GB2128179A

GB2128179A - Rapid hardening compositions

Info

Publication number: GB2128179A
Application number: GB08229117A
Authority: GB
Inventors: William Harold Kellett; Peter Shelley Mills
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1982-10-12
Filing date: 1982-10-12
Publication date: 1984-04-26
Also published as: GB2128179B

Abstract

An extremely rapid setting and rapid hardening composition is prepared from a hydraulic cement, fly ash, water and a special inorganic flocculant selected from aluminium chlorohydrate, aluminium chloride, aluminium sulphate, ferric sulphate, ferrous sulphate and polyaluminium chloride. The invention is particularly useful in underground mining.

Description

SPECIFICATION Rapid hardening compositions This invention concerns rapid hardening com- positions, more especially it concerns rapid hardening hydraulic cement compositions.

Rapid hardening hydraulic cements have been proposed and manufactured in the past.

While grades of cement are marketed in Britain as Rapid Hardening Portland Cement and Extra Rapid Hardening Portland Cement, these and mixtures of cements and accelerators are fairly expensive and still take an appreciable time to set and harden. It is an aim of the present invention to provide a hydraulic cement composition which exhibits almost instantaneous setting and rapid hardening.

Accordingly, the present invention provides a hydraulic cement composition comprising hydraulic cement, fly-ash, an inorganic flocculant as hereinafter defined and water. Preferably, the composition is in the following proportions by weight: hydraulic cement 2-45%, fly ash 20-80%, inorganic flocculant 0.05-25% and water 15-50%, the components together adding up to 100%.

The composition of the invention exhibits extremely fast setting, so that if the components are separated into first and second flowable mixtures and are rapidly mixed, a composition is obtained which sets with little or no slump. This fast or instantaneous setting property means that coatings may be sprayed or a monolithic cementitious mass built up with only rudimentary shuttering. Previously, expensive watertight materials and strong structures have been required for shuttering for cementitions masses. The properties of the composition of the invention are especially useful in underground mining, as will be described hereinafter, but the invention has applications in many diverse fields where rapid setting and hardening are of interest.The invention also provides a method of preparing a rapid setting and hardening cementitious coating or mass comprising admixing hydraulic cement, fly ash, an inorganic flocculant and water, preferably in the above-mentioned proportions.

The hydraulic cement used in the present invention may be a Portland type or one which liberates lime when contacted with water or lime itself. Suitable Portland cements include Ordinary Portland Cement (OPC) Rapid Hardening Portland Cement (RHPC), Portland Blastfurnace Cement, Sulphate Resisting Portland Cement, Extra Rapid Hardening Portland Cements and Portland Cements containing a higher than usual alumina content.

RHPC is normally preferred because of its high rate of hardening and ready availability.

Fly ash is the principal waste product from power stations burning pulverised fuel (coal), and is collected in cyclones and electrostatic precipitators as an environmental protection measure. Fly ash has a similar particle size range to the hydraulic cement and is suitably expressed as surface areas of 200 to 800 m2/Kg compared to Portland Cement of 300-500 m2/Kg.

The presence of the inorganic flocculant is believed to be the key factor in the achievement of practically instantaneous setting in the present invention and rapid hardening.

An inorganic flocculant as used in the present invention is an inorganic compound which is soluble in water to form an acidic solution and forms positively charged ions in aqueous solution. Suitable flocculants include aluminium chlorohydrate, aluminium chloride, aluminium sulphate, ferric sulphate, ferrous sulphate, polyaluminium chloride, and inorganic complexes based thereon. Aluminium sulphate is normally preferred because of its cost effectiveness and its powder form. The composition of the invention may contain other components, such as aggregates, including run-of-mine coal and rock, provided that these do not interfere with the desired rapid setting and hardening properties.

Conveniently, the fly ash is mixed with water to make a first slurry which is thick a slurry as is pumpable. This slurry is nonsetting. A chosen proportion of one or more of the inorganic flocculants is admixed with the slurry, and this may be done at any convenient point. The resulting slurry has a considerable workability time, thus enabling it to be pumped a long distance to a point of use.

Additives such as those known to confer antibleed and/or water reducing properties to slurries, for example bentonite and lignosulphonates, may also be admixed with the slurry.

A second slurry containing cement is also prepared, and may have mixed therewith one or more of the additives mentioned above in respect of the first slurry. The second slurry also has a considerable workability time and may also be pumped a long distance to the point of use. Additional components such as conventional cement retarders and suspension agents may be added to the cement-containing slurry, to enable the slurry to be left for long periods in supply lines. When the two slurries are pumped simultaneously into a conventional static mixer device at the point of use, the mixture may be sprayed using conventional equipment into a cavity defined by shuttering or otherwise or onto a surface, and a mass of set material or a coating is easily built up.

Optionally, the cement may be preblended with the fly ash and a powdered inorganic flocculant and the resulting dry mixture is blown pneumatically to the point of use, where it is spray mixed with water. In a further embodiment of the invention, a blend of cement and fly ash is blown pneumatically to the point of use, where it is spray mixed with a solution of inorganic flocculant in water.

In other embodiments, the cement is blown pneumatically or pumped hydraulically in the form of a slurry and at the point of use is mixed with blended or separate fly ash and inorganic flocculant, either of which may be pneumatically or hydraulically transported to the point of use.

