EP3578730B1 - Method for producing concrete staircases and staircase obtained by said method - Google Patents

Description

FIELD OF THE INVENTION

The invention relates, in the first place, to a process for the production on site or in the factory of concrete stairs, more particularly but not limited to the type with a central shaft.

The invention also relates to the concrete stairs obtained by the aforementioned method.

PRIOR STATE OF THE TECHNIQUE

Traditionally, the construction of concrete stairs, in particular of the one-piece type, are carried out on site. However, more and more, these stairs are made in the factory, then transported and set up on site.

Thus, in the context of the production of such concrete stairs directly on site, they are produced in the following manner, for example in the case where the staircase comprises a central shaft.

First of all, a mold is placed, defining a central column intended to form the barrel. The latter is made by pouring concrete through the upper end of the mold defining such a central barrel. Then we proceed to pour the concrete on the areas of the mold intended to define the steps and risers. The concrete thus deposited is vibrated, then the operator evens out the steps thus produced, in particular using a shovel or a trowel, then smooths the concrete that has not yet solidified with a trowel.

Indeed, conventionally, it is created concomitantly with the pouring of the concrete, air bubbles, which rise to the surface during the caking of the concrete. These air bubbles can freeze in the mass of concrete, but can also burst on the upper surface of each of the steps, causing craters to appear, which should be eliminated. This phenomenon of bubbling, well known in the field considered, generates the need to carry out a second smoothing operation when the concrete has begun to set.

Moreover, it is not uncommon, notwithstanding this double smoothing operation, for another coating or coating to be deposited on the facing of the concrete parts, for the sake of aesthetics in particular, in order to completely eliminate this bubbling phenomenon.

Already, it will be easily understood that the production of one-piece concrete stairs, as described above, whether these stairs are made on site or in the factory, entails significant finishing work, which is particularly time-consuming.

Moreover, although certain techniques, such as the vibration of concrete, have been developed to reduce this problem, the product nevertheless comes out bubbled and then requires significant finishing work to hide these bubbles.

In addition, the finish must be strong enough to allow repeated passages of users without showing any wear or bursting due to the presence of air bubbles. This explains the need for the presence of at least two layers of coating, increasing the loss of time accordingly.

In addition, the realization of such stairs is accompanied by great difficulty for the operator or operators, insofar as the latter must proceed, in addition to pouring the concrete, to its equalization at the level of each of the steps, in particular at the using a shovel, it being emphasized that this operation is to be carried out even when the concrete is not solidified, and that the operator is more or less in a balancing act on any buttresses of the mould. In addition to this aspect of arduousness, there is also a safety problem, precisely because of the positioning of the operator as best he can, to ensure this operation of leveling the steps and then smoothing the concrete, the operator having to work in the staircase in progress, curved on the mold several meters high, the risk of falling being very present.

Finally, due to the implementation of a relatively firm concrete, it is traditionally advisable to carry out an operation of vibration of the mold or internal with vibrating needles, adding to the aforementioned disadvantages a noise nuisance, affecting in an additional way the conditions of operator work.

Solutions have been proposed to remedy these drawbacks. Thus, the document CN 206170284 describes a method of manufacturing a staircase from a mould. The mold is thus available in several parts, including a bottom giving their shapes to the different steps and risers, side walls, an upper cover closing the mold and constituting the future underside of the staircase. These different parts are then assembled to form a mold into which concrete is poured. However, the staircase is not manufactured in position, therefore directly in operational mode for example on the site in question, but upside down. As a result, the air bubbles that rise to the surface of the concrete are then found on the underside of the staircase. They are therefore no longer on the surface of the steps and the passage of users then no longer constitutes a problem for the holding of the coating layer providing the finish. The finishing step therefore turns out to be much less crucial.

On the other hand, although the part affected by the phenomenon of bubbling no longer affects the visible surface of the steps, the finishing stage remains necessary, the specifiers of this type of staircase demanding a finished product free from any defect, including at the level of the lower face of the staircase, that is to say the face opposite to that receiving the steps.

But on the other hand and above all, on the one hand the process described does not allow the realization of the staircase in place in its final place, and on the other hand, it allows the manufacture of only one step height per mould, and therefore implies having as many molds as there are types of stairs to be made.

Also described in the document JP H05 287901 , a method for producing one-piece concrete stairs using a closed mould, consisting of a lower mold and an upper mould, said mold being intended to be filled with concrete, consisting in fixing the lower mould, positioning the upper mold opposite the lower mold and fixing it to the latter, and injecting concrete into the volume defined by the two molds.

