A dry mortar composition

Abstract

The invention relates to a dry mortar composition comprising a hydraulic binder and aggregates, said aggregates comprising particles of ground concrete in an amount of 0.5 to 5.0wt% with respect to the weight of dry mortar.

Description

A dry mortar composition

[0001] The present invention relates to a dry mortar composition and to a method for depositing a plaster or a render.

[0002] Plasters and renders are mineral layers deposited on building substrates, especially walls, in particular exterior walls (for renders) and interior walls or ceilings (for plasters). Renders provide waterproofing and make the outside façade more visually appealing, while plasters contribute to the aesthetics of the room, either directly, when they are not covered by paint or wallpapers, or otherwise indirectly by providing a smooth and flat surface.

[0003] Plasters and renders are deposited by applying a wet mortar, obtained by mixing a dry mortar composition with water. A dry mortar composition is a mixture of a hydraulic binder (such as Ordinary Portland Cement, also called OPC), aggregates (fillers and / or sands) and optionally additives. The application can be made manually using a trowel or a float, but techniques such as pneumatic spraying are more efficient.

[0004] Pneumatic spraying equipment traditionally comprise a compressor, a pump and spray gun connected by hoses to the compressor and the pump. It is important when using this technique that the mortar composition shows a good pumpability. This term can be defined as the ability to flow through pipes and hoses by the help of a pump while maintaining the fresh and hardened properties of the mortar. To this end, it has been observed in the past that a small amount of hydrated lime acted as a lubricant and therefore greatly improved the pumpability of the mortar. The production of hydrated lime (Ca(OH)2) however involves calcination of calcium carbonate (limestone) at high temperatures, followed by addition of water. This process creates a huge amount of CO2emissions, both because of the chemical reaction of calcination itself, that releases CO2, and because of the fuel combustion process used to heat the kiln for the calcination process.

[0005] The invention aims at providing a dry mortar composition showing a good pumpability together with a low CO2footprint.

[0006] To this end, an object of the invention is a dry mortar composition comprising a hydraulic binder and aggregates, said aggregates comprising particles of ground concrete in an amount of 0.5 to 5.0wt% with respect to the weight of dry mortar.

[0007] The invention also relates to a method for depositing a plaster or a render on a building substrate, comprising mixing the abovementioned dry mortar composition with water to obtain a wet mortar, pumping said wet mortar, and projecting said wet mortar on said building substrate.

[0008] Another object of the invention is a plaster or a render able to be obtained by this method.

[0009] The inventors have shown that the use of particles of ground concrete as aggregates made it possible to improve the pumpability of the wet mortar, as well as its workability, and allowed the deposition of thicker renders or plasters. Particles of ground concrete therefore play the same role as hydrated lime, but in the same time are much less corrosive and have a much better CO2footprint since they are based on wastes.

[0010] In order to better play their lubricating role and avoid particle segregation during pumping, the particles of ground concrete advantageously have a particle size distribution in volume such that the D50 is 5-20 µm, preferably 10-15 µm. Such distribution can be determined by laser granulometry. As conventional in the technique, D50 corresponds to the median diameter.

[0011] In a preferred embodiment, the particles of ground concrete are particles of ground autoclaved aerated concrete.

[0012] Autoclaved aerated concrete (AAC) is a lightweight, precast, foam concrete building material suitable for producing concrete masonry unit like blocks. AAC products are manufactured by curing under heat and pressure in an autoclave a mixture of quartz sand, calcined gypsum, lime, cement, water and aluminum powder. During its manufacturing, some wastes are produced, for example blocks that do not comply with the specifications. These blocks can be ground in order to obtain a powder that can be used in the composition according to the invention.

[0013] The amount of particles of ground concrete, especially of ground AAC, is preferably 0.8 to 3.0wt%, especially 1.0 to 2.0wt%.

[0014] Preferably, the aggregates additionally comprise aggregates selected from siliceous, calcareous aggregates, dolomitic aggregates and mixtures thereof. Examples are ground limestone or dolomite and silica sand. A mixture of silica sand and limestone is preferred. The aggregates preferably comprise sands (size 0-5 mm) and fillers (size 0-0.1 mm).

[0015] The total amount of aggregates in the dry mortar composition is preferably 50 to 95wt%, even 65 to 90wt%.

[0016] It has been observed that particles of ground AAC show a high water absorption rate, much higher than sands, and even than fillers, with a bulk density close to that of hydrated lime.

[0017] The hydraulic binder is preferably selected from Ordinary Portland Cements, Calcium Aluminate Cements, Calcium Sulfoaluminate Cements, fly ashes, ground granulated blast furnace slags, hydraulic lime, source of calcium sulfate and mixtures thereof.

[0018] In a preferred embodiment, the hydraulic binder is Ordinary Portland Cement (OPC), especially of the CEM I type, as defined in EN 197-1 Standard.

[0019] The amount of hydraulic binder in the dry mortar composition is preferably 5-30wt%, especially 8-25wt%.

[0020] The dry mortar composition may further comprise additives selected from redispersible polymer powders, plasticizers, superplasticizers, accelerators, retarders, rheological modifiers, water-retention agents, pigments, defoaming agents and mixtures thereof.

