WO2013072454A1

WO2013072454A1 - Self-setting mortar, method for making same, and uses thereof

Info

Publication number: WO2013072454A1
Application number: PCT/EP2012/072818
Authority: WO
Inventors: Sylvain BARBOT; Pascale BRIEULLE; Michel Charpentier
Original assignee: Commissariat à l'énergie atomique et aux énergies alternatives
Priority date: 2011-11-18
Filing date: 2012-11-16
Publication date: 2013-05-23
Also published as: FR2982856B1; JP2014533645A; EP2780298A1; FR2982856A1

Abstract

The invention relates to a mortar composition containing silica sand, cement, a limestone filler, silica dust, a viscosifier, a water-reducing plasticizer, and water. The invention also relates to a method for preparing same, and to the uses thereof.

Description

SELF-PLATING MORTAR, ITS PREPARATION METHOD

AND ITS USES

DESCRIPTION TECHNICAL FIELD

The present invention belongs to the field of the packaging of nuclear waste and, more particularly, to the field of packaging by immobilization of waste such as radioactive technological waste of low and medium activity in a cement matrix meeting the criteria of durability of confinement, with a view to their storage in a dedicated center.

The present invention proposes a self-placing mortar formulation, its method of preparation and its use for confining radioactive technological waste in packages intended to be stored in a nuclear waste storage center.

STATE OF THE PRIOR ART

The operation of nuclear installations and dismantling operations generate nuclear waste classified according to their level of radiological activity.

Evacuation and storage channels were created based on the radiological activity and the half-life of the radionuclides contained in the waste. In particular, there is a special sector for short-lived low and medium-level waste (FA-MA-VC) which must comply with the requirements of the National Agency for the Management of Radioactive Waste (ANDRA).

Short and medium-lived short-lived waste means waste having a level of radioactivity ranging from a few hundred Bq / g to 1 million Bq / g and this radioactivity is halved over a shorter period or equal to 31 years. This waste is essentially derived from the exploitation nuclear installations or dismantling of stationary installations such as laboratory glassware, piping, pumps, scrap metal and rubble.

Cementation is the oldest and most common process for packaging such waste. Various cement-based formulations have been exploited to either inject waste packages or prefabricate internal packaging envelopes for receiving such waste.

Different formulations are defined according to the elements that constitute them. Thus, grouts are formulations mainly made of water and cement, mortars include, in addition to water and cement, sand and concretes include, in addition to water, cement, sand and gravel. These differences in composition lead to differences in their performances, in particular mechanical and rheological, and consequently in their use. Thus, grouts and mortars are used to coat the waste or to block it in containers, while the concrete is mainly used to manufacture storage containers.

Much work has been done to provide new formulations with improved containment qualities and to meet the requirements and specifications of recognized toxic waste management organizations, particularly nuclear waste. By way of illustrative and nonlimiting examples, mention may be made of the patent application FR 2 763 584, in the name of Electricité de France, published on November 27, 1998; international application WO 2009/053541, on behalf of Ciments Français, published on April 30, 2009; and the international application WO 2007/135067, on behalf of the CEA, published on November 29, 2007.

The patent application FR 2 763 584 proposes a confinement concrete mainly comprising siliceous sand of small particle size dispersion; a binder composed of a low tricalcium aluminate cement and very fine additives of smaller particle size than cement; water with a ratio (weight of water) / (weight of binder) of less than 0.4; gravel and admixtures favoring the deflocculation of the fine elements. International application WO 2009/053541 describes a mixture of rheology modifying adjuvants for self-placing concrete without filler. This mixture comprises at least one ¹ increasing agent predominantly to the shear threshold of the concrete in the fluid state and at least one ^2nd increasing viscosity modifier predominantly the viscosity of the concrete in the fluid state. ¹ agent is preferably a natural polysaccharide ether modified by the introduction of lateral grafts including hydrophobic, or a hydroxyalkyl guar ether modified by the introduction of lateral grafts particularly hydrophobic. The concrete formulation further comprises a Portland cement, a calcareous filler, a cohesion agent, siliceous or silico-calcareous granules, a superplasticizer and water, the E / C ratio being equal to 0, 6.