However, in this process, the concrete is injected through orifices made within the upper mould, always requiring the vibration of the mould, and also generating air bubbles.

In addition, the molds used in this process remain after the concrete has solidified, thus prohibiting their reuse.

The present invention proposes a method for obtaining a staircase with a core or balanced with a barrel, or not, finished at the outlet of the mould, and requiring only very minor alterations, reducing the arduousness and the danger associated with work on the mold while allowing the manufacture of several step heights per mold.

BRIEF DESCRIPTION OF THE INVENTION

To this end, the invention relates to a process for the production of one-piece concrete stairs, in particular but not exclusively of the central shaft type, implementing a closed mold, composed of a lower mold and an upper mold or cover, defining between them a volume intended to be filled with concrete.

• ▪ à fixer et installer le moule inférieur en position opérationnelle ;
• ▪ à positionner le moule supérieur ou capot en regard dudit moule inférieur et à le fixer sur ledit moule inférieur ;
• ▪ à injecter dans le volume défini par les deux moules respectivement inférieur et supérieur, et à partir de la base inférieure dudit volume, du béton de type auto-plaçant, jusqu'à combler l'intégralité dudit volume ;
• ▪ après prise en masse du béton, à ôter le moule supérieur et le moule inférieur, et donc à démouler l'escalier ainsi réalisé.

This process consists of:

• ▪ fixing and installing the lower mold in the operational position;
• ▪ positioning the upper mold or cover opposite said lower mold and fixing it to said lower mold;
• ▪ injecting into the volume defined by the two respectively lower and upper moulds, and from the lower base of said volume, concrete of the self-compacting type, until all of said volume is filled;
• ▪ after the concrete has solidified, to remove the upper mold and the lower mould, and therefore to unmold the staircase thus produced.

In other words, unlike conventional and traditional methods of making concrete stairs, the invention consists first of all in implementing a closed mould, the shape of which corresponds to the shape of the stairs to be made, and on the other hand, to inject the concrete of a much more liquid consistency than the traditional concretes used for the stairs, from the lower end of the mold according to an upward movement, in particular by means of a suitable pump, and more particularly a peristaltic pump. Self-compacting concrete therefore does not need to be vibrated, a usually very physical and painful operation, and has a greatly reduced number of air bubbles, making it possible to obtain a finished product that is smoother on the surface.

According to the invention, the various constituent elements of the upper mold or cowl can be made up of several sectors, in order to promote, on the one hand their production, on the other hand their movement, their storage, their installation on the site and their demoulding.

According to another characteristic of the invention, the internal face of the upper mold or cover, that is to say the surface called upon to define the shape of the various steps and risers of the future staircase, is coated, in particular by spraying, with a mortar, prior to injecting the self-compacting concrete. This mortar is mainly intended to trap the air resulting from the solidification of the concrete between said concrete and the mortar. The particular choice of self-compacting concrete on the one hand, and mortar on the other hand, makes it possible to prevent air bubbles from piercing the upper surface of the staircase after demoulding.

The mortar, which differs from concrete by the absence of gravel in its constitution, comes to form a perfectly smooth layer in contact with the internal wall of the cover. The self-compacting concrete is then injected into the mold and comes into contact with the mortar. The last air bubbles likely to remain are then trapped between the upper part of the concrete and the lower part of the mortar. They therefore no longer appear on the surface of the step, which appears to be smooth.

• ▪ entre 5 et 50 % en masse de ciment ;
• ▪ entre 40 et 95 % en masse d'agrégats fins (notamment sables, filler) ;
• ▪ un mélange d'adjuvants choisis dans le groupe comprenant les super-plastifiants, les accélérateurs de prise en masse, les retardateurs de prise en masse, les agents anti-retrait, etc..

In fact and according to the invention, the mortar used comprises:

• ▪ between 5 and 50% by mass of cement;
• ▪ between 40 and 95% by mass of fine aggregates (in particular sands, filler);
• ▪ a mixture of adjuvants chosen from the group comprising super-plasticizers, solidification accelerators, solidification retarders, anti-shrinkage agents, etc.

Advantageously, the internal wall of the cap is covered with mortar before the assembly of the cap on the lower mould. More advantageously, said mortar is projected onto this surface, thus making it possible to reduce the duration of preparation of the cover of the mold.

Furthermore, and according to another characteristic of the invention, the lower and upper molds or cover are coated beforehand, on their internal face, that is to say on their face intended to receive the self-compacting concrete, with a component capable of promoting mold release, and in particular mold release oil.

When the cover receives on its internal face the aforementioned mortar, the mold release oil is previously deposited on said internal face.

