On the majority of roads, sealing the pavement is achieved by surface dressing. This consists of the application of a layer of bitumen emulsion to the road surface, followed by a layer of chippings. The bitumen seals the surface, and the chippings provide friction to allow safe passage of traffic. Surface dressing can be carried out over kilometres of road at a time using conventional plant, or over localised sections where the seal of the road has deteriorated using all in one sprayer/gritters, either way the technique represents the most efficient and cost effective method of sealing a road pavement and providing skid resistance as part of normal maintenance. Depending on traffic volumes, roads should be surface dressed on a cycle varying from seven to ten years to seal the surface and extend the life of the pavement. This frequency has not been achieved over much of the country during the last decade, as the focus of many road authorities has been on pavement renewal rather than pavement maintenance. [login type="readmore"]
This approach will not be possible in a period of more limited resources. The focus will have to shift to sealing pavements in order to extend their life and engineers will have to become more involved in the surface-dressing process. When constructing roads paved with layers of bitumen or macadam/asphalt, the seal of the road is achieved by the use of bond coats of bitumen emulsion between the various layers of pavement – these both seal the road and bind layers together to make a laminated structure. Omission of bond coats or inadequate application of bond coat is a cause of pavement failure. TRENCHES A controllable source of road surface defects is inadequately restored trenches or excavations. The large majority of road excavations are carried out by the road authority, other public undertakers or contractors operating on their behalf. It is unacceptable that the location of underground services is often found by following the tell-tale depressions in the road surface. The majority of trenching operations are carried out in a planned environment. The need to have trenching carried out can be anticipated in advance and as an absolute minimum, the adequacy of reinstatement should be assured through a system of quality control on the part of the Roads Authority. The standard to which a local authority reinstates its own excavations will set a target for other undertakers. Guidelines for trench reinstatement have been prepared by the City and County Engineers Association (CCEA). These have been adopted by the Department of Transport, Tourism and Sport (DoTTS) and the Department of Environment, Community and Local Government (DoECLG) and the recommendations in these should be applied to all trench works. Common problems with trench reinstatement are: • Unsuitable fill material used in backfilling; • Inadequate compaction of backfill; • Failure to seal over and around the edges of the trench surface, resulting in the saturation of the granular material; and • Subsequent pavement failure. These problems are avoidable if work is properly specified and supervised. Equally, road authorities should keep an accurate database of trench works, road cuttings, inspections and remedial works. REPAIR OF ROAD-SURFACE DEFECTS To the road user, the immediate evidence of an inadequately maintained road network is the ubiquitous pothole, a cause of genuine concern and a source of much indignation. Potholes are a symptom of underlying deficiencies in the road (inadequate drainage being the most common), a road pavement being badly fatigued through overloading, lack or renewal or, commonly, roads of minimal construction depth built for light traffic being subjected to repeated heavy-axle loadings. It is probably a measure of the effectiveness of road-repair techniques that so many roads are still capable of functioning, albeit at a low serviceability, while carrying loads far in excess of their structural capacity. The City & County Engineer’s Association, in conjunction with the DoECLG, has prepared and distributed a document entitled, ‘Road Surface Repairs’, which has been adopted by the DoTTS and the DoECLG. This document gives an overview of the techniques, materials and operating methods currently in use in this country. The reader is advised to study this document, which offers a comprehensive guide to the topic. The following points deserve to be highlighted briefly: • Repairing road-surface defects is an expensive operation – the operating costs of a conventional truck mounted patching unit run to €2,500 per day, regardless of the effectiveness of the repairs carried out. • Quality control of the materials used is critical – use of incorrect or substandard materials will result in poor-quality work, which will rapidly disintegrate. • There are many different methods of carrying out road-surface repairs, which vary according to the machinery used and materials employed. The CCEA document sets out an indication of suitable methods for use on different types or road construction, the choice of method depending more on construction of the existing road than its classification into national, regional or minor road. • Repair of road surface defects is wasted effort unless drainage problems are attended to – repairs to roads that are either waterlogged, or may be expected to be so, will not last for any length of time. • Repair crews must be adequately trained and skilled in the techniques they are using; they should understand not only the ‘hows’ but also the ‘whys’ of what they are doing. Their efforts should be directed at achieving effective and durable repairs. • The two most common causes of repair failure are inadequate compaction as well as failure to seal the repair surface and perimeter, allowing subsequent water penetration and pavement disintegration. All repair techniques depend on the compaction of the repair material – this will not be achieved by the back of a shovel or a lorry wheel. Suitable portable compaction equipment is an essential tool in surface repairs; similarly, the repaired area and its surrounds must be waterproof. • Effective repairs will be carried out if the repair crews are directed by engineers with a thorough understanding of the methods, machines and materials being used, and the ability to encourage the crews to develop their skills in a worthwhile manner. Information on methods of repair is available