The discussion in this Section relates to the treatment of individual cracks in bituminous seals or asphalt layers of pavements. Cracks and joints in concrete pavements will require a different approach (see Section 4.8 and the AGTPT Part 5 (Austroads 2009f)).
Where cracking is widespread or extensive the use of a SAM or SAMI may be more appropriate (see
described in this section may be required in conjunction with a SAM or SAMI (e.g. seal individual wide cracks and then apply a SAMI to also deal with smaller cracks), or other treatment as described in Sections 4.4.5 and 4.4.6.
Provided there is not excessive movement, the most commons treatments for filling and sealing cracks involve the use of an appropriate proprietary or purpose-made crack filling/sealing product.
Reference should also be made to Section 4.11 which deals with the use of polymer modified and multigrade binders.
4.4.4.1 Function
Crack filling and sealing extends pavement life primarily by waterproofing the pavement surface to prevent softening of the structural layers by water from the surface. Other waterproofing measures, such as sealing granular shoulders and pavement edge drains, are separate treatments to prevent water ingress from other areas.
Crack filling and sealing of cracks that are to be overlaid may be undertaken in conjunction with treatments described in Sections 4.4.5 and 4.4.6 to mitigate the effects of reflective cracking.
4.4.4.2 Appropriate Uses
Appropriate uses for crack filling and sealing include the following:
• To treat transverse, reflective, longitudinal and diagonal cracks, and cracks around manholes, etc.
• To treat cracking of longitudinal and other construction joints.
• For cracks that have a ‘medium’ to ‘large’ width. Where required a groove needs to be formed (routed) before the crack is filled and sealed (see Section 4.4.4.6).
• As a preventative maintenance measure. A crack-sealing program should be established and maintained following construction of every new pavement with a bituminous layer or seal for a period of at least five years. Cracks should be filled or sealed in a timely fashion such that the pavement’s integrity is maintained.
4.4.4.3 Inappropriate Uses
It is inappropriate to apply crack filler or sealant to a dirty and wet surface, as good adhesion cannot be achieved.
The treatment is generally inappropriate in the following cases:
• Where the cracking is widespread and extensive. Its use is also generally uneconomical in such cases.
• Where cracking is caused by a structural pavement failure (i.e. asphalt fatigue, the use of a poor paving material, inadequate thickness, etc).
• Where there is excessive movement of cracks, especially if it is the only treatment proposed.
• Where the product used may cause skid resistance issues for road users (e.g. cyclists and motorcyclists).
4.4.4.4 Materials
Proprietary products are typically used. These products and how they are applied should comply with the suppliers and/or manufacturer’s requirements, except where these conflict with TMR specifications and technical standards. Relevant TMR specifications and technical standards include the following:
• MRTS17 Bitumen (TMR 2009c).
• MRTS18 Polymer Modified Binder (TMR 2009d).
• MRTS19 Cutter Oil and Flux Oil (TMR 2009e).
• MRTS20 Cutback Bitumen (TMR 2009f).
• MRTS21 Bituminous Emulsion (TMR 2009g).
• MRS30 and MRTS30 Dense Graded and Open Graded Asphalt Pavements (TMR 2010h).
• MRS57 and MRTS57 Geotextiles for Paving Applications (TMR 2009j).
4.4.4.5 Design Considerations
Crack filling and sealing materials should have the following design properties:
• Low stiffness and high ability to deform.
• Waterproof integrity.
• Good resistance to oxidation and ultraviolet degradation (where they are left exposed).
• Strong adhesion to bituminous surfaces.
• Safe to heat to high (application) temperatures.
• Softening point generally >80°C.
4.4.4.6 Construction Considerations
Relevant TMR specifications and technical standards include the following:
• MRS30 and MRTS30 Dense Graded and Open Graded Asphalt Pavements (TMR 2010h).
• MRS57 and MRTS57 Geotextiles for Paving Applications (TMR 2009j).
