- Simon Kiragu
You may have noticed road works when travelling on major highways in the country with erections of footbridges, installation, and replacement of road signs to recarpeting of worn-out sections.
When roads are built, the durability depends on the maintenance of the infrastructure with drainage and reinforcing of existing sections.
Recently, a road maintenance practice along Thika Superhighway raised eyebrows among motorists with the workers seen laying another layer over the tarmac which had no potholes - loose chippings on the already tarmac road.
There is an explanation behind the method which Kenya National Highways Authority (KeNHA) uses to reinforce and protect the tarmac on major highways.A picture showing road works in progress when a bituminous film is sprayed on the road.KeNHA
Defined as surface dressing, road workers spray the existing road surface with a coating of bitumen, then spread stone chippings on top.
The chippings are rolled into the bitumen and once the bitumen has set, it is swept to remove any loose chippings.
This is done to protect the road from wear and tear as the bituminous film acts as a waterproof seal preventing the entry of surface water into the road structure.
The stone chippings protect the film from damage by vehicle tyres which improve the durability of the road.
Surface dressing is preventative, for roads that are in relatively good condition. It can last around ten years, roads can be re-dressed up to three times, and is very cost-effective.KeNHA workers conducting road maintenance work on Thika Super HighwayKeNHA
Also, the work is done relatively quickly, minimising the inconvenience for residents and motorists.
It needs to be done where minimum road surface temperature is 25-30 degrees celsius which means it can only be done during the day.
This will usually be done after 24 hours, but during hot weather, this may take longer. The bitumen is thereafter allowed to set for a period of seven to ten days before road marking can be initiated.
Vehicles are allowed onto the new surface, at a reduced speed, to help to push the chippings into the road.
Drivers are advised to keep to the temporary low-speed limits and avoid sharp turns. This allows the surface to stabilise, and also prevents any damage to the vehicle.
Motorists have reported damage to their vehicles from the chippings with some damaging their windscreens that fly into the air when driven on at a high speed.
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