on www.coldchon.ie. FOOTPATHS One might assume that the maintenance of footpaths for pedestrian use would not present difficult problems to road engineers. The high proportion of claims received by local authorities arising from trips and falls on footpaths would seem to belie this assumption, however. The major contributors to footpath defects are: bad construction; traffic mounting paths; and badly reinstated excavations in the path. Many footpaths lack the strength to perform their function due to inadequate foundations or poor construction methods or materials. The law prohibits mounting pavements with vehicles, yet many drivers disregard this, the most significant offenders being drivers or delivery vehicles. Excavations in the path should be an avoidable problem, but it seems to be a most common difficulty. Excavations are carried out routinely but, in many cases, adequate reinstatement is omitted. At times, the local authority staff may themselves be part of the problem by excavating footpaths to repair underground services. An important step in footpath maintenance is the preparation of a footpath inventory by the person responsible for maintaining the footpath. This will allow an assessment of the relative condition of portions of path, and the estimation of the necessary resources to effect an adequate repair programme. This can be a chastening exercise because aside from the problems caused by large areas of exhausted pavements, the engineer will repeatedly come across minor defects which can be repaired at low cost, but yet represent a threat to pedestrians. These repairs should be effected immediately. Major repairs or renewal should be planned in the same way as other roadworks operations to ensure high quality work and sections should be laid out in a manner to ensure efficient work. Many footpaths are not accommodating to people affected by physical disability. In preparing a scheme of footpath repair or renewal, the engineer should be aware of the needs of people with a disability and take advantage of the opportunities to facilitate their mobility. Liaison with local disability action groups will prove fruitful in revealing unsuspected barriers to mobility. REPAIRS AND ROAD EDGES While defective concrete pavements can generally only be usefully repaired by the removal of defective areas and the construction of a new section of pavement, it is possible to renew bituminous paths by using a bituminous slurry seal, which will provide a slip-resistant and level surface without appreciably raising the profile of the path. This method can also be used on concrete paths suffering from surface ravelling. The unit costs are favourably compared with the cost of removal of the existing path and reconstruction. With the increased mechanisation of road sweeping, a growing problem is the ravelling of the road edge at the kerbside. This may be caused in part by inadequate sealing of the area between the kerb and the edge of the road, particularly if the kerb was originally placed after the road was constructed, but the action of mechanical brushes will affect all but well constructed roads. Possible solutions are repairs using patching methods or the application of a slurry seal 3mm-500mm wide at the kerb edge. The latter has been tried and found to provide a satisfactory solution. RESOURCE USAGE Given that in the current economic climate, resources are typically inadequate, it is imperative that engineers should target and direct the use of available resources so as to maximise the gain to the road network from the maintenance programme. The emphasis on local authority auditing has traditionally been to ensure that monies are spent in a legal and correct manner. It is inevitable that the question of value for money and the efficient use of resources must be addressed by engineers directing road maintenance operations. In Ireland, the road maintenance engineer can carry out the functions of a number of people involved in construction projects. He or she may fulfil the duties of surveyor, designer, resident engineer, site agent and certifier, often all within the same morning. The flexibility inherent in this arrangement can allow for the imaginative use of materials and techniques to maximise the return on investment of public funds. While acknowledging that resources are limited, engineers must ensure that work under their direction is carried out in accordance with the relevant standards. Work badly done will lead to a waste of resources in rectifying defects. LABOUR RESOURCES A consequence of the low level of funding for road maintenance and of increasing mechanisation of activities is that the labour force available to local authorities has shrunk during the last 10-15 years. There is a huge availability of talent and experience in road maintenance available within local authorities, which must be properly mobilised to achieve efficient work. It is essential that engineers ensure that staff working with them have an appreciation of the tasks to be accomplished and the correct methods of tackling these tasks. This can only be done through training, both formal and informal. The formal training should be by means of lectures and seminars geared towards the needs of the particular workers and aimed at improving their knowledge of the methods and techniques being used. More importantly, informal training and encouragement should be given on site by the engineer, supervisor and foreman. Road maintenance staff should be encouraged to develop their skills in the wide range of operations to be achieved. This should not be a one-way process – while road workers do not have the technical training of engineers, in many cases, they will have a long experience of the work they are doing and an appreciation of the practicalities of the task, of which engineers should take heed. CONCLUSION Achieving a high standard of road maintenance is a difficult task for engineers. Good standards will only be achieved if the disparate maintenance operations are integrated together in a practical manner. Limitations on resources will ultimately limit what can be achieved, but the task facing engineers from day to day is to achieve the highest standards within the constraints of available resources. It is hoped that the methods and suggestions outlined in this paper will be of some assistance towards this. Jim Campbell is the chief engineer with Cold Chon (Galway) Ltd.