GB1594516A

GB1594516A - Manufacture of lightweight concrete

Info

Publication number: GB1594516A
Application number: GB24447/78A
Authority: GB
Original assignee: Internationella Siporex AB
Current assignee: Internationella Siporex AB
Priority date: 1978-05-30
Filing date: 1978-05-30
Publication date: 1981-07-30

Description

(54) IMPROVEMENTS IN THE MANUFACTURE OF LIGHT-WEIGHT CONCRETE (71) We, INTERNATIONELLA SIPOREX AB., a Swedish Company, of Hans Michelsensgatan 9, Malt5, Sweden, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a method for the manufacture of cellular steam-cured light-weight concrete and is an improvement in or modification of the invention described in our Specification No. 1,452,818.

Specification No. 856,218 describes the setting of hydraulic binders by admixing with the hydraulic binder a finely divided magnesium carbonate in an amount of from 0.1 to 5% based on the weight of the binder. It has also been suggested to employ this method in connection with the manufacture of cellular concrete. For this purpose, the hydraulic binder is mixed with basic magnesium carbonate and with other conventional components in suitable proportions. The use of magnesium carbonate, however, has certain disadvantages as explained in our Specification No. 1,452,818 which can be substantially or completely avoided by using an alkali metal hydroxide in a relatively large quantity relative to the dry weight of the raw mixture as a compound capable of accelerating the binding of the low-quality hydraulic binder.

Specification No. 1,452,818 describes and claims a method for the manufacture of steam-cured cellular lightweight concrete which comprises casting into a mould an aqueous slurry comprising (a) 20 to 60% by weight of one or more materials rich in silica as therein defined, (b) 10 to 70% by weight of one or moreldw-quality hydraulic binders as therein defined, and (c) 0.1 to 5% by weight of one or more added alkali metal hydroxides, and, if desired, (d) up to 30% by weight of one or more high-quality hydraulic binders as herein defined, the amounts of (a), (b), (c) and (d) being calculated on the total dry weight of the aqueous slurry, said slurry also comprising a gas-developing agent capable of forming gas under alkaline reaction conditions to cause expansion of the slurry to take place, permitting the cast slurry to expand with formation of a body, permitting said cast body to set, and steam-curing the latter.

We have now found that a satisfactory product can be obtained if, instead of using a material rich in silica as defined therein (that is, material containing SiO2 in an amount of more than 60% by weight), there is used a material containing from 35 to 60%, preferably from 40 to 60%, for example, 45 to 60%, by weight of SiO2.

The present invention provides a method for the manufacture of steam-cured cellular light-weight concrete which comprises casting into a mould an aqueous slurry comprising (a 20 to 60% by weight of one or more materials containing from 35 to 60% by weight of SiO2, having substantially no hydraulic binding properties, (b) 10 to 70% by weight of one or more low-quality hydraulic binders as herein defined, and (c) 0.1 to 5% by weight of one or more added alkali metal hydroxides, the amounts of (a), (b) and (c) being calculated on the total dry weight of the aqueous slurry, said slurry also comprising a gas-developing agent capable of forming gas under alkaline reaction conditions to cause expansion of the slurry to take place, permitting the cast slurry to expand with formation of a body, permitting said cast body to set, and steam-curing the latter.If desired, the aqueous slurry may also contain one or more high-quality hydraulic binders (as herein defined), preferably up to 30% by weight calculated on the total dry weight of the slurry.

The present invention also provides a composition for use in this method which comprises components (a), (b) and 'tic) as specified above and in the amount specified above. The composition may include a gas-developing agent capable of forming a gas under alkaline conditions.

The invention further provides an aqueous slurry of the above composition.

As the constituent (a) containing from 35 to 60% by weight of SiO2, there may preferably be used shale ash, coke ash or, more especially, fly ash.

A low-quality hydraulic binder is used as component (b) and there may also be used, if desired, a high-quality hydraulic binder.

In the cement/concrete field a binder is a substance which can be used to bind together sand and broken stone or other forms of aggregate into a solid mass.

A hydraulic binder is a substance which produces its binding action as a result of reaction with water and water only. Common hydraulic binders used in concrete owe their action mainly to the formation of hydrated calcium silicates, aluminates and/or aluminate silicates. A hydraulic binder such as Portland cement sets and hardens when mixed with water at ordinary temperatures; others such as blast furnace slag need "activation" by a catalyst to set at ordinary temperatures. By the term "highquality hydraulic binder" there should be understood a hydraulic binder which when made into a slurry with water is capable of reacting with water to cause the slurry to set in less than 6 hours at room temperature of slightly increased temperature (below 100"C) into a soft cheese-like mass that can be cut into blocks by cutting wires.By the term "low-quality hydraulic binder" there should be understood a hydraulic binder which when made into a slurry alone with water does not have such cementing properties.

