SURFACE MAINTENANCE 31
Footway slurry surfacing being carried out
Slurry surfacing
In the latest article from the Road Surface Treatments Association (RSTA), chief executive Howard Robinson discusses the area of slurry surfacing
Slurry surfaces incorporating micro-surfaces are cold-applied, thin bituminous surface courses using bitumen emulsion binders and fi ne graded aggregates with fi llers and other additives. There are two broad categories; thin slurry surfaces used for treating footways and thicker polymer modifi ed surfaces called micro-surfacing or micro-asphalt for carriageways.
Where can they be used?
These materials can be used to restore the surface condition on roads, footways, cycleways, car parks, playgrounds, central reservations, traffi c islands and amenity areas.
Slurry surfacing is ideal for any type of surfacing receiving mainly pedestrian traffi c e.g. footways and cycleways.
Micro surfacing is ideal for use on urban roads and roads carrying up to 250 commercial vehicles per lane per day. Some products have a HAPAS certifi cate which enables them to be used on more heavily traffi cked roads.
What is the difference between slurry and micro surfacing?
Slurry surfacing is normally a single coat application laid mechanically or manually up to a dried fi lm thickness of 6mm. Micro-surfacing incorporates a polymer modifi ed bitumen emulsion and is often a two-coat application laid mechanically or manually to a maximum dried fi lm thickness of typically 15mm.
These materials are usually referred to as micro-asphalts.
What are the benefi ts?
è These treatments are very cost effective compared to conventional resurfacing
è Restores surface texture and improves skid resistance
è Rapid curing characteristics – some micro-surfacings can receive traffi c about 20 minutes after installation
è High daily outputs mean minimal traffi c disruption and congestion
è They seal the surface preventing ingress of water into the pavement structure thereby helping to minimise pothole formation
è Suitable for overlay on a wide range of existing surfaces
è Micro-surfacing has the ability to reshape and re-profi le existing surfaces by fi lling shallow defects such as potholes, cracks and ruts
è Able to provide a smooth or textured fi nish
è Available in a range of colours providing an aesthetically pleasing fi nish.
When to use slurry and micro-surfaces
è Before the footway or carriageway surface deteriorates to the stage where expensive major patching and/or reconstruction is required
è Before surface skidding levels fall below the investigatory level for the class of road in question
è When the road surface profi le needs minor restoration.
Cost effectiveness
è Slurry surfacing costs in the region of £2.50m2
and micro-surfacing costs £3 to £4m2 , towards the higher
end if the process involves surface regulating and ironworks
è They also provide good value offering an average service life in excess of 10 years or a cost life index of less than £0.40 per year.
Some important
considerations è Slurry surfaces and micro-surfaces can be specifi ed in accordance with the specifi cation for highway works clause 918
è These materials are recognised as products regulated by the Construction Products Regulations (CPR) and European Standard BSEN 12273. Contractors must now provide a CE mark and a declaration of performance for each type of slurry surfacing and micro-surfacing product placed on the market
è Further guidance is available within the Design Manual for Roads and Bridges (DMRB) HD37
è These products are designed by the contractor to meet the requirements of the road surface on which they are laid
è The work should be carried out by an experienced contractor who can demonstrate a good track record of high quality work
è All contractors who are members of the RSTA have achieved accreditation to the national highway sector scheme 13 for the supply and application of surface treatments to road surfaces.
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