CS215240B1 - A method of preparing a ductile composition for producing water-resistant artificial stone - Google Patents

Abstract

Method for preparing a moldable mixture for the production of artificial stone resistant to water from quartz sand with a grain size of 10-^ to 3 mm and 5 to 15 wt. % of an epoxy resin solution in an organic solvent, e.g. toluene in a concentration of 25 to 100 wt. % of the compound RSi(ORÍ·, where R is alkyl, aryl or aralkyl with C^ to C12 and R is alkyl with C-^ to Cg, after which the resulting mixture is homogenized and processed in a conventional manner. The moldable mixture for the production of artificial stone according to the invention is applicable in particular in the replenishment of damaged stone and sculptural objects, where long-term resistance to water and weathering is required, while maintaining the original appearance of the object and aesthetic effect. Similarly, the described moldable mixture can be used in the production of copies or facsimiles, etc. The essence of the invention is described by two examples.

Description

The invention relates to the preparation of a malleable mixture for the production of artificial stone resistant to the effects of water.

It is generally known that the presence of water is the main source of damage to natural stones and sealants containing disintegrated natural material and classic binders such as lime or cement or binders made of plastic materials. Weathering occurs, for example, by increasing the volume of water upon freezing, leaching of soluble parts of the bonding sealant or migration of aqueous solutions and the formation of efflorescence. The presence of water conditions the growth of microorganisms, which also accelerate the weathering process with their life processes. The presence of water in the material also allows chemical reactions to occur with harmful substances in the exhalations leading to the destruction and disintegration of the material.

In the case of artificial stones, where the binding component is organic plastic materials, there has been a certain improvement in this respect compared to classic building materials, because plastic as an organic material already has hydrophobic properties in itself. For example, water absorption has been significantly reduced compared to classic materials. However, a significantly more pronounced effect can be achieved by additional hydrophobization of the sealant using various types of hydrophobization agents, e.g. organosilicon. Hydrophobization using these active substances is very effective even when applied in relatively small quantities, but it only penetrates the sealant to a certain limited depth, which does not exceed 2 to 3 cm. For this reason, an interface between the hydrophobic and hydrophilic layers is created inside the sealant, which can result in various disadvantageous phenomena, e.g. accumulation of soluble salts. If the hydrophobicized sealant is not very strong or the hydrophobic layer is thin, it may fall off, and the crack will form at the interface between the hydrophobic and hydrophilic layers.

This very harmful condition can be prevented by hydrophobizing the sealant throughout the mass, which can be done by adding suitable hydrophobizing additives already during the preparation of the sealant. Organosilicon compounds of the ester type are proposed as suitable additives, which have at least one organic group with a Si-C bond on the silicon. Organosilicon compounds of the ester type, i.e. those that contain a Si-0-C bond in the compound, have the essential property that upon contact with moisture present in the material or in the air, hydrolysis of alkoxyl groups occurs and silanols are formed, which can condense with hydroxyl groups on the silicate substrate and form a very strong chemical bond. At the same time, in suitable cases, a chemical bond can also occur between organosilicon esters and organic binders.

The essence of the invention is a method of preparing a moldable mixture for the production of artificial stone resistant to water, in which 5 to 15% by weight of the epoxy resin mixture in a concentration of 25 to 100% in an organic solvent, e.g. toluene, a hardener and 0.5 to 5% of the compound RSi(OR'J ₃ , where R is alkyl, aryl or aralkyl with up to C^ ₂ ^and R'j® alkyl with up to Cg is added to quartz sand with a grain size of 10~ to 3mm, after which the ^mixture is homogenized and processed in a conventional manner.

Below we present examples of a method of preparing a malleable mixture for the production of artificial stone according to the invention.

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Example 1

Κ 1 kg of silica sand with a grain size of 0.05 to 0.6 mm was added 30 g of fine silica with a particle size of up to 0.0001 mm. The material was thoroughly mixed for 20 minutes and then 100 g of epoxy resin (50% by weight solution in toluene), 7 g of diethylenetriamine as a hardener and 8 g of methyltriethoxysilane were added. After thorough homogenization, a malleable mixture was formed, from which 4 test samples (cubes with an edge of 5 cm) were pressed into a metal mold, the surface of which was provided with a microlayer of methylsilicone oil with a viscosity of 0.2 Pa.s. After curing for 24 hours at a temperature of 18 °C, the samples were removed from the mold and left undisturbed for 14 days. After this time, 2 samples were tested for compressive strength and the values obtained were compared with samples in which no hydrophobic agent was used.

Compressive strength of samples Compressive strength of samples with the addition of methyltrietoxysilanes · without methyltrietoxysilane

MPa

26

24 average value 24.5 MPa ' average value 25 MPa ^y The water absorption of 2 samples was determined by immersing them together with the comparison samples in a container of water. The results showed that the water absorption of the samples with the addition of the hydrophobic agent was 1.2% in 200 minutes, while the water absorption of the comparison samples of sandstone from the Mšeno site was 11.8

Example 2

To a mixture of 7 kg of silica sand with a grain size of 0.05 to 0.2 mm and 3 kg of sand with a grain size of 0.2 to 0.6 was added 200 g of fine silica with a particle size of 10~®mm. After thorough mixing - 800 g of epoxy resin, g of diethylenetriamine as a hardener and 240 g of phenyltributoxysilane were added to the bulk material. After kneading, a malleable mixture was formed, which was blown into a three-part plaster mold in the shape of a baroque balustrade cone, which was wiped with a release agent methyl silicone oil with a viscosity of 0.2 Pa.s. After 24 hours of curing at a temperature of approximately 20 °C, the exhaust was removed from the mold and exposed to the weather for 14 days. After 4 years, no damage caused by the aggressive effects of water and aqueous solutions was observed.

The molding mixture for the production of artificial stone according to the present invention is particularly useful in the repair of damaged stone and sculptural objects, where long-term resistance to water and weathering is required while maintaining the original appearance of the object and its aesthetic effect. Similarly, the described molding mixture can be used in the production of copies or facsimiles, etc.

Claims (1)

SUBJECT OF THE INVENTION Process for the preparation of a ductile mixture for the production of water-resistant artificial stone made of quartz sand, grain size 10 "® to 3mm · and 5 to 15 wt. % of a solution of epoxy resin in an organic solvent such as toluene at a concentration of 25 to 100 wt. % with a hardener in an amount of 6 to 10 wt. % by weight of the epoxy resin, characterized in that from 0.5 to 10% is added 5 wt% of the compound RSi (OR) ,, where R is alkyl, aryl or aralkyl group with C, to C, _o · lb * J Q x to C, whereupon the mixture is homogenized and worked up in conventional manner. is alkyl s