GB2078897A - Cartridge for use with bolt anchors - Google Patents

Abstract

Cartridges for bolt anchors comprise a frangible casing 1 containing a liquid-settable solid component 3 and in a separate compartment a reactive liquid component 4. The solid component 3 occupies a volume which is less than the normal free volume of the casing, preferably by being pelletised or encased by a liquid-permeable or liquid- degradable material 11 which serves to restrict the cross-sectional area occupied by the solid component in the casing. When required for use, the liquid component 4 is caused to be released from its compartment and to come into contact with the solid component 3, such as by breaking the weak heat seal 2. The free space 5 around the solid component 3 allows the liquid component 4 to come into contact with the solid component 3. This can be enhanced by providing a partial vacuum in the space 5. Organic or inorganic self setting systems may be used. <IMAGE>

Description

SPECIFICATION Cartridge for use in anchor bolting This invention relates to the anchoring of reinforcing or fixing elements such as anchor bolts in a borehole drilled in a substrate such as an underground mine roof, and is concerned with an anchoring cartridge containing a liquid-settable solid component and a separate reactive liquid component which when brought into contact with the solid component reacts therewith to form a self-setting grouting composition.

Two principal non-mechanical methods of anchoring a reinforcing element in a borehole in a substrate have been utilised, one based on hydraulic cement systems and the other on hardenable synthetic resin systems, generally an unsaturated polyester resin system. Both systems have been employed as cartridged systems, in which the reactive components of the system are both packaged in a frangible cartridge, generally in separate compartments, and the cartridge is introduced into the borehole and then broken and the contents mixed in situ by means of a rotating reinforcing element to form a selfsetting grouting composition around the reinforcing element Cartridges containing unsaturated polyester resin systems exhibit high flammability and toxicity and hence their use in confined areas such as coal mines gives rise to an unacceptable risk which has recently become of increasing concern and which has therefore given rise to increased interest in the use of cartridged hydraulic cement systems, additionally because of the increasing cost of polyester resins resulting from higher oil prices.

French Patent Specification No. 2202548 (which corresponds to German Offenlegungsschrift 2350298) describes a cartridge in which a rapidly setting dry hydraulic cement mortar is packaged in a porous paper tube. When required for use, the paper tube is immersed in water for a time sufficient to allow water to penetrate through the tube and hydrate the dry mortar and the moistened tube is then inserted into the borehole priorto insertion of the reinforcing element. This cartridge has disadvantages, the major one being that the porous tube becomes weakened after immersion in water and hence is difficult to handle when wet particularly if the cartridge is longer than about 200 mm.

A similar immersion-activated cartridge is described in British Patent Specification No. 2004965A, the cartridge casing consisting of a liquid-permeable paper or a perforated plastics film material, but also having a rigidifying member, for example a rigid but brittle plastics netting, which serves to make the moistened cartridge more manageable.

Cartrides such as those described in the aforementioned prior specifications, i.e. cartridges which must be activated by immersion in water prior to insertion in a borehole, suffer from a number of disadvantages, for instance: 1. It is necessary to pack the cartridges in an outer waterproof container.

2. Immersion time is critical - about 3 minutes is required which can cause practical difficulties, since over soaking of the cartridges may cause absorption of too much water and hence an increase above the optimum water/cement ratio. This is particularly a problem in hydraulically setting systems containing significant quantities of aggregate or other fillers.

The rate of water absorption and the total quantity absorbed is largely dependent on the bulk density of the dry mortar mix within the cartridge and this may vary considerably during transport and storage prior to use.

3. In the case where the cartridge casing is formed from a perforated plastics film, a proportion of the hydratable powder tends to escape from the casing so that the cartridges are unpleasant to handle.

4. Similarly after immersion a proportion of the wetted mortar tends to seep from the casing so that again handling is unpleasant.

5. In practice the cartridge filling is limited to simple dry powder cement admixtures, since the presence of other materials, for example, plasticisers or accelerators, can give rise to practical difficulties when the cartridge is activated by immersion in water during underground mining and tunnelling operations.

It is an object of the present invention to provide an anchoring cartridge based on a liquid-activated solid component which avoids the disadvantages possessed by the immersion-activated cartridges described above.

