FR2805533A1 - Ready-to-use cement composition for concrete and mortars resistant to the very high temperatures encountered in chimney flues incorporates an artificial Portland cement combined with an air-entraining additive - Google Patents

Abstract

The composition of a concrete or mortar resistant to very high temperatures, ready for use and in the dry state and made up of a cement, some glass fibres and a granulate is characterized in that it incorporates an artificial Portland cement combined with an air-entraining additive. An independent claim is included for the fabrication of a flue using a concrete or mortar made of this composition.

Description

The present invention relates to ready-to-use, high temperature, dry and divided concrete compositions or mortars referred to herein as "premix". The invention also relates to concrete slabs or mortar in bulk, which can be cut on demand, as produced by a concrete batching plant.The invention also relates to any structure or construction element that can be obtained with Such a paste and the invention more particularly relates to chimney flues, or flue gases, obtainable from compositions or pastes as defined above.

As regards mortars, the present invention is more particularly concerned with refractory mortars.

The French standard XP P 51-321 relating to flues requires, for heat-resistant concretes, and more specifically for a chimney-resistant concrete duct, that these satisfy the thermal resistance specifications corresponding to their classification, for example class T 400, and furthermore withstand an additional heat shock of 1000 C for 30 minutes, without the air permeability exceeding 3 liters / s / m 2. Among the aggregates that can be used in accordance with this standard, include pozzolan, or pozzolan type aggregates.

According to the patent application 98.14296 of November 9, 1998 in the name of the Applicant, there has previously been described and proposed a composition, ready to use, in the dry state and divided, comprising an aluminous cement or fused, fibers of alkali-resistant glass, in a proportion by weight of between 0.125 and 4 by weight, having a diameter of between 12 and 20 μm, and a length of between 12 and 50 mm, as well as, optionally, a granulate, and this in order to obtain a concrete resistant to very high temperatures.

It has now been discovered that a concrete or mortar having substantially the same thermomechanical performance as that of a concrete or mortar conforming to the subject of the aforementioned patent application is obtained, by replacing the aluminous cement with an artificial Portland cement. (abbreviated as CPA), but on the condition of combining it with or adding an air-entraining adjuvant. By artificial Portland cement is meant any cement meeting the definition and characteristics of the French standard NF P 15 301.

By air-entraining adjuvant is meant any agent having the function of developing in a concrete or mortar, fine air bubbles uniformly distributed, and which remain after hardening (see French standard pr EN 934-2). These adjuvants are generally fatty acids or sulphured products.

When the term "granulate" is used, in the description below, all mineral materials, of natural origin or not, are optionally targeted in the form of fines.

This discovery is particular for two reasons - It is known that a CPA cement normally loses its hydraulic binder properties from 480 C; above this temperature, the use of aluminous or molten cement is mandatory. - Air-entraining admixtures have never been used or recommended for concretes or mortars exposed to high temperatures; on the contrary, these adjuvants were rather recommended for concretes subjected to freeze / thaw cycles.

The present invention generally relates to a composition for concrete or mortar resistant to high temperatures, ready for use, and in the dry state and divided. A composition according to the invention comprises an artificial Portland cement (abbreviated to CPA), combined with an air-entraining aid, and a granulate.

Preferably, the CPA cement represents at least 10, and preferably between 12 and 45% by weight of said composition, with granulate.

By way of example, the air-entraining admixture represents at least 0.1 and preferably between 0.1 and 0.25% by weight of the CPA cement.

The composition according to the invention further comprises alkali-resistant glass fibers, preferably having a diameter of between 12 and 20 μm, and for example a length of between 12 and 50 mm. These glass fibers represent, for example, a weight ratio of 0.125% to 5% by weight of the CPA cement. The composition according to the invention may comprise a quantity of pozzolan-type granules, for example between 60 and 85% by weight of the composition. If necessary, a material resistant to a temperature of at least 1000 C, different from a pozzolan type granulate, for example a slag, fly ash, refractory bricks, pumice, silica, Chamotte, shale, expanded clay, or coke, may be added to the Pouzzolan granulate. This or these materials resistant to a temperature of at least 1000 C constitute for example a weight proportion of 10 to 80% of said composition, with granulate.

