NL9002659A - METHOD FOR PROCESSING OLD ASPHALT CONCRETE TO USE NEW ASPHALT CONCRETE. - Google Patents

Description

Title: Method for processing old asphalt concrete into usable new asphalt concrete.

The invention relates to a method for processing old asphalt concrete into usable new asphalt concrete, wherein the old asphalt concrete is heated to temperatures above the softening point.

It is known to remove an old asphalt concrete road surface by milling or breaking, possibly further reducing the coarse pieces in a crusher and heating them in a rotating drum with hot gases, which have been heated by a burner, to a temperature of approximately 160 eC.

It is also known that old asphalt concrete is made into new asphalt concrete to be processed by heating this old asphalt concrete in a so-called parallel drum to 120 ° è 150 ° C and then by adding extra-high heated mineral, the last being bitumen in the total mixture. admixed, the total mixture reaches a temperature of about 160 ° C.

The milling and breaking up of old asphalt concrete and any further breaking is accompanied by a lot of noise and dust, with high energy consumption.

Heating old asphalt concrete in a rotating drum is a difficult controllable process, such as preventing local overheating of the pieces of old asphalt concrete, for example. This often causes damage to the binder bitumen to be regenerated and there is talk of undesired emissions, among other things, by the escape of hydrocarbon vapors. In addition, when rotating flame furnace is used, there is a risk of blockage. It is known that rotary kilns can no longer be used after processing a certain amount of asphalt concrete due to caking and clogging and must then be cleaned or replaced.

The object of the invention is to provide a method indicated in the preamble which is considerably more environmentally friendly than the known method and with which a considerable amount of energy can be saved.

According to the invention, the old asphalt concrete is heated for this purpose by means of superheated steam at a temperature higher than 160 ° C.

Preferably, the heating of coarse pieces of old asphalt concrete into a plastic slurry takes place in a closed autoclave. The coarse pieces have, for example, dimensions of approximately 0.5 i long and 40 cm thick.

This means that coarse pieces no longer need to be broken into small pieces, so that no dust is released and noise nuisance is a thing of the past.

It has been found that heating with superheated steam is not effective if the pieces of old asphalt have dimensions of the order of 1 to 50 mm, as usual with old asphalt concrete milled off the road or carried through a crushing plant. In that case, the temperature of the old asphalt - despite the high steam temperature - hardly rises above 100 ° C after heating.

On the other hand, it has been found that if the dimensions exceed 80 mm, the heating process is effective, so that a temperature of 130 ° C can be reached in a short time.

With dimensions of 100 mm and more, an asphalt temperature of 150 ° C can be reached in a short time.

The above is related to the accessible cavity in asphalt concrete. With a small lump, a relatively large amount of water penetrates into the surface, which in turn evaporates, after steaming, to extract a lot of heat from the small lump.

Pollution of the environment by volatile substances such as hydrocarbons and PCAs is a thing of the past. Afterburning of these substances is no longer necessary to meet maximum permitted emissions. Also, filters are no longer needed in this context to catch the dust that is generated during the entire process.

An additional great advantage is the fact that, due to the absence of very hot gases, the bitumen does not overheat, so that the loss of quality of the binder no longer occurs and no more needs to be added.

If a certain milling technique or breaking method already involves finer pieces of old asphalt concrete, it is possible to have the pre-heating up to 100 ° C made of milled or broken old asphalt concrete using steam.

In this case, from the finer, disintegrated parts of old asphalt concrete, due to their property of low resistance to plastic deformation obtained by increasing the material temperature, it is possible to compress into larger blocks, which can then be very effectively exposed to the heating process by means of superheated steam.

The result of this method is a plastic slurry that can be easily used on a new road surface.

In a highly effective variant, coarse pieces of old asphalt concrete are preheated in a first heating phase by means of superheated steam in a closed autoclave to 130 ° C, and the thus preheated asphalt concrete is poured on a belt which is passed through a microwave oven, in which in a second heating phase the old asphalt concrete is heated to approximately 160 ° C.

This two-phase method is extremely effective in terms of cutting through heating of the asphalt concrete, saving energy, maintaining the quality of the binder and minimizing environmental impact.

In the first phase during heating to 130 ° C, no volatile substances, such as hydrocarbons, escape from the bitumen of the asphalt concrete and other possible admixtures.

In the second phase, only the rock is mainly heated by the micro waves, this rock heating the bitumen and other substances indirectly, so that the bitumen and other admixtures will hardly degenerate regarding their properties. Also, hardly any volatile vapors will be generated during this last phase.

The microwaves used preferably have a frequency of 916 MHz to obtain an economically effective heating.

Another embodiment is that superheated steam is blown onto the old asphalt concrete located on a road and that heat-soaked asphalt concrete is thus removed from the road and discharged.

This method is very effective when applied to old road pavements of permeable or so-called open or very open asphalt concrete.

This method has the advantage that no breakout machine or cutter is required to obtain manageable chunks.

In this case, when the old asphalt concrete is removed, there is no longer any mechanical breakage at all. The advantage is that there is no crushing of the stone fraction and no dust formation, mainly stone dust.

This provides technological advantages for the regeneration process of the asphalt concrete and, moreover, the dust can now be fully reused in the regeneration processes, in contrast to the limited reuse of the dust that has been created according to existing techniques.

The above-described methods have in common that old asphalt concrete is heated by superheated steam so that softening occurs and the asphalt concrete breaks up into smaller parts, which parts can be easily reused. All kinds of variants are conceivable within the scope of the invention.

Claims (5)

1. Method for processing old asphalt concrete into usable new asphalt concrete, wherein the old asphalt concrete is heated, characterized in that old asphalt concrete is heated by means of superheated steam with a temperature higher than 160 ° C. Method according to claim 1, characterized in that the heating of coarse pieces of old asphalt concrete to a plastic slurry takes place in a closed autoclave. Method according to claim 1, characterized in that coarse pieces of old asphalt concrete are preheated in a first autoclave by means of superheat steam in a closed autoclave, and the thus preheated asphalt concrete is poured onto a belt which is passed through a microwave oven. in which - in a second heating phase - at least the rock content of the asphalt concrete is heated. 4. Method according to claim 2 or 3, characterized in that, after heating to a plastic knit, small-pieces of asphalt concrete are first compressed into coarse chunks, after which these coarse chunks are further heated. Method according to claim 1, characterized in that superheated steam is blown onto the old asphalt concrete which is on a road and the soaked asphalt concrete thus heated is removed from the road.