As mentioned in Specification No. 1,452,818, the natural low-quality hydraulic binders are less expensive than the high-quality hydraulic binders and there has always been a trend in the manufacture of cellular light-weight concrete to substitute low-quality hydraulic binders for high-quality hydraulic binders but only limited amounts of high-quality binder have in the past been replaced, as the replacement can lead to unacceptable results in the final steam-cured product and/or to unacceptable setting times.

The surprising advantages stemming from the use of a relatively large quantity of an alkali metal hydroxide as component (c) are described in our parent Specification No. 1,452,818 and apply equally to the present invention. In particular, the amount of high-quality hydraulic binder formerly thought necessary may be reduced, and in some cases no high-quality binder need be used. Thus it is possible in some cases to obtain a high-quality cellular light-weight concrete product using as binder granulated basic blast furnace slag with only a low percentage of Portland cement,~~for example 0 to 10%, suitably 6%. Corresponding results may also be obfained by using other low-quality hydraulic binders.The effect of substantially or completely avoiding salt efflorescence may also be obtained with starting mixtures containing no, or only small amounts of, Portland cement or other high-quality hydraulic binders.

It is also possible substantially to decrease the amount of water in the aqueous raw mixture, for example to 35% or less calculated on the total weight of the slurry, with the result that particularly improved strength properties may be obtained.

As hydraulic binders there may be used, for example, any of the appropriate materials mentioned in Specification No. 856,218, that is, usually inorganic binders containing calcium silicate and/or calcium aluminate as hydraulic components. As examples, there may be mentioned Portland cement, natural cement, hydraulic slags (for example ground basic blast furnace slag), slag cement and hydraulic lime.

However, as in the case of the invetnion of the parent Specification, the amount of high-quality binders (for example Portland cement) necessary in order to obtain a reasonable quality product can be substantially reduced and, indeed, satisfactory results are obtained without the use of a high-quality hydraulic binder at all.

Moreover, it is possible to reduce or substantially to avoid undesired salt efflorescence, even when less than 30%, for example up to 10%, by weight of high-quality hydraulic binder is used.

In the manufacture of light-weight concrete of the present invention there is needed a material containing from 35 to 60% by weight of silica (SiO2). Provided they contain not more than 60% silica, sand and waste products (such, for example, as shale ash, fuel or fly ash and coke ash) are examples of such materials. The waste products may have slight hydraulic properties depending on the method of manufacture, but generally these properties are too weak to render the materials suitable as hydraulic binders used in the present invention and the waste products exemplified above and which may be used as component (a) have no substantial hydraulic binding properties.

The low-quality hydraulic binder used as component (b) is usually a hydraulic slag, especially blast furnace slag. An especially suitable combination is fly ash as component (a) and blast furnace slag as component (b).

The slurry may, if desired, contain hydraulic lime or Portland cement (highquality hydraulic binder). It may also contain other components than those specified, for example limestone (CaCO3) or hydrated lime.

The alkali metal hydroxide is usually added to the other components of the raw mixture as a solution, for example a 40% by weight aqueous solution. Of course, solid alkali metal hydroxide can also be added. The alkali metal hydroxide is suitably dissolved in, or a concentrated solution thereof is mixed with, the water in which the solid starting materials are dispersed. The amount of added alkali metal hydroxide used is preferably at least 0.2%, calculated on the dry weight of the preparation. Above 5% there is in general no further appreciable increase in the effect obtained according to the invention. An amount of 0.2 to 3% is especially preferred.

It should be understood that the alkali metal hydroxide (component (c)) is additional to any that may be present in the other components of the slurry.

According to a preferred embodiment of the invention a composition for use in accordance with the invention may be as follows: A. material containing 3560% SiO2 20 to 60% low-quality hydraulic binder 10 to 70% Portland cement 0 to 30% alkali metal hydroxide 0.1 to 5% or B. fly ash 20 to 60% blast furnace slag 10 to 70% alkali metal hydroxide 0.1 to 5% Preferably composition B also contains from 0 to 30% of Portland cement.

Preferably there is used 2030%, more especially 2025%, by weight of component (a); 6070%, more especially 6570%, of component (b), and 0--10%, more especially e-5%, of high-quality binder.

