ITUB20155712A1 - Lightweight concrete with high elastic modulus and its use - Google Patents

Description

"Lightweight concrete with a high modulus of elasticity and its use"

The present invention relates to a lightweight concrete with a high elastic modulus and its use.

In particular, the present invention relates to a light concrete with a high elastic modulus comprising light aggregates in the form of hollow spheres.

The demand for construction materials in lightweight concrete is increasingly significant: of particular interest are above all lightweight structural materials characterized by high mechanical strength and high stiffness. The lighter the structural concrete is, while at the same time satisfying the necessary mechanical specifications, the more it will be possible to create structural elements which, with the same mechanical characteristics, will be lighter, more airy, i.e. for example it will be possible to use thinner beams, pylons tighter, etc ..

In general, the greater loads derive from the operation of the structure (accidental loads), but it is also true that light structural elements reduce the permanent loads allowing to reduce the resistant sections.

Structural elements made in this way also require a reduced quantity of concrete, with a consequent reduction in costs and energy consumption.

The main characteristics of lightweight concretes are related to the density of the material which is lower than the density of ordinary concrete. This involves:

- a reduction of the own weight and therefore of the permanent loads applied to the reinforced concrete structures;

- a different relationship between the two fundamental mechanical characteristics: compressive strength and elastic modulus. In particular, in lightweight concretes, the ratio between mechanical strength (defined as the maximum mechanical stress of the material before failure) and elastic modulus is higher than that which characterizes ordinary concretes. 1 / Eurocode 2 (i.e. the European standards for structural design dedicated to non-reinforced, reinforced and prestressed concrete structures) provides two different relationships for ordinary concretes and for lightweight concretes. These relationships are represented in Figure 1.

To better understand this criticality of lightweight concretes it is important that, for the purposes of the structural calculation, the law that links the deformation of the material to the mechanical stress in the elastic-linear range is taken into consideration, i.e. Hooke's law, expressed as follows:

σ = Εε (1)

where is it :

σ [MPa]: stress state -> force applied on the surface unit

Ξ [-]; relative deformation (ΔΙ / l) where "1" is the initial dimension and "Δ1" is the measured deformation (therefore dimensionless)

E: elastic modulus -> expresses the tension theoretically necessary to compress a specimen by 100%.

Considering the example of a compressed column and assuming that the column is subjected to a load Q [N] and has a section A [mm <2>], the load / section ratio (stress state) is normally set at 1/3 the mechanical strength of the concrete. So in the case of a concrete with Rck (characteristic resistance) equal to 30 MPa, the Q / A ratio will be 10 MPa.

The column is made of concrete characterized by an elastic modulus E [MPa] and the deformation of the column is easily obtained from the relation (1) above.

The stress state is given by the applied load divided by the section, therefore by the relation:

Q / A = Es (2)

by making the deformation ε explicit, we obtain:

e = Q / AE

e = Q / A * l / E

Therefore the deformation is directly proportional to the load applied to the column and indirectly proportional to the section and to the elastic modulus. The product A * E is called stiffness of the pillar and corresponds to the ability to oppose the deformations generated by a load and depends on the elastic modulus of the material.

In the case of an ordinary concrete (Rc = 35MPa -> Q / A = 11.5; E 30000 MPa):

ε = 11.5 * 1/30000 - 0.00038.

In the case of a lightweight concrete (Rc = 35MPa -> Q / A = 11.5; E 20000 MPa):

ε = 11.5 * 1/20000 = 0.00057.

The deformation of the pillar made with lightweight concrete is higher than that of the pillar made with ordinary concrete, although the mechanical strength of both concretes is the same. The only way that allows the deformation of the lightweight concrete column to be comparable to the deformation of the ordinary concrete column is to increase the section (in this case almost 50%) of the column, reducing the stress state (Q / A).

Lightweight concretes according to the state of the art are generally made using porous aggregates or aggregates, obtained with different methods. These porous aggregates, certainly lighter than a classic aggregate, however, present problems of water absorption and mechanical resistance, when used in the production of a lightweight concrete. The absorption of water involves both a heavier aggregate, which thus loses the desired property of lightness, and an increase in the consumption of water necessary for the formation of lightweight concrete.

As an alternative to these porous aggregates, aggregates or hollow aggregates in non-porous material were also used which, however, once used as aggregates in a lightweight concrete did not allow to obtain a concrete that was characterized at the same time by high mechanical resistance, high stiffness and with a high modulus of elasticity.

