.2 4.8 5.5 6.2

Effective k over 100mm DLCKg/cm2/cm

5.6 9.7 16.6 20.8 27.8 38.9

Effective k over 150mm DLCKg/cm2/cm

9.7 13.8 20.8 27.7 41.7 -

APUSP-Rigid pavements Key design parameters

● Characteristics of sub grade and sub-base● Design wheel load depending on nature and

width of road● Design traffic intensity● Temperature differential● Foundation strength and surface characteristics ● Flexural strength of concrete mix● Slab design based on critical stress condition

Characteristics of Concrete

● Design Strength● Workability ● Durability ● Modulus of elasticity● Poisson’s ratio● Coefficient of thermal expansion● Creep ● Permeability ● Fatigue behaviour

Materials for CC Roads Cement: OPC/PPC 33 grade or 43 grade ● Content: Min. 350 kg/m3; Max.425 kg/m3

Coarse Aggregate: Graded aggregate as per Table 2 of IS-383LA abrasion value < 35%

● MSA: up to 25 mmWater absorption not > 2%

Fine Aggregate: conform to IS: 383

● Min. required flexural strength: 45 kg/cm2

● Water cement ratio: 0.50 maximum● Workability: Slump 30+/- 15 mm

Design Standards used

● IRC: 58 Design of Rigid Pavements for Highways

● Applicable for roads having a daily commercial traffic of over 150

● IRC 15: 2002 Construction of rigid pavements

● IRC SP: 62 Guidelines for the Design and Construction of CC Pavements for Rural Roads

New Features of IRC: 58 - 2002

● Computation of flexural stress due to placement of single & tandem axle loads along edge

● Consideration of Fatigue behaviour of CC● Cumulative Fatigue Damage for different

axle loads shall be < 1.0 ● Stress Ratio(SR)=Flexural Stress/Flexural

strength● No.of allowable load repetitions for a wheel

load unlimited if SR is <0.45

Critical Stress Condition

● Additive flexural stresses: Due to load and temperature differentials – critical

● Curling: Top convex during the day and top concave during the night

● Edge: Discontinuous in one direction. Critical during the day as load and temp. stresses are cumulative when there is max. temp. differential

● Corners: Discontinuous in two directions; More critical during the night as they tend to warp up; More critical if no dowel bars are provided; Critical if aggregate interlock is absent

CC Pavement Details

Transverse joints-Necessity of providing dowel bars

Load transfer without dowel bars

Load transfer with dowel bars

Transverse Joints

● Contraction Joints

● Control plastic cracking and irregular cracking

● Relieve tensile stresses due to temperature

● Load transfer thro’ aggregate interlock & thro’ dowels

● Dowel bars enable load transfer & reduce joint fault

● Expansion joints

● Used at slab junction with bridge/culvert slabs

● Relieve compressive stresses due to temperature

Transverse Joints

● Construction joints are provided

● Whenever concreting is completed after a day’s work

● Concreting is suspended for more than 30 minutes

● Usually coincide with contraction joints

● Control irregular cracking

SEALERFILLER

Expansion Cap Partly Filled with

Cotton

7.5 cm

2.5 cm

T

T/2

20 to 25mm

±1.5mm

Expansion Joint

Filler board: compressible Joint filler 20 to 25mm ± 1.5mmFiller depth 25mm ± 3mm lower than slab thickness

Dowel bars (MS rounds) to be covered with plastic sheathing for ½ length +50mm

Expansion joint-Dowel bars with sheathing and caps

Groove cutting in progress

Joints 3 to 5mm wide are to be cut to 1/3 to ¼ depth. Dowel bars are to be placed at mid depth and covered with thin plastic sheathing for 2/3 length. Dowel bars at dummy contraction joints increase service life under heavy vehicular traffic.

Contraction Joint maximum spacing: 4.5M

Mild Steel Dowel Bar

Contraction Joint SpacingThickness of un-reinforced

slabsContraction joint spacing

in meters15 4.520 4.525 4.530 5.035 5.0

Ex

Expansion joints may be omitted when dowels are provided at contraction joints except when CC pavement abuts structures. For heavy traffic and for slab thickness >= 150mm, dowel bars should be provided at contraction joints.

