Formwork for concrete pillar

Abstract

 Formwork for a thermally insulated concrete pillar, comprising a casing (12) of predetermined thickness, made of rigid polyurethane foam PUR/PIR, which is manufactured in a single molding piece, having an internal surface (14) provided to receive a concrete casting, wherein said casing (12) is destined to remain permanently associated to said pillar, after hardening of concrete, for achieving thermal insulation.

Description

Technical field

[0001] The present invention generally relates to the construction field, and more in particular to a formwork for the fabrication of thermally insulated concrete pillars.

[0002] The present invention refers also to a method for fabrication of said formwork.

Known art

[0003] In particular in the construction sector, the widespread use of thermal insulating panels made of plastic foam material, in particular extruded polystyrene foam is known, for thermally insulating brick walls, and also for insulating concrete pillars, in order to reduce the heat dispersion and energy consumption for heating purposes of such structures, as is required by current regulations.

[0004] In particular, the need for thermal insulation of a concrete pillar is particularly important in this sector, since in normal brick wall structures, which are usually composed of brick walls and pillars, at each pillar higher thermal losses are recorded with respect to adjacent or neighboring walls, of same structure. In other words, at the pillar, a so called thermal bridge is formed, which represents a weak point for thermal insulation of wall structure.

[0005] Normally, a thermally insulated pillar is fabricated using a wooden or iron formwork, which is prepared on building site around an iron rod framework, and in which concrete is cast; it is composed of four rigid wooden or iron plates, which are disposed in order to form a parallelepiped, and are fixed at four corners, and a panel, or slab, of extruded polystyrene foam, with low thermal conductivity.

[0006] In particular, the panel is glued at pillar, after concrete hardening, and plates removal, on the pillar side facing the structure's external side.

[0007] Although the known formwork is advantageous under various respects, generally solving the problem, it has drawbacks, which are still unsolved.

[0008] The primary drawback is that thermal insulation obtained by said extruded polystyrene panel is not completely acceptable, since, at pillar, thermal dispersion is still measured, and this dispersion is not completely neglectable, with respect to adjacent walls. In other words, applying said panel does not solve the thermal bridge problem completely.

[0009] A further drawback of known art is that it requires multiple steps in order to fabricate the formwork, install the same, remove the wooden plates, and finally secure the thermal insulating plastic panel.

[0010] The technical problem to be solved by the present invention is therefore to create a formwork for a thermally insulated concrete pillar, which overcomes above said drawbacks with respect to the known art, and in particular which allows for a sufficient thermal insulation, and which may be installed with a low number of parts and low number of operating steps.

Summary of the invention

[0011] This technical problem is solved by a formwork for a thermally insulated pillar, comprising a casing of predetermined thickness, made of rigid polyurethane foam PUR/PIR, which is manufactured in a single molding piece, having an internal surface provided to receive a concrete casting, wherein said casing is destined to remain permanently associated to said pillar, after hardening of concrete, for achieving thermal insulation.

[0012] In other words, the formwork according to the invention is a prefabricated monolithic product, which lacks rigid iron or wooden plates, and has an internal surface completely continuous and without junctions. '

[0013] Said casing is generally formed by a tubular body or jacket having side walls, which, depending on the pillar's section to be obtained, have a rectangular, square or circular cross section. In other words, the casing has walls having an internal surface complementarily formed with respect to the pillar to be obtained, and an external surface, which, after concrete casting, and preferably following a successive cement coating, provides the external surface for finished pillar.

[0014] The rigid polyurethane PUR/PIR foam, also called rigid PUR/PIR foam, belongs to a well known family of materials having high thermal insulation characteristics, high mechanical strength and long life ("Federation of European Rigid Polyurethane Foam Associations, report n. 1, October 2006 "Thermal insulations materials made of rigid polyurethane foam PUR/PIR, Av. E. Van Nieuwenhuyse).

