EP4161883A1

EP4161883A1 - Grout for the injection of prestressing cables and method for installing a cable comprising such a grout

Info

Publication number: EP4161883A1
Application number: EP21737703.5A
Authority: EP
Inventors: Christian Tourneur; Julien Mercier; Ivica Zivanovic; Xavier HALLOPEAU
Original assignee: Soletanche Freyssinet SA
Current assignee: Soletanche Freyssinet SA
Priority date: 2020-06-05
Filing date: 2021-06-03
Publication date: 2023-04-12
Also published as: CA3185982A1; WO2021245359A1; FR3111134B1; US20230212073A1; KR20230021698A; AU2021283736A1; JP2023529635A; FR3111134A1; MX2022015389A

Abstract

The invention relates to a geopolymer grout for protecting prestressing reinforcements, the geopolymer grout comprising metakaolin, fly ash and an activator mixture, the activator mixture comprising sodium hydroxide and sodium silicate, wherein the molar ratio Na 2O:SiO2 of the sodium silicate is between 0.40 and 0.70.

Description

Title: GROUT FOR THE INJECTION OF PRE-STRAINING CABLES AND PROCEDURE FOR INSTALLING A CABLE INCLUDING SUCH GROUT Technical field

The present invention relates to the field of reinforcements for construction works. It relates more particularly to the grout injected into conduits of prestressing cables and to the method of manufacturing this grout as well as to the method of installing a structural cable comprising the installation of a conduit and the injection. of a grout in the duct.

Prior art

[0002] Prestressing cables generally consist of a bundle of reinforcements, most often made of steel, the tensioning of which makes it possible to exert the prestress. The reinforcements are arranged in a tubular conduit (generally formed in a sheath) filled with a protective material after tensioning. The prestressing cables can be placed inside (embedded in the structure to be stressed) or outside the concrete (the cables are anchored to the structure only by their anchors at the ends). In all cases, the post-stress of the concrete is obtained in the first place by the concreting of a structure (for example a beam) comprising a conduit (for example a sheath) empty of reinforcements. Reinforcements are then threaded into this conduit and then tensioned. Once the reinforcements have been put under tension, a grout is injected into the sheath in order to ensure the durability of the cables on the one hand, in particular by protecting them from corrosion, in order to transmit the forces to the concrete of the structure, in the case of internal prestressing and adherent to concrete on the other hand.

[0003] A grout is generally composed of a mixture based on cement and water, the mixture being sufficiently fluid to fill the duct and coat the bundle of reinforcements without leaving a vacuum. Cement is a hydraulic binder, ie capable of setting in water. A classic cement comes under the form of a very fine powder which, when mixed in water, forms a paste which sets and gradually hardens over time. An example of a well-known classic cement is Portland cement. The hardening of cement is due to the hydration of certain mineral compounds. The basic composition of current cements is a mixture of silicates and calcium aluminates, resulting from the combination of lime (CaO) with silica (S1O2), alumina (AI2O3), and oxide iron (Fe203). The necessary lime is supplied by limestone rocks, alumina, silica and iron oxide by clays. These materials are found in nature in the form of limestone, clay or marl and contain, in addition to the oxides already mentioned, other oxides and in particular Fe202, ferric oxide. The water-cement suspension, that is to say the mixture based on cement and water, is always added to improve fluidity and delay setting; this mixture is called a cement grout.

The observations made on the works show that the corrosion of the post-tensioning cables can occur (possibly early) in places where the grout would be lacking (due to the presence of pockets or air-filled bubbles and / or aqueous solution), the location of these defects depending in particular on the layout of the prestressing cables. For example, as illustrated in FIG. 1, the prestressing cables 10 often have a path of sinuous shape comprising high points 12 and low points 13, the prestressing force exerted by the cable 10 being directed downwards. in the vicinity of high points and vice versa. At these high points 12, one can observe an absence of grout in contact with the reinforcements of the cable 10 and the presence of air and / or of aqueous solution or of particles less dense than the cement, which can promote corrosion. reinforcements. For cement grouts, the absence of grout results from a lack of stability of the grout or from infill imperfections in the injection operation. The lack of stability of the grout results in a phenomenon of segregation of the grout in the duct, by sedimentation (solid deposit) or filtration (water rising along the reinforcements), which can consequently lead to a bleeding phenomenon. In order to avoid this phenomenon, the injection of the grout into the duct must be done without entraining or trapping air in the duct, particularly in the high points or behind the anchors. In addition, the grout, once hardened, must be chemically stable and protective vis-à-vis the steel constituting the cables during the service life of the structure. In addition, for its injection, the grout must be sufficiently fluid to be pumped and conveyed in the hoses, the conduits and must remain stable and homogeneous before and during the setting. It is therefore necessary to control bleeding.

