ITTO20120952A1 - CEMENTITIOUS MIXTURE FOR THE USE OF CONCRETE IN THE WET LAND. - Google Patents

Description

DESCRIPTION of the industrial invention entitled: "Cement mixture for use in damp earth concrete"

DESCRIPTION

The present invention refers to the technical field of cement mixtures for use in a "damp earth" concrete, typically used for the construction of artifacts such as curbs, self-locking, large pipes and large boxes and channels in SCC.

The main characteristics sought in the development of the relative formulations are (a) the rapidity of dismantling, as well as (b) the development of high mechanical strengths in the short term. Thanks to these characteristics it is possible, in fact, to significantly speed up the shifting of the formwork, consequently favoring an increase in production per work shift and a rapid clearing of the warehouses, as well as allowing a rapid response to the needs of the market, with a response time of 1-2 days.

Moreover, the cement mixtures - based solely on Portland cement - traditionally used in the above-mentioned context have a rather long curing time of the order of 28 days.

In order to obviate the aforementioned drawback of the prior art, the subject of the present invention is therefore a cement mixture, comprising the ingredients in the percentages indicated in claim 1 below. It goes without saying that the sum of the percentage values of the aforementioned ingredients of a specific additive formulation (as well as those of any additional ingredients, such as calcium oxide which can be present in an amount up to 4%) must be 100%. Unless otherwise indicated, these percentages are expressed by weight and refer to the formulation as a whole. It should also be noted that calcium sulfate can be present in any of its forms, namely gypsum, anhydrite and hemihydrate, in particular anhydrite.

The cement mixture of the invention could still contain one or more of the following ingredients in the quantities indicated:

- calcareous filler in quantities of less than 30%, - fly ash in quantities of less than 20%, - granulated slag from blast furnaces in quantities of less than 20%,

- silica fumes in quantities lower than 10%, and - electrofilter dust or by-pass dust in quantities lower than 30%.

The mixture object of the invention is characterized by a considerable development of mechanical resistance over time, essentially in "damp earth" application conditions, or in the case in which the amount of water added to form the concrete is modest. On the contrary, the same mixture has a slower development of resistance in applications that require the addition of larger quantities of water.

A prerogative of the cementitious mixture of the invention with respect to a mixture based solely on Portland cement consists in achieving the performance characteristics necessary for the transport and installation of the related concrete products after only 7 days of curing, instead of 28, thus allowing timeliness of delivery in the case of urgent orders.

Therefore, further objects of the present invention are a concrete comprising: - a cementitious composition of the aforesaid type in a quantity comprised between 230 and 500 kg / m <3>,

- aggregates in quantities between 1800 and 2200 kg / m <3>, e

- water in a quantity between 60 and 250 l / m <3>, as well as a process for the production of a “damp earth” product by casting a concrete of the type just indicated.

For companies producing "wet earth" products that have already started, or in possession of equipment useful for large productions, the main advantage is therefore to create a more efficient production cycle capable of minimizing waste; the very short and short-term development of high resistances can be exploited to minimize inventory assets and simplify the introduction of new products. With this speed of removal and delivery of the products, it is in fact conceivable to serve the customer ad hoc, on the basis of particular requests and high quantities, without having to have a sufficient stock in the yard to satisfy the needs of the market.

The ability to respond to customer requests in a very short time, with very small production batches and with the solution that best suits their needs, can therefore constitute an indispensable competitive advantage.

For an emerging company, the use of the cementitious mixtures of the invention allows to reduce the costs for the preparation of new equipment useful for production, reducing them to the bone and allowing the prefabricator to produce only what is actually necessary, eliminating all the superfluous.

It is also possible to reduce prototyping / validation times of products, validation of the production cycle, modification of products and immediate production parameters. This change in production approach brings with it not only advantages for the customer / prefabricator relationship, but above all a more efficient exploitation of energy resources aligned with the actual needs of the market, effectively eliminating the movement of raw materials and personnel, and consumption. of energy, which are normally used to satisfy warehouse and storage needs and not those of the market.

On the other hand, mixtures based solely on sulfoaluminate clinker are characterized by extreme rapidity in the development of mechanical strengths. However, the costs associated with such mixtures would not be compatible with the economic needs of the prefabrication industry.

Advantageously, the lithium salt used in the mixtures of the invention can be a carbonate, a nitrate or a mixture thereof, while the retardant can be based on organic acids, such as for example citric, tartaric, gluconic acids, their salts, such as for example sodium citrate, sodium tartrate, etc., or inorganic compounds, such as for example boric acid, sodium borate, boric anhydrite.

Preferably, the sulphoaluminate clinker used in the mixtures of the invention meets one or more of the following conditions:

- a C4A3S content> 20%;

- a C2S content <70%, preferably equal to 20%;

- an overall content of C4AF, CaO, MgO, C2AS and C5S2S <15%, preferably <10%;

- an overall content of CaCO3 and MgCO3 <15%, preferably <10%; And

- an overall content of pozzolan, slag and fly ash, silica smoke, electrofilter dust, by-pass dust <50%, preferably 0%.

In particular, the mixture of the invention includes:

- sulphoaluminate clinker in a quantity ranging from 20 to 40%, preferably 28%,

- calcium sulphate in an amount of between 6 and 15%, preferably 8%,

- lithium salts in an amount ranging from 0.1 to 0.3%, preferably 0.2%,

- retardant in an amount comprised between 0.2 and 0.4%, preferably 0.3%, e

- Portland cement in an amount ranging from 60 to 70%, preferably 64%.

