Natural pozzolan-based building coating material and dry mass kit for preparing such a material

Abstract

A building coating material based on natural pozzolan and a dry mass kit for preparing such a material. The invention relates primarily to a building coating material comprising a mixture of water and dry mass, said dry mass comprising a mixture of air lime and reactive mineral matter consisting exclusively of unprocessed natural volcanic pozzolan particles with a particle size of less than 2 millimeters. The invention further relates to a dry mass kit for preparing such a building coating material, in which said dry mass comprises a mixture of air lime and mineral matter consisting exclusively of unprocessed natural volcanic pozzolan particles with a particle size of less than 2 millimeters. The coating material of the invention can be used as a plaster, finishing plaster, or paint. Figure to be published with the abstract: Fig. 1

Description

Title of the invention: Natural pozzolan-based building coating material and dry mass kit for preparing such a material technical field

[0001] The invention falls within the field of ecological building materials, and more particularly within the field of wall, floor and ceiling coverings for interior or exterior use.

[0002] The invention relates more particularly to the field of coatings and paints. PRIOR ART AND DRAWBACKS OF PRIOR ART

[0003] Construction materials have a significant impact on the environment. For example, cement accounts for approximately 7% of global greenhouse gas emissions. Concrete, like mortar, is made from cement, which acts as a binder in the mixture and provides mechanical strength to the finished material.

[0004] In the more specific field of masonry mortars applied to finished walls, floors or ceilings, then called plasters, it is known to mix a mineral material, most often sand, with cement and water. A vegetable material may optionally be added.

[0005] Depending on whether the mortar is a construction, coating, or finishing mortar, the compositions differ according to the required properties, particularly in terms of mechanical strength and breathability. When a construction site requires the use of different mortars, it is therefore necessary to prepare several different compositions, which generates significant labor and material costs. The same applies to paints applied to plaster, which are known to have completely different formulations from mortar formulations. OBJECTIVE OF THE INVENTION

[0006] The invention aims to overcome the aforementioned drawbacks by providing a cement-free construction coating material that offers the required mechanical strength properties when used as mortar. The invention also aims to provide a construction coating material whose composition is suitable for all types of construction, covering, and finishing mortars, as well as for paints.

[0007] The invention also aims, in addition to the absence of the use of cement, to offer a completely ecological material.

[0008] The invention finally aims at a ready-to-use construction material kit for use on site by adding water for all the applications concerned. Description of the invention

[0009] For this purpose, the invention relates to a construction coating material, which is essentially characterized in that it comprises a mixture of water and dry mass, said dry mass comprising a mixture of air lime and reactive mineral matter consisting exclusively of natural volcanic pozzolan particles of a grain size of less than 2 millimeters which have not undergone any transformation.

[0010] The material of the invention may also include the following optional characteristics considered individually or according to all possible technical combinations: • the said material is free from sand, clay, fixing agent and water-retaining agent. • Natural volcanic pozzolan particles have a grain size of less than 1 millimeter. • Natural volcanic pozzolan is red natural volcanic pozzolan. • the volume ratio between lime and pozzolan in the dry mass is greater than 1. • the volume ratio between lime and pozzolana in the dry mass is 1.5. • according to a first variant intended for a coating application, the volume ratio between dry mass and water is between 2 and 3.5, preferably between 2.5 and 3.3, and in that the particle size of the pozzolan particles is less than 2 millimeters. • advantageously according to this variant for which the volume ratio between dry mass and water is between 2 and 3.5, preferably between 2.5 and 3.3, the pozzolan particles are from one or more granulometric cuts between 100 and 300 microns, preferably between 200 and 300 microns and more preferably between 200 and 250 microns. • according to a second variant intended for paint application, the volume ratio between water and dry mass is between 0.8 and 1.4 and in that the average particle size of the pozzolan particles is less than 0.5 millimeters.

[0011] The invention also relates to a dry mass kit for preparing a construction coating material as previously defined, which is essentially characterized in that said dry mass comprises a mixture of air lime and mineral matter consisting exclusively of natural volcanic pozzolana particles with a grain size of less than 2 millimeters which have not undergone any transformation.

