GB2210655A - Ethyl ortho silicate treatment for decomposing concrete structures - Google Patents

Abstract

A method and apparatus for the treatment of a porous matrix such as masonry, for the purpose of consolidating or introduction of a water resistant barrier, comprises placing one or a plurality of open-sided containers 32 against the masonry at an appropriate point, after having exposed the masonry (if necessary) by removal of any covering coatings, sealing the containers 32 by sealing elements (30, 31 Fig. 2) around their periphery and introduction to the volume enclosed by the container 32 and the vertical surface against which it is held of a treatment liquid such as an ethyl ester of silicic acid, allowing the liquid fully to saturate the matrix and subsequently removing the container and allowing the solvents to evaporate and the ester to cure. <IMAGE>

Description

CONSOLIDATION TREATMENT FOR DECOMPOSING CONCRETE STRUCTURES The present invention relates to a consolidation treatment for decomposing masonry structures.

The constraints on the use of calcium aluminium silicate cements as binders for mineral aggregates have not always been fully understood in the past and at various periods, and in particular in regions where mining waste was readily and economically available, masonry and concrete structures have been made using mineral aggregates which are chemically impure and resulted in unsatisfactory concrete or mortar which, particularly with the ingress of moisture over a period of time, has started-to lose its cohesion and compressive strength.

A wide range of contaminant materials may be present in the mineral aggregate, although specifically the presence of sulphides, especially iron sulphide, decomposed slate, and other impurities can have a detrimental effect on the cohesive strength of the aggregate following reactions which take place in the presence of moisture. The calcium aluminium silicate cement may also be affected so that the matrix becomes friable. When such structures are domestic houses the devastating effect of the deterioration in the structural strength can be traumatic and many properties in mining areas where mine waste has in the past been used as an aggregate for the production of concrete blocks, are suffering from disintegration due to the breakdown in the aggregate bound by the cementitious material.When the compressive strength of concrete blocks fails the whole structure is in serious danger of collapse, which is evidenced by the appearance of significant cracking in both horizontal and vertical directions even in render coats which are otherwise sound.

When such evidence of deterioration is found the conventional solution is demolition. Since such deterioration is not an insurable risk, however, the expense of demolition and replacement is usually out of the reach of the average householder.

The present invention, seeks, therefore, to provide a solution to this problem by providing a method and apparatus, and a material, by means of which degenerated concrete structures can be restored. In this context, the term "concrete" will hereinafter be understood to refer to a structure composed of mineral aggregate bound by a calcium aluminium silicate cement.

In providing a solution to the above described problem attention has been given to the fact that such structures are porous and any treatment must not block the pores and prevent the movement of air or humidity through the capillary structure. The material used in any method for restoretiDn of the cohesive strength of such concrete structures must likewise leave the restored structure impervious to future attack, particularly by envl ronmental sulphates.

Tests conducted on decomposing concrete structures have established that about 20S by weight of the material can be dissolved in dilute hydrochloric acid, except for surface regions subjected to weathering, where less than 105 by weight of the material can be dissolved in dilute hydrochloric acid. It has been found that the acid soluble material comprises mainly of carbonates, although sulphides are also present. It is believed that the decay of such concrete is caused by a catalysed oxidation process which is encouraged by the presence of moisture.

Thus, the rate of decay is dependent on the amount of moisture present and this is exacerbated by salt contamination of the mineral aggregate used for the concrete. It is believed that other reactions also take place and the present invention seeks to provide a method and means by which the effect of such reactions can be reversed and future such reactions inhibited.

According to one aspect of the present invention, therefore, a method of consolidating concrete structures comprises the impregnation thereof with an ethyl ester of silicic acid dissolved in one or a plurality of solvents.

After impregnation of the solution the structure is left for a period to allow evaporation of the solvents and the silicic ester cures to form silica which acts as a permanent binding material insoluble in water and-all common solvents.

The solvents used in the solution are preferably white spirit and alcohol although other suitable solvents for the ethyl ester of silicic acid may be employed. The volume of material treated in this way is substantially increased and tests conducted on samples treated by the method of the present invention have established that the compressive strength is substantially greater than the minimum required for such concrete structures by building regulations currently in force.

During curing of the silicic ester to form silica the matrix is water-repellent due to the hydrophobic effect of the silica, but this effect decreases with time and the method of the present invention thus further includes the step of providing protection for the concrete structure against water penetration. This final step may be performed in any one of a number of ways.

