• reflective cracks
• surface generated cracks
• shrinkage cracks
• longitudinal lane joints
• concrete spalling
• asphalt/concrete interface joints
• mid bay cracking

Cracks generated from the surface are caused by fatigue from traffic, especially HGV’s. These types of cracks when excavated, will often not show further cracking in the layers below the surface course.

Cracks generated from movement in the sub-base are called reflective cracks and will show through in the wearing course because movement in the underlying layers is being mirrored in the top surface. Traditional asphalt road surfaces, whilst being called ‘flexible’ roads when compared to concrete ones, are not able to contain concentrations of such high movement.

Why is this movement taking place? This all depends on the structure of the road. Traditionally roads are built in layers and these layers are designed to bear the load of traffic in varying degrees. Many roads have concrete in those lower layers. As temperatures change, road surfaces (like other materials), expand and contract. Concrete is designed in slabs and designed to focus this movement at the joint between slabs. Lean mix and continually reinforced concrete also focuses movement in concentrated points. Asphalt reacts differently to temperature changes, expanding and contracting evenly over the entire surface area.

This incompatibility of the concrete and asphalt to react similarly, leads to asphalt overlays cracking when laid on top of concrete sub-bases.

Couple this with variations in which the different layers of the road surface heat up from the sun, the lower layers expand at a slower rate to the surface ones, and it is no wonder that a road surface cracks as it does.

What is important to consider is that in most cases, a substantial crack in the road surface is likely to be in a position where movement is the cause. Repair methods should consider materials with the flexibility to accommodate that movement when it occurs again in the future.

Other companies do not offer the full range hence their advice will steer the user to their particular approval. For truly independent advice, come to Rhino.

At Rhino we use

(1) Safetrack Simple overband for cracks up to 5mm (where no further movement expected)
(2) Safetrack Fill and overband for cracks 5mm to 40mm (where no further movement expected)
(3) Jointmaster 'F' grade for shallow rebated flexible repairs (i.e. 10mm or 20mm)
(4) Jointmaster 'H' grade for deep repairs in non-flexible environments (i.e. 40mm to 100mm deep)
(3) Combined Jointmaster 'F' & 'H' grade for deep repairs requiring a flexible topping

The BBA through HAPAS have specifications and approvals in place for many highway products, such as high friction surfacing, thin surfacing, modified bitumens and bridge deck waterproofing.

BBA HAPAS certification is a prerequisite for crack sealing and a mandatory requirement for all public procurement bodies covered by the Specification for Highway Works, but why is this?

A key requirement for approved installers of crack sealing is to achieve minimum skid resistance values. A longitudinal band with inadequate skid resistance is a very real threat to the safety of all road users but especially motorcyclists when braking.

To tackle this issue, Highway Authorities tasked the BBA to address this problem and back in 1999 following a spate of motorcycle skid related accidents, the current BBA HAPAS standards were introduced.

Prior to this, crack sealing was an unregulated industry and simple bitumen over-band sealing systems were used to seal the crack. However, motorists and particularly motorcyclists were vulnerable to skidding accidents on smooth, wide bands of these fairly basic bituminous sealants.

BBA HAPAS was introduced to remove the need for individual Highway Authorities to independently test each proprietary system and to set a standard that was agreed by the various overseeing organisations.

Jointmaster has been approved for use on highways since 2007 and has seen extensive use on the UK motorway network including M25, M3, M4 and the A1.

It is the approved bituminous system for repairing cracks in the highway where further movement can be expected and flexibility with excessive depth is required.

Stage 1 & 2
All defective and loose material is removed using a Wirtgen W350 cold milling machine. This is a mini version of the big road planers. Typically, we cut out the asphalt to 200mm wide and 20mm deep. The operator ensures the crack is in the centre of the planed recess which is then mechanically swept to remove the planings.

Stage 3 & 4
The recess is then cleaned and dried with a hot air lance which will blow out any lingering loose materials and liven up any binder left in the road surface.

The Jointmaster material is then poured into the recess and screeded to a smooth level finish. The material is a hot applied (180⁰c) polymerised bituminous material with added sand, aggregates and fibres. This material flows into the bottom of the recess, filling the crack, sealing the edges and providing a watertight seal.

Stage 5 & 6
A dressing of high PSV (polished stone value) aggregate is applied to the surface, sticking to the Jointmaster material to leave a skid resistant finish.

The finished job is left to cool (anything from 20 mins to 1 hour) before a final sweep removes any excess aggregate and the road is reopened to traffic.

Cracking in the highway will lead to a severe and rapid deterioration of a road surface, due to the ingress of water into the underlying structure of the road. Once water penetrates the surface, there are a number of factors that generate accelerated decline.