In the more particular case of making one-piece concrete stairs with a central shaft, the injection of the concrete is carried out from the base of a column, able to define said central shaft, said column communicating with the volume defined by the two molds respectively lower and upper, by means of through lights. In doing so, the concrete being injected at the level of the base or lower end of the column, rises in it and, as it goes, fills the volume defined by the two moulds, so as to obtain a staircase of character. monobloc also integrating the central shaft.

Advantageously, the self-compacting concrete used belongs to class SF2 (spread between 660mm and 750mm), or class SF3 (spread between 760mm and 850mm), these two classes being defined by standard NF EN 206, the spreading being a test described by standard NF EN 12350-8.

According to the invention, and when required, stiffeners are integrated and fixed to the lower mold before the upper mold or cover is put in place.

The invention also relates to one-piece concrete stairs implementing the method described above.

BRIEF DESCRIPTION OF FIGURES

• La figure 1 est une vue en éclaté des éléments constitutifs du moule pour obtenir un escalier exempt de fût central conforme au procédé de l'invention.
• La figure 2 est une vue analogue à la figure 1 mais d'un escalier à fût central.
• La figure 3 est une représentation schématique en perspective du moule inférieur pour la réalisation d'un escalier à fût central, dont la figure 4 est une vue de détail et la figure 5 une vue en section sagittale.
• La figure 6 est une représentation schématique en perspective du moule inférieur pour la réalisation de l'escalier à fût central, faisant apparaître les raidisseurs le cas échéant mis en œuvre dans le cadre du procédé de l'invention.

The manner in which the invention can be implemented, and the resulting advantages, will emerge more clearly from the examples of embodiment which follow, given by way of indication and not limitation in support of the appended figures.

• The figure 1 is an exploded view of the components of the mold to obtain a staircase free of central shaft according to the method of the invention.
• The picture 2 is a view analogous to figure 1 but of a staircase with central shaft.
• The picture 3 is a schematic representation in perspective of the lower mold for the realization of a staircase with a central shaft, whose figure 4 is a detail view and the figure 5 a sagittal section view.
• The figure 6 is a schematic representation in perspective of the lower mold for making the staircase with a central shaft, showing the stiffeners, if any, implemented within the framework of the method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The figure 1 therefore represents the fundamental elements for the realization of a one-piece staircase free of any central shaft, and in this case a bench staircase.

More precisely, the reference (1) designates the staircase resulting from the implementation of the method according to the invention, the reference (2) designates the lower mold and the references (3) and (4) designate two sectors of the cover or upper mould, intended to cooperate with the lower mold (2)..

As already indicated above, the method of the invention aims to produce a one-piece concrete staircase in position. For this purpose, the lower mold is fixed to the ground to avoid lifting during the demoulding phase of the stairs. This lower mold, typically made of steel, has in this case a flat and inclined bottom (5), since both the underside of the staircase has no specific technical function.

On the other hand, the lower mold (2) is intended to receive a cover or upper mold (3) and (4), also made of steel, the shape of which corresponds specifically to the different steps and risers of the staircase to be produced.

The upper cover (3) and (4) is therefore intended to be positioned on the lower mold (2), the latter being provided for this purpose with lateral cutouts (6) capable of receiving said upper cover (3) and ( 4) of corresponding shape, and this, as already said, to define the steps and risers. Typically, the fixing of the upper mold or cover on the lower mold is obtained by means of bolts and centering devices distributed along the central barrel on the one hand, and at the level of the external edges, by means of rods and nuts or even bolts associated with centralizers.

There is illustrated in this figure, and in particular at the level of the lower mold (2), through holes (7), positioned as desired on or under riser number 1, or at the level of the inner or outer edge of said mold. It should indeed be recalled that according to the invention, the concrete constituting the staircase (1) to be produced is injected from the base, therefore from the lower end of the mould.

This concrete is of the self-compacting type with a minimum class of SF2, that is to say, having a spread at the cones of Abrhams greater than 660 mm. The objective of such a relatively liquid concrete is, on the one hand, to allow its rise within the mould, in particular by implementing a peristaltic pump and, on the other hand, to reduce macro-bubbling, an element constituting one of the drawbacks of the methods of the prior art.

By way of example, such concrete has a gravel/sand ratio of between 0.5 and 1.4, typically close to 1. Cement, the main element of concrete, is dosed between 280 and 500 kg/m ³ of concrete, and typically close to 340 kg/m ³ . The water/equivalent binder ratio within the meaning of the EN206 standard is 0.3 to 0.6, typically close to 0.5.