In a first embodiment of the invention the surfaces of the structure are protected against water penetration by a treatment with a water-repellent based on methyl siloxane which results in cured silicone lining the pores of the structure with a membrane having a low surface tension. Such a treatment inhibits the ingress of water yet allows the structure to "breathe". This treatment may be effected by direct application of the water repellant although it is preferred for the final waterproofing step to be achieved by coating the surfaces of the structure with water impermeable layers, for example a render coat of cement and/or paint, which nevertheless allows the movement of air through the pores of the structure: such a render coat preferably has a methyl siloxane or methyl ethoxy siloxane additive.

In another aspect the present invention provides a method of consolidating a decomposed structure of mineral aggregate bound by calcium-aluminium-silicate cement, comprising the steps of applying a plurality of open sided receptacles to at least one vertical face of the structure, sealing around the edges of the receptacles with a chemically resistant liquid-tight sealant material, and introducing a solution comprising an ethyl ester of silicic acid dissolved in at least one solvent, allowing the solution to penetrate the structure to saturste the matrix thereof, draining the receptacles of surplus solution and allowing the solvents to evaporate prior to applying a surface finish.

This method has the particular advantage of ensuring that the whole of the structure is saturated at the same time with the solution. It has been found that subsequent saturations of such structures result in a decrease in the acquired strength and should be avoided. A dye may be added to the treatment liquid to aid visualisation of the degree of impregnation into the porous matrix.

Preferably, the receptacles when fitted to the vertical face of the structure are sealed against evaporation from a free surface of liquid contained therein.

Of course, care must be taken to ensure that the liquid within the receptacles does not become exhausted before the matrix of the structure is entirely suffused with the chemical solution and the method of the present invention therefore includes the further step of monitoring the level of liquid within the receptacles and introducing additional solution through a closable opening thereof prior to final draining if necessary.

According to another aspect, the present invention comprises apparatus for use in the treatment of masonry or other structural components, particularly but not exclusively for consolidating a decomposed matrix structure of mineral aggregate bound by a calcium aluminium silicate cement, comprising a receptacle for a consolidating solution, having a major face with an aperture therein, a rim surrounding the said aperture with a channel or groove for receiving a sealing element or compound by which the receptacle can be sealed in a liquid-tight manner to a vertical face of the structure whereby to allow the penetration by absorption of the liquid without substantial evaporation thereof from the free surface of liquid within the receptacle.

Preferably, the sealing element or compound in the channel or groove in the rim surrounding the aperture in the major face of the receptacle is an adhesive which also holds the receptacle in place against the vertical face of the structure.

In a preferred embodiment of the invention the channel or groove is formed in a lip or flange surrounding the aperture in the major face of the receptacle.

Means for draining the receptacle, when in position adhered to a vertical face of a structure to be consolidated, may comprise a drainage opening closable by a tap or valve.

In order to monitor the level of liquid within the receptacle there is provided a vertically elongate transparent panel in one face of the receptacle. The panel may be marked with graduations indicating the level of liquid therein.

In the preferred embodiment of the invention the receptacle is largely made from a unitary blank folded to shape and welded or brazed to form liquid-tight seams.

Preferably the receptacle includes a cover or upper wall with closable openings through which liquid can be introduced when the receptacle is sealed in place against the vertical surface of a structure.

The invention will now be more particularly described in detail with reference to the attached drawings which illustrate a preferred embodiment of the invention by way of example only.

In the drawings: Figure 1 is a sectional view through a domestic dwelling house illustrating the points at which treatment with the consolidating solution is applied; Figure 2 is an enlarged sectional view illustrating a part of the wall of the structure illustrated in figure 1 with a receptacle according to the invention adhered thereto; Figure 3 is a perspective view of a receptacle formed according to the principles of the present invention; Figure 4 is a diagram illustrating the composition of a suitable silicic ester; and Figure 5 is a diagram ilustrating an ethyl orthosil icate.

Because of the use of contaminated aggregates in the manufacture of concrete, especially concrete blocks produced in the early part of this century, there are many buildings which are now in an advanced stage of decomposition, and many which are deteriorating at a rate which will require serious structural remedial work in the near future if the risk of collapse is to be avoided.