The equipment used for mixing the components of the rapid setting mixture according to the invention is not critical, and all that is required is that adequate mixing is achieved.

In all embodiments the constituents and feed rates are chosen in the correct proportion to give the desired final rapid setting and hardening mixture.

The invention has particular use in underground mining, especially in the formation of monolithic "packs" at the sides of roadways.

Packs are large blocks of material built up out of rock, coal, dirt or stacked timber blocks but increasingly nowadays are monolithic blocks of concrete-like material, which are positioned at the sides of underground roadways in place of the excavated coal or rock to help support the overlying strata. Monolithic packing has been found to greatly improve the conditions in the roadway, which otherwise can become badly distorted because of the enormous rock pressures encountered and also greatly improve ventilation problems, acting as a seal to prevent leakage of methane out of worked out areas and to prevent the passage of air which might cause spontaneous combustion or heating. Monolithic packing has, however, required sturdy and leak-proof shuttering to contain the liquid cementitions pack before it set, even with the use of rapid hardening cement mixtures.The present invention requires only lightweight shuttering to, form a pack which can be easily and quici;iy erected and dismantled and, importantly, easily handled and transported. Other uses for the invention in mining include the construction of "stoppings" in the form of monolithic blocks or coatings on a support such as brattice cloth, to prevent air leakage into abandoned workings or the access of air to a fire or heating, and generally in the filling or stowing of cavities.

The invention will now be described by way of example only.

EXAMPLE Fly ash is slurried with half its weight of water and 5% of its weight of aluminium sulphate, Al2(SO4)3. 1 4H2O, and pumped to a pack hole. A cement slurry containing Rapid Hardening Portland Cement together with 60% by weight of water, is pumped to the pack hole at one third of the rate by volume of the fly ash slurry, and is spray mixed therewith. The resulting deposited mixture is non-flowing and comprises by weight: Fly ash 47% RHPC 17% Al2(SO4)3. 1 4H2O 2.4% Water 33.6% The material shows essentially instantaneous setting and has developed a 2 hour compressive strength of 0.54 MPa and a 4 hour compressive strength of 0.95 MPa. Its strength increases progressively thereafter.

Claims

1. A rapid setting and hardening hydraulic cement composition comprising hydraulic cement, fly-ash, an inorganic flocculant as hereinbefore defined and water.

2. A composition according to claim 1, in the following proportions by weight: hydraulic cement 2-45%, fly ash 20-80%, inorganic flocculant 0.05-25% and water 1 5-50%, the components together adding up to 100%.

3. A composition according to claim 1 or 2, wherein the hydraulic cement is selected from Portland-type cements, lime and cements which liberate lime when contacted with water.

4. A composition according to claim 3, wherein the hydraulic cement is Rapid Hardening Portland Cement.

5. A composition according to anyone of the preceding claims, wherein the inorganic flocculant is selected from aluminium chlorohydrate, aluminium chloride, aluminium sulphate, ferric sulphate, ferrous sulphate, polyaluminium chloride, and inorganic complexes based thereon.

6. A composition according to claim 5, wherein the inorganic flocculant is aluminium sulphate.

7. A composition according to claim 1, substantially as hereinbefore described.

8. A composition according to any one of the preceding claims, in the form of two or more aqueous slurries which only when mixed yield the composition according to the invention.

9. A method of preparing a rapid setting and hardening cementitious composition, comprising admixing hydraulic cement, flyash, an inorganic flocculant as hereinbefore defined and water.

10. A method according to claim 9, wherein the components of the composition are in the following proportions by weight: hydraulic cement 2-45%, fly ash 20-80%, inorganic flocculant 0.05-25% and water 15-50%.

11. A method according to claim 9 or 10, wherein two or more aqueous slurries containing components of the composition are prepared which only when mixed yield the composition according to the invention, and mix ing the slurries.

12. A method according to claim 9, substantially as hereinbefore described.

1 3. A method of stowing or filling a cavity whereby only rudimentary shuttering is required to define the cavity, comprising conveying to and rapidly mixing in or immediately adjacent the cavity, the components of a composition according to any one of claims 1 to 8.

14. A method according to claim 13, comprising the preparation of a first slurry containing fly ash, water and inorganic flocculant and a second slurry containing cement and water, conveying the slurries to a point of use, mixing the slurries to yield a composition according to any one of claims 1 to 7, filling the cavity and permitting the composition to set.

15. A method according to claim 13, comprising preparing a dry flowable preblend of cement, fly ash and powedered inorganic flocculant, conveying the dry preblend to a point of use, mixing the preblend with water to yield a composition according to any one of claims 1 to 7, filling the cavity and permitting the composition to set.

16. A method according to claim 13, comprising preparing a dry flowable mixture of cement and fly ash, conveying the mixture to a point of use, mixing the mixture with a solution of inorganic flocculant in water to yield a composition according to any one of claims 1 to 7, filling the cavity and permitting the composition to set.

1 7. A method according to claim 13, comprising conveying dry cement or a cement slurry to a point of use, mixing the cement or slurry with blended or separate fly ash and inorganic flocculant to yield a composition according to any one of claims 1 to 7, filling the cavity and permitting the composition to set.