WO2005082812A2

WO2005082812A2 - Surface treatment of elements comprising a hydraulic binder

Info

Publication number: WO2005082812A2
Application number: PCT/DK2005/000143
Authority: WO
Inventors: Lars Børthy PETERSEN
Original assignee: Dansk Betonselskab Aps
Priority date: 2004-03-01
Filing date: 2005-03-01
Publication date: 2005-09-09
Also published as: WO2005082812A3

Abstract

The present invention relates to a process for surface treatment of elements comprising a hydraulic binder where the process comprises the following steps: Placing the elements under a pressure lower than the ambient air pressure for a certain period of time; arranging a mist of an impregnating agent immediately around at least part of the element, where the molecular size of the impregnating agent is less than or equal to 0.2µm. Furthermore, the invention also relates to apparatuses for carrying out the process.

Description

Surface treatment of elements comprising a hydraulic binder

The present invention relates to a process for surface treatment of elements comprising a hydraulic binder. Furthermore, the invention also relates to apparatuses for carrying out the process.

Materials comprising a hydraulic binder such as for example cement are widely used. One of the characteristics of this type of materials is that they are relatively cheap compared to the characteristics which are obtainable by said materials. Especially, when it comes to surfaces such as floors or other very-exposed surfaces or surfaces which might be exposed to aggressive media such as acids whether or not said acids are contained in chemical compositions or in food stuffs such as red wine and the like, these surfaces have serious drawbacks in that the surface comprises pores or micro pores wherein these materials may adhere or be absorbed and result in discolouring or disintegration of the surface layers all together. The disintegration is especially true when concrete materials are exposed to certain acids.

There is therefore a desire to be able to use these materials in environments where they might be exposed to discolouring or corrosive ingredients such as acids without this exposure having any influence on the elements or surfaces as such.

The present invention addresses this desire by providing a process for surface treatment of elements comprising a hydraulic binder where the process comprises the following steps: - Placing the elements under a pressure lower than the ambient air pressure for a certain period of time; arranging a mist of an impregnating agent immediately around at least part of the element, where the molecular size of the impregnating agent is 0.2 μm, preferably less than or equal to 0.02 μm.

Although surface treatment of concrete or composite surfaces is well-known in the art, they all have the drawback that the surface will severely deteriorate with time due to the characteristics of the surface treatment. One such example is disclosed in JP 2000 327453, wherein a cement tile is placed on a box whereafter an underpressure is created inside the box, and thereby on the underside of the tile. The upper side of the tile, i.e. the side of the tile not facing the box, is thereafter treated in a spray coating process with a mixture composed of an epoxy resin. The tiles have prior to the spray coating been exposed to a heating process, wherein water contained in the tiles has evaporated. Due to the underpressure in the box, the spray coating will, where the tile is porous, be sucked through the tile due to the pressure differential between the surface and underside of the tile. In this manner, it is only possible to impregnate and thereby close through-going pores in that the un- derpressure will have no effect on pores in the material which are only present in the upper side surface of the material in that the vacuum created inside the box will not create a corresponding underpressure in the surface pores.

A further prior art method is disclosed in JP 02-088478, wherein in a localised area a part of the surface of the material to be treated is sealed off whereafter an underpressure is introduced underneath the sealing plate. When the underpressure has been established for some time, the impregnating agent is led into the area between the sealing plate and the surface to be treated in order to establish a surface treatment. With this method, it is not assured that all pores are treated in that there is no variance in the underpressure in the pores or otherwise such that the impregnating agent cannot be guided into the places where it is most desired, namely in the surface pores.

In the art, it has been tried to give these types of surfaces a finish in the shape of epoxy paintings, varnishes or impregnations. Common for all these attempts has been that firstly the wear characteristics of regular paints are rather poor, and the paint adhesion to the surface is also rather poor. For other materials, they do not provide an adequate protection against corrosive acids in that most of these materials comprise an environmentally friendly solvent which is characterised in that the size of the molecules of the solvents are such that they will not be able to penetrate and adhere to the micro pore structure of the material comprising a hydraulic binder such as for example very compact concrete and composite materials.

