RU2484036C1 - Complex organic additive for inhibiting alkaline corrosion - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the industry of construction materials and can be used in making concrete on an aggregate which contains active reactive silica. The complex organic additive contains superplasticiser S-3 and is characterised by that the superplasticiser S-3 is used in amount of 0.3% of the mass of cement and additionally contains citric acid in amount of 0.05% of the mass of cement.

EFFECT: preventing reaction of alkali in the cement with silica in the aggregate and controlling longevity of the concrete mixture.

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Description

The invention relates to the building materials industry and can be used in the production of concrete on aggregate containing active reactive silica.

Known additives to slow down the reaction of alkali cement and silica aggregate - lithium salts: LiNO ₃ , LiCO ₃ . (1. New observation on the mechanism of litium nitrate against alkali silica reaction (ASR). Feng X., Thomas MDA, Bremner TW, Folliard KJ, Fournier B. Cem. And Concr. Res. 2010. 40. No. 1. P .94-101. 2. Experimental investigation of the mechanisms by which LiNO ₃ is effective against ASR. Tremblay C., Berube MA, Fournier B., Thomas MD, Folliard KJ Cem. And Concr. Res. 2010. 40. No. 4. P.583-597. 3. Alkali-silica reactions of mortars produced by using waste glass as fine aggregate and admixtures such as fly ash and Li ₂ CO _3. Topcu Ilker Bekir, Boga Ahmet Raif, Bilir Turhan. Waste Manag. 2008 28. No. 5. P.878-884. 4. Rosenthal, HK Protection of concrete on a reactive aggregate against internal corrosion by lithium compounds / N.K. Rozental, G.V. Chechny, G.V. Lyubarskaya, A.N. .Rozental. // Building materials. - No. 3. - 2009. - P.68-71.)

Lithium salts are introduced either with mixing water, or hardened concrete is treated in a solution of lithium salt under the influence of electric current. It is believed that the lithium-containing low-calcium gel formed on the surface of active silica, which has a dense and rigid structure, is unable to absorb moisture and swell.

The main disadvantage of the known additives is the high cost and scarcity of lithium compounds, and therefore they have limited use.

The closest technical solution adopted for the prototype is an organic additive superplasticizer C-3, which is an oligomer of naphthalene-formaldehyde type. Additive C-3 at a dosage of 0.7% by weight of cement provides a reduction in expansion strains to 0.0052% at the required 0.1% according to GOST 8269.0-97 (4. Morozova, NN The problem of alkaline corrosion of concrete in the Republic of Tatarstan and Ways of its solution / N.N. Morozova, V.G. Khozin, A.I. Mateyunas, and others // Izvestia KGASU, 2005. - No. 2. - P. 58-63. 5. Morozova, N.N. .Internal corrosion of concrete on aggregates of river deposits in Tatarstan / N.N. Morozova, A.I. Mateyunas, V.G. Khozin and others // Building materials, 2005. - No. 11. - S.27-28).

The disadvantage of C-3 additive is its high cost and impact on the survivability of the concrete mix: it can extend or reduce the setting time depending on the type of cement, which negatively affects the efficiency of production of building materials.

The aim of the invention is to prevent the reaction of alkali cement with silica aggregate and regulation of the survivability of the concrete mixture. The goal is achieved due to the fact that the complex organic additive contains C-3 superplasticizer, characterized in that C-3 superplasticizer is used in an amount of 0.3% and additionally contains citric acid in an amount of 0.05% (by weight of cement).

The dosage of citric acid should be selected depending on the properties of the cement used, namely the setting time. Citric acid plasticizes and accelerates the setting of cement systems at low dosages of 0.015-0.05% or extends the setting time at dosages of 0.06-0.1%. The additional introduction of citric acid additives in an amount of 0.05% allows to reduce the consumption of C-3 to 0.3% (by weight of cement).

To measure the expansion strains of the samples, a standard Le Chatelier ring was used, which is used to measure changes in cement volume according to GOST 30744-2001. To accelerate silica-alkaline reactions, an additional 3% sodium hydroxide by weight of a binder mixed with water was added to the mixture.

The following materials were used for the experiment: CEM I 42.5 N (CJSC Belgorodsky Cement) with an alkali content of 0.55% crushed natural perlite from the Mukhor-Talinsky deposit (fraction 0.63-25 mm), superplasticizer C-3, lemon acid.

The test results are shown in Fig. 1.

Studies have shown that samples with the addition of C-3 practically did not expand in the observed period of time, which is confirmed by the literature data [4, 5] on the “suppression” of the reactions of aggregate silica with alkalis by the addition of C-3.

The results of the experiment showed that the proposed complex additive C-3 + citric acid reduces the expansion deformations of the cement-perlite mixture closed with a 3% sodium hydroxide solution: during the first 2 weeks the distance between the rods was insignificant (about 0.5 mm). By 28 days, the difference between the ends of the rods in these samples was 1 mm.

The proposed additive can improve the following properties:

- by reducing the consumption of expensive C-3 additives (up to 0.3%) and replacing part of it with citric acid - reduce the cost of the additive;

- C-3 superplasticizer can shorten or extend the life of a concrete mix depending on the type of cement. In such cases, citric acid, acting as an inhibitor of alkali and aggregate reactions, allows one to simultaneously solve the technological problem of regulating the setting time (Table 1).

Table 1 The effect of additives on the properties of cement paste and concrete Additive Cement paste properties The tensile strength of samples of fine-grained concrete 25 × 25 × 100 mm ng,% Setting time R _izg , MPa R _compress MPa Start end - 26.3 2 h 48 min 4 h 05 min 5.80 22.75 C-3 (0.7%) 23,2 3 h 15 min 4 h 30 min 5.52 23.12 C-3 (0.3%) + citric acid (0.05%) 24.1 2 h 58 min 4 h 00 min 5.40 22.87

Thus, the possibility of using cheaper and more affordable compounds than lithium and C-3 salts has been established, which makes it possible to combat corrosion caused by the reaction of alkalis and aggregates.

Claims (1)

A complex organic additive containing S-3 superplasticizer, characterized in that C-3 superplasticizer is used in an amount of 0.3% by weight of cement and additionally contains citric acid in an amount of 0.05% by weight of cement.