Quality Control - Pavement

COMPONENTS OF A ROADSUB GRADESUB BASEBASEBITUMINOUS LAYERS

THREE LAYERED PAVEMENT SYSTEM

SUB GRADEThe sub grade is the prepared and compacted soil layer forming the foundation of the pavement system. The top 500mm thickness of an embankment is considered as sub grade.SUB BASE The Sub base is the layer between the sub grade and the Base. The sub base may consist of one or more layers of stabilized or granular materials properly compacted BASE This is a layer of granular material, which lies immediately below the wearing surface. SURFACING It is the component of pavement with which the wheels of vehicle comes into actual contact. The purpose is to provide smooth riding surface.

STAGES OF QUALITY CONTROLEMBANKMENT FORMATION

SUB GRADE FORMATION

GRANULAR SUB BASE

BASE

EMBANKMENT FORMATIONThe materials used for the formation of embankment should haveLiquid Limit < 70Plasticity Index < 45Free swell index < 50The size of the coarse material shall not exceed 75mmCompaction Requirement Not less than 95 Percentage of maximum Laboratory dry densityIndividual Layer thickness not to exceed 200mmAny vegetation has to be thoroughly removed from the fill material since the decay leads to voids formation

EMBANKMENT FORMATIONIf the road is to be formed in water logged areas proper embankment design shall be obtained

SUB GRADEField density - Not less than 1.75 gm/ccSize of the coarse material shall not exceed 50mm Compaction Requirement Not less than 97% of maximum Laboratory dry densityCBR Shall preferably be 7 10 %

GRANULAR SUB BASELiquid Limit -Not greater than 25 Plasticity Index- Non PlasticMinimum CBR - 20% up to 2 msa - 30% traffic exceeding 2 msaCompaction Requirement Not less than 98%of maximum Laboratory dry density

GRADATION REQUIREMENT FOR GRANULAR SUB BASE GRADE I as per Table 400-1 of MORTH IV

IS Sieve DesignationGrading - IGrading IIGrading III75.0 mm100--53.0 mm80 100100-26.555 - 9070 1001009.50mm35 - 6550 8065 954.75 mm25 - 55 40 6550 802.36 mm20 - 4030 5040 650.425 mm10 -2515 2520 350.075 mm3 -103 103 10CBR Value (Minimum)302520

Granular BaseWET MIX MACADAM

IS sievesize, mmPercent by passing531004595-10022.460-8011.240-604.7525-402.3615-30600mic8-2275mic0-8

Granular BaseWET MIX MACADAM

Minimum Thickness 75mmMaximum single layer thickness 200mm, if Vibratory Roller is usedGradation as per Table 400-11 of MORTH Revision IV

TESTS ON SOIL BELOW PAVEMENTAtterberg Limits

Sieve Analysis

Maximum Dry Density

Optimum Moisture Content

California Bearing Ratio

TESTS ON SOILField density Sand Replacement method Soil density guageSieve analysisTo classify the soil To assess the bearing capacity of the soilMaximum Dry DensityMaximum Dry Density and Optimum Moisture Content is obtained from the Proctor Density tests

FREQUENCY OF TESTSGRANULAR SUB BASE as per Table 900-3 of MORTH revision - IV

Test Frequency GradationOne test per 200 m3 Atterberg limitsOne test per 200 m3 Moisture content prior to compactionOne test per 250 m2 Density of compacted layerOne test per 500 m2 Deleterious ConstituentsAs required C.B.RAs required

FREQUENCY OF TESTSWET MIX MACADAM as per Table 900-3 of MORTH Revision -IV

Test Frequency Aggregate Impact valueOne test per 200m3 of aggregate GradationOne test per 100m3 of aggregate Flakiness and Elongation indexOne test 200m3 of Aggregate

Atterberg limits of binding material One test per 25m3 of binding material Atterberg limits of portion of aggregate passing 425 micron sieveOne test per 100 cubic metre of aggregate

FAILURE OF PAVEMENTS as per IRC-82:1982Surface Defects

Cracks

Deformation

Disintegration

SURFACE DEFECTS-Types &CausesFatty Surfaces - Accumulation of Bitumen - Due to Excess of Bitumen,Fines,Poor Quality of Aggregates and Heavy axle loads leading to deformation of wearing surface.

