GB2036759A

GB2036759A - A process for producing bituminous mixtures

Info

Publication number: GB2036759A
Application number: GB7937510A
Authority: GB
Original assignee: Wibau GmbH; WIBAU INDUSTRIE und VERWALTUNG GmbH
Current assignee: Wibau GmbH; WIBAU INDUSTRIE und VERWALTUNG GmbH
Priority date: 1978-10-30
Filing date: 1979-10-30
Publication date: 1980-07-02
Also published as: FR2441018A1; DE2847184A1

Abstract

Old road surfacing material which has been lifted and broken down, is reused by being mixed with additional undried mineral solids and with liquid bituminous binder, followed by strong heating to form a uniformly mixed hot bituminous mixture.

Description

SPECIFICATION A process for producing bituminous mixtures This invention relates to the production of hot bituminous mixtures containing bituminous binder and granular mineral material.

British Patent Specification No. 1,209,449 describes such a process, in which dust is bound to the sand and aggregate components by surface water, these components being used undried. The water is subsequently driven off by heating during mixing of the minerals with bituminous binder, the dust then being bound by the bituminous binder, so that the process is substantially dust-free. The dust-free preparation of the hot bituminous mixture can for example be carried out in apparatus as described in German Patent Specification No. 2102328. This is a drum mixer, heated by co-current firing, in which the mineral materials are blended in a mixing zone downstream of an intake zone in the form of a flame burn-out zone, with slight preheating, before they enter the drying and coating zone.

The experience gained in the preparation of bituminous mixtures with moist mineral materials makes it seem desirable to use the process in the recycling procedures which are becoming increasingly important as the result of the increasing cost of energy.

In recycling, existing solid bituminous/aggregate compositions, in particular old road surfacing material, usually damaged by furrow formation, is lifted by scarifying, planing or milling apparatus, and the material (usually after having been comminuted to an approximately uniform grain size) is blended, under the action of heat, with additional bituminous binder, and is then re-laid.

Owing to the mechanical lifting operation, and the comminution to provide uniform grain size, the proportion offine particles, in particularthefiller fraction, in the reprocessed material is often increased to such an extent that the material can only be used under restrictions and/or for minorconstruc- tion work.

An object of the present invention is to provide a process in which recycled bituminous material can be used to form a valuable hot bituminous mixture, capable of use substantially without restriction.

The present invention in one aspect provides a method of preparing a hot bituminous mixture, in which a previously formed solidified material, comprising a granular filler andlor aggregate and bituminous binder, is broken down into fragments, the fragments are mixed with liquefied further bituminous binder and undried further granular filler and/or aggregate, and the mixture is heated to form the hot bituminous mixture.

In another aspect, the present invention provides a method of preparing a hot bituminous mixture, in which: broken bituminous surfacing material, comprising solid mineral material and a bituminous binder is reduced to fragments of approximately equal size and then is charged, with still-moist sand and chippings into a mixing and drying drum, in which the aforesaid materials are mixed with further binder and slightly warmed; and the warm mixture is then strongly heated to form a unitary bituminous mixture; the composition of the mixture being so selected that the binder derived from the broken material and the further binder, and the mineral solids comprising the mineral material derived from the broken material and the added sand and chippings substantially correspond to the prescribed binder fraction and to the prescribed sieve profile.

According to a further aspect of the invention there is provided a process for coating powdered to granular solid materials with liquefied bituminous binder for the production of hot mixed material for road construction, in which undried solid materials are blended with the liquefied binder and then mixed, with intense heating, characterised in that completely or partly dried, rather than undried, powdered to granular solid materials of bituminous origin or milled bituminous material are used.

By the combination of the broken old material in an unseparated state, with still-moist undried solid material, and by the common mixing of these with liquefied bituminous binder followed by strong heating of the mixture, the binder in the broken old material is liquefied and, as the old material at least partly disintegrates, a substantially uniform distribution of the added solid material in the old material, with uniform and unitary coating of the added solid material and the solid material released from its original bonds in the old material, is obtained.

The material thus prepared can be regarded as a bituminous mixture of full value in every respect.

The amount of additional mineral material needed cannot be specified here, since it depends on the circumstances of use of the mixture to be prepared and in particular whether it is necessary to provide a mixture having a finer or coarser formulation, or the sameformulation as the old material. Normally, because of the reduction in particle size of the solids in the old material, mentioned above, it will be necessary to make the mixture coarser.

However, in general, there will be added about 3331% of fresh granular mineral material having substantially the same sieve profile as the lifted old material.

The softening point of the binder in the lifted old material is substantially raised by aging and thermal stress in the lifting. This can be counteracted by the addition of bitumen of a softer grade, preferably B300.

1. A method of preparing a hot bituminous mixture, in which a previously formed solidified material, comprising a granular filler and/or aggregate and bituminous binder, is broken down into fragments, the fragments are mixed with liquefied further bituminous binder and undried further granular filler and/or aggregate, and the mixture is heated to form the hot bituminous mixture.