[0012] The kit of the invention may also include the following optional features considered individually or according to all possible technical combinations: • the dry mass is free of clay, fixing agent and water-retaining agent. • Natural volcanic pozzolan particles have an average grain size of less than 1 millimeter. • natural volcanic pozzolana and natural red volcanic pozzolana. • the volume ratio between lime or lime mixture and pozzolana in the dry mass is greater than 1, preferably 1.5.

[0013] The invention further relates to the use as a coating or as a finishing coating of the construction coating material of the invention for which the volume ratio between dry mass and water is between 2 and 3.5, preferably between 2.5 and 3.3, and the average particle size of the pozzolan particles is less than 2 millimeters.

[0014] The invention finally relates to the use as an interior or exterior wall paint of the construction coating material of the invention for which the volume ratio between water and dry mass is between 0.8 and 1.4 and the average particle size of the pozzolan particles is less than 0.5 millimeters. PRESENTATION OF THE FIGURES

[0015] Other features and advantages of the invention will become clear from the description given below, by way of example and not limitation, with reference to the attached figure:

[0016] [Fig. 1] Fig. 1 is a photograph of the surface of the coating material of construction of the invention where the particle size of the natural pozzolana is between 100 and 300 microns, the surface being naturally covered with a varnish on which drops of water have been applied to characterize the hydrophobic properties of the varnish. DETAILED DESCRIPTION OF THE INVENTION

[0017] The invention relates mainly to a building coating material, which comprises a dry mass comprising an exclusively reactive mineral material consisting of natural volcanic pozzolana particles with a grain size of less than 2 millimeters and aerial lime, mixed with water.

[0018] Reactive mineral material is defined as mineral material that directly contributes, either with or in reaction with air lime, to the mechanical properties of the coating material. For example, natural pigments that contribute to the aesthetic modification of the coating material are excluded from reactive mineral materials. Consequently, the invention covers a coating material that comprises, in addition to air lime and pozzolan particles, natural pigments, but contains no other reactive mineral material besides natural pozzolan.

[0019] In this respect, the invention is particularly remarkable in that the material contains neither sand, nor clay, nor a fixing agent to prevent the rise of fine lime particles (powdery effect), nor a water-retaining agent. The material obviously does not contain cement. Nor does the material contain hydraulic lime. Optionally, and as previously indicated, the mixture may contain natural pigments.

[0020] As will be seen later, depending on the amount of water added and the particle size of the pozzolana particles, the material can be a construction mortar, a coating mortar, a finishing mortar, or even paint.

[0021] The pozzolan used in the invention is exclusively natural pozzolan, namely volcanic aggregates with an alveolar structure. The natural pozzolan of the invention has not undergone any physicochemical transformation. Only mechanical modifications are applied to give it the desired particle size. For this purpose, and by way of example, the pozzolan is first crushed and then sieved. It is an essential element of the invention that the pozzolan be in the form of particles with an average particle size of less than 2 millimeters in order to give the resulting material, in particular the mortar, the required mechanical properties.

[0022] Without limitation, the pozzolan used is red pozzolan from Réunion Island or grey pozzolan. Without limitation, red pozzolan is preferred since it allows for the production of a material with superior mechanical properties compared to a material made from grey pozzolan.

[0023] As is known, pozzolanic materials are defined as siliceous or silico-aluminous materials that do not exhibit binding activity on their own but, in the presence of calcium hydroxide, form a material with binding properties. The pozzolanic activity index, ranging from 0.67 to 1, describes the rate of reaction between the pozzolanic material and the lime.

[0024] In the literature, the term pozzolana or pozzolanic material most often refers not to natural pozzolan, but to other materials exhibiting pozzolanic activity. For example, in the literature, the term pozzolanic material, or even simply pozzolan, is understood to refer to calcined pozzolan, shale, calcined shale, volcanic ash, or clays such as crushed brick or metakaolin. All these components are excluded from the scope of the invention. The advantageous properties of a material made from natural pozzolan according to the invention, compared to a material made from crushed brick, will be shown later, highlighting the lesser properties of a material made from a clay compound.