The fluidity of the grout is a critical point that is difficult to control due to the inconstancy of the production of the cement, climatic variations during the injection operations, the application pressures exerted, the kinematics of progression of the grout in the duct, filtration through the fittings etc.

[0006] More specifically, the fluid grout is a suspension of cement grains dispersed in a large quantity of water containing adjuvants, the roles of which are generally to thin and delay the setting of the mixture. The cement sets by a phenomenon of hydration, in which water is the main reagent, which triggers a crystallization reaction. There is always excess water in the grout. In general, the grouts are dosed with a mass ratio of water relative to the cement which is of the order of 0.34 to 0.40 while the water content necessary for the hydration of the cement particles is only about 0.17. If the suspension is stable, the excess water turns into microporosities distributed, during setting, in the hardened material. Otherwise, segregation effects occur by filtration and / or sedimentation which cause water to rise to the high points before setting, and sometimes to rise of particles of materials less dense than cement. When this occurs, these particles form in the high points of the cable route an accumulation of "white paste" which does not harden and whose chemical properties are different from those of the cured grout. This effect can be combined with the presence of air and water pockets in the high points if the injection is not properly controlled. It is precisely in these injection fault zones that one can potentially observe premature cable breaks due to the corrosion effect of the steel of the reinforcements. Indeed, water in significant relative quantity, although necessary for the chemical hydration reaction, has drawbacks such as bleeding or the accumulation of white paste.

[0007] For example, according to patent EP0875636A1, it is known a solution aimed at alleviating the problems of poor injection by adding vents at the high points of the cable, allowing air and water, which could be in contact with the reinforcements, to escape from the duct. However, this solution is not satisfactory because the discharge through the vent requires several subsequent steps of reinjecting the grout into the duct. This solution is therefore long and difficult to implement. [0008] Other known solutions consist in replacing the cement grout with a substitute for this grout, such as, for example, inhibitor gels, petroleum waxes or organic resins. These substitutes have many drawbacks such as for example a lack of adhesion between the injected product and the prestressing reinforcements or for waxes the implementation at high temperature, in particular to be in a temperature range located above the point fusion of the substitute used, and thus obtain a fluid of low viscosity and therefore injectable. This hot processing also causes a contraction (or shrinkage) on cooling of the product.

Another alternative is to replace the cement grout with a grout of alternative composition. It is for example known from document FR2623492A1 a cement slurry comprising a mineral filler such as for example sand.

A mineral material can also be considered. This type of material is stable in liquid form and requires only a small amount of water compared to a cement grout intended for injection. These are products of the poly (silico-oxo-aluminate) type, commonly called a “geopolymer”. Due to the absence of cement in a geopolymer grout, the hydration reaction of the mixture is not involved in the setting and hardening of the grout. This avoids the problems due to the massive presence of water in the grout. This type of material is known for example from document FR2949227A1. The geopolymer grout disclosed by this document offers the rheological performance and mechanical resistance defined by specifications in which, at 28 days depending on its manufacture, the compressive strength of the grout must be greater than 30 MPa. On the other hand, this material does not meet the usual criteria of fluidity necessary for injection of the grout. This fluidity is usually measured according to a standardized test described in European standard “NF EN 445” relating to the flow time through a Marsh cone with a 10 mm diameter nozzle, which must theoretically remain less than or equal to 25. seconds, 5 hours after mixing the grout (equivalent to a viscosity of 0.5 Pa.s).

[0011] In addition, the grout must be able to be injected into a conduit intended to contain tensioned reinforcements. It is known from document FR2713690A1 a method for the injection of a grout. However, this process is specifically developed for a cement grout and therefore cannot be used for a geopolymer grout.

[0012] The grout proposed by the invention therefore aims to solve the problems encountered in grouts known among those which set, whether it is cement grout or geopolymer grout. Thus, the grout disclosed by the present invention aims in particular to solve the problems caused by both the presence of water in the cement grout, and the lack of fluidity of the existing geopolymer grouts.

