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

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

Description Title: GROUT FOR INJECTING PRESTRESSING CABLES AND METHOD FOR INSTALLING A CABLE COMPRISING SUCH A GROUT Technical Field

[0001] The present invention relates to the field of reinforcement for construction works. It relates more particularly to grout injected into prestressing cable conduits and to the method of manufacturing this grout as well as to the method of installing a structural cable comprising the placement of a conduit and the injection of grout into the conduit. Previous technique

[0002] Prestressing cables are generally composed of a bundle of reinforcing bars, most often made of steel, which, when tensioned, exert prestressing force. The reinforcing bars are placed in a tubular conduit (usually within a duct) filled with a protective material after tensioning. 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 end anchors). In all cases, post-stressing of the concrete is first achieved by pouring concrete into a structure (for example, a beam) containing a conduit (for example, a duct) empty of reinforcing bars. Reinforcing bars are then threaded into this conduit and tensioned.Once the reinforcements have been tensioned, a grout is injected into the sheath 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 bonded to the concrete on the other hand.

[0003] Grout is generally composed of a cement-based mixture of water and cement, the mixture being fluid enough to fill the conduit and encase the reinforcement bars without leaving any voids. Cement is a hydraulic binder, meaning it sets in water. A typical cement comes in the form of... Cement takes the form of a very fine powder which, when mixed with water, forms a paste that sets and hardens gradually over time. A well-known example of a classic cement is Portland cement. The hardening of cement is due to the hydration of certain mineral compounds. The basic composition of modern cements is a mixture of calcium silicates and aluminates, resulting from the combination of lime (CaO) with silica (SO₂), alumina (Al₂O₃), and iron oxide (Fe₂O₃). The necessary lime is supplied by limestone, while the alumina, silica, and iron oxide are obtained from clays. These materials are found in nature as limestone, clay, or marl and contain, in addition to the oxides already mentioned, other oxides, particularly Fe₂O₂, ferric oxide. The water-cement suspension, that is to say the mixture based on cement and water, is always treated with additives to improve fluidity and delay setting; this mixture is called cement grout.

[0004] Observations of the structures show that post-tensioning cable corrosion can occur (possibly prematurely) where grout is lacking (due to the presence of pockets or bubbles filled with air and / or aqueous solution). The location of these defects depends, in particular, on the path of the prestressing cables. For example, as illustrated in Figure 1, prestressing cables 10 often have a sinuous path with high points 12 and low points 13. The prestressing force exerted by the cable 10 is directed downwards near the high points and vice versa. At these high points 12, a lack of grout may be observed in contact with the reinforcement bars of the cable 10, along with the presence of air and / or aqueous solution, or particles less dense than cement, which can promote corrosion of the reinforcement bars.For cement grouts, the absence of grout results from a lack of grout stability or imperfections in the filling process during injection. The lack of grout stability leads to segregation within the conduit, either through sedimentation (solid deposit) or filtration (water rising along the reinforcement), which can consequently cause bleeding. To avoid this, the grout must be injected into the conduit without introducing or trapping air, particularly at high points. behind the anchors. Furthermore, the grout, once hardened, must be chemically stable and protective of the steel components of the cables throughout the service life of the structure. Moreover, for injection, the grout must be sufficiently fluid to be pumped and conveyed through flexible hoses and conduits, and must remain stable and homogeneous before and during setting. Therefore, it is necessary to control bleeding.

[0005] The fluidity of the grout is a critical point that is difficult to control due to the inconsistency of cement production, climatic variations during injection operations, the pressures exerted during implementation, the kinematics of grout progression in the conduit, filtration through reinforcements, etc.

[0006] More specifically, fluid grout is a suspension of cement grains dispersed in a large quantity of water containing admixtures whose roles are generally to fluidize and delay the setting of the mixture. Cement sets through a hydration process, in which water is the main reactant, triggering a crystallization reaction. The water content of the grout is always in excess. Generally, grouts are formulated with a water-to-cement ratio of approximately 0.34 to 0.40, while the water content required for the hydration of the cement particles is only about 0.17. If the suspension is stable, the excess water transforms into micropores distributed throughout the hardened material during setting.Otherwise, segregation occurs through filtration and / or sedimentation, causing water to rise to the surface at high points before setting, and sometimes particles of materials less dense than cement to rise to the surface. When this happens, these particles form an accumulation of "white paste" at the high points of the cable run, which does not harden and whose chemical properties differ from those of the hardened grout. This effect can be compounded by the presence of air and water pockets at high points if the injection is not properly controlled. It is precisely in these injection failure zones that premature cable breaks can potentially occur due to corrosion of the reinforcing steel. Indeed, the relatively large quantity of water... Although necessary for the chemical hydration reaction, it presents disadvantages such as bleeding or the accumulation of white paste.