To overcome these problems, cellular concretes have also been used, i.e. concretes that incorporate a porous cement mixture in which the voids are produced from expandable polystyrene in the form of small particles, subjecting the material to sintering and thus causing the expansion of the polymeric material. due to the effect of heat during polymerization (US3021291).

The present invention aims to identify a lightweight concrete that does not have the disadvantages of lightweight concretes according to the state of the art, which as mentioned are not able to guarantee at the same time characteristics of lightness, mechanical strength, rigidity and modulus. elastic, those characteristics that make lightweight concrete optimally usable as structural lightweight concrete.

The Applicant has in fact surprisingly found an improved lightweight concrete, which can be used in a particularly effective way as structural lightweight concrete, being provided at the same time with high mechanical strength, high stiffness and with a high elastic modulus, thus solving the technical problem faced by the present invention.

The object of the present invention is therefore an improved structural lightweight concrete with a high elastic modulus, which comprises a mixture of cement, water, hollow spherical lightweight aggregates, inert aggregates, preferably calcareous or silico-calcareous aggregates, where the weight ratio in the mixture in dry conditions, cement / hollow spherical light aggregates ranges from 0.6 to 0.9, preferably from 0.80 to 0.85 and where the water / cement ratio by weight is equal to 0.44. A further object of the present invention is the use of a light concrete with a high elastic modulus, which comprises a mixture of cement, water, hollow spherical light aggregates, inert aggregates, preferably inert calcareous or silico-calcareous aggregates, where the weight ratio, in the dry mix, cement / hollow spherical lightweight aggregates ranges from 0.6 to 0.9, preferably from 0.80 to 0.85 and where the water / cement ratio by weight is equal to 0.44, such as structural lightweight concrete .

Object of the present invention are also structural elements obtained with the lightweight concrete according to the present invention such as pillars, beams, walls, etc. etc.

A further object of the present invention is also a hollow light aggregate having the shape of a hollow sphere, where said hollow sphere has a size ranging from 0.6 mm to 1.5 mm, preferably from 0.7 to 1.1 mm, with a wall thickness equal to about 1 mm and a smooth or rough outer surface, preferably rough, in ceramic or cementitious material and the use of such hollow lightweight aggregate, as a lightweight aggregate in a structural lightweight concrete with a high modulus of elasticity.

A fundamental advantage of the light concrete with a high elastic modulus according to the present invention is that it allows the creation of lighter, more airy structural elements, that is, for example, it allows the creation of thinner beams, narrower pillars, etc. of mechanical characteristics, also allow to use a reduced quantity of concrete, with a consequent reduction of costs and energy consumption.

Furthermore, the particular light aggregate of hollow spherical shape present in the lightweight concrete according to the present invention also allows to eliminate the problem of water absorption, a typical problem of porous light aggregates according to the state of the art.

According to the present invention, the term "cement" means a powder material which, when mixed with water, forms a paste which hardens by hydration, and which, after hardening, maintains its strength and stability even under In particular, the cements according to the present invention include the so-called Portland cement, slag cement, pozzolane cement, fly ash, calcined shale, limestone and so-called composite cements. For example, type I cements can be used. , II, III, IV or V according to the ENI97-1 standard. Particularly preferred cements are CEM I cement and CEM II cement. The particularly preferred class of cement is class 52.5 for CEM I cement.

The term "inert aggregate" according to the present invention means inert aggregates such as powders and sands, suitably selected from calcareous, silico-calcareous and siliceous aggregates of any shape.

These inert aggregates are divided into sands, having an average diameter ranging from 0.5 to 5 mm, and in powders or fillers, that is, fine aggregates, having an average diameter ranging from 50 to 100 microns.

Particularly preferred are calcareous or silico-calcareous aggregates. The preferred aggregate is constituted by natural or crushed silico-calcareous sand and by filler or fine calcareous aggregate.

According to the present invention, the term "hollow spherical light aggregate" means a light aggregate having the shape of a hollow sphere, characterized by high mechanical strength and high stiffness. The surface of the rigid shell that constitutes the hollow sphere is not porous, said hollow sphere being obtained from sintered ceramic or mineral powders. The hollow sphere has a thickness of about 1 mm, a density ranging from 1.5 to 1.7 (mg / m <3>) and a size ranging from 0.6 mm to 1.5 mm, preferably from 0 , 7 to 1.1 mm.