International application WO 2007/135067 proposes a cementitious composition for coating an aqueous solution containing boron such as borated liquid waste. This composition consists of siliceous sand, sulfoaluminous cement and possibly gypsum.

The difficulties encountered during the implementation of containment mortars or coating relate to:

the exothermic phenomena that accompany the hydration of the cement contained in the mortar and its setting;

- bleeding or exudation corresponding to the layer of water that forms on the surface of a fresh mortar, between the moment of compaction and the beginning of setting, under the effect of the different density of the water and other elements constituting this mortar;

- the blockage of injection pipe;

- insufficient mechanical performance;

a shrinkage problem which may be a pre-set shrinkage caused by the evaporation of part of the water contained in the mortar, a heat shrinkage, after setting, due to the return of the mortar to room temperature or else hydraulic shrinkage, after setting, due to a decrease in volume resulting from the hydration and hardening of the mortar.

These difficulties are related to the climatic conditions but also directly to the formulation of the mortar used and in particular to the dosage in cement, the dosage in water, the performance of the admixtures, the setting of the mortar too quickly or the mortar being too short.

The inventors have therefore set themselves the goal of preparing a mortar formulation that eliminates these nuisances and exhibits containment properties that meet the requirements and needs at the same time:

(i) nuclear operators,

(ii) technological waste disposal and storage systems, and

(iii) mortar suppliers,

each of these 3 groups wishing that the formulation has particular characteristics.

In fact, the nuclear operators who package and immobilize technological waste want a product that is simple to manufacture, flexible to use, of constant quality, insensitive to the temperatures of the injection site, which does not need to be subjected to a vibration. when it is used and which does not show segregation or bleeding.

For waste disposal and storage of technological waste, the mortar should be used to obtain a matrix based on hydraulic binder for immobilizing technological waste, having a very low diffusion with tritiated water and which is confining, insensitive to gamma irradiation, resistant to freeze-thaw cycles, insensitive to the alkali-reaction, not very diffusive to chloride ions and not very permeable to gases.

Finally, the mortar supplier wishes to have a simple formulation to manufacture, simple to deliver, simple to inject, remaining homogeneous on the high heights (without dynamic segregation) and having high performances at a young age and a low total withdrawal. STATEMENT OF THE INVENTION

The inventors have achieved the goal and solved the technical problems presented above by implementing a particular formulation of mortar meeting the requirements and needs of nuclear operators, technology waste disposal and storage systems and suppliers of mortars.

The particularity of the invention lies in the simplicity of manufacture, the flexibility of implementation and in the high and durable performance of the mortar listed below:

- high mechanical performance,

- resistant to radiation,

- very weakly permeable to radioactive liquids and gases,

- insensitive to freezing / thawing,

- easy to manufacture from an ordinary concrete plant in 15 minutes,

- usable 5 hours after production, kept stirred in a truck between 5 ° C to

35 ° C,

- injectable,

- at low total withdrawal,

- without dynamic segregation or bleeding.

More particularly, the present invention relates to a mortar composition comprising:

- siliceous sand,

- cement,

- limestone,

- silica fume,

a viscosity agent,

a plasticizer reducing water and

- some water.

The composition according to the invention essentially comprises the 7 aforementioned elements and, advantageously, is constituted by these elements, ie the composition according to the invention does not include any other element than the 7 aforementioned elements. For example, the composition according to the invention does not comprise granules or polymers.

In the context of the present invention, the term "siliceous sand" is intended to mean sand that is more than 90%, in particular more than 95%, in particular greater than 98%, and more particularly more than 99%. silica (Si0 ₂ ).

It should be noted that the tests carried out by the inventors with crushed limestone sands were inconclusive since the mortars thus prepared had a capillary absorption that was too high and a handling that was too delicate. The limestone sands have, in fact, been abandoned. In the context of the present invention, the siliceous sands thus constitute a motivated selection among the sands.

Advantageously, the siliceous sand used is a non-reactive sand with alkali-silica.

In addition, in the context of the invention, the siliceous sand is sand washed prior to its implementation, for example, a siliceous sand supplied and delivered washed so as to eliminate a maximum of impurities. Thus, the silica sand used is clay-free.

