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STONE MASTIC ASPHALT(SMA)INTRODUCTION2Stone Matrix Asphalt (SMA) is a hot paving mixture that was developed in Germany in the late sixtiesSMA - gap graded mix with high amount of coarse aggregates firmly bonded together by a strong asphalt masticEmployed in many countries as an overlay or surface course to resist load induced

INTRODUCTION contd.3High resistance to permanent deformation due to high coarse aggregate content

Enhanced durability as a result of higher bitumen content, and lower air voids content

Main disadvantages of SMA mixtures are related to its binder drainage

Fibers or polymers added to prevent draindown of the mix, increase the stability and durability of the mix INTRODUCTIONSMA - Deformation resistant, durable surfacing material suitable for heavy traffic loads

Stone skeleton - resist permanent deformation by transmitting heavy load through stone-stone contact

Bitumen mastic - Improved binder durability & flexibility by holding aggregate without segregation

Fibre network - prevents drainage of bitumen by stabilizing it during transport and placement

HISTORYStarted by Strabag ,Germany and later spread across

Asphalt paving mix against rutting by studded tyres

Durable pavements to combat wear & tear even by slow moving heavy traffic

National standards for SMA in many nations, in India (IRC:SP:79:2008)

Increasing popularity among authorities & industries

Countries using SMA as high stable asphalt conceptCOMPOSITIONTypical SMA composition consists of:7080% coarse aggregate812% filler67% binder0.3% fibre

High stone content is used to form an interlocked gap graded skeleton structure to transmit heavy loads

High viscosity bituminous mastic fills the voids & the mix is stabilized during the entire process

Addition of fibre enhances physical properties & doesnt cause any chemical changeCOMPOSITION

Composition of Stone Mastic Asphalt (SMA)

MATERIALS USEDCoarse and Fine aggregate - qualities of aggregates is checked by different tests (16mm-75 micron)

Bitumen - Different grade of bitumen are used which acts as binder (60/70 bitumen)

Fibre natural or artificial is used to increase the strength & stability and decrease the drain

Filler it includes dust, slag, flyash, lime, cement etc. or fine aggregates below 75 micron for better binding

European specifications SMA 13108-5

German specification SMA-TL Asphalt StB 07IS Sieve (mm)Cumulative percent by weight of total aggregate passingLower limitMid valueUpper limit19100100-12.590951009.55065804.752027.5352.361620241.18---0.600---0.300---0.07589.511Gradation of SMA as per AASHTOIS Sieve (mm)Cumulative percent by weight of total aggregate passingLower limitMid valueUpper limit19100100-13.290951009.55062.5754.752024282.361620241.181317.5210.6001215180.3001015200.07581012Gradation of SMA as per IRCPERFORMANCE CHARACTERISTICSGood stability at high temperatures

High wearing resistance

High adhesive capacity between the stone granules and the bitumen

A mix with no tendency to separate

Good skid resistance

Reduced water spray

Lower traffic noise

PERFORMANCE CHARACTERISTICS

Stability in SMA mixMANUFACTURE & PLACEMENTBatch mixing plant or Continuous mixing plant may be used after an extended mix design test for SMA

Mixing time is increased to ensure homogenous distribution of fibre throughout the mix

Mixing temperature is controlled to avoid overheating & damage of fibresMANUFACTURE & PLACEMENTMethod of compaction is to use heavy, non-vibrating, steel-wheeled rollers

Minimum layer thickness placed is 2.5-3 times the nominal maximum aggregate particle size

Production temperature 150-165 C

PAVING & COMPACTIONPaving & compaction is similar to standard asphalt

Trucks must be covered until the SMA is discharged into the material hopper at front of the road paver

Asphalt content of SMA is very high, a tack coat is given to ensure and improve the bond between the layers

The temperature of the SMA in the road paver should be at least 150C.

Compaction should be started as soon as possible and the roller should move as close to the paver as possible Should not be opened to traffic until surface temperature falls below 40

PAVING & COMPACTION

Paving and Rolling of SMALAYING

Unloading SMA into the paver machineLaying 14mm SMA using paver machineROLLING

Clouds of steam due to water used in rolling

Edge of the newly laid mat before rollingCOMPACTING

Compacting with a vibratory smooth wheeled roller

Finished and compacted 14mm SMA surfaceADVANTAGES20-30% increase in pavement lifeGood aggregate interlock for strength & stiffnessDeformation resistance for heavy trafficLow permeability, high durabilityTextured and rut resistant wearing courseSurface texture reduce noise & glare on roadsReduce reflective cracking due to flexible mastic100% recyclable after service lifeDISADVANTAGESMajor construction problems are drainage & bleeding, where temperature cannot be loweredIncreased material costIncreased mixing temperature & mixing timeCarefully monitor the composition at mixing plantWhite fines on the surface of the pavementsstripping of asphalt layer & potholing may take place

APPLICATIONSStone Mastic Asphalt has proved superior on heavily trafficked roads and industrial applications:high vehicle frequency & intense wheel trackingat traffic signals & intersectionson highways, gradients, bridges & service lanesin car parks, bus-stops & toll plazasin harbours & airport runwayson loading & unloading areas