Such concrete is also likely to receive additives within the meaning of the EN206 standard of the dairy type, metakaolin, fly ash, limestone filler, to complete the grain size, optimize costs or mechanical performance.

Advantageously, adjuvants are incorporated into the mixture: a superplasticizer or water reducer with a dosage close to 3 l/m ³ . A superplasticizer thus added can be of the high water reduction type, such as a polycarboxylate.

According to an advantageous characteristic, prior to the injection of concrete into the mold consisting of the elements (2), (3) and (4), the internal walls of the said mold are coated with a release oil applied for example with a sprayer. Such a release oil can consist of a solvent (for example marketed under the reference Grace wax E-31), a synthetic oil (for example marketed under the reference Chryso Dem Oléo 64), a vegetable oil or plant-based (for example marketed under the reference Grace Décobio S33).

According to yet another advantageous characteristic of the invention, the internal face of the covers (3) and (4) is coated, in particular by spraying, that is to say including at the level of what will be the step and the riser of the staircase, a mortar intended, as already said, in particular to trap any bubbles resulting from the concrete between said mortar and the concrete, in addition to promoting the external appearance of the steps.

• ▪ entre 5 à 50 % en masse de ciment ;
• ▪ entre 40 et 95 % en masse d'agrégats fins, typiquement inférieurs à 1 millimètre ;
• ▪ et un mélange d'adjuvants comprenant un super-plastifiant et/ou des accélérateurs ou retardateurs de prise en masse du béton et/ou des agents anti-retrait.

This mortar includes:

• ▪ between 5 and 50% by mass of cement;
• ▪ between 40 and 95% by mass of fine aggregates, typically less than 1 millimetre;
• ▪ and a mixture of adjuvants comprising a super-plasticizer and/or accelerators or retarders of concrete setting and/or anti-shrinkage agents.

In this respect, it is specified that the mold release oil having previously coated the internal face of said covers (3) and (4) is chosen so that the mortar adheres to the cover when fresh, but not to the hardened state. It may be an oil of the type of those previously described. This oil is selected precisely following the performance of various tests, during which we observe any detachment of the mortar from the mold and the phenomena of micro-bubbling or stains that may appear on the facings. The selection of the oil therefore depends on the locally available materials for making the mortar, the concrete and the equipment used for the application (spraying, scouring or not).

Due to the method of making a one-piece concrete staircase of the invention, cast in position, it is possible with the same lower mold (2) to be able to make stairs with a step height slightly different from the bottom of the mold, by choosing the appropriate covers (3) and (4). These variations in relation to the base height of the mold are generally established with a difference of 2 to 4 millimetres, in order to limit the extra thickness of the trays or the staircase bench at the level of its foot or its head. In other words, with the same lower mould, it becomes possible to make stairs with different step heights, by adapting the upper cover.

We represented, in relation to the figure 2 , an exploded view similar to the figure 1 , but this time for the realization of a one-piece staircase provided with a central shaft (8). In this configuration, the lower mold (2) comprises, in its central position, a column part, intended to cooperate with the upper covers, each provided with a complementary column part with that of the lower mold, in order to define a cylinder (in this case with a circular base) capable of defining the shaft or central core.

In addition, in the context of the production of such a staircase with a central shaft, the injection of concrete is always carried out at the lower level, but through the column intended to constitute the central shaft. For this purpose, the elements defining the column are pierced with through slots (9), allowing the concrete undergoing the ascent within the column, to be distributed in the volume defined between the upper cover and the lower mould, and thus create and build the steps and risers of the desired staircase. These lights have been schematized on the figures 3 to 5 . They are of size, and in particular of height, which are substantially less than the risers.

We have illustrated, within the figure 6 , the implementation when required, of stiffening elements (10), in this case both horizontal and vertical.

The main function of these stiffeners is to take up the thrust of the concrete resulting from the injection, in particular at the lower level. This thrust of the concrete is exerted perpendicular to all the surfaces, and it may prove necessary to block the vertical but also the horizontal forces, in order to avoid in particular a rotation of the cowls during the injection of the concrete.

These stiffeners may consist of tubular reinforcement bars, in particular of square cross-section, arranged on the upper cover, vertical to each of the risers, the diagonals of the square sections being oriented horizontally and vertically respectively. The stiffeners can also result from an assembly of folded and welded sheets. These stiffeners can be fixed with a rod / nut clamp, by means of a profile notched for this purpose, allowing a certain flexibility in the initial positioning of the cover, and the inclination of the profiles at 45° allows a good recovery of the horizontal forces and vertical. The tightening then tends to position the cover in the optimum position.