The siliceous sand is advantageously used dry in order not to have any influence on the water dosage of the formulation. It may be silica sand supplied and delivered dry.

The siliceous sand used in the context of the present invention is advantageously an uncrushed sand and this, to limit both the effects of active silica release with the binder and the abrasive effects of the mortar in the pipes of injection.

Finally, the siliceous sand used in the context of the present invention advantageously has a regular granular spindle in order not to interfere with the workability of the mortar.

The size of the siliceous sand used in the formulation according to the invention is advantageously less than 6 mm, in particular less than 5 mm and, in particular, less than 4 mm. Therefore, the composition according to the invention does not include any element of the sand, gravel or granular type having a particle size (average grain size) greater than 6 mm.

In one particular form of implementation, the siliceous sand used in the composition according to the invention is in the form of two siliceous sands of different particle sizes. Indeed, the inventors have tested different granulometries with different formulations to find the maximum compactness. These tests were carried out using laboratory mixers of 2.5 L and 25 L. The best compromise was found with 2 siliceous sands of different and complementary grain sizes.

Thus, in this form of implementation, the siliceous sand used in the composition according to the invention is advantageously constituted:

- a ^1, siliceous sand, preferably natural, washed, dried and screened, which aggregates the dimensions are within the range of 0.63 mm to 3 mm, and

- A 2 ^nd siliceous sand, advantageously natural, washed, dried and screened, the dimensions of the aggregates are in the range of 0.16 mm to 1.25 mm.

More particularly, ¹ silica sand implemented present granular time as defined in Table 1 below:

Table 1 Even more particularly, the 2 ^nd siliceous sand used has the granular spindle as defined in Table 2 below.

Table 2

Mineral addition is an important element in the composition of self-compacting concretes. In the context of the mortar composition according to the invention, the mineral addition chosen is a calcareous filler.

As a reminder, a limestone filler is a dry, finely divided product derived from the cutting, sawing or working of natural limestone rocks in the lime, aggregates and ornamental stone industry.

Advantageously, the calcareous filler used has a fineness ie a particle size similar to that of the cement used to limit the phenomena of temperature rise during setting, to ensure the holding of the cement matrix and, in fact, to prevent a dynamic segregation and settlement of the mortar fresh.

More particularly, the calcareous filler used in the context of the present invention has an average grain size of between 5 and 20 μιη, in particular between 10 and 15 μιη, and in particular of the order of 12 μιη (ie 12 μιη ± 1 μιη). More particularly, the calcareous filler used in the context of the present invention is a limestone filler resulting from a marble quarry. In their experiments, the inventors have been able to observe that such a mineral addition combined with the other constituents of the formulation has made it possible to obtain a mortar exhibiting good workability, absence of bleeding and an increase in the duration of workability.

Moreover, this addition plays a vital role in facilitating the injection of pumping. The lubrication of the pipes before injection, previously carried out using a water + cement mixture, is no longer necessary.

The properties listed above were verified during the suitability tests of the confining mortar (on a volume of 25 I) and during the characterization tests using the mixer of the concrete batching plant (on a batch of 1 m ³ ). .

Like the mineral addition, silica fume is also an additive widely used in the formulation of mortars and concretes. Its properties are recognized to improve the compactness and limit the permeability of concretes and mortars, and consequently improve the mechanical performance of concretes and hardened mortars.

Advantageously, the silica fume used in the context of the present invention is derived from the filters of the silicon metal manufacturing process.

In particular, this silica fume is a powder whose particle size is at least 2 times smaller, in particular at least 5 times smaller and, in particular, 10 times smaller than that of the cement used in the composition according to the invention. It is the finest element of this composition.

In addition, the silica fume used in the context of the present invention is a densified silica fume which is distributed homogeneously during the kneading. Densified silica fume is, as a reminder, produced by treating an undensified silica fume to increase its bulk density to a maximum of between 400 and 720 kg / m ³ . The treatment usually used consists of polishing the smoke particles in a silo, resulting in an accumulation of surface charges.

The addition of the silica fume to the other constituents of the composition according to the invention and their combination made it possible to obtain a mortar having a low porosity, high mechanical performance in the range of high performance concretes, low shrinkage and low oxygen permeability.