[0025] According to the invention, the pozzolan particles have an average particle size of less than 2 millimeters, which makes it possible to produce all types of mortar, as well as paints, and to obtain the required mechanical properties. A particle size of less than 2 millimeters is defined as a particle size obtained by particle size cutting, for example, by sieving natural pozzolan using a sieve with an opening diameter of 2 millimeters, resulting in pozzolan particles with a particle size of less than 2 millimeters. Thus, pozzolan particles obtained from a 2-millimeter particle size cutting process have a particle size, or average diameter, of less than 2 millimeters. Preferably, the particle size is less than 1 millimeter, since this particle size has been observed to confer better mechanical properties, as will be seen later.This particle size of less than 1 millimeter also allows for the preparation of all types of mortars as well as paints.

[0026] For construction mortars, the particle size shall preferably be less than 2 millimeters. For coating mortars, the particle size shall preferably be less than 1 millimeter. For finishing mortars, the particle size shall preferably be less than 0.5 millimeters. For paints, the particle size shall preferably be less than 0.5 millimeters. Furthermore, the water content of the material relative to its dry mass shall vary depending on whether the material is used as mortar or as paint, as will be explained later.

[0027] As regards lime, a person skilled in the art, aiming to avoid the use of cement and knowing pozzolanic materials, would naturally have been led to use hydraulic lime for its properties closer to those of cement than aerial lime, in order to give the finished material advantageous properties in terms of mechanical resistance.

[0028] However, it was unexpectedly noted in the course of the invention that air lime alone and in mixture with pozzolan, preferably in particular proportions defined in relation to the natural pozzolan particles, allowed to give the finished material both mechanical properties similar to those obtained with hydraulic lime, and also advantageous breathability properties. Breathability is one of the essential criteria for mortars and plasters. Indeed, tests carried out with hydraulic lime instead of air lime resulted in the creation of impermeable surfaces, causing condensed water to run down the surface and leading to the development of mold at the base. A mortar or plaster made according to the invention using only air lime, on the other hand, resulted in a surface capable of absorbing surrounding water and releasing it when the humidity level allows.This capacity is particularly important in tropical environments where ambient humidity is high and where the proliferation of fungi due to moisture accumulation on or at the base of walls is particularly noticeable. Conversely, and advantageously, the composition of the material of the invention allows for the creation of a coating material capable of absorbing water when the environment is humid and releasing the absorbed water when the ambient humidity permits.

[0029] It was further observed during tests carried out within the framework of the invention that the use of hydraulic lime, alone or mixed with air lime, resulted in a non-smooth surface, which is particularly disadvantageous when the material of the invention is used as a finishing plaster. Furthermore, when hydraulic lime is used mixed with natural pozzolan, the resulting material presents application difficulties for operators.

[0030] It was expected that the use of air lime would cause lime fines to rise to the surface of the finished material, particularly finishing plasters and paints, characterized by the presence of a white powder after drying. Unexpectedly, no rise of fines was observed with the coating material of the invention. Most often, the compositions of plasters or paints containing air lime also include additives, for example, casein, which acts as a binder, or in other words, a glue for the fine lime particles, preventing them from rising to the surface. The presence of such additives with this function is excluded from the scope of the invention since, unexpectedly, the mixture of natural pozzolan and air lime does not cause lime fines to rise to the surface.

[0031] According to the invention, the volume ratio between lime and pozzolana in the dry mass is greater than 1, preferably 1.5. These proportions allow the material to have good mechanical properties, as will be seen later.

[0032] According to the invention, when the material of the invention is used as a coating, the volume ratio between the dry mass and the water is between 2 and 3.5, preferably between 2.5 and 3.3, in addition to the associated particle size indicated previously. These volume ratios allow for the creation of a mortar with an optimal consistency for application on walls, floors, or ceilings.