[0007] For example, patent EP0875636A1 describes a solution to address grout misalignment problems by adding vents at the highest points of the cable, allowing air and water that might be in contact with the reinforcement to escape from the conduit. However, this solution is not entirely satisfactory because venting requires several subsequent grout reinjection steps into the conduit. This makes the process lengthy and difficult to implement.

[0008] Other known solutions involve replacing cement grout with a grout substitute, such as inhibitor gels, petroleum waxes, or organic resins. These substitutes have several drawbacks, including poor adhesion between the injected product and the prestressing reinforcement. For waxes, application requires high temperatures, specifically above the melting point of the substitute, to achieve a low-viscosity, injectable fluid. Furthermore, this hot application causes contraction (or shrinkage) of the product as it cools.

[0009] Another alternative is to replace the cement grout with a grout of an alternative composition. For example, a cement grout containing a mineral filler, such as sand, is described in document FR2623492A1.

[0010] 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 poly(silico-oxo-aluminate) type products, commonly called "geopolymers." Due to the absence of cement in a geopolymer grout, the hydration reaction of the mixture does not play a role in the setting and hardening of the grout. This avoids problems caused by the presence of large amounts of water in the grout. This type of material is described, for example, in document FR2949227A1. The geopolymer grout disclosed in this document offers the rheological and mechanical resistance performance defined by a specification in which, at 28 days Depending on its manufacturing process, the compressive strength of the grout must be greater than 30 MPa. However, this material does not meet the usual fluidity criteria required for grout injection. This fluidity is usually measured using a standardized test described in the European standard "NF EN 445" concerning the flow time through a Marsh cone of a 10 mm diameter nozzle, which should 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] Furthermore, the grout must be able to be injected into a conduit intended to contain tension reinforcement. A method for grout injection is described in document FR2713690A1. However, this method is specifically designed for cement grout and therefore cannot be used for geopolymer grout.

[0012] The grout proposed by the invention aims to solve the problems encountered with known setting grouts, whether cement-based or geopolymer-based. Thus, the grout disclosed by the present invention is specifically designed to resolve the problems caused by both the presence of water in cement grout and the lack of fluidity in existing geopolymer grouts. Summary of the invention

[0013] The invention provides a geopolymer grout for the protection of prestressing reinforcement, the geopolymer grout comprising metakaolin, fly ash and an activator mixture, the activator mixture comprising sodium hydroxide and sodium silicate, in which the Na2O:SiO2 molar ratio of sodium silicate is between 0.40 and 0.70. In particular, the Na2O:SiO2 molar ratio of sodium silicate is between 0.51 and 0.60.

[0014] In the geopolymer grout, sodium silicate may also have a water mass content between 52.1% and 72.1% and the activator mixture may have a water mass content of less than 65%.

[0015] In geopolymer grout, the activator mixture may also have a water content by mass of between 40% and 65%. In particular, the water content by mass is between 56% and 63%.

[0016] In the geopolymer grout, the mass ratio of metakaolin:fly ash:alkaline silicate solution:sodium hydroxide can be 1:1:2-3:0.15-0.35.

[0017] In the geopolymer grout, the mass ratio of metakaolin:fly ash:alkaline silicate solution:sodium hydroxide can further be 1:1:2.4-2.6:0.19-0.23.

[0018] The geopolymer grout can also have a pH between 13 and 14.

[0019] The geopolymer grout may also exhibit a bleed of aqueous reaction solution of less than 0.5% of the total mass of the grout.

[0020] In geopolymer grout, the BET specific surface area (Brunauer, Emmett and Teller theory) of metakaolin alone or of a mixture including metakaolin and fly ash can be greater than or equal to 25m² 2 / g and preferably greater than or equal to 30m 2 / g.

[0021] The invention also proposes a method for 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, in which the manufacturing method includes an activation step during which the metakaolin and fly ash are activated by the activator mixture in order to achieve polymerization of the whole.

[0022] The manufacturing process may also include a preliminary step of homogenizing metakaolin and fly ash.