In the composition according to the invention, the cement used is advantageously a ternary compound cement composed of clinker, blast furnace slags and fly ash.

By "clinker" is meant a mixture comprising one (or more) element (s) chosen from the group consisting of a limestone; a limestone with a CaO content of between 50 and 60%; a source of alumina such as ordinary bauxite or red bauxite; a clay and a sulphate source such as gypsum, calcium sulphate hemihydrate, plaster, natural anhydrite or sulphocalcic ash, said element (s) being crushed, homogenized and raised (s) at high temperature above 1200 ° C, especially above 1300 ° C, in particular of the order of 1450 ° C. By "about 1450 ° C" is meant a temperature of 1450 ° C ± 100 ° C, preferably a temperature of 1450 ° C ± 50 ° C. The high temperature cooking step is called "clinkerization".

In particular, the cement used in the context of the present invention is a CEM V and consists of 20 to 64% clinker, 18 to 50% blast furnace slag and 18 to 50% fly ash. More particularly, the cement used in the context of the present invention is a CEM V / A and consists of 40 to 64% clinker, 18 to 30% blast furnace slag and 18 to 30% ash. flying.

Advantageously, the cement used in the composition according to the present invention is a CEM V / A having a low heat of hydration The notions of "heat of hydration" and, more particularly, "low heat of hydration", are defined in the standard NF EN 197-1 / A1 of December 2004 "Cement Composition, specifications and conformity criteria of common cements". Thus, the heat of hydration corresponds to the amount of heat developed by the hydration of a cement in a given time. The heat of hydration of low cements heat of hydration must not exceed the characteristic value of 270 J / g determined:

- after 7 days according to the dissolution method as defined in standard EN 196-8 published in December 2010 or

- at 41 h according to the semi-adiabatic method as defined in the EN standard

196-9 published in December 2010.

Common cements with low heat of hydration are designated by the letters LH. As a particular example of CEM V / A LH cement that can be used in the context of the present invention, mention may be made of CLC 32.5 cement from CALCIA.

The composition according to the invention comprises, in addition to the constituents exposed above, two adjuvants which are:

a viscosity agent intended for producing concrete and fluid / self-compacting mortars which increases the viscosity of the mortar and having, as a side effect, a plasticizing and water-reducing function to limit bleeding in the fresh state,

a water-reducing plasticizer intended for carrying out pumping over long distances, with, for a secondary effect, a set-retarding function for increasing the duration of use.

The skilled person knows different adjuvants used to prepare mortars, each of them bringing its particularity in a formulation. The difficulty with the use of these products lies in the apprehension of their dosage, their compatibility with each other or with the other components of the formulation and depending on the implementation environment. Indeed, the temperature of the mortar during the injection can influence the maneuverability of the latter.

In the suitability tests carried out by the inventors, certain combinations of known adjuvants have been discarded because of the appearance of significant segregation only in the fresh state in wet formulation ie by dosing the dry elements to the minimum of the tolerances formulated and by dosing the wet elements to the maximum tolerances formulated. The result of the suitability tests of the mortar according to the present invention were decisive for the reasoned choice of the adjuvants to be used in this mortar. Indeed, the formulation of the mortar according to the present invention was tested at the limits of the tolerances of dosage and the limits of the temperatures of mortars (+ 5 ° C / + 35 ° C).

Maintainability was also verified in a Marsh cone flow range (with a 12.5 mm nozzle) between 50 and 120 sec, up to 5 hours of age.

The absence of harmful interaction of adjuvants on the rheological properties of the mortar in the fresh state has been verified at low temperature (+ 5 ° C), at hot temperature (+ 35 ° C), and this, for at least 5 hours after manufacture.

In the end, the adjuvants retained as the viscosity agent and the water-reducing plasticizer are compatible with each other and with the other constituents of the mortar according to the present invention. Those skilled in the art know various viscosity agents that can be used in the context of the present invention. As a reminder, a viscosity agent is a water-soluble product that increases its viscosity. Viscosity agents are composed of molecules of long chains of polymers that adhere to the periphery of water molecules and adsorb a part of them.