[0015] In particular ("Handbook of Polimeric Foams and Foam Technology"/ed. By D.KLEMPNER and K.C.FRISCH - MUNICH; VIENNA; NEW YORK; BARCELLONA: HANSER, 1991"), rigid polyurethane foam PUR is produced by polyaddition reaction of polyfunctional isocyanates (OCN-R-NCO) and polyhydroxy compounds (HO-R'-OH) or polyols, which produce a urethane bond OCN-R-(NH-CO-O)-R'-OH, in presence of catalyzers and expanding agents.

[0016] As also known from above said literature, with certain catalyzers, the isocyanates may react among each other, by cyclotrimerization reaction, forming macromolecules with isocyanurate structure (polyisocyanurate = PIR). Since the reactions among isocyanates and polyols or isocyanates may run simultaneously, it is also possible to obtain, in the same product, macromolecules containing urethane bonds (PUR) and, in a predetermined percentage, also isocyanurate bonds (PIR); the "rigid polyurethane foam PUR/PIR" may therefore foresee the presence of polyisocyanurate PIR macromolecules, as well as of polyurethane PUR. In order to provide a rigid polyurethane foam with a polyisocyanurate foam PIR, it is necessary to increase the isocyanate quantity with respect to the polyol mix, in order to achieve cyclotrimerization, in addition to polyaddition reaction.

[0017] Within the present invention, said casing is made of rigid polyurethane foam PUR/PIR with an optional predetermined percentage of polyisocyanurate, provided by cyclotrimerization. The casing is fabricated by means of injection, or casting, in a predefined mold of isocyanates and polyols, which is of common use throughout the construction sector, for producing rigid polyurethane foam PUR/PIR, and which are for example cited in above said publications.

[0018] In a preferred embodiment, MDI based isocyanates (methyl diphenyl diisocyanates, also known as difenilmethane-diisocyanate or diisocyanate-difenilmethane) and a mix of polyols like polyester or polyether are used.

[0019] Such a mix of polyols like polyester and polyether also contains water, which takes part in the polymerization reaction (water reacts with polyisocyanate forming polyurea and carbon dioxide, which acts like a co-foaming agent, but may also act as a single foaming agent); n-pentane as expanding gas; glycerin, as a wetting agent, Kitane, which is a solvent for expanding gas/pentane; TCPP, as a flame retardant; silicone as a surfactant; and potassium octoate, and amino ester of formic acid, i.e. reaction activators.

[0020] Alternatively, the expanding gases and stabilizers may be added to isocyanate reactant.

[0021] In said preferred embodiment, in order to produce a foam of polyisocyanurate PIR, it is necessary to increase the quantity of isocyanate MDI with respect to the polyol mix of the polyester and polyether type in order to achieve trimerization, with respect to polyaddition reaction.

[0022] As said above, rigid polyurethane foam PUR/PIR provides a high mechanical strength.

[0023] To this regard, it is to be noted that the wall thickness of tubular body and rigidity of rigid polyurethane foam PUR/PIR are chosen so that they ensure the required thermal insulation and rigidity to resist the forces applied during the concrete casting, with optional help from reinforcing frameworks.

[0024] Preferably, the wall thickness is greater or equal to 2,5 cm. In particular, by providing a thickness greater than 2,5 cm, an even more efficient thermal insulation may be achieved.

[0025] More preferably, the tubular body is made of rigid polyurethane foam PUR/PIR with density ranging from 30 to circa 80 kg/m³.

[0026] In an embodiment, the tubular body is made of rigid polyurethane foam PUR/PIR with density ranging from approx. 50 to approx. 80 kg/m³, and thickness greater or equal to 2,5 cm.

[0027] In another preferred embodiment, the tubular body is made of rigid polyurethane foam PUR/PIR with density ranging from approx. 30 to approx. 50 kg/m³ and thickness greater or equal to 2,5 cm. In this latter embodiment, considering the comparatively low density, a stiffening of the formwork is provided, by stiffening elements, which may be inserted into the casing walls, or outside the casing, wherein they may be removed, after concrete hardening.

[0028] In an embodiment, the stiffening is provided by a framework, which is embedded into the casing walls.

[0029] Preferably, the framework comprises metal grids.

[0030] Alternatively, the framework is made of metal rod-like inserts.