Cartridged hydraulic cement systems designed for in-hole mixing without prior immersion in an activating liquid have generally consisted of inner and outer concentric frangible containers with the inner container holding water and the outer container holding a powdered hydraulic cement mortar, see for example British Patent Specification No.

1293619. However in practice the in-hole mixing of such powder/liquid systems is both difficult and inconsistent so that the degree of mixing obtainable in the borehole is normally insufficient to give a cementitious grout of uniform strength. Hence such cartridges have not achieved technical or commercial success.

To overcome this shortcoming, it has been proposed in United States Patent Specification No.

4096944 to package in a single frangible cartridge a hydraulic cement and water in the form of microcapsules. In-hole mixing can be achieved by rotation of the reinforcing element or in certain circumstances merely by mechanical insertion of the element.

Effective anchors have been reported using such cartridges, but there appear to be difficulties in commercial manufacture, storage and transportation of such cartridges. Various attempts have therefore been made to devise paste/paste systems comprising cement, gypsum or other reactive solids which may be packaged in a frangible twocompartment cartridge and activated by in-hole mixing, see for example British Patent Specification No.2003851A.

These paste systems tend to suffer from partial deactivation of the reactive pastes on storage. In general they are only effective with special cements and plasters and are not suitable for employment with a wide range of reactive solid/liquid systems.

It is therefore a further object of the invention to provide an anchoring cartridge which will not tend to exhibit the disadvantages possessed by the cartridged dual component hydraulically setting systems hereinbefore described.

According to the present invention, there is provided an anchoring cartridge for use in anchoring a reinforcing or fixing element in a borehole in a substrate by means of a self-setting grouting composition formed from a liquid-settable solid component and a reactive liquid component which is capable of reacting with the solid component so as to cause it to set, the cartridge comprising a frangible casing containing the liquid-settable solid component and the reactive liquid component in a separate compartment arranged so that when required the liquid component can be caused to be released from its compartment and to come into contact with the solid component, and the solid component being in a form such that it occupies a volume which is less than the normal free volume of the casing, whereby in use the liquid component is enabled to come into contact with the solid component over substantially it whole length within the casing.

If desired, the cartridge can be at least partially evacuated so as to cause that part of the casing in which the liquid-settable solid component is contained to be in contact with the solid component over substantially its whole length within the casing, whereby in use the liquid component is caused to be drawn rapidly into the evacuated space adjacent the solid component and hence to come rapidly into contact with the solid component over substantially its whole length within the casing.

The presence of the evacuated space adjacent the solid component within the cartridge casing helps to accelerate the activation of the liquid-settable solid component over the whole length of the solid component and thereby helps to ensure the formation of a self-setting grouting composition of substantially uniform strength when the activated cartridge is introduced into a borehole and then broken in situ by means of a reinforcing or fixing element inserted with or without rotation to form a required self-setting grouting composition around therein- forcing or fixing element.The evacuted space within the cartridge also serves to minimise the inclusion of air within the activated cartridge, which not only helps to retain the cartridge in a sufficiently rigid state to assist the insertion of the activated cartridge into a borehole, but also helps to ensure effective void-free anchoring of the reinforcing or fixing element in the borehole.

In one preferred embodiment of the invention, the anchoring cartridge comprises a frangible casing containing the liquid-settable solid component and the reactive liquid component in separate compartments, the compartment containing the liquid component being in communication with the compartment containing the solid component by means of a passageway having breakable or removable sealing means such that the liquid component is restrained from entering the compartment containing the solid component prior to use but can flow through the passageway to contact the solid component when said sealing means is broken or removed. Mixing of the solid and liquid components may be assisted, if necessary, by external manipulation of the cartridge casing.

In another preferred embodiment of the invention, the liquid component is contained in a separate inner casing which can be broken or ruptured in use in order to release the liquid component therefrom and allow it to come into contact with the solid component.

