WO2007043021A1

WO2007043021A1 - Catalyzed mixture for supporting and foundation courses of civil and road works, of the type providing high stabilitty and allowing immediate use thereof

Info

Publication number: WO2007043021A1
Application number: PCT/IB2006/053752
Authority: WO
Inventors: Guerrino Pivato; Nicola Pivato; Luciano Brenda
Original assignee: Guerrino Pivato S.P.A.
Priority date: 2005-10-14
Filing date: 2006-10-12
Publication date: 2007-04-19
Also published as: ITVI20050273A1; EP1945591A1; MA29945B1

Abstract

The present invention finds application in the field of materials for civil and road works and relates to a catalyzed mixture for supporting and foundation courses of civil and road works, of the type providing high stability and allowing immediate use thereof, which is particularly suitable for making road pavement courses. The catalyzed mixture comprises a base mixture of aggregates, at least one hydraulic binder, at least one setting catalyst and water. The base mixture of aggregates comprises reclaimed asphalt pavement materials and natural aggregate or industrial byproducts and has a controlled particle size of about 0 to 30 mm, to keep a low vacuum index and allow the mixture to exhibit stability and a high capacity to load ratio as soon as it is laid down and before binder setting.

Description

CATALYZED MIXTURE FOR SUPPORTING AND FOUNDATION COURSES OF CIVIL AND ROAD WORKS, OF THE TYPE PROVIDING HIGH STABILITY AND ALLOWING IMMEDIATE USE THEREOF

Field of the invention

The present invention finds application in the field of materials for civil and road works and particularly relates to a catalyzed mixture for supporting and foundation courses of civil and road works, of the type providing high stability and allowing immediate use thereof.

This mixture is particularly suitable for making road pavement course and for all ordinary or special foundation works using recycled aggregate, such as reclaimed asphalt pavement materials, heavy ashes from incinerators and industrial sand- or gravel-like byproducts in general.

Background art

Pavement structures for construction or reinforcement of roads, highways, runways, container terminals and any platform designed to support a specific vehicular traffic typically consist of a load-bearing pavement, lying on the sub-base and supporting road traffic, and covered by an upper road surfacing.

The latter is usually comprised of a wearing surface course, which is designed to come in contact with the vehicular traffic, and a lower course, usually known as binder course.

These courses generally have a thickness of 7 to 13 cm, as a function of the expected traffic load on the road structure.

In normal applications, the pavement is formed by laying a sub-base directly above the road subgrade, and a base course thereon, which is covered by road surfacing. In common applications the sub-base course is made of a material selected and formed, for example, from a cement or granular mix, which is stabilized, leveled and suitably compacted.

In semirigid structures, the base course is usually composed of an asphalt or cement bound mixture, which has to be leveled and compacted to properly support the expected traffic.

Nevertheless, these common applications have the apparent drawback of requiring two separate layers to be laid down to form the load-bearing pavement, thereby creating a discontinuity that affects the mechanical resistance of the whole structure, the operation further being cost ineffective.

Another important drawback is that the road materials traditionally required to make the road pavement are not easily available due to the decreasing number of quarries, which makes them increasingly expensive.

Finally, another drawback associated to the works of pavement reinforcement or resurfacing is the difficult disposal of the removed surfacing, i.e. the asphalt pavement material, before laying a new pavement or surfacing.

Such asphalt pavement is mainly comprised of asphalt courses and/or courses bound together with a cement binder or other binders and involves a difficult and expensive disposal, which increases the overall costs for the works.

It is known from prior art that, during road resurfacing, the reclaimed asphalt pavement obtained from the removal of the surface to be replaced is mixed with a bituminous compound and reused for the new surfacing. Particularly a first layer of foamed asphalt may be used for the sub-base course and an asphalt layer may be used for the upper course.

However, these solutions also involve high costs, due to the need of using new asphalt, and do not solve the problem of the availability of materials for forming reinforcement courses, if any. Several solutions have been envisaged in an attempt to obviate some of the above drawbacks, in which the sub-base course and the base course have been replaced by catalyzed hydraulic mixtures whose components include materials from incineration of municipal or industrial waste, even polluting waste, blast-furnace slag or other industrial processing residues.

