Pavement Preventative Maintenance Program
In the Department of Public Works’ on-going effort to maintain the City’s infrastructure in a cost effective and efficient manner we are continuously looking for new tools to keep our roads in good condition. Over the past three construction seasons the City has resumed a stone chip sealing process which had been discontinued several years ago. Advances in technology in the form of computerization control of both the oil and stone spreading process have lead to a more uniform and user friendly application. This type of preventative maintenance (PM) treatment is best suited to roads that are still in fair condition, have reasonably well defined cross sections, and are not high traffic streets. Stone chip sealing will usually improve streets from fair condition to good or even very good condition, and is consistent with modern pavement management goals. The typical stone chip seal is expected to last 4-7 years before needing another application or other form of maintenance.
This year we have added a new treatment, known as a double chip seal. Double chip seals are better suited for roads in more densely populated areas, such as residential cul-de-sac areas. Adams Street and Debbie Court (off of Scotland Road), were recently treated with this method in July 2013. This process entails first applying a thin layer of asphalt emulsion (tar), followed by a layer of 3/8” stone, which is compacted into the emulsion layer (this first process is essentially a standard chip seal, as described earlier). Immediately after applying the first treatment to the roads, the same equipment then goes back over the road applying another layer of emulsion, followed by a layer of smaller ¼” stone. The advantages of this process are that the smaller stone from the second application tends to be less of a nuisance than the larger stone. By nuisance we mean loose stone that gets kicked up by vehicle tires, loose stone on the sides of the road, rough initial riding surface, etc. Structurally, the smaller stone integrates nicely with the larger stone below creating a smoother, denser surface than the single chip seal process. The double chip seal costs approximately 80% more than a standard chip seal and has an expected life of 7-10 years.
Another process that the Public Works Department is considering is called micro-paving. This process combines asphalt emulsion, stone dust, and cement to form a slurry product which is spread over the road in two thin applications at a total thickness of approximately 3/8”. The main advantage of this process is that there are no loose stones and the finish product is much smoother than with a standard or double chip seal. Both of these characteristics make this process suitable for roads with higher traffic volumes. However, micro-paving does not provide the structural benefit of a chip seal. The cost of micro-paving is about the same as a double chip seal and the expected life is approximately 5-8 years.
The success of all of these different treatments is dependent on the condition of the roadway prior to the maintenance. It is very important to apply the PM before the condition of the road deteriorates beyond fair condition to poor or failed condition. Often a crack sealing treatment is applied to a roadway prior to applying the surface treatment. Doing so will extend the life of the PM treatment. The goal of PM treatments is to save money over the long term by postponing the need for costly pavement reconstruction. Two dollars spent today (the cost of a square yard of single chip seal) will postpone having to spend twenty dollars tomorrow (the cost of a square yard of pavement reconstruction). It costs roughly $24,000 to chip seal one mile of road (single chip seal), whereas it costs approximately $275,000 to reconstruct one mile of road.
Please do not hesitate to contact the Director of Public Works or the City Engineer if you have any questions about our preventative maintenance programs.