calihas.blogg.se - Stone asphalt texture

Stone asphalt texture cracked#

Stone asphalt texture cracked#

SMA surfacings may provide reduced reflection cracking from underlying cracked pavements due to the flexible mastic.SMA may be used at intersections and other high traffic stress situations where OGA is unsuitable.SMA can be produced and compacted with the same plant and equipment available for normal hot mix, using the above procedure modifications.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.SMA provides a textured, durable, and rut resistant wearing course.Fibre content is generally 0.3% (by mass) of the total mix. Other fibre types, including glass fibre, rockwool, polyester, and even natural wool, have all been found to be suitable but cellulose fibre is generally the most cost-effective. Polymer modified binder - increasingly used in heavy traffic conditions to provide additional resistance to flushing and rutting.Ĭellulose fibre is most commonly used in SMA work in Australia.

Multigrade binder - used to provide enhanced performance at higher traffic levels.

Class 320 bitumen - used in many general applications.

Greater layer thicknesses assist in achieving appropriate standards of compacted density.Īggregates used in SMA must be of high quality – well shaped, resistant to crushing and of suitable polish resistance. SMA is normally placed with a minimum layer thickness of 2.5 to 3 times the nominal maximum aggregate particle size. Achieving high standards of compacted density and low field air voids has been identified as an important factor in the performance of all SMA work. The use of polymer modified binder may decrease mix workability and necessitate increased compactive effort to achieve high standards of compacted density. Should be kept to a minimum to avoid fracture of coarse aggregate particles, or drawing of binder to the surface of the mix. If these are not available, vibrating rollers may be used but vibration The preferred method of compaction is to use heavy, non-vibrating, steel-wheeled rollers. Trafficking of the newly placed asphalt while still warm may have the same effect and it is generally preferable for surfaces to cool below about 40 ☌ before opening to traffic. 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. The primary difference in placing SMA, compared to DGA is in compaction procedures. Pelletised fibres may be added through systems designed for addition of recycled materials, 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. Filler systems that add filler directly into the drum rather than aggregate feed are preferred. In drum plants, 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. Mixing times may be extended to ensure that fibre is homogeneously distributed throughout the mix and temperatures controlled in order to avoid overheating or damage to the fibre.

In batch plants, the fibre additive is added direct to the pugmill using individually wrapped press packs or bulk dispensing equipment. SMA is mixed and placed in the same plant as that used with conventional hot mix. In the US, 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. The essential features, which are the coarse aggregate skeleton and mastic composition, and the consequent surface texture and mixture stability, are largely determined by the selection of aggregate grading and the type and proportion of filler and binder. There are no precise design guidelines for SMA mixes available in Europe. Addition of a small quantity of cellulose or mineral fibre prevents drainage of bitumen during transport and placement. This high bitumen content also improves flexibility. Improved binder durability is a result of higher bitumen content, a thicker bitumen film, and lower air voids content. 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).