Summary of the invention

The invention provides a geopolymer grout for the protection of prestressing reinforcements, the geopolymer grout comprising metakaolin, fly ash and an activator mixture, the activator mixture comprising sodium hydroxide and sodium silicate, in wherein the Na2O: SiO2 molar ratio of the sodium silicate is between 0.40 and 0.70. In particular, the Na 2 O: SiO 2 molar ratio of the sodium silicate is between 0.51 and 0.60.

In the geopolymer slurry, the sodium silicate may also have a water content by weight of between 52.1% and 72.1% and the activator mixture have a water content by weight of less than 65%.

In the geopolymer grout, the activator mixture may also have a water content by mass of between 40% and 65%. In particular, the mass water content is between 56% and 63%. In the geopolymer grout, the metakaolin: fly ash: alkaline silicate solution: sodium hydroxide mass ratio can be 1: 1: 2-3: 0.15-0.35.

In the geopolymer slurry, the metakaolin: fly ash: alkaline silicate solution: sodium hydroxide mass ratio can further be 1: 1: 2.4-2.6: 0.19-0.23.

The geopolymer grout can also have a pH of between 13 and 14.

The geopolymer grout may also have a bleeding of the aqueous reaction solution of less than 0.5% of the total mass of the grout.

In the geopolymer grout, the BET specific surface (Brunauer, Emmett and Teller theory) of metakaolin alone or of a mixture comprising metakaolin and fly ash may be greater than or equal to 25 m ² / g and preferably greater than or equal to 30m ² / g. The invention also provides a method of manufacturing a geopolymer grout, the geopolymer grout comprising metakaolin, fly ash and an activator mixture, the activator mixture comprising sodium hydroxide and sodium silicate, the Na2O: SiO2 molar ratio of the sodium silicate being between 0.40 and 0.70, wherein the manufacturing process comprises an activation step in which the metakaolin and the fly ash are activated by the activator mixture in order to 'obtain a polymerization of the whole.

[0022] The manufacturing process can further comprise a preliminary step of homogenizing the metakaolin and the fly ash. The manufacturing process can further comprise a mixing step during which the activator mixture is mixed with the metakaolin and the fly ash.

In one embodiment of the manufacturing process, water is added at the start of the mixing step, the amount of water added being between 1% and 4% by weight of the geopolymer slurry. The added water is only useful to improve the fluidity of the grout. Water is in fact not necessary for the polymerization step, which reduces its use to a minimum. Compared to the quantities of metakaolin, fly ash and activator mixture required for the manufacture of the grout, the water thus represents a marginal quantity, thus avoiding the risks associated with the quality and stability during the setting of the grout.

In one embodiment of the manufacturing process, in a preliminary grinding step, the metakaolin alone or a mixture comprising the metakaolin and the fly ash is ground in order to obtain a BET specific surface area greater than or equal to 25 m ² / g and preferably greater than or equal to 30 m ² / g. The invention also provides a method of installing a structural cable, comprising:

- the installation of a duct containing at least one reinforcement,

- the tensioning of the reinforcement,

- the injection of a geopolymer grout into the pipe, and in which the geopolymer grout comprises metakaolin, fly ash and an activator mixture, the activator mixture comprising sodium hydroxide and sodium silicate, the molar ratio Na20: Si02 of the sodium silicate being between 0.40 and 0.70.

[0027] The installation method may further comprise, before the injection of the geopolymer grout into the duct, a mixing of the geopolymer grout for 2 to 5 minutes with an energy of about 9 kilojoules per liter, thus obtaining an equivalent fluidity to the Marsh cone with a 10 mm diameter nozzle between 25 seconds and 35 seconds.

[0028] The installation method may further comprise, during the injection of the geopolymer grout into the conduit, the use of a hose, the hose having an internal diameter greater than 25 mm and a length limited to 100 m.

In one embodiment of the installation process, the grout is pumped during the injection, the pumping rate of the grout being between 0.5 m ³ / h and 1.5 ^{m 3} / h. It should be noted that neither the manufacturing process of the geopolymer grout, nor the installation process requires a step of heating the components of the geopolymer grout or grout itself. These processes can be implemented at room temperature, as opposed, for example, to the injection of petroleum wax which requires heating the wax above its melting point. As a result, the phenomenon of shrinkage of the geopolymer grout after its injection is insignificant or even non-existent.