By using solvents having a molecular size in the impregnating agent which is less or equal to 0.2 μm, it is possible for this impregnating agent to penetrate and adhere to ultra fine pores in the surface of the material comprising the hydraulic binder. In this manner, it is possible to impregnate the top surface of such materials to such a degree that they become resistant to corrosive acids, dirt, discolouring etc. Furthermore, as impregnating agent a transparent impregnating agent may be chosen such that the ma- terial characteristics of the hydraulically bound material may be maintained. Furthermore, it may be possible to select an impregnating agent such that the surface of the treated element may be more or less glossy.

In a further advantageous embodiment of the invention, the elements are in the shape of tiles and that in a first chamber means are provided for maintaining an air pressure lower than the ambient pressure and that means are provided for moving the tiles through said chamber and into a second chamber in which second chamber the impregnating mist is provided and that means for moving the tiles are provided for moving the tiles out of the second chamber for example to a packaging station, and that the means for moving provided in the first chamber may be continuous into the second chamber, such that the moving means in said first and said second chamber is one single means.

When the elements are introduced into the first chamber, they may be introduced hav- ing a temperature between 50-90° C, preferably around 80° C, or they may be heated within the first chamber itself. The air pressure inside the first chamber is lowered such that the combination of pressure and temperature will cause the water in the pores of the introduced elements to boil and evaporate, and thereby leave the pores. The steam created by the boiling of the water is removed from the chamber, and when the steam production has seized, the free water content in the pores has been diminished to a negligible amount.

Thereafter, the elements are introduced into the second chamber, where the same underpressure as in the first chamber is maintained. For practical purposes, the first and second chamber may be one common chamber where both procedures take place, one after the other.

When the steam production has seized, the impregnating materials is introduced in the shape of a mist, and at the same time the pressure inside the chamber is increased such that the pressure inside the chamber may be equivalent to the ambient air pressure outside the chamber. Hereby, due the to the correlation between temperature and pressure, the remaining water vapour and adhered water in the pores will have a volume reduction (due to the phase transformation vapour → liquid) which will created a local underpressure inside the pores, whereby a localised vacuum will arise such that the impregnating materials will be sucked into the pores, and thereby impregnate the surface layers. Typically, the surface layers in a thickness of 2-500 μm will be impregnated by this method.

For carrying out the method it is not important whether two separate chambers or one common chamber is used as long as the process steps are carried out in the order and in the relationships as described above. For reasons of clarity, however, the method will be described as having two separate chambers, but the practical manufacturing installation only has one common chamber, where both processes take place.

By confining the process in two chambers and moving the elements in the shape of tiles through the chambers, it is possible to fully control all parameters of the process such that an optimum impregnation may be achieved. Furthermore, by maintaining the impregnating agent in the shape of a mist inside the second chamber, the undesirable effects which the solvents used in the impregnating agent may exhibit can be eliminated such that the process may be carried out with due regard and respect to the surrounding environment and at the same time, provide a surface treatment which has superior characteristics relating to resistance against corrosive materials such as acids compared to any other method.

In a further advantageous embodiment of the invention, the elements to be introduced into a first chamber are transferred from a curing chamber such that the elements have a temperature of approximately 80° C when entering the first chamber; that the impregnating mist in the second chamber comprises urethane and solvents; that an evacuation source is provided in the second chamber, which source is connected to a regenerating installation such that surplus urethane and solvents are captured, regenerated and optionally reintroduced into the mist in the second chamber; and further that the elements are processed in the second chamber for substantially one minute at a pressure approximately four atmospheres below the ambient pressure. From thermodynamics, it is well-known that there is a relationship between pressure, temperature and the phase in which a material is present. For water, it is such that the lower the ambient air pressure, the lower temperature is necessary in order to make water boil - i.e. make a phase transformation from liquid to gas. For the present inven- tion, therefore, the under pressure shall be adjusted to the actual temperature such that the phase transformation in the pores and capillaries in the material is achieved. By subjecting the elements entering the first chamber either before entering or in the chamber to a temperature of approximately 80° C, the lower pressure provided in the first chamber will create a phase transformation of the physically bound water in the pores of the material comprising the hydraulic binder such that a substantial part of the water adhered to the surface of the elements and stored as free water in the pores due to capillary pressure will evaporate and thereby be removed from the material of the elements. As the elements thereafter are transferred into the second chamber and optionally to a higher pressure (i.e. less vacuum) and thereby exposed to the mist of the impregnating agent, the impregnating agent will enter into the pores and capillaries of the material, and during the lowering of the temperature which will happen as the elements being 80° C entering the process will strive to equalize temperature-wise with the surroundings and, thereby, diffuse heat energy to the surroundings will condensate impregnating agent in the pores and capillaries of the top material layers of the elements.