The hollow sphere-shaped lightweight aggregates used in the lightweight concrete according to the present invention have been produced using different possible matrices for the rigid shell and more precisely

- a ceramic-type material;

- a cement paste.

The cement paste can be hardened with accelerated curing in an autoclave with supersaturated steam (180 ° C and 13 atm) or it can be hardened with curing in "natural" conditions at a temperature of 22 ° C and relative humidity close to 100%.

The aggregate in cementitious material or in ceramic material according to the present invention can be obtained by means of a process which comprises a first step of granulating a dry mixture of ceramic material or cementitious paste on spherical polystyrene cores sprayed with latex suspensions in a concrete mixer or granulator plate; and, in the case of the aggregate in ceramic material, a subsequent phase of ceramizing the granulated spheres thus obtained, carried out in suitable electric furnaces; or, in the case of the aggregate in cementitious material, a subsequent hardening phase of the granulated spheres thus obtained, with accelerated curing in an autoclave with supersaturated steam, at 180 ° C and 13 atm, or with curing in "natural" conditions at the temperature of 22 ° C and relative humidity close to 100%.

The first step of the process for the production of the light aggregate in the shape of a hollow sphere to be used in the light concrete according to the present invention therefore provides for a granulation of the dry mixture of ceramic material or cement paste on spherical cores of virgin polystyrene.

The ceramic-type material comprises three essential components: a clayey raw material, a flux component and a stabilizing component.

The clayey raw material can be chosen from kaolite, bentonite, meta kaolin, etc., and is present in an amount ranging from 30 to 50% by weight with respect to the total weight of the ceramic type material; the dark component can be chosen from feldspar, limestone, dolomite, talc, etc. and is present in an amount ranging from 20 to 40% by weight with respect to the total weight of the ceramic-type material; the stabilizing component can be chosen from quartz sands, silica, etc. and is present in an amount ranging from 10 to 20% by weight with respect to the total weight of the ceramic-type material.

Clay is the fundamental raw material for the preparation of ceramic materials obtained by firing at high temperatures, while the stabilizing component is made up of minerals or rocks, used in their original form or thermally pre-treated, having as their main requisite dimensional stability or even a tendency to expand. When added to a ceramic body, they form the backbone, thus counteracting the shrinkage to which the product is subject, for causes of a chemical nature (dehydration, thermal decomposition or other) and / or physical (tighter structure of the constituent particles the mixture). The flux component has a lower melting temperature than the basic constituents of ceramic products (silica and alumina), but has the property of further reducing the melting temperature, if present in a mixture with them, and favors the sintering process of clays.

In the case of ceramic materials, the following preparation is therefore reported, by way of example, starting from a raw mixture consisting of

- meta kaolin with the ceramizing base function, 65% by weight with respect to the total weight of the raw mixture;

- quartz with the function of volumetric stabilizer, fraction 0 - 0.100 mm, 20% by weight with respect to the total weight of the raw mixture;

- feldspar with the function of flux, fraction <0.150 mm, 15% by weight with respect to the total weight of the raw mixture.

The formation of the sphere takes place through a process of granulation of the dry / dry mixture powder where the cores from which the spheres grow are made of virgin expanded polystyrene beads, preferably with two nominal particle size distributions equal to 2-3 mm and 3- 5 mm.

Latex suspensions are used to allow the adhesion of the raw mixture powder to the polystyrene beads (hydrophobic) and subsequently to continue the granulation obtaining compact spheres.

The thickness of the spheres, as mentioned, is an important parameter: for each gram of polystyrene about 200 g of dry powder are needed to obtain a shell with a thickness of about 1 mm, regardless of the nominal size of the pearls used, while the amount of latex required is about 67.5 g, considering an average concentration of the dispersion of 30% by weight.

The thickness of 1 mm is the most suitable thickness for the spheres of the desired size, size ranging from 0.6 mm to 1.5 mm, preferably from 0.7 to 1.1 mm, because a thickness of less than 1 mm it would make it too delicate to withstand the mechanical operations of the concrete mix and a greater thickness would negatively affect the nominal density parameter that considers the closed cavity.

Both spheres with a substantially smooth surface and spheres with high roughness can be made, as shown in figure 2 (2a and 2b, respectively).