As mentioned above, the only solution to the problem of loss of cohesive strength in masonry has been demolition and rebuilding, but this is frequently an enormous cost which cannot be met by the householder. Attempts have been made to effect repairs to specific areas by the removal of badly decomposed block work and the introduction of new block work set in place. This, in many respects, is counter productive since the rate of decomposition of the contaminated block work is dependent on some extent on the moisture and humidity levels, and these are increased by the presence of water in the mortar used to set the new block work.The results that in a very short time the area immediately surrounding the repair deteriorates and disintegrates leaving the new area surrounded by unstable material which has decomposed more rapidly than the remainder of the building, and the repair itself is therefore dangerous. Even if the entire wall is dismantled and rebuilt, and tied into the existing walls using metal ties, the old structure nevertheless breaks away from the new and the ties themselves are insufficient to retain cohesion in the structure without the bonding of the calcium aluminium silicate cementitious material.

Figure 1 illustrates a conventional structure in very broad outline, as an aid to describing the steps which must be taken to remedy decomposition in masonry. The structure illustrated in Figure 1 comprises footings 11, 12 for respective masonry walls 13, 14 each provided with a respective water impermeable damp proof course 15, 16 tied together at mid height by the joists 17 which support a suspended floor, and by the roof joists 18 which are tied together by tie beams 19 to form an A-frame, thereby limiting the outward pressures on the walls 13, 14 exerted by the weight of the roof supported by the beams 18. Drainage of the roof is provided by gutters 20 which discharge collected rain water into a downpipe 21 leading to a gulley 22 from which the water is carried away by a land drain 23.The outer surfaces of the walls 13, 14 may be coated in a render coat 24, and/or painted to protect the masonry from'water.

However, during the course of time various problems may occur which allow the ingress of moisture into the masonry of the walls 13, 14. These may include: (a) loss of waterproof roof clading materials (slstes or tiles) allowing water ingress to the top of the walls; (b) blockage or clogging of the downpipe 21 allowing overspill from the gutter 20 or leakage from joints in the downpipe 21; (c) cracking or peeling of the render coat or paint layer 24, 25 allowing direct ingress of rain water; (d) accumulation of earth or detritus at the foot of the walls, as illustrated at the base of the wall 14 in Figure 1, bridging the damp proof course 16.

Other causes of water penetration into masonry exist, but need not be enumerated here. In the presence of such water ingress it is believed that the mineral salts contaminating the aggregate react to cause decomposition of the masonry so that the calcium aluminium slicate cement originally binding the material is left as a sponge-like matrix which, itself, does not have sufficient compressive strength to support the weight of the material above it and/or the roof. In such circumstances settlement of the structure and/or catastrophic collapse may take place.

When such mineral contamination of aggregate is detected the remedial work to be performed in accordance with the invention comprises consolidation of the contaminated masonry and correction of the faults allowing water ingress. Even sound masonry is subject to deterioration by water ingress and although the results are not as damaging as in the case of masonry made from contaminated aggregates, increased internal humidity, unsightly staining and increased risk of fungal attack to woodwork all result from such water ingress which, therefore, must be addressed first. Once the sources of water ingress have been dealt with consolidation of the masonry can take place, in accordance with the invention, using the apparatus illustrated in Figures 2 and 3.This apparatus comprises a series of elongate receptacles, only one of which is illustrated in Figures 2 and 3, which in the specific embodiment illustrated have a triangular cross section with a major opening 26 in one wall surrounded by a rim 27 defining respective channels 28, 29 into which a mastic bead 30, 31 can be introduced whereby to fix the receptacle (generally indicated with the reference numeral 32) onto a vertical face of the masonry as illustrated in position on the wall 14 in Figure 1.

The receptacle 32 also includes triangular end walls 33, 34, a top wall 35 and an inclined major face 36. The upper wall or cover 35 has openings 37, 38 by means of which liquid can be introduced into the interior of the receptacle and the major face 36 has a drain outlet 39 and an elongate slot 40 extending from top to bottom thereof and covered with a transparent panel 41 sealed around the edges by a gasket 42 through which the level of liquid within the receptacle can be observed from the outside.

In use of the apparatus described mastic beads 30, 31 are applied to the channels 28, 29 (which may be completed by corner pieces, not illustrated) and the receptacle 32 then offered up to the vertical faces of a wall to be consolidated, which has preliminarily been stripped of any water impermeable render coat or paint and/or provided with appropriate holes drilled part way into the thickness of the masonry to encourage the introduction of the consolidating solution.