The composition according to the invention may comprise other adjuvants, for example a deflocculating agent.

The present invention also relates to a concrete paste or mortar in bulk, obtainable by mixing a composition as defined above, with 10 to 20% volume of water for a volume of said composition.

The invention also relates to a structure or construction element that can be obtained by shaping and drying a concrete paste according to the invention, such a structure or element then being particularly resistant to very high temperatures.

By way of example, but without limitation, the invention also relates to a smoke pipe, particularly resistant to very high temperatures, obtainable from a composition as defined above, constituted for example by a single wall plug, having a thickness of between 3 and 6 cm.

The invention also relates to a method of manufacturing a plug comprising the following steps: a) filling of a plug mold with a bulk concrete paste according to the invention, b) high frequency vibration of the paste at the same time. inside the mold, c) pounding, d) extraction, e) drying and conditioning, according to this method, the operations (a) to (d) are carried out in about 120 seconds. The invention also relates to any use of an air-entraining admixture for concrete or mortar, for obtaining, from a CPA cement, a concrete or mortar resistant to very high temperatures, for example at least equal to 700 C.

The mixing water, in percentage of water volumes, also includes the quantity of water possibly present in the various aggregates.

The aggregates are optionally natural pozzolans, for example of origin of the Massif Central, or artificial pozzolans, for example slag, or their mixture. The pozzolan is crushed and calibrated in particles, suitable for a composition according to the present invention.

Alkali-resistant glass fibers, for example VETROTEX Cem-FIL fibers, sold by the company VETROTEX, are added in any composition according to the invention.

Below 0.125% fiberglass in the ready-to-use composition, the finished and dry concrete or mortar may have insufficient mechanical strength at a temperature of 1000 ° C, and cracks may appear following treatment with the indicated temperature.

Above 5% of glass fibers in the ready-to-use composition, the volume may then be too large and kneading becomes impossible.

The glass fibers preferably have a suitable length and diameter - below a length of 12 mm, the fibers are possibly ineffective and above a length of 50 mm, they can break or agglomerate during kneading, and below a diameter of 12 μm, the fibers can be inoperative and above a diameter of 20 μm, the number of fibers can be insufficient per d m3 and requires to increase the load .

A ready-to-use composition according to the invention may also comprise other ingredients, such as materials resistant to a temperature of 1000 ° C., and adjuvants other than the air-entraining agent, incorporated in a small proportion so that to modify, improve or supplement some of the characteristics of the concrete or mortar, finished and dry. As regards adjuvants other than the air-entraining agent, mention may be made, for example, of adjuvants acting on setting and hardening time, such as accelerators which shorten the time between the hydration of the binders and their setting. , and the retarders which lengthen the time between the hydration of the particles of a binder and the beginning of its setting. As accelerators, mention may be made, for example, of calcium or sodium chlorides, certain alkalis (sodium hydroxide, potassium hydroxide, ammonia) or their salts (sulphate of potash or soda). Examples of retardants are carbohydrates (sugars, glucose, starch, cellulose), various acids or salts of acids, or zinc oxide or alkaline phosphates.

Mention may also be made of adjuvants acting on plasticity and compactness, such as plasticizers and fluidifiers, so-called water reducers. As a plasticizer, for example, bentonite, fatty lime, ground limestone, fly ash and kieselguhr may be incorporated. As a plasticizer, lignosulphates, resin soaps or synthetic detergents may be used.

