Process for reducing radon inside buildings

Description

BACKGROUND OF THE INVENTION

The present invention relates to a process for reducing radon inside buildings.

Radon is a radioactive gas of natural origin arising from the disintegration of the uranium and radium contained in the Earth's crust, and which is naturally present in variable amounts depending on the region and the type of soil.

It is present throughout the entire surface of the Earth and particularly in regions with granitic and volcanic subsoil, and can migrate from the soil into the atmosphere, where it tends to accumulate in enclosed spaces, and especially in buildings.

The presence of radon in the air inside buildings thus results from the level of formation of this gas in the soil, but also from the characteristics of the surface of the building in contact with the soil, and especially of the presence of cracks, holes and/or porosity.

The presence of radon is of particular concern for buildings in which people reside over long periods (dwellings, schools or public establishments). This radioactive gas can in fact reach concentrations in the air that are liable to represent a risk factor for lung cancer to the occupants of the buildings, more particularly in the case of simultaneous exposure to tobacco.

This is why public authorities are concerned about limiting the average annual concentration of radon in buildings. Thus, the European Union recommends that new buildings should be designed such that this average annual concentration does not exceed 200 Becquerel per m³ (Bq/m³). France has adopted a value of 1000 Bq/m³ as the alarm threshold, and 400 Bq/m³ as a warning level.

Processes for reducing the concentration of radon in the air inside buildings already exist.

The renewal of air can thus be increased by means of natural or mechanical ventilation, which has little effect on changing the penetration of radon into the building, but promotes the dilution and evacuation of the gas.

Other treatments consist in acting at the interface between the soil and the building to prevent the entry of radon originating from the soil. Attempts have thus been made to use plastic groundsheets to cover the soil. However, these groundsheets do not allow hermetic sealing capable of completely preventing radon from escaping from the soil into the building.

Chemical treatments of the interface between the soil and the building have also been envisaged. U.S. Pat. No. 5,399,603 thus describes the use of an emulsion containing a sulfopolyester, an acrylic copolymer and a plasticizer.

It is moreover known practice in the construction field to use crosslinkable epoxy resins of bisphenol A type (i.e., a bisphenol A crosslinkable epoxy resin), for the preparation of cement- or concrete-based supports that are subject to capillary rising of moisture from the soil, optionally prior to the application of leveling coats (also known as resurfacing coats) for the laying of floor coverings such as parquets, carpets, linoleum or floor tiles.

BRIEF SUMMARY OF THE INVENTION

One aim of the present invention is to propose another method for the chemical treatment of the interface between the soil and the building, which makes it possible to substantially reduce the concentration of radon inside buildings, and especially to improve the impermeability to this gas of the parts of buildings that are in contact with or in the region of the soil.

Another aim of the present invention is to propose treatment for simultaneously obtaining a reduction in radon inside a building and for improving the impermeability to moisture of the parts of the building that are in contact with or in the region of the soil.

It has now been found that these aims are totally or partly achieved by applying a limited surface density, which is within a specific range, of crosslinkable epoxy resin of bisphenol A type.

According to an embodiment of the invention, a process is disclosed for reducing radon inside a building susceptible to radon accumulation. The process includes a step of applying to at least an inner surface of a structural component of the building a composition comprising a crosslinkable epoxy resin of bisphenol A type (i.e., a bisphenol A crosslinkable epoxy resin) and a crosslinking agent. The composition is applied in an amount corresponding to a surface density of the resin of between 300 and 1300 g/m2, and preferably between 400 and 950 g/m², and most preferably between 450 and 950 g/m². In one application the structural component is a concrete base slab covered with a screed.

The process is particularly suitable for buildings that have an inner atmosphere which is capable of reaching a radon concentration greater than 100 Bq/m³, greater than 200 Bq/m³, greater than 400 Bq/m³, or greater than 1000 Bq/m³. In addition, the process is preferably performed on buildings in which people reside over long periods or public establishments.

The crosslinkable epoxy resin of bisphenol A type is preferably obtainable by reacting halo epoxides with bisphenol A, bisphenol AD or bisphenol F. Moreover, the crosslinkable epoxy resin of bisphenol A type is preferably a mixture of bisphenol A diglycidyl ether and of bisphenol F diglycidyl ether. In an embodiment of the invention, the crosslinking agent is a mixture of a modified polyamide and of an aliphatic polyamine. Preferably, the ratio of the weight of crosslinkable epoxy resin of bisphenol A type to the weight of crosslinking agent is between 0.1 and 10, and more preferably between 1 and 2.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an apparatus for measurement of the efficacy of reduction of radon emission.

DETAILED DESCRIPTION OF THE INVENTION

One subject of the present invention involves a process for reducing radon inside a building whose inner atmosphere is capable of reaching a radon concentration of greater than 100 Becquerel per m³, the process comprising the application to the inner surface of a component of the structure of the building, placed in contact with or in the region of the soil, of a composition comprising a crosslinkable epoxy resin of bisphenol A type and a crosslinking agent, the composition being applied in an amount corresponding to a surface density of the resin of between 300 and 1300 g/m² and preferably between 400 and 950 g/m².

