EP2107180A2

EP2107180A2 - Prestressed concrete component, suitable for providing outdoor walkable surfaces and for cladding walls, and associated production method

Info

Publication number: EP2107180A2
Application number: EP09157215A
Authority: EP
Inventors: Riccardo Valente
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-04-04
Filing date: 2009-04-02
Publication date: 2009-10-07
Also published as: ITUD20080074A1; EP2107180A3

Abstract

A component (10) made of prestressed concrete, suitable for providing both outdoor walkable surfaces and wall cladding, comprising an elongated body (11) made of concrete, which has a base surface (13) and an upper surface (15), which is opposite and parallel to the base surface (13). The elongated body (11) has a length comprised between approximately 1 m and approximately 8 m, a constant width comprised between approximately 80 mm and approximately 300 mm, and a constant thickness, comprised between approximately 20 mm and approximately 60 mm. At least two reinforcement elements (12) are arranged within the elongated body (11), parallel to a longitudinal central axis (X), which is arranged in the direction of the length of the elongated body (11) The reinforcement elements (12) are arranged so as to be substantially mutually offset with respect to a central transverse plane (Y), which is parallel to the base surface (13).

Description

The present invention relates to an elongated prestressed concrete component suitable for providing both outdoor walkable surfaces and wall claddings. The prestressed concrete component according to the present invention has a length that is variable, according to the different construction requirements, from approximately 1 m to approximately 8 m, a width comprised between approximately 80 mm and approximately 300 mm, and a thickness comprised between approximately 20 mm and approximately 60 mm.
The prestressed concrete component according to the present invention has the external appearance of a classic wood stringer for outdoor use and has completely innovative aesthetic, mechanical, durability and cost characteristics; it is in fact a new product that is capable of replacing, in the various cases of application and with the best characteristics of strength and durability ensured by the concrete, traditional staves and boarding made of wood. The geometry of the cross-section, the variable length, the non-slip surface shaping with mass-pigmented finish, combined with an original and sophisticated use of prestress technology, make the prestressed concrete component according to the present invention particularly suitable for providing any walkable outdoor surface that is subjected to intense mechanical and chemical wear, as in the case of sidewalks, cycling and pedestrian paths, driveways, steps of indoor and outdoor stairs, pedestrian gangways, pavings of swimming pools, wharves, piers and quays, cladding of building faces, road and rail tunnels, noise abatement barriers, or others, that can be technologically and aesthetically compatible.
In all of the above-mentioned fields of application, the materials, essences and the products known and used, also with appreciable aesthetic results, are countless and range from more or less resistant wood essences to natural stones (granites and porphyries), from composite stones mixed with cement to self-locking clinker tiles. The materials, in the forms and formats offered by the market, do not provide solid assurances of durability if subjected to mechanical or chemical agents for prolonged periods. Consider simply the action of water and of the sun on wood, or the action of acid compounds (which are present in atmospheric precipitations) on natural stones, as well as the mechanical action that induces abrasion and flexural stresses. The problems linked to wear and maintenance have greatly limited the use of these materials in situations that are not suitable for them, whereas as regards flexural stresses the market offers products that can be used only with very small spans.
Components made of prestressed concrete are also known which are shaped like plates for providing drivable ramps, each of which has a length of approximately 3 m, a width of approximately 3.6 m and a thickness of approximately 230 mm, and are made of concrete reinforced by two rows of cables: one is aligned proximate to the upper surface and one is aligned proximate to the lower surface. However, these known components have the drawback of being very thick, too heavy and difficult to handle, normally with the aid of cranes.
A prestressed concrete component is also known which is shaped like a beam, has a length between 1 m and 30 m, a width between 300 mm and 1200 mm, a thickness between 80 mm and 120 mm and is reinforced with a row of steel bars or cables. Even this known component, which is adapted to be arranged on an underlying base layer to form the road surface or walkable surface, has the drawback of being rather thick and of not being self-supporting.
Moreover, the prestressing of this prestressed concrete component is obtained by embedding therein strands or bars made of steel or other elastic material which are pre-tensioned and are arranged symmetrically with respect to the central longitudinal plane that is perpendicular to its faces, i.e., on a same plane of the transverse cross-section.
Another drawback of this prestressed concrete component consists in that it enters easily an instability condition which causes its spontaneous torsional warping or flexural bending, which compromises its correct use.
The aim of the present invention is to provide a component for the building sector, made of prestressed concrete, of the elongated type, which is made of low-cost materials that are easily commercially available and at the same time is very thin and highly resistant, even to flexing.
Within this aim, an object of the present invention is to provide a component for the building sector made of prestressed concrete, of the elongated type, whose shape is durably stable over time, without having spontaneous flexural bendings or torsional warpings.
Another object of the present invention is to provide a method for providing a prestressed concrete component of the type described above easily and at low costs.
This aim and these and other objects, which will become better apparent hereinafter, are achieved by a prestressed concrete component, particularly adapted to provide walkable surfaces of outdoor spaces, comprising an elongated concrete body, which has a base surface and an upper surface, which is opposite and parallel to said base surface, wherein said elongated body has a length comprised between approximately 1 m and approximately 8 m, a width comprised between approximately 80 mm and approximately 300 mm, and wherein at least two reinforcement elements are arranged inside said elongated body, parallel to a longitudinal axis, which is arranged in the direction of the length of said elongated body, characterized in that said reinforcement elements, constituted for example by strands, bars or rods made of metal, are arranged so as to be substantially mutually offset with respect to a transverse plane that is parallel to said base surface, and said prestressed concrete component has a thickness comprised between approximately 20 mm and approximately 60 mm.
In a preferred embodiment, such prestressed concrete component has a thickness of approximately 30 mm.
In an alternative embodiment, such concrete component has constant width and/or thickness.
Further characteristics and advantages of the present invention will become better apparent from the following detailed description of a preferred but not exclusive embodiment thereof, illustrated by way of nonlimiting example in the accompanying drawings, wherein:

