FR2474479A1 - MORTAR FOR COATING AND BUILDING WITH DELAYED GRIP - Google Patents

Abstract

Mortar contains, based on its binder content, 1-5% of an additive which contains 10-50% of a setting retardant and 1-10% of an air-entraining agent. Thanks to such an additive, the mortar is modified such that it has an extended workability time but hardens rapidly after use.

Description

The subject of the invention is a mortar to be coated and to be built, the setting time of which is sufficiently extended so that it can be delivered to the site from a concrete plant and be kept, ready to use, for about two days.

Different processes are used to prepare mortar for masonry work in bricks, recons stones
titled or made of cement facing elements.

In the classic process of making on site, the mortar is prepared continuously using a small concrete mixer. the site is supplied with sand, mostly special masonry sand, as well as cement, to which water and possibly an additive are added.

In the prefabricated mortar, the site receives a mixture prepared in advance, comprising sand, cement and powder additives. This product is supplied in bags or silos. In the case of silos, it is possible to mount a concrete mixer under the unloading hopper in which water is added for mixing. It is thus possible to produce, as in the case of site preparation, mortar according to temporary needs. as the prefabricated mixture contains binders, it must not get wet during storage.

 Finally, in the case of plant mortar, the site is supplied with a wet mortar, fully prepared and mixed, using a transport vehicle. As such transport can only be profitable if it conveys fairly considerable quantities to the site and if the same vehicle must be able to supply several sites during the same transport, it is essential to keep the mortar ready for use. use for a period of up to 48 hours, which is carried out using delay-setting additives. the method of making such a delay-setting mortar is known from Swiss patent NO 601 129. The delay-adjuvant proposed for the mortar described in this document is molasses. At the same time, the mortar is added with an aerating agent having the effect of giving the mortar, for a prolonged period, workability properties that are both good and durable. Finally, the mortar described has the property of starting to set as soon as it is laid, despite the delay-additive contained therein.

the process for delaying the setting of the cement is today a well-known technique. The delay time depends essentially on the dosage of the admixture, its nature, the temperature of the mortar during the delay time and the brand of cement used, as well as the dosage of cement and the water-cement ratio. For mortars to be coated and to be built, mixed binders are often used, in addition to pure Portland cement, forming so-called "elongated" or "mortar" mortars, for example Portland cement with hydraulic lime or fly ash.

It is also known that delay aids which contain sucrose, for example molasses, can lead, in the event of an overdose, to uncontrollable delays in setting.

In the extreme case, delays of more than four weeks can even be found. Maintaining the state of preparation for use and delaying the start of setting is only desirable for the mortar which is in the container used by the mason. In the joint, that is to say in a built situation, it is, on the contrary, necessary for the hardening process to undergo little delay, taking into account the resistance required of the walls and pillars in masonry or concrete blocks. This process can, however, be ordered free of error-free addition of chemically definable additives.

Another problem is that of the stability of the mortar during storage and its water retention capacity. hS adding an aerating agent, we can partially avoid sedimentation and exudation, ie separation between sand, binder and water. But when such mortars are used to join building bricks, it may nevertheless happen that, owing to the considerable absorption capacity of the bricks, they "suck" enough water from the mortar to make it impossible correct hydration of the binder. As soon as the water content of the mortar drops below the theoretical value necessary for the hydration of the binder, it is said that said mortar is "crossed out". The consequences are insufficient hardening after setting and a lack of adhesion. Likewise, the waterproofing of these mortars is considerably compromised. The corresponding masonry joints remain highly absorbent for a long time and enter the masonry leaks.

The object of the invention is therefore to avoid these drawbacks and to succeed in controlling the setting delay while regulating the cohesion of the wet mortar and its hydrological balance, in order to obtain correct hydration of the binder in the building mortar. At the same time, the impermeability of said mortar must be considerably reinforced by means of additives.

The basic composition of these mortars can correspond to different existing standards, for example cement mortar "C" or elongated mortar XV "according to Swiss standard SIA 113, or else" group 2 and 3 "mortars according to DIN standard. 1053.

 The invention is explained below using a few examples without limitation.