The present process thus concerns buildings whose inner atmosphere is capable of reaching a radon concentration of greater than 100 Becquerel per m³ (Bq/m³). Such a concentration—corresponding to an annual average—generally results from an accumulation, in the case of a confined atmosphere, of the radon that diffuses into the air from the soil or from water, for buildings constructed in a region whose subsoil is of granitic and/or volcanic nature. In the case of France, for example, the regions that are most concerned are Brittany, Corsica, the Massif Central and the Vosges. The determination of the concentration of radon in the air is performed by means of known measurements of radioactive disintegrations of radon atoms, using a dosimeter.

On account of the resulting increased health risk factor, it is preferred to implement the process according to the invention for buildings whose inner atmosphere is capable of reaching a radon concentration of greater than 200 Bq/m³, preferably greater than 400 Bq/m³ and even more preferentially greater than 1000 Bq/m³.

The buildings with which the present process is concerned are preferably buildings in which people reside over long periods, such as dwellings, schools, public establishments or premises for professional use. Public establishments are more particularly preferred.

The composition used in the process according to the invention comprises one or more crosslinkable epoxy resins(s) of bisphenol A type and one or more crosslinking agent(s).

For the purposes of the present invention, the crosslinkable epoxy resins of bisphenol A type are defined as compounds comprising two epoxy groups, which may be obtained by reacting halo epoxides such as epichlorohydrin (also known as 2-(chloromethyl)oxirane) or β-methyl-epichlorohydrin with bisphenol A, bisphenol AD or bisphenol F.

Bisphenol A (or 2,2-bis(4-hydroxyphenyl)propane) has the formula:

Bisphenol AD (or 1,1-bis(4-hydroxyphenyl)ethane) has the formula:

Bisphenol F (bis(4-hydroxyphenyl)methane) has the formula:

A mixture of bisphenol A diglycidyl ether (also known by the abbreviation BADGE) and of bisphenol F diglycidyl ether (BFDGE), having the respective formulae:

is preferably used as epoxy resin of bisphenol A type.

The crosslinking agents used in the composition used in the present invention are chosen from usual agents such as aliphatic or aromatic polyamines, acid anhydrides, imidazoles, polymercaptans and polyamides, in pure form or as a mixture.

A mixture of modified polyamide and of aliphatic polyamine is preferably used as crosslinking agent.

The crosslinking agent (also known as a curing agent) is present in the composition in an amount expressed as the equivalent number of active hydrogen atoms of the amino group (or other group bearing active hydrogen, depending on the nature of the crosslinking agent used) ranging from 0.8 to 1.2 and preferably from 0.9 to 1.1 per one equivalent of epoxy group present in the crosslinkable epoxy resin.

In practical terms, the ratio of the weight of crosslinkable epoxy resin of bisphenol A type to the weight of crosslinking agent is generally between 0.1 and 10 and preferably between 1 and 2.

The composition used may also comprise other ingredients, such as a reactive or non-reactive diluent to better control its ease of application, one or more mineral fillers or rheological agents.

This composition is generally prepared prior to its application by homogeneous mixing of two commercially available compositions:

• • a composition A comprising the crosslinkable epoxy resin of bisphenol A type, and
  • a composition B comprising the crosslinking agent.

The mixture may be applied over a period of time within about 20 to 60 minutes of its preparation, at a temperature of greater than 5° C. and preferably between 10 and 40° C.

Chemical crosslinking (or polymerization) of the epoxy resin by the curing agent over a time of about 24 hours leads to the formation of a strong, homogeneous coat of crosslinked epoxy resin on the support, which, on account of its adhesion, is very strongly bonded to the treated support.

According to one preferred variant of the process according to the invention, the amount of composition to be applied per unit area corresponds to a surface density of crosslinkable epoxy resin of bisphenol A type of between 450 and 950 g/m². This amount may be applied in one or more coats, preferably two coats. When it is applied in two coats, the second coat is generally applied 24 hours after the first coat.

The structural components that may be treated via the process according to the invention include any part of the structure ensuring the stability of the construction, which is in contact with or in the region of the soil, especially such as:

• • the concrete base slab poured onto the soil, constituting the seat of the building, which may or may not be covered with a screed, in the case of constructions on an earth platform,
  • the foundations, basements or support walls, in the case of buildings with basements,
  • the vertical walls surrounding the crawl space (of a height generally ranging from about 10 to 80 cm) on the base of which rests the concrete base slab of the ground floor,
  • the impermeability elements of the walls of an underground premises (also known as the casing).

The structural component that is preferred for the application of the process according to the invention is a concrete base slab covered with a screed.

These structural components generally consist of concrete, mortar, cement, plaster or metal. It is on their inner surface oriented horizontally or vertically towards the interior of the building, in naked form or optionally provided with a covering such as pre-existing tiling, that the composition based on epoxy resin of bisphenol A type is applied via usual techniques such as by roller, float or toothed spatula for horizontal surfaces, or by brush for vertical surfaces.

