Porous Asphalt Maintenance Cleaning
| In Europe, highway
authorities routinely clean Porous Asphalt pavements in order to retain hydraulic conductivity and low acoustic values, indeed some sections of motorways around Rotterdam are cleaned three times annually. The work is usually carried out under ‘rolling-block’ traffic management at night or at off peak periods hours in the day- time. Using the hydrology process, we apply water to the surface in the same way as other activities but through wider angled jets (40 degrees) which in turn loosens and releases the detritus deep down in the matrix and then the water and detritus are removed from the surface by the vacuum recovery device. At that time, the Porous Asphalt had been laid some 4 years and there were then problems with surface spray during heavy rain because the draining ability of the material had reduced. Water outflow tests were carried out and pre-treatment rates of outflow were recorded in excess of 6 minutes! Newly laid material would normally give outflow rates of between 8 – 10 seconds. Using the captive hydrology process, we achieved post-treatment results of between 9-13 seconds. There is a strong economic and environmental case for regular cleaning of porous or other materials with negative texture. In environmental terms, regular cleaning maintains the low acoustic values inherent in the asphalt meaning quieter surfaces for drivers and local residents alike. Experience in Holland
has shown that because of their regular cleaning regime, the life of the |
Concluding comments and acknowledgements
| Captive hydrology is
now widely accepted and used by most local authorities in Europe but mainly for Retexturing, however only a relatively small amount of work is done each year amounting to around 1 million square metres. A great deal more work could be done if financial constraints were eased and that highway engineers would consider Retexturing instead of surface dressing. If a pavement is basically structurally sound but is likely to be slippery when wet, then Retexturing is a viable, cost effective solution and is environmentally responsible. Using hydrology as a reusable intervention as suggested: - DMRB – Vol. 7 – Chap 11 derives the following additional benefits for the Highway Engineer: • No quarrying of new and irreplaceable materials • No planing’s to dispose of • Contaminants removed at the point of treatment and not abandoned to verges or drainage systems • A reduced need for fossil materials as bitumen use is reduced and fuel oil requirements are minimized, thus saving on energy and keeping CO² emissions to a minimum. • Minimal exposure of highway personnel to moving traffic. It is still relatively early days in the development of hydrology in highway maintenance but interest is growing as the positive benefits of the process are realized and there is a huge potential market in the UK and Internationally. |