2. A method of preparing a hot bituminous mixture, in which: broken bituminous surfacing material, comprising solid mineral material and a bituminous binder, is reduced to fragments of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A process for producing bituminous mixtures This invention relates to the production of hot bituminous mixtures containing bituminous binder and granular mineral material. British Patent Specification No. 1,209,449 describes such a process, in which dust is bound to the sand and aggregate components by surface water, these components being used undried. The water is subsequently driven off by heating during mixing of the minerals with bituminous binder, the dust then being bound by the bituminous binder, so that the process is substantially dust-free. The dust-free preparation of the hot bituminous mixture can for example be carried out in apparatus as described in German Patent Specification No. 2102328. This is a drum mixer, heated by co-current firing, in which the mineral materials are blended in a mixing zone downstream of an intake zone in the form of a flame burn-out zone, with slight preheating, before they enter the drying and coating zone. The experience gained in the preparation of bituminous mixtures with moist mineral materials makes it seem desirable to use the process in the recycling procedures which are becoming increasingly important as the result of the increasing cost of energy. In recycling, existing solid bituminous/aggregate compositions, in particular old road surfacing material, usually damaged by furrow formation, is lifted by scarifying, planing or milling apparatus, and the material (usually after having been comminuted to an approximately uniform grain size) is blended, under the action of heat, with additional bituminous binder, and is then re-laid. Owing to the mechanical lifting operation, and the comminution to provide uniform grain size, the proportion offine particles, in particularthefiller fraction, in the reprocessed material is often increased to such an extent that the material can only be used under restrictions and/or for minorconstruc- tion work. An object of the present invention is to provide a process in which recycled bituminous material can be used to form a valuable hot bituminous mixture, capable of use substantially without restriction. The present invention in one aspect provides a method of preparing a hot bituminous mixture, in which a previously formed solidified material, comprising a granular filler andlor aggregate and bituminous binder, is broken down into fragments, the fragments are mixed with liquefied further bituminous binder and undried further granular filler and/or aggregate, and the mixture is heated to form the hot bituminous mixture. In another aspect, the present invention provides a method of preparing a hot bituminous mixture, in which: broken bituminous surfacing material, comprising solid mineral material and a bituminous binder is reduced to fragments of approximately equal size and then is charged, with still-moist sand and chippings into a mixing and drying drum, in which the aforesaid materials are mixed with further binder and slightly warmed; and the warm mixture is then strongly heated to form a unitary bituminous mixture; the composition of the mixture being so selected that the binder derived from the broken material and the further binder, and the mineral solids comprising the mineral material derived from the broken material and the added sand and chippings substantially correspond to the prescribed binder fraction and to the prescribed sieve profile. According to a further aspect of the invention there is provided a process for coating powdered to granular solid materials with liquefied bituminous binder for the production of hot mixed material for road construction, in which undried solid materials are blended with the liquefied binder and then mixed, with intense heating, characterised in that completely or partly dried, rather than undried, powdered to granular solid materials of bituminous origin or milled bituminous material are used. By the combination of the broken old material in an unseparated state, with still-moist undried solid material, and by the common mixing of these with liquefied bituminous binder followed by strong heating of the mixture, the binder in the broken old material is liquefied and, as the old material at least partly disintegrates, a substantially uniform distribution of the added solid material in the old material, with uniform and unitary coating of the added solid material and the solid material released from its original bonds in the old material, is obtained. The material thus prepared can be regarded as a bituminous mixture of full value in every respect. The amount of additional mineral material needed cannot be specified here, since it depends on the circumstances of use of the mixture to be prepared and in particular whether it is necessary to provide a mixture having a finer or coarser formulation, or the sameformulation as the old material. Normally, because of the reduction in particle size of the solids in the old material, mentioned above, it will be necessary to make the mixture coarser. However, in general, there will be added about 3331% of fresh granular mineral material having substantially the same sieve profile as the lifted old material. The softening point of the binder in the lifted old material is substantially raised by aging and thermal stress in the lifting. This can be counteracted by the addition of bitumen of a softer grade, preferably B300. CLAIMS

2. A method of preparing a hot bituminous mixture, in which: broken bituminous surfacing material, comprising solid mineral material and a bituminous binder, is reduced to fragments of approximately equal size and then is charged, with still-moist sand and chippings into a mixing and drying drum, in which the aforesaid materials are mixed with further binder and slightly warmed; and the warm mixture is then strongly heated to form a unitary bituminous mixture; the composition of the mixture being so selected that the binder derived from the broken material and the further binder, and the mineral solids comprising the mineral material derived from the broken material and the added sand and chippings, substantially correspond to the prescribed binder fraction and to the prescribed sieve profile.

3. A process for coating powdered to granular solid materials with liquefied bituminous binderfor the production of hot mixed material for road construction, in which undried solid materials are blended with the liquefied binder and then mixed, with intense heating, characterised in that completely or partly dried, rather than undried, powdered to granular solid materials of bituminous origin or milled bituminous material are used.