The process according to the invention may optionally comprise, just after applying the composition to a horizontal structural component, and before the polymerization is complete, the application of sand with a granulometric cut-off of between 0.2 and 1 mm, in an amount of 3 to 4 kg/m².

FIG. 1 is a scheme of an experimental device for determining the efficacy, in terms of reducing the radon concentration of the air, of a specimen consisting of a reinforced cement support covered with a coat of epoxy resin of crosslinked bisphenol A type.

This device comprises:

• • a chamber consisting of a lower hemisphere (1) functioning as a radon reservoir in which is present a high concentration of radon; this concentration is obtained using a source (2) of radium-226 and the pump (3);
  • the specimen (4) described above, attached to the hemisphere (1) by means of a silicone seal (5), the coat of crosslinked resin being on the upper surface of the support;
  • a chamber consisting of an upper hemisphere (6) attached to the specimen (4) in which is measured the level of emission of radon through the specimen (4);
  • a detector (7) attached to the top of the hemisphere (6), which is connected with the hemisphere (1) to a multi-channel analyzer (8) and a computer (9).

The description of an example and also of a comparative example are now given for better understanding of the invention, for purely illustrative purposes and without in any way limiting the scope of the present patent application.

EXAMPLE 1

Application of a Crosslinkable Epoxy Resin of Bisphenol A Type at a Surface Density of 500 g/m²:

A two-pack epoxy kit is used, comprising:

• • an epoxy resin essentially comprising a mixture of bisphenol A diglycidyl ether (BADGE) and of bisphenol F diglycidyl ether (BFDGE) and of reactive diluent;
  • a curing agent essentially comprising a mixture of modified polyamide and of triethylenetetramine.

Such a kit is commercially available, for example, under the name Eponal® 336 from the company Bostik S.A., which is a product known for giving supports in contact with or in the region of the soil an improvement in the impermeability to moisture.

A masterbatch is prepared at room temperature by simple mixing of the above two components, at a rate of 100 g of resin per 60 g of curing agent, using a beater mounted on an electric blender.

Immediately after, 100 g of this mix are applied by spatula to the surface of a square support with a side length of 50 cm, consisting of a reinforced cement tile 5 mm thick. The amount of mix applied is determined by weighing. Immediately after, sand with a granulometric cut-off of between 0.4 and 0.9 mm is applied in an amount suitable to cover the entire tile. After 24 hours, the excess sand is brushed off.

A second coat of 100 g of the masterbatch is then applied to the surface previously obtained under the same conditions, without, however, applying sand.

The total amount of mix applied to the support consequently corresponds to a surface density of crosslinkable epoxy resin of 500 g/m².

After total crosslinking, the tile thus prepared is covered with a coat of crosslinked epoxy resin. The weight of this coat (per unit area) is 800 g/m², and its thickness (measured using a micrometer) is 1.8 mm.

The efficacy of reduction of the radon emission resulting from the tile thus prepared is measured by the assembly shown in FIG. 1.

After attaching the test specimen to the hemisphere (1), the radon arising from the source (2) is placed in circulation by means of the pump (3) and mixed with the air in the hemisphere (1). The radon concentration in the air in the hemisphere (1) is about 1 million Bq/m³.

After obtaining a constant radon concentration gradient between the air in the hemisphere (1) and the free surface of the specimen (4), the second hemisphere (6) is attached to the upper surface of the specimen (4) and sealed by means of the seal (5) as indicated in FIG. 1.

The radon flux passing through the specimen in the direction of the hemisphere (6) is measured by electrostatic deposition (using the detector (7) and a suitable electric field) of the positively charged ions of polonium-218 and polonium-216 resulting from the disintegration of the radon, and then by alpha spectroscopy.

The increase in radon concentration in the hemisphere (6) is recorded as a function of time, the signal obtained being processed by the analyzer (8) and the computer (9).

The diffusion length (or relaxation length) is then calculated.

A relaxation length of 0.55 mm is thus measured.

It is estimated that a coat of resin applied to the support is impermeable to radon once its thickness is greater than the triple of the measured relaxation length.

The application to the support of the epoxy resin at the applied surface density makes the coated support impermeable to radon.

COMPARATIVE EXAMPLE

Application of a Crosslinkable Epoxy Resin of Bisphenol A Type at a Surface Density of 250 g/m²:

Example 1 is repeated, applying to the square support with a side length of 50 cm 100 g of the prepared masterbatch instead of 200 g, which corresponds to a surface density of crosslinkable epoxy resin of 250 g/m².

After total crosslinking, a thickness of 1 mm is measured for the coat of crosslinked epoxy resin (whose weight per unit area is 400 g/m²).

A relaxation length of 2.66 mm is deduced from the measurements taken by means of the assembly in FIG. 1.

Since this length is less than the triple of the thickness measured for the coat, it results that the application to the support of the epoxy resin of bisphenol A type at the applied surface density does not make the support impermeable to radon.