Suspension of clays in water for addition to e.g. concrete

Field of the Invention

The present invention relates to a suspension of clay particles in water where the suspension is used as an admixture for the manufacturing of for example concrete.

Background of the Invention

For the so-called high quality concretes a microfiller is often used and in particular microsilica is a preferred material. The addition of microsilica to a concrete mixture provides added strength and density.

It has also previously been suggested to add the clay mineral palygorskite to a concrete mixture in combination with a superplastifier. This was suggested in EP 1152994 Bl which is the inventor of the present invention's earlier patent, in which a self- levelling, self-compacting concrete is described which comprises a Portland cement or other hydraulic binders such as pozzolans, water and aggregate in combination with a content of palygorskite and one or more superplastifiers. The object of adding the palygorskite was to create a high-performance concrete which is self-levelling, self- compacting and tolerant to minor changes in water content.

From JP 01063034 is suggested to prepare a water dispersion agent containing a clay mineral where the suspension in order to disperse the clay mineral in the water, contains an amount of an organic acid or a weak inorganic acid, which aids in dispersing the clay minerals in the water suspension and at the same time lowers the pH value. The suspension produced by this method is, according to the application usable in production of cosmetics, medicines or lubricating agents and helps to maintain a high viscosity in the liquid content of such products.

Also in WO 9301145 is suggested a method for preparing aqueous mineral suspensions where the invention relates generally to the processing of solids into slurries, more specifically to the processing of minerals into aqueous suspensions where the most important mineral is crude kaolin clay. The method uses a so-called blunger which is a high-energy mixer and furthermore the invention describes that all compo-

8UBSTtTUTE SHEET

nents of the suspension either prior to the mixing process or during the mixing process shall be heated, e.g. by adding steam.

Similar compositions are suggested in US 20040016369 and US 20020033121.

Common for the prior art compositions, mentioned above is the fact that they all contain an agent which either will improve the dispersion of the clay minerals in the aqueous suspension or maintain the dispersed clay minerals in a suspended state in the produced suspension. Concrete, and in particular the hardening process of concrete, i.e. the chemical process where the cement particles and other micro-particles react with water in order to create the crystalline structure with gives concrete its relative high strength, in particular compressive strength, is a very complex reaction involving a number of factors, such as for example water content, temperature, particle size and distribution, chemical substances involved and a host of other factors. For these rea- sons it is very undesireable to include further substances which depending on circumstances may influence the mixing properties, the hardening process and thereby the resulting material.

Object of the Invention The present invention aims at providing a suspension containing water and a clay mineral only where the clay mineral due to solely mechanical agitation of the mineral containing liquid, will attain a dispersion of the clay minerals in the liquid which makes it suitable to be used as an additive for, for example concrete mixtures.

Summary of the Invention

The novel invention achieves this by providing a method for the production of a suspension containing water and clay minerals wherein the suspension is created solely by mechanical dispersion of the clay minerals in water.

By being able to disperse the clay minerals in the water solely by mechanical means a number of advantages are achieved. Li the art, as described above, it was suggested to disperse clay minerals in liquids with addition of other substances such as e.g. acids, plastifiers and the like.

SUBSTiTUTE SHEET

A concrete mixture is a very complex structure, and the characteristics, which are obtained by the concrete mixture are very dependent on the constituents of the mixture, the temperature during mixing and curing as well as other minor factors. By being able to better control the design of the concrete, i.e. to control the ingredients, additives and aggregates going into the concrete mixture, it is easier or more predictable to forecast the characteristics relating to strength, density, pore distribution etc. of the resulting concrete. Therefore, a suspension only containing water and clay minerals provides better control for the concrete designer in that no other materials having an influence or interaction with other additives or the like is added to the mix, which could have an influence on the resulting characteristics of the concrete.

Certain clay minerals have a substantial water adsorbing capacity and may act in the concrete mixture as a water buffer, i.e. as a water reservoir that may, to a certain degree compensate for varying water contents in the other components of the concrete mixture. The water content of a given concrete mixture has influence on the flow- ability of the concrete in the fresh, i.e. unhardened, concrete as well as its ability to reach certain strength parameters, air void distribution etc.

By nature clay minerals exhibit colloidal characteristics, i.e. the minerals will tend to form agglomerates where a large number of mineral particles due to their mutual attraction forms a relatively large particle. Depending on the type of clay they may form a more or less open structure. For example smectite minerals have a generally plate like structure, but may at low ionic strength form a semi-stable "card-house" structure, i.e. one plate will bond to the edge of another plate.

The admixture of clay minerals is thereby advantageous in that it improves the homogeneity of the fresh and the hardened concrete. Furthermore, as described above the water content in combination with the cement content and other factors is decisive for the size of the pores and the distribution of pores/air voids in the fresh and hardened concrete. By adding a suspension containing water and clay minerals as suggested in this application therefore improves and makes more consistent the distribution of the strength generating components, and the pores in the hardened material.

