FR2609480A1 - METHOD AND DEVICE FOR PREFILIATION OF CHAIRS OF TREADS TREATED WITH HYDRAULIC BINDERS - Google Patents

Abstract

FOR THE PREPISSURING OF PAVEMENT BASES TREATED WITH HYDRAULIC BINDERS, WE OPEN AT CHOSEN LOCATIONS, 2 Furrows IN THE LAST SPREADED LAYER 1, BEFORE ITS DEFINITIVE COMPACTION, A PRODUCT 4 CREATES DISCONTINUITY WITH THE MATERIAL IS PROJECTED IN THESE Furrows. , THE SAID Furrows 2 ARE CLOSED AND THE COMPACTION OF THE SAID LAYER IS PROCEEDED. PREFERentially, the product forms a film in contact with the material of the furrow; THIS IS FOR EXAMPLE A CATIONIC BITUMEN EMULSION, AT LOW PH AND HIGH RUPTURE SPEED.

Description

Process and device for pre-cracking treated pavement

to hydraulic binders

  The invention relates to a method and a device

  intended to prevent or at least delay

  the transmission of cracks in the layers of

  from a roadway to the layers of bearings.

  For more than 20 years, France has been using materials treated with hydraulic or pozzolanic binders extensively to create the roadbed layers for high and medium traffic roads. An important part of the connecting motorways built since the 1960s and most of the heavy reinforcements on national roads since 1969

call to this technique.

  High mechanical performance (resistance

  this and deformation module that confers to the aggregates the addition of a hydraulic binder -cement or derivative,

  granulated blast furnaces activated- or

  lantern - ash from thermal power plants + lime or

  , natural zolanes + lime-) are highly appreciated by designers and builders. In addition this technique leads to pavement structures often

  economic. Finally, the use as binders of sub-

  products or industrial waste allows for

  of these products and regulates certain

environmental problems.

  On the other hand, the findings made on the

  French road water using hydraulic binders show that for the French climate and for the binders and the formulations chosen since

  twenty years, the basic and basic layers

  tion are subject to unavoidable thermal shrinkage cracking. This cracking is transmitted to the wearing course and appears on the surface in the form of transverse cracks whose spacing varies most often between 5 m and 10 m and whose opening, usually limited to a few millimeters, depends on the temperature. The spacing of the cracks depends on the nature and dosage of the binder, the period of production of the base layer and the quality of the adhesion of the hydraulic binder-treated layer to the lower layer. At the same temperature, the opening of the cracks depends essentially on the nature of the granulate treated (the coefficient of expansion of a limestone and a siliceous material varies in a ratio close to 2) and the spacing between cracks. The speed of appearance

  the surface crack depends, apart from the conditions

  climatic conditions, the thickness and the nature of the wearing course and the quality of the coupling between the wearing course and the layer treated with

a hydraulic binder.

  To prevent or at least delay

  the transmission of cracks from the foundation layers to the wearing courses, several techniques can be used jointly or separately: Reduction of the opening and the movements of the edges of the cracks, interposition, at the level of the crack, between the layer the wearing course and the wearing course, of a product or

  of a decoupling complex partially the two cou-

  , use for the wearing course of suitable bituminous mixtures resistant to tensile stresses,

  pre-cracking of the layer treated with the hy-

  draulic. The purpose of the pre-cracking is to locate, as soon as it is used, the thermal shrinkage cracks of the layer treated with a hydraulic binder, which, for the formulas used in France, would most often occur only during the first winter following the

construction site.

  In this technique, the spacing between the induced cracks is greatly reduced compared to that found on a site where cracks have occurred "naturally" (2 m to 3 m for example instead

from 5 m to 10O m).

  The advantages of pre-cracking

  The cracking pitch is reduced compared to that of "natural" cracks, the blast of these cracks (variation of the crack opening) is smaller during temperature variations because it is related to shrinkage and dilation of slabs of shorter length The cracks being localized before their appearance,

  prior treatment to delay the amortization

  cracking in the wearing course

  can be done before running the latter.

  The solution of the sawing and the garnishing of the bleeding thus carried out by a suitable product is not

  can be used in the case of seat layers of

  Sees. Indeed, the low curing speed of the formulas generally used does not make it possible to obtain a material that can be sawn without degradation. This

  classic technique for hydraulic concrete pavements

lique is otherwise expensive.

  The techniques already studied or used consist in creating a discontinuity in the layer treated with a hydraulic binder, ie by reducing

  local thickness of the layer, be more general-

  by priming the crack on the layer completely

or partially compacted.