As the gas-developing agent used in the slurry there may be used, for example, a metal capable of reacting with alkali to form hydrogen gas, for example aluminium. The amount of gas-developing agent, preferably aluminium powder, may be, for example, 0.05 to 0.20 per cent, calculated on the dry weight of the slurry.

In order to avoid any possible disadvantage arising from too rapid gas formation because alkali metal hydroxide is added in a relatively high amount, the gas-developing agent may, if desired, be rendered passive, e.g. with sodium dichromate.

The following Examples illustrate the invention, the parts and percentages being by weight unless otherwise stated: Example I For the manufacture of cellular light-weight concrete, fly ash and granulated basic blast furnace slag were used. The ash and the slag were wet-ground to a very fine, comparatively readily flowing, dispersion (the maximum residue on a 0.086 mm sieve being 20 per cent).

The dispersion obtained by the grinding process was then carefully mixed with carefully weighed quantities of aluminium powder, a regulator, an aqueous solution of sodium hydroxide and water to a mass with a consistency suitable for casting.

The mixture obtained had the following composition: fly ash 30 kg granulated basic blast furnace slag 70 kg aluminium powder 0.1 kg regulator (CaSO4 . -21H2O) 1.9 kg an aqueous solution of 40 per cent sodium hydroxide 3.5 kg water 48 kg 153.5 kg The content of sodium hydroxide calculated on the dry mixture was thus 1.35%.

In order to avoid the disadvantages of the high addition of alkali metal hydroxide in respect of reactivity against the aluminium metal the latter was made passive with sodium dichromate.

The fly ash had been obtained as a residue after combustion of coal or coke in steam power stations and had a content of SiO2 amounting to 42 per cent. The ash was added to the mixture after grinding and homogenization.

The slag contained 40 to 45 per cent of calcium oxide and 35 to 40 per cent of silica. The aluminium powder consisted of thin flakes having a percentage of elemental aluminium amounting to 90 to 95 per cent. The powder had been thermally degreased prior to the treatment with the chromate.

After steam-curing in an autoclave for 12 hours at 10 atmospheres over pressure a product having good properties was obtained.

Compressive strength in kilopond/sq. cm: 47 Shrinkage /OO 0.28 Salt efflorescence: none Density in kg/cu. dm: 0.5 Example 2 For the manufacture of cellular light-weight concrete, fly ash and granulated basic blast furnace slag were used. The ash and the slag were wet-ground to a very fine, comparatively readily flowing, dispersion (the niaximum residue on a 0.086 mm sieve being 20 per cent).

The dispersion obtained by the grinding process was then carefully mixed with carefully weighed quantities of aluminium powder, a regulator, an aqueous solution of sodium hydroxide, water and Portland cement as a high-quality hydraulic binder to a mass with a consistency suitable for casting. the mixture obtained had the following composition: fly ash 25 kg granulated basic blast furnace slag 66 kg Portland cement 4 kg aluminium powder 0.1 kg regulator (CaSO4 . +H2O) 1.9 kg an aqueous solution of 40 per cent sodium hydroxide 2.5 kg water 50 kg 149.5 kg The content of sodium hydroxide calculated on the dry mixture was thus 1.02%.

The fly ash presented a content of SiO2 amounting to 47 per cent and a content of CaO amounting to 4-5 per cent and was then added after grinding and homogenization.

The slag contained 40 to 45 percent of calcium oxide and 35 to 40 per cent of silica. The aluminium powder consisted of thin flakes having a percentage of elemental aluminium amounting to 90 to 95 per cent. The powder had been thermally degreased prior to the treatment with the chromate.

Compressive strength in kilopond/sq. cm: 46 Shrinkage 0/or: 0.32 Salt efflorescence: none Density in kg/cu. dm: 0.5 WHAT WE CLAIM IS: 1. A method for the manufacture of steam-cured cellular light-weight concrete which comprises casting into a mould an aqueous slurry comprising (a) 20 to 60% by weight of one or more materials containing from 35 to 60% by weight of silica having substantially no hydraulic binding properties, (b) 10 to 70% by weight of one or more low quality hydraulic binders as herein defined, and (c) 0.1 to 5% by weight of one or more added alkali metal hydroxides, the amounts of (a), (b) and (c) being calculated on the total dry weight of the slurry, said slurry also comprising a gas-developing agent capable of forming a gas under alkaline conditions to cause expansion of the slurry to take place, permitting the cast slurry to expand with formation of a body, permitting said cast body to set, and steam-curing the latter.

