WO2000029350A1

WO2000029350A1 - Two component system, a method for producing a building element using said system and a method for repairing a building construction using said system

Info

Publication number: WO2000029350A1
Application number: PCT/SE1999/002077
Authority: WO
Inventors: Satish Chandra; Lars Bohman
Original assignee: Satish Chandra
Priority date: 1998-11-16
Filing date: 1999-11-15
Publication date: 2000-05-25
Also published as: SE9803893L; AU1594100A; SE9803893D0

Abstract

A two-component system is described, whose first component comprises an aqueous solution of an alkali silicate including sodium silicate, potassium silicate or lithium silicate or a mixture thereof, and whose second component comprises an aqueous solution of a calcium salt. Methods for manufacturing building elements and repairing building constructions using the two-component system are also described.

Description

Two _Component System, a Method for Producing a Building EJement _Using Said System and a Method for Repairing a Building Construction Using Said System.

The present invention relates generally to the field of building materials and building constructions and specifically to a two-component system for use when manufacturing building elements and repairing existing building constructions.

Cement is a binder which has been used and tested for a long time in the building technique and which is used m, inter alia, tne production of concrete. The basic cement type is Portland cement . The raw material for Portland cement consists essentially of limestone which is ground to a fine powder together with clay or sand. The ground raw material is fed through a kiln plant whose most important part is a slightly inclined rotary kiln which is heated m its lower end. When the kiln slowly rotates, the material is moved towards the hottest zone where it reaches a temperature of about 1400 °C, at which it sinters to form a gravel-like material which is called Portland clinker. At the same time a chemical reaction takes place, m which calcium oxide combines with silicon oxide to form calcium silicate. This is the most important ingredient m Portland cement. After burning, the Portland clinker is cooled, whereupon it is ground together with a small amount of gypsum. When the cement is mixed with water, a chemical reaction starts which is referred to as hydration, which means that calcium silicate and water form calcium silicate hydrate. This is the most important strength-ensuring component m cement. As is well-known, concrete is a mixture of cement, aggregate and water. By varying the mixing ratios between these three components, different types of concrete are obtained which are adapted to specific applications.

The production of cement is capital- and energy- consuming apart from being harmful to the environment above all because of the emission of contaminating smoke and dust but also as a result of the generation of noise. These are significant drawbacks.

EP-A2-0, 307, 066 discloses a shotcrete lining process, in which cement and sand are mixed in a hopper and supplied by compressed air to a nozzle. A suspension of water and pyrogenic silica is added to the mixture of cement and sand in the nozzle. Neither silicate solutions nor any other salt solutions are used.

SE-B-444,532 discloses a method for intermediate storage and preparation of sand or crushed aggregate for laying a bed of sand. To reduce the formation of dust, sodium and/or potassium silicate in liquid form are supplied to the sand or crushed aggregate.

The idea on which the invention is based is to pro- vide calcium silicate hydrate and so to say integrate this into building material without using cement. This eliminates the above drawbacks and offers above all a technique which is not harmful to the environment . Other advantages will appear from the following description. The present invention thus relates to a two-component system according to claim 1.

According to other aspects of the invention, it relates to a method for manufacturing a building element and to a method for repairing or renovating existing building constructions, using the above-mentioned two- component system.

Before preferred embodiments of the invention will be described in detail, the expressions and terms used herein will be defined more closely. "Aggregate material" relates to stone material essentially consisting of sand, gravel and crushed rock which is used when preparing concrete and mortar. The term "building element" relates to different types of blocks, columns, walls, beams, staircases, roofing tiles, slabs etc. for building purposes. "Building constructions" should be interpreted in a very wide sense and relate generally to constructions based on cement, for example concrete constructions, such as bridges, reservoirs, water towers, prefabricated elements (walls, staircases) etc. An example of non-cement -based constructions is marble floors. The first component in the two-component system according to the invention comprises an aqueous solution of alkali silicate, the alkali silicate consisting of sodium silicate, potassium silicate or lithium silicate or a mixture thereof. In contrast to most silicates, alkali silicates are easily soluble in water. They are thermally stable, which makes them technically useable in a large number of different applications, such as in the building industry. The alkali silicate concentration of the aqueous solution is not critical according to the invention but depends on factors, such as the particle size of the material to be treated with the alkali silicate solution. The alkali silicate solution should have such a concentration and, thus, such a viscosity as to allow it to penetrate into the material and its pores . A person skilled in the art can, before each application, select an adequate concentration. As a non-limiting target, the range 5-18 % by weight is indicated, but this range should not limit the invention in any way.

The second component in the two-component system comprises an aqueous solution of a calcium salt containing, for example, calcium nitrate, calcium chloride and calcium polyphosphate . It is also possible to use a mixture of calcium salts. According to a preferred embodiment, the second component comprises at least one calcium salt and at least one aluminium salt. Non-limiting examples of aluminium salts are aluminium chloride and aluminium nitrate. This embodiment is particularly advantageous if a silicate hydrate with increased stability is desired. A suitable non-limiting salt concentra- tion is 8-18 % by weight. This second component is added after the treatment with the first component and is preceded by drying, preferably with hot air at a temperature of e.g. 50-100°C to remove water before treatment with the second component takes place. It goes without saying that the drying time varies and depends on, inter alia, what consistency and what strength are desirable. After the application of the two-component system, i.e. first one component and then the other, a reaction occurs so that calcium silicate hydrate/calcium aluminium silicate hydrate forms and constitutes the binder between the particles of the aggregate material. In other words, largely the same results, or even better results than in the use of cement are achieved according to the invention, but without the significant drawbacks that are associated therewith and have been described above.