The suspension being produced solely by mechanical dispersion is due to the fact that the water's low ionic strength in combination with the mechanical impact, i.e. dispersion of the clay minerals in the water, creates the suspension. In this connection it is preferable to use de-ionized or distilled water as the ion strength is lower, when com- pared to regular tap water. The suspension, however, is a so-called non-stable suspension which makes it necessary to vibrate or shake the suspension vigorously prior to adding it to a mixture such as e.g. concrete.

The relatively pure constitution of the suspension foresees that the addition of suspen- sion of this type to a mixture does not chemically influence any of the other constituents. In this context it is important to note that the different clay materials used within the present invention are as pure as possible. That is to say that the clay minerals, usually in powder form are as free from other substances as possible.

In a further advantageous embodiment of the invention the mechanical dispersion is created by mechanically shaking and/or vibrating the water and clay minerals. The vibration or shaking provides the mechanical energy which together with the low ionic strength of the water over time is able to create a sufficient dispersion of the clay minerals in the water, so that a suspension is achieved consisting of non-agglomerated mineral particles of micron-size (e.g. kaolinite, illite, palygorskite, vermiculite, sepio- lite) or nano-size (smectite).

m a further advantageous embodiment the suspension comprises the method step of mechanically disintegrating the clay minerals in the water. The mechanical disintegra- tion may be achieved e.g. by having a mixer inserted into the suspension for a period of time, whereby the mixing of the suspension containing the minerals will mechanically disintegrate the mineral agglomerates so that primary clay mineral particles are suspended in the water. In this context it is important that the clay minerals are reduced to very small particles (see above) in that an agglomerate of clay minerals may have a detrimental influence on the resulting compressive strength of the concrete.

In a further advantageous embodiment the clay minerals are selected from the group smectite (e.g., in bentonite), illite, sepiolite, vermiculite, palygorskite, kaolinite (e.g., in kaolin).

Bentonite is dominated by the mineral smectite, but the other constituents of bentonite still makes the material usable, and at the same time pure smectite is usable.

In order to achieve the disintegration and dispersion of the clay minerals in the water, the mechanical dispersion in a further advantageous embodiment is created by means selected from one or more means of the following types : ultrasound, vibrating table, rotating or oscillating mixer.

The mechanical disintegration and/or dispersion is carried out over an extended period of time in order to ensure that the clay mineral fraction is reduced in size to very small clay particles in that as already mentioned above agglomerates of clay minerals may have a detrimental effect on the resulting mixture, in particular when the resulting mixture is a concrete. Typically the clay particles shall be of micron-size (e.g. kaolinite, illite, palygorskite, vermiculite, sepiolite) or nano-size (smectite). However a compromise between the mechanical agitation of the suspension (time, intensity) and the result has to be determined. Thorough testing has indicated that convincing results are achieved when the mixing time is as mentioned.

Therefore, the mechanical discretion is carried out from between 1 and 30 hours, more preferred from 2 to 24 hours and most preferred from 8 to 18 hours.

As already mentioned above, the suspension has been developed using concrete as a target application, but it may naturally also be used for other purposes where the same conditions apply. The invention, however, also addresses the use of a suspension in a further advantageous embodiment in a materials mixing process where one of the ma- terials is a hydraulic binder. The hydraulic binder could e.g. be a Portland cement, or any other type of binder.

In a further advantageous embodiment, use of the suspension according to the invention is preferable with a hydraulic binder being a Portland cement and that the suspension and the cement are mixed before further material fractions are added to the mixture. Tests have indicated that a thorough mixture of the suspension with the cement which is also a very fine particle material achieves a higher degree of uniform dispersion throughout the resulting mix.

In a still further advantageous embodiment the use of the suspension according to the invention is advantageous where an additional water and/or micro-particles fraction optionally are added and thereafter an aggregate fraction and possibly further additives such as plastifϊers, air entrainment agents and the like are added at last to said mixture. By adding the components of a mixture in this particular order is achieved that the resulting mixture achieves a very high degree of dispersion of the active ingredients so that a substantially homogenous mixture with regard to distribution of strength form- ing components, air voids/pore distribution etc. is achieved.

Examples

Example 1 : An amount of clay mineral and water in a relationship 1 :4 by weight or less is dispersed by shaking, stirring or ultrasound for 2 to 24 hours.

Example 2: 3.2 litres distilled water is introduced into a 5 litres container into which 800 grams of bentonite is added. The container including its contents is arranged in a vibrating apparatus, and vibrations are applied for 18 hours. At this time the container is removed and a complete dispersion of the clay minerals in the water is achieved.

Example 3: 3.6 litres distilled water is introduced into a 5 litres container and 400 grams of palygorskite is added. The container including its contents is arranged in a vibrating apparatus and exposed to vibrations for 24 hours after which a complete dispersion of the clay minerals in the water is achieved.

Example 4: 1 part bentonite is added to 4 parts water in a container after which a rotating mixer is started. The mixing is carried out for 18 hours after which a complete dispersion of the bentonite in the water is achieved. In the laboratory a rotating mixer using a mixing aggregate normally used for mixing small batches of mortar, concrete and the like arranged in an electric hand drill was used.