The quantity of polystyrene beads corresponding to the quantity of hollow spheres to be produced is arranged in a suitable concrete mixer equipped with a gear device which allows a continuous adjustment of the angle of inclination. The mixer also has a modulable rotation speed that varies linearly between 9.5 and 24 revolutions per minute. The granulation phase is carried out at maximum speed. Obviously, the spheres can also be produced with a granulator plate.

The dry powder is then fed, the quantity of which is defined according to the quantity of spheres to be produced, and the rotation of the concrete mixer is started.

The latex suspension is then sprayed by means of a suitable nebulizer on the polystyrene beads, the latex wets the polystyrene beads which, rolling, end up in the mass of dry powder that slides on the wall of the bin, remaining covered with it. The ceramization of the granulated spheres thus obtained is carried out in suitable electric ovens, after air drying the spheres and sieving them to remove the granulation waste and the dusting that occurs in each movement of the spheres themselves. This operation is necessary as during the cooking phase any waste not removed, by cooking, would stick to the spheres, gluing them to each other permanently.

The thermal cooking cycle includes the following three phases:

- in the first phase the temperature is increased from ambient T to 300 ° C, with a gradient of 2 ° C / min, followed by one hour of maintenance. In this phase there is the complete drying of the free water of the spheres and in the plateau phase a first elimination of the hydration water. At the same time, the degradation of the polystyrene of the nucleation bead and therefore the formation of the cavity takes place in this phase; - in the second phase the temperature is increased from 300 ° C to 700 ° C, with a gradient of 2 ° C / min, followed by one hour of maintenance. In this phase there is the complete elimination of the crystallization water and the first phase of cooking; - in the third phase the temperature is increased from 700 ° C to 1300 ° C, with a gradient of 5 ° C / min, followed by three hours of maintenance. In this phase the ceramization of the material takes place, which undergoes a substantial reduction in volume estimated between 20 and 30% compared to the volume of the raw spheres.

As previously indicated, the light aggregates in the shape of a hollow sphere can also be obtained starting from cementitious pastes, where the cementitious paste can be hardened with accelerated curing in an autoclave with supersaturated steam (180 ° C and 13 atm) or it can be hardened with maturation in "natural" conditions at a temperature of 22 ° C and relative humidity close to 100%.

In the first case we speak of a binder for autoclaved maturation and, by way of example, a binder obtained from the following composition is reported

• Clinker Scafa 70% by weight;

• Quartz silica 30% by weight

by co-grinding of Scafa clinker and a quartz silica to a high fineness, 6000 Blaine (cm <2> / g). The granulation phase is carried out exactly as described for the hollow spheres in ceramic material with the only difference that the latex is nebulized only initially, that is until the polystyrene beads have been covered with a first "veil" of dry powder of binder, the rest of the granulation then proceeds simply using water as the liquid part.

For each gram of virgin polystyrene beads there is a consumption of 200 g of binder, about 6.5 g of latex (ready to use) and 45 g of water.

The maturation of the spheres produced with this binder takes place in two phases, the first at low temperature at ordinary pressure and the second at high temperature and pressure (180 ° C and 13 atm).

The first phase of maturation lasts between 7 and 18 hours and has the purpose of giving the spheres a minimum of mechanical resistance to withstand the autoclaving phase. The ripening temperature is 60 ° C and the humidity is that which is established at this temperature in a closed environment with free water. At the end of this first cycle of maturation in the oven, the spheres are introduced into the autoclave, set at 180 ° C and the equilibrium pressure, once the temperature is reached, is about 13 atm. This phase lasts about 24 hours.

In the case of a hardened cement paste with maturation in "natural" conditions, we speak of a binder for natural maturation and this binder is produced by grinding Scafa clinker (100%) to a high fineness, 8000 Blaine (cm <2> / g), The granulation is carried out as described for the autoclaved curing binder and for each gram of virgin polystyrene beads there is a consumption of 200 g of binder, about 6.5 g of latex (ready to use) and about 57 g of water.

The maturation phase of this type of spheres is carried out through a first phase in which, at the end of the granulation and after a surface wetting, the spheres are placed in a container, then closed and sealed. Within the first hour of maturation the material being hydrated develops a large amount of heat and the surface of the container reaches a temperature of about 80 ° C, producing a sort of steam maturation, with autogenous heat. The rest of the maturation, for a total of 28 days, takes place at a temperature of 22 ° C and a relative humidity close to 100%, corresponding to that established in the closed container with a small excess of water to wet the spheres.

The ceramic hollow spheres and autoclaved cement paste, produced as described above, were characterized with reference to the physical characteristics as aggregates and precisely the density, water absorption and crash test were measured, the results of which are reported in the following table 1.