As the solvents used for the inventive process are detrimental to health and to the ambient environment, an evacuation source is provided in the second chamber which source may collect surplus impregnating agent mist and optionally regenerate/rework the impregnating agent such that it may be reintroduced into the mist whereby the environment is not exposed to the potentially environmentally hazardous solvents.

In a still further advantageous embodiment of the invention, the process provides that before the first chamber, a first pressure chamber having a pressure higher than the ambient pressure is arranged, and further that optionally between the first and second chambers a second pressure chamber is arranged having a pressure higher than the ambient pressure, and optionally as a last process step the elements may be subjected to a heat treatment in order to cure the impregnating agent. By providing pressure chambers where the pressure is higher than the ambient air, it is possible to "squeeze" out surplus material or force the capillary water even further into the material matrix of the elements. For materials comprising a hydraulic binder, water is a necessary ingredient in order to activate the hydraulic binder and create the struc- ture which gives the material its integrity. The action process between the hydraulic binder such as for example cement and water diminishes when there is no free water available in the matrix, and the amount of adhered water in the pores and capillaries is such that the capillary tension/pressure in the pores is greater than the ability of the hydraulic binder to pull water molecules out of the pores. Therefore, by forcing the capillary water due to the subjection to overpressure further into the matrix does not have any influence on the integrity of the element as such and may ideally force some capillary bound water into cavities where the tension/pressure in the capillary structures is released due to the physical distance in the pore being greater whereby extra water is made available for the reaction with the hydraulic binder. By subjecting the elements to overpressure, it, thereby, becomes possible to introduce more impregnating agent into the element whereby a deeper and more thorough impregnation of the element is achieved.

One preferred material for use as impregnating agent is a urethane (mono or poly) based material comprising a solvent as described above. In order to fully cure this impregnating agent, it might be desirable and advantageous to subject the elements to heat treatment in order to accelerate the curing of the impregnating agent.

The present invention has been carried out where the impregnating material was ep- oxy-based materials, acrylic-based materials and silicone-based materials where different solvents were used such as toluene, exylene and methylethylketones.

Although only these materials and combinations of materials were tested, it is clear that other materials exhibiting similar characteristics may be used within the scope of the present invention.

Examples of such materials are suggested in US 3980604 and IT 1131355. For some purposes, it may be advantageous to use water based impregnating materials having molecule sizes up to 0.2 μm in that environmental or working environment requirements may dictate the use of water based, and thereby less harmful substances, for the particular purpose. It should, however, be noted that impregnating substances using other solvents than water, for example substances having molecular sizes below

0.02 μm provides a far better impregnation of the surface layers. This is due to the fact that the smaller molecules are able to penetrate further into the surface layers, and naturally also further into the smaller pores or capillars such that an extremely effective impregnation is achieved.

In a further advantageous embodiment of the invention, the element is a surface, and that an installation comprising an upper gas and liquid impermeable membrane, and a lower gas and liquid permeable membrane is arranged on said surface such that along the perimeter of said installation it is in pressure tight connection with the surface, and that means for providing an air pressure lower than the ambient air pressure is provided connectable to the upper membrane, and that inlet openings are provided for allowing an impregnating agent comprising solvents and having a molecular size equal to or less than 0.02 μm also is provided in either the upper or lower membrane, and that first the surface under the installation is evacuated such that pore water and physically bound water in the upper regions of the hydraulically bound material is evaporated, after which the impregnating agent is introduced into the installation, and allowed to cure on the surface and in the evacuated pores.

Above the invention has been described as applied to elements such as for example tiles but it could also be elements such as plate members which may be used for furniture construction, floorings, panels and the like.