Brief description of the drawings

[0031] Other features, details and advantages of the invention will become apparent on reading the detailed description below, and on analyzing the accompanying drawings, in which: FIG. 1

[0032] [Fig. 1] is a block diagram illustrating an example of a prestressing cable.

Description of the embodiments

[0033] The geopolymer grout according to the invention is a mineral material in stable liquid form, the formulation of which does not contain or only very little free water. It is more precisely a product of the Poly "silico-oxo-aluminate" or (-Si-0-Al-0) n type (for which n is the degree of polymerization). This geopolymer grout is particularly advantageous for the protection of prestressing cables in their conduit. Indeed, this geopolymer grout guarantees better filling of the duct and better coating of the reinforcements while having no harmful effect with regard to the prestressing reinforcement.

The geopolymer grout mainly comprises powders, referred to as a filler element, and a liquid activator mixture. The charging elements are metakaolin and fly ash. Metakaolin is also called calcined kaolin. Metakaolin is a dehydroxylated alumina silicate of general composition Al203.2SÎ202. Metakaolin is, for example, a powdered product marketed under the name Argical 1200®, the composition of which is detailed in the following table [Table 1]. [0036] [Table 1]

The above table [Table 1] details the chemical composition of metakaolin with the trade name Argical 1200® [0037] The metakaolin used is finely ground. More precisely, metakaolin has a BET specific surface area greater than 15 m ² / g. Preferably, the BET specific surface is greater than 25 m ² / g. For example, the BET specific surface of metakaolin is greater than 30 m ² / g. Metakaolin makes it possible in particular to obtain a smoother grout than with a conventional cement, by limiting the deposits of mineral salts on the surface of the cement (also called “efflorescence”). Furthermore, the fineness of the grinding of metakaolin makes it possible to improve the mechanical compressive strengths and to reduce the viscosity of the geopolymer grout obtained. Indeed, among the load elements, an increase in the share of metakaolin relative to the share of fly ash leads to an increase in the mechanical strength and viscosity of the grout. Since metakaolin is elongated and irregular in shape while fly ash is spherical in shape, grinding metakaolin improves its stacking properties with fly ash, resulting in an increase in the share of metakaolin among the charging elements. In addition, metakaolin is a component that requires little energy for its extraction compared to ordinary cement, which makes the manufacture of geopolymer grout environmentally attractive. Indeed, the manufacture of metakaolin is obtained by calcining kaolinite (natural clay), which can be carried out at low temperature (between 600 ° C and 800 ° C) compared to the manufacture of a cement which requires a chemical combination of clay and limestone at very high temperature (around 1450 ° C).

Fly ash is class F fly ash. More specifically, the fly ash used comes from the combustion of pulverized coal in the boilers of thermoelectric power stations, by collection in electrostatic dust collectors. For example, the ashes flywheels used are marketed under the trade name “Silicoline ®”. Fly ash makes it possible in particular to improve the workability of the grout and the mechanical performance thereof in the long term.

The fly ash used can be finely ground. In this case, the fly ash has a BET specific surface area greater than 15 m ² / g. Preferably, the BET specific surface is greater than 25 m ² / g. For example, the BET specific surface area of fly ash is greater than 30 m ² / g. The fineness of the fly ash grinding improves the mechanical compressive strengths of the geopolymer grout obtained. The activator mixture comprises sodium hydroxide, sodium silicate and water. The activator mixture makes it possible to initiate the chemical reactions by breaking chemical bonds of the elements of metakaolin and fly ash, in order to form an amorphous gel then to start the polymerization reaction and to polymerize the whole in order to obtain the geopolymer whose three-dimensional structure contains the Si-O-Al bond.

Sodium silicate is an alkaline silicate solution. More precisely, sodium silicate has an Na 2 O: SiO 2 molar ratio of between 0.40 and 0.70. For example, the molar ratio is preferably between 0.51 and 0.60. For example, the molar ratio is between 0.55 and 0.59. According to another example, the molar ratio is 0.57. In addition, the sodium silicate has a water content by mass of between 52.1% and 72.1%. For example, sodium silicate comprises 62.1% of its weight in water.