Figure 1 is a top view of a prestressed concrete component according to the invention, highlighting the antislip surface roughness and the longitudinal axes of the reinforcement elements;
Figure 2 is a side view of the prestressed concrete component of Figure 1;
Figure 3 is a sectional view of the prestressed concrete component, taken along the line III-III of Figure 1;
Figure 4 is a detailed cutout view of the prestressed concrete component, taken along the lines IV₁-IV₁ and IV₂-IV₂ of Figure 1;
Figure 5 is a detailed enlarged-scale sectional view of the prestressed concrete component, taken along the line III-III of Figure 1.

With reference to the figures, a prestressed concrete component 10 according to the present invention, particularly for providing both outdoor walkable surfaces and the cladding of walls, comprises an elongated body 11 which has a longitudinal axis X and is made of cement-like material. The component 10 can have a length up to approximately 8 m, an advantageously constant width comprised between approximately 80 mm and approximately 300 mm, and an advantageously constant thickness comprised between approximately 20 mm and approximately 60 mm and preferably of approximately 30 mm.
In the specific case, in Figure 1 the component 10 according to the present invention is shown, due to graphic requirements, with a length equal to 1 m. The transverse cross-section (Figure 3 and Figure 5) is greatly reduced with respect to the length, is substantially rectangular and is slightly flared towards a base surface 13 (on the right in Figure 5). An upper surface 15 (on the left in Figure 5) is parallel to the base surface 13 and is shaped so as to have rounded edges 14 and antislip grooves 18.
Advantageously, the elongated body 11 is constituted by a high-strength concrete mix (Rck 52.5 N/mm²), for example of the type I 52.5 R (manufactured by Buzzi UNICUN), or, in an environment-friendly version, of the TX ARIA gris type (CEM I 52.5 N CE - produced by ITALCEMENTI) and inert materials.
Such inert materials are of variable size, are highly resistant and frostproof, predominantly coarse, medium and fine sands (from 0.5 mm to 5 mm in diameter) obtained by crushing fine pebbles (diameter comprised between 0.5 mm and 10 mm).
Such mix can also comprise particular lightweight inert materials of a per se known type, which are capable of lightening it without compromising its mechanical performance.
The resulting mix is cast into formwork, made for example of steel, having a length comprised between approximately 1 m and approximately 8 m, with a rectangular cross-section and contoured appropriately to obtain the surface finish as well as the particular configurations of the lateral surfaces, depending on the intended use for the component 10.
Prestressing is obtained by pre-tensioning, for example by means of hydraulic jacks, of an elastic reinforcement frame constituted by two pairs of reinforcement elements, such as strands 12 (Figures 4 and 5), made of spring steel, each of which has a diameter comprised between 2 mm and 4 mm. In the continuation of the description, the term "strands" shall be used although it is understood that it is also possible to use, instead of strands, bars, rods or another suitable reinforcement element.
The strands 12 are arranged according to a geometry devised by the Applicant through long experimentation, so that the tensions induced in the resisting cross-section self-balance and consequently no bending along the longitudinal axis or instability and transverse torsion phenomena occur.
In particular, according to a characteristic of the present invention, the two pairs of strands 12 are arranged longitudinally, along longitudinal axes X₁ and X₂ (Figure 4), which are symmetrical with respect to the central longitudinal axis X of the transverse cross-section, whereas with respect to the resisting cross-section (Figure 5) they are arranged on planes Y₁ and Y₂ which are substantially equidistant from a central transverse plane Y, which is parallel to the base surface 13.
It should be noted that such a cross-section, with the dimensions described above, would immediately enter an instability condition with consequent collapse if the prestress frame, i.e., the strands 12, were arranged on a same plane of the transverse cross-section, as occurs in the background art.
The stability of the component 10 with respect to torsional deformations and longitudinal inflections caused by prestressing forces, as well as the longitudinal and transverse horizontal linearity, are achieved by means of an axial offset, or eccentricity "e", of the position of the strands 12 in the transverse cross-section. This eccentricity "e" between the two strands 12 in the transverse cross-section (Figure 5) is comprised advantageously between 6 mm and 20 mm.