These mixtures are also used for reinforcement of road structures, where they are directly applied on the old pavement and possibly covered by the new binder and wearing courses only.

W0-A1 -02/34691 discloses a catalyzed hydraulic mixture whose aggregate component mainly consists of materials recovered from civil work demolition processes.

Such materials are bound together by ashes and slag from blast furnaces or municipal waste incinerators.

The mixture also uses a setting catalyst adapted to create a basic environment in the mixture to allow immobilization of the potentially polluting materials contained in the ashes or slag.

While this solution provides a catalyzed mixture which solves the pavement material availability problem by using waste materials, it does not solve the problems associated to the disposal of the removed asphalt pavement material.

Summary of the invention

The object of this invention is to obviate the above drawbacks by providing a catalyzed mixture for supporting and base courses of civil and road works, of the type providing high stability and allowing immediate use thereof, that is highly efficient and relatively cost-effective.

A particular object is to provide a catalyzed mixture that allows to use, as aggregate, reclaimed asphalt pavement material recovered from pavement courses which are either bound together by asphalt or cement or have no binder therein, thereby allowing to use easily available waste materials.

A further object is to provide a catalyzed mixture that allows to reduce the costs for the works in which it is used.

Yet another object of this invention is to provide a mixture that uses a catalyst to provide immediate high stability even when using materials that would not otherwise be suitable to make supporting layers and foundations of civil works.

These and other objects, as better explained hereafter, are fulfilled by a catalyzed mixture for supporting and foundation courses of civil and road works, of the type providing high stability and allowing immediate use thereof, which comprises a base mixture of aggregates, at least one hydraulic binder, at least one setting catalyst and water.

The invention is characterized in that the base mixture of aggregates comprises reclaimed asphalt pavement and natural aggregate or industrial sand- or gravel-like byproducts, the base mixture having a controlled particle size of about 0 to 30 mm.

Thanks to this feature, the invention provides a catalyzed mixture having a low vacuum index, which is characterized by high stability and a high capacity to load ratio as soon as it is laid down and before binder setting, even when using easily available reclaimed asphalt pavement waste.

Advantageously, the reclaimed asphalt materials in the base mixture may include asphalt surfacing materials.

Also, the reclaimed asphalt pavement materials may include hydraulic binders selected from cement, lime and pozzolan cement.

Thanks to this feature, the invention provides a catalyzed mixture which allows to reduce the costs for the works in which it has to be used, and to form the pavement as a single supporting or foundation course, while further using easily available materials.

Advantageously, the catalyst may include lime in the form of calcium oxide or hydrated lime, having a particle size of less than 20 μm and a lime content of 10% to 50% by weight with respect to the total weight of the catalyst.

Preferably, the free lime content may be more than 90% by weight with respect to the total weight of the line.

Also, the catalyst may include anhydrous gypsum, in hydrated, dihydrated or even synthetic form, from 50% to 90% by weight with respect to the total weight of the catalyst.

Thanks to this particular configuration, the invention provides a catalyzed mixture that exhibits high stability as soon as it is laid down, even when using aggregate that would not otherwise be suitable to make supporting layers and foundations of civil works, such as a road pavement.

Brief description of the drawings

Further features and advantages of the invention will be more apparent from the detailed description of a preferred, non-exclusive embodiment of a catalyzed mixture for supporting and foundation courses of civil and road works according to the invention, which is described as a non-limiting example with the help of the annexed drawings, in which:

FIG. 1 is a schematic view of a prior art road pavement; FIG. 2 is a schematic view of an embodiment of a road pavement that uses a catalyzed mixture according to the invention; FIG. 3 shows another use of a catalyzed mixture according to the invention.

Detailed description of a preferred embodiment

Referring to the above figures, the mixture of the invention is particularly suitable to form road pavement or reinforcement courses and for all ordinary or special foundation works, such as raft foundations, inverted arcs for tunnels, foundation beams for port crane runways.