Sodium hydroxide is in the initial form of sodium hydroxide tablets. The sodium hydroxide tablets are incorporated into the sodium silicate solution, according to the sodium hydroxide: sodium silicate mass ratio of 8.53: 100. For example, 85.3g of soda are incorporated into 1000g of sodium silicate solution. The basic nature of the soda increases the pH of the geopolymer grout, which helps protect the reinforcements against corrosion. For example, the grout has a pH of between 13 and 14. According to another example, the geopolymer grout has a pH of between 13.3 and 13.5. According to a preferred example, the geopolymer grout has a pH close to 13.4. Therefore, if the grout should exhibit a bleeding phenomenon, which will only be very limited due to the marginal amount of water added, the aqueous solution of the penetrant testing has a basic pH included in the ranges detailed above. The penetrant water therefore does not cause corrosion of the reinforcements. In particular, the grout may have an aqueous solution bleeding of less than 0.5% of the total mass of the grout.

[0043] Soda also makes it possible to obtain adequate Na / Si or Na / Al molar ratios, which makes it possible to obtain a geopolymer grout of chemical formulation meeting the desired criteria.

[0044] The activator mixture further comprises water. Water is understood here to mean water which is added in addition to the water entering into the composition of the sodium silicate solution. Therefore, the water described here is not part of the water making up sodium silicate and is therefore excluded from the range of 52.1% to 72.1% by weight of sodium silicate water by weight discussed above. The added water represents less than 4% by total mass of the geopolymer grout. By "total mass of geopolymer grout" is meant the mass of the grout comprising metakaolin, fly ash, sodium hydroxide, sodium silicate and added water. For example, the added water represents between 1% and 4% of the total mass of geopolymer grout. According to another example, the added water represents between 1 and 2% of the total mass of the geopolymer grout, and preferably 1.86%. According to yet another example, the added water represents between 3 and 4% of the total mass of the geopolymer grout, and preferably 3.64%. This quantity remains marginal compared to the total mass of the geopolymer grout.

In other words, the activator mixture has a water content by mass of less than 65%. Here, the mass water content takes into account the water contained in the sodium silicate as such and the water added to the sodium silicate and the sodium hydroxide. Therefore, the mass content here is a ratio of the mass of water contained in the sodium silicate and the water added to the total mass of the activator mixture (i.e. sodium silicate, hydroxide sodium and added water). For example, the activator mixture has a water content by mass of between 40% and 65%, and for example between 56% and 63%. For example, the activator mixture has a mass water content between 58% and 59% According to another example, the activator mixture has a water mass content of between 59% and 60%

Advantageously, the addition of water to the activator mixture makes it possible to improve the fluidity of the geopolymer grout while reducing only to a limited extent the mechanical resistance after setting and hardening, the latter always respecting the criterion according to which the resistance the compression of the grout must be greater than 30 MPa at 28 days.

The geopolymer grout of the invention has the advantage of causing very limited bleeding and better homogeneity of the grout given the small amount of water incorporated. In addition, this small amount of water results in the absence of filtration in the bundle of reinforcements constituting the cable. The small amount of water added also results in a porosity of the geopolymer grout much lower than a porosity of the cementitious grout of the prior art. For example, the porosity of the geopolymer grout detailed here has a porosity at least six times lower than the porosity of a cement grout. In addition, the kinetic progression of injection of the geopolymer grout into the duct is facilitated and the grout coats the reinforcements more easily than does a conventional cement grout, which prevents the appearance of air pockets (or bubbles). occluded.

The geopolymer grout is manufactured according to the process detailed below, comprising certain alternatives.

In an initial step, the metakaolin and the fly ash are homogenized in a mechanical mixer.

Alternatively, first, the metakaolin alone (that is to say without the fly ash) is ground in order to obtain a BET specific surface area greater than or equal to 25 m ² / g and preferably greater than or equal to 30 m ² / g. For example, metakaolin is ground using a grinder. The mill used can be a ring mill or a ball mill. According to another alternative, the load elements (that is to say the metakaolin and the fly ash) are ground in order to obtain a BET specific surface area greater than or equal to 25 m ² / g and preferably greater than or equal to 30 m ² / g. In the case of a ball mill, for example a mass of 5 kg of metakaolin is introduced, which is ground for 12 hours at a speed of 39 revolutions per minute. Depending on the grinding time, different BET specific surfaces are obtained for metakaolin, some examples of which are grouped together in the following table [Table 2].