Table 1

Hollow spheres

pasta Hollow spheres Hollow spheres

cementitious ceramic paste

autoclaved cement

Apparent density pLa (Mg / m <3>) 1.60 1.52 1.66 Density pre-dried in oven pLtd

1.48 1.21 1.35 (Mg / m <3>)

Dry saturated surface density

1.55 1.41 1.54 pLssd (Mg / m <3>)

Water absorption at 5 min

4.3 4.5 8.2 WA5. (%)

Water absorption at 1 hour 4.7 8.4 12.4 WAlh * (%)

Water absorption after 24 hours

5.0 17.3 14.1 WA24h. (%)

Crash Test (N / mm <z>) 2.7 5.5 4.1

The previous characterizations were conducted according to the following standards:

the density or density was measured according to the method EN 1097-6: 2013;

water absorption is measured according to the EN 1097-6: 2013 method;

the crash test is conducted according to the EN 13055-1: 2002 method.

The particle size distribution of the hollow spheres, measured with a videogranulometer, is shown in figure 3.

The following table 2 shows the physical characterization for the hollow ceramic spheres shown in figure 2, smooth 2a) and rough 2b).

Table 2

Absorption Absorption Absorption Crush Mass Light aggregate water water water

volume test 5 min 1 h 24 h

[MPa] [%] [%] [%] [kg / m <; f>] Ceramic hollow spheres

3.36 3.1 3.8 4.8 1.40 smooth

Ceramic hollow spheres

3.48 3.9 4.4 5.2 1.64 rough

The lightweight concrete with a high elastic modulus according to the present invention comprises a quantity of cement ranging from 300 to 550 kg / m <3>, more preferably from 350 to 500 kg / m <3>, even more preferably from 420 to 480 kg / m <3>.

Preferred cement is CEM I class 52.5 cement and CEM II cement.

The lightweight concrete with a high elastic modulus according to the present invention comprises an amount of water ranging from 132 to 242 kg / m <3>, preferably from 160 to 230 kg / m <3>.

The water / cement ratio is equal to 0.44 (by weight). The lightweight concrete with a high elastic modulus according to the present invention comprises an amount of inert aggregate ranging from 450 to 800 kg / m <3>. More preferably, the inert aggregate according to the present invention consists of sand, preferably natural or crushed silico-calcareous sand, in an amount ranging from 450 to 650 kg / m <3> and of fine aggregate, preferably calcareous filler, in an amount ranging from 0 to 150 kg / m <3>.

The light concrete with a high elastic modulus according to the present invention comprises an amount of hollow spherical light aggregate ranging from 333 and 918 kg / m <3>, preferably from 500 to 612 kg / m <3>.

The preferred aggregate consists of hollow spheres of ceramic or cementitious material, preferably of ceramic material.

The ratio between the quantity of cement and the quantity of light aggregate is fundamental: the weight ratio, in the dry mix, cement / hollow spherical light aggregates varies from 0.6 to 0.9, preferably from 0.80 to 0.85 .

The lightweight concrete with a high elastic modulus according to the present invention can also comprise superplasticizing additives or other additives, in insignificant quantities.

A preferred lightweight high-modulus concrete according to the present invention provides the following composition:

- CEM I 52.5 cement in an amount ranging from 350 kg / m <3> to 500 kg / m <3>;

- water in an amount ranging from 160 kg / m <3> to 230 kg / m <3>;

- hollow spherical lightweight aggregates in ceramic material in an amount ranging from 500 to 612 kg / m <3>, where preferably 60% by volume of the aggregates has a rough surface and 40% by volume of the aggregates has a smooth surface, the percentages by volume refer to the total volume of light aggregates;

- silico-calcareous sand in an amount ranging from 450 kg / m <3> to 650 kg / m <3>;

- calcareous filler in an amount ranging from 0 to 100 kg / m <3>;

- super-thinner in an amount ranging from 2 kg / m <3> to 5 kg / m <3>;

- the water / cement weight ratio being equal to 0.44 e

- the cement / hollow spherical light aggregate ratio, by weight, in the dry mixture, being equal to 0.82.

The solution according to the present invention has surprisingly identified a light concrete with a high elastic modulus which simultaneously has a mechanical compressive strength higher than 53 MPa (at 28 days), an elastic modulus higher than 25000 MPa (at 28 days) and a density or density in the hardened state between 1800 and 1900 kg / m <3>.