[0033] According to the invention, when the material of the invention is used as paint, the volume ratio between the dry mass and the water is between 0.8 and 1.4, in addition to the associated particle size indicated above. These volume ratios make it possible to produce a paint that is sufficiently fluid for application with a whitewash brush on walls, floors, or ceilings.

[0034] According to the invention, a surprising property has been observed of the material of the invention when used as a coating or paint, for a particle size of pozzolan obtained from one or more particle size sections between 100 and 300 microns, and more particularly between 200 and 300 microns, more preferably between 200 and 250 microns. For this particle size range, and for a material in which the volume ratio between air lime and pozzolan in the dry mass is greater than 1, preferably 1.5, and the volume ratio between the dry mass and water is between 2 and 3.5, preferably in this case 2.5, a transparent and hydrophobic varnish layer appears on the surface of the material after drying. Reference is made to [Fig.[l] illustrating the varnish layer on the surface of the material of the invention when red pozzolan particles with an average particle size between 200 and 300 microns are used. Water drops applied to the surface illustrate the strongly hydrophobic nature of the surface, in addition to the visibility of the varnish on the surface of the material.

[0035] The appearance of this varnish layer has advantages, particularly aesthetic ones, since the use of this particle size can allow the production of paints without additives and without the additional addition of a varnish layer.

[0036] The invention also relates to a dry mass kit for manufacturing the construction material of the invention, comprising the dry mass of the material as previously described. Before use, the dry mass of the kit is mixed with water in the proportions previously indicated, depending on the application of plaster or paint.

[0037] Comparative tests are set out below to highlight the advantageous properties of the coating material of the invention.

[0038] Example 1: Comparative tests between the material of the invention comprising air lime and a material comprising hydraulic lime

[0039] In this example, a mortar is made from a dry mass consisting of natural red pozzolana from Réunion Island with a particle size of less than 2 millimeters, and aerial lime or hydraulic lime for the counter-example. The volume ratio between lime and pozzolan in the dry mass is 1.5. The volume ratio between the dry mass and water is 2.5.

[0040] A block of mortar with dimensions of 4 cm x 4 cm x 16 cm is prepared and dried for 28 days.

[0041] Mechanical resistance tests in bending are carried out according to the French standard NF EN 1015-11. The results are shown in Table 1 below. [Tables 1] Tested Material Tensile Strength (Newtons) Tensile Strength (MPa) Average Stress (MPa) Counter-example: pozzolan + hydraulic lime 140 0.33 0.32 137 0.32 Example: pozzolan + air lime 113 0.26 0.30 147 0.34

[0042] It is observed that, contrary to what could have been expected, the mechanical performance of the material is similar to that of the lime used in the mixture, whether aerial lime or hydraulic lime.

[0043] Example 2: Comparative tests between the material of the invention comprising natural pozzolana and a material comprising crushed brick.

[0044] As in Example 1, a mortar is made with a dry mass consisting of natural red pozzolan from Réunion Island with a particle size of less than 0.5 millimeters and less than 1 millimeter (particle sizes of 0.5 millimeters and 1 millimeter respectively), or crushed brick of the same particle sizes, and air lime. The volume ratio between the lime and the pozzolan or crushed brick in the dry mass is 1.5. The volume ratio between the dry mass and water is 2.5.

[0045] A block of mortar with dimensions of 4 cm x 4 cm x 16 cm is prepared and dried for 28 days.

[0046] Mechanical resistance tests in bending are carried out according to the French standard NF EN 1015-11. The results are shown in Table 2 below. [Tables 2] Tested material Tensile strength (Newtons) Tensile strength (MPa) Average stress (MPa) Counter-example: crushed brick (0.5 mm) + air lime 120 0.28 0.28 120 0.28 Counter-example: crushed brick (1 mm) + air lime 364 0.85 0.48 48 0.11 Example: pozzolan (0.5 mm) + air lime 340 0.80 0.85 386 0.90 Example: pozzolan (1 mm) + air lime 400 0.94 0.64 150 0.35