[0023] The manufacturing process may further include a mixing step during which the activator mixture is mixed with metakaolin and fly ash.

[0024] In one embodiment of the manufacturing process, water is added at the beginning of the mixing stage, the amount of water added being between 1% and 4% by weight of the geopolymer grout. The added water is only useful for improving the The grout's fluidity is excellent. Water is not required during the polymerization stage, thus minimizing its use. Compared to the quantities of metakaolin, fly ash, and activator mix required for grout production, water represents a marginal amount, thereby avoiding risks related to grout quality and stability during setting.

[0025] In one embodiment of the manufacturing process, in a preliminary grinding step, metakaolin alone or a mixture comprising metakaolin and fly ash is ground to obtain a specific surface area BET greater than or equal to 25 m² 2 / g and preferably greater than or equal to 30 m 2 / g.

[0026] The invention also proposes a method for installing a structural cable, comprising: - the installation of a conduit containing at least one reinforcement, - the tensioning of the armature, - the injection of a geopolymer grout into the conduit, and in which the geopolymer grout comprises metakaolin, fly ash and an activator mixture, the activator mixture comprising sodium hydroxide and sodium silicate, the Na2O:SiO2 molar ratio of sodium silicate being between 0.40 and 0.70.

[0027] The installation process may also include, before injecting the geopolymer grout into the conduit, mixing the geopolymer grout for 2 to 5 minutes with an energy of approximately 9 kilojoules per liter, thus obtaining a fluidity equivalent to the Marsh cone with a 10 mm diameter nozzle between 25 seconds and 35 seconds.

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

[0029] In one embodiment of the installation process, the grout is pumped during injection, with the grout pumping rate being between 0.5 m 3 / h and 1.5m 3 / h.

[0030] It should be noted that neither the manufacturing process of the geopolymer grout nor the installation process requires a heating step for the components of the Geopolymer grout or grout itself. These processes can be carried out at room temperature, unlike, for example, petroleum wax injection, which requires heating the wax above its melting point. As a result, the shrinkage of the geopolymer grout after injection is negligible or even nonexistent. Brief description of the drawings

[0031] Other features, details and advantages of the invention will become apparent from the detailed description below and from the analysis of the accompanying drawings, in which: Fig. 1

[0032] [Fig. 1] is a schematic diagram illustrating an example of a prestressing cable. Description of the implementation methods

[0033] The geopolymer grout according to the invention is a stable liquid mineral material whose formulation contains little or no free water. More precisely, it is a poly-silico-oxo-aluminate or (-Si-O-Al-O)n type product (where n is the degree of polymerization). This geopolymer grout is particularly advantageous for protecting prestressing cables within their conduits. Indeed, this geopolymer grout ensures better conduit filling and improved reinforcement coverage without having any detrimental effect on the prestressing reinforcement.

[0034] The geopolymer grout mainly comprises powders, referred to as fillers, and a liquid activator mixture. The fillers are metakaolin and fly ash.

[0035] Metakaolin is also called calcined kaolin. Metakaolin is a dehydroxylated aluminum silicate with the general composition Al₂O₃·2Si₂O₂. 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] Table 1 above details the chemical composition of metakaolin, trade name Argical 1200®.

[0037] The metakaolin used is finely ground. More precisely, the metakaolin has a BET specific surface area greater than 15m² 2 / g. Preferably, the specific surface area BET is greater than 25m² 2 / g. For example, the specific surface area BET of metakaolin is greater than 30m² 2Metakaolin, in particular, allows for a smoother grout than with conventional cement by limiting mineral salt deposits on the cement surface (also known as efflorescence). Furthermore, the fine grinding of the metakaolin improves the compressive strength and reduces the viscosity of the resulting geopolymer grout. Indeed, among the aggregates, an increased proportion of metakaolin relative to fly ash leads to an increase in both the mechanical strength and viscosity of the grout. Since metakaolin is elongated and irregular in shape, while fly ash is spherical, grinding the metakaolin improves its packing properties with the fly ash, thus increasing its proportion among the aggregates.Furthermore, metakaolin is a component that requires little energy for its extraction compared to ordinary cement, making the production of geopolymer grout environmentally attractive. Indeed, metakaolin is produced by calcining kaolinite (natural clay), a process that can be carried out at low temperatures (between 600°C and 800°C) compared to cement production, which requires a chemical combination of clay and limestone at very high temperatures (around 1450°C).