Advantageously, the viscosity agent used in the context of the present invention is an aqueous solution based on modified polyalcohols. More particularly, it is a viscosity agent with water reducing plasticizing side effect for the production of fluid or self-placing mortars. As a specific example of viscosity agent used in the context of the present invention, mention may be made CHRYSO ^® Plast V70.

Advantageously, the water-reducing plasticizer used in the context of the present invention is a superplasticizer.

By "superplasticizer" is meant a synthetic polymer manufactured for the concrete industry. This adjuvant makes it possible to increase very significantly the workability of a concrete without adding water, or decrease the amount of water to increase the mechanical strength without changing the workability of the concrete. Superplasticizers can reduce water requirements by about 30 percent.

In the context of the present invention, the water-reducing plasticizer is advantageously an aqueous solution based on modified phosphonate. More particularly, it allows very long maintainability of workability and is suitable for long-distance pumping. As a specific example of usable water reducing plasticizer in the context of the present invention include the CHRYSO ^® Fluid Optima 100.

Finally, the composition according to the present invention comprises water whose accuracy of dosage is preponderant for obtaining the confinement properties of the mortar according to the invention, more particularly as regards the porosity, the permeability to gas and the diffusion of tritiated water (the excess water creating voids after hydration of the cement).

The systematic search for the lowest possible water dosage should not affect the workability of the mortar when fresh. The water has a function of transporting fine elements and admixtures during mixing for better hydration of the components and a uniformly distributed action of the adjuvants and, consequently, for a better homogeneity of the mortar.

The suitability tests carried out by the inventors made it possible to define a water dosing range without any trace of exudation, nor segregation without impact on the expected handling, whatever the temperature of use of the mortar. This dosage range is such that the mass ratio Water / Cement, designated E / C, is between 0.35 and 0.45, in particular of the order of 0.4 ie 0.4 ± 0.02, or even 0 , 4 ± 0.01.

In a particular embodiment, the mortar composition according to the invention consists of:

- from 50 to 60% and, in particular, from 53 to 57% of siliceous sand,

from 20 to 30% and, in particular, from 22 to 28% of cement, from 5 to 10% and, in particular, from 6 to 8% of a calcareous fiber,

from 1 to 2% and, in particular, from 1.2 to 1.8% of silica fume,

from 0.2 to 0.6 and in particular from 0.3 to 0.5% of a water-reducing plasticizer,

from 0.05 to 0.3 and in particular from 0.1 to 0.25% of a viscosity agent and from 8 to 12% and, in particular from 9 to 11% of water,

the percentages given being% by weight expressed relative to the total mass of the composition.

In a more specific form of implementation, the mortar composition consists of:

from 32 to 34%, in particular from 32.3 to 33.7% and, in particular, 32.99% of a siliceous sand whose aggregate dimensions are in the range of 0.63 mm to 3 mm,

from 21 to 23%, especially from 21.6 to 22.7% and, in particular, 22.13% from a siliceous sand whose aggregate dimensions are in the range of 0.16 mm to

1.25 mm,

from 24 to 27%, in particular from 25 to 25.7% and, in particular, 25.38% of cement

EMC V,

- from 6.5 to 7.8%, especially from 7 to 7.4% and, in particular, 7.20% of a calcareous filler,

from 1.4 to 1.7%, in particular from 1.5 to 1.6% and, in particular, 1.56% of silica fume,

from 0.4 to 0.45%, in particular 0.42 to 0.44% and, in particular, 0.43% of a water-reducing plasticizer,

from 0.12 to 0.2%, in particular from 0.15 to 0.17% and, in particular, 0.16% of a viscosity agent, and

from 9.5 to 10.5%, in particular from 9.8 to 10.3% and, in particular, 10.15% of water, the percentages given being% by weight expressed relative to the total mass of the composition. The experimental part below shows a more particular formulation of the composition according to the present invention.

The present invention relates to a process for preparing a mortar composition as defined above.

This method comprises the steps of:

a) preparing a mixture comprising ^1, a silica sand such as defined above, in particular the cement as defined above, in particular silica fume as defined above, the limestone filler such as defined above and water in particular as previously defined;

b) kneading the mixture obtained in step (a);

c) adding to the kneaded mixture obtained in step (b) the viscosity agent in particular as previously defined;

d) kneading the mixture obtained in step (c);

e) adding to the kneaded mixture obtained in step (d) the water-reducing plasticizer in particular as previously defined and

f) kneading the mixture obtained following step (e).