The light concrete with a high elastic modulus according to the present invention has the advantage of being characterized, at the same time, by a high mechanical resistance and a high elastic modulus which allows, contrary to expectations, to create lighter, more airy structural elements, such as for example thinner beams, narrower pillars, etc. These structural elements, with the same mechanical characteristics, also allow the use of a reduced quantity of concrete, with a consequent reduction in costs and energy consumption. Furthermore, the particular hollow light aggregate of spherical shape of the light concrete according to the present invention also allows to eliminate the problem of water absorption, typical problem of porous light aggregates according to the state of the art. Other features and advantages of the invention will be evident from the following examples given for illustrative and non-limiting purposes.

Example 1

A lightweight concrete with a high elastic modulus was prepared with the composition (C — 1) reported in the following table 3.

Table 3

C-l Kg / m <3>

Cement CEM I 52.5 469

Water 205

Silico-limestone sand 511

Limestone filler 99

Spherical Light Aggregates 568

ceramic cables

Superplasticizer 2.5

The quantities shown in the table are expressed in kg / m <3>.

The cement is a Portland cement type I 52.5R in accordance with the UNI EN 197-1 standards, coming from the Italcementi cement plant in Calusco d'Adda, with a fineness equal to 4960 cm <2> / g (Blaine) and an equal density at 3.151 kg / dm <3>.

The calcareous filler is a fine calcareous aggregate with a maximum diameter equal to about 100 | lm. This aggregate has a density equal to 2.7 kg / dm <3>.

The silico-calcareous sand is a washed alluvial sand, with a density equal to about 2.6 kg / dm <3>.

The lightweight ceramic aggregates having a hollow sphere shape were obtained as indicated above, from the raw mixture consisting of

- meta kaolin with the ceramizing base function, 65% by weight with respect to the total weight of the raw mixture;

- quartz with the function of volumetric stabilizer, fraction 0 - 0.100 mm, 20% by weight with respect to the total weight of the raw mixture;

- feldspar with the function of flux, fraction <0.150 mm, 15% by weight with respect to the total weight of the raw mixture

and are made up of 60% by volume of ceramic aggregates with a rough surface and 40% by volume of aggregates with a smooth surface, the percentages by volume refer to the total volume of light aggregates.

The water / cement ratio is equal to 0.44, while the cement / light aggregate ratio is equal to 0.82.

The superplasticizer, produced by SIKA Italia (Creactive 4K), is an acrylic additive with the function of water reducer.

For complete homogenization, the cement, water, light aggregate and other aggregates and additives are mixed in a construction site concrete mixer or other similar equipment, in the appropriate proportions, until a homogeneous mixture free of lumps is obtained. was suitably characterized with the measurement of the slump and the density or density.

After hardening, the density values, mechanical resistance to compression, dynamic elastic modulus, static elastic modulus and thermal conductivity were measured as shown in the following table 5,

Example 2 (comparative)

For comparative purposes, a light concrete was prepared using classical light aggregates, i.e. expanded clay (C-2) and an ordinary concrete (without light aggregates, C-3), having the compositions reported in the following table 4.

Table 4

C-3

Cement CEM I 52.5 469 466

Water 205 206

Silico-limestone sand 939 1559

Limestone filler 96 111

Expanded clay 98 -Superplasticizer 2,5

The quantities shown in the table are expressed in kg / m <3>.

The cement is a Portland cement type I 52.5R in accordance with the UNI EN 197-1 standards, coming from the Italcementi cement plant in Calusco d'Adda, with a fineness equal to 4960 cm <2> / g (Blaine) and an equal density at 3.151 kg / dm <3>.

The calcareous filler and the silico-calcareous sand are the same used in example 1.

The water / cement ratio is equal to 0.44.

The superplasticizer is produced by SIKA Italia (Creactive 4K) and is an acrylic additive with the function of water reducer.

For complete homogenization, the cement, water, light aggregate (if present) and the other aggregates and additives are mixed in a construction site concrete mixer or other similar equipment, in the appropriate proportions, until a homogeneous mixture is obtained. free of lumps which has been suitably characterized with the measurement of the slump and the density or density.

After hardening, the density values, mechanical resistance to compression, dynamic elastic modulus, static elastic modulus and thermal conductivity were measured as shown in the following table 5.

The density or density in the fresh state was measured according to the UNI EN 12350-6 method.