Streaking Appearance of alternate thin and heavy lines of Bitumen Due to non uniform application of Bitumen, low temperature of Bitumen during mixing.

Hungry surface Loss of aggregates Due to less bitumen in surfacing and poor quality of aggregates.

CRACKS Types & CausesIndication of defective pavement.

Hair-line crack- Due to insufficient Bitumen, Improper compaction.

Alligator cracks- Due to excessive deflection, excessive overloading on unstable sub base or sub grade and brittleness of Bitumen due to ageing or overheating.

Longitudinal cracks- Appearing along the road at the joint between pavement and shoulder and between two paving lanes due to poor drainage and weak joints of adjoining lanes.

CRACKS Types & Causes contd..,Edge cracks Due to lack of lateral support, settlement of underlying layers and inadequate pavement width.

Shrinkage cracks Forming large blocks without deformation-Due to shrinkage of bituminous layers with age and loss of ductility.

Reflection cracks Frequently appear on bituminous surfacing laid over concrete pavement joints and cracks underneath. Also appear on bituminous surfacing on old unrepaired defective bituminous layer.

DEFORMATION - Types & CausesChange in the original shape of the pavementSlippage Relative movement of surface layer with reference to layer below Due to inadequate tack coat, lack of bonding between surface layer and base and unusual thrust of wheels in a particular direction.Rutting Longitudinal depression along wheel track - Due to repeated channelised traffic, inadequate compaction of pavement layers and yielding of sub gradeSettlement and Upheaval Large deformation of pavement due to inadequate compaction, excessive moisture in sub grade inadequate pavement thickness.

DISINTEGRATION - Types & CausesStage that necessitates complete rebuilding of pavement.Stripping Separation of Bitumen adhering from surfaces of aggregates in presence of moisture Due to inferior aggregates, Poor mix composition, Continuous contact of water with bitumen coated aggregates, Initial overheating of Bitumen prior to mixing, Presence of Dust or moisture on aggregate prior to mixing, rain or storm immediately after laying.Loss of Aggregates Due to loss of adhesive property of Bitumen, stripping of bitumen, insufficient binder, Poor compaction, Loss of temperature in mix before compaction.

MIX DESIGN OF GSB GRADE-I & WMMSuitability of material for its physical properties like Gradation, Impact value and Flakiness.Optimisation of ratio of size components,moisture,Density and strength.Batching of aggregates based on their size.Mixing of aggregates of different sizes at various ratios and different moisture content to find out CBR for each

GSB Grade I Mix Design Trial-1

Total Weight of Sample 9000 gmsSieve size, mmWeight by percentageMoisture contentTotal weight of mixCBR, %75-26.5254693726.5-9.520570989.5-4.753067408344.75-0.07525

GSB Grade I Mix Design Trial-2

Total Weight of Sample 9000 gmsSieve size, mmWeight by percentageMoisture contentTotal weight of mixCBR, %75-26.5204699026.5-9.515572209.5-4.753567435614.75-0.07530

GSB Grade I Mix Design Trial-3

Total Weight of Sample 9000 gmsSieve size,mmWeight by percentageMoisture contentTotal weight of mixCBR, %75-26.5204718026.5-9.525573359.5-4.752567165614.75-0.07530Same procedure is adopted for WMM except the upper sieve being 53mm.

Dos & Do nots for GSB and WMMDosGradation Test at collection stage.Ensure material brought from the same quarry for which design mix is obtained.Correct proportion of components during mixing.Loose volume of materials shall be 1.30-1.50 m3 of compacted volume.Field density test shall be done frequently to verify compaction.CBR tests on GSB mix shall be done during spreading to confirm laboratory results.

Dos & Do nots for GSB and WMMDonot

Add excess of water during mixing as this leads to seggregation of materials.

Allow oversize material.

Allow flaky material as this leads to poor interlocking.

Compact total thickness in single layer as poor compaction is achieved.

HIGHWAY DRAINAGEDirectly governs the performance of the pavement.Classified as Surface and Sub surface drainage.Surface drainage is effected by Longitudinal & Transverse gradients.Failure of surface drainage leads to stripping of Bitumen, Potholes and slow deterioration of pavement.When a road does not run on embankment or adjoining ground is at higher level, where surface drainage cannot be provided sub surface drainage is necessitated.Vertical drains can be effective to drain surface water to permeable sub strata at shallow depths.