EP0086188B1 - Process for baring a concrete slab - Google Patents

Abstract

In a method of roughening the surface of a concrete slab for roads to provide anti-skid properties, an agent for retarding the setting of the concrete is distributed over the slab which has been recently laid and a water-impermeable sheet of plastics material is spread over the upper surface simultaneously with the spraying operation. After the underlying or subjacent layer of concrete has set, the plastic sheet is lifted away and the still soft upper layer of concrete is removed by brushing and spraying with pressurized water.

Description

The present invention relates to a surface treatment process for a road concrete slab, according to which a fresh surface retarding agent is spread over the freshly laid slab and a top layer of mortar is removed using 'a brush.

The purpose of the process is to remove the top layer of mortar from the concrete slab between the aggregates in order to obtain rough concrete. It is particularly applicable to the finishing of the coating of a concrete road, in order to give it good non-slip characteristics. The invention also relates to a device designed to implement the method according to the invention.

There is a known method of mechanical stripping of concrete which consists in eliminating the surface mortar, when the setting phenomenon has started, using a rotary brush supplied with water by its axis. The removed mortar is sprayed into a receiving tank from which it is pushed laterally by a squeegee chain.

The disadvantage of this process lies in the fact that the machine which carries the rotary brushes must necessarily be mounted astride the concrete slab.

However, as the width of the concrete slab can reach approximately 12 meters, the cantilever assembly requires a sufficiently solid chassis to take up the weight and the efforts of the rotary brushes extending over the entire width of the slab as well as the weight of the concrete receiving tank removed by the brushes and the squeegee chain intended to remove the concrete laterally.

A second drawback of this known method lies in the difficulty of determining the moment when it must be implemented. This moment is difficult to choose because the setting time of the concrete is closely linked to the inevitable variations in the water content of the fresh concrete, to the variations of the atmospheric conditions and, in particular, to the ambient temperature, to the action of the wind and from the sun, which influence the setting process on the concrete surface.

The concrete setting time can, in fact, vary within wide limits, between 1 and 15 hours, and even more, if the temperature is low.

Another disadvantage of the known methods consists in the fact that it is difficult to communicate to the chemical stripping machine the rate of unloading of the concrete trucks which supply the concrete laying machine.

Also known from patent application FR-A-2473579 is a process for the chemical stripping of concrete which consists in very regularly applying an aqueous solution containing 15% sugar at the rate of 200 to 250 g of solution per square meter to the surface of a freshly poured concrete slab. This sugar water solution delays the setting of the cement in the upper layer of the slab. After five to twelve hours, depending on weather conditions, the top layer of concrete is removed by brushing or by jets of sand or water.

The disadvantages are similar to those described above. Thus, it is still difficult to predict the right moment to remove the mortar from the surface layer whose setting has been delayed.

In addition, the maximum delay of setting delay is limited for this process. This may require working at night.

In addition, the process cannot be used in rainy weather. There is indeed a risk of washing the retarding agent in the rain.

Finally, to avoid the formation of cracks in the concrete, it must be sprayed on the latter, after spreading the setting retarding agent, curing products consisting inter alia of latex. These products prevent the evaporation of water on the upper surface of the concrete slab. However, cure products are quite expensive. They offer protection only after drying, that is to say only after the formation of a thin film which has become waterproof. As long as they have not dried, they can therefore be washed out by rain.

Finally, we know from an article entitled “Afwerking van het oppervlak van een beton-weg published in the journal WEGEN, vol. 49, n ° 6, June 1975 by SHAGEN different possible methods for treating the surface of a concrete slab.

The article mentions the spreading of sand on said slab. This sand is kept moist by spraying with water. The article also describes the use of polyester mats that are kept wet, or the placement of a straw blanket on the slab, but then in combination with a curing product.

The article also teaches that to ensure an ideal degree of humidity for the hardening of concrete, it is necessary to finely spray a certain amount of water on the slab or cover it with waterproof sheets.

Finally, the article recognizes that the most common method consists in combining the spraying of a curing product and the installation of a movable roof in order to prevent possible washing out by rain or, by protecting the slab from concrete from direct sunlight, avoid drying too quickly.

This known process does not however protect the concrete slab from the action of the wind which, by influencing the rate of evaporation of water, influences the setting process on the surface of the concrete. It does not ensure a sufficiently rigorous constancy of the time between the spraying of the setting retardant agent and the brushing.