The slump test was conducted according to the UNI EN 12350-2 method.

The density or density in the hardened state was measured according to the UNI EN 12390-7 method.

The mechanical resistance to compression was measured according to the UNI EN 12390-3 method.

The thermal conductivity was measured according to the UNI EN 12664 method - Thermofluximeter method.

The secant elastic modulus (MES) was measured according to the UNI 6556 method.

The dynamic elastic modulus (MED) was measured according to the ASTM C215 method.

Table 5

C-1 C-2 C-3 Invention Light Ordinary prior art

(CER) (LECA1) <REF) Slump [mm] 230 210 230 Density in the cool state [kg / m <3>] 1813 1815 2308 Density in the hardened state [kg / m <3>] 1805 1802 2292 Compressive strength

{1 day) [MPa] 26.8 28.1 32.2 Compressive strength

{7 day) [MPa] 51.6 35.5 72.4 Compressive strength

(28 days) [MPa] 54.3 38.4 77.5 Dynamic elastic modulus

(1 day) [MPa] 24546 19586 32713 Dynamic elastic modulus

(28 days) [MPa] 28847 24927 39421 Static elastic modulus

(28 days) [MPa] 25692 20173 33875 Thermal conductivity [W / mK] 0.96 0.93 1.19

Example 3

A lightweight concrete was prepared with a composition identical to that reported in example 1 with the only difference that the lightweight ceramic aggregates having a hollow sphere shape consist exclusively of ceramic aggregates with a smooth surface.

After hardening, the density, compressive mechanical strength and static elastic modulus values reported in the following table 6 were measured.

Table 6

C-3 C-l

C-4

Ordinary Invention Invention

(REF) (CER) Density in the hardened state [kg / m <3>] 2292 1823 1805 Compressive strength

{28 days) [MPa] 77.5 47.6 54.3 Static elastic modulus

(28 days) [MPa] 33875 24887 25692

As can be seen from Figure 4, the surface roughness does not substantially affect the elastic modulus, but allows to improve the compressive strength. From the previous comparisons it is evident that the light concrete with a high elastic modulus of the present invention presents an optimal combination of physical properties which allow to obtain a light concrete which, at the same time, is characterized by

a decidedly improved mechanical resistance to compression and a static elastic modulus with respect to light concretes already known in the state of the art, physical characteristics that allow optimal use of the light concrete according to the present invention as a structural element;

a reduced, but sufficient mechanical resistance and a reduced, but sufficient elastic modulus with respect to ordinary concretes (respectively about 70% and 76% of the values of the ordinary reference concrete of Example 2) (Figure 5);

an elastic modulus approximately 10% higher than that envisaged according to the algorithms according to Eurocode2 (EC2) for a lightweight concrete (Figure 6) and consequently greater stiffness; Figure 6 shows the Elastic Modulus values measured in the laboratory (red bars) for each exemplified concrete. These experimental values are compared with the prediction of the elastic modulus value (given strength and density) according to the EC2 models (blue bars). As can be seen both in relative terms (between forecast and real - blue and red bars) and in absolute terms (final values of the red bars), the lightweight concrete according to the present invention has a higher elastic modulus (with the same density and of mix design); such values of elastic modulus allow, for example, to make a pillar in lightweight concrete which has a deformation very close to that of the same pillar made with ordinary concrete, with the same mechanical strength, without the need to increase the section;

reduced water absorption compared to classic lightweight concretes.

Claims (14)

