ITUB20153036A1 - High thermal conductivity mortar and its use - Google Patents

Description

"Mortar with high thermal conductivity and its use"

The present invention relates to a mortar with high thermal conductivity and its use.

In particular, the present invention relates to a Ready Mix mortar, ie produced by concrete mixing on site, for the realization of filling material for underground cable power lines.

Increasingly, high and very high voltage transmission lines are buried both to comply with the relevant specifications and as a matter of smaller footprint. A particularly important aspect of burying high and very high voltage transmission lines is that of being able to keep the temperature of the transmission line under control, a temperature that depends both on the transmitted amperage and on the thermal conductivity of the material in which the line is housed. Currently, lean concretes or sands are used as filling / housing materials, which favor the heat dissipation of underground cables in operation. The thermal conductivity of these materials must be guaranteed even at high transmission line temperatures, for example equal to about 70 ° C.

Similarly, it is of particular importance that this filling / housing material has a low workability, understood as a good ability to be modeled, and is easily removable, once laid and hardened, to allow intervention on cables or transmission lines for works of Extraordinary maintenance.

An example of a mortar characterized by a high thermal conductivity is reported in EP 2476658. This document describes, in fact, a mortar comprising very high quantities of aggregate (82-84%), specifically quartz, together with cement and a percentage of graphite which varies from 1 to 4% by weight. This mortar is used to make a screed that has good mechanical characteristics and good thermal conductivity characteristics at the same time.

The present invention aims to identify a mortar with high thermal conductivity that does not present the disadvantages of mortars according to the state of the art, mortars that are not able to guarantee at the same time mechanical and thermal conductivity characteristics that make them usable as a filler. for underground cable power lines.

The Applicant has in fact surprisingly found an improved mortar, which can be used in a particularly effective way as a filling material for underground cable power lines, being provided at the same time with high thermal conductivity, low workability and low mechanical resistance to compression, thus solving the technical problem faced by the present invention.

The object of the present invention is therefore a mortar with high thermal conductivity, which consists of a mixture of cement, water, fine-grained aggregates and graphite, where the amount of graphite varies from 20 to 40% by weight, preferably from 20 to 30% by weight, with respect to the total weight of cement and graphite and having a water / cement ratio ranging from 0.5 to 1.2, preferably from 0.75 to 0.9.

A further object of the present invention is the use of a mortar with high thermal conductivity, which consists of a mixture of cement, water, fine-grained aggregates and graphite, where the amount of graphite varies from 20 to 40% by weight, preferably from 20 to 30% by weight, with respect to the total weight of cement and graphite and having a water / cement ratio from 0.5 to 1.2, preferably from 0.75 to 0.9, as filling material for underground cable power lines .

It is therefore a high thermal conductivity mortar used in a moist earth consistency (such as wet sand) to cover / house electrical underground cables, especially at high voltage. Thanks to the high thermal conductivity of the mortar, in fact, it is possible to keep the temperature of the cables under control, avoiding the loss of efficiency due to overheating.

The binder mixture consisting of cement, fine-grained aggregates and graphite is mixed with water for the time necessary to obtain a mortar having the consistency of moist earth (also called semi-dry consistency).

The high thermal conductivity mortar used in moist earth consistency is characterized by a low workability that allows the mortar to be easily modeled both in contexts involving inclined surfaces and in contexts involving horizontal surfaces in which a flat final surface is not required.

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 water. In particular, the cements according to the present invention include the so-called Portland cement, the slag cement, the pozzolane cement, the fly ash, the calcined shale, the limestone and the so-called composite cements. For example, type I, II, III, IV or V cements can be used according to the EN197-1 standard. A particularly preferred cement is CEM I and III cement. The particularly preferred cement class is class 52.5 for CEM I cement and 42.5 for CEM III cement.

The term "fine-grained aggregate", according to the present invention, refers to fine aggregates such as powders and sands, defined in the UNI EN 12620 standard, and having a maximum diameter, Dmax, of less than 4 mm.

The aggregates can be suitably selected from calcareous or silico-calcareous aggregates of any shape, or crushed, or spherical, for example marble powders, ceramic coated. Particularly preferred are calcareous silica aggregates and calcareous sands.

According to the present invention, the term "graphite" means a natural graphite with a carbon content varying between 89% and 98%, preferably between 94% and 98%.

By way of example only, a natural graphite of the TIMREX 50x100 Mesh type with a carbon content of 94-98% and a grain size of less than 180 microns or a natural graphite of the TIMREX M100 Mesh type with a carbon content of 94- can be used. 98% and a particle size of less than 150 microns. A natural graphite of the TIMREX M100 Mesh type is preferred.

The high conductivity mortar according to the present invention comprises an amount of cement ranging from 260 to 400 kg / m <3>, more preferably from 300 to 370 kg / m <3>, even more preferably from 315 to 361 kg / m <3>. The high conductivity mortar according to the present invention comprises an amount of water ranging from 200 to 300 kg / m <3>, preferably from 210 to 220 kg / m <3>. The water / cement ratio must vary from 0.5 to 1.2, preferably from 0.75 to 0.9.