[0038] The fly ash used is Class F fly ash. More specifically, the fly ash used comes from the combustion of pulverized coal in the boilers of thermoelectric power plants, captured by electrostatic precipitators. For example, the ash The fly ash used is marketed under the trade name "Silicoline®". Fly ash helps to improve grout workability and its long-term mechanical performance.

[0039] The fly ash used can be finely ground. In this case, the fly ash has a specific surface area greater than 15m². 2 / g. Preferably, the specific surface area BET is greater than 25m² 2 / g. For example, the specific surface area BET of fly ash is greater than 30m² 2 / g. The fineness of the fly ash grinding improves the compressive mechanical strength of the resulting geopolymer grout.

[0040] The activator mixture comprises sodium hydroxide, sodium silicate, and water. This mixture initiates chemical reactions by breaking the chemical bonds of metakaolin and fly ash, forming an amorphous gel. This then triggers the polymerization reaction, resulting in a geopolymer with a three-dimensional structure containing the Si-O-Al bond.

[0041] Sodium silicate is an alkaline silicate solution. More precisely, sodium silicate has a Na₂O:SiO₂ molar ratio between 0.40 and 0.70. For example, the molar ratio is preferably between 0.51 and 0.60. Another example is between 0.55 and 0.59. In another example, the molar ratio is 0.57. Furthermore, sodium silicate has a water content by mass between 52.1% and 72.1%. For example, sodium silicate contains 62.1% water by weight.

[0042] Sodium hydroxide is initially presented in the form of sodium hydroxide pellets. These pellets are incorporated into the sodium silicate solution at a sodium hydroxide:sodium silicate mass ratio of 8.53:100. For example, 85.3 g of sodium hydroxide are incorporated into 1000 g of sodium silicate solution. The basic nature of sodium hydroxide increases the pH of the geopolymer grout, thus protecting the reinforcement from corrosion. For example, the grout has a pH between 13 and 14. In another example, the geopolymer grout has a pH between 13.3 and 13.5. In a more favorable example, the geopolymer grout has a pH close to 13.4. Therefore, if the grout is to exhibit bleeding, which The effect will be very limited due to the minimal amount of water added; the aqueous solution from the bleeding test has a basic pH within the ranges detailed above. Therefore, the bleeding water does not cause corrosion of the reinforcement. In particular, the grout may exhibit an aqueous solution bleeding of less than 0.5% of the total grout mass.

[0043] In addition, sodium hydroxide allows for obtaining suitable Na / Si or Na / Al molar ratios, which allows for obtaining a geopolymer grout with a chemical formulation that meets the desired criteria.

[0044] The activator mixture also includes water. Here, water refers to water added in addition to the water that makes up the sodium silicate solution. Therefore, the water described here is not part of the water content of the sodium silicate and is thus excluded from the 52.1% to 72.1% mass water content range of sodium silicate mentioned earlier. The added water represents less than 4% by mass of the geopolymer grout. "Total mass of the geopolymer grout" refers to the mass of the grout including metakaolin, fly ash, sodium hydroxide, sodium silicate, and the added water. For example, the added water represents between 1% and 4% of the total mass of the geopolymer grout. In another example, the added water represents between 1% and 2% of the total mass of the geopolymer grout, and preferably 1.86%.In 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.

[0045] In other words, the activator mixture has a water content by mass of less than 65%. Here, the water content by mass takes into account the water contained in the sodium silicate itself and the water added to the sodium silicate and sodium hydroxide. Therefore, the mass content is the ratio of the mass of water contained in the sodium silicate and the added water to the total mass of the activator mixture (i.e., the sodium silicate, sodium hydroxide, and added water). For example, the activator mixture has a water content by mass between 40% and 65%, and for example, between 56% and 63%. For example, the activator mixture has a water content by mass of... between 58% and 59% According to another example, the activator mixture has a water content by mass between 59% and 60%

[0046] Advantageously, adding water to the activator mixture improves the fluidity of the geopolymer grout while only slightly reducing the mechanical resistance after setting and hardening, which still meets the criterion that the compressive strength of the grout must be greater than 30 MPa at 28 days.

[0047] The geopolymer grout of the invention offers the advantage of very limited bleed-through and improved grout homogeneity due to the small amount of water incorporated. Furthermore, this low water content eliminates the need for filtration within the reinforcement bundle of the cable. The small amount of added water also results in a geopolymer grout with a porosity significantly lower than that of prior art cement grout. For example, the porosity of the geopolymer grout described here is at least six times lower than that of a cement grout. In addition, the kinetic progression of the geopolymer grout injection into the conduit is facilitated, and the grout more readily coats the reinforcement than a conventional cement grout, thus preventing the formation of air pockets (or bubbles).