During step (a) of the process according to the invention, the elements used are in the form of powder or in liquid form (water used in step (a)). These elements are advantageously added one after the other.

The mixture of step (b) is obtained by mixing / kneading all these elements together using a worm gear mixer at a speed of between 20 and 26 rpm for the main arm and between 87 and 127 rpm for the secondary arm. This mixing / kneading can last between 30 sec and 10 min, in particular between 45 sec and 5 min and, in particular, of the order of 1 min (i.e. 1 min ± 10 sec).

In step (c) of the process, the viscosity agent is added.

The mixture of step (d) is obtained by mixing / kneading all these elements together using a worm gear mixer at a speed of between 20 and 26 rpm for the main arm and between 87 and 127 rpm for the arm secondary. This mixing / kneading can last between 30 sec and 10 min, in particular between 45 sec and 5 min and, in particular, of the order of 1 min (ie 1 min ± 10 sec).

In step (e) of the process, the water-reducing plasticizer is added. The mixture of step (f) is obtained by mixing / kneading all these elements together using a worm gear mixer at a speed of between 20 and 26 rpm for the main arm and between 87 and 127 rpm for the secondary arm. This mixing / mixing can last between 60 sec and 15 min, in particular between 90 sec and 10 min and, in particular, of the order of 2 min (i.e. 2 min ± 15 sec).

The different steps of any of the variants of the process according to the invention are carried out at a temperature of between 5 and 35 ° C.

The present invention further relates to the use of a mortar of a composition as defined above or capable of being prepared by the process as defined above, for confining waste. This waste is in particular short-lived and low-level waste as defined previously.

This use consists in coating or trapping this waste in a fresh mortar of composition as defined above or capable of being prepared by the process as previously defined. By "fresh mortar" is meant a mortar having a plasticity allowing such a coating or trapping. The concept of fresh mortar is opposed to that of a hardened mortar.

The characteristics of the mortar according to the present invention make it possible not to implement any vibration during confinement. However, a slight vibration can be applied in the case where there is a risk of imprisonment of air bubbles in the waste package. In any case, this vibration should not exceed 10 sec to guard against any risk of exudation of the fresh mortar.

The present invention also relates to a package of waste confined in a mortar of composition as defined above or likely to be prepared by the process as previously defined and packaged in drums or boxes including drums or metal or concrete boxes. According to this aspect, the mortar of the invention forms a confining envelope surrounding the waste and in particular short-lived and low-level short-lived waste as previously defined.

Other features and advantages of the present invention will become apparent to those skilled in the art on reading the examples below given for illustrative and non-limiting.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

I. Process for preparing a mortar according to the present invention

The production of the industrial batch was carried out in less than 15 minutes as follows:

- introduction of siliceous sand 3 / 0.63 (Sable VX 3000, FULCHIRON): 760 kg,

- introduction of 1.25 / 0.16 silica sand (Sand VX 1200; FULCHIRON):

510 kg,

introduction of CEM V cement (CLC 32.5 type cement: CALCIA): 584 kg,

- introduction of densified silica fume (Condensil S95): 36 kg, - introduction of calcareous filler (Calgar 40, Provençale SA): 166 kg,

- introduction of water: 233 kg,

- mixing 1 min,

- introduction of the viscosity agent (CHRYSO ^® Plast V70): 3.72 kg,

- mixing 1 min,

- introduction of the water-reducing plasticizer (CHRYSO ^® Fluid Optima 100):

9.99 kg,

- mixing 2 min,

- Stopping the mixing and emptying in a truck. II. Characterization of the mortar according to the present invention.

The characterization test was carried out from the industrial tool, namely, the mixer of the concrete batching plant designed to make one cubic meter of waste in the concrete industry. When carrying out this test, more than 80 test pieces (specimens 11 cm in diameter and 22 cm in height, hereinafter referred to as standard test specimens) were made to characterize from the same batch and by an accredited laboratory. the performance of the mortar according to the invention.

Throughout the test, the mortar was kept stirred in the truck for more than 6 hours at slow speed.