In preferred embodiments, a concrete produced using the mixture of the invention comprises:

- this mixture in a quantity between 280 and 330 kg / m <3>,

- aggregates in quantities between 1850 and 1950 kg / m <3>, in particular 1900 kg / m <3>, and

- water in a quantity between 100 and 150 l / m <3>.

A concrete produced using the mixture of the invention may further comprise a filler in an amount of up to 500 kg / m <3>, as well as a fluidifier in an amount of between 0.5 and 3%, preferably between 1.5 and 2.0. %, of the total mass.

Examples of implementation of the invention are now provided for illustrative and non-limiting purposes only.

EXAMPLES

A cement mixture according to the invention was prepared, a traditional one based on Portland cement and one based solely on sulphoaluminate clinker, which have the compositions shown in Table I below.

TABLE I

PORTLAND SULFALUMINATE INVENTION

Clinker sulfur-% 32 81.6

aluminized

Anhydrite% 8 18

Port cement-% 59.6 100 land II A-LL

42.5 R

Li2CO3% 0.1 0.1

Citric acid 0.3 0.3%

The three mixtures of Table I were used to produce “damp earth” concrete using the ingredients and quantities shown in Table II below. This table also shows the data obtained by subjecting the concretes thus obtained to a test to determine the indirect tensile strength according to the NT Build 427 standard.

TABLE II

PORTLAND SULFALUMINATE INVENTION

Mixture kg / m <3> 330 330 330 H2O kg / m <3> 100 100 100 Fluidifikg / m <3> 1,5 1,5 1,5 cante

Aggregates kg / m <3> 1900 1900 1900

Indirect tensile strength

(cylinder 10 mm x

10 mm)

RES. 2H N / mm <2> - 0.7 1.1 RES. 4H N / mm <2> - 1.3 1.4 RES. 6H N / mm <2> 0.3 1.5 1.6 RES. 24H N / mm <2> 1.7 2.0 2.0 RES. 28 GG N / mm <2> 3.8 4.0 4.2 The three mixtures in Table I were used to produce “damp earth” concrete using the ingredients and quantities shown in Table III below. This table also shows the data obtained by subjecting the concretes thus obtained to a test to determine the indirect tensile strength according to the UNI EN 196-1 standard.

TABLE III

PORTLAND SULFALUMINATE INVENTION

Cement mixture kg / m <3> 500 500 500 H2O kg / m <3> 250 250 250 Additive fluidifikg / m <3> 0,8 0,8 0,8 cante

Normal sand kg / m <3> 1900 1900 1900

Compressive strength on (mortar

4x4x16 cm)

RES. 2H N / mm <2> - 20 -RES. 4H N / mm <2> - 25 2 RES. 6H N / mm <2> - 30 10 RES. 24H N / mm <2> 15 35 30 RES. 28 days N / mm <2> 45 50 50

As can be seen from the data shown in Tables II and III, the mixture of the invention is decidedly advantageous compared to the conventional one based solely on Portland cement in "damp earth" applications, since it develops a short-term resistance more quickly. At the same time, this mixture has performances comparable to that based solely on sulphoaluminate clinker, which is, moreover, so expensive as to be practically unusable.

Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to what is described purely by way of example, without thereby departing from the scope of the invention as defined in the attached claims.

Claims (2)

CLAIMS 3. Mixture according to claim 1, wherein said calcium sulfate is present in the form of anhydrite. 4. Mixture 1 or 2, further comprising calcium oxide in an amount up to 4% referred to its sum with the amounts of sulphoaluminate clinker, calcium sulphate, lithium salts and retarder. 5. Mixture according to any one of the preceding claims, wherein said sulphoaluminate clinker satisfies one or more of the following conditions: - a C4A3S content> 20%; - a C2S content <70%, preferably equal to 20%; - an overall content of C4AF, CaO, MgO, C2AS and C5S2S <15%, preferably <10%; - an overall content of CaCO3 and MgCO3 <20%, preferably 0%; And - an overall content of pozzolan, slag, fly ash, silica smoke, electrofilter dust, by-pass dust <50%, preferably 0%. 1. Cement mixture comprising: - sulphoaluminate clinker in a quantity between 20 and 40%, - calcium sulphate in a quantity between 6 and 15%, - lithium salts in a quantity between 0.1 and 0.3%, - retardant in a quantity between 0.2 and 0.4%, e - Portland cement in quantities between 60 and 70%. 2. Mixture according to claim 1, comprising: - sulphoaluminate clinker in a quantity of 28%, - calcium sulphate in a quantity of 8%, - lithium salts in an amount equal to 0.2%, - retardant in an amount equal to 0.2%, e - portland cement in an amount equal to 64%, 6. Concrete comprising: - a cement mixture according to any one of claims 1 to 5 in a quantity ranging from 230 to 500 kg / m <3>, - aggregates in quantities between 1800 and 2200 kg / m <3>, e - water in a quantity between 60 and 250 l / m <3>. 7. Concrete according to claim 6, comprising: - a cement mixture according to any one of claims 1 to 5 in an amount ranging from 280 to 330 kg / m <3>, - aggregates in quantities between 1850 and 1950 kg / m <3>, e - water in a quantity between 100 and 150 l / m <3>. Concrete according to claim 6 or 7, further comprising a fluidifier in an amount comprised between 0.5 and 3%, preferably between 1.5 and 2.0%, of the total mass. 9. Production process of a “damp earth” product which involves casting a concrete according to any one of claims 6 to 8.