FR2765572A1 - Use of colloidal alkali metal silicate solution - Google Patents

Abstract

The use of a colloidal alkali metal silicate solution, for treating openings in concrete affected by alkali reaction, is new. Also claimed is a process for treating alkali reaction-affected openings by application of a colloidal alkali metal (preferably sodium, potassium or lithium) silicate solution, especially containing 30-70 (preferably 40) wt.% silica and 5-20 (preferably 11.5) wt.% sodium. Further claimed is an alkali reaction-affected opening in concrete which has been treated with a colloidal alkali metal silicate solution.

Description

Method of treating concrete structures
affected by the alkali-reaction.

 The present invention relates to a method of treating concrete structures affected by the alkali-reaction.

The alkali-reaction is a solid-liquid chemical reaction developing in concrete.

Concrete affected by the alkali-reaction comprises a solid phase, consisting of aggregates, and a liquid phase, called interstitial solution.

This interstitial solution has the particularity of being strongly alkaline.

When the alkali-reaction develops, this interstitial solution will dissolve the silica contained in the aggregates. The product resulting from this solution will precipitate in the form of a silico-calc-alkaline gel.

This gel is called an expansive gel, that is to say that it has swelling properties. The gels thus formed will have the effect of causing swelling of the concrete and thus cause overvoltage of the latter. This surge will result in abnormal cracking of these structures.

The alkali-reaction reaction may occur sooner or later after construction of the concrete structure. Nevertheless, in both cases, the alkali reaction reaction, once in place, develops very rapidly. Crack opening evolution rates of 0.05 mm per year have been observed. The alkali-reaction will therefore result in a significant and rapid deterioration of the structures affected.

Its importance depends on the abundance and reactivity of the mineral species, the amount of alkaline and the presence of water.

In some countries, such as Canada, alkali reaction is the leading cause of deterioration of concrete structures. In
France, the North and North West regions have the most affected works.

 In order to determine if the concrete structures are deteriorated by the alkali-reaction, a simple visual examination may suffice.

 By the presence of numerous cracks, the structures attacked by the alkali-reaction are easily spotted. These cracks may be in the form of a network of small anarchic cracks called crazing or in the form of a network of fissures of larger size and greater depth. Oriented fissures, which reproduce the outline of the reinforcement, have also been observed. A swelling of the structure can also be visualized, such as for example the total closure of the expansion joints with an abutment of the structure, or differential movements of parts of structures causing a rejection of certain cracks (facing upward) . In some cases, the expansion of the concrete may cause the breaking of some passive steel reinforcements.

 In order to diagnose the alkali-reaction, it is also possible to take samples of concrete that can be visualized by microscopy and thus to highlight the alkali-reaction gels. An observation by scanning electron microscope (SEM) will confirm this diagnosis.

 The first attempts to treat this disease consisted of the injection of epoxy resins into the cracks. These attempts were unsuccessful; indeed, some cracks reopened again and new cracks appeared next to those treated.

 Coatings have also been used on structures with alkali-reaction: - the painting of the structures did not prevent the development of the alkali-reaction, - the application of acrylic resin on the surface of the sick books was disappointing; after a period of stagnation, it was found that the alkali-reaction continued to progress, - applications of silanes were also attempted. Although having a good resistance to the penetration of water, concrete does not withstand long-term alkali-reaction.

The only effective treatments to date are mechanical treatments consisting in sawing the concrete to release the internal stresses of the latter. Nevertheless, this method is very unsightly and can only be applied on works of very large size.

 The Applicant has now surprisingly discovered a treatment using a colloidal solution of alkali metal silicates to effectively stop the alkali-reaction.

 The present invention therefore relates to the use of a colloidal solution of alkali metal silicates for the treatment of concrete structures affected by the alkali-reaction.

The alkali metals are preferably selected from sodium, potassium and lithium. A colloidal solution of alkali metal silicates according to the present invention is defined as a colloidal solution of sodium silicates and / or potassium silicates and / or lithium silicates.

In a particular form of the invention, the alkali metal silicate used is a sodium silicate and the colloidal solution of sodium silicates comprises, on analysis, from 30 to 70% by weight of silica, 5 to 20% by weight. sodium and preferably 40 to 55% by weight of silica and 8 to 14% by weight of sodium relative to the total weight of the composition.

Another object of the invention is the use of a solution of alkali metal silicates further comprising potassium and / or iron and / or aluminum and / or magnesium salts. These are included in the solutions used in the present invention in proportions by weight of less than 1%.

The present invention also relates to the use of a colloidal solution comprising, on analysis, 40% by weight of silica, 11.5% by weight of sodium and potassium, iron, aluminum and potassium salts alone. or mixed in proportions of less than 1% by weight relative to the weight of the composition.

 The present invention also relates to a method of treating works affected by the alkali-reaction consisting of the application of a colloidal solution of alkali metal silicates as defined above on said structures.

 According to one embodiment of the process according to the invention, a solution based on Ca 2+ ions is initially applied and, after drying, a colloidal solution as defined above is applied.

