NO329540B1 - Self-leveling concrete with high performance, its manufacture and application - Google Patents

Description

The present invention relates to a self-leveling concrete with very high performance. According to the present invention, "very high performance concrete" means a concrete that exhibits a characteristic resistance to compression at 28 days of more than 150 MPa, a modulus of elasticity at 28 days of more than 60 GPa and a resistance to compression of more than 100 MPa at 40 hours, as these values apply to a concrete kept at 20°C. The invention also relates to a method for its production as well as applications of this concrete and a dry-mixed ready-to-use concrete to obtain such concrete.

According to the invention, "concrete" means a body of cement material which, depending on the method of manufacture, may include fibres, and which has been obtained by hardening a cement-containing mixture mixed with water.

High-performance concrete is already known, however, their application without passive reinforcement is limited.

Specific mixtures for the production of a concrete with ultra-high resistance ductile metal fibers which allow the construction of optionally prestressed elements and which do not include any reinforcement, described in FR 2 708 263. However, this concrete necessitates the incorporation of ground quartz and/or a thermal curing in order to achieve the required benefits.

The present inventors have been able to find a self-leveling concrete to which fibers can be added, which exhibits an excellent resistance to compression, an excellent modulus of elasticity, an excellent short-term strength without necessitating any other addition and without thermal curing, which constitutes an economic advantage and a great simplification in application.

Such concrete exhibits a characteristic resistance to compression after 28 days of at least 150 MPa, a modulus of elasticity after 28 days of at least 60 GPa and a resistance to compression after 40 hours of at least 100 MPa, these values applying to a concrete that has been preserved and held at 20°C, characterized in that it comprises: a cement with a granulometry corresponding to a harmonic mean diameter

less than or equal to 7 µm and preferably between 3 and 7 µm;

a mixture of sand with different granulometries comprising calcined bauxite sand, the finest sand having an average granulometry of less than 1 mm and the coarsest sand having an average granulometry of less than 10 mm;

fumed silicon dioxide where 40% of the particles have a dimension below 1 µm and the harmonic mean diameter is close to 0.2 µm and preferably close to 0.1

around;

an antifoam agent;

a superplasticizing water reducing agent selected from modified

polycarboxylates or polyacrylates;

possibly fibers; and

water;

as the cement, sand and fumed silicon dioxide exhibit a granulometric distribution so that you have at least 3 and at most 5 different granulometric classes where the ratio between the harmonic diameter average for one granulometric class and the class immediately above it is around 10.

This concrete also exhibits a very high wear resistance. When it is further free of fibres, it exhibits a direct tensile strength of over 10 MPa.

The cement produced shows an increased amount of bi- and tri-calcium silicates C2S and C3S (HTS cement) which is preferably over 75%. It can be chosen from cements of the Portland CEMI type which preferably have complementary characteristics such as "Prise Mer - PM", or even better "Prise Mer et Résistant aux Sulfates - PM-ES" or their mixtures. For reasons of fluidisation, it is preferred to use a cement which also has a low amount of C3A, preferably below 5%.

According to the invention, "mixture of sand with different granulometries comprising calcined bauxite sand" means not only a mixture of calcium bauxite sand with different granulometry but also a mixture comprising calcined bauxite sand together with another type of sand or also with granules which exhibit a very high resistance and hardness which especially granules of corundum, emery or metallurgical residues such as silicon carbide.

Within the framework of the invention, a mixture of two or three types of calcined bauxite sand with different granulometries is preferably used. According to a particular embodiment of the invention, the sand mixture consists of: a sand with an average granulometry of less than 1 mm comprising 20% granules

with dimensions below 80 microns,

a sand with granulometry between 3 and 7 mm, and

possibly a sand with a granulometry between 1 and 3 mm.

The sand with the lowest granulometry can be completely replaced with:

cement, mineral additives such as ground slag, fly ash or also calcined bauxite filler where the mean harmonic diameter is close to that of cement,

for that which is the fraction of 20% of the granules with a diameter of less than 80 µm, and sand with a granulometry above 1 mm, for example 3 to 7 mm, for that which is the

second faction.

The fumed silicon dioxide used in the concrete according to the invention can be compressed or non-compressed, that is to say it has a density between 200 and 600 kg/m<3>. This fumed silicon dioxide must, once it is dispersed in the concrete, carry at least 40% particles with dimensions below 1 micron, the dimension of the remaining particles remaining below 20 µm.

The bauxite used can be calcined in different ways in rotary kilns or in vertical kilns. It is then crushed and ground up to achieve the desired granulometry. The maximum granulometry is determined by an inherent resistance in the granulate in relation to the desired compression performance for the concrete.

