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have the same effect and it is generally preferable for surfaces to cool below about 40 °C before opening to traffic. The preferred method of compaction is to use heavy, non-vibrating, steel-wheeled rollers. If these are not available, vibrating rollers may be used but vibration should be kept to a minimum to avoid fracture of coarse aggregate particles, or drawing of binder to the surface of the mix. The use of
111:, particular care must be taken to ensure that both the additional filler content and fibre additive are incorporated into the mixture without excessive losses through the dust extraction system. Filler systems that add filler directly into the drum rather than aggregate feed are preferred. Pelletised fibres may be added through systems designed for addition of
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The primary difference in placing SMA, compared to DGA is in compaction procedures. Multi-tyred rollers are not used due to the possible working of binder-rich material to the surface of the asphalt and consequent flushing and pick-up. Trafficking of the newly placed asphalt while still warm may
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The deformation resistant capacity of SMA stems from a coarse stone skeleton providing more stone-on-stone contact than with conventional dense graded asphalt (DGA) mixes (see above picture). Improved binder durability is a result of higher bitumen content, a thicker bitumen film, and lower air voids
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prevents drainage of bitumen during transport and placement. There are no precise design guidelines for SMA mixes available in Europe. The essential features, which are the coarse aggregate skeleton and mastic composition, and the consequent surface texture and mixture stability, are largely
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has been identified as an important factor in the performance of all SMA work. SMA is normally placed with a minimum layer thickness of 2.5 to 3 times the nominal maximum aggregate particle size. Greater layer thicknesses assist in achieving appropriate standards of compacted density.
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are added to provide adequate stability of bitumen and to prevent drainage of binder during transport and placement. Typical SMA composition consists of 70−80% coarse aggregate, 8−12% filler, 6.0−7.0% binder, and 0.3 per cent fibre.
115:, but a more effective means is addition through a special delivery line that is combined with the bitumen delivery, so that the fibre is captured by bitumen at the point of addition to the mixture.
91:, detailed mix design guidelines have been developed for SMA and published by the US National Asphalt Pavement Association in their Quality Improvement Publication QIP 122 as given in the references.
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The surface texture characteristics of SMA are similar to Open graded asphalt (OGA) so that the noise generated by traffic is lower than that on DGA but equal to or slightly higher than OGA.
34:. It provides a deformation-resistant, durable surfacing material, suitable for heavily trafficked roads. SMA has found use in Europe, Australia, the United States, and Canada as a durable
241:) may be low until the thick binder film is worn off the top of the surface by traffic. In critical situations, a small, clean grit may need to be applied before opening to traffic.
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Material is removed by milling in subsequent overlays because the void in the gap grading will hold water and freeze initiating stripping in the asphalt binder.
178:, have all been found to be suitable but cellulose fibre is generally the most cost-effective. Fibre content is generally 0.3% (by mass) of the total mix.
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and necessitate increased compactive effort to achieve high standards of compacted density. Achieving high standards of compacted density and low field
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Waanders, G.; Els, H. (1995). "Splittmastixasphalt und Dränasphalt in den
Niederlanden. Erfahrungen und Untersuchungen in der Provinz Overijsel".
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Possible delays in opening to traffic as the SMA mix should be cooled to 40 °C to prevent flushing of the binder to the surface (bleeding).
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SMA is mixed and placed in the same plant as that used with conventional hot mix. In batch plants, the fibre additive is added direct to the
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using individually wrapped press packs or bulk dispensing equipment. Mixing times may be extended to ensure that fibre is
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Polymer modified binder - increasingly used in heavy traffic conditions to provide additional resistance to flushing and
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Aggregates used in SMA must be of high quality – well shaped, resistant to crushing and of suitable polish resistance.
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National
Asphalt Pavement Association (1999) Designing and Constructing SMA Mixtures — State-of-the-practice. QIP 122.
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distributed throughout the mix and temperatures controlled in order to avoid overheating or damage to the fibre. In
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SMA surfacings may provide reduced reflection cracking from underlying cracked pavements due to the flexible mastic.
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Cellulose fibre is most commonly used in SMA work in
Australia. Other fibre types, including glass fibre,
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Austroads (2003) Selection and Design of
Asphalt Mixes: Australian Provisional Guide. APRG Report 18.
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SMA may be used at intersections and other high traffic stress situations where OGA is unsuitable.
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The durability of SMA should be equal, or greater than, DGA and significantly greater than OGA.
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content. This high bitumen content also improves flexibility. Addition of a small quantity of
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Increased mixing time and time taken to add extra filler, may result in reduced productivity.
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SMA can be produced and compacted with the same plant and equipment available for normal
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270:- Texas Expert System for the selection of Hot-Mix Asphalt (HMA) based on TxDOT (2004).
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Multigrade binder - used to provide enhanced performance at higher traffic levels.
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determined by the selection of aggregate grading and the type and proportion of
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surfacing option for residential streets and highways. SMA has a high coarse
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content that interlocks to form a stone skeleton that resists permanent
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Austroads (2003) Guide to the selection of road surfacings, AP−G63/03
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AAPA (2000) Stone Mastic
Asphalt Design and Application Guide,
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Class 320 bitumen - used in many general applications.
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SMA provides a textured, durable, and rut resistant
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324:(2002) Asphalt Guide AP−G666/02
318:AAPA Implementation Guide IG−4.
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148:Binders used in SMA include:
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352:Road construction materials
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16:Road construction material
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331:ARRB Transport Research
126:polymer modified binder
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28:stone-matrix asphalt
20:Stone mastic asphalt
274:Highway engineering
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346:Categories
310:References
301:(4): 8–17.
182:Advantages
357:Pavements
322:Austroads
172:polyester
141:Materials
134:air voids
119:Placement
76:cellulose
58:to which
40:aggregate
252:See also
239:friction
233:Initial
168:rockwool
295:Asphalt
199:hot mix
160:rutting
101:pugmill
52:bitumen
36:asphalt
268:TexSys
237:(road
85:filler
60:fibres
56:filler
48:mastic
280:Notes
80:fibre
176:wool
54:and
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