1. Water expands when it freezes. In the UK, the repeated freeze-thaw cycle that takes place from night to day on a daily basis puts extreme pressure on a road surface. As the ice expands with such regularity in a confined space, the surrounding asphalt soon breaks up as it is weaker than the expanding frost. The result is that the cracks get wider and bigger, eventually causing potholes to form until large sections of the road surface detach altogether and the road needs resurfacing.
2. Water collecting in pockets under the road surface is subjected to ‘pumping’ from vehicles, especially HGV’s. The pressure from this pumping action forces the water underneath and between asphalt layers, further detaching sections of the road.

The direct results of leaving cracks untreated is firstly, a enlarging of the crack. Secondly, the formation of potholes as sections break out. Thirdly, delamination of the various layers of surfacing and lastly, a wholesale failure of the road surface.

What is it:

• A simple band of bitumen or alternatively MMA pulled over the crack. Some versions have added aggregate of very small grading to give skid resistance.

Pros:

• Cheapest application available 
• Large quantities can be treated in a shift
• Seals the crack
• BBA HAPAS approved systems available

Cons:      

• Maximum width limited to 40mm by overseeing authorities due to potential skid hazard
• Very thin band of material unable to cope with further movement. Will crack through

Ideal uses:

• Where no further movement is expected
• Where the surface is due to be overlayed afterwards (negating skidding risk)
• Where budgets are limited and cracking is minor

What is it:

• A two component system involving the application of a sealant either bituminous, thermoplastic or MMA in the base of the crack to ‘fill’ it, followed by a surface screed dressed with aggregate for skid resistance.

Pros:       

• Protects the arrises and gives a skid resistant finish
• Some systems approved for use by BBA HAPAS

Cons:      

• No requirement for any movement capability, so unlikely to withstand further movement
• When used on transverse cracks, can leave a significant up-stand much like a rumble strip which will generate noise.
• New to the market place, performance in situ stil being evaluated

Ideal uses:  

• Treatment of longitudinal seam joints

What is it:

• Cutting out the area around the crack and filling up with traditional hot road asphalt.

Pros:       

• Protects the arrises temporarily
• Can be carried out by traditional hot patching crew, so not necessary to bring in specialists

Cons:      

• Not able to cope with the likely movement
• Will crack again and probably create two cracks in place of the original one, at either edge of the patch
• When it cracks through, the repair required will be larger than the original problem. Continued treatment of the surface with this method will exacerbate the problem until resurfacing the entire road is necessary

Ideal uses:

• Asphalt patching is not ideal for the treatment of cracks unless you are sure that there will be no further movement in the road surface

What is it:

• Using specialist mini cold road planers, the surface is milled out centrally over the crack. After cleaning and drying, a specialist hot-poured, self-levelling polymer modified bitumen compound is poured into the rebate and dressed with a high performance aggregate finish.

Pros:       

• Systems available approved by BBA HAPAS
• Quick to apply, treating large quantities in a shift
• Will accommodate future movement without cracking
• Will adhere to the surrounding surface without cracking
• Good skid resistant finish
• Ideally suited to repairing patches and potholes situated alongside the cracks
• Work can be done under lane closure or night shift, road fully open to traffic at end of shift 

Cons:      

• Requires specialist contractors to install

Ideal uses:

• Treatment of all cracks, longitudinal and transverse
• Treatment in concrete, asphalt and mixed surfaces
• Depths of 10mm minimum up to the depth of the surfacing
• Used extensively on motorways, trunk roads, feeder roads, housing estates and airfields

Grade ‘F’ offers more flexibility, but in consequence has a slightly reduced resistance to deformation i.e. rut resistance. Grade ‘F’ is the grade required where flexibility is a requirement of the repair material and is therefore the most commonly used grade. After all, if the road has cracked in the first place, the chances are that same movement is still current and likely to continue. Recommendation from the Specifcation for Highway Works suggests Grade F where significant crack movement is anticipated, for example in cracks in overlays to jointed concrete carriageways.

Grade ‘H’ has no requirement for flexibility under the BBA HAPAS test parameters and has a higher resistance to deformation. Recommendation from the Specifcation for Highway Works, suggests Grade H for use where cracks do not penetrate through the pavement structure and significant movement is unlikely to occur; or for small patches in wheel tracks.

The Jointmaster system is available in both Grade ‘F’, approved under certificate 07/H126 and in Grade ‘H’, approved under certificate 09/H149. This means that we can offer impartial advice as to the most suitable grade for the circumstances.

Outputs:

Anything up to 1000 lin.m can be achieved in a day. The type of site and type of work will dictate what this figure will be.

Transverse joints 300-400 Lin.m per day

Overseal banding upto 3,500 Lin.m per day