[0031] In an alternative embodiment, the framework also comprises synthetic reinforcing fibers.

[0032] All reinforcements are particularly advantageous in pillars having large sections, in which the concrete casting pressure is very high.

[0033] Preferably, the formwork, after concrete casting, is covered by a concrete and sand coating or other coating layer, which is put on the external casing surface.

[0034] Above said technical problem is moreover solved by a method for fabricating a formwork for a thermally insulated concrete pillar, the formwork comprising a casing having walls of predetermined thickness, with an internal surface for receiving a concrete cast, and an external surface providing the external pillar surface, in which the method comprises following steps:

• preparing doses of reactants for polymerization reaction of rigid polyurethane foam PUR/PIR of predetermined density,
• pouring doses of reactants into the mold and mixing,
• waiting until polymerization completion and consolidation of rigid polyurethane foam PUR/PIR,
• removing the mold, in order to obtain a monolithic formwork made of rigid polyurethane foam PUR/PIR.

[0035] In particular, the reactant's doses are chosen in order to preferably produce a density between approx 30 and 80 kg/m³.

[0036] In an embodiment, the reactants comprise a first isocyanate (MDI) based reactant, which is mixed into the mold with a second reactant comprising a liquid mix based on polyols of the polyester and polyether type, including expanding gases and water.

[0037] Preferably, the form is comprised of a first hollow mold of predetermined size and shape being complementary to the external casing surface to be obtained, and a second smaller sized mold, which is inserted inside the first mold, having a shape and size conjugated to the internal surface of casing, in which the interstice between the two molds correspond to the shape and final thickness of casing walls.

[0038] Preferably, prior to reactant pouring, reinforcing elements are disposed inside the form, in order to be included into the thickness of rigid polyurethane foam PUR/PIR casing.

[0039] Preferably, such reinforcing elements are provided inside the form with distancing and supporting elements, also in rigid polyurethane foam PUR/PIR.

[0040] Preferably, prior to reactant pouring, the form is covered with a separating agent, such as wax, and other materials, such as sand, which cover the external form surface.

[0041] More preferably, after polyurethane foam hardening, the method comprises temporary fixing of additional reinforcing elements on external surface of formwork. These additional elements have to simplify the positioning in-situ on building site of formwork prior to concrete casting, acting like mechanical securing elements, for aligning the formwork.

[0042] Further characteristics and advantages of formwork according to the invention and corresponding fabrication method will become apparent from following description of an illustrative non limiting embodiment, with reference to accompanying drawings.

Brief description of drawings

[0043] 

Fig. 1 schematically shows a perspective view of formwork according to the invention,

Fig. 2 schematically shows a perspective view of formwork of fig. 1, partially sectioned,

Fig. 3 schematically shows a perspective view of formwork of fig. 1, during a fabrication step of pillar.

Detailed description

[0044] With reference to attached figures, reference numeral 10 generally indicates a formwork for a thermally insulated pillar, or column, according to present invention, which has to remain permanently associated and adhering to pillar to be fabricated.

[0045] Formwork 10 comprises a casing 12 of rigid polyurethane foam PUR/PIR, comprising a tubular body or jacket having walls of predetermined thickness, of 2,5 cm, in this example.

[0046] The exemplary tubular body, with X-X axis, has a polygonal cross section, in particular a rectangular section, but may also be of circular or similar section, or may even have a mixed line shape, according to requirements. Anyway, it has axially extending corners 13, or generating lines, in case of circular or similar section.

[0047] The tubular body has an internal surface 14, for receiving a concrete cast for pillar, and an external surface 15, which, following concrete hardening and preferably a coating step, provides the external surface of pillar.

[0048] The rigid polyurethane foam of casing 12 has a density equal to 70 kg/m³, which is able to withstand the force of concrete casting.

[0049] In the solution shown, the formwork 10 is reinforced, i.e. it comprises a reinforcing framework 17, which is included inside the wall thickness of casing 12.