The ability of the mortar to be injected is verified by measuring the passage time of one liter of mortar through the Marsh cone with 12.5 mm nozzle. The passage time should be in the range of 50 to 120 sec. At the end of the 6 hours of brewing, the maneuverability measured at the Marsh cone was 92 sec and therefore was still in the desired range.

In the characterization test, a test piece 340 cm high and 9 cm in diameter was filled with the mortar according to the present invention. No trace of exudation has appeared. The total shrinkage at 28 days of age is less than 2 mm over the height of the specimen. The test piece was then cut into 3 sections longitudinally at the bottom, middle and high. The examination of the three cuts shows a distribution of the homogeneous granular skeleton (absence of segregation), each section has a bulk density greater than 2310 kg / m ³ . III. Summary of the specific characteristics of the mortar according to the invention.

MORTAR: with mechanical characteristics of concrete

HIGH PERFORMANCE: thanks to its mechanical characteristics with a compressive strength greater than 50 M Pa at 28 days. In fact, the measurements of the compressive strength on an industrial batch carried out on standard specimens kept at room temperature under water, according to the standard NF EN 12390-3 (compressive strength of the test pieces) are 84.5 M Pa at 28 days and from 105.8 M Pa to 90 days.

EASE OF MANUFACTURE: manufacturing time with industrial tool less than 15 min.

The manufacture of the mortar is also easily achievable from pre-dosed dry loads.

EASE OF IMPLEMENTATION: Self-positioning

The vibration of the mortar is not obligatory for its installation.

FLEXIBILITY OF USE:

The mortar is injectable within 5 hours after manufacture in both dry and wet form, at low and high temperatures and at the dosage tolerance limits.

COMPACT:

Density measured from standard specimens is 2.4 to 48 hours and 2.32 to 28 days

SUITABLE FOR MANUFACTURING PRE-BILLET PACKAGES:

The mortar remains stable even for high-altitude injections (340 cm high test specimen tests)

LOW REMOVAL:

The mortar has a shrinkage of 370 μιη / ιη measured according to standard NF P15-433 of February 1994. LOW PERMEABILITY TO GAS:

The apparent gas permeability is measured on standardized mortar specimens, stored in laboratory water, after drying at 105 ° C ± 5 ° C to constant mass. A determined pressure gas percolates through the specimens, its flow rate is measured and the coefficient of permeability is determined based on the Poiseuille law. The coefficient thus obtained is 73.10 ¹⁸ m ² .

LOW POROSITY:

The porosity accessible to water corresponds to the ratio of the void volumes accessible to water and the apparent volume of the mortar. It is measured by hydrostatic weighing on mortar samples kept in water in the laboratory (submerged saturated mass), on immersed saturated water-saturated mortar specimens (saturated mass) and on specimens dried at 105 ° C ± 5 ° C up to constant mass (dry mass). The porosity accessible to the water thus obtained is 9.4%.

NOT REACTIVE TO ALCALIS:

This characteristic is particularly related to the use of sands unreactive alkali-reaction.

LOW DIFFUSION ION CHLORIDES:

The average experimental value of the apparent diffusion coefficient of chlorides in the electric field according to the method of Tang Luping and Lars-Olof Nilsson, 1993 (Materials Journal, vol 89, pages 49-53) is 0.13 10 ¹² m ² / s.

INSENSITIVE TO THE CYCLES GEL / DEGEL:

After 100 cycles of freezing (at -18 ° C +/- 2 ° C) and thaw (at + 9 ° C +/- 3 ° C), no variation in mass, resonance frequency and length of the mortar according to the invention was observed. LOW COEFFICIENT OF DIFFUSION WITH TRITIATED WATER:

The water diffusion coefficient tritiated is measured on standardized mortar test pieces, placed in a sealed manner, between a ¹ containing water compartment tritiated and ^2nd containing water initially not tritiated. The tritium activity detected in the 2 ^nd compartment is monitored as a function of time until the appearance of a constant material flow. The effective diffusion coefficient of tritiated water evaluated by application of Fick's law is less than 1.10 ¹³ m ² / s.