2. A method as claimed in claim 1, wherein the slurry also contains one or more high-quality hydraulic binders (as herein defined).

3. A method as claimed in claim 2, wherein the slurry contains up to 30% by weight of the high-quality binder or binders, calculated on the total dry weight of the slurry.

4. A method as claimed in claim 3, wherein the amount of high-quality hydraulic binder is not more than 10% by weight, calculated on the total dry weight of the slurry.

5. A method as claimed in claim 4, wherein the amount is substantially 6%.

6. A method as claimed in any one of claims 1 to 5, wherein component (a) contains from 40 to 60% by weight of silica.

7. A method as claimed in claim 6, wherein component (a) contains from 45 to 60% by weight of silica.

8. A method as claimed in any one of claims 1 to 7, wherein component (a) is fly ash.

9. A method as claimed in any one of claims 1 to 7, wherein component (a) is shale ash or evoke ash.

10. A method as claimed in any one of claims I to 9, wherein component (b) is a hydraulic slag.

Il. A method as claimed in claim 10, wherein component (b) is blast furnace slag.

12. A method as claimed in any one of claims 1 to 11, wherein the amount of component (c) is at least 0.2%.

13. A method as claimed in claim 12, wherein the amount of(c) is from 0.2 to 3% by weight.

14. A method as claimed in any one of claims I to 13, wherein the component (c) comprises sodium hydroxide.

15. A method as claimed in any one of claims 1 to 14, wherein the slurry also contains limestone.

16. A method as claimed in any one of claims 1 to 15, wherein-the slurry also contains calcium sulphate in the form of gypsum.

17. A method as claimed in any one of claims 2 to 16, wherein the high-quality hydraulic binder comprises Portland cement.

18. A method as claimed in any one of claims I to 17, wherein the amount of water is not more than 35% by weight, calculated on the total weight of the slurry.

19. A method as claimed in any one of claims 1 to 18, wherein the gasdevelopong agent is aluminium powder.

20. A method as claimed in claim 1, wherein the slurry has the composition substantially as described in Example I or Example 2 herein.

21. A method as claimed in claim 1, substantially as described in Example 1 or Example 2 herein.

22. A method for the manufacture of steam-cured cellular light-weight concrete which comprises casting into a mould an aqueous slurry comprising (a) 20 to 60% by weight of fly ash, shale ash or coke ash or mixture of two or more such products,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Compressive strength in kilopond/sq. cm: 46 Shrinkage 0/or: 0.32 Salt efflorescence: none Density in kg/cu. dm: 0.5 WHAT WE CLAIM IS:

1. A method for the manufacture of steam-cured cellular light-weight concrete which comprises casting into a mould an aqueous slurry comprising (a) 20 to 60% by weight of one or more materials containing from 35 to 60% by weight of silica having substantially no hydraulic binding properties, (b) 10 to 70% by weight of one or more low quality hydraulic binders as herein defined, and (c) 0.1 to 5% by weight of one or more added alkali metal hydroxides, the amounts of (a), (b) and (c) being calculated on the total dry weight of the slurry, said slurry also comprising a gas-developing agent capable of forming a gas under alkaline conditions to cause expansion of the slurry to take place, permitting the cast slurry to expand with formation of a body, permitting said cast body to set, and steam-curing the latter.

5. A method as claimed in claim 4, wherein the amount is substantially 6%.

(b) 10 to 70% by weight of one or more low-quality hydraulic binders as herein defined, and (c) 0.1 to 5% by weight of one or more added alkali metal hydroxides, the amounts of (a), (b) and (c) being calculated on the total dry weight of the slurry, said slurry also comprising a gas-developing agent capable of forming a gas under alkaline conditions to cause expansion of the slurry to take place, permitting the cast slurry to expand with formation of a body, permitting said cast body to set, and steam-curing the latter.

23. A method as claimed in claim 22, wherein component (b) is blast furnace slag.

24. Cellular light-weight concrete whenever obtained by a method as claimed in any one of claims 1 to 23.

25. A composition for use in the method claimed in any one of claims 1 to 23, which comprises components (a), (b) and (c) as specified in any one of those claims and in the amounts specified therein.

26. A composition as claimed in claim 25, which also contains a gas-developing agent capable of forming a gas under alkaline conditions.

27. An aqueous slurry of a composition as claimed in claim 25 or claim 26, suitable for use in the method claimed in any one of claims 1 to 23.