[0050] The framework 17 comprises a first grid 16 of synthetic fibers, in this example starched glass fibers, and a second metal grid 18. Grids 16, 18 have generally tubular shape, in this example a rectangular cross section, wherein the cross section of one grid 16 is smaller than the other 18, and wherein the grids are integrated in a coaxial position inside the wall thickness of casing 12.

[0051] In particular, first grid 16, which is the internal one, has a smaller mesh (1 cm x 1 cm) with respect to second metal mesh 18, which is the external one, and has a wider mesh (for example 10 cm x 10 cm).

[0052] Formwork 10 is completed by removable reinforcing elements, associated to the external surface of casing 12.

[0053] Such reinforcing elements comprise, in the example shown, angular profiles 22, inverted U profiles 23, and metal hoops 25 for locking the angular profiles 22.

[0054] In particular, each angular profile 22 is put at a respective corner 13, along the same.

[0055] The inverted U profiles 23 are instead positioned with the U backside facing the casing 12, and the concavity oriented towards the outside, in order to internally receive the metal hoops 25.

[0056] The inverted U profiles 23 and the metal hoops 25 form hooping means for casing 12 and angular profiles 22, and are moreover distributed along the longitudinal extension of formwork 10, with a certain pitch depending on the formwork's length, which is chosen in order to provide at least four hoopings along the entire length.

[0057] Such external reinforcing elements are meant to simplify the positioning of formwork prior to concrete casting, in that they act as mechanical securing elements for aligning the formwork.

[0058] Recesses 30 are moreover provided, which are composed of portions opposed with respect to casing top 12, for attaching the formwork 10, on building site during installation and construction step of pillar, as illustrated in the following.

[0059] Formwork 10 is fabricated as follows.

[0060] Casing 12 made of rigid polyurethane foam PUR/PIR is provided by molding, in this example, by casting or injecting polyurethane polymerization reactants into a mold which is a negative, as regards shape and wall thickness of casing 12 to be produced.

[0061] The polymerization reaction is achieved according to conventional procedures known in the art. In particular, the reactants for polymerizing rigid polyurethane foam are dosed, and successively injected into the mold, for obtaining a predetermined polyurethane density.

[0062] In the example shown, reactants comprise a first reactant based on isocyanate (MDI), which is injected and mixed into the mold with a second reactant comprising a liquid mix based on polyols of the polyester and polyether type including also expanding gasses and water.

[0063] In particular, in order to facilitate preparation of casing, it's possible to use prepared doses of commercial reactants, which allow to achieve desired density, in this example 70 kg/m³, of final rigid polyurethane foam.

[0064] In particular, the mix of polyols and polyether/polyester also contains water, which participates in the polymerization reaction; n-pentane as an expanding gas; glycerin as a wetting agent; Kitane, which is a solvent for expanding gas/pentane; TCPP as a flame-retardant; silicone as a surfactant; and reaction activators. The reaction also yields CO₂ which takes part in the foam expansion.

[0065] Alternatively, also carbon dioxide is added as an expanding gas, or a mix of same with expanding gases derived from oil, such as alcanes (n-pentane and iso-pentane) or synthesis products of same, like for example fluoro-alcanes (R365, R245) or chlorofluorocarbons.

[0066] As said, the reactants are poured into a mold of negative shape and thickness corresponding to the walls of casing 12 to be produced.

[0067] In this case, since the casing is a tubular body, with a rectangular section, the mold is comprised of two molds of rectangular section, a first larger hollow mold, and a second smaller mold, which is coaxially inserted into the first mold.

[0068] More in particular, the first mold is sized and shaped in conjugated way with respect to the external surface 15 of casing 12 to be formed, and the second mold has a shape and size, which are conjugate to those of the internal surface 14 of casing 12, so that the interstice formed between the molds have a negative shape and thickness corresponding to walls of casing 12.

[0069] Prior to pouring the reactants, in said interstice the reinforcing grids 16, 18 are placed.

[0070] In particular, the grids 16, 18 are placed by positioning spacers of polyurethane foam between the internal and external molds.

[0071] Successively, the reactants are poured and mixed and the mould is closed by means of lids. Due to above said polymerization reaction, the polyurethane is formed, which expands until it occupies all the free space, and then hardens.

