Micro-asphalt

Figure 7.2 Pathways in Walsall in the UK have been resurfaced using a micro-asphalt product (Rejuvoflex) that contains waste tyre crumb. Reproduced with permission from the WRAP Quality Protocol, Waste and Resources Action Programme, Banbury, UK. WRAP (see note with Figure 7.1)...

Waste Tyres Case Study - Rejuvoflex Micro-asphalt, WRAP, Banbury, UK. 

Adding enough molten sulfur to hot aggregate—asphalt mix increases its fluidity and produces a mix which can be molded or shaped. Casting these mixes requires little or no consolidation effort, and, specifically with pavements, rolling is not required. It has been demonstrated by micro-... 

Marblewhite A 325 Marblewhite A 4500 45-55 Mastic Asphalt Filler Micro-White 07 Slurry Micro-White 10 Codex Micro-White 10 Slurry Micro-White 14 Micro-White 14 Slurry Micro-White 15 Micro-White 15 Slurry Micro White 20 Micro-White 25 Micro-White 25 Codex Micro-White 25 Slurry Micro-White 40 Micro-White 50 Codex Micro-White 100 Micro-White 100 Codex Micro-White Superamide No. 1 White ... 

Mixtures to which fibres are added are the SMA and porous asphalt and occasionally in micro-surfacing. Dense asphalt mixtures with fibres were also found to have high resistance to fatigue (Samanos and Serfass 1993). The addition of plastic or iron fibres was found to increase the resistance to permanent deformation (Courard and Rigo 1993). The percentage of iron fibres added was 0.4% to 1.5%, while for the plastic fibres, it was 0.1 to 0.7%, by mass of bitumen. 

Cold asphalts are divided into two general categories, those for surface, binder, base or subbase courses, or for pothole filling known as cold asphalt mixtures (CAM), and those for slurry surfacing (SS), known as slurry seals (SSI) or micro-surfacings (MS). 

Cold asphalts for slurry surfacing are specified by international standards, specifications and guidelines, such as CEN EN 12273 (2008) for slurry surfacing, ASTM D 3910 (2011) or International Slurry Seal Association (ISSA) A105 (2010) for slurry seals and ASTM D 6372 (2010) or ISSA A143 (2010) for micro-surfacing. 

With respect to slurry seals, the aggregate requirements by the Asphalt Institute and ISSA are as follows Los Angeles abrasion loss, grading C or D, <35%, sand equivalent 45 (Asphalt Institute MS-19 2008 ISSA A105 2010). ISSA also has a requirement for soundness of aggregate, which is the same as for aggregates for micro-surfacing. 

For the surface layer, in particular, the asphalts most commonly used nowadays are (a) asphalt concrete for very thin layers (AC-VTL), (b) porous asphalt (PA), (c) open-graded friction course mixture (OGFC), (d) stone mastic asphalt (SMA), (e) single or double surface dressing (S-SD or D-SD) and (f) micro-surfacing (MS). Table 10.17 gives the comparative properties/characteristics for all the abovementioned surfacing materials. 

The surfacing layer is chosen from the following bituminous mixtures asphalt concrete for very thin layers, PA, SMA, dense asphalt concrete (for low traffic areas) or micro-surfacing. 

Generally, the repair/maintenance of surface distortions may range from hot asphalt filling, complete removal of the affected area and replacement with new material, thin or full-depth patching or application of micro-surfacing. 

Slippery surface may result from polishing and abrasion of the surface aggregate or asphalt bleeding. Both factors reduce the macro- and micro-texture of the pavement surface and the surface skid resistance provided. 

As surfacing material, the following may be considered asphalt concrete for very thin layers, porous asphalt, SMA and micro-surfacing. Details can be found in Chapter 5. Surface dressing technique may also be considered as an alternative (see Section 15.15). 

When scaling is less than approximately 10 mm in depth, temporary repair is carried out by micro-surfacing otherwise, the surface should be overlaid by asphalt. Application of the proper amount of tack coat and a clean surface are of vital importance. 

Hot asphalt surfacing overlay restores micro- and macro-texture and is the most suitable treatment for restoration of skid resistance of continuously reinforced pavement surface. All types of hot asphalts used in restoration of skid resistance of flexible pavements can be used, namely asphalt concrete for very thin layers, SMA and porous asphalt. 

On jointed concrete pavements when hot asphalt surfacing overlay is used for texture restoration, reflective cracks at the joints are expected to appear after a certain period. The same applies when micro-surfacing or surface dressing technique is applied, but reflective cracks will appear sooner. To avoid the above, it is recommended that all joints be replaced after laying the hot asphalt, micro-surfacing or surface dressing. 

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