RU2361848C2 - Method for preparation of concrete mix - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: method includes mechanical-chemical activation of gaging water with addition of nitrate-nitrite alkaline water for 1 min, mechanical-chemical activation of cement containing 60-70% of previously activated gaging water, in mixer for 1.5-2 min. and further mixing in mixer with sand, crushed stone and remaining part of activated gaging water for 2 min. Fine filler is washed coarse-grained sand. Mechanical activation of gaging water and used additive is carried out in mechanical-chemical activator at 1,100 rpm.

EFFECT: lower consumption of Portland cement and increased compression and stretching strength.

3 cl, 1 tbl

Description

The invention relates to the preparation of concrete mixtures for monolithic products and precast using mechanically activated cement slurry for building structures from cast concrete and the manufacture of precast.

A known method of preparing a concrete mixture / 1 /, according to which in the mixers forced or gravitational action carry out two-stage mixing of the components, including pre-mixing sand and gravel with 40-60% mixing water for 3-4 minutes and the addition of 40-45% plasticizer solution in the amount of 5-9% by weight of cement, the subsequent addition of cement and additional mixing with the introduction of the remainder of the mixing water (RF Patent No. 2028279, С04В 28/04, С04В 40/00. BI No. 4, 1995).

The disadvantage of this method is that it does not provide the necessary workability of the concrete mixture and the required compressive and cracking strength, and also requires an increased consumption of cement.

Closest to the proposed invention is a method / 2 /, comprising pre-mixing the aggregates with part of the mixing water and the additive, followed by the introduction of cement and the rest of the mixing water. Pre-mixing is carried out for 2-2.5 minutes with aggregates with 70-80% of mixing water, 2-5% by weight of cement using nitrate-nitrite alkaline water, and additional mixing of all components is carried out for 1 minute.

The disadvantage of this method is that it requires significant material costs for a preliminary examination and preparation of ash and slag waste. This delays the practical implementation of the invention (RF Patent No. 2158719, С04В 40/00, С04В 22/08. BI No. 31, 2000).

The technical result achieved by the present invention is to reduce the consumption of Portland cement, increase workability and increase compressive and tensile strength.

This technical result is achieved in that in a method comprising mechanical activation of mixing water with the addition of nitrate-alkaline water for one minute and mechanical activation of cement with 60-70% mechanically activated mixing water in concrete mixers for 2 minutes, followed by mixing with sand , crushed stone and the remainder of the activated mixing water for 1.5-2 minutes.

The tensile strength of concrete is increased by increasing the adhesion of cement stone to the surface of sand and gravel particles. This is due to the fact that cement grains, obeying the laws of molecular attraction, tend to unite into larger particles. The distribution of water within and between such particles is highly uneven. Increasing the uniformity of the distribution of water in cement and the separation of adhering particles in the process of mechanical activation leads to the formation of a more uniform coagulation structure, which improves the technological properties of the concrete mixture and higher quality of the hardened concrete.

According to the proposed method, the mixture is prepared in three stages. At the first stage, mechanochemical activation (1100 rpm) of mixing water is carried out with the addition of nitrate-nitrino-alkaline water in an amount of 1-2% by weight of cement, calculated on the anhydrous substance of the additive for one minute. At the second stage, Portland cement of grade M 500 (240 kg / m ³ ) with a portion of mixing water (from 60% to 70% of its total water consumption of 150 kg / m ³ ) is loaded and mechanochemical activation of the water-cement solution is carried out for 1.5-2 min At the third stage, 1300 kg / m ³ crushed stone, 692 kg / m ³ sand and the rest of the mixing water are loaded into the mixer. Stirred for two minutes.

The proposed method was tested under the conditions of a construction laboratory (Accreditation certificate No. 05.18.2067 of 10.20.2006). Portland cement grade ПЦ 500 Д 20 Б of the Novorossiysk cement plant “Proletary” was used as a binder. Crushed stone of the 5-20 mm fraction with a bulk density ρ equal to 1465 kg / m ^{3 was} used as a large aggregate, the tests of which were carried out in accordance with GOST 8269.0-97 (Crushed stone and gravel from dense rocks and industrial waste for construction work. Methods physical and mechanical tests). Fine aggregate is coarse-grained sand of the Krasnodar deposit with the fineness modulus Mkr-2.6 and bulk density ρ equal to 1730 kg / m ³ . Sand tests were carried out according to GOST 8735-88 (Sand for construction work. Test methods). To mix the concrete mix, tap water is used (GOST 23732-79. Water for concrete and mortars. Technical conditions). As an additive, nitrate-nitrite-alkaline waste from the catalyst production of the Novocherkassk Synthetic Products Plant is used, containing mass in a percentage ratio: 25% sodium nitrate (NaNO ₃ ), 9% sodium nitrite (NaNO ₂ ) and 6% caustic soda (NaOH), the remaining 60% - water.