Another treatment method consists in the application of a solution based on alkali metal silicates as defined above followed, after drying, by the application of an ion-based solution.
Ca 2+. A solution based on Ca 2+ ions is, for example, a solution of saturated lime.

 One embodiment of a composition as defined above consists in spraying this composition over the entire surface of the concrete structure.

 Another mode of application consists in the injection under pressure of a colloidal solution of silicates as defined above.

For this, it will be sufficient to drill the concrete beforehand and inject the solutions recommended above. This pressure can be maintained for a certain time in order to optimize the penetration of the solutions in the concrete. The holes are then filled with mortar.

 Another method of treating works affected by the alkali-reaction consists in the application on a horizontal surface of said structures of a colloidal solution so that this solution enters by gravity into said structures.

 Other modes of application may also be suitable, such as ultrasonic or electrical processes.

 These application methods can also be used to apply a solution based on Ca 2+ ions.

 One of the particularly preferred methods of the present invention consists of one or more applications of a colloidal solution as defined above and in one or more applications of a solution based on Ca 2 + ions, these applications being able to be successive and / or or alternating.

For example, it is possible to apply several layers of colloidal solutions defined above, these solutions can be diluted differently.

A solution based on Ca2 + ions can then be applied to the treated structure.

This structure can also be treated first with a solution based on Ca2 + ions and then with colloidal solutions defined above, which can be of different dilutions. A solution of Ca2 + ions can then be applied. These applications can be followed by the application of a colloidal solution, preferably diluted.

 Another object of the invention relates to concretes with alkali-reaction treated with a colloidal solution of alkali metal silicates.

 An object of the invention also relates to concrete structures with alkali-reaction treated by a method as defined above.

 The following examples are intended to illustrate the invention, without being limiting in nature.

Example 1
At first, the alkali-reaction was diagnosed on balconies. In particular, these balconies had a distinct gap between their floor and the floor of the adjacent balconies. This difference could reach several centimeters. The tiles on the surface of the balconies have been deformed. It has also been found the presence of a large network of cracks.

By SEM analysis, clear signs of alkali-reaction in the form of gels and sometimes silico-calco-potassium crystals were highlighted.

On these balconies, the following treatment has been applied
a) Initially a Ca 2+ solution, in this case a solution of saturated lime, was dispersed on the surface of the balcony.

After drying, a spraying solution A, containing 40% silica, 11.5% sodium and less than 1% potassium and traces of iron and aluminum, diluted to 80% water was sprayed on the balcony surface.

After drying, the same solution A, but diluted to 70% water was sprayed onto the surface of the balcony.

After drying, a solution of Ca 2+, in this case a solution of saturated lime was dispersed on the balcony.

Finally, solution A, diluted to 30% water was applied to the surface of the balcony.

 b) 25 holes per m2 were drilled in which a solution of saturated lime was injected under pressure, then 60% diluted solution A was injected under pressure; this pressure being maintained for 4 hours. The holes were then filled with mortar.

 c) The balcony was then placed over a height of 4 cm of solution A diluted with 80% water.

Three days later, a loading of the balcony on a height of 4 cm with city water was carried out.

The balconies thus treated exhibit resistance to the alkali-reaction.

Example 2
Comparative tests were carried out on concrete prisms prepared with a potentially reactive grit.

Five sets of prisms were tested, three of these series being doped with alkali by adding NaOH to the mixing water, this addition making it possible to accelerate the alkali-reaction by placing itself under very severe conditions.

Solution A is a solution according to the present invention based on sodium silicates.

Solution B is a solution according to the present invention based on potassium silicates.

The treatment of the prisms is carried out according to alternating cycles immersion in a solution A or B diluted in water drying. The cycles are as follows immersion in solution A or B, 10% by volume 5 days air-drying at 20 OC 3 days immersion in solution A or B, 20% by volume 5 days air-drying 20 OC 3 days immersion in solution A or B, 30% by volume 5 days air-drying 20 OC 3 days immersion in solution A or B, 50% by volume 5 days air-drying 20 "C 2 days
Another series of prisms (series 5) underwent the above cycles after immersion for 5 days in a solution of Ca ++ ions followed by 2 days of drying at 200C.

Another series of prisms (series 4) has undergone the cycles described above, after prior preservation in a reactor at 600C and 100% relative humidity; it is thus possible to test the ability of the solutions of the present invention to quench an ongoing alkali-reaction reaction.

 The results obtained have been summarized in Table I.