[0072] After a relatively short time, for example in the illustrated solution, 10-15 minutes after injection, the polymerization takes place, and this means that the reactant's mix hardens, forming rigid polyurethane foam PUR/PIR.

[0073] Then, the mold's lids are removed, and the casing 12 is extracted, which is ready to be completed by means of external reinforcements, comprised of above said U-shaped profiles 23, angular profiles 22, and metal hoops 25 for fixing said profiles.

[0074] Formwork 10 is therefore ready to be transported on building site and installed at the place where the pillar is to be erected. In particular, the formwork 10 is inserted on a conventional framework of iron rods 31a, the leveling of which is controlled, as known, by using wood boards 33, for successively receiving the concrete cast 31b, as shown in fig. 3. The concrete, which acts as a glue, adheres to the internal surface of casing 12, so that the casing is integrated with the pillar.

[0075] During all these steps, the formwork is raised and moved by suspending the same at the recesses 30.

[0076] After the concrete has been cast, and following a period of time required for hardening, the reinforcing profiles 22, 23, 25 are removed.

[0077] In order to demonstrate the efficiency of formwork 10 according to the invention, the correction of the thermal bridge has been verified.

[0078] For example, a pillar formed of masonry reinforced concrete with a thickness of 35 cm, comprised of cellular concrete blocks having a volumetric density of 600 kg/m³ and conductivity of 0,180 W/m²K has been tested (such a concrete is for instance known under the trademark of Gasbeton).

[0079] A 3,3 m wide wall is considered, wherein said non thermally insulated pillar is placed at the center of the wall, representing a typical brickwall structure. The wall was coated on both sides with concrete coating with a thickness of 1,5 cm.

[0080] The brickwall without the pillar has a thermal transmittance of 0,44 W/m²K, which is a good value. Such value decreases to 0,62 W/m²K at the non thermally insulated pillar.

[0081] If said pillar is externally insulated by an 5 cm extruded polystyrene foam slab, as those of above said known art, the performance worsens to 0,49 W/m²K.

[0082] On the contrary, if the pillar is insulated by a formwork of extruded polyurethane foam PUR/PIR according to the inventions, with a 2,5 cm thick wall casing, at the pillar a wall transmittance of 0,45 W/m²K is achieved, with a neglectable thermal bridge contribution (also called PSI, or lineic transmittance) of 0,01 W/mK.

[0083] The primary advantage of the present invention is the possibility to create formworks, even in greater quantities, in a simple way and using a reduced number of operating steps, which allow for efficient thermal insulation of finished pillar, and for a good thermal insulation of brickwall structure.

[0084] In other words, the primary advantage of the present invention is the fact that the formwork, besides the conventional function as container for the concrete cast, represents a permanent and efficient thermal insulation casing for the finished pillar.

[0085] A further advantage is the fact that the concrete pillar inside the formwork according to the invention has an invisible, perfectly continuous surface, without any irregularities and local interruptions, in other words, a perfect surface from the point of view of structural strength.

[0086] Moreover, all molding operations on formwork may take place on the manufacturing site, in order to provide factory ready formworks which do not require any assembling of parts on building site.

[0087] A further advantage is the fact that it's possible to vary the rigidity of rigid polyurethane foam PUR/PIR of the formwork according to specific needs, in order to withstand the stress brought about by the concrete cast, with the option of using reinforcing framworks.

[0088] A further advantage is the fact that the formwork may be manufactured in any format and size, in a simple, precise and fast way, for instance it may be manufactured according to following internal measures required by the market: cm 25 x cm 25 height cm 300, cm 25 x cm 30 height cm 300, cm 30 x cm 30, height cm 300, cm 30 x cm 40, height cm 300, cm 30 x cm 50, height cm 300, cm 40 x cm 40, height cm 300, cm 40 x cm 50, height cm 300, cm 50 x cm 50, height cm 300.

[0089] A further advantage is the fact that the formwork is a monolithic piece, without holes, keys and parts which have to be left inside and contacting concrete.