The solid component, which in the context of the present invention means a non-fluid component, i.e.

a component which will not readily flow within the cartridge casing, may be in the form of a compressed solid rod or discrete pellets, granules, tablets or capsules, or in the form of a powder or stiff paste. In one embodiment of the invention, in order to ensure that the solid component remains in a substantially fixed position within the cartridge casing, the solid component is encased by a liquid-permeable or liquid-degradable material which restricts the crosssectional area occupied by the solid component so as to provide sufficient space to enable the liquid component to contact the solid component over substantially its whole length.

The liquid-permeable material in which the liquidsettable solid component is contained may be an absorbent paper or a perforated plastics film. Thus suitable materials include, for example, cloth or mat or gauze made from thermoplastic fibres, cotton, wool, sisal, glass, cellulose, rock wool, asbestos or steel; porous paper; perforated polyvinyl alcohol film; perforated cellulose or cellulose derivative film; porous collagen; porous cork; porous clay or ceramic; porous metal foil; and porous animal or vegetable skin. The liquid-degradable material may be polyvinyl alcohol film, which if desired may be made permeable to the reactive liquid.

Insertion of the cartridge containing the mixed grouting composition into a borehole prepared for a reinforcing or fixing element is facilitated if the cartridge is firm and relatively rigid. This may be achieved by squeezing the mixed composition to one end of the casing to fill it firmly and then twisting, tying or clipping the other end of the casing.

Alternatively, rigidity may be assisted by incorporating a relatively rigid member, for example a rod or tube, within the cartridge casing or by an outer sleeve partially or fully surrounding the cartridge.

The frangible casing of the cartridge can be made from any material which is not permeable to, or readily attacked by, the unmixed or mixed contents of the cartridge and which will rupture under the force of stemming the cartridge in a borehole or of inserting an anchor bolt through the cartridge. To facilitate the latter operation, relatively weak materials are preferred for use as the cartridge casing.

Examples of these are tubular thermoplastics film, e.g. polyester, polyethylene, polyamide, polyvinyl chloride or polyvinylidene chloride film, laminate film, e.g. thermoplastics/thermoplastics or thermo plastics/cellulose laminates, waterproofed paper/ cloth laminates, metal foil and laminates of metal foil with plastics or paper sheeting. These materials are flexible and allow the cartridge to be manipulated so as to aid mixing of the liquid and solid components.

However, certain rigid materials may alternatively be used as the outer envelope, or part of it. Such rigidity can assist in placing of the intra-mixed cartridge in the hole. Examples of suitable rigid envelope materials are tubular polystyrene or modified polystyrene, polymethyl methacrylate, waterproofed cardboard, wood and glass.

The sealing of the outer casing of the cartridge, and of the liquid-permeable or-degradable casing for the solid component when present, may be effected in any suitable manner, for example by heat sealing, stitching, clipping, tying or the use of an adhesive.

The cartridge of the invention can comprise various combinations of liquid-settable solid components and reactive liquid components. Thus the liquid-settable component, which may be in the form of a powder, stiff paste or solid, may be hydraulic cement, for example a Portland cement, high alumina cement, blast furnace cement, pozzolanic cement or calcium sulphate (gypsum) plaster, either alone or in admixture, in which case the reactive liquid component will comprise water. Other modifying inorganic materials, for example lime, anhydrite, fly ash or other pozzolans, may be present in the hydraulic cement component, together with metals or inorganic salts to accelerate or retard the rate of hydration and/or strength development and to promote expansion or minimize shrinkage.Such inorganic additives are well known in the art and include, for example, sulphoaluminates, finelydivided metals such as iron, aluminium and zinc, and ammonium, sodium, potassium, lithium, calcium, magnesium, zinc and aluminium salts of inorganic or organic acids.

Other organic materials may be present as plasticisers, or as agents for the control or air entrainment, rheology or setting rate.

Organic polymers may be used to modify the physical characteristics of the hydraulic materials.

The polymers may be present in the form of dry powders or granules which may be dissolved or dispersed in either the solid or liquid component.

Such polymers include water-soluble resins, for example urea-formaldehyde or melamineformaldehyde resins, polyacrylic acids or acrylic esters, or thermoplastic emulsion or suspension polymers.

Besides the self-setting systems based on hydraulic cements, there may be used systems based on other settable inorganic materials, for example a system comprising: (a) at least one acidic oxyphosphorus compound selected from phosphoric acids, e.g. H3PO4, anhydrides of phosphoric acid, e.g. P2O5, and salts of phosphoric acid with multivalent metal cations, e.g.

