Composite binder

Abstract

FIELD: building materials.SUBSTANCE: invention relates to the field of building materials, namely to corrosion-resistant multicomponent binders based on Portland cement for the manufacture of concrete structures in countries with hot, dry and hot humid climates. The composite binder includes 61.0-63.5 wt.% Portland cement, 18.3-20.5 wt.% of dolomite filler and water-the rest. At the same time, an additional 5.8-6.1 wt.% of metacaolinite was added to it, 3.9-4.0 wt.% microsilicon, 0.04-0.06 wt.% organosilicon modifier based on polyhydrosiloxanes and 0.76-0.88 wt.% of the shut-off agent, which uses a 1 wt.% aqueous solution of powdered lithium nitrate. Dolomite crushing screening is used as a filler.EFFECT: invention makes it possible to increase the strength of cement stone, reduce the setting time, increase density, reduce shrinkage deformations and water demand, and also increase the durability of concrete when used in humid conditions by preventing the development of destructive processes during alkali‑silicate corrosion of concrete.1 cl, 2 tbl

Description

[0001] The invention relates to the field of building materials, specifically to corrosion-resistant multicomponent binders based on Portland cement for the production of concrete structures in countries with hot, dry, and hot, humid climates. Concrete structures made from silica-containing opal-containing or carbonate aggregates made from dolomitized limestone, when used in an aqueous (wet) environment, are susceptible to destruction as a result of an internal alkali-silicate and alkali-carbonate reaction when exposed to alkalis in the cement. The invention can be used in the cement and construction industries.

[0002] The closest to the proposed solution is a dolomite binder obtained by the method described in the article “Sustainable use of waste dolomite powder in mitigating alkali-silica reaction in cement mortars” (authors: Haibo Hu, Xiaosong Ma, Ling Luo, Yongqi Wei, Anming She, Wu Yao, Min Wu), published in September 2025 in the journal “Emergent Materials” (https: / / doi.org / 10.1007 / s42247-025-01180-y). This dolomite binder includes Portland cement, dolomite filler, and water. The disadvantage of such a binder is the reduced strength of the cement stone, increased setting times, reduced density of the cement stone, high shrinkage deformations and water demand, as well as reduced resistance of concrete when used in humid conditions due to the development of destructive processes during alkali-silicate corrosion of concrete.

[0003] The technical result of the proposed solution is to increase the strength of the cement stone, reduce setting time, increase density, reduce shrinkage deformation and water demand, and improve the durability of concrete in humid conditions by preventing the development of destructive processes during alkali-silicate corrosion of concrete. Furthermore, the proposed solution allows for a wider range of composite binders.

[0004] Concrete structures made from siliceous opal-containing or carbonate fillers from dolomitized limestones, when used in an aqueous (wet) environment, are subject to destruction as a result of an internal alkali-silicate reaction under the influence of alkalis in cement (Portland cement contains alkalis ( and alkali-carbonate reaction. The cause of destruction is the presence of a saturated calcium hydroxide solution in the system, the effect of alkaline compounds of Portland cement on reactive aggregates, the increase in concrete volume, the accumulation of internal stresses, and the subsequent formation of cracks, leading to further destruction.

[0005] Alkali-silicate corrosion manifests itself as the formation of gel-like deposits at the interface between reactive silica-containing opal-containing aggregate and cement stone. In the case of alkali-carbonate corrosion, brucite, calcium carbonate, and alkali carbonate form in the contact zone between the binder and carbonate aggregate made of dolomitic limestone. These deposits contribute to the development of internal stresses, leading to the separation of the aggregate from the cement matrix and subsequent cracking and failure of the concrete.

[0006] Furthermore, the proposed solution allows to expand the range of composite binders.

[0007] The said technical result is achieved by the fact that metakaolinite, microsilica, an organosilicon modifier based on polyhydrosiloxanes and a sealant, which is a 1% by weight aqueous solution of powdered lithium nitrate, are added to the composite binder, which includes Portland cement, dolomite filler and water, according to the invention, and dolomite crushing screenings are used as a filler, in the following ratio, wt. %:

[0008] Portland cement 61,0-63,5; dolomite filler 18,3-20,5; metakaolinite 5,8-6,1; microsilica 3,9-4,0; organosilicon modifier based on polyhydrosiloxanes 0,04-0,06; shutter 0,76-0,88; water rest.

[0009] The proposed composite binder increases the strength of cement stone, reduces setting time, increases density, reduces shrinkage deformations and water demand, and also increases the resistance of concrete when used in humid conditions by preventing the development of destructive processes during alkali-silicate corrosion of concrete.