[0090] A further advantage is represented by reinforcing grids, one made of metal and the other made of glass fibers, which strengthen the structure without excessively increasing the thickness of container walls.

[0091] In particular, the grid with the larger mesh has to stiffen the container, whereas the smaller mesh has the task of holding together the casing in a compact way, even in the event of occasional casing damages, which may take place on building site during the formwork installation, due for example to sudden blows or impacts.

[0092] Obviously, the skilled in the art, in order to meet contingent and specific needs, may introduce various modifications and changes to above said formwork and to the method for its manufacture, which all fall inside the protection scope of the invention, as defined by following claims.

Claims

1. Formwork for thermally insulated concrete pillar, characterized in that it comprises a casing (12) of predetermined thickness, made of rigid polyurethane foam PUR/PIR, which is manufactured in a single molding piece, having an internal surface (14) provided to receive a concrete casting, wherein said casing (12) is destined to remain permanently associated to said pillar, after hardening of concrete, for achieving thermal insulation.

2. Formwork according to claim 1, characterized in that the casing (12) wall's thickness is greater or equal 2,5 cm.

3. Formwork according to claim 1 or 2, characterized in that it comprises a reinforcing framework (17) embedded into the walls of casing (12).

4. Formwork according to any of claims 1 to 3, characterized in that the rigid polyurethane foam PUR/PIR has a density in the range between approx. 30 and approx. 80 kg/m³.

5. Formwork according to claim 3, characterized in that rigid polyurethane foam PUR/PIR has a density between approx. 30 and approx. 50 kg/m³.

6. Formwork according to any of preceding claims, characterized in that it comprises reinforcing elements (22, 23, 25), which are removably secured to an external surface of walls of casing (12), opposed to said internal surface.

7. Formwork according to any of preceding claims, characterized in that the casing comprises a tubular body with a predetermined axis (X-X), having a polygonal cross section with corners (13), which extend in an axial direction.

8. Formwork according to claim 7, characterized in that it comprises two coaxial tubular grids (16, 18), which are embedded in the thickness of walls of casing (12), which act as reinforcing elements.

9. Formwork according to claim 8, characterized in that the two grids comprise a first internal grid (16) made of synthetic fibers and a second external grid (18) made of metal.

10. Formwork according to claim 8 or 9, characterized in that it comprises angular profiles (22) which are placed at respective corners (13) along the same, and inverted U shaped profiles (23) and metal hoops (25) which are arranged as hoopings around the casing (12).

11. Concrete pillar, characterized in that it comprises a thermal insulating reinforcing jacket comprising a formwork according to any of preceding claims 1 to 10.

12. Method for manufacturing a formwork for a thermally insulated concrete pillar, the formwork comprising a casing (12), having walls of predetermined thickness, an internal surface (14) destined for receiving a concrete casting, and an external surface (15) destined to represent the external surface of pillar, characterized in that it comprises the following steps:

- preparing doses of reactants for polymerization reaction of rigid polyurethane foam PUR/PIR of predetermined density,

- providing a mold with a negative shape with respect to internal (14) and external (15) surfaces and corresponding to a thickness of walls of casing (12) to be manufactured,

- pouring the doses of reactants into the mold and mixing,

- waiting until polymerization completion and consolidation of rigid polyurethane foam PUR/PIR,

- removing the mold, in order to obtain a monolithic formwork made of rigid polyurethane foam PUR/PIR.

13. Method according to claim 12, characterized in that the reactant doses are chosen in order to achieve a density between approx. 30 and approx 80 kg/m³.

14. Method according to claim 12 or 13, characterized in that the mold is comprised of a first hollow mold of predetermined size and shape, which correspond to those of the external surface (15) of casing (129 to be manufactured, and a second mold smaller than the first, which is inserted into the first mold, and is shaped and sized in order to correspond to the internal surface (14) of casing (12), wherein the interstice between the first and second mold corresponds to wall thickness of casing (12).

15. Method according to any of claims 12 to 14, characterized in that, prior to pouring the reactants, reinforcing elements, to be embedded inside the wall thickness of casing (12), are placed into the mold.

Drawing