Road structures typically include a pavement immediately above the subgrade, which normally consists of an embankment and a foundation for the supporting pavement.

The latter is usually covered by a surfacing layer, which is composed of an upper asphalt course, known as wearing layer or course, which is designed to come in contact with the vehicular traffic, and a lower course, usually known as binder course.

However, before laying the two surfacing layers, the pavement must be always compacted by suitable rubber tired vibratory compactors, which exert such a pressure thereon as to impart the required mechanical strength.

Compaction has the main purpose of reducing the vacuum index in each pavement course, to impart higher density and strength thereto.

Pavement behavior during compaction depends on its stability coefficient, which provides a measure of the transverse deformations produced in the pavement by the compactor.

In practice, the stability coefficient, also known as bearing ratio, corresponds to the ratio of the calculated bearing capacity of the pavement to the load applied by the compactor and represents a factor of safety against failure during compaction exerted by the compactor wheel.

FIG. 1 particularly shows an embodiment of a prior art road structure S in schematic form, in which the supporting pavement A is formed by laying a first sub-base course F above the platform P and the embankment R, and a base course B thereon, which is covered by the surfacing T composed of the binder course L and the wearing course U.

The sub-base course F is generally comprised of a mixture of aggregates selected from sands and gravels, whereas the base B is composed of conglomerates.

FIG. 2 is a schematic view of an embodiment of a road pavement 2 using a catalyzed mixture according to the invention, generally designated by numeral 1 , which is interposed as a single layer between the road sub-grade 3 and the surfacing 4 composed of the binder and wearing courses 5, 6, whereas the road sub-grade 3 lies above the embankment 7.

The catalyzed mixture 1 of the invention comprises a base mixture of aggregates, at least one hydraulic binder, at least one setting catalyst and water.

A peculiar feature of the invention is that the base mixture of aggregates comprises reclaimed asphalt pavement and natural aggregate or industrial sand- or gravel-like byproducts. A further feature is that such base mixture has a controlled particle size of about 0 to 30 mm, to obtain a low vacuum index and allow the catalyzed mixture 1 to exhibit stability and, as a result, a high capacity to load ratio as soon as it is laid down and before binder setting.

The reclaimed asphalt pavement course materials may include asphalt surfacing materials or hydraulic binders selected from cement, lime and pozzolan cement which are recovered from road works.

Also, the aggregates to be mixed to the reclaimed asphalt pavement in the base mixture may be natural materials or industrial byproducts and may be selected from the group consisting of sands, gravels, heavy ashes from incinerators, blast furnace slag, marble or other stone powder, sludges from crushing and/or screening plants, recycling aggregate, phosphogypsum, powders from industrial filtering plants.

The base mixture is about 78% to 95% by weight with respect to the dry weight of the catalyzed mixture 1.

Preferably such amount is 84% to 91 % with respect to the total dry weight of the catalyzed mixture 1. The natural aggregates may be materials belonging to several different particle size classes, in a range from 0 to 30 mm and may or may not be crushed.

The type of aggregate and its particle size depend on the desired particle grading curve characteristics of the catalyzed mixture 1 , which in turn depend on the particular expected use of the mixture 1.

Nevertheless, no envelope is for inscribing the grading curve of the mixture 1 , the only relevant parameters being the curvature coefficient, preferably of 1 to 3, and the uniformity coefficient, preferably above 6.

Furthermore, the natural aggregates may have any mineralogical composition and be of any geological origin.

The amounts of the various components of the base mixture may be determined by tests for defining the above grading curve and the minimum value of the corresponding bearing ratio.

The binder used in the catalyzed mixture 1 is preferably a byproduct from the processing of cast iron and other metals and consists of granulated blast furnace slag or fly ash from coal power plants.

The binder is about 8% to 20%, preferably 10% to 15% by weight with respect to the dry weight of the catalyzed mixture 1.

Furthermore, its particle size may be unchanged from the blast furnace slag granulator, although a better setting and improved mechanical properties of the mixture 1 may be achieved by grinding the binder to a particle size of less than 2 mm and a 0.070 mm underside above 10%.