  A solution that consists of creating crack initiation or shock cracking on the layer

  hardening course has also been considered or

cated.

  The local reduction technique of thickening

  The layer consists of introducing a discontinuity at the base or at the top of the layer which will reduce the thickness of the material. Various solutions were used: wooden battens, rubber tubes,

  plastic sheets, etc. This technique has the

  following disadvantages: on the one hand, to be adapted to the pace of road works, it requires heavy specialized equipment, and is therefore expensive and ill-suited to small construction sites; on the other hand, at the crack crack created, the contact area between the two slab edges is reduced, which hinders the load transfer between two slabs during the passage of a vehicle and may accelerate the degradation of the slabs. fatigue cracks. The technique of priming the crack by notching on the surface is the most common; it is still little used in France, but more developed in

  Germany in particular. This technique consists of

  ler the layer implemented to a depth of a few centimeters by a vibrating knife, a blade or

  a vibrating wheel or by any other means.

  To be effective "notching" of the seat must actually be performed on the at least partially compacted material. This condition entails: on the one hand the need to provide a significant mechanical energy, which imposes an effective material and results in a significant cost; secondly, the risk of altering the unity of the layer, the operation involved at the end of implementation. Moreover, by disorganizing the material in the vicinity of the crack, pre-cracking risks creating a weak zone whose

  Behavior under traffic will be mediocre.

  The technique of impact cracking on the layer being cured initiates both transverse and longitudinal cracks; it certainly affects the life of the structure under the effect of traffic. Furthermore, since the shape and the exact location of the created crack primers are not manageable, this technique does not allow a crack treatment before the implementation of

the wearing course.

  The present invention aims to provide a pre-cracking process which does not have these disadvantages.

  This goal is achieved within the framework of

  by a method of the type of introducing a discontinuity to the upper part of the last layer spread, and characterized in that it opens, at selected locations, grooves in said layer before its final compaction. A product creating said discontinuity with the surrounding material is projected into these grooves, said grooves are closed and

  compacts said layer.

  The groove can be opened by appropriate mechanical means or directly by the product creating the discontinuity emitted in the form of a liquid jet under high pressure (opening of the groove

  and the projection of the product are then simultaneous).

  In the preferred embodiment of the invention, a film forming product is

contact of the furrow material.

  The product should be sprayable; that it freezes on the material as soon as spraying (without diffusion in the material, nor flow at the base of the layer) so as to create said film constituting the desired discontinuity; finally, that the product is compatible with the bitumen (or other product) that will be used as a binder for the wearing course and with the products possibly used for a treatment

  located before implementation of the wearing course.

  The product will preferably be chosen from hydrocarbon binders (bitumens, tars, etc.). This product can generally be thinned by heating to pulverize it. The formation of the film is due to the freezing of the product during cooling in contact with

granular materials of the furrow.

  A particularly advantageous product for carrying out the invention is the bitumen in the form of an emulsion. Indeed, its cost is low, its fluidity is sufficient to allow spraying without

  it is necessary to bring the product to a

  high erection; it has good compatibility with the wearing course of the road (in general

  bitumen) and with the products possibly used

  for localized treatment (also bituminous).

  nous); the product is available on any paving site and road companies are used to

to use it.

  The bitumen emulsion is preferably

  low pH (close to 3) and at high breaking speed. By its aqueous phase at low pH, it partially inhibits the setting of the hydraulic binder and therefore creates

  a weaker zone of resistance favorable to the location

  removal cracks. By its bituminous phase

  neuse, it creates the discontinuity that accentuates

  leads and allows accurate pre-positioning of the crack

  re. In addition, the bituminous phase makes the material, at the crack surface, insensitive to water and

sensitive to abrasion.

  A bitumen emulsion with other characteristics

  The methods can be used for a second embodiment of the invention. By projecting into the furrow

  an emulsion of cationic, nonionic or anionic type

  that at low speed of rupture, it penetrates a few centimeters in the material creating in this zone a mixed material (hydraulic binder - bitumen)

  whose resistance is lower than that of

  of origin but whose deformability allows local

  the diffusion of withdrawal constraints.

  The invention also applies to the pre-

  cracking of layers made of compact concrete with low water content, implemented by materials similar to those used for making the layers of foundations, and which do not require layers

rolling.

  The implementation of the method according to the invention can be done from a vehicle integrated in the yard and circulating in the direction of

  the progress of the construction site, or from the engine

  pandage itself. The fact of intervening on a material little or not compacted offers the advantage of requiring a weak mechanical energy for the opening of a groove

  over the entire thickness of the layer.