It is also possible to mention adjuvants improving resistance to external agents, such as antifreezes, which protect the material against the effects of the gel until hardening; water repellents, which improve the tightness of concrete by reducing the possibilities of capillary penetration of water; curing products, which prevent the premature evaporation of the mixing water and maintain the necessary hydration. As antigens, it is possible to use, for example, calcium chloride, or sodium aluminate. As hydrofuges, it is possible to use silicones, fluosilicates, colloids or resins. As curing products, it is possible, for example, to use paraffin emulsions, waxes, oils, resins and various petroleum derivatives.

Adjuvants will be added in a small proportion and must comply with the French standard NF P 18-103.

The flue elements considered by the present invention are hollow elements and stackable, for interlocking, for the construction of flue gas exhaust ducts and flue gases resulting from combustion. Bushings for flue pipes are single wall (thickness 3 to 6 cm), or double wall (dimpled bushels), thickness greater than 6 cm. Their inner section may be round, square or rectangular, and in the latter two cases, the interior corners are rounded, to facilitate the flow of fumes and sweeping and limit preferential crack initiation. Standard internal hydraulic diameters range from 250 to 1,600 cm2. Some models are biased, for offsets, the latter must not exceed 20 compared to the vertical. The height of the plugs is 25 or 33 cm, for double-walled elements, and 25 to 50 cm for single wall elements of 3 to 6 cm thick.

The implementation of concrete plugs according to the invention complies with the requirements of the French standard NF P 51-321.

In a preferred embodiment according to the invention, a flue element is a plug, and in particular a single wall plug having a thickness of between 3 and 6 cm.

It is more particularly, but not exclusively, in the field of concrete flues, that the present invention demonstrates its interest.

In this particular field, in France, manuportable conduit elements, whether single-walled (commonly called bushel), or multiple walls (commonly called composite ducts), must meet the French standard XP P51-321.

Such a duct element must in particular withstand a chimney fire, according to the aforementioned standard. For this purpose, the duct element must first meet the thermal shock specifications in its designation class, for example T400, and then be subjected to it, without modification of air permeability (remaining below 3 liters / s / m2). a complementary heat shock of 1000 C 50 C for 30 minutes, the temperature rise rate being 100 C 20 C per minute.

In general, with conventional concrete, such resistance can be obtained only with an element comprising two concentric ducts. Indeed, in this case, the internal conduit in contact with high temperatures loses any compressive strength, and is ultimately permeable; the external conduit continues to meet the requirements of the aforementioned standard.

Thanks to the present invention, the quality of the concretes and mortars obtained makes it possible to produce a single-wall duct element resistant to a chimney fire. In practice, at very high temperatures, a concrete or mortar according to the present invention has a high compressive strength, and a relatively low air permeability. In particular, even if the cement or mortar cracks at high temperature, these cracks close again after returning to ambient temperature.

The phenomenon of elasticity of the cementitious matrix, observed according to the present invention, results from the fact that the physico-mechanical characteristics of the cement remain essentially preserved at high temperatures, thanks to the presence of the air-entraining admixture. The thermal and physical stresses generated by the high temperatures are divided into a multitude of micro-voltages, which are distributed at the ends of the different glass fibers and then trapped in the micro-air bubbles within the cement matrix.

Without the air-entraining adjuvant, CPA cement would have its physico-mechanical characteristics destroyed beyond 480 ° C.In fact, beyond such a temperature, the cohesion of the cement matrix is no longer important enough. , to withstand the considerable internal forces generated by the expansion of concrete at high temperatures. There is then in this case cracking of the concrete, without any return to the initial state when the temperature decreases.

The table below comprises three columns, from left to right, identifier before mixing, respectively an example of concrete according to the present invention, the percentages by weight of different ingredients, entering a composition according to the invention, and the percentages by weight. air-entraining admixture and deflocculant, optionally preferred according to the invention.