[0052] [Table 2]

The table [Table 2] above illustrates the grinding of 5 kg of metakaolin by a ball mill at a speed of 39 revolutions per minute.

The sodium silicate solution in which the sodium hydroxide tablets are incorporated is then prepared. For example, a dose of 85.3 g of soda is incorporated per 1000 g of sodium silicate solution. The mixture is stirred until the soda tablets are completely dissolved. Then, in a kneading step, the activator mixture is kneaded with the metakaolin and the fly ash. This step allows to obtain a polymerization of the whole and therefore the geopolymer grout.

More specifically, the mixture of metakaolin and fly ash is introduced into the activator solution. The whole is then mixed enough to guarantee deflocculation of the mixture (homogeneous mixture without lumps)

The water is then added to the whole. The addition of water makes it possible to thin the mixture so as to obtain a geopolymer grout having a fluidity at the cone of Marsh (with 10 mm diameter nozzle) between 25 seconds and 35 seconds, and for example 30 seconds.

[0057] Alternatively, water is added before mixing the whole. Alternatively, water is added during mixing. Indeed, the instant during which water is added during the mixing step does not modify the rheological properties and the mechanical resistance of the geopolymer grout. In particular, it should be understood that the added water does not participate in the polymerization of the whole. In other words, water is not a reactive component of the polymerization step. The addition of water to the mixture is therefore independent of the polymerization.

[0058] Alternatively, the assembly is then kept at rest for 90 seconds.

Then the whole is mixed for 60 seconds at a speed of 630 revolutions per minute, for example. [0060] By way of example, the geopolymer grout prepared has the characteristics grouped together in the following table [Table 3].

[0061] [Table 3]

The table [Table 3] above groups together examples of geopolymer grout formulation.

Consequently, the geopolymer slurry has a metakaolin: fly ash: alkaline silicate solution: sodium hydroxide ratio. 1: 1: 2-3: 0.15-0.35. For example the mass ratio is 1: 1: 2.4-2.6: 0.19-0.23. Preferably, as illustrated in the formulation examples of the table [Table 3], the mass ratio is 1: 1: 2.489: 0.212.

Rheological measurements and mechanical strength tests were carried out on the geopolymer grout obtained, according to the test methods of standard NF EN 445. The results are collated in the following table [Table 4].

[0064] [Table 4] The table [Table 4] above groups together the results of compressive strength and viscosity measurement.

[0065] The method of installing a structural cable is now described. The installation process mainly comprises the placement of a conduit containing at least one reinforcement as well as the tensioning of the reinforcement, then the injection of a geopolymer grout into the conduit.

Once the geopolymer grout has been prepared according to the manufacturing process described above, the geopolymer grout is mixed in order to obtain sufficient fluidity, measured with a Marsh cone according to the NF EN 445 standard of between 25 seconds and 45 seconds. For example, the geopolymer grout is kneaded for 2 to 5 minutes (eg 4 minutes) with an energy of about 9 kilojoules per liter. Mixing is carried out for example by a turbo-type mixer making it possible to disperse in the mixture an energy of approximately 9 kilojoules per liter. This mixing is an important step of the injection process because it makes it possible to improve the fluidity in the same way, in other words to reduce the flow time measured with the Marsh cone. Indeed, the geopolymer mixture before turbo-mixing may have a flow time greater than 50 seconds, while the turbo-mixing described above makes it possible to reduce it to a value of between 25 and 45 seconds (viscosity values of between 0.5 and 0.9 Pa.s). These flow time values may remain greater than the usual criterion of standard NF EN 445 (time less than or equal to 25 seconds) without preventing the injection of the grout.

Subsequently, the geopolymer grout is injected into the conduit by a flexible. The hose has, for example, an internal diameter greater than 25 mm. Preferably, the internal diameter of the hose is greater than 35 mm. In addition, the hose has a length for example limited to 100 m. The geopolymer grout is injected, for example, by means of a pump (nominal pressure 25 bar) with a pumping rate of between 0.5 m ³ / h and 1.5 ^{m 3} / h.

