CS199426B1 - Additive for cement mixtures and method of producing the same - Google Patents

Description

Additives of bentonite are known to increase the thixopropy of fresh cement mixtures and to increase the water tightness of the hardened cement mixtures.

However, the addition of bentonite undesirably deteriorates the processability of the fresh mixtures if the same aqueous coefficient is maintained over the comparison mixture without the additive. If a blend of the same processability as my comparative blend without additive is made with the bentonite additive, this is only possible as a result of an undesirable increase in the aqueous synergism and / or the additive. amount of mixing water.

. Thus, the addition of bentonite, especially at amounts exceeding 2 to 3% by weight of cement, reduces the initial and final strengths of cementitious mortars and concretes and increases their shrinkage.

Some improvement in the processability or reduction of the amount of mixing water can be achieved by adding a plasticizing agent based on the salts of ligninoleic acid to the bentonite. A disadvantage of lignosulfonic acid salt additives is that they reduce the initial. mortar and concrete strength. Increasing their dose above a certain level, typically 0.20 to 0.25% of the weight of the cement, will cause their retarding effects to an undesirable extent.

The above-mentioned disadvantages are eliminated by the cementitious additive according to the invention, characterized in that it consists of 100 parts by weight of bentonite, containing at most 20% of particles in BW than 45WW and 2 to 30 parts of a dispersant consisting of a condensation product of formeldehyde and aromatic sulfo acid. and / or sulfonic melamine formaldehyde resin.

The additive according to the invention can be prepared by grinding the dried bentonite in the presence of a dried formaldehyde condensation product with an aromatic aulfoacid and / or an eulfonated melamine-formaldehyde nutrient until the milled mixture has a fineness such that at most 20% of its particles are larger than 45%. the product acts as a grinding intensifier.

The milling can be carried out, for example, by a discontinuous method in a ball mill or by a continuous epphisob in a vibratory mill.

Example 1

The following mortars were produced with the SPC 325 cement according to the procedure specified in ČSN 73 2117:

a comparative mortar, denoted by (a) according to the quoted standard required in / o equal to 0.5;

- mortar marked b) in which 5% by weight of cement was replaced by an additive according to the invention, consisting of ground dried bentonite so fine that it contained no more than 10% by weight of particles larger than cm, with 100 parts by weight of bentonite accounting for 10% parts by weight of sulfonated melamine-formaldehyde resin. When incorporating the same process (measured as plasticity according to CSN 72 2441 No. 4 to 9) as the reference mortar without additive, it was not necessary to increase the water efficiency above 0.5;

- mortar, designation c), in which 5% by weight of cement has been replaced by dried bentonite, ground to a fineness containing more than% of particles greater than 45 <* · β. In order to have the same workability as the mortars labeled a and b), it was necessary to increase the water efficiency to 0.58.

The results measured on eu mortars are given in the following table. no. First

As can be seen from the results shown in Table 1, mortar b) contains an additive according to the invention which has neither deteriorated strength nor creasing relative to the comparative mortar, thus avoiding the disadvantages of using bentonite alone.

Instead of the sulfonated melamine-formaldehyde resin, it is possible to use a formaldehyde condensation product with an aromatic aulfoacid, for example sodium dinaphthalmethane disulfonate, or a combination thereof.

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199426 ^: · .- - 4 Example 2

Two concretes were made, comparative and β additive according to the invention, consisting of dried bentonite, ground, 10% by weight of dried and laminformaldehyde resin to a fineness such that the additive had no more than 20% by weight of particles larger than 45 µm.

The composition of the concrete mix, the compressive strength and the watertightness of the concrete are given in Table 2 below.

The test specimens - 20 cm crushed cats for testing the compressive strength and 20 x 20 x 12 mm for watertightness testing - were compacted by vibration and treated for the first 7 dhi in humid air (above 90% relative humidity of about 20 ° C), then into the investigation, ie within 28 days of manufacture, were stored in dry air.

TabuTka 2

entry comparative concrete concrete with an additive according to the invention • ò · ® Λ § ?. 'o m «A O o> S 8 cement SPO 325 300 285 river aggregates, frakeia 0/4 mm 950 • 950 river aggregates, frakeia 4/16 mm 943 943 an additive according to the invention «· 15 Water 187 181 consistency of the bet-mixture 5,3 cm eadnutí kuž. 6,5 cm eadnutí kžeTa concrete properties after 28 dnioeh compressive strength (MPa) 20 22.5 Water overflowed at pressure (MPa) 0.4 MPa 1.2 MPa Degree of watertightness Bsn 73 1321 61 9b V2 8 V 8

-5- 199426

The additive according to the invention is suitable for substantially increasing the watertightness of mortar and concrete without adversely affecting their strength and shrinkage. It is preferably used for the production of waterproof plasters, even those which are mechanically applied, or other cementitious mixtures, which may also contain other conventional components, for example pozzolan, preferably in the form of flying ash, even ground, lime and the like.

Object of the invention

Claims (2)

An additive for cementitious compositions comprising 100 parts by weight of bentonite containing not more than 20% of particles larger than 45 µa and 2 to 20 parts of a dispersant consisting of a condensation product of formaldehyde and an aromatic sulfoacid and / or a sulfonated melamine-formaldehyde resin. 2. A process according to claim 1, wherein the dried bentonite is ground in the presence of a dried formaldehyde condensation product. and an aromatic sulfoacid and / or sulfonated melamine-formaldehyde resin until the milled mixture has a fineness such that at most 20% of its particles are greater than 45 µm.