RU2443648C2 - Complex additive for concrete mixture - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: complex additive for a concrete mixture contains, wt %: Melflux 265IF - 50-75, polyethylene glycol -PEG 2000 - 25-50.

EFFECT: preservation and improvement of technological properties of concrete mixture, higher compression strength of cement stone and concrete with more rational use of the plasticising additive.

3 tbl, 1 dwg

Description

The invention relates to compositions of complex additives for concrete mixtures used for the production of concrete, reinforced concrete products and in monolithic construction.

Polycarboxylate-based highly effective plasticizing additives are known which have a high plasticizing-water-reducing effect in concrete mixtures. The high efficiency of chemical additives based on polycarboxylates is explained by the chemical structure of molecules and their mechanism of action in cement systems. Molecules of polycarboxylate plasticizers have a main chain (base) with negative charges, which is adsorbed on a cement particle and uncharged side chains (figure 1). It is the side chains that create the adsorption volumetric protective shell around the particles of the solid phase, preventing the aggregation of cement particles and facilitating their mutual steric repulsion. Cement particles with such molecules on the surface are always at a certain distance from each other, which provides increased mobility of the mixture [Kaprielov S.S. Modified concretes of a new generation: reality and perspective / S.S. Kaprielov, V.G. Batrakov, A.V. Sheinfeld // Concrete and reinforced concrete. - 1999. - No. 6. - S.6-10; Usherov-Marshak A.V. Additives in concrete: progress and problems / A.V. Usherov-Marshak // Building materials. - 2006. - No. 10. - S.8-12].

Due to the above features, polycarboxylate plasticizers are highly effective plasticizing additives for cement and other systems. The effectiveness of their action is expressed in relatively low optimal dosages, high water-reducing effect, reduced sensitivity to the type and composition of cement, long-term preservation of the properties of the concrete mixture and increased connectivity, the possibility of using self-compacting concrete mixtures [Batrakov V.G. Modifiers of concrete: new opportunities and prospects / V.G. Batrakov // Building materials. - 2006. - No. 10. - C.4-7; Nesvetaev G.V. Technology of self-compacting concrete / G.V. Nesvetaev // Building materials. - 2008. - No. 3. - S.24-28]. The disadvantage of polycarboxylate plasticizers is their relatively high cost.

The purpose of the invention is the development of compositions of a complex (binary) chemical additives, ensuring the preservation and improvement of the technological properties of concrete mixtures and physico-mechanical characteristics of concrete with a more rational use of plasticizing additives on a polycarboxylate basis due to its joint use with cheaper and more affordable chemical raw materials as part of a complex additives.

To achieve this goal, the following raw materials were used. In the form of a polycarboxylate plasticizer, Melflux 265 IF was used. An additional chemical reagent used in conjunction with Melflux was selected polyethylene glycol (PEG 2000) with a molecular weight of 2000, which has the same chemical structure as the side chains of the Melflux hyperplasticizer (figure 2).

Figure 2 - The structural formula of the molecule of polyethylene glycol (PEG 2000).

The choice of this chemical reagent is due to the fact that, as shown earlier, polycarboxylates are polymers that include a basic carboxyl-containing chain represented by methacrylic acid and side polyethylene oxide (polyethylene glycol) chains introduced into these macromolecules. From theoretical assumptions it follows that the addition of polyethylene glycol instead of part of the polycarboxylate will allow you to replace part of the side polymer chains involved in creating the steric repulsive effect and thereby save the dosage of a more expensive polymer with maximum preservation of their effectiveness in cement systems.

The effectiveness of the developed complex chemical additives was tested on cement paste and stone, as well as on concrete mixtures and concretes. Concrete mixtures were prepared using Portland cement M500 (GOST 10178), quartz sand with M _cr = 2.1 (GOST 8736), and crushed granite crushed stone. 5-20 mm (GOST 8267). The mobility of concrete mixtures was evaluated by the standard cone draft (GOST 10181), the strength of concrete was determined on samples of 10 × 10 × 10 cm cubes, hardened under normal conditions (GOST 10180).

The total amount of the complex additive Melflux + PEG 2000 was taken constant and equal to 0.37; 0.5; 0.75 and 1% by weight of cement. The amount of introduced PEG 2000 ranged from 25 to 75% in the composition of the complex additives. The Melflux + PEG 2000 complex was introduced into the cement paste in the form of an aqueous solution.

During the tests on the cement test, rational dosages of the complex additive Melfux + PEG 2000 and the optimal ratio between these components, providing the maximum water-reducing effect, were determined. The water-reducing effect was determined by reducing the water consumption as a percentage of the control composition, with a constant rheological characteristic, estimated by the size of the spread of cement paste, which was 13-14 cm by Suttard viscometer.

The results of determining the water-reducing effect of the Melflux + PEG 2000 additive are presented in Table 1. As can be seen from the table, for each dosage of the complex Melflux + PEG 2000 additive, the optimal ratio of components was established, providing the maximum water-reducing effect, which is slightly less compared to the water-reducing effect that occurs when introducing pure Melflux. So, with the introduction of the complex additive Melflux + PEG 2000 in an amount of 0.37% by weight of cement, the maximum water-reducing effect is observed when replacing 25% Melflux, at 0.5-25%, 0.75-50%, 1-50%, respectively.

Thus, by replacing part of the Melflux polycarboxylate plasticizer with PEG 2000, the effect of water reduction in cement systems can be achieved, which is close in value to the effect achieved using pure polycarboxylate.

The data on the assessment of the effect of the complex (binary) additive on the physicomechanical properties of cement stone (table 2) showed that the use of the binary additive Melflux + PEG 2000, in which a part of Melflux is replaced, does not lead to a decrease in strength compared with the use of the Melflux monoadditive, the same total dosage, despite an insignificant decrease in water-reducing action. This effect is observed when using all the studied dosages of complex (binary) additives from 0.37 to 1% by weight of cement.

Thus, the use of the proposed complex additives, including Melflux 265 IF and PEG 2000, makes it possible to more rationally use a polycarboxylate plasticizer due to the replacement of part of it with cheaper and affordable chemical raw materials, while maintaining their effectiveness in cement systems and improving the properties of cement stone and concrete.

Claims (1)

A comprehensive additive for concrete mix, including the Melflux 265 IF polycarboxylate plasticizer, characterized in that, in order to more rationally use the polycarboxylate plasticizer, Melflux 2651F, part of it is replaced by cheaper and more affordable raw materials, polyethylene glycol - PEG 2000 with preservation of their effectiveness and improving the properties of cement stone and concrete in the following ratio of components, wt.%:
Melflux 2651F 50 ... 75 PEG 2000 25 ... 50

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