ITTO20120897A1 - MALTA FOR FILLING ROAD TRAINS. - Google Patents

Description

"Mortar for filling road trenches"

DESCRIPTION

The present invention refers to a mixture for CLSM mortar, in particular for filling road trenches.

In international technical literature, the acronym CLSM stands for Controlled Low Strength Materials, and is in particular used with reference to controlled-strength cement mortars with low binder content and high porosity, whose main use is the replacement of earth and mixed granules in the filling of road trenches in which underground utilities such as cable ducts, aqueducts, sewers are laid. More recently, CLSM mortars have also been used in massive fillings for structural works, such as retaining walls, bridge abutments and surface foundations.

It is known that traditional granular materials are subject to generating differential settlements both with respect to the stable masses present in the surroundings, and over time, complicating the laying operations and lengthening the general processing times. This is due to the objective difficulty of compacting these materials in trenches and excavations of reduced size compared to the surfaces on which the compacting vehicles are able to operate. Vice versa, during the laying phase, the CLSM mortars completely fill the excavation as they are fluid and do not require any tamping. Furthermore, immediately after their installation, they harden quickly acquiring those strengths and stiffnesses that allow the immediate completion of the subsequent construction operations.

However, the CLSM mortars used up to now have some disadvantages that have affected their diffusion, namely: (a) poor development of short-term strengths (1-2 days after casting); (b) excessive long-term stiffness and strength due to progressive hardening due to the continuous hydration of the cement over time.

In the long term, in fact, structural inhomogeneities are created between the CLSM mortar inside the trench and the natural material that is around it, which are associated with differences in permeability and thermal conductivity that can lead to the formation of structural defects in the works. Furthermore, the excessive mechanical strength and stiffness developed over time makes removal with traditional excavation machinery difficult, and makes it necessary to use burglary equipment, such as pneumatic hammers and the like.

The aim of the present invention is therefore to obviate the drawbacks highlighted above in the known art.

According to the invention, this purpose is achieved thanks to a mixture for mortar CLSM comprising water, aggregate and binder which is present in quantities less than 200 kg / m <3>, in which said binder is of the sulphoaluminate type and it has a C4A3S content between 30 and 70% and an overall content of gypsum, anhydrite and calcium sulphate hemihydrate <20%.

Such a mixture is of particularly advantageous use since it is characterized by rapidity in the development of short-term resistances and a low long-term increase of such resistances.

Advantageously, the binder used in a composition of the invention satisfies one or more of the following conditions:

- a C2S content <50%, preferably equal to 20%;

- an overall content of C4AF, CaO, MgO, C2AS and C5S2S <15%, preferably <5%;

- an overall content of CaCO3 and MgCO3 <20%, preferably 0%;

- an overall content of pozzolan, slag and fly ash <50%, preferably 0%;

- an overall content of organic acids <1.5%, preferably 0.5%; And

- an overall content of lithium salts <0.5%, preferably 0%.

Preferably, a mixture according to the invention comprises:

- sulphoaluminate binder in quantities between 50 and 200 kg / m <3>,

- aggregate in a quantity between 1200 and 1800 kg / m <3>,

- water in a quantity between 200 and 400 kg / m <3>, and - aerating additive in a quantity between 0.1 and 1 kg / m <3>.

This mixture can also include a filler in an amount up to 500 kg / m <3>.

Examples of realization of the invention are now provided for illustrative and non-limiting purposes with the aid of the attached drawing in which:

the single figure is a diagram illustrating the development over time of the mechanical strength of a mixture of CLSM mortar according to the invention and a comparison mixture.

EXAMPLES

A mixture of CLSM mortar according to the invention and a mixture of comparative CLSM mortar were prepared having the compositions reported in the following Table I. This table also shows the data relating to the temporal development of the respective mechanical resistance and to the times of the setting and hardening process.

TABLE I

TRADITIONAL MIX IN-TIONAL MIX VENTION

Cement dosage

kg / m <3> 160 -Portland II B-LL

Binder dosage

kg / m <3> - 100 sulfoaluminate

H <3>

2O kg / m 245 220 Air-entraining additive kg / m <3> 0.5 0.5 Sand kg / m <3> 1300 1500

RES. 7H kPa - 150 RES. 24H kPa 520 241 RES 5 GG kPa 1196 272 RES. 28 days kPa 1596 391 RES. 90 days kPa 1863 413 RES. 360 days kPa 4250 450

Air content in

% 18 23

globata

Loss of labor min 480 160 bility

Start setting min 660 465 End setting min 900 705

As can be seen from the data reported in table I, the mixture of the invention is decidedly advantageous with respect to the conventional one, since it develops a short-term resistance more rapidly. Moreover, after a transient period, this resistance remains substantially stable tending to a rather low asymptotic value, while the resistance of the conventional mixture continues to increase significantly with the passage of time even in the long term.

Without being tied to a specific theory, it can be asserted that the mixtures made with traditional binders (Portland binders) do not reach the performance of those of the invention, since, in the case of very low doses of cement, the mortar does not harden in the first 24-36h, while, if the cement dosage is considerably increased, very high mechanical strengths are achieved in the long term.

Naturally, the principle of the invention remaining the same, the details of construction and the embodiments may vary widely with respect to those described purely by way of example, without thereby departing from the scope of the invention as defined in the attached claims.

Claims (9)

CLAIMS 1. Mix for mortar CLSM comprising water, aggregate and binder in quantities less than 200 kg / m <3>, in which said binder is of the sulphoaluminate type and has a C4A3S content between 30 and 70% and an overall content of gypsum, anhydrite and calcium sulphate hemihydrate <20%. 2. Blend according to claim 1, wherein said binder has a C2S content <50%, preferably equal to 20%. 3. Blend according to any one of the preceding claims, wherein said binder has an overall content of C4AF, CaO, MgO, C2AS and C5S2S <15%, preferably <5%. 4. Blend according to any one of the preceding claims, wherein said binder has an overall content of CaCO3 and MgCO3 <20%, preferably 0%. 5. Mixture according to any one of the preceding claims, wherein said binder has an overall content of pozzolan, slag and fly ash <50%, preferably 0%. 6. Blend according to any one of the preceding claims, wherein said binder has an overall content of organic acids <1.5%, preferably 0.5%. 7. Blend according to any one of the preceding claims, wherein said binder has an overall content of lithium salts <0.5%, preferably 0%. 8. Mixture according to any one of the preceding claims, comprising: - sulphoaluminate binder in quantities between 50 and 200 kg / m <3>, - aggregate in a quantity between 1200 and 1800 kg / m <3>, - water in a quantity between 200 and 400 kg / m <3>, and - aerating additive in a quantity between 0.1 and 1 kg / m <3>. 9. Blend according to claim 8, further comprising a filler in quantities up to 500 kg / m <3>.