  The machine allowing the industrial realization

  The trielle of the process consists essentially of a mobile carriage moving on a rail attached to a vehicle (tractor-van-small truck). This apparatus comprises means respectively providing three functions: the opening of a groove, by a soc of adapted form; projecting the amount of bitumen emulsion required (or other product); and the closing of the furrow. These operations can be done with the vehicle stopped, or continuously the vehicle moving slowly and forming an oblique groove (if the rail is transverse). Other features and benefits of

  the invention will emerge from the following description

  with reference to the accompanying drawings, in which:

  FIG. 1 is a diagrammatic perspective view

  tick of the seat layer in which is practiced

  the groove where the desired emulsion is projected.

  FIG. 2 is a diagrammatic view from above showing the furrow opening means,

  product projection and furrow closure.

  FIG. 3 is a diagrammatic view from above showing the vehicle for supporting the means of

Figure 2.

  FIG. 11 shows the last layer of seat 1, generally between 15 and cm thick, made of materials treated with hydraulic binders. The particle size of these materials is commonly of the order of 0.20 mm, but also includes materials with average grain size (0.10 mm) or fine sand. Layer 1 is intended to receive,

  after compaction, the wearing course.

  According to the invention, or opens in the layer 1 not yet compacted, at selected locations (for example within two or three meters) grooves 2. Is projected in the grooves 2, by means of a nozzle 3, the bitumen emulsion 4 in the form of a jet which comes into contact with the material of groove 2 and breaks in

  creating the wanted movie. Then, the said silencing

  lon 2, and one can proceed to compact the layer

  1 and all subsequent conventional operations.

  The bituminous emulsion maintaining disconti-

  night, the operation can be performed on the material simply regaled and roughly adjusted. The mechanical effort required to open the "groove" is in

  this weak case. The compaction and adjustment operations

  ge are not disturbed and the effects of the process

are null on the uni.

  The operation does not require large means

  mechanical and little disturbance the progress of the site.

  The quantity of bitumen emulsion required for a 20 cm thick hydraulic depth and a 3 m pre-crack spacing is at most 0.2 1

per m2 of roadway.

  The overall cost of treatment brought down to the meter

  Linear ground is therefore weak.

  Figures 2 and 3 schematically illustrate the essential means for carrying out the method. These means consist of a V-shaped plow 5 slitting the layer I to form the groove 2; in a spray nozzle or nozzle 3 distributing the product 4; and in two inverted V plates 7 bringing between them the material spread by the share 5 so as to close the groove. The direction of advancement is represented by the arrow 6. These three means 5,3,7 can be mounted integral on a carriage 8 (FIG 3) slidably mounted (direction 6 and 6 ') on a rail 11 of the width of the traffic lane (3.5 cm for example), carried by a vehicle 9. The vehicle comprises a lagoon 10 insulated emulsion and a pump and connecting means for bringing this emulsion to the nozzle 3 ensuring the projection. Given the small quantities of bitumen used for the process, the capacity of the emulsion storage can be limited to a few

hundreds of liters.

  The nozzle 3 linked to the mobile carriage 8 can be

  replaced by a projection ramp with simultaneous

the entire length of the furrow.

Claims (8)

  A method of pre-cracking hydraulically bonded pavement courses of the type consisting of introducing a discontinuity in the upper part of the last spread layer (1),   characterized by opening b selected locations   sis, furrows (2) in said layer before its final compaction, is projected in these grooves a product (4) creating said discontinuity with the surrounding material, said furrows (2) is closed and one proceeds compacting said layer.   2. Method according to claim 1, characterized   rised by projecting an inhibiting product (4) into   less partially taking hydraulic binders.   3. A method according to any of the claims   I or 2, characterized in that a project is   forming a film (4) in contact with the material of the sil- lon.   4. Process according to any one of the   cations 1 to 3, characterized in that a binder is hydrocarbon.   5. Process according to claim 4, characterized   rised by projecting an emulsion of bitumen.   6. Method according to claim 5, carecté   rised by projecting an emulsion of bitumen   low pH and high rate of failure.   7. Procedure for implementing the procedure   die according to any one of claims I to 6,   characterized in that it comprises means (5) for opening grooves (2) in a layer, means (5) for projecting a product into these grooves (2), and   means (7) for closing said grooves (2).   8. Device according to claim 7, characterized   characterized in that said means are supported on a movable carriage (8) on a rail (11) fixed on a vehicle (9).