Al(H2PO4)3; (b) a basic component comprising at least one particulate basic compound of a Group II or Group Ill metal capable of reacting with the oxyphosphorus compound in the presence of water to form a monolithic solid, e.g. magnesium oxide or hydroxide, magnesium silicate, magnesium aluminate or calcium aluminate; and (c) an aqueous component.

Here the reactive liquid component of the cartridge consists of (c) alone, or (c) plus part or all of (a).

A further example of an inorganic settable composition usable in the cartridge of the invention comprises, in essence, burned magnesite as the solid component and an aqueous solution of magnesium chloride and/or magnesium sulphate as the liquid component. Alternatively a dry powder mixture of burned magnesite and magnesium chloride may comprise the solid component contained in the cartridge casing in which case the activating liquid can comprise water.

Other suitable self-setting systems may be based on the gelation of an aqueous alkali metal silicate by reaction with an acidic or acid-releasing substance and/or with a bivalent or multivalent cation. For example, the liquid component can be aqueous sodium silicate solution whilst the solid component comprises a hydrolysable ester (e.g. glyceryl acetate) and a particulate filler (e.g. calcite flour), or is a cement based on a calcium silicate and/or a calcium aluminate.

Filled organic self-setting compositions which may be utilized in this invention may be based on epoxy, polyurethane, unsaturated polyester, phenolformaldehyde, urea-formaldehyde or melamineformaldehyde resins. Such organic systems will normally include hydratable or inert fillers. The solid component present in the cartridge may contain particulate fillers, for example silica, calcite, limestone, dolomite or granite and/or fibrous fillers, for example asbestos, glass fibre, steel fibre, rock wool, cellulose fibres, shredded paper, or synthetic resin fibres, e.g. polyamide, polyolefin or polyester fibre.

The use of a proportion of fibrous filler may assist liquid penetration into the solid component.

Examples of anchoring cartridges in accordance with the invention are shown in the accompanying drawings, in which Figure 1 shows a cartridge having a casing 1 formed from a flexible tubular synthetic film which is divided into two compartments buy a relatively weak heat seal, one compartment containing a solid component packaged in a liquid-permeable material 11 so that a part-annular space 5 exists around the solid component 3, and the other compartment containing the liquid component 4 of a self-setting system.

Figure la, which is a cross-section through the compartment containing the solid component 3, shows more clearly the part-annular space 5.

Figure 2 shows a similar cartridge in which the heat seal is replaced by a seal comprising a plug 6 of deformable sealant material, for example wax, grease, hot melt sealant, putty or flexible foam, and an external removable clip 7 of metal or plastics material.

Other breakable or removable sealing means may be employed, for example tying with a string or tape, or securing with an adhesive tape. If required, the cartridge casing may be folded or twisted at the sealant position before tying or taping to assist in preventing any premature rupturing ofthe seal.

When required for use, the seal is broken open or removed and light pressure is exerted on the compartment containing the liquid component 4 in order to displace the liquid component through the passageway previously sealed up and into the compartment containing the solid component 3 so that it flows into the available space 5 adjacent to the solid component and contacts the latter over the whole length thereof. Mixing of the solid and liquid components may be assisted by external manipulation of the cartridge casing 1.

Figure 3 of the drawings shows a cartridge in which the liquid component 4 is contained in a separate inner casing 8, which may be flexible or rigid. When required for use, the casing 8 is fractured or ruptured by compressing a rupturing device 9, which may be made of metal or plastics, on to the casing 8, and the liquid component 4 thereby released can flow into contact with the solid component 3 which can be packaged in a liquid-permeable material 11 as in the cartridges of Figures 1 and 2.

Figure 4 shows a similar cartridge in which the liquid component 4 is again contained in its own separate flexible casing 8, but the rupturing device is absent and the solid component is present in the form of discrete pellets 10. When required for use, the casing 8 is ruptured by pressure applied by squeezing or by piercing through the outer casing 1 of the cartridge and the liquid component 4 thereby released flows readily through the interstices between the pellets 10 to contact the solid component over substantially its entire length in the casing.