The high conductivity mortar according to the present invention comprises an aggregate quantity ranging from 1200 to 1600 kg / m <3>, preferably from 1250 to 1350 kg / m <3> and with a Dmax between 0 and 4 mm.

It should also be pointed out that the high thermal conductivity mortar according to the present invention does not contain either bentonite, quartz, super-brightening additives or other additives.

If on the one hand it is known that the presence of carbonaceous compounds, such as graphite, in combination with cement, allows to increase the thermal conductivity values, on the other hand these carbonaceous compounds possess strong characteristics of water absorption and, of consequently, they make it difficult to prepare mortars with the necessary workability.

Furthermore, the use of a mortar with a consistency of moist earth, a consistency necessary to obtain at the same time the characteristics of mechanical resistance and the required moldability / workability, can generate problems during the application of the product. In fact, in this type of application, heat is transported almost exclusively by conduction; consequently also the compaction of the mortar is fundamental for obtaining a mortar with high thermal conductivity: the presence of air inside the mortar negatively affects the transport of heat, creating areas in which the thermal flow is blocked.

Compaction of the mortar by pressing and not by vibration is therefore preferred, since the pressed mortar has a better thermal conductivity than the corresponding vibrated product.

The solution according to the present invention has surprisingly identified a high conductivity mortar which simultaneously has a thermal conductivity higher than 1.8 W / mK, preferably higher than 2.2 W / mK, and, in the dry state, a mechanical resistance to compression lower than 14 MPa, preferably between 2 and 14 MPa and, always in the dry state, a specific mass or density between 1750 and 2000 kg / m <3>.

Thermal conductivity is measured according to the internal method (ISOMET). This is a test method that works with an APPLIED PRECISION Isomet instrument, equipped with a needle probe which, through the application of a thermal flux, allows to measure the thermal characteristics of solid state materials. This methodology is used specifically for the use of the products of the present invention since if the measurement were made after hardening the needle probe could not penetrate and the surface probe would give incorrect values due to the imperfect flatness of the surface of the audition .

The density or density 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.

For complete homogenization, the cement, water, fine-grained aggregate and graphite are mixed in a construction site concrete mixer or other similar equipment, in the appropriate proportions, until a homogeneous mixture free of lumps and consistency like "damp earth".

The mixing time must be adjusted according to the amount of water added to the ready-to-use premixed mortar and is generally between 1 and 10 minutes.

The mixture thus obtained is then distributed through a channel on the cable to be buried and suitably pressed.

The application of pressure on the high conductivity mortar according to the present invention or compaction step can be carried out manually or mechanically, for example by means of a shovel, a roller, a paver, etc.

The hardening times are variable and depend on the environmental conditions.

The high conductivity mortar according to the present invention has the advantage of being characterized at the same time by an excellent thermal conductivity which allows an optimal use as filling / housing of power lines in underground cables, a reduced but sufficient mechanical resistance which makes the mortar , once hardened, easily removable, to allow intervention on cables or transmission lines for extraordinary maintenance works.

A further advantage of the mortar according to the present invention is linked to the fact that it has a low workability, understood as a good ability to be molded. Furthermore, the density of the mortar is such as to allow the minimization of the compaction / pressing process in the application of the mortar itself.

Other features and advantages of the invention will be evident from the following examples given for illustrative and non-limiting purposes.

Example 1

A high conductivity mortar (G-D-20) was prepared with the composition shown in the following table 1.

Table 1

G-D-20

concrete 361

Fine-grained aggregates 1325

graphite 89

Water 211

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, the fine-grained aggregates are calcareous sand with a Dmax between 0 and 4 mm, identified such as Vinci sand, whose particle size distribution is shown in figure 1. This aggregate has a density equal to 2.62 kg / dm <3>.

Graphite is a natural graphite of the TIMREX M100 Mesh type with a carbon content of 94-98% and a grain size of less than 150 microns and is present in an amount equal to 20% with respect to the total weight of cement and graphite.

The water / cement ratio is equal to 0.58.

The mortar in the present example, with a consistency of moist earth, once applied as a filler for underground cable power lines, pressed and hardened, was tested and the values of density, thermal conductivity and mechanical resistance to compression, reported in the following table 4.

Example 2

A high conductivity mortar (G-D-30) was prepared with the composition shown in the following table 2.

Table 2

G-D-30

concrete 315

Fine-grained aggregates 1330

graphite 133

Water 220

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, the fine-grained aggregates are a calcareous sand with a Dmax between 0 and 4 mm, identified as Vinci sand, whose particle size distribution is shown in figure 1. This aggregate has a density equal to 2.62 kg / dm <3>.

Graphite is a natural graphite of the TIMREX M100 Mesh type with a carbon content of 94-98% and a grain size of less than 150 microns and is present in an amount equal to 30% with respect to the total weight of cement and graphite.

