EP0475824A1 - Multi-layered covering for metal bridges - Google Patents

Abstract

The multilayer coating according to the invention is characterised in that it comprises: - a bituminous membrane consisting essentially of a bitumen modified by the addition of thermoplastic copolymers, - a course of cold-poured bituminous mix consisting of a granulate and a bituminous binder. The course of cold-poured bituminous mix may be a single course or a twin course. When applied in a sufficient thickness it can be used not only as a thermal shield for the bituminous membrane but also as a surfacing course. The surfacing course can also be a course of hot bituminous mixes with modified bitumen.

Description

The present invention relates to a multilayer coating for metallic structures.

The coating of a work comprising a metal deck - in addition to having the properties and characteristics of a wearing course of a conventional highway pavement - must also respond to certain specific problems caused by the technique of orthotropic slabs , some of these properties being moreover contradictory.

• présenter une surface convenable au roulement des véhicules du point de vue sécurité et confort (propriétés antidérapantes et uni convenables),
• résister à diverses sollicitations, les unes verticales, les autres horizontales, provoquées par le trafic : résistance au poinçonnement, au cisaillement, au fluage, à la fatigue,
• être peu susceptible aux conditions atmosphériques et éventuellement posséder une bonne résistance aux produits de déverglaçage.

In particular, he must:

• present a suitable surface for the rolling of vehicles from the point of view of safety and comfort (suitable non-slip and even properties),
• resist various stresses, some vertical, others horizontal, caused by traffic: resistance to punching, shearing, creep, fatigue,
• be unlikely to weather conditions and possibly have good resistance to de-icing products.

• adhérence parfaite et durable du revêtement sur la dalle (même par températures extrêmes),
• grande souplesse pour suivre les déformations du support sans donner lieu à des fissurations ou à des décollements.

In addition to these usual road properties, the coating on a metal deck with orthotropic slab must have certain special qualities:

• perfect and lasting adhesion of the coating to the slab (even in extreme temperatures),
• great flexibility to follow the deformations of the support without giving rise to cracks or detachments.

• flexion générale de l'ouvrage : les ouvrages métalliques à dalles orthotropes sont généralement à longue portée et possèdent une très grande flexibilité,
• flexion locale : au passage d'une charge, la rigidité est plus grande au droit des raidisseurs qui se comportent comme des points durs fixes.

These deformations are of two orders:

• general bending of the structure: metal structures with orthotropic slabs are generally long-span and have very great flexibility,
• local bending: when passing a load, the rigidity is greater in line with the stiffeners which behave like fixed hard points.

The coating is therefore subject to compressive and tensile stresses, while being stressed by high shear stresses.

• solutions épaisses (supérieures à 5 cm).
• solutions minces (1 à 3 cm).
• solutions ultra-minces (de l'ordre du cm).

Different solutions have been considered to solve these problems:

• thick solutions (greater than 5 cm).
• thin solutions (1 to 3 cm).
• ultra-thin solutions (of the order of cm).

Whatever the solutions chosen which have all their disadvantages and advantages, it appeared, from the first studies, that the stresses are such that all coatings based on conventional binder will be destroyed within a very short time.

Various solutions based on poured asphalt, pitch or epoxy bitumen, bitumen improved either by natural rubbers or not synthetic rubbers were then proposed.

In most cases, despite promising results at the laboratory level, the coatings produced had a short lifespan, either, which was the most general case, for lack of adhesion to the support, or again for lack of elasticity or by tendency to creep.

• d'une part, suffisamment souple pour pouvoir suivre les déformations de la suface métallique du pont sans se fissurer (élasticité du liant),
• d'autre part, suffisamment résistant pour pouvoir être appliqué sur un support rigide (plaque d'acier) sans risque d'orniérage (cohésion du liant).

We then sought to improve the rheological properties of a bituminous binder so as to obtain a binder capable of allowing the preparation of a mix:

• on the one hand, flexible enough to be able to follow the deformations of the metal surface of the bridge without cracking (elasticity of the binder),
• on the other hand, strong enough to be able to be applied on a rigid support (steel plate) without risk of rutting (cohesion of the binder).

