EP0810277A1

EP0810277A1 - Method for recycling reclaimed asphalt

Info

Publication number: EP0810277A1
Application number: EP97201462A
Authority: EP
Inventors: Rudolf Carlo Reintjes
Original assignee: KONINKLIJKE WEGENBOUW STEVIN BV
Current assignee: KONINKLIJKE WEGENBOUW STEVIN BV
Priority date: 1996-05-30
Filing date: 1997-05-15
Publication date: 1997-12-03

Abstract

The invention relates to a method for recycling reclaimed asphalt, wherein the reclaimed asphalt is heated. Between 1 and 3 % by weight cement and between 1 and 3 % by weight bitumen emulsion are added to the heated asphalt. Highly advantageous fatigue characteristics and low susceptibility to rutting are obtained by use of the method according to the invention.

Description

The invention relates to a method for recycling reclaimed asphalt, wherein the reclaimed asphalt is heated to a temperature of between 70 °C and 120 °C. It is known to recycle tar-containing asphalt by breaking this into pieces and, while heating at temperatures of up to 90 °C to 100 °C, mixing it with a binder, such as a bitumen emulsion, this procedure being known as semi-hot processing.
Cold processing of reclaimed asphalt in broken form is also known, the pieces being mixed with a bitumen emulsion and cement. With this procedure, the bitumen/cement mixture causes the asphalt pieces to adhere to one another.
One problem with reclaimed asphalt processed by the semi-hot method, in which only a bitumen emulsion is added, is that the rigidity is limited and that the susceptibility of such products to rutting is very high. The known cold-processed products are very sensitive to overloading, as can be seen from the fatigue characteristics. Road surfaces produced from cold-processed reclaimed asphalt therefore have to be much thicker, with the result that asphalt of a layer thickness of 1 cm can be replaced by a layer thickness of cold-processed, reclaimed asphalt of 2.5 cm.
One aim of the present invention is to solve the abovementioned problems.
To this end, the method according to the invention is characterised in that between 1 and 3 % by weight cement and between 1 and 3 % by weight binder, such as bitumen emulsion, are added to the heated asphalt. A number of surprising characteristics of the recycled asphalt are obtained by adding the cement to the asphalt to be recycled while heating (such as, for example, with steam) to a temperature of, for example, 100 °C. The rigidity of the product formed, which is important for distribution of the forces exerted by the tyres acting on the road surface, is substantially improved by the extra addition of cement (in addition to addition of the emulsion). Because a relatively large amount of bituminous binder is present in addition to the rigid element made up by the cement, the fatigue characteristics are advantageous.
In the case of the mixture according to the invention, which is prepared semi-hot, the pieces of asphalt become soft and relatively fluid, the grain structure of the asphalt (coarse minerals up to about 15 millimetres in size, sand and very fine filler) being able to rearrange. As a result a very compact structure of high density is produced. Because the reclaimed asphalt recycled according to the invention has characteristics which very largely correspond to the characteristics of newly applied asphalt, the use of a relatively thin layer can suffice. Because the slope of the fatigue curve for the recycled asphalt according to the invention is gentle, this product can be subjected to occasional heavy overload without fracture occurring.
The product according to the present invention also has very favourable rutting characteristics, inter alia in comparison with gravel asphalt concrete. Consequently, the known gravel asphalt concrete, which is widely used as a base layer, can be replaced by the product according to the present invention. Using the method according to the invention, it is possible to achieve inexpensive and environmentally friendly processing of very large quantities of reclaimed asphalt, which at present are not utilized to a sufficient extent.
It is furthermore surprising that addition of cement to the asphalt to be recycled, at temperatures of between 70 °C and 120 °C, does not result in such rapid setting that processing of the recycled product is made more difficult.
A method for recycling reclaimed tar-containing asphalt, with which the emission of harmful substances remains restricted as far as possible, is described in Netherlands Patent Application No. 1003236, in the name of the Applicant, which is incorporated herein by reference. Although the method according to the present invention can be used for recycling tar-containing asphalt, said method is not restricted to this and can also advantageously be used for the semi-hot recycling of non-tar-containing asphalt. The use of cement in semi-hot recycling is in no way obvious because it can be expected that the setting speed would increase to such an extent that the product would have set too much before the road surface was completed.
The characteristics of the asphalt obtained by the method according to the invention are given in the appended drawing: In the drawing:

Figure 1 shows a fatigue characteristic for cold-recycled asphalt concrete (curve a), hot-recycled asphalt concrete (curve b), a recycled asphalt layer according to the invention (curve c) and a base layer of cement-stabilised sand, which, in a ratio of 1:2.5, can also serve as replacement for hot-recycled asphalt or old asphalt (curve d).
Figure 2 shows a wheel rutting test for three strips of road surface produced according to the present invention and three strips of road surface produced by adding only an emulsion to the semi-hot-recycled asphalt, and
Figure 3 shows the average values for the sets of three strips in the test from Figure 2.

In Figure 1, curve a for the cold-recycled asphalt concrete, where the asphalt contains 3 % by weight emulsion and 3 % by weight cement, has a steep gradient. The same applies in the case of curve d, which shows the fatigue characteristics of a sand/cement mixture. The layers according to curves a and d show good load distribution but are relatively sensitive to overloading, such as axle loads which are occasionally too high. Consequently, layers of this type must be made thicker (2.5 times).
Curve b shows the fatigue characteristic for conventional hot-recycled asphalt concrete, whilst curve c shows recycled asphalt according to the present invention containing 2 % by weight emulsion and 2 % by weight cement. It can be seen that the recycled asphalt according to curve c displays characteristics which are very close to the characteristics of new hot asphalt.
Figures 2 and 3 show the percentage rutting for hot-recycled asphalt to which only a bitumen emulsion has been added and for hot-recycled asphalt according to the invention, to which both cement and a bitumen emulsion have been added. It can clearly be seen that an average constant percentage rutting of less than 2 % is obtained with the asphalt which has been recycled in the manner according to the present invention.

Claims

Method for recycling reclaimed asphalt, wherein the reclaimed asphalt is heated to a temperature of between 90 °C and 120 °C, characterised in that between 1 and 3 % by weight cement and between 1 and 3 % by weight binder, such as bitumen emulsion, are added to the heated asphalt.
Method according to Claim 1, characterised in that the reclaimed asphalt is tar-containing asphalt.
Method according to Claim 1 or 2, characterised in that about 2 % by weight cement is added.
Method according to one of the preceding claims, characterised in that the asphalt is heated by means of steam.