STONE MASTIC ASPHALT

WHAT IS SMA Stone 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 AGGREGATE FINE AGGREGATE BINDER FILLER FIBRE

PROPERTIES OF COARSE AGGREGATE Hard Durable Free from the organic mattrer Resistance to stripping Water 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 rutting Good durability due to high binder content Good flexibility and resistance to fatigue Good wear resistance Good 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 traffic Initial 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˚c BINDER 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. where S1 = average tensile strength of dry subset S2 = average tensile strength of moisture conditioned subset

Tensile Strength Ratio, TSR

DRAINDOWN Mass 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