The embodiment of the invention described above may be used in situ i.e. on construction or elements being of such a size that they will not be able to be treated in an in- stallation comprising chambers as described above. For this purpose, a "chamber" is created in situ, i.e. on the surface. The surface may for example be an in situ cast concrete surface such as a floor, bridge deck or the like. The chamber is created by providing an upper gas and liquid impermeable membrane and a lower gas and liquid permeable membrane. By firstly subjecting the surface to under pressure, i.e. what is known in the art as a vacuum treatment, surplus water is removed from the top surface layers of the element. As is the case described above with reference to how the impregnating agent is introduced into the element, the same will be true for the element being a surface.

In a similar manner, it may be advantageous that the surface after the impregnating agent is introduced is subjected to a heat treatment in order to cure the impregnating agent.

From the previous description, it is clear that impregnation of the surface layers is achieved due to the fact that the water is evaporated due to the boiling created by the combination of pressure and temperature such that the pores are accessible for the im- pregnating agent. The important aspect with the present invention is the fact that after the water has been removed by the phase transformation from liquid to vapour, and the vapour is removed, the pressure is increased in the surface layers such that the remaining water in the pores will contract and the reverse phase transformation will occur, i.e. vapour → liquid, and thereby reduced volume which creates an underpressure locally in the pores, which underpressure will suck in the impregnating agent, and in particular impregnating agents having a molecule size less than 0.2 μm creates an extremely effective and reliable impregnation of the surface layers. In this manner, it is possible to render the surface resistant to a wide variety of substances which normally would be considered aggressive to materials comprising hydraulic binders.

The invention also relates to an apparatus for carrying out the process where the process relates to treatment of elements which will fit inside a chamber construction. In one advantageous embodiment, the apparatus comprises at least two chambers, and that in a first chamber conveyor means are provided and further means for providing a pressure lower than the ambient air pressure in said first chamber is provided, and that in a second chamber arranged such that the conveyor means of said first chamber are in connection with conveyor means arranged in said second chamber for moving elements to be treated, and that in said second chamber means are provided for creating a mist of an impregnating agent. The advantages obtained with the inventive apparatus according to the invention are discussed above with respect to the advantageous process embodiments.

The advantageous apparatus according to the invention may be further expanded to comprise any of the following: a) a first overpressure chamber arranged before the first chamber; b) a second overpressure chamber arranged between the first and second chambers; c) a curing chamber arranged after the second chamber, where said curing chamber comprises heating means; d) evacuation and regeneration means connected to the second chamber for treating, disposing, regenerating and/or reusing surplus impregnating agent; e) a single through-going conveyor means through the at least two chambers.

In this manner, it is possible to design the apparatus such that pending on the impregnating agent used and especially the solvents comprising the impregnating agent as well as the material composition of the elements to design and control the impregnating process such that the apparatus will provide and optimal impregnation.

In a further advantageous embodiment, the invention also provides an apparatus for carrying out the treatment of larger surfaces as discussed above where the surface may be a floor, road or bridge deck.

The apparatus comprises at least an upper gas and liquid impermeable membrane; a lower gas and liquid permeable membrane, means for creating a pressure tight connection along the periphery of said membranes and the element to be treated; means for connecting a source of under pressure, said means being arranged in the upper membrane; means for connecting a source of impregnating agent and optionally connection means for a heating source such as steam for curing the impregnating agent in the upper material layers of the surface.

The advantages deriving from such an apparatus are discussed above with relation to the relevant process steps. In fig. 1, a process line is illustrated where the raw materials are stored in silos 17 and in a known manner led to a mixing station 18 where the desirable material mixture is produced. As an example, a material comprising a hydraulic binder such as a composite material will be discussed. The composite material is mixed in the mixing station 1. The mixture is cast into special tile moulds and vibrated in order to achieve the compactness necessary. This is carried out in the casting facility 19.

After this the moulds are transported to a storage facility and placed in a curing chamber 2. In the curing chamber, a pre-curing takes place at a temperature of approxi- mately 20° C. The pre-curing may last from 5 to 24 hours at different temperatures i.e. from 15° C to 30° C depending on the composite material used.

After the pre-curing, the temperature in the curing facility is elevated to a maximum temperature of for example 80° C which temperature is maintained for up to 24 hours. A temperature in the interval 50° C to 90° C is preferred.

After the curing, the elements are removed from the curing facility, and the elements are de-moulded and, placed on a special trolley 20.

The trolley is placed in a cylindrically first chamber.

