FR2528441A1 - AGENT FOR SEALING AND / OR CONSOLIDATING SOILS AND / OR BUILDING MATERIALS AND METHOD FOR IMPLEMENTING SAME - Google Patents

Abstract

WATERPROOFING AND OR CONSOLIDATION AGENT FOR SOILS AND BUILDING MATERIALS, USED BY INJECTION. IT IS IN THE FORM OF A CONCENTRATED ALKALINE SOLUTION OF SILICA, NON COLLOIDAL, OBTAINED BY DISSOLUTION AT ROOM TEMPERATURE OF SILICA WITH AN AVERAGE DIAMETER OF PARTICLES LESS THAN ABOUT 100M IN SODA, THE SIONAO RATIO BEING LOWER A2 AND THE CONTENT SILICA SOLUTION BEING ABOUT ABOUT 20 BY WEIGHT

Description

The present invention relates to a sealing agent

  and / or consolidation of soils and building materials such as mortars,

  concretes, masonry and a process for its implementation.

  More particularly, the sealing and / or consolidation agent is intended for the treatment of alluvium or rock presenting

voids.

  Soils, whether they are fissured rocks or alluvial deposits, must sometimes be consolidated to ensure stability.

  excavation or drilling, to prevent landslides.

  The installation of bridge pillars or buildings on these soils may also require consolidation to prevent their collapse. In addition, a waterproofing of these soils can prove

  necessary when they support works such as dams.

  Mortars, binders and concretes may present certain volume variations that may result in cracks of varying depth and width, which are detrimental to watertightness, the protection of reinforcement and possibly to the stability of structures. In addition, alterations may occur. produce over time under the influence of certain external agents likely to cause porosity more or less

  accentuated by dissolution of hydrated salts.

  Subsequent processing of these materials is therefore necessary in order to

  to improve the watertightness and / or to consolidate them.

  The problem posed by the sealing and / or consolidation of soils and building materials is therefore essentially the same, namely to reach the voids of the cracks and those present in the alluvium with the aid of an agent that is likely to penetrate them easily. and fill them with

sustainable way.

  The sealing and / or consolidation agents currently used belong essentially to two categories, namely synthetic resin solutions and alkali silicate soda silicates

or potash.

  Resins or resin-based products which lead to the formation of polymeric compounds may in certain cases prove to be useful but they are relatively expensive products whose fluidity does not always make it possible to reach the microcracks or micropores in depth. the injection of resins is a relatively recent technique so that the durability of structures or soils treated with these products is not

certain.

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  The current technique is therefore essentially to use alkali suspensions of sodium silicate, readily available products

  but have proven to have many disadvantages.

  Indeed lime, present in the building materials and some soils, once in contact with the sodium silicate causes the formation of a silica gel, due to excess silica compared to the soda in the

treatment solutions.

  Sodium silicate is indeed a colloidal solution of silicic acid in sodium hydroxide and its neutralization leads to its transformation into gel by electric discharge of the silicic ions which condense to form

polysilicic ions.

  The inadvertent formation of a silica gel has the effect of blocking the injection so that certain voids can not be reached In addition the gelation is never complete because soda remains in the structure of the gel On the other hand the gels obtained are not stable over time, and tend to dissociate by releasing soda again which

  constitutes a significant source of pollution and instability.

  The present invention overcomes the drawbacks of the known agents in that it provides a sealing agent and / or consolidation easily injectable even in microcracks of the order of p and having a very high reactivity vis-à-vis lime screw capable of leading to a mineralization of soils and building materials by formation of stable and insoluble hydrated silicate silicates, more particularly of tobermorite (2 Si O 2 3 Ca O 3 H 20),

  thus ensuring the durability of the treatment exerted on these soils and materials.

  The tests carried out on test pieces have in fact made it possible to show that, with the aid of the agent according to the invention, no gelling occurred by percolation through porous micro-mortars, no more

  any appearance of a gel layer at the exit of the test pieces.

  The formation of hydrated lime silicate crystals, more particularly tobermorite, with the aid of the agent according to the invention could be confirmed by the various X-ray diffractometry examinations. The sealing agent and / or The consolidation method according to the invention thus makes it possible to ensure: (a) an excellent injection into the voids and microvoids present in the soils and / or building materials, (b) the formation of stable and insoluble hydrated silicate silicates, (c) ) long-term stability of the products formed after injection, -3-

  and (d) an almost total absence of pollution.