[0047] Mechanical resistance tests in compression are also carried out according to the French standard NF EN 1015-11. The results are shown in Table 3 below. [Tables 3] Tested Material Average Strength at Break (Newtons) Tensile Strength (MPa) Average Stress (MPa) Counter-example: crushed brick (0.5 mm) + air lime 1162 0.75 0.71 1155 0.74 1021 0.66 Counter-example: crushed brick (1 mm) + air lime 1008 0.65 0.62 925 0.58 999 0.64 Example: pozzolan (0.5 mm) + air lime 1211 0.80 0.80 1243 0.82 1211 0.80 Example: pozzolan (1 mm) + air lime 1481 0.97 0.88 1447 0.95 1102 0.72

[0048] It is observed that the mechanical performance of the material according to the invention, comprising pozzolana as a mineral material, is substantially superior to that of a material comprising crushed brick, even though crushed brick induces pozzolanic reactions with air lime.

[0049] Example 3: Comparative tests between the material of the invention comprising natural pozzolana and a material comprising crushed brick.

[0050] As in Example 1, a mortar is made on a dry mass basis consisting of natural red pozzolan from Réunion Island with a particle size less than 0.5 millimeters, less than 1 millimeter, and less than 2 millimeters (particle sizes of 0.5 millimeters, 1 millimeter, and 2 millimeters respectively), and air lime. The volume ratio between lime and pozzolana or crushed brick in the dry mass is 1.5. The volume ratio between the dry mass and water is 2.5.

[0051] A block of mortar with dimensions of 4 cm x 4 cm x 16 cm is prepared and dried for 28 days.

[0052] Mechanical resistance tests in bending are carried out according to the French standard NF EN 1015-11. The results are shown in Table 4 below. [Tables 4] Tested Material Tensile Strength (Newtons) Tensile Stress (MPa) Average Stress (MPa) Pozzolan (0.5 mm) + air lime 340 0.80 0.85 386 0.90 Pozzolan (1 mm) + air lime 400 0.94 0.64 150 0.35 Pozzolan (2 mm) + air lime 113 0.26 0.30 147 0.34

[0053] Mechanical resistance tests in compression are also carried out according to the French standard NF EN 1015-11. The results are shown in Table 5 below. [Tables 5] Tested Material Average Strength at Break (Newtons) Tensile Strength (MPa) Average Stress (MPa) Pozzolan (0.5 mm) + air lime 1211 0.80 0.80 1243 0.82 1211 0.80 Pozzolan (1 mm) + air lime 1481 0.97 0.88 1447 0.95 1102 0.72 Pozzolan (2 mm) + air lime 937 0.62 0.63 963 0.63 965 0.63

[0054] It is observed that the compressive mechanical performance of the material according to the invention for a pozzolan particle size of less than 1 millimeter is significantly higher than that obtained for a pozzolan particle size of less than 2 millimeters. While decreasing mechanical performance might be expected with increasing particle size, it is nevertheless observed that the results obtained for a particle size of less than 1 millimeter exceed what could be expected, particularly with regard to compressive strength.

[0055] Example 4: Comparative particle size tests and demonstration of the presence of a varnish layer.

[0056] As in Example 1, a mortar is made from a dry mass comprising a mixture of air lime and natural red pozzolan from Réunion Island with a particle size of less than 2 millimeters. The volume ratio between the lime and the pozzolan or crushed brick in the dry mass is 1.5. The volume ratio between the dry mass and water is 2.5.

[0057] Several mortar blocks measuring 4 cm x 4 cm x 16 cm are prepared from pozzolan particles of varying particle sizes obtained through different particle size distributions, for example by sieving with sieves having aperture diameters ranging from 50 microns to 2 millimeters. The mortar blocks are then dried for 28 days.