The invention is further illustrated by way of the following non-limitative Examples.

Example 1 A dual compartment cartridge (as shown in Figure 2) consisted of a 40 mm diameter tube of polyester film as casing, one compartment containing 200 ml of a 1:2 by volume mixture of Revacryl 344 (a commercially available styrene-acrylic copolymer marketed by Harlow Chemical Company) and water.

This was separated from the other, larger compartment by a mastic sealant plug held in position by an external wire tie. The other compartment contained a 550 mm long porous paper capsule of 35 mm diameter containing 6009. of a 1:1 by weight mixture of Herculite Stone and Herculite No. 2 (these being commercially available alpha-gypsum type plasters marketed by British Gypsum).

By removing the tie and applying pressure to the smaller compartment of the cartridge, the liquid was forced past the mastic sealant and into the annular space in the larger compartment, thereby wetting out the encapsulated powdered plaster mix rapidly along its length. Two such cartridges were then packed into a 43 mm diameter borehole of 1500 mm length which had been drilled in sandstone rock. A 36 mm diameter wooden dowel was then driven into the borehole to a depth of 1450 mm., thereby bursting the cartridges, the contents of which formed a grouting paste which filled the annulus between the dowel and the wall of the borehole. This grouting paste subsequently set to anchor the dowel firmly in the rock. A pull-out test which was conducted after 2 days at 15"C resulted in the dowel not breaking until a load of 10 tonnes was applied.

Example 2 A dual compartment cartridge similar to that described in Example 1 was produced, except that the casing was formed from a 32 mm diameter tube of polyethylene film and the two compartments were separated by a weak heat seal (as shown in Figure 1). The smaller compartment contained 140 ml of a 35% aqueous sodium silicate solution and the larger compartment contained a 700 mm long polyester fibre cloth capsule of 29 mm diameter containing 500 g of a 20:2:1 by weight mixture of high-alumina cement, P.F.A. Cenospheres (holiow inorganic spherical particles of 10-250 microns separated from pulverised fuel ash) and china clay. By the application of pressure to the smaller compartment, the heat seal was broken permitting the silicate solution to flow into contact with the encapsulated cementitious mixture along its entire length.Two of these cartridges were then placed in a 35 mm diameter borehole of 700 mm length drilled in a concrete slab and a 19 mm diameter rebar (i.e. a deformed concrete reinforcing bar) was then driven into the cartridges to a depth of 680 mm. After the resulting mixed grouting composition had been allowed to cure for 24 hours at 20"C, the bolt broke at a pull-out test load of 14tonnes.

Example 3 A cartridge (as shown in Figure 3 but without the rupturing device) formed from a 31 mm diameter tube of polyester film contained an inner casing formed from a 210 mm long polyethylene film of 30 mm diameter holding a mixture of 125 ml of water and 20 ml of Melment (Registered Trade Mark) L 10 (a category A superplasticiser marketed by Hoechst), and also a 540 mm long polyester film capsule of 28 mm diameter containing a mixture of 500 g of ordinary Portland cement and 5 g of 10 mm long alkali-resistant glass fibres. The polyester capsule was perforated with 0.1 mm diameter holes on a 10 mm grid pattern.

By the application of pressure to that part of the cartridge containing the inner liquid-containing casing, the latter was ruptured and the liquid was allowed to flow into the annular space between the; perforated capsule and the outer casing, thereby - wetting out the encapsulated cement mix and allowing mixing to be effected within two minutes. Two' such cartridges were then firmly packed, by means of a ramming stick, into a 37 mm diameter borehole of 600 mm length which had been drilled in a dense concrete slab. A 19 mm diameter galvanised rebar bolt was then hammered into the cementitious cartridges to a depth of 580 mm. The resulting cement anchor was allowed to cure for four days at 10"C. after which a pull-out test resulted in the bolt not breaking until a load of 15 tonnes was applied.

Example 4 A cartridge (as shown in Figure 4) formed from a 32 mm diameter tube of polyester film contained an inner casing formed from a 30 mm diameter polyethylene tube holding 100 ml of water, in a manner similar to that described in Example 3.