The water / cement ratio is equal to 0.69.

The mortar in the present example, with a consistency of moist earth, once applied as a filler for underground cable power lines, pressed and hardened, was tested and the values of density, thermal conductivity and mechanical resistance to compression, reported in the following table 4.

Example 3

A high conductivity (G-D) mortar was prepared with the composition shown in the following table 3,

Table 3

G-D

cement 265

Fine-grained aggregates 1326

graphite 177

Water 231

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, the fine-grained aggregates are a calcareous sand with a Dmax between 0 and 4 mm, identified as Vinci sand, whose particle size distribution is shown in figure 1. This aggregate has a density equal to 2.62 kg / dm <3>.

Graphite is a natural graphite of the TIMREX M100 Mesh type with a carbon content of 94-98% and a grain size of less than 150 microns and is present in an amount equal to 40% with respect to the total weight of cement and graphite.

The water / cement ratio is equal to 0.87.

The mortar in the present example, with a consistency of moist earth, once applied as a filler for underground cable power lines, pressed and hardened, was tested and the values of density, thermal conductivity and mechanical resistance to compression, reported in the following table 4.

Table 4

Density dry Quantity Thermal conductivity

[Kg / m31 of graphite [% 1 7 days [W / mKl Re 28 days [Mpal

G4t 2103 0 1.4 34

G-D 1793 40 2.2 7

G-D-20 1827 20 1.8 11

G-D-30 1951 30 2.3 14

The comparison mortar G-0 was made by mixing 450 kg / m <3> of cement, 1350 kg / m <3> of fine-grained aggregates and 200 kg / m <3> of water, in the absence of graphite. The cement and the fine-grained aggregates are the same compounds used for the mortars according to the present invention. All the products were evaluated with the same consistency (damp earth), therefore the quantities of cement were varied according to the quantity of graphite (which absorbs different water).

Figure 2 also shows how, with the same graphite content, a compaction of the mortar by pressing leads to a better thermal conductivity than the corresponding product obtained by vibration.

From the previous comparison it is evident that the mortars according to the present invention have an optimal combination of physical properties which allow to obtain a mortar which, at the same time, is characterized by

an excellent thermal conductivity that allows an optimal use as filling / housing of power lines in underground cables;

a reduced, but sufficient mechanical resistance that makes the mortar, once hardened, easily removable, to allow intervention on cables or transmission lines for extraordinary maintenance works;

a low workability, understood as a good ability to be modeled.

Claims (10)

CLAIMS 1. Mortar with high thermal conductivity consisting of a mixture of cement, water, fine-grained aggregates and graphite, where the amount of graphite varies from 20 to 40% by weight, preferably from 20 to 30% by weight, with respect to weight total of cement and graphite and having a water / cement ratio ranging from 0.5 to 1.2, preferably from 0.75 to 0.9. 2. High conductivity mortar according to claim 1, where the mortar comprises an amount of cement ranging from 260 to 400 kg / m <3>, more preferably from 300 to 370 kg / m <3>, even more preferably from 315 at 361 kg / m <3>. High conductivity mortar according to one or more of the preceding claims, where the mortar comprises an amount of water ranging from 200 to 300 kg / m <3>, preferably from 210 to 220 kg / m <3>. 4. High conductivity mortar according to one or more of the preceding claims, where the mortar comprises a fine-grained aggregate in an amount ranging from 1200 and 1600 kg / m <3>, preferably from 1250 to 1350 kg / m <3> and with a Dmax between 0 and 4 mm, preferably a calcareous silica aggregate or a calcareous sand. 5. High conductivity mortar according to one or more of the preceding claims, where the mortar has a thermal conductivity higher than 1.8 W / mK, preferably higher than 2.2 W / mK, and, in the dry state, a mechanical resistance to compression lower than 14 MPa, preferably ranging from 2 to 14 MPa and, always in the dry state, a specific mass or density ranging from 1750 to 2000 kg / m <3>. 6. High conductivity mortar according to one or more of the preceding claims, where the cement is a CEM I or III cement, preferably a CEM I 52.5 cement or a CEM III 42.5 cement, the fine-grained aggregate is a silico-limestone aggregate with a Dmax between 0 and 4 mm, and graphite is a natural graphite with a carbon content of 94-98% and a particle size of less than 150 microns of the TIMREX M100 Mesh type. 7. High conductivity mortar according to one or more of the preceding claims, where the mortar has a consistency of moist earth. 8. Use of a mortar with high thermal conductivity, which consists of a mixture of cement, water, fine-grained aggregates and graphite, where the amount of graphite varies from 20 to 40% by weight, preferably from 20 to 30% by weight , with respect to the total weight of cement and graphite and having a water / cement ratio ranging from 0.5 to 1.2, preferably from 0.75 to 0.9, as a filling material for underground cable power lines. Use of a high thermal conductivity mortar according to any one of claims 2 to 7, as filling material for underground cable power lines. 10. Use according to claims 7 or 8 where the mortar is applied by pressing.