It can also be made with a nut and centering device, ensuring better repeatability than the rod/nut system, but on the other hand less tolerant of initial positioning deviations.

The invention relates to one-piece concrete stairs cast in position obtained by the method of the invention. If the mechanical properties of these stairs do not differ or little from the stairs made with traditional production processes, on the other hand they have a very clearly improved state of finish, due to the absence or quasi-absence of micro-bubbling coming from bursting. on the upper surface of the steps, resulting in a considerable gain in terms of construction time.

At the same time, due to the method of making these stairs, i.e. integral molding (lower face and upper face), the conditions for making these stairs are much more comfortable for the operators and, above all, allow significant increase in safety, since the operator no longer has to spread the concrete in a precarious position or smooth it. Any final finishing operations, when they may prove necessary, are carried out on a staircase whose concrete has solidified and therefore hardened, considerably facilitating these operations.

Claims (12)

1. Method used for producing monobloc concrete staircases in situ using a closed mould comprising a lower mould (2) and an upper mould or cover (3, 4), defining between each other a volume designed for filling with concrete, consisting in:

   ▪ Attaching and installing the lower mould (2) in an operational position, that is, directly on the site in consideration;

   ▪ Positioning the upper mould or cover (3, 4) opposite the said lower mould (2) and attaching it to the said lower mould;

   ▪ Injecting concrete into the volume formed by the two respectively lower mould (2) and upper mould (3,4) until the said volume is full;

   Characterised:

   ▪ in that the type of concrete is of the self-levelling type, and injected from the lower base of the volume formed by the two moulds, respectively the lower and upper moulds;

   ▪ and in that, after the concrete is fully set, the upper mould and lower mould are released and the staircase thus built is turned out in its final location.
2. Method used for producing monobloc concrete staircase with a fine or central core in situ using a closed mould comprising a lower mould (2) and an upper mould or cover (3, 4), defining between each other a volume designed for filling with concrete, consisting in:

   ▪ attaching and installing the lower mould (2) in an operational position, that is, directly on the site in consideration;

   ▪ positioning the upper mould or cover (3, 4) opposite the said lower mould (2) and attaching it to the said lower mould;

   ▪ injecting concrete into the volume formed by the two respectively lower mould (2) and upper mould (3,4) until the said volume is full;

   Characterised:

   ▪ in that the type of concrete is of the self-levelling type, and injected from the lower base of the column designed to form the end or central core, the said column connecting to the volume defined by the two respectively lower and upper moulds, by means of through holes (9),

   ▪ and in that, after the concrete has set in full, the upper mould and lower mould are released, and the staircase thus built is turned out in its final location.
3. Method used for producing monobloc concrete staircases according to one of claims 1 and 2, and wherein the upper mould or cover (3,4) consists of several sectors
4. Method used for producing monobloc concrete staircases according to one of claims 1 to 3, wherein, before the injection of self-levelling concrete into the volume defined by the two moulds, the inner face of the upper mould or cover (3,4), that is the surface that will define the shapes of the steps and risers of the future staircase with a mortar, in particular by spraying.
5. Method used for producing monobloc concrete staircases according to claim 4, in which the mortar comprises:

   ▪ between 5 and 50% cement by weight;

   ▪ between 40 and 95% fine aggregates by weight;

   ▪ a mixture of admixtures chosen from the group comprising super-plasticisers, setting accelerators, setting retardants and anti-shrinkage agents.
6. Method used for producing monobloc concrete staircases according to one of claims 4 and 5 in which the inner wall of cover (3, 4) is coated with mortar before the assembly of said cover on lower mould (2).
7. Method used for producing monobloc concrete staircases according to one of claims 4 to 6 in which the mortar is spray cast onto the inner surface of cover (3, 4).
8. Method used for producing monobloc concrete staircases according to one of claims 1 to 7, in which the lower mould (2) and higher mould or cover (4,4) are previously coated, on the inside, that is the side intended to receive the self-levelling concrete, with a component that is liable to favour mould release, and more particularly mould release oil.
9. Method used for producing monobloc concrete staircases according to claim 8, in which, when cover (3, 4) is coated with mortar on the inside according to one of the claims 4 to 7, the mould release oil is already applied to the said inside surface.
10. Method used for producing monobloc concrete staircases according to one of claims 1 to 9 in which the self-levelling concrete used belongs to Class SF2 or class SF3.
11. Method used for producing monobloc concrete staircases according to one of claims 1 to 10, in which stiffeners (10) are incorporated into and attached to lower mould (2) before the upper mould or cover (3, 4) is put in place.
12. Monobloc concrete staircase obtained by the use of the method according to one of claims 1 to 11.

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