Engineers' Angle | Asphalt vs concrete roads - Cost, care and convenience
I have been involved with the design and construction of roads working at the Public Works Department (PWD), the Urban Development Corporation (UDC), and Wallace Evans Jamaica Ltd for more than 50 years.
Before the 1950s, most asphalt road surfaces were semi-penetration macadam with two layers of spray and chip on a layer of two inches of crushed stone. The base varied from using on-site materials like marl, bauxite, hard shale, stone packing, to just grading and rolling the existing dirt surface.
Much of this still exists, and in areas with low rainfall, good drainage and light traffic has served us well.
With the increasing size and weight and volume of vehicles, the PWD started to rebuild and realign roads with 'engineered' foundations and asphalt concrete surfaces. The PWD acquired Barber-Greene equipment in the 1950s, and thereafter, Jamaicans referred to these surfaces as Barber Greene.
In many areas, the PWD was able to resurface the road without reconstructing the base, e.g., Gutters to Santa Cruz.
Examples of new alignments with marl base include Queens Highway (1953) Mandeville to Spur Tree (1955), Linstead to Ewarton (1958), and the Three Miles to Spanish Town Highway (1972), all of which gave 20 to 30 years of service before being repaved.
In Kingston, Washington Boulevard, Tom Redcam Drive, Oxford, Hope, Old Hope roads have been similarly reconstructed, with appropriate drainage, and have given excellent service.
The UDC rebuilt all the roads at the Kingston Waterfront in 1972 but stabilised the marl base with three per cent cement only recently repaved. Recently, all the north coast highway from Negril to Port Antonio has been reconstructed with an asphalt surface.
There are some sections of roads like Fern Gully, where, because of the terrain, geology, storm water volumes, and where the roadway has to be part of the drainage solution, asphalt surfaces will not stand up and a concrete surface is the appropriate solution.
Concrete road surfaces are substantially more expensive than asphalt surfaces, so we use concrete surfaces only where necessary.
Concrete surfaces will normally last longer than asphalt surfaces but even after periodic resurfacing of an asphalt road, it still makes far more economic sense to use an asphalt or concrete surface.
The analysis requires taking into account the initial and long-term costs reduced to net present value.
Generally, one would not use concrete surfaces on roads with a multiplicity of underground services or where the soil conditions will cause differential settlement and hence break-up of a concrete surface.
A concrete surface is also very good where there are tight curves/ hairpin bends, where the road is steep and to minimise damage from heavy multiaxle trucks, or where water, frequently or constantly, flows on or across the road.
There are some significant road problems still to be dealt with, including the main road from Harbour View to Port Antonio. Here, overloaded trucks carrying sand and gravel have caused significant failure to the original base.
The last, and present, administrations have been endeavouring to arrange for this reconstruction to be done as a priority.
MAJOR ROAD ISSUES
There are 5,500 miles of National Works Agency roads, and about the same amount of parish council roads, most of which are not main roads, and these are where we have our major road issues.
Many of the problems are in the non-limestone areas where rainfall is often high, soil conditions are poor, drains block easily, and landslides happen frequently.
With such a great mileage of secondary and tertiary roads, we need a cheaper solution than asphaltic concrete surfacing. A double-surface dressing costs about half of what an asphaltic concrete surface costs and one-tenth of a concrete surface.
Clearly, concrete surfacing is out of the question for these roads.
There is a system available (micro-surfacing) using premixed materials, which produces a much better quality and a more durable 'spray and chip' solution but more costly than traditional spray and chip. This needs to be pursued more vigorously.
As traffic increases and drainage and other conditions demand, it is logical to resurface sections of secondary roads with asphaltic concrete as has been done on Widcombe Road, and recently, on the Gordon Town Road.
Compare, for example, repaving Widcombe Road or Gordon Town Road with 40 millimetres of asphaltic concrete or a 200-milometer thick unreinforced concrete surface on the existing base. The former is about $1,400 per square yard as against concrete at $6,500 per square yard. You can immediately see the price difference.
There are no concrete paving and finishing machines in Jamaica. To remedy this would require both substantial capital and a guarantee of work to justify the investment. Hand-placing/finishing is OK for the short length in Fern Gully but not for a highway.
Further, asphalt roads are very much easier and cheaper to repair than concrete roads.
- John Allgrove worked at the PWD from 1962-1969 in the capacity of executive engineer and later as senior executive engineer, chief engineer, director of technical services, and deputy general manager at the UDC, and at Wallace Evans Consulting Engineers from 1991-2011 as director and managing director.
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