METHOD FOR REMOVING OLD ASPHALT CONCRETE FROM A ROAD

Abstract: In order to remove old asphalt concrete from a road without crushing the stone fraction thereof and without emission of harmful gases, superheated steam is blown onto the old asphalt concrete and the asphalt concrete softened in this way is pushed off and removed using a slide or shovel.

Description: Title: Method for removing old asphalt concrete from a road. The invention relates to a method for removing old asphalt concrete from a road. It is known to divide old asphalt concrete, which has to be replaced by new, into manageable lumps and fragments using crushing machines or milling machines and to remove said lumps and fragments using a mechanical shovel. A disadvantage of this method is that, as a result of the crushing of the stone fraction of the old asphalt concrete, the particle size distribution of said fraction is changed, that is to say the proportion of the finer fraction increases. There is an ever increasing tendency to produce the top layer of an asphalt road from very open asphalt concrete, that is asphalt concrete which, as a result of the choice of a specific particle size distribution, has 20 to 2 % cavities which ensure perfect drainage. Crushing of the stone fraction of the very open asphalt concrete by crushing or milling results in a substantial increase in the proportion of fine particles and in it therefore no longer being possible to process the removed old asphalt concrete into a new mixture which is able to form a layer of very open asphalt concrete- Another drawback of crushing or milling is the dust formation, mainly caused by crushing of the stone fraction. The aim of the invention is to overcome the abovementioned disadvantages and to this end superheated steam is blown on to the old asphalt concrete and the asphalt concrete softened in this way is pushed off and removed using a slide or shovel. Since mechanical crushing or milling can be dispensed with, the particle size distribution of the old asphalt concrete to be processed into new asphalt concrete will be unchanged with respect to the particle size distribution in the relevant layer. There is no formation of substances hazardous to health (fine grit, hazardous gases formed on combustion) . Softening of old asphalt concrete with the aid of infrared radiators or gas flames is unacceptable in connection with the emission of carcinogenic gases. The use of superheated steam surprisingly leads to outstanding results. Softening can be achieved to an extent such that the asphalt concrete can be pushed off and removed without crushing of the stone fraction of the old asphalt concrete and without emission of hazardous gases, the particle size distribution of the stone fraction undergoing no change. Preferably, the superheated steam has a temperature of at least 105°C The invention is outstandingly suitable for the removal of a layer of very open asphalt concrete lying on a layer of dense asphalt concrete, the very open asphalt concrete layer being softened by blowing superheated steam on to it and pushed off, while the dense layer of asphalt concrete, which is more difficult to heat, remains behind. Indeed, as a consequence of 20 to 25% cavities, the --. to 5 cm thick top layer of very open asphalt concrete takes up the heat originating from the superheated steam much more rapidly than the layer of dense asphalt concrete below it. The relatively expensive open top layer having a very specific particle size distribution can then also be processed separately to give new very open asphalt concrete. The invention thus makes it possible to remove the open top layer without damaging the dense underlayer. An essential feature of the invention is that old asphalt layers can be removed rapidly and effectively without emission of hazardous gases and without stone dust being formed as a result of crushing and with retention of the original particle size distribution, by means of treating with superheated steam and pushing off mechanically using a slide or shovel.

Claims: Claims 1. Method for removing old asphalt concrete from a road, characterised in that steam is blown on to the old asphalt concrete and the asphalt concrete softened in this way is pushed off and removed using a slide or shovel. 2. Method according to Claim 1, characterised in that the steam has a temperature of at least 10 β C. 3. Method according to Claim 1 or 2, characterised in that the layer of very open asphalt concrete from a layer of very open asphalt concrete lying on a layer of dense asphalt concrete is softened by blowing steam on to said layer of very open asphalt concrete and pushed off, while the dense layer of asphalt concrete which is more difficult to heat remains behind.

Inventors: KEMPS ANDREAS GOVERDINA, KEMPS, ANDREAS, GOVERDINA
Applicants: HOLLANDSCHE BETONGROEP NV, HOLLANDSCHE BETON GROEP N.V.
Application year: 1991
Main classification: E01C19
IPC codes: E01C19, E01C23