However the solid component was present in the form of cylindrical powder pellets (500 g) each having a diameter of 8 mm and a length of 5 mm and containing a 200:50:11 mixture of respectively Her culite Stone, Aerolite FFD (a urea-formaldehyde resin marketed by Ciba-Geigy) and powdered har deners (a 2:1 mixture of L38 and L80 hardeners marketed by Ciba-Geigy).

By the application of pressure in the manner described in Example 3, the water was caused to wet out the plaster composition and mixing was thereaf ter effected. Two such cartridges were packed into a 35 mm diameter borehole of 700 mm length drilled in shale strata. A 16 mm diameter polyurethane coated bolt was then driven into the cartridges to a depth of 675 mm. After curing for 24 hours at 20"C a pull-out test resulted in the bolt not breaking until a load of 8 tonnes was applied.

Example 5 A dual compartment cartridge (as shown in Figure 2) consisted of a 40 mm diameter tube of cellulose/ polyethylene laminate film as casing, one compart ment containing 200 ml of water. This was separated from the other, larger compartment by a mastic sealant plug held in position by an external wire tie.

The other compartment contained a 550 mm long porous paper capsule of 36 mm diameter containing Herculite Stone (a commercially available alpha gypsum type plaster marketed by British Gypsum Limited).

After filling and sealing the liquid compartment the filled porous paper capsule was placed in the second compartment and a vacuum applied to the open end of the casing to withdraw air from the voids. The outer casing collapsed onto the inner porous paper cartridge and the open end was then heat sealed while maintaining the applied vacuum.

On removing the external tie the water quickly entered the second compartment and was absorbed by the plaster contained in the porous paper car tridge. The entry and absorption of the water was complete within 50 seconds, whereas approximately 3 minutes was required for activation of a similar but non-evacuated cartridge.

Cartridges of this type were used to bond a 36 mm diameter wooden dowel into a 43 mm diameter borehole drilled in sandstone rock. Atensile test load i applied to the dowel after 42 hours resulted in failure of the wood only after a load of 11.5 tonnes was applied.

Claims (7)

1. An anchoring cartridge for use in anchoring a reinforcing or fixing element in a borehole in a substrate by means of a self-setting grouting com position formed from a liquid-settable solid compo nent and a reactive liquid component which is capable of reacting with the solid component so as to cause it to set, the cartridge comprising a frangible casing containing the liquid-settable solid component and the reactive liquid component in a separate compartment arranged so that when required the liquid component can be caused to be released from its compartment and to come into contact with the solid component, and the solid component being in a form such that it occupies a volume which is less than the normal free volume of the casing, whereby in use the liquid component is enabled to come into contact with the solid component over substantially its whole length within the casing.

2. A cartridge as claimed in Claim 1, wherein the cartridge is at least partially evacuated so as to cause that part of the casing in which the liquid-settable solid component is contained to be in contact with the solid component over substqntially its whole length within the casing, whereby in use the liquid component is caused to be drawn rapidly into the evacuated space adjacent the solid component and hence to come rapidly into contact with the solid component over substantially its whole length within the casing.

3. A cartridge as claimed in Claim 1 or 2, wherein the cartridge comprises a frangible casing containing the liquid-settable solid component and the reactive liquid component in separate compartments, the compartment containing the liquid component being in communication with the compartment containing the solid component by means of a passageway having breakable or removable sealing means such that the liquid component is restrained from entering the compartment containing the solid component priorto use but can flow through the passageway to contact the solid component when said sealing means is broken or removed.

4. A cartridge as claimed in Claim 1 or 2, wherein the liquid component is contained in a separate inner casing which is adapted to be broken or ruptured in use in order to release the liquid component therefrom and allow it to come into contact with the solid component.

5. A cartridge as claimed in Claim 3 or 4, wherein the solid component is encased by a liquidpermeable or liquid-degradable material which restricts the cross-sectional area occupied by the solid component in the casing.

6. An anchoring cartridge substantially as hereinbefore described with reference to, and as shown in, Figure 1, or Figure 2, or Figure 3, or Figure 4 of the accompanying drawings.

7. An anchoring cartridge substantially as described in any one ofthe foregoing Examples.