The present invention aims to remedy the drawbacks of the above methods. It relates to a process for the chemical stripping of a road concrete slab according to claim 1.

The invention also relates to a machine for implementing the method described above. This machine, comprising a frame, mounted astride a concrete slab and a spraying boom extending over the entire width of the above-mentioned slab, is essentially characterized in that it comprises, in the immediate vicinity of the ramp, means for supporting a mandrel intended to carry a roll of plastic sheet.

Other features and details of the invention will appear during the description of the appended drawings which schematically and without limitation, an embodiment of the device according to the invention.

• la figure 1 montre debout une machine pour la mise en oeuvre du procédé de dénudage chimique d'une dalle de béton suivant l'invention ;
• la figure 2 est une vue en élévation latérale de la machine représentée à la figure 1 ;
• la figure 3 montre la paire de galets destinés à porter le mandrin du rouleau de feuille de matière plastique et le rouleau tendeur.

In these drawings:

• Figure 1 shows a standing machine for implementing the chemical stripping process of a concrete slab according to the invention;
• Figure 2 is a side elevational view of the machine shown in Figure 1;
• Figure 3 shows the pair of rollers for carrying the mandrel of the plastic sheet roll and the tension roller.

In these figures, the same reference notations designate identical elements.

As shown in FIG. 1, the machine for implementing a chemical stripping process of a concrete slab according to the invention comprises a chassis designated as a whole by the reference notation 1 and mounted astride a freshly poured concrete slab 2.

The machine is used following a compacting-finishing machine, not shown, used to lay and smooth a concrete slab 2.

This chassis carries a spray boom 3, extending over the entire width of the slab 2. It also comprises support means 4 consisting of a pair of rollers of similar diameter, mounted along each of the side faces of the machine, at identical heights, so as to carry a roll 5 of plastic material allowing it to rotate around a substantially horizontal axis I-l '.

The distribution of the setting retarding agent is carried out by spraying using an agricultural-type spraying boom, connected to two reservoirs 10. The boom 3 extends over the entire length of the slab 2, so as to spread the setting retardant evenly over the concrete slab 2 using the nozzles 6.

In order to allow a visual control of the homogeneity of the distribution of the setting retarding agent, a pigment is advantageously added to the solution to be sprayed. This pigment makes it possible to best approach the intended dosage. It also makes it possible to adjust the level of the spraying boom 3 relative to the concrete so that there is mutual overlap of the jets of the various nozzles 6. This adjustment of the level of the boom makes it possible to obtain a uniform distribution of the agent retarder on the concrete slab 2.

The spray boom 3 is protected from the wind by a cap 8 completely surrounding the boom and a fairing 9 down to 10 to 15 cm from the concrete surface.

The quantity of retardant solution to be sprayed per square meter is determined experimentally, depending on the degree of stripping required or desired.

This dosage being fixed, the calibration is carried out according to the flow rate of the boom and the speed of movement of the machine, which must be constant within the narrowest possible limits.

Slight variations are accepted provided that the quantity of retarder provided per square meter is of the order of 500 g / m ² of solution. Such a concentration limits the incidence of variations in dosage due to variations in the speed of movement of the spraying machine.

It is imperative to respect the imposed dosage. In this regard, it is useful to point out that a defect in the delaying agent can lead to too low stripping and even at the limit impossible. The only alternative, in this case, to meet the charges, is bush hammering, a very expensive process.

An excess of product leads to too deep stripping which, possibly, may cause the stones to come off during the subsequent brushing operation.

When the machine which carries the spray boom 3 stops, the nozzles 6 letting the concrete run over what remains in the boom, it must be avoided by providing a movable gutter which is slid under the boom to each stop.

In the process according to the invention, a sheet of waterproof plastic material 7 is spread over the upper surface of the freshly poured and smoothed concrete slab.

The above-mentioned plastic sheet 7 is best stretched on the concrete slab 2 using a tension roller 11 mounted at the end of a pair of levers 12 adjustable in height by means of threaded rods 13, fixed to the frame of the chassis 1 by springs 14 and actuated by a flywheel 15.

The plastic sheet 7 is applied to the concrete slab 2, possibly covering it with a jute fabric 16 which is dragged over it and wetted if the intensity of the wind so requires.

The elimination of the surface layer of concrete whose setting is delayed is done as soon as the underlying layer offers sufficient mechanical strength to admit the evolution of the brushing machine on the slab in any deterioration thereof, usually at least after 24 hours.