By means of a Rausch pump 21, the pressure inside the first chamber is lowered to approximately 0.2 ata at 80° C, but for 50° C the corresponding pressure is 0.12 ata, and for 40° C the corresponding pressure is 0.07 ata.

The lower the temperature, the lower pressure is necessary in order to create the phase transformation from liquid to gas whereby the capillary water may be brought from a liquid phase to a gas phase such that it may easily be removed. The water in question is free water, adhered water and physically bound water present in the pores and capil- laries of the material. Water which is absorbed or chemically bound due to the interaction with the hydraulic binder will not be freed during this process. The water vapours will be removed due to the under pressure. After this, the tiles are introduced into the second chamber 22 where an impregnating agent is introduced in the shape of a mist and such that the molecule size of the impregnating agent is equal to or less than 0.02 μm.

Alternatively, materials which are water based, i.e. have water as the solvent, may be used. However, water molecules are larger than 0.02 μm limit, typically up to 0.2 μm. These larger molecules are therefore not able to enter into pores smaller than the average molecule size such that although a very good impregnation is achieved, impregnation of pores smaller than the average molecule size will not be achieved.

Again, by increasing the pressure after the water has boiled off, the reverse phase transformation will occur in the pores in that the steam left in the pores will, due to the higher pressure condense, whereby the volume inside the pores will decrease such that a sucking effect will be created inside the pores which positively draw the impregnat- ing material inside the pores. In this manner, a very efficient impregnating process is achieved.

Advantageously more than one nozzle may be provided in the second chamber in order to achieve an optimum distribution of the impregnating agent on the surface of the elements to be treated. The size of the molecules is very important in that in order to be able to penetrate into the capillaries and pores of the material, it is desirable to have the minimal size molecules. For impregnating agents of this type, it is necessary in most cases to use solvents which are environmentally hazardous and, therefore, are not commonly used. It should also be noted that the materials exhibiting the best charac- teristics relating to acid resistance and cohesion with the material to which they are introduced, usually are materials comprising solvents which are environmentally hazardous.

The present invention has been carried out where the impregnating material was ep- oxy-based materials, acrylic-based materials and silicone-based materials where different solvents were used such as toluene, exylene and methylethylketones. Although only these materials and combinations of materials were tested, it is clear that other materials exhibiting similar characteristics may be used within the scope of the present invention.

It is, therefore, with the present invention important that the entire process may be carried out under controlled circumstances such that none of these hazardous solvents are evacuated to the atmosphere but are maintained in the closed circuit of the installation.

After the impregnation process, the under pressure is equalized whereby the water vapours still present in the capillaries and pores of the material will condense, i.e. go from the gas phase to liquid, and thereby create a volume change. By this volume change, a certain under pressure will arise in the pores and capillaries whereby the impregnating agent will be pulled into the capillaries and pores of the material. In this manner, it is ensured that the impregnating agent is not just left on the surface of the element but really penetrates into the upper layers of the material.

The under pressures and impregnating agents used within the scope of the process as described above may be varied and designed according to the pore size and capillary size of the materials being treated with the inventive process.

After the under pressure treatment in the chamber 2, the elements may be exposed to a second heat treatment in order to cure the impregnating agent. This heat treatment may advantageously be carried out in a separate chamber 23.

In order to ensure that the material tensions inside the elements are minimised, the process may advantageously be controlled and monitored such that no temperature differences higher than 25-30° C between the surface and the interior of the elements are achieved. Thereafter, the elements are ready for further packaging and transport to the user.

In fig. 2, a cross-section through a second embodiment of the apparatus according to the invention is illustrated. In this embodiment, an installation according to the second embodiment of the invention is arranged on a surface 10 of an element. The surface may be a floor, a road or any other large surface. The apparatus comprises an upper impermeable membrane 11 and a lower permeable membrane 12.

The permeability relates to membranes being gas and liquid permeable or imperme- able respectively. Along the periphery 13 of the apparatus, a pressure tight connection with the surface 10 is provided such that a chamber 14 is created between the two membranes and the surface 10,11,12. Furthermore, means 15 are provided in the apparatus, which means 15 may be connected to a source of under pressure (not illustrated). Furthermore, means 16 in the shape of inlets may be provided for being able to introduce the impregnating agent into the chamber 14. By carrying out the process steps as described above, it will be possible to impregnate the surface within the periphery 13 of the apparatus.