Moreover, the eccentricity "e" constitutes a particular characteristic of the component 10 and allows to obtain the exceptional characteristics of slenderness, stability, strength and low cost. The value of the eccentricity "e" is selected as a function of the prestressing tension, of the strength characteristics adopted for the mix and of the geometry of the transverse cross-section adopted.
The aesthetic particularities, also the fruit of technological and design refinement that required years of studies and prototyping, contribute to complete the original identity of the component 10 according to the present invention.
The concrete mix with which the body 11 of the component 10 is provided can in fact have various treatments of the outer surface finish layer and can be provided with a finish in pigmented cement grout, or can receive the addition of pigments of a different color, colors which are close to wood essences, or more lively colors, depending on the end user's choice.
As regards the method for providing the component 10, the mix, after being cast into the formwork and reinforced with the strands 12, is vibrated for a time comprised between 2 and 5 minutes and is left to cure with temperatures from 50°C to 80°C for a time comprised between 210 minutes and 300 minutes, with normal refinements, which are per se known, for avoiding microcracks.
A test on various components 10 manufactured according to the method described above, each one 500 mm long, rested at its ends with a theoretical calculation span of 420 mm, loaded at the center with a concentrated load, recorded breaking loads of approximately 1600 N and flexural stresses in prestressed concrete comprised between 2400 N/mm² and 3200 N/mm².
The insertion of the prestressed reinforcement frame, constituted by the strands 12 and arranged as specified above, gives, in addition to the ultimate bearing capacity, a considerable elastic behavior, with deflections on the order of approximately 2 cm prior to the yielding of the strands 12 and to the collapse of the prestressed concrete.
Shapes and cross-sections that are geometrically similar to the one described here and having the structural and finish characteristics expressed in the appended claims, even with modification of the number and cross-section of the reinforcement elements, are all within the protective scope defined by the appended claims. These characteristics, as described above, are the result of many years of experimentation in the field of thin prestressed structures conducted by the Applicant, and it is only by means of the specific particle sizes of the mix, the type of concrete and curing, the eccentricity and the pre-traction tension of the reinforcement elements with respect to the dimensions of the transverse cross-section that a component of such an order of length and of such exceptionally thin cross-section, which has uniformity of mechanical performance and of stability with respect to stresses induced by prestressing is obtained.
It is clear, in any case, that the prestressed concrete component 10 described so far is susceptible of modifications and/or additions of components without thereby abandoning the scope of the protection of the appended claims. For example, the number of strands 12 can be more than two.
With reference to Figure 5, it is also evident that an arrangement of the strands 12 that is symmetrical along the central transverse plane Y with respect to the one shown is substantially equivalent thereto.
The prestressed concrete component according to the present invention combines the aesthetic characteristics of wood (in the various colors) with the durability of concrete, with the considerable surface endurance of such material and with the compactness and flexural performance that derive from a special prestressing technology. This entails the following advantages:

light weight and low cost in relation to the technical characteristics;
no need for surface maintenance;
durability of the concrete mix compacted by prestressing and consequent protection of the reinforcement even in humid or aggressive environments;
considerable length of such component in relation to the slenderness and extremely limited transverse cross-section, particularly the thickness;
ease of installation with cement adhesives or coupling systems;
possibility of installation even on underlying structures according to the double-support static diagram;
easy cutting without losing the properties that derive from prestressing;
strength and endurance of the final product;
no limitation in the decorative details and in color choices.