To determine the tensile strength, tests were carried out on prototypes of cubes with an edge of 100 mm at the age of 28 days of normal hardening by cracking in the “on the edge” position according to GOST 10180-90 Concretes. Methods for determining the strength of control samples. To obtain comparative data, the concrete mixture is prepared in the usual two-stage way according to the patent | 2 |, as well as according to the proposed method.

In the invention, three experimental variants of concrete mixture samples are investigated (method 1, 2 and 3).

As the source we take the composition No. 1 of heavy concrete of class B-15 with a consumption of materials in kg / m ³ : cement (grade M-500) - 300, sand with Mkr-2.6 - 813, crushed stone of fraction 5-20 mm - 1216 ; water - 210. Mechanochemical activation was not carried out. The draft of the cone is 12 cm, W / C (water-cement ratio) - 0.7.

Unlike the original composition, in the second version (composition No. 2), the amount of cement is reduced by 20%. The consumption of materials for producing concrete of class B-15, in kg / m ³ , was adopted as follows: cement - 240, sand with a fraction of Mkr-2.6 - 692, crushed stone of a fraction of 5-20 mm - 1300; water - 160. Additive nitrate-alkaline water in an amount of 5% by weight of cement, calculated on the anhydrous substance of the additive. Mechanochemical activation was carried out at 900 rpm in a mechanochemical activator (grade M-500). Draft of the cone - 14 cm, W / C - 0.66.

The proposed composition No. 3 of heavy concrete of class B-15 provides the following consumption of materials in kg / m ³ : cement - 240, sand with Mkr-2.6 - 692, crushed stone fraction 5-20 mm - 1300; water - 150. Additive nitrate-alkaline water in an amount of 2% by weight of cement, calculated on the anhydrous substance of the additive. Mechanochemical activation was carried out at 1100 rpm in a mechanochemical activator. Draft of the cone - 15 cm, W / C - 0.63.

The test results are presented in table 1.

The tests carried out allow us to establish that the preparation of concrete mixture according to the proposed method, which consists in mechanochemical activation of mixing water with the addition of nitrate-alkaline water in an amount of 1-2% by weight of cement for 1 min, mechanochemical activation of cement pulp containing 60-70% previously activated mixing water for 1.5-2 minutes, and subsequent mixing in a mixer with sand, gravel and the remaining part of activated mixing water for two minutes, reduces the amount cement by 20%, increase workability and compressive and tensile strength.

Table 1 - Test cubes test results No. p / p Storage mode Cone draft, cm Bulk weight, g · cm ³ Test results at the age of 28 days ultimate compressive strength, MPa /% tensile strength, MPa /% Composition No. 1 (one-stage without additives) one Steam heating in the pit chamber at the landfill 12 2500 22.85 4.13 2 2460 23.35 4.11 3 2510 22.37 4.12 Average value: 2490.0 22.86 / 100 4.12 / 100 Composition No. 2 (preparation of mixing water and cement-sand mixture at 900 rpm with 5% additive NNSCH) one Steam heating in the pit chamber at the landfill fourteen 2430 29.81 6.86 2 2500 30.80 6.37 3 2520 30.02 6.69 Average value: 2483.3 30.21 / 132 6.64 / 161 Composition No. 3 (preparation of mixing water and cement-sand mixture at 1100 rpm with 2% addition of NSNI) one Steam heating in the pit chamber at the landfill fifteen 2450 31,45 7.45 2 2470 32.78 7.61 3 2420 33.10 7.52 Average value: 2446.7 32.44 / 142 7.53 / 183

Claims (3)

1. A method of preparing a concrete mixture, including mechanochemical activation of mixing water with an additive, mechanochemical activation of cement pulp and subsequent mixing in a mixer with sand, gravel and the remaining part of activated mixing water, characterized in that the preliminary mechanochemical activation of mixing water is made with the addition of nitrate-alkaline water for 1 min, then mechanochemical activation of cement with 60-70% pre-activated mixing water for 1.5-2 minutes, and then All components are mixed with the remainder of the activated mixing water for 2 minutes. 2. The method according to claim 1, characterized in that as a fine aggregate use washed coarse sand Mkr - 2.6. 3. The method according to claim 1 or 2, characterized in that the mechanochemical activation of the mixing water and the additive used is carried out in a mechanochemical activator at 1100 rpm.