In order to avoid the inclusion of air bubbles which reduce the resistance in the concrete, an anti-foaming agent is used which is classically used for oil wells, that is to say in applications which necessitate a very precise regulation of the density of the poured material. These anti-foaming agents are called "defoamer and deaerator admixtures". These agents are available in the form of dry matter or in liquid form. Examples of such agents include mixtures of dodecyl alcohol and polypropylene glycol, dibutyl phthalates, dibutyl phosphates, silicone polymers such as polydimethylsiloxane, and modified silicates.

According to a special embodiment of the invention, a silicate treated with a polymerized glycol, marketed by TROY CHEMICAL CORPORATION under the designation TROYKYD® D126, is used as an anti-foaming agent.

The superplasticizing water reducing agent according to the invention is selected from modified polycarboxylates or polyacrylates, such as modified polycarboxylate and in particular GLENIUM® 51 from the company MBT France. This product can be available in liquid or powder form.

Complementarily, the total amount of alkali can be reduced (if the nature of the granulate or the amount of vaporized silicon dioxide is over 10% of the cement mass), the neutralization of fluidizing agents can be chosen on a calcium basis rather than a sodium basis.

In order to improve the properties of the concrete according to the invention for certain applications, fibers are incorporated into the concrete. These fibers are selected in particular from carbon fibers, Kevlar®, polypropylene fibers or metal fibers, or mixtures thereof. It is preferred to use steel fibres.

These fibers can have any shape, but to achieve a good handleability for the concrete, it is preferred to use straight fibers. These fibers have a diameter between 0.1 and 1.0 mm, preferably between 0.2 and 0.5 mm and most preferably between 0.2 and 0.3 mm, and a length between 5 mm and 30 mm, preferably between 10 and 25 mm and most preferably between 10 and 20 mm.

When these fibers are introduced, the granular matrix is modified. The fibers can be sheathed, but it is necessary that the amount of finely divided substances, i.e. particles with a diameter of less than 0.1 mm, increases. The amount of vaporized silicon dioxide, cement, sand with the smallest granulometry and/or mineral additives is thus greater than that of a concrete without fibres.

According to a particular embodiment of the invention, the concrete comprises in parts by weight: 100 cement; 5 to 200, preferably 60 to 180 and most preferably 80 to 160 of the mixture of calcined bauxite sand; 6 to 25 and preferably 6 to 20 fumed silicon dioxide;

0.1 to 10 and preferably 0.2 to 5 antifoam;

0.1 to 10 and preferably 0.5 to 5 superplasticizing water reducing agent;

0 to 50 and preferably 2 to 20 and most preferably 4 to 16 fibers; and 10 to 30 and preferably 10 to 20 water.

Furthermore, 0.5 to 3 parts by weight and preferably 0.5 to 2 parts by weight, preferably 1 part by weight of calcium oxide or calcium sulphate can be added to the concrete mixture according to the invention. The calcium oxide or calcium sulfate is added in the form of powder or micronized form and should allow to compensate for the inherent endogenous shrinkage for formulations based on hydraulic binders in connection with very small amounts of water.

It is also possible to use calcined bauxite fillers (whose mean harmonic diameter is below 80 µm) by partially replacing the cement and the fumed silicon dioxide, which for example allows adjusting the modulus of elasticity, which can thus vary from 60 GPa to 75 GPa. This same adjustment also corresponds to modifications in the different deformation characteristics (flow shrinkage).

The quantities of the different components in the concrete can be adjusted by the professional as a function of the application and the desired properties of the concrete.

A low dose of fumed silicon dioxide of 6 to 8 parts allows to obtain an increased resistance in a short time while dosages between 15 and 20 parts allow to valorize all performance gains in the medium and long term such as manageability of the mixture when the concrete is stored and kept at 20°C. The addition of more than 25 parts of fumed silicon dioxide shows no advantage because it does not allow to increase the performance of the resulting material but increases the cost.

The invention also relates to a method for producing a fiber concrete, characterized by mixing all the components in the concrete to obtain concrete with a desired fluidity or by first mixing in all granular dry substances such as cement, sand, fumed silicon dioxide and any superplasticizer and anti -foaming agent, then water is added to the mixture and any superplasticizer and anti-foaming agent if these are in liquid form, as well as fibres, and that the whole is mixed to obtain a concrete with the desired fluidity.

All the components of the concrete according to the invention are introduced into a mixer, mixed and a concrete ready for casting or pouring is obtained, with very good workability.

In a preferred manner, the mixture is first prepared from powders and at the time of use these powders are then mixed with the desired amounts of fibers and water and any superplasticizing water-reducing agent and antifoam to the extent that these are in liquid form. In an advantageous manner, safe or other types of packaging (for example "big bag") are produced from the pre-mixed product in a dry state, ready for use, and which is then stored and stored easily provided that it contains a very small amount of water. At the moment of use, it is then sufficient to bring the premix to a mixer together with the desired amounts of fibers and water and any superplasticizing water reducing agent. After mixing, for example for 4 to 16 minutes, the concrete obtained according to the invention is ready for casting without difficulty, in view of the very high leveling properties.