Thanks to this installation process, the geopolymer grout remains stable (that is to say homogeneous by absence of segregation). Indeed, no bleeding is observed around and through the reinforcements constituting the cable. In comparison with a cement grout, any risk associated with a poor hydration reaction, and in particular the production of an unstable grout, is therefore avoided here. After setting and hardening of the geopolymer grout, one can find in cavities or bubbles a resurgence of aqueous solutions whose pH is between 13 and 13.5 and representing less than 0.5% by mass of grout. We find in the composition of these solutions the main chemical elements resulting from the different components (sodium ions Na ⁺ , sulphates SO4 ^{2 '} , silicate H2SÏ04 ² , and aluminates AI (OH) 4) _> these do not present any risk vis- with respect to the protection against corrosion of reinforcements. In addition, the volume of residual air in the duct is six times less than that of a conventional cement grout. It has also been observed that when the duct into which the geopolymer grout is injected is inclined, the geopolymer grout progresses with a front which is slightly offset between the upper and lower parts of the duct.

Claims

[Claim 1] Geopolymer grout for the protection of prestressing reinforcements, the geopolymer grout comprising metakaolin, fly ash and an activator mixture, the activator mixture comprising sodium hydroxide and sodium silicate, in which the molar ratio Na20: Si02 of sodium silicate is between 0.40 and 0.70.

[Claim 2] A geopolymer grout according to claim 1, the sodium silicate having a water content by mass of between 52.1% and 72.1% and the activator mixture having a water content by mass of less than 65%.

[Claim 3] A geopolymer grout according to claim 2, in which the activator mixture has a water content by mass of between 40% and 65%.

[Claim 4] A geopolymer grout according to any preceding claim wherein the metakaolin: fly ash: alkaline silicate solution: sodium hydroxide mass ratio is 1: 1: 2-3: 0.15-0.35. [Claim 5] A geopolymer grout according to any one of the preceding claims, in which the grout has an aqueous solution bleeding of less than 0,

5% of the total mass of the grout.

[Claim 6] A geopolymer grout according to any preceding claim wherein the grout has a pH between 13 and 14.

[Claim 7] geopolymer grout according to any one of the preceding claims wherein the BET specific surface area of metakaolin alone or of a mixture comprising metakaolin and fly ash is greater than or equal to 25m ² / g and preferably greater than or equal to at 30m ² / g.

[Claim 8] A method of manufacturing a geopolymer grout, the geopolymer grout comprising metakaolin, fly ash and an activator mixture, the activator mixture comprising sodium hydroxide and sodium silicate, the molar ratio Na20: Si02 sodium silicate being between 0.40 and 0.70, in which the manufacturing process comprises an activation step during which the metakaolin and the fly ash are activated by the activator mixture in order to obtain a polymerization of all.

[Claim 9] The manufacturing method according to claim 8 further comprising a prior step of homogenizing metakaolin and fly ash.

[Claim 10] The manufacturing method according to claim 8 or 9 further comprising a kneading step in which the activator mixture is kneaded with the metakaolin and the fly ash.

[Claim 11] The manufacturing method according to claim 10 wherein water is added at the start of the mixing step, the amount of water added being between 1% and 4% by weight of the geopolymer slurry.

[Claim 12] The manufacturing method according to any one of claims 8 to 11, wherein, in a prior grinding step, the metakaolin alone or a mixture comprising the metakaolin and the fly ash is ground in order to obtain a specific surface area. BET greater than or equal to 25 m ² / g and preferably greater than or equal to 30 m ² / g.

[Claim 13] A method of installing a structural cable, comprising:

- the installation of a duct containing at least one reinforcement,

- the tensioning of the reinforcement,

[Claim 14] A method of installation according to claim 13, comprising, before injecting the geopolymer grout into the duct, kneading the geopolymer grout for 2 to 5 minutes with an energy of about 9 kilojoules per liter, thus obtaining a fluidity at the Marsh cone with a 10 mm diameter nozzle between 25 seconds and 35 seconds.

[Claim 15] Installation method according to any one of claims 13 or 14 in which, during the injection, the geopolymer grout is injected into the duct by a flexible, the flexible having an internal diameter greater than 25 mm. and a length limited to 100m. [Claim 16] The method of claim 15 wherein the grout is pumped during injection, the pumping rate of the grout being between 0.5 m ³ / h and 1.5 ^{m 3} / h.