An improvement has been obtained by combining bitumen with two polymers which are compatible with each other and whose combination with bitumen made it possible at the same time to improve the two desired properties: elasticity and cohesion (BF 72.17111).

The object of the present invention is to provide an improved coating, as well as a method for applying said coating to a metallic road structure.

• une membrane bitumineuse constituée essentiellement par un bitume modifié par addition de copolymères thermoplastiques,
• une couche d'enrobé coulé à froid constitué par un granulat et un liant bitumineux.

The coating for metallic structures according to the invention is a multilayer coating characterized in that it comprises:

• a bituminous membrane consisting essentially of a bitumen modified by the addition of thermoplastic copolymers,
• a layer of cold-cast mix consisting of an aggregate and a bituminous binder.

The cold-poured asphalt layer consists of a bituminous binder and an aggregate, the maximum particle size of which remains less than approximately 10 mm.

The aggregate is preferably fully crushed, with 0/6, 0/4 or 0/2 sand being more preferred. The thickness of the cold-cast coating layer is preferably between 3 and 12 mm. It is essentially a function of the grain size of the sand. Thus, for a 0/2 sand, the thickness is of the order of 3 to 5 mm; for 0/4 sand, it is 5 to 7 mm; for 0/6 sand, it is 7 to 10 mm.

The bituminous binder essentially contains a bitumen. The bitumen is chosen from bitumens, preferably from bitumens of grades 60/70, 80/100 and 180/220 modified by the addition of thermoplastic copolymers, either by direct hot mixing of pure bitumen and of copolymer, or by mixing indirect cold emulsion of pure bitumen and aqueous dispersion of copolymer at the time of manufacture of the mix to be poured. Preferably, ethylene vinyl acetate (EVA) or styrene butadiene styrene styrene (SBS) or ethylene methacrylate (EMA) copolymers will be used. However, it is also possible to use the styrene butadiene rubber block copolymers (SBR) and the acrylic copolymers as well as various mixtures of these copolymers.

The copolymer content is at most equal to about 5% by weight. The addition of such copolymers has the effect of a less rejection on commissioning, a better binder-aggregate bond, increased brine resistance, a reduction in sensitivity to heat and cold, greater cohesion as well as '' better deformability.

A mineral filler can optionally supplement the particle size of the aggregates such as for example a crushed rock powder, preferably limestone, cement, natural or artificial rock fibers. The mineral filler content is less than 10%.

In a variant of the invention, the bituminous binder also contains synthetic fibers. The fibers used are ultra-fine synthetic fibers (a few decitex) and relatively long (4 to 8 mm). They are chosen according to the elastic modulus of the material of which they are made, in order to obtain a fibrous mix whose deformability is compatible with that of the support on which it will be applied. The low modulus fibers will be used for the most deformable supports. The proportion of fibers is advantageously between 0.05 and 3% by weight. This proportion may be very low, but given the extreme fineness of these fibers, their number per square meter of asphalt poured is considerable, as well as the length of the network that they constitute.

The cold poured asphalt layer can be a monolayer or a bilayer.
When applied with sufficient thickness, it can serve not only as a thermal barrier for the bituminous membrane, but also as a wearing course. In this case, it is desirable to use for the wearing course of the cold-poured asphalt, an aggregate having a discontinuous particle size. The aggregate can be of the discontinuous type 0/6 or 0/10. The surface texture of the cold-poured asphalt layer thus obtained is very grainy, which has many advantages: reduction in glare, better evacuation of water, improvement in the level of adhesion, even at high speed.

The cold poured mix is prepared by cold coating with a bitumen emulsion, a mortar made up of the above-mentioned aggregate and with an emulsion rupture regulator. The regulator can be a cement.

When the cold-cast mix contains fibers, these fibers are integrated into the mortar.

The binder emulsion is generally a cationic, single-phase, slow-breaking and controlled emulsion.

The mortar pre-wetting water may contain a surfactant as an emulsion rupture regulator.

A typical composition is for example the following, expressed in parts by weight

The coating according to the invention may comprise a layer of hot asphalt modified with modified bitumen as a wearing course, this layer being applied to the layer of cold-poured asphalt.

