Surface dressing

In the UK, BS 63 [8.3] specifies requirements for single-sized aggregates (50, 40, 28, 20, 14,10, 6 and 3 mm) for general purposes and for surface dressing (although limestone is rarely used for surface dressing). The single sizes may be recombined to produce the particle size distribution required for a particular application. 

Aggregates for bituminous mixtures and surface dressings for roads, airfields and other trafficked areas (prEN 13043)... 

When limestone is applied as a top dressing, it initially affects only the surface layer of soil. Thus, when a soil is acidic throughout its depth, or when lower soil layers are more acidic than the surface layer, it is generally advisable to apply half of the limestone before ploughing and to spread the remainder as a surface dressing. 

The determination of PSV is considered necessary for determining the suitability of aggregate for any type of surfacing asphalt and surface dressing. Aggregates are considered to be suitable when their PSV is greater than or equal to the value given by the national specification. These values are related to traffic level and the type of site. 

Max.AAV for chippings for hot rolled asphalt and surface dressing, and for aggregate in slurry and microsurfacing systems... 

The classification of the tars is carried out mainly in reference to the equiviscous temperature (EVT). According to BS 76 (1974), there are eight different tar types, from 30 C to 58°C EVT. EVT is the temperature in which 50 ml of tar has a flow time of 50 s when passing through the 10 mm hole of the tar viscometer. As a consequence, the higher the EVT, the more viscous the tar is. Tar with 50°C-58°C EVT is suitable for dense bituminous mixtures in heavy traffic volume sites, whereas tar with 30°C-38°C EVT is used in open graded bituminous mixtures for low traffic volume sites. Tar with 34°C-46°C EVT is usually used for surface dressings. 

The cohesion of stabilised binder from polymer-modified cut-back and fluxed bituminous binders, which are used for surface dressings, shall be determined in accordance with CEN EN 13588 (2008). For binders used in asphalt mixes, the test methods given in either CEN EN 13587 (2010) or CEN EN 13589 (2008) rosy be used. For binders used in other applications,any one of the three methods listed above, CEN EN 13587 (2010), CEN EN 13589 (2008) or CEN EN 13588 (2008), msy be used. 

In the beginning of the 1990s, an additive that fully controlled the breaking rate of the emulsion, depending on the type of application, was developed. The additive was an aqueous solution (neutraliser) in oil (reverse emulsion) and it was added to the bitumen emulsion shortly before its use. This additive gave excellent results both on surface dressings and on cold bituminous mixtures of any type with conventional or modified bitumen (Redilius 1993). 

The use of anti-stripping agents applies both to surface dressings (Cawsey and Gourlet 1989 Woodside and Macoal 1989), where excellent and permanent adhesion is required, and to hot or cold bituminous mixtures (Anderson et al. 1982 Christensen and Anderson 1985). In both cases, the bitumen-aggregate adhesion is improved and the mixture resistance to the disastrous impact of water is increased, in case hydrophilic aggregates are used. 

Usage of anti-stripping agents 3.7.2./ Anti-stripping agents in surface dressings... 

As it was mentioned, the anti-stripping agents are used in surface dressings. They may be incorporated using one of the following ways ... 

Finally, for surface dressings, the Vialit plate shock test method is used (CEN EN 12272-3 2003). 

The Vialit plate test, according to CEN EN 12272-3 (2003), determines the binder aggregate adhesivity and the influence of adhesion agents or interfacial dopes in adhesion characteristics as an aid to design binder aggregate systems for surface dressing. 

The test is suitable for all bituminous binders for surface dressings, such as conventional or polymer-modified bitumen, cut-back bitumens, fluxed bitumen or bituminous emulsions with conventional or modified bitumen. 

Modified bitumen can be used in the whole range of bitumen works, namely, for producing bituminous mixtures (hot to cold), in surface dressings, surface sealing, water insulation and so on. Modified bitumens may be employed directly or in the form of cut-backs or emulsions, or blended with, for example, natural asphalt. 

Finally, improvement of the adhesion between bitumen and aggregate particles positively affects the life of surface dressings, as well as open graded and porous asphalts, and eliminates the development of ravelling. 

The thermosetting modifiers - two liquid compounds (resin and hardener) - are first blended together and then with the bitumen a few seconds before application as surface coating/surface dressing (main use) or before mixing with aggregates for the production of hot asphalts (occasional use). 

In some countries, such as the United Kingdom, for high-quality surface dressings with calcined bauxite chippings, the thermosetting polymer-modified bitumen is the only binder recommended to be used. 

Experimental measurements carried out in 2009-2011 on the use of multigrade bitumens in chip sealing (surface dressing) did not show any advantage for multigrade bitumens compared to standard binders with a similar 25°C penetration value (Herrington et al. 2011). Multigrade bitumens do not replace polymer-modified bitumens. 

One cohesion method shall be chosen on the basis of end application. Vialit cohesion (CEN EN 13588 2008) shall only be used for surface dressing binders. 

This test method is applicable for graded bitumen, modified bitumen and fluxed bitumen and is used only when the binders are going to be used in surface dressings. 

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. 

Surface dressing is cheaper than micro-surfacing but both do no not have anywhere near the same life expectancy as epoxy resin treatment. 

Crack sealing/filling is only applied to crack widths greater than 3 mm. Cracks with width less than 3 mm (hairline cracks) are treated more effectively by micro-surfacing, surface dressing (chip seal), sand seal or fog seal. 

In cases where the formation of alligator cracking is at the beginning, and the width of the cracks is less than 3 mm, a temporary maintenance such as slurry surfacing, or surface dressing, may be considered. This will only extend the time before permanent repair is needed. 

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