Widening a Motorway :
In previous methods, widening motorways was approached without effective conservation. The method would involve a complete removal of the emergency lane within a road. This would occur before the new lane would be installed so as to have a linear transition from old road to new. Excavating land and creating a new road with new materials would mean a longer shelf life of the road, but you would have to go through all the cbr testing procedures that you normally would. New materials also mean wasting the incomplete operating life of currently used material therein lied a problem and an opportunity.
The approach that had been recycled before was of making the road anew. This would mean, to destroy part of the existing road which would be the emergency parking lane, and combine the new road with the old using new material entirely. Mainly consisting of asphalt construction. The new approach is to layer the road with cement, and other combinations of materials in the form of layers proving to be cheap and reliable.
For more information on the standards for Highways click here for further information.
New Approach to Motorway Widening
A new, less environmentally consuming means of operating was to recycle and continue using older materials. The material costs saved in the emergency lane alone include:
- 6cm asphalt
- 10cm unbound gravel acting as the base of the road
- 50-80cm of sub base material
All founded in sequence one after the other. Regardless of road length. This was the universally accepted norm, the only foreseeable option.
Then, the layering of road when widening motorways has became an alternative method. This superior method has the following steps in construction:
- Excavation occurs, setting a new formation level. This formation is positioned toward the right of the existing lane. Resulting in the motorway being widened.
- Sub base materials for the new Emergency lane are added.
- Asphalt is milled from the current emergency lane
- Asphalt and gravel extracted from the emergency lane are then laid over the pre-existing emergency lane, as well as the new lane.
- Afterward, new materials are laid over both the old and new lanes, this is to level both parts of the road. The underside of the asphalt will now be evenly level making room for more asphalt to be placed over it
- Watering of materials occurs.
- Cement is placed on the widened portion of the road-to-be.
- Mixing and homogenizing with cement occurs. This goes on to the extent of 25cm.
- Compaction and leveling all layers that have been established thus far occurs
- Transverse crack inducing or TCI.
- Sealing the surface comprised of cement.
- 20cm of asphalt layer is added all forming a good base, binder and wearing course of the cement.
- The old and new pavements share one longitudinal joint, which is supported by a stepped assembly and net reinforcement.
Processes for function:
Crack inducement while seemingly counterproductive, is a preventative operation that prevents cracks from forming randomly. Achieved by placing the cracks in positions that do not cause failure. This is incredibly useful for materials that are not flexible. Examples of these would be the cement bound layer in the motorway. Cracks tend to occur as transverse every ten to twenty meters. This is a byproduct of contraction and expansion when temperature and moisture content fluctuate. These cracks are induced by a drag plate that creates a crack of one third depth and no more than 2.5 meters of that distance. The result is a weakened transverse section with a fine crack throughout the rest of that layer. This serves to reduce movements of the cracks, decreasing crack propagation speed and volatility.
According to calculations in design, hydraulically bound base-layers show a better bearing capacity than that of asphalt construction. This is due to high traffic volume on the asphalt requiring thickness of thirty-two centimeters. The function of the cement bound layer achieves the same result through replacing and a combination of layers, including unbound gravel base and the lower asphalt base layer.