[0058] The presence or absence of a varnish on the surface of each mortar is observed after drying. The ease or difficulty of applying the mortar to the work surface before drying is also observed. The results are shown in Table 6 below. [Tableauxô] Particle size distribution of pozzolan powder particles in mortar. Varnish effect. Ease of application: 50 microns ++ - 100 microns ++ + 150 microns ++ + 200 microns ++ ++ 250 microns ++ ++ 300 microns + ++ 400 microns - ++ 500 microns - ++ 1 mm - ++ 2 mm - ++

[0059] "Varnish Effect" column: • - No varnish present • + Presence of varnish • ++ Pronounced presence of varnish

[0060] "Ease of application" column: • - Difficult application • + Moderately easy application • ++ Easy application

[0061] It is observed that the presence of a varnish on the surface of the mortar corresponding to [Fig.1] is observed for pozzolan particle size sections less than 300 microns and particularly pronounced for pozzolan particle size sections less than 250 microns.

[0062] It is observed that the application of the mortar on the working surface is easy for particle size cuts between 2 millimeters and 200 microns, that the application is average for particle size cuts of 150 and 100 microns and that the application is difficult for a particle size cut of 50 microns.

[0063] It follows that the varnish effect obtained by the material of the invention on the mortar is optimal for a particle size of the pozzolan particles between 100 and 300 microns, preferably between 200 and 300 microns and more preferably between 200 and 250 microns for which particle size cuts the application of the mortar is also easy.

[0064] Within the framework of the invention, it is possible to provide a mixture of pozzolana particles resulting from several particle size cuts according to the values ​​previously explained.

Claims

Demands

1. Construction coating material, characterized in that it comprises a mixture of water and dry mass, said dry mass comprising a mixture of air lime and reactive mineral material consisting exclusively of natural volcanic pozzolan particles of a grain size less than 2 millimeters which have not undergone any transformation.

2. Construction coating material according to the preceding claim, characterized in that said material is free from sand, clay, fixing agent and water-retaining agent.

3. Construction coating material according to any one of the preceding claims, characterized in that the natural volcanic pozzolan particles have a particle size of less than 1 millimeter.

4. Construction coating material, characterized in that the natural volcanic pozzolan is red natural volcanic pozzolan.

5. Construction coating material according to any one of the preceding claims, characterized in that the volume ratio of lime to pozzolana in the dry mass is greater than 1.

6. A building coating material according to any one of the preceding claims, characterized in that the volume ratio of lime to pozzolan in the dry mass is i 5

7. 1,J. Construction coating material according to any one of the preceding claims, characterized in that the volume ratio between dry mass and water is between 2 and 3.5, preferably between 2.5 and 3.3, and in that the particle size of the pozzolan particles is less than 2 millimeters.

8. Construction coating material according to the preceding claim, characterized in that the volume ratio between dry mass and water is between 2 and 3.5, preferably between 2.5 and 3.3, and in that the pozzolan particles are obtained from one or more particle size cuts of between 100 and 300 microns, preferably between 200 and 300 microns and more preferably between 200 and 250 microns.

9. Construction coating material according to any one of claims 1 to 6, characterized in that the water-to-dry-mass volume ratio is between 0.8 and 1.4 and in that the particle size of the pozzolan particles is less than 0.5 millimeters.

10. Dry mass kit for preparing a construction coating material according to any one of the preceding claims, characterized in that said dry mass comprises a mixture of air lime and mineral matter consisting exclusively of natural volcanic pozzolan particles of a grain size less than 2 millimeters having not undergone any transformation.

11. Kit according to the preceding claim, characterized in that the dry mass is free of clay, fixing agent and water-retaining agent.

12. Kit according to any one of claims 10 and 11, characterized in that the natural volcanic pozzolan particles have an average grain size of less than 1 millimeter.

13. Kit according to any one of claims 10 to 12, characterized in that natural volcanic pozzolan and natural red volcanic pozzolan.

14. Kit according to any one of claims 10 to 13, characterized in that the volume ratio of lime or lime mixture to pozzolan in the dry mass is greater than 1, preferably of

15. Use of the construction coating material of claims 7 and 8 as a coating or as a finishing coating.

16. Use of the construction coating material of claim 9 as an interior or exterior wall paint.

Images