Table I

<tb><SEP> Series <SEP> Processing <SEP> Prisms <SEP> Doping <SEP> Expansion
<tb><SEP> NaoH <SEP> (m / m) <SEP>
<tb><SEP> + <SEP> yes
<tb><SEP> -non <SEP> 3 <SEP> months <SEP> 6 <SEP> months <SEP> 12 <SEP> months
<tb><SEP> 1 <SEP> Concrete <SEP> Control <SEP> Without <SEP> Treatment <SEP> + <SEP> 640 <SEP> 730 <SEP> 830
<tb><SEP> 2 <SEP> Solution <SEP> A <SEP> 50 <SEP> 60 <SEP> 185
<tb><SEP> Cycles <SEP> Immersion / Drying <SEP>
<tb><SEP> 3 <SEP> Solution <SEP> A <SEP> + <SEP> 110 <SEP> 210 <SEP> 260
<tb><SEP> Cycles <SEP> immcrsionlsecba <SEP> e <SEP>
<tb><SEP> 4 <SEP> Solution <SEP> A <SEP> - <SEP> Enabled <SEP> + <SEP> 80 <SEP> 80 <SEP> 200
<tb><SEP> Cycles <SEP> inimersionisecha <SEP> e <SEP>
<tb><SEP> 5 <SEP> Ca2 + <SEP> then <SEP> solution <SEP> A <SEP> 10 <SEP> 85 <SEP> 180
<tb><SEP> Cycles <SEP> submissive <SEP> e <SEP>
<tb><SEP> 6 <SEP> Solution <SEP> B <SEP> + <SEP> 30 <SEP> 85 <SEP> 200
<tb><SEP> Cycles <SEP> Immersion / Drying <SEP>
<Tb>
After 12 months in a reactor at 600 ° C. and 100% relative humidity, the control concrete shows a very large swelling, whereas the concretes treated according to the present invention have a swelling approximately four times less.

By SEM analysis, it was observed that the control concrete contains silico-calc-alkaline gels while the concretes treated according to the present invention do not contain or contain more for the series 4.

Claims (21)

 1. Use of a colloidal solution of alkali metal silicates for the treatment of concrete structures affected by alkalinity.  2. Use according to claim 1, characterized in that the alkali metals are selected from sodium, potassium and lithium.  3. Use according to claim 1 or 2, characterized in that the colloidal solution of alkali metal silicates is a colloidal solution of sodium silicates and / or potassium silicates and / or lithium silicates.  4. Use according to claim 3, characterized in that the colloidal solution of silicates is composed in the analysis of 30 to 70% by weight of silica and 5 to 20% by weight of sodium, preferably 40 to 55% by weight. silica weight and 8 to 14% by weight of sodium relative to the total weight of the composition.  5. Use according to claim 3 or 4, characterized in that the colloidal solution of sodium silicates comprises 40% by weight of silica and 11.5% by weight of sodium relative to the total weight of the composition.  6. Use according to any one of claims 1 to 5, characterized in that the colloidal solution of alkali metal silicates further comprises potassium and / or iron and / or aluminum and / or magnesium salts in proportions by weight less than 1% relative to the total weight of the composition.  7. A method of treating works affected by the alcaliréaction, characterized in that one applies on said works a colloidal solution of alkali metal silicates.  8. A method of treating works according to claim 7, characterized in that the alkali metals are selected from sodium, potassium and lithium.  9. A method of treating works according to claim 7 or 8, characterized in that the colloidal solution of alkali metal silicates is a colloidal solution of sodium silicates and / or potassium silicates and / or lithium silicates.  10. Process according to Claim 9, characterized in that the colloidal solution of sodium silicates comprises, on analysis, 30 to 70% by weight of silica and 5 to 20% by weight of sodium, preferably 40 to 55%, of silica. and 8 to 14% of sodium, based on the total weight of the composition.  11. The method of claim 9 or 10, characterized in that the colloidal solution comprises analysis 40% by weight of silica and 11.5% by weight of sodium relative to the total weight of the composition.  12. Process according to any one of Claims 7 to 11, characterized in that the colloidal solution of alkali metal silicates used furthermore comprises potassium and / or iron and / or aluminum and / or magnesium salts. in proportions of less than 1% by weight relative to the total weight of the composition.  13. A method of treating concrete structures affected by the alkali-reaction, characterized in that the application of a solution as defined in any one of claims 7 to 11, is preceded by the application of a solution based on Ca2 + ions.  14. A method of treating works affected by alkaliréaction, characterized in that the application of a solution as defined in any one of claims 7 to 11, is followed by the application of a solution to base of Ca2 + ions.  15. A method of treating works affected by alkaliréaction, characterized in that a solution as defined in any one of claims 7 to 1 1 is applied to said structures by spraying.  16. A method of treating works affected by alkaliréaction, characterized in that a solution as defined in any one of claims 7 to 1 1 is applied inside said structures by injection pressure.  17. A method of treating works affected by alkaliréaction, characterized in that a solution as defined in any one of claims 7 to 11 is applied to a horizontal surface of said structures so that this solution penetrates by gravity in said works.  18. A method of treating works affected by the alkaliréaction according to any one of claims 11 to 13, characterized in that the application of a solution as defined in any one of claims 7 to 11 is preceded and / or followed by the application of a solution based on Ca2 + ions.  19. A method for treating structures affected by the alkali-action characterized in one or more applications of a solution as defined in any one of claims 7 to 11, and in one or more applications of a solution based on Ca2 + ions, these applications may be successive and / or alternating.  20. Concrete work affected by the alkali reaction treated with a colloidal solution of alkali metal silicates.  21. Concrete work affected by the alkali-reaction treated according to one of the processes defined in any one of claims 7 to 19.