4.4.4.6.1 Crack Filling and Sealing
Where a specification, technical standard or other contract document does not specify a treatment regime it is best to classify the cracks according to their width as follows:
• Width from hairline to 6 mm: The most practical and economical means of sealing cracks of this size is to place an overband of sealer on the pavement surface centering on the crack. The overband should be approximately 50 mm to 100 mm wide. This can best be accomplished by using a pour pot and with a second operator with a 'V' shaped squeegee. The crack filler should be hot enough to readily flow in front of the squeegee, which should be controlled to provide a thickness not greater than 2 mm to 3 mm. One alternative to over banding is to route the cracks. However routing is a costly method and it has been found that over banding will achieve excellent results. Another alternative is to use strain alleviating fabric strips. These too are costly.
• Width from >6 mm to 12 mm: Cracks of this size can be readily cleaned and dried to a minimum depth of 20 mm to 25 mm, and then filled flush to the surface with the crack filler. Alternatively, a strain alleviating fabric strip may be used.
• Width >12 mm: Wide cracks in pavements can be filled completely with crack filler and sealed. Care must be taken that excess moisture does not come into contact with a hot crack filler as rising moisture vapour will interfere with its bond with the sides. These cracks are filled level with, or just below, the pavement surface. Alternatively, strain alleviating fabric strip may be used.
Where a specification, technical standard or other contract document does specify a treatment regime the specified treatment regime shall be followed.
4.4.4.6.2 Sanding or Dusting
Sanding or dusting is normally not necessary, provided traffic can be kept off the freshly filled/sealed crack for the curing period of the product. However it is recommended in the following circumstances:
• Any location where tyres are likely to be parked directly on the recently poured crack filler.
• In pedestrian areas subjected to high volumes of foot traffic.
• Areas where constant turning and stopping occurs, especially areas subject to trafficking by heavy equipment/vehicles.
Problems in these instances are aggravated by high ambient and pavement temperatures.
4.4.4.6.3 Priming
It is not essential to prime cracks in asphalt. However priming does help to overcome minor inadequacies in the cleaning process.
4.4.4.6.4 Heating Crack Filler
Storage, heating and mixing shall be in accordance with the supplier’s and manufacturer’s requirements.
Hot crack fillers are typically heated to application temperatures of 160°C to 180°C depending on the width of crack or joint and the crossfall/superelevation and longitudinal grade of the road. Temperatures at the high end of this range are used to reduce the viscosity for improved penetration of narrow cracks.
A wide range of methods have been used over the years for applying hot joint and crack sealers, ranging from modified buckets and cans, to sophisticated pumping units with heat-traced hoses.
4.4.4.6.5 Crack and Joint Filling
As the hot sealer may contract 10% to 15% when cooled to ambient temperatures, it is sometimes necessary to fill the crack to 90% of its depth, allow it to cool and then fill the crack to the final level.
With cracks that are expanding by more than 50% of the joint width, because of temperature or other causes, it may be necessary to apply a strain alleviating fabric strip 100 mm to 150 mm wide depending on the joint size, to help maintain their waterproof integrity after sealing.
4.4.4.7 Expected Performance or Comments
There is a need for ongoing research and technical improvement of crack and joint filling and sealing. The research should look for ways to improve the effectiveness of sealing cracks, from both a technical and operational perspective.
4.4.4.8 Further reading
Relevant publications include the following:
• The PSM (TMR 2011b).
• AGTPT Part 3: Pavement Surfacings (Austroads 2009a).
• AGTPT Part 4F: Bituminous Binders (Austroads 2008b).
• AGTPT Part 9: Pavement Work Practices (Austroads 2008c).
• Guide to the Selection and Use of Polymer Modified Binders and Multigrade Bitumens (Austroads 2006b).
• Pavement Work Tips (Austroads and AAPA various).
4.4.5 Treatment of Existing Reflective and Surface Cracking for pavements other than