  The subject of the present invention is a sealing and / or consolidation agent for soils and / or building materials that can be used by injection, characterized in that it is in the form of a concentrated alkaline solution of silica, -colioldale, obtained by dissolution at room temperature of silica with an average particle diameter of less than h in sodium hydroxide, the SiO 2 / Na 2 ratio being less than 2 and the content

  silica of the solution being greater than about 20% by weight.

  The non-colloidal nature of the agent according to the invention could be qualitatively highlighted by the Tyndall effect (measurement of the nephelometric index). The silica used may be pure silica or preferably siliceous products containing at least 80 to 90% by weight of silica.

If O 2 of non-vitreous structure.

  Among the preferred compounds, mention may be made in particular of pyrogenic silicas also known as fumed silicas which come from

  industrial waste, kieselguhr, gaize or silica aerogels.

  The particle size of the silica or the siliceous product having a great importance with a view to obtaining a rapid and complete dissolution in the soda, should therefore be, if possible, less than 100%, but preferably less than 50%. It goes without saying that according to the invention other siliceous products such as those mentioned above may be employed to the extent that they

  meet the necessary solubility criteria.

  The sodium hydroxide used for the dissolution of the silica is preferably in the form of a solution of between 35 and 370 B, that is to say

  having a density of from about 1.32 to 1.35.

  During the dissolution there is a certain exothermicity that is not necessary to control since there is no adverse effect on the reactivity of the sealing agent and / or

consolidation.

  The SiO 2 / Na 2 ratio is also of great importance, which as indicated above must be less than 2 but preferably between 1.5 and 1.8. In the case of a higher ratio, the silica would tend to form a gel and thus prevent a good injection at most

  deep micro-cracks or microvoids.

  The maximum silica content is not critical insofar as the SiO 2 / Na 2 O ratio is less than 2. However, for practical reasons relating in particular to the viscosity of the agent according to the invention, this content

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  is generally not greater than about 30% by weight and is preferably

between 23 and 27%.

  It has indeed been observed that to obtain a good injection it was desirable for the viscosity of the sealing and / or consolidation agent according to the invention to be between approximately 5 and 50 cP, preferably between 20 and 30 cP. , an appropriate viscosity obtainable

by dilution with water.

  The agent according to the invention may further contain certain additives

  likely to improve penetration into cracks or voids.

  According to a variant of the invention, the sealing agent and / or consolidation may contain lime or a calcium salt such as by

  example chloride, formate, acetate or calcium propionate.

  The addition of lime or a calcium salt is more generally recommended for the treatment of certain soils and / or materials which are poor in

lime.

  In soils and materials rich in hydrated lime, the silica dissolved in the agent according to the invention makes it possible to conduct, after reaction, the formation of hydrated lime silicates (tobermorite). However, this is not the case with soils and / or or materials which are particularly poor in hydrated lime, for which it is necessary to supply this absence directly by adding lime or indirectly to

using a calcium salt.

  When the agent according to the invention contains lime, it is generally present in an amount such that the CaO / SiO 2 ratio is

  greater than 0.3, the maximum ratio being 1.50.

  According to the invention, a calcium salt, more particularly calcium chloride, is preferably used, since after neutralization with sodium hydroxide it leads, in addition to the lime formed, to a salt.

(sodium chloride) non-polluting.

  The dissolved silica then reacts with the lime formed to give

  hydrated lime silicates insoluble and stable.

  The amount of calcium salts must be sufficient for the total neutralization of the sodium hydroxide, an excess of sodium hydroxide being likely to cause pollution phenomena Although an excess of calcium salt may be used, it is preferable to the invention to use the stoichiometric amount necessary for the neutralization of the

soda contained in the agent.

  If the calcium salt enrichment of the sealing and / or consolidation agent according to the invention is a preferred embodiment, this addition can nevertheless be achieved by injecting a solution of the calcium salt prior to the injection. However, such a process requires two successive injections and thereby makes

  longer and more expensive treatment.

  The various studies carried out with the aid of the agent according to the invention have made it possible to show that the formation of the tobermorite crystals occurred approximately 10 hours after the injection and that their formation takes place

  continued until about 7 days after the injection.