In order to realize the mixture, one can use classic forms of wood, metal and so on, or thermal joint forms whose sole aim is to allow a reduction of the time that passes and a rapid increase of the resistance. The concrete according to the invention has no need to be subjected to a thermal treatment in order to reach the desired and required performances. Of course, a thermal treatment can take place to further improve performance, but this entails an additional cost. On the contrary, a simple insulation of the formwork allows the pozzolanic reactions of the vaporized silicon oxide to develop and thereby provide significant gains in terms of resistance as fresh concrete. For example, 160 MPa has been measured at 40 hours on a concrete beam with a thickness of 11 cm and where the temperature has not exceeded 60°C.

The present invention also relates to the pre-mixed products in a dry state, ready for use, which allow a concrete according to the invention to be obtained after the addition of water and possibly fibres.

The concrete according to the invention can be used in all the areas of application that apply to possibly reinforced concrete. More specifically and considering the fact that the concrete is self-levelling, it can be cast in place to produce posts, small and large beams, floors and so on and it can likewise be used in all precast applications, such as posts, beams, girders, floors, pavements, art objects, prestressed concrete objects, composite materials, or elements for drainage circuits. Taking into account the properties for cohesion and viscosity, the concrete can be used for formwork that includes deposits. It can also be used to realize joint elements between structural elements.

The concrete can also be used to make tiles, gutters, works of art, prestressed objects or composite materials. Taking into account the high values for the resistance, the concrete can further be used in the nuclear area, for example to produce containers for radioactive waste, parts that are necessary for the renovation of coolants in nuclear centres. Furthermore, the increased resistance to compression and the increased modulus of elasticity allow a reduction in the dimensioning of objects that use the concrete and this is particularly useful, for example, for all elements, pipes, containers and the like that are used for soil cleaning. The concrete also exhibits a very low coefficient of friction which does not change over time, which makes the concrete absolutely suitable for the transport of materials which are classically corrosive to concrete. Furthermore, taking into account that the amount of fumed silicon dioxide can be reduced compared to classic high-performance concrete types, the pH value is very high, which makes the concrete a preferred material for protecting metal pipelines against corrosion.

The invention will be explained in more detail below with the help of the following illustrative examples.

Example 1

5 formulations of concrete according to the invention are prepared by varying the respective amounts of the different components. The composition for each of these formulations, concrete A to concrete E is reproduced in table 1 below.

The cement used is an HTS Le Teil cement marketed by the company Lafarge.

For the concretes B and D, a commercially available fumed silicon dioxide from the company ELKEM, marketed under the designations 983U or 940U of refractory quality, is used. For the concretes A and C, vaporized silicon dioxide is used, which is marketed by the company PECHINEY and which originates from the factories in Laudun, and for concrete E, a thermal silicon dioxide from SAINT-GOBAIN SEPR is used.

The fibers used are straight fibers with a diameter of 0.3 mm and a length of 20 mm.

A superplasticizing water-reducing agent, marketed by the company MBT France under the name GLENIUM® 51, has been used.

As anti-foaming agent, a commercially available anti-foaming agent from the company TROY, marketed under the name TROYKYD® Dl26, is used.

For each of the formulations, a normalized equalization test was carried out on a shaking table and the results obtained are shown in table 2 below.

With each of the formulations, test pieces of 11 cm x 22 cm are produced on which normalized tests are carried out to measure the resistance to compression after 7, 14 and 28 days in accordance with the standard NFP 18406 as well as to measure the modulus of elasticity after 28 days. The results obtained are also shown in table 2.

Example 2: Modification of the fiber quantity.

New concrete formulations are produced by taking up the formulation for concrete B in example 1, in which the quantity of introduced fibers is particularly varied. Thus, 4 different types of concrete are produced with respective fiber amounts of 0, 1, 1.5, 2 and 3% by volume. To produce these concretes, the cement HTS Le Teil from the company LAFARGE, fumed silicon dioxide of refractory quality 983U from ELKEM, straight fibers with a diameter of 0.3 mm and a length of 20 mm, superplasticizing water-reducing agent GLENIUM® 51 from the company MBT France and the anti-foaming agent are used TROYKYD® D126 from company TROY.

The composition of these formulations is given in table 3 below (concrete 0%, 1%, 1.5%, 2% and 3%).

For each of these formulations, the equalization is measured as in example 1 and the results obtained can be found in table 3 below.