HELD WITH IRRADIATION GAMMA:

The mortar according to the present invention was subjected to 8.10 Gray ⁵ under 300

Gray / h. After this irradiation, have been observed:

a dimensional variation of less than 500 μιη / m,

- a similar speed of sound,

a small variation of the fundamental resonant frequency, an absence of impact on the mechanical performances,

a lack of modification of the microstructure of the mortar after examination under a scanning electron microscope.

Claims

1) Mortar composition for the containment of waste, consisting of: - siliceous sand,

- cement,

- a limestone filler,

- silica fume,

a viscosity agent, increasing the viscosity of the mortar,

a plasticizer reducing water and

- some water,

said siliceous sand being in the form of two siliceous sands of different grain sizes. 2) Composition according to claim 1, characterized in that said siliceous sand is constituted:

- a ¹ silica sand with aggregates of the dimensions are within the range of 0.63 mm to 3 mm, and

- a 2 ^nd siliceous sand whose dimensions of aggregates are in the range of 0.16 mm to 1.25 mm.

3) Composition according to claim 1 or 2, characterized in that said calcareous filler has an average grain size of between 5 and 20 μιη, in particular between 10 and 15 μιη, and, in particular, of the order of 12 μιη.

4) Composition according to any one of the preceding claims, characterized in that said silica fume is a powder whose particle size is at least 2 times smaller, in particular at least 5 times smaller and, in particular, 10 times smaller than that of cement used in said composition. 5) Composition according to any one of the preceding claims, characterized in that said silica fume is densified silica fume.

6) Composition according to any one of the preceding claims, characterized in that said cement is a ternary compound cement composed of clinker, blast furnace slag and fly ash and, advantageously, a CEM V.

7) Composition according to any one of the preceding claims, characterized in that said viscosity agent is an aqueous solution based on modified polyalcohols.

8) Composition according to any one of the preceding claims, characterized in that said water-reducing plasticizer is a superplasticizer and, in particular, an aqueous solution based on modified phosphonate.

9) Composition according to any one of the preceding claims, characterized in that the water / cement mass ratio, designated E / C, is between 0.35 and 0.45, in particular of the order of 0.4. 10) Composition according to any one of the preceding claims, characterized in that it consists of:

- from 50 to 60% and, in particular, from 53 to 57% of siliceous sand,

from 20 to 30% and, in particular, from 22 to 28% of cement,

from 5 to 10% and, in particular, from 6 to 8% of a calcareous fiber,

from 1 to 2% and, in particular, from 1.2 to 1.8% of silica fume,

from 0.05 to 0.3 and in particular from 0.1 to 0.25% of a viscosity agent and

- from 8 to 12% and, in particular from 9 to 11% of water,

the percentages given being% by weight expressed relative to the total mass of the composition. 11) Composition according to any one of the preceding claims, characterized in that it consists of:

- from 32 to 34%, in particular from 32.3 to 33.7% and, in particular, 32.99% of a siliceous sand whose aggregate dimensions are in the range of 0.63 mm to

3 mm,

from 21 to 23%, in particular from 21.6 to 22.7% and, in particular, 22.13% from a siliceous sand the aggregate dimensions of which are in the range of 0.16 mm to 1.25. mm

from 24 to 27%, especially from 25 to 25.7% and, in particular, 25.38% of cement

EMC V,

from 9.5 to 10.5%, in particular from 9.8 to 10.3% and, in particular, 10.15% of water, the percentages given being% by weight expressed relative to the total mass of the composition.

12) Process for preparing a mortar composition as defined in any one of claims 1 to 11, comprising the steps of:

a) preparing a mixture comprising a ^1, siliceous sand, cement, silica fume, the limestone filler and water;

b) kneading the mixture obtained in step (a);

c) adding to the kneaded mixture obtained in step (b) the viscosity agent;

d) kneading the mixture obtained in step (c); e) adding to the kneaded mixture obtained in step (d) the water-reducing plasticizer and

f) kneading the mixture obtained following step (e).

13) Use of a mortar composition as defined in any one of claims 1 to 11 or capable of being prepared by the method as defined in claim 12, for confining waste.

14) Packages of waste confined in a mortar of composition as defined in any one of claims 1 to 11 or capable of being prepared by the method as defined in claim 12 and packaged in drums or boxes.