  X-ray diffraction or scanning electron microscopy showed a high abundance of lime silicate crystals

hydrated from 7 days.

  The very good reactivity observed is explained by the activity of the

  dissolved silica and by the freshness of the solution.

  The subject of the present invention is also a method of sealing and / or consolidation, this process consisting in injecting under pressure the agent according to the invention as defined above in voids or microvoids of soils, or in cracks or microcracks of

  building materials, using conventional injection equipment.

  The method according to the invention is particularly intended for the treatment of soils to be sealed or consolidated whether it is rocks

cracked or alluvium.

  For cracked rocks, drilling is first carried out and then the agent according to the invention is injected by the so-called injection techniques.

  to advancement or injection by going up.

  For alluvium because of the risk of landslides one uses a now-known process known as "tube with cuffs" (French patent

No. 986,619).

  The injection pressure is generally between 5 and 20 bar and the amount of the consolidation agent and / or sealing between 30 to

  % of the soil volume that is being considered for treatment.

  During the sealing work, the treatment can be checked by taking a sample that is subjected to permeability measurements. Alluvial soils of permeability of about 10 m / s will pass

  injection and curing at a permeability of about 10 6-10 m / s.

  In order to better understand the invention, will now be described by way of illustration and without any limiting character an embodiment and implementation of the sealing agent and / or

consolidation according to the invention.

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EXCIPES

  -2 In a soil rich in very permeable lime (permeability of 10 m / s) a 10 m deep drilling is carried out for the treatment of sealing of a volume of soil of lm 3 An injection tube is introduced in the borehole, and then an initial pressure of 3 bars is applied to the injection of a solution obtained by dissolving 170 kg of silica with an average particle size of approximately 50 μ in 300 liters of 36 B sodium hydroxide and 70 liters of sodium hydroxide. water (the characteristics of the solution after formation were as follows: Si O 2 / Na 20 = 1.8%, Si O 2 = 26.6%, Na 20 = 14.8%, H 20 = 58.6 viscosity 40-50 cP) When the refusal pressure is stabilized at about 10 bar, the injection is stopped which has been found to correspond to a quantity

  of the injected solution of the order of 320 liters.

  After a week, a new permeability measurement showed that it had increased to 10-6 m / s, denoting a perfect

sealing the treated soil.

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Claims (10)

  1 sealing agent and / or consolidation for floors and building materials, usable by injection, characterized in that it is in the form of a concentrated alkaline solution of silica, non-colloidal, obtained by dissolution at room temperature silica having a mean particle diameter of less than about 100 l in sodium hydroxide, the SiO 2 / Na 2 ratio being less than 2 and the silica content of the solution   being greater than about 20% by weight.   Agent according to Claim 1, characterized in that the silica used is a siliceous product containing at least 80 to 90% by weight   Si O 2 weight of non-vitreous structure.   Agent according to any of claims 1 and 2,   characterized in that the silica is pyrogenic silica (silica   smoke), kiselguhr, gaize or silica airgel.   Agent according to any one of the preceding claims,   characterized in that the SiO 2 / Na 2 ratio is preferably included between 1.5 and 1.8.   Agent according to any one of the preceding claims,   characterized in that the maximum silica content is not greater than   about 30% by weight and preferably between 23 and 27%.   Agent according to any one of the preceding claims,   characterized in that its viscosity is between about 5 and 5 Oc P, preferably between 20 and 3 Oc P.   Agent according to any one of the preceding claims,   characterized in that it contains lime in a ratio Ca O / Si O 2   greater than 0.3 with a maximum of 1.5.   Agent according to any one of claims 1 to 6,   characterized in that it contains a calcium salt such as chloride,   formate, acetate or calcium propionate.   Agent according to claim 8, characterized in that the calcium salt is present in an amount to neutralize totally soda.   A process for sealing and / or consolidating soils and building materials, characterized in that it consists in injecting under pressure - according to the conventional techniques, a sealing and / or consolidation agent according to any one of the Claims 1 to 9.   11 Process according to claim 10, characterized in that prior to the injection of the sealing agent and / or -a 2528441   consolidation according to any one of claims 1 to 6 is injected a solution of a calcium salt.   Process according to claim 11, characterized in that   the calcium salt solution is a solution of calcium chloride.