For each of the formulations, test pieces are prepared, test pieces of 11 cm x 22 cm are prepared on which the resistance to compression is measured after 28 days as well as the modulus of elasticity after 28 days, as described in example 1.

The results obtained from these tests are reproduced in table 3.

Claims (12)

1. Self-leveling high-performance concrete with a characteristic resistance to compression after 28 days of at least 150 MPa, a modulus of elasticity after 28 days of at least 60 GPa and a resistance to compression after 40 hours of at least 100 MPa, these values being for a concrete that has been preserved and kept at 20°C, characterized by the fact that it comprises: a cement with a granulometry corresponding to a harmonic average diameter less than or equal to 7 µm and preferably between 3 and 7 µm; a mixture of sand with different granulometries extensively calcined bauxite sand, the finest sand having an average granulometry of less than 1 mm and the coarsest sand having an average granulometry of less than 10 mm; fumed silicon dioxide where 40% of the particles have a dimension below 1 µm and the harmonic mean diameter is close to 0.2 nm and preferably close to 0.1 µm; an antifoam agent; a superplasticizing water reducing agent selected from modified polycarboxylates or polyacrylates; possibly fibers; and water; as the cement, sand and fumed silicon dioxide exhibit a granulometric distribution so that you have at least 3 and at most 5 different granulometric classes where the ratio between the harmonic diameter average for one granulometric class and the class immediately above it is around 10. 2. Concrete according to claim 1, characterized in that the cement is selected from among cements that have a content of bi- and tricalcium silicates above 75%. 3. Concrete according to claim 2, characterized in that the cement is selected from cements of the Portland CEM I type, preferably with complementary characteristics such as "Prise Mer - PM", or more preferably "Prise Mer et Résistant aux Sulfates - PM-ES" or mixtures thereof. 4. Concrete according to any one of claims 1 to 3, characterized in that the mixture of sand consists of: a sand with an average granulometry of less than 1 mm comprising 20% granules with dimensions below 80 microns, a sand with a granulometry between 3 and 7 mm, and possibly a sand with a granulometry between 1 and 3 mm, the sand with the smallest granulometry can be replaced in whole or in part with: cement, mineral additives such as ground slag, fly ash or calcined bauxite filler where the harmonic diameter average is below 80 um in relation to the fraction of 20% of the granules with a dimension below 80 um, and sand with a granulometry above 1 mm in relation to the other fraction. 5. Concrete according to claim 4, characterized in that the superplasticizing water-reducing agent is a product based on modified polycarboxylate. 6. Concrete according to any one of claims 1 to 5, characterized in that the fibers are preferably selected from metal, carbon, Kevlar® or polypropylene fibers or mixtures thereof. 7. Concrete according to claim 6, characterized in that the fibers are metal fibers, preferably of steel, with a length comprised between 5 and 30 mm, preferably between 10 and 25 mm and most preferably between 10 and 20 mm, and with a diameter comprised between 0.1 and 1.0 mm, preferably between 0.2 and 0.5 mm and most preferably between 0.2 and 0.3 mm. 8. Concrete according to any one of claims 1 to 7, characterized in that it comprises on a weight basis: 100 parts cement; 5 to 200 parts, preferably 60 to 180 parts and most preferably 80 to 160 parts of calcined bauxite sand mixture; 6 to 25 parts and preferably 6 to 20 parts fumed silicon dioxide; 0.1 to 10 and preferably 0.2 to 5 parts antifoam; 0.1 to 10 and preferably 0.5 to 5 parts superplasticizing water reducing agent; 0 to 50 and preferably 2 to 20, most preferably 4 to 16 parts of fibers; and 10 to 30 and preferably 10 to 20 parts of water. 9. Concrete according to any one of claims 1 to 8, characterized in that it additionally contains 0.5 to 3 and preferably 0.5 to 2 and most preferably around 1 part of calcium oxide or calcium sulphate in micronized or powder form. 10. Process for producing a fiber concrete according to any one of claims 1 to 9, characterized by mixing all the components in the concrete to obtain concrete with a desired fluidity or by first mixing in all granular dry substances such as cement, sand, fumed silicon dioxide and possibly superplasticizing agent and anti-foaming agent, then water and possibly superplasticizing agent and anti-foaming agent if these are in liquid form, as well as fibres, are added to the mixture, and that the whole is mixed to obtain a concrete with the desired fluidity. 11. Dry-mixed ready-to-use concrete which allows to obtain a concrete according to any one of claims 1 to 9 after the addition of water and possibly fibres. 12. Use of a concrete as indicated according to any one of claims 1 to 9 or as produced by the method according to claim 10 for the production of prefabricated elements such as posts, beams, girders, floors, pavements, works of art, prestressed concrete objects or composite materials, joints between structural elements or elements for drainage circuits.