The polyethylene sheet 7 is first removed by section of road over a length corresponding to that which is expected to be able to be brushed immediately. This avoids removing the polyethylene on too large a surface because the mortar dries on the surface and forms a crust more difficult to remove. To avoid the formation of this crust in hot weather, it is even advantageous to water the surface to be treated beforehand.

• protéger le béton des risques de fissuration, jusqu'au moment du brossage de la couche superficielle ;
• protéger le retardateur de tous les risques d'intempéries ;
• maintenir l'efficacité de l'agent retardateur de prise quelles que soient les conditions atmosphériques, soleil, vent, pluie et ce, jusqu'au moment du brossage qui peut aller jusqu'à 72 heures (soit ± 3 jours après la mise en oeuvre du béton).

The role of the protective plastic sheet, used in combination with the use of the retarder, according to the invention, is multiple:

• protect the concrete from the risk of cracking, until the surface layer is brushed;
• protect the retarder from all risks of bad weather;
• maintain the effectiveness of the setting retardant agent whatever the atmospheric conditions, sun, wind, rain and this, until the time of brushing which can go up to 72 hours (that is ± 3 days after the implementation concrete).

It is the use of the retarder and its simultaneous protection by the plastic sheet, which brings the aforementioned advantages.

By protecting and isolating the retarder under the plastic sheet, efficiency is maintained over time.

The process described above makes it possible to use concrete, even in rainy weather, with certain constraints, namely, covering the concrete refueling trucks and working as close as possible to the concrete processing machine. . This is a significant advantage for the performance of construction sites.

The use of a polyethylene sheet can under these conditions become more advantageous than the use of a curing product until the moment of removing the mortar and it is certainly so when the time between spraying the retarder and brushing takes approximately 72 hours because the curing agent no longer becomes necessary after this time.

The polyethylene sheet is easily removed from the concrete surface and the top layer of mortar thus exposed and not yet set can be removed without much effort.

It is thus possible to adjust the degree of penetration of the brush into the concrete in a precise manner to carry out the stripping operation.

We work best by adjusting the level of the strands a few millimeters below the concrete surface.

In this way, the dynamic projection effect produced by the rotating strands is used in the best conditions, there is no premature wear and the strands do not tend to bend permanently.

The plastic sheet placed on the surface of the concrete slab, immediately after its implementation, very advantageously and more safely replaces the curing product until the time chosen for the stripping operation and saving performed becomes even more appreciable when the concrete execution conditions making it possible to remove the mortar after ± 72 hours.

The present invention makes it possible to adapt the composition of the aqueous solution of the setting retarding agent, in order to obtain reproducible results, whatever the atmospheric conditions and also to be able to vary the time between spraying the retarder and disposal of mortar.

It also allows a sufficiently viscous solution to be used to avoid the natural flow of the product on the slopes normally encountered on roads. To achieve this condition, the kinematic viscosity measured with the Ubbelohde viscometer is of the order of 12 - 10 - ⁴ m ² / sec.

This viscosity does not prevent the penetration of retarder into the concrete, as could be the case for other known methods. In addition, this process gives a little more latitude in the delay of penetration of the retarder, since the plastic sheet protects this operation permanently.

Thanks to the process according to the invention, it becomes possible to fix the time which must elapse between the spraying of the retarding agent and the passage of the brushing machine intended to remove the delayed mortar, to at least twenty-four hours. This eliminates any risk of damage to the concrete slab.

Claims (2)

1. A method of chemically stripping a concrete slab, in which an agent for retarding setting of an upper layer of concrete is distributed by means of a spraying row onto the recently laid concrete slab, and an upper layer of mortar, setting of which has been retarded, is then removed between the surface aggregates of the slab by brushing together with spraying of pressurized water, removal being carried out as soon as the concrete in the layer of the slab subjacent to the upper layer has set, characterised in that simultaneously with spraying of the agent retarding setting, a water-impermeable sheet of plastics material (7) is spread over the upper layer of the concrete slab (2), immediately downstream of said spraying row (13), in such a manner as to thus stabilize the retarding functions for at least 24 hours, and this sheet of plastics material is lifted off before removing said layer of mortar.

2. A machine for chemically stripping a concrete slab for roads according to the preceding claim, comprising a frame mounted above and astride a concrete slab and a spraying row extending over the complete width of said slab, characterised in that it comprises means (4) for supporting a chuck for supporting a roll of plastics material sheet (7).

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