The bituminous membrane preferably has a thickness of between approximately 2 and approximately 4 mm, corresponding to approximately 2 to 4 kg / m². It consists essentially of a bituminous binder similar to that used in the composition of the cold-cast mix. It therefore contains a bitumen, preferably of penetration 60/70, 80/100 and 180/220, modified by the addition of thermoplastic copolymers. Preferably, ethylene vinyl acetate (EVA) or styrene butadiene styrene styrene (SBS) or ethylene methacrylate (EMA) copolymers will be used. However, it is also possible to use the styrene butadiene rubber block copolymers (SBR) and the acrylic copolymers as well as various mixtures of these copolymers.
The maximum content of copolymer is imposed by the limited viscosity of the modified bitumen to which it flows by a heating and heat-insulated spreading ramp while remaining at a temperature below the degradation temperature of the copolymer.
The bituminous binder intended to form the bituminous membrane advantageously contains a resin, preferably a terpene-phenolic resin. Such a resin improves the tackiness of the bituminous membrane. The amount of resin is of the order of 5% by weight. Mention may be made of the DERTOPHENE TL resin manufactured by "Resin and terpene derivatives SA". In addition, to decrease the viscosity of the binder, it is desirable to incorporate a dope into it. A suitable amount of dope is of the order of 3% by weight.
The coating according to the invention must be applied to a clean surface, free from rust and out of water. The surface is prepared by shot blasting. Then, a protective varnish is applied to the pickled metal, in order to remove it from the climatic conditions. This varnish may have corrosion-inhibiting properties allowing more effective protection of the sheet. The protective varnish may be a bitumen-based varnish modified by the addition of elastomers and comprising adhesive agents.

• 1) la membrane bitumineuse par répandage à chaud d'un liant bitumineux
• 2) la couche d'enrobé coulé à froid.

The process for preparing the coating according to the invention consists in applying, to a metal support previously pickled and covered with a protective varnish,

• 1) the bituminous membrane by hot spreading of a bituminous binder
• 2) the cold poured asphalt layer.

If necessary, if the cold-poured asphalt layer is intended solely to serve as a heat shield for the bituminous membrane, a suitable wearing course is applied by known methods.

The present invention is described in more detail by the following examples, given by way of illustration, without limitation.

EXAMPLE 1 a) Preparation of the support

About 100 g / m² of Impression Parafor, a protective varnish marketed by Siplast, was applied by spraying on a metallic support stripped by shot blasting.

b) Application of the bituminous membrane

bitume 80/100

77

Copolymère EVA 33/45

18

Résine DERTOPHENE TL

5

Dope

0,3

Was applied by spreading at a rate of 3 kg / m², a mixture, called "Mobilplast A", brought to a temperature of about 180 ° C, having the following composition, expressed in parts by weight

bitumen 80/100

77

EVA 33/45 copolymer

18

DERTOPHENE TL resin

5

Dope

0.3

The membrane obtained has a thickness of approximately 3 mm.

c) Application of a cold poured asphalt layer (heat shield).

Mobilplast G3® sold by the applicant, containing 958 by weight of emulsifiable bitumen 80/100 and 3% by weight of an EVA 33/45 copolymer, was used as bituminous binder.

liant Mobilplast G3®

600

agent émulsifiant

9

HCl (d-1,19)

2,15

Eau

400

An emulsion, known as a 60% emulsion, having the following composition, expressed in kg, was prepared:

Mobilplast G3® binder

600

emulsifying agent

9

HCl (d-1,19)

2.15

Water

400

- pH

2 à 3,5

- viscosité Engler

2 à 6 degrés

- refus sur tamis de

 

- 0,630 mm

< 0,1%

- 0,160 mm

< 0,25%

- indice de rupture LCPC

> 160

- diamètre médian

2 à 4 µm

- sédimentation à 7 jours

< 5%

The characteristics of this emulsion are as follows:

- pH

2 to 3.5

- Engler viscosity

2 to 6 degrees

- rejection on sieve of

- 0.630 mm

<0.1%

- 0.160 mm

<0.25%

- LCPC rupture index

> 160

- median diameter

2 to 4 µm

- sedimentation at 7 days

<5%

The composition intended to form the layer of cold-cast mix was prepared by kneading the following mixture for 2 min, in which the proportions are expressed in parts by weight:

The thickness of the cold poured asphalt layer is of the order of 8 mm.

d) Application of a layer of cold-cast mix constituting the tread (Betonplast 0/10)

The MOBILPLAST A mixture of step b) was used and the following composition was prepared, in the same manner as in c):

The thickness of the layer is of the order of 5 cm.