[0048] The geopolymer grout is manufactured according to the process detailed below, including some alternatives.

[0049] In an initial step, metakaolin and fly ash are homogenized in a mechanical mixer.

[0050] Alternatively, the metakaolin alone (i.e., without fly ash) is first ground to obtain a BET specific surface area greater than or equal to 25 m² 2 / g and preferably greater than or equal to 30 m 2 / g. For example, metakaolin is ground using a mill. The mill used can be a ring mill or a ball mill. Alternatively, the feedstocks (i.e., metakaolin and fly ash) are ground to obtain a BET specific surface area greater than or equal to 25 m² 2 / g and preferably greater than or equal to 30 m 2 / g.

[0051] In the case of a ball mill, for example, a 5 kg mass of metakaolin is introduced and ground for 12 hours at a speed of 39 revolutions per minute. Depending on the grinding time, different specific surface areas (BET) are obtained for the metakaolin, some examples of which are grouped in the following table [Table 2].

[0052] [Table 2] Table 2 above illustrates the grinding of 5 kg of metakaolin by a ball mill at a speed of 39 revolutions per minute.

[0053] Next, the sodium silicate solution is prepared, into which the sodium hydroxide pellets are incorporated. For example, 85.3 g of sodium hydroxide is added to 1000 g of sodium silicate solution. The mixture is stirred until the sodium hydroxide pellets are completely dissolved.

[0054] Next, in a mixing step, the activator mixture is mixed with metakaolin and fly ash. This step allows for polymerization of the entire mixture, resulting in the geopolymer grout.

[0055] More specifically, the mixture of metakaolin and fly ash is introduced into the activator solution. The mixture is then thoroughly mixed to ensure deflocculation (a homogeneous mixture without lumps).

[0056] Water is then added to the mixture. Adding water makes the mixture more fluid, resulting in a geopolymer grout with a cone fluidity of Marsh (with 10 mm diameter nozzle) between 25 seconds and 35 seconds, and for example 30 seconds.

[0057] Alternatively, water can be added before mixing. Another alternative is to add water during mixing. The timing of water addition during the mixing stage does not alter the rheological properties or mechanical strength of the geopolymer grout. Specifically, it is important to understand that the added water does not participate in the polymerization process. In other words, water is not a reactive component of the polymerization step. Therefore, adding water to the mixture is independent of the polymerization process.

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

[0059] Then the mixture is blended for 60 seconds at a speed of, for example, 630 revolutions per minute.

[0060] As an example, the prepared geopolymer grout has the characteristics grouped in the following table [Table 3].

[0061] [Table 3] Table [Table 3] above lists examples of geopolymer grout formulations

[0062] Therefore, the geopolymer grout has a metakaolin:fly ash:alkaline silicate solution:sodium hydroxide ratio of 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 in Table [Table 3], the mass ratio is 1:1:2.489:0.212.

[0063] Rheological measurements and mechanical resistance tests were carried out on the geopolymer grout obtained, according to the test methods of standard NF EN 445. The results are grouped in the following table [Table 4].

[0064] [Table 4] Table 4 above groups together results for compressive strength and viscosity measurement.

[0065] The installation procedure for a structural cable is now described. The installation procedure mainly comprises the placement of a conduit containing at least one reinforcement bar, the tensioning of the reinforcement bar, and then the injection of a geopolymer grout into the conduit.

[0066] Once the geopolymer grout has been prepared according to the manufacturing process described above, it is mixed to obtain sufficient fluidity, measured using the Marsh cone test according to standard NF EN 445, which is between 25 and 45 seconds. For example, the geopolymer grout is mixed for 2 to 5 minutes (e.g., 4 minutes) with an energy of approximately 9 kilojoules per liter. Mixing is carried out, for example, using a turbo mixer, which disperses approximately 9 kilojoules per liter of energy into the mixture. This mixing is an important step in the injection process because it improves fluidity and, in other words, reduces the flow time measured by the Marsh cone test. Indeed, the geopolymer mixture before turbo mixing can have a flow time exceeding 50 seconds. While the turbo-mixing described above allows it to be reduced to a value between 25 and 45 seconds (viscosity values ​​between 0.5 and 0.9 Pa.s). These flow time values ​​can remain higher than the usual criterion of the NF EN 445 standard (time less than or equal to 25 seconds) without preventing the injection of the grout.