The presence of water allows reaction of the granulated slag and compaction of the material. Either freshwater, not necessarily drinkable, or saltwater may be used, provided it does not contain oils and organic matter. Water may be provided in variable amounts, as determined as a function of the best value obtained from the Modified Proctor test.

Nevertheless, the binding power of blast furnace slag, as well as any other hydraulic binder, may only be activated by a setting catalyst.

The amount of the latter in the mixture 1 is about 0.2% to 2%, preferably 0.8% to 1.5% by weight with respect to the dry weight of the catalyzed mixture 1. In the preferred formulation, the catalyst may include lime, in the form of either calcium oxide (CaO) or hydrated lime (CaOH₂) having a particle size of less than 20 μm.

In this formulation, the lime content is preferably of about 10% to 50% by weight with respect to the total weight of the catalyst.

Furthermore, the amount of free lime, in the form of calcium oxide, is advantageously above 90% by weight with respect to the total weight of the lime in the catalyst.

Furthermore, the catalyst includes gypsum from 50% to 90% by weight with respect to the total weight of the catalyst.

Such gypsum may be present in the form of dehydrated, hydrated or anhydrous calcium sulfate, or may be a synthetic gypsum obtained from industrial chemical processes.

The catalyst may further comprise an organic antiflocculating agent whose amount is 1 % with respect to the total weight of the catalyst.

In a second formulation of the catalyst, about 30% caustic soda with respect to the weight of the catalyst is added to lime, gypsum and the antiflocculating agent.

Also, in this second formulation, the total lime content may be reduced to about 10% to 20% with respect to the total weight of the catalyst. In a further formulation, the catalyst may be obtained by replacing caustic soda with cement, also in a preferred amount of about 30% with respect to the weight of the catalyst.

Also, in another formulation, the caustic soda or cement as provided in the previous formulations is replaced with an optimum amount of about 15% barium sulfate with respect to the total weight of the catalyst.

This formulation is particularly useful to create particular bonds for immobilization of any heavy metals, particularly hexavalent chromium, in the industrial processing waste materials used as aggregate.

A last catalyst formulation may finally include 49% to 80% calcium oxide, 20% to 50% caustic soda, about 1 % organic antiflocculating agent, with respect to the total weight of the catalyst.

It shall be understood that the amounts of each component of the catalyst are intended as optimum amounts and may be varied depending on design requirements.

As shown in FIG. 3, the catalyzed mixture 1 described above may be conveniently used for reinforcement of road pavements 8.

In this case, a layer of mixture 1 may be directly laid on the old pavement 8 and later covered by the binder course 5 and, if so designed, by the wearing course 6.

In any application, the components may be advantageously mixed in a mixing plant at the construction site, having as many batchers as there are materials, and a mixer, whose size is a function of the supply requirements at the construction site.

Each material will be batched as determined by specific tests.

Particularly, some natural aggregates may also act as particle size regulators for the whole basis mixture. Furthermore, water batching, as determined by the optimum water content resulting from laboratory tests, may be adjusted directly on site in the mixing plant, also depending on environmental conditions.

The catalyst, in powder or possibly liquid form, is preferably added immediately upstream from the mixer, which will homogenize the whole catalyzed mixture 1.

The layer of catalyzed mixture 1 has a variable thickness, depending on design requirements and on the type of works to be made, and may be determined, for example, by the finite-element method (FEM).

The above disclosure clearly shows that the invention provides a catalyzed mixture using easily available reclaimed asphalt pavement and other low-cost materials from industrial processing, thereby reducing the costs for the specific civil or road works.

This will prevent or at least reduce the use of quarry materials, and avoid the need of landfill disposal of otherwise non-reusable materials. This new technology fully meets the directives of the Ministry for the Environment concerning quarries and landfills.

Thanks to the use of a catalyst, according to each of the above formulations, the catalyzed mixture 1 may be also prepared using materials that are generally individually unsuitable for use as a supporting or foundation course in civil and road works.

The mixture of this invention is susceptible of a number of changes and variants, within the inventive principle disclosed in the appended claims. All the details thereof may be replaced by other technically equivalent parts, and the materials may vary depending on different needs, without departure from the scope of the invention.