EXAMPLE 2

• vernis Parafor : 100 g/m²
• membrane bitumineuse : 3 Kg/m² soit environ 3mm
• couche d'enrobé coulé à froid (écran thermique) 8 mm
• couche de Bétonplast constituant la bande de roulement : épaisseur après compactage: 5 cm;
  compacité : 94 %

The complex as described in Example 1 was subjected to a fatigue test. The tests were carried out using test pieces prepared for the compacting table in the following manner: a steel sheet of 270 mm by 590 mm having a thickness of 12 mm and provided with a projecting central foot, a was coated with a multilayer as described in Example 1:

• Parafor varnish: 100 g / m²
• bituminous membrane: 3 Kg / m² or about 3mm
• 8 mm cold-rolled asphalt layer (heat shield)
• Bétonplast layer constituting the tread: thickness after compaction: 5 cm;
  compactness: 94%

Three similar test pieces were tested. The results of the tests are shown in Table I below.

The test piece, fixed on a rigid frame, is subjected to alternating negative flexions, at a frequency of 4 hertz and at different temperatures.

The force imposed, at the center of the central core, corresponds to a stress of 8.33 daN / mm² on the steel sheet. This constraint is that which would be caused by an 11-ton axle for a 12-mm thick sheet.

The cracks are monitored by means of strain gauges positioned by gluing on the surface of the mix and the detachments by gauges on the vertical edge, in line with the weld seams

Usually, an undegraded coating after 1,000,000 cycles is considered to be a good coating.

It thus appears that the multilayer coatings according to the invention are particularly well suited for road structures with a metal deck.

Claims (14)

Multilayer coating for a road structure with a metal deck, characterized in that it consists of: - a bituminous membrane consisting essentially of a bitumen modified by the addition of thermoplastic copolymers, - a layer of cold-cast mix consisting of an aggregate and a bituminous binder. Coating according to claim 1, characterized in that the cold-cast mix consists of a bituminous binder and an aggregate whose maximum particle size remains less than approximately 10 mm. Coating according to claim 2, characterized in that the aggregate is entirely crushed. Coating according to any one of Claims 1 to 3, characterized in that the aggregate can comprise an amount of less than 10% by weight of a mineral filler. Coating according to any one of Claims 1 to 4, characterized in that the bituminous binder of the cold-cast coating layer and / or of the bituminous membrane essentially contains a bitumen of penetration 60/70, 80/100, or 180/220. Coating according to any one of Claims 1 to 5, characterized in that the bituminous binder of the cold-cast coating layer and / or of the bituminous membrane is modified by the addition of thermoplastic copolymers. Coating according to any one of Claims 1 to 6, characterized in that the thermoplastic copolymers are chosen from ethylene vinyl acetate (EVA) or styrene butadiene styrene styrene (SBS) or ethylene methacrylate (EMA) copolymers, styrene butadiene rubber copolymers bisequenced (SBR) and acrylic copolymers as well as various blends of these copolymers. Coating according to any one of Claims 1 to 7, characterized in that the bituminous binder of the cold-cast coating layer contains synthetic organic fibers. Coating according to any one of Claims 1 to 8, characterized in that the cold-poured asphalt layer is a monolayer serving as a heat shield and in that it is coated with a wearing course. Coating according to claim 9, characterized in that the wearing course is a layer of hot bituminous mixes with modified bitumen. Coating according to any one of claims 1 to 8, characterized in that the cold-poured asphalt layer is a two-layer serving as a wearing course, the upper part containing a discontinuous aggregate. Process for the preparation of a coating according to any one of Claims 1 to 11, characterized in that it consists in applying, to a metal support previously stripped and covered with a protective varnish, 1) the bituminous membrane by hot spreading of a bituminous binder 2) the cold poured asphalt layer. Method according to claim 12, characterized in that a second layer of cold-cast mix used as a wearing course is applied. Method according to claim 12, characterized in that a layer of hot mix asphalt is applied to the layer of cold poured mix.