[0010] The specified result is achieved due to the combination of components included in the composition of the composite binder.

[0011] Activated dolomite microfiller, obtained by the combined activation of dolomite screenings and an organosilicon modifier, has a positive effect on the binder's water demand, significantly plasticizing the cement paste. It increases the density of the cement stone, and significantly reduces porosity. This is achieved through the formation of hydrosilicates and calcium hydrocarboaluminates, which stabilize the cement stone matrix and can ensure the formation of a denser and more uniform contact zone between the cement stone and the filler. Dolomite filler is used in an activated form, obtained by the combined grinding of dolomite screenings and an organosilicon modifier.

[0012] The introduction of an organosilicon surfactant to intensify the grinding of microfiller based on screening of crushed dolomite in a ball mill helps to intensify the grinding process and obtain particles with a predominant fraction size of 1.99-5.68 μm, prevent their aggregation, and when introduced into the concrete mixture, plasticize it, improve cohesion and technological properties, increase strength and durability, ensuring a uniform distribution of pores throughout the volume of concrete, reducing their diameter, reduces capillary porosity, water absorption, capillary suction, reduces destructive processes, increases the water resistance and homogeneity of cement stone.

[0013] The introduction of highly active microsilica and metakaolinite promotes a rapid reduction in the concentration of calcium hydroxide in the liquid phase with the formation of low-basic calcium hydrosilicates and the elimination of exchange reactions and unwanted deformations.

[0014] Lithium nitrate is used as an inhibitor of alkali-silicate and alkali-carbonate corrosion in the case of introducing particularly reactive fillers into concrete that react with alkalis.

[0015] The introduction of pozzolanic admixtures with high pozzolanic activity leads to a compaction of the cement stone structure, a reduction in its permeability and porosity, which is explained by the formation of poorly soluble compounds in the form of calcium silicate hydroxides. Microsilica and metakaolinite, which have high pozzolanic activity, bind free calcium hydroxide, leading to alkali-silicate and alkali-carbonate exchange reactions at the aggregate-cement stone interface.

[0016] Microsilica consists primarily of silicon dioxide SiO2. Metakaolinite consists primarily of dehydrated aluminosilicates, which react with calcium hydroxide at temperatures ranging from 20 to 50°C to form calcium hydrosilicates, calcium hydrosulfoaluminates, and hydrogehlenite, which subsequently transforms into hydrogarnets.

[0017] The durability of concrete during service was studied using the method of determining, within a specified time period (no more than 1 month), the relative deformations of fine-grained concrete specimens made from the studied materials (GOST 35301-2025 "Aggregates for concrete and building mortars. Methods for determining reactivity"). The method of accelerated determination of the potential alkali-silica reactivity of a multi-component composite binder makes it possible to determine the expansion of specimens from a 1:2.25 cement-sand mortar made using polyfractional sand within 28 days. Specimens prepared in accordance with GOST 30744-2001 "Cements. Test methods using polyfractional sand" are stored for 24 hours in a normal curing chamber, which are then subjected to formwork removal and measurement of geometric dimensions.Next, the samples are kept for 24 hours in a 1M sodium hydroxide solution at a temperature of 80°C, followed by cooling and measurement of relative deformations.

[0018] A multi-component corrosion-resistant composite binder includes the preliminary preparation of a mixing agent in the form of an aqueous 1% (wt.) solution of powdered lithium nitrate with the amount of mixing water needed to prepare a dough of normal consistency.

[0019] Multi-component corrosion-resistant composite binder is obtained by:

[0020] • grinding in a ball mill of crushed dolomite screenings together with a modifier based on polyhydrosiloxane;

[0021] • homogenization of crushed dolomite screenings in the presence of Portland cement, metakaolinite and microsilica;

[0022] • preparing a mixing agent in the form of an aqueous 1% mass solution of powdered lithium nitrate with the amount of mixing water required to obtain a dough of normal consistency;

[0023] • mixing all components of the composition until a homogeneous consistency is obtained.

[0024] The results below were obtained as a result of the studies conducted. The following components were used in the following proportions (wt.%) to prepare the composite binder:

[0025] • Portland cement CEM I 52.5 N (with an average particle size of 16.43-27.39 μm and a specific surface area of ​​3773 cm 2 / g) - 61.0-63.5;

[0026] • dolomite filler activated together with an organosilicon modifier (with an average particle size of 1.99-4.78 μm and a specific surface area of ​​7251 cm 2 / g) - 18.3-20.5;

[0027] • metakaolinite (with an average particle size of 11.46-22.91 μm and a specific surface area of ​​4850 cm 2 / g) - 5.8-6.1;

[0028] • microsilica (with an average particle size of 8.22-27.39 μm and a specific surface area of ​​6747 cm 2 / g) - 3.9-4.0;

[0029] • organosilicon modifier based on polyhydrosiloxanes (with a true density of 1.01 g / cm 3 ) - 0.04-0.06;

[0030] • lithium nitrate based sealant - 0.76-0.88;

[0031] • water - the rest.