Mild Steel Dowel barsat Contraction joint

Groove cutting machine

Contraction joint3 to 5 mm wide

1/3 to 1/4 in depth

Longitudinal Joint

•Longitudinal Joints provided when width > 4.5m•Relieve curling & warping stresses •Joints are to be saw cut to 1/3rd slab thickness ± 5mm. •Tie bars (HYSD or MS) to be placed at middle third of slab thickness and coated with bitumen paint for 75mm on either side

Tie Rod

Tie rods at Longitudinal joint

Reinforcement● It does not increase the structural

capacity of slab● But it helps to increase the joint spacing● Bars keep the cracked concrete together

– to maintain load transfers thro’ aggregate interlock

● When steel is used, it is assumed that steel alone takes all tensile stresses

Dowel bars and Tie bars

Dowel bars (plain): provided across transverse jts. ● They ensure load transfer to adjoining slab● Stress & deflection at joint likely to be smaller● Dowels can minimize faulting and pumping ● Use of dowels is a factor in thickness design

Tie bars (deformed): provided at longitudinal jts.● Tie the two slabs together to keep joint tightly

closed● Ensure load transfer across the joint

View of cc pavement showing joints, dowels and tie rods

Contraction Joints - Construction● Contraction joints shall consist of a mechanical sawn

joint groove as stipulated in the drawings● The contraction joints shall be cut as soon as the

concrete has undergone initial hardening and is hard enough to take the load of joint sawing machine without causing damage to the slab

● It should be sealed immediately after curing with approved sealing compound

● Construction joints should as far as possible coincide with contraction joints/ expansion joints

● The distance between construction joint and a contraction/expansion joint shall not be less than 1.8 m

Expansion joints- Construction

● They shall be provided at 50m interval● Approved compressible joint filler shall be

used conforming to IS 1838 ● The expansion/ contraction joints shall be

sealed with approved sealing compound conforming to AASHTO M 282 (hot poured type) or BS 5212 (Part 2) for cold applied sealant

Joints - Maintenance● The joints shall be maintained preferably at

yearly intervals preferably before monsoon ● They shall be cleaned of grit, sand etc., and

sealed with bituminous sealant/poly sulphide● Otherwise, the grit, sand etc. will prevent

transfer of wheel load thro’ aggregate interlock ● It will also lead to mud pumping through ingress

of moisture through open joints

Nominal Mix Proportions

● Nominal mix proportions preferred in case of small jobs

● Strength supposed to increase with increase in quantity of cement & better compaction

● Tried to achieve a dense combination of aggregate with least voids. Ratio of FA:CA lying between 1:1.5 and 1:2.5

● Water arbitrarily added to give required workability

Design mix for pavements● Pavements have to resist the combination of

flexural tensile stresses due to temperature diffenrential and loads

● Pavements often fail in flexural tension● The minimum flexural strength to resist combined

tension due to temp. and loads is about 45 kg/cm2● To obtain the same, the concrete should be at least

M30 design mix● Design mix is specifically designed for the

specified strength and workability for the given materials

Specifications for design mix

● Design strength required● Workability required● Materials like cement, CA, FA and water● Durability requirements● Type of use Level of quality control

Preparation for slump test,casting cubes (150 mm) and

beams(70 х 15 х 15 cm)

Internal Lane - Onsite (width

between drains <=

2m)

a) Sand / Crusher dust - 50mm thick

a) Sand / Crusher dust - 75mm thick

a) Sand/crusher dust - 100mm thick

b) Lean Concrete in VCC (1:4:8) 75 mm thick using 40mm HBG graded m/c metal



c) Separation membrane 125 microns th. of impermeable plastic sheeting



d) VCC 1:2:4 mix 75 mm thick using 20mm graded HBG m/c metal



Internal Lane - On Site (width

between drains > 2m <= 3.50 m) No through

traffic

a) One layer of 150 mm thick compacted course sand

b) Close graded Granular Sub-base - 75 mm th. compacted as per Section 401 of MORTH and Table 400-1 Gr III

