STONE MASTIC ASPHALT

WHAT IS SMAStone mastic asphalt (SMA), also called stone-matrix asphalt. It is homogeneous mixture of selected well graded aggregate , filler and bitumen in such proportions as to yield a plastic and voidless mass which Act as a very dense impermeable surfacing.It was developed in Germany in the 1960s.

COMPOSITION OF SMA

COARSE AGGREGATEFINE AGGREGATEBINDERFILLERFIBRE

PROPERTIES OF COARSE AGGREGATE

HardDurableFree from the organic mattrerResistance to strippingWater absorpton should not be greater than 2%

GRADING OF COARSE AGGREGATE

Sieve SMA 12.5 mm

19.0 mm 100

12.5 mm 90 – 99

9.5 mm 50 – 85

4.75 mm 28 – 40

2.36 mm 16 – 28

75 μm 8 – 11

PROPERTIES OF FINE MATERIAL

Water absorption of a fine aggregate of any nominal size from any source must not exceed 3.5%. Soundness:- The weighted percent loss from a fine aggregate must not exceed 12% of the test portion.

PROPERTIES OF FILER

The filler shall be limestone powder passing the 0.075 mm sieve .Calcium carbonate content shall not be less than 80% by weight.

ADVANTAGE OF SMA

Resistance to permanent deformation or ruttingGood durability due to high binder contentGood flexibility and resistance to fatigueGood wear resistanceGood surface texture

DISADVANTAGE OF SMA

Increased cost Increased mixing time and time taken to add extra filler, may result in reduced productivity.Possible delays in opening to trafficInitial skid resistance may be low.

MIX DESIGN

HARDNESS NUMBER At the time of manufacturing of 60 to 80 at 25˚c At the time of laying 10 to 20 at 25˚cBINDER CONTENT: 14 to 17% by weight of total mix.

MIX PROPERTIES

Design Parameter Design Criteria

Air Voids % 4.0

Voids in Mineral Aggregate, VMA %

17 Minimum

Tensile Strength Ratio % 70 Minimum

Draindown % 0.3 Maximum

TENSILE STRENGTH RATIO, TSR

Checks the moisture susceptibility of the asphalt mixture.

whereS1 = average tensile strength of dry subsetS2 = average tensile strength of moisture conditioned subset

Tensile Strength Ratio, TSR

DRAINDOWNMass of asphalt mortar that has drained from total asphalt mass

Where:Pi = Initial paper plate mass (grams)Pf = Final paper plate mass (grams)W = Mixture mass (grams)D = % Drain-down