CLAIMS 1. Lightweight structural concrete with a high modulus of elasticity, comprising a mixture of cement, water, hollow spherical light aggregates, inert aggregates, preferably inert calcareous or silicocalcareous aggregates, where the weight ratio, in the dry mix, cement / hollow spherical light aggregates it varies from 0.6 to 0.9, preferably from 0.80 to 0.85 and where the water / cement ratio by weight is equal to 0.44. 2. Lightweight concrete according to claim 1, where the mixture comprises an amount of cement ranging from 300 to 550 kg / m <3>, more preferably from 350 to 500 kg / m <3>, still more preferably from 420 to 480 kg / m <3>, said cement being preferably chosen between CEM I class 52.5 cement and CEM II cement. Lightweight concrete according to one or more of the preceding claims, where the mixture comprises an amount of water ranging from 132 to 242 kg / m <3>, preferably from 160 to 230 kg / m <3>. 4. Lightweight concrete according to one or more of the preceding claims, where the mixture comprises an amount of hollow spherical lightweight aggregate ranging from 333 to 918 kg / m <3>, preferably from 500 to 612 kg / m <3>, said aggregate light hollow spherical being made up of hollow spheres in ceramic or cementitious material, preferably in ceramic material. 5. Lightweight concrete according to one or more of the preceding claims, where the mixture comprises an amount of inert aggregate ranging from 450 to 800 kg / m <3>, said inert aggregate preferably being sand, more preferably natural or crushed silico-calcareous sand , in an amount ranging from 450 to 650 kg / m <3> and powder or fine aggregate, preferably calcareous filler, in an amount ranging from 0 to 150 kg / m <3>. 6. Lightweight concrete according to one or more of the preceding claims, where the mixture consists of - CEM I 52.5 cement in an amount ranging from 350 kg / m <3> to 500 kg / m <3>; - water in an amount ranging from 160 kg / m <3> to 230 kg / m <3>; - hollow spherical lightweight aggregates in ceramic material in an amount ranging from 500 to 612 kg / m <3>, where preferably 60% by volume of the aggregates has a rough surface and 40% by volume of the aggregates has a smooth surface, the percentages by volume refer to the total volume of light aggregates; - silico-calcareous sand in an amount ranging from 450 kg / m <3> to 650 kg / m <3>; - calcareous filler in an amount ranging from 0 to 100 kg / m <3>; - super-thinner in an amount ranging from 2 kg / m <3> to 5 kg / m <3>; - the water / cement ratio being equal to 0.44 by weight e - the weight ratio, in the dry mix, of cement / hollow spherical light aggregates being equal to 0.82. 7. Lightweight concrete according to one or more of the preceding claims, wherein said concrete has a compressive mechanical strength higher than 53 MPa at 28 days, an elastic modulus higher than 25000 MPa at 28 days and a density or density in the hardened state comprised between 1800 and 1900 kg / m <3>. 8. Use of a light concrete with a high modulus of elasticity, comprising a mixture of cement, water, hollow spherical light aggregates, inert aggregates, preferably inert calcareous or silicocalcareous aggregates, where the weight ratio, in the dry mix, cement / light aggregates spherical hollow ranges from 0.6 to 0.9, preferably from 0.80 to 0.85 and where the water / cement weight ratio is equal to 0.44, such as structural lightweight concrete. Use of a lightweight concrete according to one or more of claims 2 to 7, such as structural lightweight concrete. 10. Use of a lightweight concrete according to any one of claims 8 or 9, for the construction of structural elements, preferably pillars, beams, walls. 11. Lightweight hollow aggregate having the shape of a hollow sphere, where said hollow sphere has a size ranging from 0.6 mm to 1.5 mm, preferably from 0.7 to 1.1 mm, with an equal wall thickness about 1 mm and a smooth or rough outer surface, preferably rough, in ceramic or cementitious material. 12. Hollow light aggregate according to claim 11, where the hollow sphere is made of ceramic material obtainable starting from a mixture that includes a clayey raw material, a flux component and a stabilizing component, where the clayey raw material is chosen among kaolite, bentonite , meta kaolin, in an amount ranging from 30 to 50% by weight with respect to the total weight of the ceramic-type material; the flux component is chosen from feldspar, limestone, dolomite, talc, in an amount ranging from 20 to 40% by weight with respect to the total weight of the ceramic material; the stabilizing component is chosen from quartz sand and silica, in an amount ranging from 10 to 20% by weight with respect to the total weight of the ceramic-type material. 13. Hollow light aggregate according to claim 11, wherein said aggregate in cementitious material or in ceramic material is obtainable by means of a process which comprises a first granulation step, where a dry mixture of ceramic or cementitious material is granulated on spherical cores of sprayed polystyrene with latex suspensions in a concrete mixer or granulator plate; and, in the case of the aggregate in ceramic material, a subsequent phase of ceramizing the granulated spheres thus obtained, carried out in suitable electric furnaces; or, in the case of the aggregate in cementitious material, a subsequent hardening phase of the granulated spheres thus obtained, with accelerated curing in an autoclave with supersaturated steam, at 180 ° C and 13 atm, or with curing in "natural" conditions at the temperature of 22 ° C and relative humidity close to 100%. 14. Use of the hollow lightweight aggregate according to one or more of claims 11 to 13, as a lightweight aggregate in a structural lightweight concrete with a high elastic modulus.