Although only one such receptacle 32 is illustrated in position on the wall 14 it will be appreciated that a plurality of such receptacles will be applied over the whole of the face of the wall and, in the case of a cavity wall, this will be repeated on the interior leaf.

Likewise, if the receptacle 32 is not sufficiently long to extend from end to end of the wall 14, additional such receptacles will be fitted either end to end or in a staggered array so that, given that the solution will be absorbed into the matrix of the masonry wall structure over an area greater than that defined by the opening 26, the whole of the wall can be suffused with a consolidating solution introduced by filling each of the containers through the openings 37, 38 with such solution. This is effected, starting from the highest receptacle, and refilling of the receptacles is continued so that a certain minimum level of solution is maintained in each receptacle for a given minimum period between 12 and 24 hours.After this the drain outlets 39 are opened and the surplus solution removed entirely and the receptacles 32 separated from the walls and any residual mastic from the beads 30, 31 scraped off to allow the walls, now saturated with the consolidating solution, to dry out by evaporation of the solvents.

In one example the solution used was an ethyl ester of silicic acid dissolved in white spirit and alcohol and it was found that a period of at least five days was required for complete evaporation of the solvents. After impregnation and evaporation of the solvents the silicic ester cures to form silica constituting a permanent natural binding insoluble in water and all common solvents. Thus, the hardnes of the treated area, as well as its abrasion resistance is increased. It was found that during the curing the masonry matrix was water-repellent, but after a period of time this hydrophobic effect became substantially reduced and in order to protect against water penetration an additional treatment with a water-repellent based on methyl siloxane was effected.This treatment results in the pores of the matrix being lined with a cured silicone membrane having a very low surface tension which inhibits the ingress of water yet allows the pores of the masonry matrix to breathe. Once this treatment is completed the application of a conventional render coat and/or painting can be effected to make good the surfaces prior to habitation.

One material found to be especially effective in performing the consolidation treatment of the present invention is one incorporating silicone-organic chemicals.

Silicone-organic chemicals may have several applications in building protection, including use as additives with an internal hydrophobic effect, as binders for coating systems, as water-repellent impregnating fluids and as consolidants for weathered masonry. Organic silicic esters or alkyl silicates have shown, both in laboratory tests and in widespread use on site, outstanding advantages over other materials in the conservation of decayed stone and masonry. It can be shown that alkoxy-silicone compounds, particularly esters of silicic acid and aliphatic alcohols, and especially ethyl silicate and ethyl polysilicate, can be used to treat decayed masonry to cure it providing the correct procedures are adopted as described herein.

Silicic ester (Figure 4) contains 4 oxygen atoms tetrahedrally surrounding the silicon atom These tetrahedrons may exist separately or within pearl chains of ethyl orthosilicate (as shown in Figure 5), bands or three-dimensional linked structures. The oxygen/silicon ratio which is 4/1 in the monomeric orthosilicate, decreases with increasing linkage of the tetrahedrons having mutual oxygen atoms. If the maximum degree of condensation is reached, the ratio is 2/1. This is the state SiC2.aq in situ. Alcohol is evolved as a by-product and eVaporates together with thesolvent carrier. Consequently these materials have the advantage that only silicic acid remains within the masonry matrix and no other chemicals are formed which may later, e.g.

as efflorescence, affect the visual and other properties of the consolidated stone.

The effect of ethyl silicate in masonry consolidation is thus based on its condensation and in situ formation of silicic acid, which cements the binder particles and aggregate minerals. It is likely that additional chemical linkages are formed so that the consolidated areas contain binding material which is chemically related to that in the sound areas. It should also be noted that ethyl silicate has only a strengthening effect, and the water-absorptive capacity of the masonry will not be permanently decreased. For this reason, organoalkoxy-silicone chemicals may be employed which react in a similar way to ethyl silicate with its SiO2 formation, but which lead to silicones with organic groups linked directly to the silicon atom.

Experimental results show that impregnation using silicic esters leads to a gradual increase in strength. Heavily weathered areas are more filled with silicic acid as the new binding material than those areas which are less decayed. It has been found in the case of a matrix which has been non-uniformly exposed to weathering that, after the treatment of the present invention the impregnated areas are mainly restricted to the weathered areas and accordingly it can be assumed that the unweathered sound matrix does not contain any significant amount of new binder. Above all abrasion resistance tests demonstrate that no crust formation occurs when the matrix was cured with silicic ester, even when three independent impregnations were applied.