Example 1
A mortar composed of 38.2 Kg of Portland cement, 153 Kg of sand with grain size 0 to 6mm, 15.3 Kg of rock powder, is mixed with 23.385 Kg of water and prepared with 0.382 Kg of an additive . The latter consists of 20% sodium hexametaphosphate and 20% sodium gluconate, dissolved in 60% water. This additive, whose dosage was based on the weight of cement, hindered a setting delay of about 50 hours at a temperature of 200C.

Example 2
In a mortar composed of 9.2 Kg of Portland cement, 23 Kg of hydraulic lime, 161 Kg of sand with grain size 0 to 6mm and 16.1 Kg of rock powder, 25 Kg of water are added. mortar is mixed with 0.323 Kg of an additive composed as follows: 40% of a partially hydrolyzed starch, composed for example of 20% of monoeaccharides, 15% of disaccharides, 12% of trisaccharides and 53% of poly
higher order saccharides /; 20% potash; 10% of a cellulose ether; finally 5% of an aerating agent, all dissolved in 25% of water. The high concentration of salts prevents the swelling of the cellulose ether. Also, the additive is in the form of a dispersion. This adjuvant, dosed at 1% calculated on the proportion of hydraulic binders contained in the mortar, made it possible to obtain a delay in setting a virion 45 hours at 20 C. The aerating agent gives the mortar, after mixing, a proportion air pores of about 20%.

On the other hand, the cellulosic ether gives the mortar excellent workability and sufficient water retention power so that the mortar does not settle and that it can still hydrate normally, even in the presence of water-hungry materials. .

Example 3
A mortar according to the composition given in Example 1 is mixed with an additive of the following composition: 15% sodium heptogluconate, 20% potassium tetra-pyrophosphate, 10% of a cellulose ether, 10% of an alkaline or amino salt of a fatty acid as well as 4% of an aerating agent, in 41% of water. The result is a mortar with a setting delay of 48 hours at 200C. The content of air inclusions in this mortar is 22%. Thanks to the presence of cellulose ether, a very good thixotropy of the mortar is obtained.

The wet cohesion is sufficient for this mortar to also be used for plastering. The addition of salts of fatty acids or of an amino compound of these acids makes the mortar hydrophobic and therefore gives it an extraordinary waterproofness. This mortar is particularly suitable for grouting exposed bricks.

the cellulose ethers mentioned in the examples may be beech, for example, methyl, hydroxyethyl or hydro-propyl ethers. Thus, phenol-alkyl ethers or sulfated fatty alcohols are particularly suitable as aerating agents. Suitable alkali or amino acid fatty acid salts are, for example, sodium oleate or amine ethanol tristearate.

All of the mortars thus described reach strengths considerably higher than the minimum specifications contained in the standards after setting. The resistance of these mortars to frost is also very high, thanks to micro-inclusions of air.

Claims (7)

 CLAIMS.  1. Mortar for coating and building with a composition in accordance with standards, characterized in that it is modified by an additive so as to remain ready for use for a prolonged period, while hardening rapidly after its application, the additive being composed from 10% to 50% of an adjuvant with retardation of setting of the hydraulic binder and from 1% to 10% of an aerating agent generating air inclusions, while the proportion of said additive is from 1% to 5% of the content of mortars in binders. 2. Mortar according to 1 claim 1, characterized in that the element constituting the delay adjuvant is composed of condensed phosphates, such as pyrophosphates, polyphosphates or hexa-metaphosphates.  3. Mortar according to claim 1, characterized in that the retardant adåuvant consists of salts of polyhydroxycarbon acids such as gluconic acid or heptonic acid.  4. Mortar according to claim 1, characterized in that the retarding adjuvant consists of combinations of condensed phosphates and salts of poly-hydroxycarbon acids. 5. Cod fisherman according to claim 1, characterized in that the retarding adjuvant consists of a starch, partially or totally hydrolyzed.  6. Mortar according to claim 1, characterized in that the additive contains up to 15% of a cellulosic ether capable of swelling, which is in a finely dispersed form.  7. Nortier according to claim 1, characterized in that it is added with alkali or amino salts of fatty acids up to a proportion of 10%.