While the mixture has been described with particular reference to the accompanying figures, the numerals referred to in the disclosure and claims are only used for the sake of a better intelligibility of the invention and shall not be intended to limit the claimed scope in any manner.

Claims

1. A catalyzed mixture for supporting and foundation courses of civil and road works, of the type providing high stability and allowing immediate use thereof, comprising the following components: a base mixture of aggregates; at least one hydraulic binder; at least one setting catalyst; water; characterized in that said base mixture of aggregates comprises reclaimed asphalt pavement materials and natural aggregate or industrial byproducts, said base mixture having a controlled particle size of about 0 to 30 mm, to keep a low vacuum index and allow the mixture to exhibit stability and a high capacity to load ratio as soon as it is laid down and before binder setting.

2. Mixture according to claim 1 , characterized in that said reclaimed asphalt pavement materials include asphalt surfacing materials.

3. Mixture according to claim 1 , characterized in that said reclaimed asphalt pavement materials include hydraulic binders selected from cement, lime and pozzolan cement.

4. Mixture according to claim 1 , characterized in that said base mixture is about 78% to 95%, preferably 84% to 91 % by weight with respect to the dry weight of the catalyzed mixture.

5. Mixture according to claim 1 , characterized in that said natural aggregates and industrial byproducts are selected from the group consisting of sands, gravels, heavy ashes from incinerators, blast furnace slag, stone powder, sludges from crushing and/or screening plants, phosphogypsum, powders from industrial filtering plants.

6. Mixture according to claim 1 , characterized in that said at least one binder comprises granulated blast surface slag and/or fly ash from coal power plants.

7. Mixture according to the preceding claim, characterized in that the particle size of said at least one binder is of less than 2 mm and a 0.070 mm underside above 10% with respect to the total weight of said binder.

8. Mixture according to claim 6, characterized in that said at least one binder is about 8% to 20%, preferably 10% to 15% by weight with respect to the dry weight of the catalyzed mixture.

9. Mixture according to claim 1 , characterized in that said at least one catalyst is about 0.2% to 2%, preferably 0.8% to 1.5% by weight with respect to the dry weight of the catalyzed mixture.

10. Mixture according to the preceding claim, characterized in that said at least one catalyst includes lime in the form of calcium oxide or hydrated lime, having a particle size of less than 20 μm.

1 1. Mixture according to the preceding claim, characterized in that the lime content is of 10% to 50% by weight with respect to the total weight of said at least one catalyst.

12. Mixture according to the preceding claim, characterized in that it includes free lime in amounts above 90% with respect to the total lime weight in said at least one catalyst.

13. Mixture according to claim 10, characterized in that said at least one catalyst comprises 50% to 90% gypsum by weight with respect to the total weight of said at least one catalyst.

14. Mixture according to the preceding claim, characterized in that the gypsum in said at least one catalyst is in the form of dehydrated, hydrated or anhydrous calcium sulfate.

15. Mixture according to claim 13, characterized in that the gypsum in said at least one catalyst is a synthetic gypsum obtained from industrial chemical processes.

16. Mixture according to claim 13, characterized in that said at least one catalyst further comprises an organic antiflocculating agent and caustic soda in amounts of about 1 % and 30% by weight respectively, with respect to the total weight of said at least one catalyst.

17. Mixture according to claim 13, characterized in that said at least one catalyst further comprises an organic antiflocculating agent and cement in amounts of about 1 % and 30% by weight respectively, with respect to the total weight of said at least one catalyst.

18. Mixture according to claim 13, characterized in that said at least one catalyst further comprises an organic antiflocculating agent and barium sulfate in amounts of about 1 % and 15% by weight respectively, with respect to the total weight of said at least one catalyst.

19. Mixture according to claim 9, characterized in that said at least one catalyst comprises calcium oxide, caustic soda and an organic antiflocculating agent in amounts of about 49% to 80%, 20% to 50%, 0% to 1 % by weight respectively, with respect to the weight of said at least one catalyst.