MATERIALS <SEP> In <SEP> weight, <SEP> or <SEP> in <SEP> By <SEP> ratio <SEP> in <SEP> weight <SEP>% <SEP> refined
<tb> liters <SEP> total <SEP> sec, <SEP> except
<tb> Cement <SEP><U> type </ U><SEP> CPA <SEP> 200 <SEP> k <SEP><U> 12-45 </ U>
<tb> Sand <SEP> 30 <SEP> k <SEP><U> 0-40 </ U>
<tb> Air <SEP> Trainer <SEP> * <SEP> 0.44 <SEP> liter <SEP><B><U> 0.05-1.00 </ U><SEP> 0.15-0.25 </ B>
<tb> Deflocculant <SEP> * <SEP> 1.00 <SEP> liter <SEP><B><U> 0.05-1.00 <SEP> 0.3-0.6 </ U></U>
<tb> Fibers <SEP> of <SEP> glass <SEP> 4 <SEP> k <SEP> 0.125 <SEP> - <SEP> 5
<tb><U> Granulate <SEP> refractory, <SEP> by <SEP> example <SEP> pozzolan <SEP> 770 <SEP> l <SEP><B> 15-88 </ U> * The percentages of the air entrainer and the deflocculant are expressed in relation to the weight of the cement.

A column of bushels obtained from a concrete whose composition is that presented in the first column of the table above, single-walled (full), with a hydraulic diameter equal to 20 cm, of external transverse dimensions equal to 29 x 29 cm, and height equal to 25 cm per element, was subjected to the tests defined by the aforementioned French standard XP P51-321, for classification T400 FC.

After testing, such a conduit has been found to perfectly meet the criteria required by the XP P51-321 standard, in the T400 FC classification.

Claims (1)

<B> CLAIMS </ B> 1 / Concrete composition or mortar resistant to very high temperatures, ready for use, and in the dry and divided state comprising a cement, glass fibers, and granulate, characterized in that it comprises an artificial Portland cement (abbreviated CPA), combined with an air-entraining admixture. Composition according to Claim 1, characterized in that the CPA cement adjuvant represents at least 10%, and preferably between 12 and 45% by weight of said composition, with granulate. 3 / Composition according to claim 1, characterized in that the air entraining admixture is at least 0.1%, and preferably between 0.1 and 0.25% by weight of the CPA cement. 4 / Composition according to claim 1, characterized in that the alkali-resistant glass fibers, have a diameter of between 12 and 20 Nm, and / or have a length of between 12 and 50 mm. 5 / Composition according to claim 4, characterized in that the glass fibers represent a weight proportion of between 0.125 and 5%, the weight of the CPA cement. 6 / Composition according to claim 1, characterized in that it comprises a quantity of pozzolan type granules, between 60 and 85% of the weight of the composition. 7 / Composition according to claim 1, characterized in that it comprises a material resistant to a temperature of at least 1000 C, different from a pozzolan type granulate, for example a slag, fly ash, bricks pounded refractories, pumice, silica, chamotte, shale, expanded clay or coal coke. 8 / Composition according to claim 7, characterized in that the material or materials resistant to a temperature of 1000 C constitute a weight proportion of 10 to 80% of said composition, with granulate. 9 / Concrete paste or mortar in bulk, obtainable by mixing a composition according to any one of claims 1 to 8, with 10 to 20% volumes of water for a volume of said composition. 10 / Work or building element that can be obtained by shaping and drying a concrete paste according to claim 9, resistant to very high temperatures. 11 / Smoke pipe resistant to very high temperatures, and complies with the French standard XP P51-321, obtainable from a composition according to any one of claims 1 to 8, characterized in that it is constituted by a single wall plug, having a thickness of between 3 and 6 cm. A method of manufacturing a bushel comprising the steps of. a) filling a dough mold with a dough according to claim 9, b) high frequency vibration of the dough inside the mold, c) pounding, d) extraction, e) drying and conditioning, characterized in that that the operations of (a) to (d) are performed in about 120 seconds. 13I Use of an air entraining admixture for concrete or mortar, for obtaining, from a CPA cement, a concrete or mortar resistant to very high temperatures, at least equal to 700 C.