Claims

1. Process for surface treatment of elements comprising a hydraulic binder where the process comprises the following steps:

- Placing the elements under a pressure lower than the ambient air pressure for a certain period of time; arranging a mist of an impregnating agent immediately around at least part of the element, where the molecular size of the impregnating agent is 0.2 μm, preferably less than or equal to 0.02 μm.

2. Process according to claim 1 wherein the elements are in the shape of tiles and that in a first chamber means are provided for maintaining an air pressure lower than the ambient pressure and that means are provided for moving the tiles through said cham- ber and into a second chamber in which second chamber the impregnating mist is provided and that means for moving the tiles are provided for moving the tiles out of the second chamber for example to a packaging station, and that the means for moving provided in the first chamber may be continuous into the second chamber, such that the moving means in said first and said second chamber is one single means.

3. Process according to claim 2 wherein the elements to be introduced into the first chamber are transferred from a curing chamber such that the elements have a temperature of approximately 80° C when entering the first chamber; that the impregnating mist in the second chamber comprises urethane and solvents; that an evacuation source is provided in the second chamber, which source is connected to a regenerating installation such that surplus urethane and solvents are captured, regenerated and optionally reintroduced into the mist in the second chamber; and further that the elements are processed in the second chamber for substantially one minute at a pressure approximately four atmospheres below the ambient pressure.

4. Process according to any preceding claim wherein before the first chamber a first pressure chamber having a pressure higher than the ambient pressure is arranged, and further that optionally between the first and second chambers a second pressure cham- ber is arranged having a pressure higher than the ambient pressure, and optionally as a last process step the elements may be subjected to a heat treatment in order to cure the impregnating agent.

5. Process according to claim 1 wherein the element is a surface, and that an installation comprising an upper gas and liquid impermeable membrane, and a lower gas and liquid permeable membrane is arranged on said surface such that along the perimeter of said installation it is in pressure tight connection with the surface, and that means for providing an air pressure lower than the ambient air pressure is provided connect- able to the upper membrane, and that inlet openings are provided for allowing an impregnating agent comprising solvents and having a molecular size equal to or less than 0.02 μm also is provided in either the upper or lower membrane, and that first the surface under the installation is evacuated such that pore water and physically bound water in the upper regions of the hydraulically bound material is evaporated, after which the impregnating agent is introduced into the installation, and allowed to cure on the surface and in the evacuated pores.

6. Process according to claim 5 wherein the surface after the impregnating agent is introduced is subjected to a heat treatment in order to cure the impregnating agent.

7. Process according to claim 2 wherein the first and second chambers are integral, and that first the process step of lowering the pressure and evacuating steam is performed, whereafter the pressure is increased and the impregnating mist is provided in the immediate vicinity of the elements to be impregnated for a specified period of time, after which time the elements are removed from the second chamber.

8. Apparatus for carrying out the process according to any of claims 1 to 4 or 7 where said apparatus comprises at least two chambers, and that in a first chamber conveyor means are provided and further means for providing a pressure lower than the ambient air pressure in said first chamber is provided, and that in a second chamber arranged such that the conveyor means of said first chamber are in connection with conveyor means arranged in said second chamber for moving elements to be treated, and that in said second chamber means are provided for creating a mist of an impregnating agent.

9. Apparatus according to claim 8 wherein the apparatus further may comprise any of the following: f) a first overpressure chamber arranged before the first chamber; g) a second overpressure chamber arranged between the first and second chambers; h) a curing chamber arranged after the second chamber, where said curing chamber comprises heating means; i) evacuation and regeneration means connected to the second chamber for treat- ing, disposing, regenerating and/or reusing surplus impregnating agent; j) a single through-going conveyor means through the at least two chambers.

10. Apparatus for carrying out the process according to any of claims 1 and/or 5 to 6 where said apparatus comprises at least an upper gas and liquid impermeable mem- brane; a lower gas and liquid permeable membrane, means for creating a pressure tight connection along the periphery of said membranes and the element to be treated; means for connecting a source of under pressure, said means being arranged in the upper membrane; means for connecting a source of impregnating agent and optionally connection means for a heating source such as steam for curing the impregnating agent in the upper material layers of the surface.