In the tests the following materials were used: - Stone hardener without hydrophobic effect; TEGOVAKON V, SiO2 - content: 26 wt.-% (Theor.), gel-precipitation: 41 + 1 wt.-t, solids (ethyl silicate): 65 + 1 wt.-%, solvent: ethanol, reaction by-product: ethanol.

- Water-repellent fluid based on TEGOSIVIN HL30 methyl ethoxy siloxane, solids: 7.5 wt.-*, solvent: white spirit, reaction by-product: ethanol.

The products TEGOVAKON V and TEGOSIVIN 30 are trade names of T H Goldschmidt AG of Essen.

Claims (20)

1. A method of consolidating concrete structures comprising the steps of impregnating the material thereof with an ethyl ester of silicic acid dissolved in one or a plurality of solvents, and allowing the solvents to evaporate and the silicic ester to cure to form silica.

2. A method according to Claim 1, wherein the solvents used in the solution include white spirit and/or alcohol.

3. A method as claimed in Claim 1 or Claim 2, further including the step of providing protection for the concrete structure against water penetration during evaporation of the solvents and curing of the silicic ester.

4. A method as claimed in Claim 3, in which the protection of the concrete structure against water penetration is effected by a treatment with a water-repellent based on methyl siloxane.

5. A method as claimed in Claim 4, in which the water-repellent is applied by the application of a coat of material including methyl siloxane or methyl ethoxy siloxane additive.

6. A method of consolidating a decomposed structure of mineral aggregate bound by calcium aluminium silicate cement, comprising the steps of applying a plurality of open-sided receptacles to at least one vertical face of the structure, sealing around the edges of the receptacles with a chemically resistant liquid-tight sealant material, and introducing a solution comprising an ethyl ester of silicic acid dissolved in at least one solvent to the volume enclosed by the receptacle and the said one face of the structure, allowing the solution to penetrate the structure to saturate the matrix thereof, draining the receptacles of surplus solution and allowing the solvents to evaporate.

7. A method as claimed in Claim 6, in which the receptacles when fitted to the vertical face of the structure are sealed against evaporation from a free surface of the liquid contained therein.

8. A method as claimed in Claim 6 or Claim 7, further comprising the step of monitoring the level of liquid within the receptacle or receptacles and introducing additional solution through a closable opening thereof prior to final draining.

9. A method as claimed in any preceding Claim, further including the step of introducing a dye to the treatment liquid for visualisation of the extent of impregnation to the porous matrix.

10. Apparatus for use in the treatment of masonry or other structural components, comprising a receptacle for a treatment solution, having a major face with an aperture therein, a rim surrounding the said aperture with a channel or groove for receiving a sealing element or compound by which the receptacle can be sealed in a liquid-tight manner to a vertical face of the structure whereby to allow penetration by absorption of the liquid without substantial evaporation thereof from the free surface of liquid within the receptacle.

11. Apparatus as claimed in Claim 10, in which the sealing element or compound in the channel or groove in the rim surrounding the aperture in the major face of the receptacle is an adhesive mastic which also serves, when the receptacle is positioned against a vertical face to be treated, to hold the receptacle in place against the said vertical face.

12. Apparatus as claimed in Claim 10 or Claim 11, in which the said channel or groove is formed in a lip or flange surrounding the aperture in the said major face of the receptacle.

13. Apparatus as claimed in any of Claims 10 to 12, in which means for draining the receptacle when in position adhered to a vertical face of a structure to be treated comprises a drainage opening closable by a tap or valve.

14. Apparatus as claimed in any of Claims 10 to 13, further including a vertically elongate transparent panel in one face of the receptacle.

15. Apparatus as claimed in Claim 14 wherein the said transparent panel is marked with graduations for indicating the level of liquid therein.

16. Apparatus as claimed in any of Claims 10 to 15, in which the receptacle is made from a unitary blank folded to shape and joined by welding, brazing or adhesive to form liquid-tight seams.

17. Apparatus as claimed in Claim 16, in which the receptacle includes a cover or upper wall with closable openings through which liquid can be introduced when the receptacle is sealed in place against the vertical surface of a structure.

18. A method of treating a porous matrix substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

19. A method of consolidating decomposed concrete substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

20. Apparatus for use in the treatment of masonry or other structural components, substantially as hereinbefore described with reference to, and as shown in Figures 2 and 3 of the accompanying drawings.