A particularly preferred embodiment of the inven- tion relates to the manufacture of concrete elements using the two-component system according to the invention. One starts from a mould, made of wood or steel, which is charged with an aggregate material having a suitable particle distribution. While being in the mould, the aggregate material is treated with an alkali silicate solution, for example, at a concentration of 10%, and this treatment can take place, for example, by spraying or immersion. Having impregnated the aggregate material with the alkali silicate solution, the mould is dried with hot air having a temperature of e.g. 50 °C and for such a period of time that complete wetting of the particles with the alkali silicate solution is achieved. This period of time can easily be established by a person skilled in the art by routine experiments. Then the con- tents of the mould are treated with a calcium salt solution, i.e. an aqueous solution containing calcium ions, to form, by hydration, calcium silicate hydrate which is difficult to dissolve. Just like in the case of concrete elements based on cement, an increase of the strength takes place in the course of time. With a concrete element in the form of a concrete block according to the invention, a tensile strength of about 30-35 Mpa has been reached after about one month. As is evident from this embodiment, use is made of a very simple technique and relatively low temperatures (in the order of 100°C), which is significantly opposed to the technique and the energy costs that are associated with the manufacture of cement . The building element obtained in accordance with the above embodiment is non-inflammable and does not decrease in strength after fire. Moreover, no formation of dust occurs as in the case of cement . According to a further most preferred embodiment of the invention, the two-component system is applied when repairing different types of building constructions. As non-limiting examples, mention can be made of balconies, water towers, bridges, columns, facades, reservoirs, em- bankments etc. Such repairs are often preceded by "old" concrete material being removed, which can of course be carried out both manually and by means of machinery. In case of slightly damaged constructions, high-pressure washing may be sufficient. Depending on how tight the cleaned surface is, different techniques can be used to treat the surface with the two-component system according to the invention. According to one such technique, it is possible to use vacuum to remove the old material from the pores, at least partially, and replace such material with an alkali silicate solution in a first step and a calcium salt solution in a second step with intermediate drying. The calcium salt solution may contain aluminium ions. Such a vacuum/pressure technique is conventional and can easily be adjusted to the technique applied ac- cording to the invention.

A further application which is closely related to repair is restoration of ancient monuments. As is well- known, ancient monuments tend to moulder apart essentially in consequence of the global environmental pollu- tion. By removing "old" material from the cavities or pores in the building constructions and replace this with the two-component system in the manner outlined above, the possibility of saving ancient monuments will increase considerably.

As is apparent from the above description, the two- component system according to the invention has a variety of applications. There are three important fields of application, viz. 1) manufacture of building elements, 2) repair of concrete structures (such as bridges, reservoirs, balconies, columns, facades etc.) and 3) restoration of ancient monuments. A further field of application is consolidation of rocks and so-called lining, i.e. lining for e.g. sealing purposes in tunnels and the like. When manufacturing "new" concrete elements for example, the aggregate may consist of re-used aggregate or concrete in accordance with modern recovery techniques. Re- garding the applications of the invention it may be mentioned in general that these applications largely coincide with those where cement -based building materials have previously been used.

Claims

1. A two-component system, c h a r a c t e r i s e d in that its first component comprises an aqueous solution of an alkali silicate including sodium silicate, potassium silicate or lithium silicate or a mixture thereof, and that its second component comprises an aqueous solution of a calcium salt.

2. A two-component system as claimed in claim 1, wherein the second component comprises at least one calcium salt and at least one aluminium salt.

3. A two-component system as claimed in claim 1 or 2, wherein the calcium salt consists of calcium nitrate, calcium chloride or calcium polysulphate .

4. A method for manufacturing a building element using the two-component system as claimed in claim 1, c h a r a c t e r i s e d in that an aggregate material is treated with an aqueous solution of an alkali silicate and, after the aqueous solution's penetrating into the aggregate material and wetting the same, is then treated with an aqueous solution of a calcium salt .

5. A method as claimed in claim 4, wherein the aggregate material is dried after being treated with the alkali silicate solution but before the treatment with calcium salt solution.

6. A method as claimed in claim 4 or 5 , wherein the aqueous solution of calcium salt contains aluminium ions.

7. A method for repairing building constructions using the two-component system as claimed in claim 1, c h a r a c t e r i s e d in that at least one surface of the building construction is treated to remove loose material, and that said surface is subsequently treated with an alkali silicate solution and after that with a calcium salt solution.

8. A method as claimed in claim 7, wherein a drying step is carried out after treating the surface with the alkali silicate solution but before treating the surface with calcium salt solution.

9. A method as claimed in claim 7 or 8 , wherein the calcium salt solution contains aluminium ions.

10. A method as claimed in claim 7, wherein the treatment with alkali silicate solution comprises step- wise treatment with an increasing alkali silicate concentration.