[0067] Subsequently, the geopolymer grout is injected into the pipe via a flexible hose. The hose has, for example, an internal diameter greater than 25 mm. Preferably, the internal diameter of the hose is greater than 35 mm. Furthermore, the hose has a length limited, for example, to 100 m. The geopolymer grout is injected, for example, using a pump (with a nominal pressure of 25 bar) with a pumping flow rate of between 0.5 m³ / s 3 / h and 1.5m 3 / h.

[0068] Thanks to this installation method, the geopolymer grout remains stable (i.e., homogeneous due to the absence of segregation). Indeed, no bleeding is observed around or through the reinforcement bars of the cable. Compared to cement grout, any risk associated with an improper hydration reaction, and in particular the development of an unstable grout, is therefore avoided. After the geopolymer grout has set and hardened, aqueous solutions with a pH between 13 and 13.5, representing less than 0.5% of the grout mass, may be found in cavities or bubbles. These solutions contain the main chemical elements from the various components (sodium ions, Na₂O). + , sulfates SO4 2' silicate H2SiO4 2 , and aluminates Al(OH)4 ) >These grouts do not pose a risk to the corrosion protection of the reinforcement. Furthermore, the residual air volume 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 relatively small offset between the upper and lower parts of the duct.

Claims

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 Na2O:SiO2 molar ratio of the sodium silicate is between 0.40 and 0.70, wherein the BET specific surface area of the metakaolin is greater than or equal to 25 m2 / g. The geopolymer grout as claimed in claim 1, the sodium silicate having a mass content of water of between 52.1% and 72.1%, and the activator mixture having a mass content of water less than 65%.The geopolymer grout as claimed in claim 2, wherein the activator mixture has a mass content of water of between 40% and 65%.The geopolymer grout as claimed in claim 1, wherein the metakaolin:fly ash:alkaline silicate solution:sodium hydroxide mass ratio is 1:1:2-3:0.15-0.

35. The geopolymer grout as claimed in claim 1, wherein the grout exhibits aqueous-solution bleeding less than 0.5% of the total mass of the grout.The geopolymer grout as claimed in claim 1, wherein the grout has a pH of between 13 and 14.The geopolymer grout as claimed in claim 1, wherein the BET specific surface area of a mixture comprising the metakaolin and the fly ash is greater than or equal to 25 m2 / g. The geopolymer grout as claimed in claim 1, wherein the BET specific surface area of a mixture comprising the metakaolin and the fly ash is greater than or equal to 30 m2 / g.A process for 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 BET specific surface area of the metakaolin is greater than or equal to 25 m2 / g, 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 polymerization of the aggregate.The manufacturing process as claimed in claim 9, moreover comprising a prior step of homogenizing the metakaolin and the fly ash.The manufacturing process as claimed in claim 9 or 10, moreover comprising a kneading step in which the activator mixture is kneaded with the metakaolin and the fly ash.The manufacturing process as claimed in claim 11, wherein water is added at the start of the kneading step, the amount of water added being between 1% and 4% of the weight of the geopolymer grout.The manufacturing process as claimed in claim 9, wherein, in a prior milling step, the metakaolin alone or a mixture comprising the metakaolin and the fly ash is milled in order to obtain a BET specific surface area greater than or equal to 25 m2 / g. A process for installing a structural cable, comprising the following steps: - fitting a duct containing at least one reinforcement, - tensioning the reinforcement, - injecting a geopolymer grout into the duct, and wherein the geopolymer grout comprises 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 BET specific surface area of the metakaolin is greater than or equal to 25 m2 / g. The installation process as claimed in claim 14, comprising, before injecting the geopolymer grout into the duct, a step of kneading the geopolymer grout for 2 to 5 minutes with an energy of 9 kilojoules per liter, thus obtaining a fluidity through a Marsh cone with a 10 mm diameter nozzle of between 25 seconds and 35 seconds. The installation process as claimed in either one of claims 14 and 15, wherein, during the injection, the geopolymer grout is injected into the duct through a hose, the hose having an inside diameter greater than 25 mm and a length limited to 100 m.The process as claimed in claim 16, wherein the grout is pumped during the injection, the pumping flow rate of the grout being between 0.5 m3 / h and 1.5 m3 / h.

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