Advantageously, each one of such reinforcement elements is as long as the entire length of the elongated body and is made of elastic material, such as iron, steel, or other metallic materials, or elastic plastics with high tensile strength.
The cement material of which the elongated body is made is advantageously concrete, even of the so-called lightweight type, which has a relative density comprised between approximately 18 kN/m³ and approximately 25 kN/m³.
It is also clear that although the present invention has been described with reference to a specific example, a person skilled in the art may certainly provide other equivalent embodiments of prestressed concrete components that have the characteristics expressed in the appended claims, all of said embodiments falling therefore within the protective scope defined by the appended claims.
The disclosures in Italian Patent Application No. UD2008A000074 from which this application claims priority are incorporated herein by reference.
Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

A component (10) made of prestressed concrete, suitable for providing both outdoor walkable surfaces and wall cladding, comprising an elongated body (11) made of concrete, which has a base surface (13) and an upper surface (15), which is opposite and parallel to said base surface (13), wherein said elongated body (11) has a length comprised between approximately 1 m and approximately 8 m, a width comprised between approximately 80 mm and approximately 300 mm, and wherein at least two reinforcement elements (12) are arranged within said elongated body (11), parallel to a longitudinal central axis (X), which is arranged in the direction of the length of said elongated body (11), characterized in that said reinforcement elements (12) are arranged so as to be substantially mutually offset with respect to a central transverse plane (Y), which is parallel to said base surface (13), and in that said element (10) has a thickness comprised between approximately 20 mm and approximately 60 mm.
The prestressed concrete component according to claim 1, characterized in that it has a thickness of approximately 30 mm.
The prestressed concrete component according to claim 1 or 2, characterized in that it has a constant thickness and/or width.
The prestressed concrete component according to one or more of the preceding claims, characterized in that said reinforcement elements comprise strands, bars or rods (12) made of spring steel, each of which has a diameter comprised between 2 mm and 4 mm.
The prestressed concrete component according to one or more of the preceding claims, characterized in that said reinforcement elements comprise two pairs of strands, bars or rods (12) arranged longitudinally along longitudinal axes (X₁ and X₂) that are substantially symmetrical with respect to a central longitudinal axis (X) of the transverse cross-section of said elongated body (11) while, with respect to the resisting cross-section, they are arranged on transverse planes (Y₁ and Y₂) that are substantially axially offset and equidistant with respect to said central transverse plane (Y).
The prestressed concrete component according to claim 5, characterized in that the axial offset or eccentricity (e) between said transverse planes (Y₁ and Y₂) of said strands, bars or rods (12) is comprised between 6 mm and 20 mm.
The prestressed concrete component according to claim 5, characterized in that the axial offset or eccentricity (e) is selected as a function of the following factors:
a) geometrical characteristics of the rectangle of the transverse cross-section;

b) prestress tension;

c) characteristics of the concretes used;

d) type and particle size of the inert material;

e) mixing and composites and drying of the mortars.
The prestressed concrete component according to any one of the preceding claims, characterized in that said elongated body (11) comprises inert materials of variable size that are resistant and frostproof, predominantly coarse, medium and fine sands, with a diameter comprised between 0.5 mm and 5 mm, obtained by crushing quartz rocks and pebbles of small size, with a diameter comprised between 0.5 mm and 10 mm, and from a high-strength concrete mix (Rck 52.5 N/mm²).
The prestressed concrete component according to one any one of the preceding claims, characterized in that said concrete has a specific gravity comprised between 18 kN/mm² and 25 kN/mm².
The prestressed concrete component according to any one of the preceding claims, characterized in that said upper surface (15) comprises an antislip surface shape and/or various types of decoration.
The prestressed concrete component according to any one of the preceding claims, characterized in that it comprises a lateral flared portion with rounded edges (14) at said upper surface (15).
The prestressed concrete component according to any one of the preceding claims, characterized in that said elongated body (11) is provided at least superficially with colorings obtained by means of natural or synthetic pigments mixed with the concrete material or added as mass-pigmented finish.
A method for manufacturing a prestressed concrete component suitable for providing both outdoor walkable surfaces and the cladding of walls, comprising an elongated body (11) made of concrete, which has a base surface (13) and an upper surface (15) which is opposite and parallel to said base surface (13), wherein said elongated body (11) has a length comprised between approximately 1 m and approximately 8 m, a width comprised between approximately 80 mm and approximately 300 mm, and wherein at least two reinforcement elements (12) are arranged within said elongated body (11), parallel to a longitudinal axis (X), which is arranged in the direction of the length of said elongated body (11), characterized in that it comprises a first step, in which a mix of inert materials and high-strength concrete is provided; a second step, in which said mix is cast into formwork having a length comprised between 5 m and 8 m and a substantially rectangular cross-section, which is conveniently contoured in order to obtain the desired surface finish; and a third step for prestressing said mix in said formwork by pre-tensioning a reinforcement frame constituted by reinforcement elements (12) that are substantially mutually offset with respect to a transverse plane (Y), which is parallel to said base surface (13), and wherein said prestressed concrete component has a thickness comprised between approximately 20 mm and approximately 60 mm.
The method according to claim 13, characterized in that said inert materials have a variable particle size, are resistant and frostproof, predominantly coarse, medium and fine sands, from 0.5 mm to 5 mm in diameter, obtained by crushing small pebbles with a diameter comprised between 0.5 mm and 10 mm.