[0032] The grouting agent is prepared in a separate container and consists of pre-mixing the mixing water, in the amount required to obtain a paste of normal consistency, with powdered lithium nitrate. Portland cement, dolomite filler, metakaolinite, and microsilica are loaded into the mortar mixer and dry-mixed until smooth. The prepared lithium nitrate solution is then added to the dry components in the mixer, where they are mixed together for 3 minutes until a homogeneous mass is obtained, corresponding to the consistency of cement paste of normal consistency, as determined using a Vicat apparatus in accordance with GOST 30744-2001. The resulting binder (example 1) has the following properties:

[0033] • Water demand - 25.2%.

[0034] • Setting time: start of setting - 150 minutes, end of setting - 185 minutes.

[0035] • Compressive strength of beam halves measuring 40x40x160 mm is 75.7 MPa.

[0036] • Linear relative shrinkage deformations at the age of 28 days of air-dry storage - 1.68 mm / m.

[0037] • Alkali corrosion resistance - 0.0022%.

[0038] The normal consistency of the cement paste, setting time, and strength were determined in accordance with GOST 30744-2001 "Cements. Test methods using polyfractional sand." The relative shrinkage deformations of the binder were determined in accordance with GOST 24544-2020 "Concrete. Methods for determining shrinkage and creep deformations" on 40x40x160 cm specimens made from paste of normal consistency under air-dry conditions. Resistance to alkali corrosion was determined in accordance with GOST 35301-2025 "Aggregates for concrete and mortars. Methods for determining reactivity" by measuring the relative deformations of samples of binder and polyfractional quartz sand of 1:2.25 composition, which were kept for 28 days in a 1M sodium hydroxide solution at a temperature of 80°C.

[0039] Some of the mixture component ratios that have been studied are shown in Table 1.

[0040] Table 1

[0041] Ratios of mixture components

[0042] Components of the mixture Example 1 Example 2 Example 3 Portland cement, wt. % 61,0 63,5 62,2 Dolomite filler, wt.% 19,5 18,3 20,5 Metakaolinite, wt. % 5,8 6,1 5,9 Microsilica, wt. % 3,9 3,95 4,0 Organosilicon modifier based on polyhydrosiloxanes, wt.% 0,04 0,06 0,05 Shuttering agent, wt. % 0,76 0,82 0,88

[0043] The physical and mechanical properties and performance characteristics of composite binders are given in Table 2.

[0044] Table 2

[0045] Physical and mechanical properties and performance

[0046] Characteristics of composite binders

[0047] Properties Example 1 Example 2 Example 3 Prototype Water demand, % 25,2 25,8 24,6 27,5 Setting time: Start, min. End, min. 150 185 155 190 145 180 175 235 Density, kg / m3 2003 2001 2005 1998 Compressive strength at the age of 28 days, MPa 75,7 76,5 74,3 56,4 Shrinkage deformation in air-dry conditions at the age of 28 days, mm / m 1,68 1,73 1,62 2,11 Expansion when kept in a 1M sodium hydroxide solution at the age of 28 days, % (alkali-silicate corrosion) 0,0022 0,0014 0,0012 0,067

[0048] Thus, the claimed composite binder has the following advantages compared to the prototype:

[0049] • Increased strength of cement stone;

[0050] • increased density;

[0051] • reduced setting time;

[0052] • Shrinkage deformation is reduced;

[0053] • water demand reduced;

[0054] • Increased resistance of concrete when used in wet conditions.

Claims

A composite binder comprising Portland cement, dolomite filler and water, characterized in that metakaolinite, microsilica, organosilicon modifier based on polyhydrosiloxanes and a sealant, which is a 1 wt.% aqueous solution of powdered lithium nitrate, are added to it, and dolomite crushed screenings are used as a filler, in the following ratio, wt.%: Portland cement 61,0-63,5 dolomite filler 18,3-20,5 metakaolinite 5,8-6,1 microsilica 3,9-4,0 organosilicon modifier based on polyhydrosiloxanes 0,04-0,06 shutter 0,76-0,88 water rest