b) Coarse graded Granular Sub-base - 100 mm th. compacted as per Section 401 of MORTH and Table 400-2 Gr III


c) One layer of 75mm thick WBM using Gr 3 HBG metal



d) Separation membrane 125 microns th. of impermeable plastic sheeting



e) VCC M30 mix 100mm thick using 20mm graded HBG m/c metal



Access road within

settlement -Off site (width

between drains <=

4.5 m)





c) One layer of WBM 75 mm thick using Gr 3 HBG metal

c) One layer of WBM 75 mm thick using Gr 3 HBG metal

c) Lean Concrete in VCC (1:4:8) 100 mm thick using 40mm HBG graded m/c metal




e) VCC M30 mix -150mm thick using 20mm HBG graded m/c metal



Through roads - Off-site

(between one part of

town to other part

of town subject to

design)





c) One layer of 75mm thick WBM using Gr 2 metal and one layer of WBM 75 mm thick using Gr 3 HBG metal



d) Primer Coat as per 502 of MORTH over granular surface



e) BM Gr 2 - 50mm thick as per 504 of MORTH



d)Tack Coat as per 503 of MORTH over bituminous surface

d)Tack Coat as per 503 of MORTH over bituminous surface

f)Tack Coat as per 503 of MORTH over bituminous surface

e) SDBC Gr 2 - 25 mm thick as per 508 of MORTH

e) SDBC Gr 2 - 25 mm thick as per 508 of MORTH

g) SDBC Gr 2 - 25 mm thick as per 508 of MORTH

Curing ● The most important aspect often neglected ● Immediately after final set, the entire surface of

newly laid concrete shall be covered against rapid drying and cured

● Curing by ponding shall be done for 21 days● It helps complete hydration of cement● Thus helps strength development of concrete● Helps reduce shrinkage● Helps increased durability of concrete

Curing-methods● By ponding ● Spreading wet hessian cloth/burlap and keeping

it moist during curing period ● By spreading polyethylene sheeting● Spraying liquid curing compound followed by

spreading of wet hessian and moistening it regularly

● Water used for curing shall be free from injurious chemicals like chlorides; conform to IS:456-2000

Testing - Cores● In case of doubt regarding the grade of

concrete used– either due to poor workmanship or– based on results of cube strength testscomp.strength tests on cores and/or load test

shall be carried out.● Core tests: the ave. equivalent cube strength of the

cores is equal to at least 85% of the cube strength of the grade of concrete specified for the corresponding age and no individual core has strength less than 75%

Defects in CC pavement

● Honeycombing● Defective joints● Improper placement of transverse joints● Non existent longitudinal joint● Lack of expansion joint at culvert/bridge slab● Exposure of metal

Distress in Jointed Concrete Pavements

● Cracking– Corner breaks, durability cracking, longitudinal

cracking, transverse cracking● Joint deficiencies

– Transverse & longitudinal joint seal damage & spalling

● Surface defects– Map cracking, scaling, polished aggregates, popouts

● Miscellaneous Distresses– Blow ups, faulting of transverse joints and cracks,

patch deterioration, water bleeding and pumping

Concrete Pavement Restoration ● Full depth repair● Partial depth repair

– Acceptable for most surface problems within upper 1/3rd of the slab

● Retrofitting dowels● Cross-stitching longitudinal cracks/joints● Diamond grinding● Joint & crack resealing● Restoration to be effective, proper engineering,

construction and timing are critical

Defective contraction joint

Joint spalling

Defective contraction joints

Water ingress thro’ shoulders

Mud pumping

Joint spalling

Scaling

Map cracking

Raised shoulders

Dhanyavaadaalu

Pavements - aphrdi.ap.gov.inAPHRDI/AEE PR/II week... · sub-grade reaction (k) given in IRC:...

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Transcript of Pavements - aphrdi.ap.gov.inAPHRDI/AEE PR/II week... · sub-grade reaction (k) given in IRC:...