[0021] The total amount of additives in the dry mortar composition is preferably 0.001 to 2.0wt%, especially 0.005 to 0.5wt%.

[0022] The dry mortar composition advantageously does not comprise hydrated lime, since it can be completely substituted by the ground concrete.

[0023] The method for depositing a plaster or a render on a building substrate comprises mixing the dry mortar composition with water to obtain a wet mortar, pumping said wet mortar, and projecting said wet mortar on said building substrate.

[0024] The building substrate is preferably a wall, for example an exterior wall for a render, or an interior wall for a plaster.

[0025] The wall may be constructed by any known method, for example by pouring concrete between formworks, by joining masonry elements such as bricks or concrete blocks, or by 3D-printing of mortar.

[0026] The building substrate may also be an insulation panel in the case of external thermal insulation systems (ETICS).

[0027] Projecting the wet mortar on the building substrate is preferably done by pneumatic spraying.

[0028] The weight ratio of water to the dry mortar composition is preferably 0.10 to 0.20.

[0029] The thickness of the render or plaster is preferably 1 to 20 mm (especially after 28 days of hardening).

[0030] Examples

[0031] The invention will be better understood with the help of the following non-limiting examples.

[0032] A comparative composition “A” comprised 10-25wt% of CEM I type OPC, 0.1wt% of additives and 1.5wt% of hydrated lime (D50 = 8 µm), the rest being sands and fillers.

[0033] In a composition according to the invention “B”, hydrated lime was replaced by ground AAC with a D50 of 12 µm and a D90 of 35 µm.

[0034] Table 1 hereafter shows the properties of the wet mortar after mixing with water, with a water / dry mortar weight ratio of 0.15. The compressive and flexural strengths were measured according to EN1015-11 Standard. The consistency was evaluated by using a flow table and measuring the diameter (in cm) of the wet mortar when it spreads on a table.

[0035] ABFresh density (g / mL) - initial1.421.43Fresh density (g / mL) – 15 min1.461.48Consistency (cm) - initial14.8014.80Consistency (cm) – 15 min14.8014.80Water retention (%)8786Setting time (h)98.5

[0036] Table 2 shows the characteristics of the hardened mortar.ABFlexural strength (MPa)2d0.540.567d0.750.7828d1.501.50Compressive strength (MPa)2d0.600.607d1.001.0728d2.052.20Length change (mm / m)2d0.050.067d0.550.4828d0.700.64Tensile adhesion strength on wall (MPa)7d0.70.7

[0037] These results show that the replacement of hydraulic lime by ground concrete does not change the behavior of the wet mortar or the properties of the hardened mortar.

[0038] Big scale applications on 5sqm walls showed that the mortar could be easily mixed and placed on walls (using a pump), without any sagging, and could be easily finished by the applicator. Therefore, it could be concluded that the mortar achieved the right level of workability.

Claims

A dry mortar composition comprising a hydraulic binder and aggregates, said aggregates comprising particles of ground concrete in an amount of 0.5 to 5.0wt% with respect to the weight of dry mortar.The dry mortar composition according to claim 1, wherein the particles of ground concrete have a particle size distribution in volume such that the D50 is 5-20 µm, preferably 10-15 µm.The dry mortar composition according to any one of the preceding claims, wherein the particles of ground concrete are particles of ground autoclaved aerated concrete.The dry mortar composition according to any one of the preceding claims, wherein the amount of particles of ground concrete is 0.8 to 3.0wt%, especially 1.0 to 2.0wt%.The dry mortar composition according to any one of the preceding claims, wherein the total amount of aggregates in the dry mortar composition is 50 to 95wt%, even 65 to 90wt%.The dry mortar composition according to any one of the preceding claims, wherein the hydraulic binder is selected from Ordinary Portland Cements, Calcium Aluminate Cements, Calcium Sulfoaluminate Cements, fly ashes, ground granulated blast furnace slags, hydraulic lime, source of calcium sulfate and mixtures thereof.The dry mortar composition according to any one of the preceding claims, wherein the amount of hydraulic binder in the dry mortar composition is 5-30wt%, especially 8-25wt%.The dry mortar composition according to any one of the preceding claims, further comprising additives selected from polymers, plasticizers, superplasticizers, accelerators, retarders, rheological modifiers, pigments, defoaming agents and mixtures thereof.The dry mortar composition according to any one of the preceding claims, which does not comprise hydrated lime.A method for depositing a plaster or a render on a building substrate, comprising mixing the dry mortar composition of any one claims 1 to 9 with water to obtain a wet mortar, pumping said wet mortar, and projecting said wet mortar on said building substrate.The method according to claim 10, wherein the building substrate is a wall.The method according to claim 11, wherein projecting the wet mortar on the building substrate is done by pneumatic spraying.The method according to any one of claims 10 to 12, wherein the weight ratio of water to the dry mortar composition is 0.10 to 0.20.A plaster or a render able to be obtained by the method of any one of claims 10 to 13.The plaster or render according to claim 14, the thickness of which is 1 to 20 mm