RU2095327C1 - Method of preparing concrete mix - Google Patents

Abstract

FIELD: building industry. SUBSTANCE: present invention describes methods for preparing mixes with microsilica additive. The claimed method for preparing concrete mix comprises stirring cement, fillers, water, microsilica and chemical additives in mixer. Microsilica and chemical additives are added to mixture in the form of complex powdery modifier with granule size within 500 mcm and relative moisture content of 1-8 %. Said modifier is obtained by drying aqueous suspension of microsilica and chemical additives. Aqueous suspension comprises (wt %): 40-70 microsilica; and the water balance. Minimum time for stirring cement, fillers, water and complex powdery modifier is 3 minutes. EFFECT: concrete mixes retain plasticity for prolonged periods, and microsilica, superplasticizer and chemical additives have stable properties during prolonged storage and are freezing resistant. 2 cl, 1 tbl

Description

 The invention relates to methods for preparing concrete mixtures with the addition of silica fume (MK).

 A known method of preparing a concrete mixture, including mixing cement (4.2-23.3%), aggregates (47.2-87.6%), silica fume (0.42-11.60%), superplasticizer (0.04- 0.65%), sodium nitrite (0.02-1.27%), lime (0.01-7.92%) and water (the rest) [1] The disadvantage of this method is the separate introduction of individual components into the mixture, which complicates the technology, requires the installation of separate supply lines of silica fume, superplasticizer and other chemical additives.

The closest in technical essence and the achieved result is a method of preparing a concrete mixture with the introduction of cement, aggregates, water and silica fume with chemical additives in the form of a single paste-like product "Sulkrem pulp" [2]
The disadvantages of the method are the tendency of the pulp to stratify, which requires periodic mixing during storage, susceptibility of the pulp to freezing, as well as the need for additional processing lines for supplying superplasticizer and other additives. In addition, the plasticity of concrete mixtures with the addition of such a pasty product with time (after 15-20 minutes from the time of preparation) noticeably decreases.

 The technical problem is to develop such a method of preparing a concrete mixture in which silica fume, superplasticizer and other chemical additives would be introduced into the mixture along one production line in the form of a single product with stable properties during long-term storage, not prone to freezing, and the resulting concrete mixtures would be preserved ductility for a long time.

The problem is solved in such a way that in a method of preparing a concrete mixture, including mixing separately supplied to the mixer cement, water aggregates, silica fume and chemical additives, silica fume and chemical additives are introduced into the mixture at the same time in the form of a complex powdery modifier of multifunctional action with a granule size in the range of 500 microns and a relative humidity of 1-8% obtained by drying in an air stream at 160-250 ^o pre-prepared aqueous suspension of microcre mnemic and chemical additives of the following composition, wt. silica fume 40-70; chemical additives 2-10; water the rest.

 The minimum mixing time for cement, water aggregates and the complex powder modifier is 3 minutes.

 The proposed method differs from the prototype in that the production technology is simplified, since the number of dosed components is reduced, accordingly, the need for several separate supply paths of silica fume and chemical additives to the mixers is eliminated, and the concrete mixtures obtained in this way retain plasticity for a longer time.

 The complex modifier introduced into the concrete mixture is a dry (relative humidity within 8%) powdery product consisting of granules no larger than 500 μm in size, which determines good flowability and stability of material properties during long-term storage even at low freezing temperatures. The powdery complex modifier is obtained by drying in an air stream a pre-prepared suspension containing MK, superplasticizer and other chemical additives necessary to give concrete mixtures and concrete some properties. Chemical additives adsorbed on the surface of MK particles form a film. At the drying stage of the suspension, aggregation of MK particles coated with an adsorption film occurs, granules are formed, which are clumps of spherical MK particles with hardened water-soluble interlayers from chemical additives.

 In the preparation of concrete mixtures, in the process of mixing the components, the granules are also disaggregated into the liquid phase, as the interlayers dissolve between the MK particles, chemical additives are added portionwise. The portioned intake of superplasticizer and other additives in the liquid phase is the main factor ensuring the long-term preservation of the plasticity of the concrete mixture, as well as the prolongation of the effects initiated by other additives (air entrainment, hardening regulators, etc.). The process of complete disaggregation of the granules usually ends after three minutes of mixing all the components of the concrete mixture.

 The consistency of the prepared mixtures and the properties of hardened concrete depends on the ratio of the components of the powdery modifier.

 Thus, the proposed method for preparing concrete mix taking into account the properties of the applied complex modifier of multifunctional action (dispersion, ratio of its component) allows us to solve the problem. Therefore, the claimed method meets the criteria of "novelty" and "inventive step".

 A method of preparing a concrete mixture is as follows.

The mixer mixes for at least 3 minutes: cement, aggregates, water and a powdery product, a complex modifier of multifunctional action with a particle size of 500 microns and a relative humidity of 1-8%, which is prepared from a suspension consisting of MK (40-60% by weight ), chemical additives (2-10% by weight), for example, such as a rheological regulator of superplasticizer, a hardening regulator - nitrilotrimethylene phosphonic acid, an air-entraining component, a neutralized air-entraining resin, against frosty additive sodium nitrite and water (the rest) by drying it in an air stream at 160-250 ^o C.

Example. Materials for the preparation of a complex modifier:
silica fume (MK) grade MK-85 according to TU 7-249533-90 "Condensed silica fume. Technical conditions";
superplasticizer (SP) of grade C-3 based on the sodium salt of the condensation product of naphthalenesulfonic acid and formaldehyde, corresponding to TU 6-36-0204229-625-90 ** "Plasticizer C-3";
nitrilotrimethylene phosphonic acid (NTP), corresponding to TU 6-09-5283-86 ** "Nitrilotrimethylene phosphonic acid. Technical conditions";
sodium nitrite (NN), corresponding to GOST 19906-74 "Technical sodium nitrite. Technical conditions";
neutralized air-entraining resin (START), corresponding to TU 81-05-75-74 *.

From the above materials in high-speed mixers, aqueous suspensions of a concentration of 35 to 72% were prepared. The resulting suspensions were dried in an air stream in a spray drying unit at an air temperature at the inlet of the drying unit of 150-260 ^o C. As a result, a powdery material was obtained, which was Essentially a complex organo-mineral concrete modifier.

The freezing temperature of the obtained product was determined by visual assessment of the behavior of the material with decreasing temperature: the change in flowability (angle of repose). When exceeding the angle of repose of 20 ^o flowability was considered unsatisfactory. Accordingly, the optimal moisture range of the material was determined, the freezing temperature and, accordingly, the angle of repose are associated with relative humidity.

 The optimal dispersion of the material was determined by the maximum strength of concrete, which was achieved by mixing the powdery modifier with other components of the concrete mixture for a fixed time of 3 minutes.

 Concrete mixtures were prepared using Portland cement M400 (GOST 10178), quartz sand with Mkr = 2.1 (GOST 8736), granite crushed stone fraction 5-20 mm (GOST 8267). In the method of preparing the concrete mixture adopted as a prototype, silica fume and chemical additives were introduced into the concrete mixture in the form of a suspension (pulp) of 50% concentration. In the proposed method, silica fume and chemical additives were introduced in the form of a powdery modifier.

The compositions of concrete mixtures with modifiers prepared according to the prototype and the proposed method were taken the same, kg / m ³ : cement 300; sand 730; crushed stone 1120; water 165.

 A powdery modifier and suspension (pulp) were introduced into the concrete mixture at the rate of 15% silica fume by weight of cement, and the water in the suspension was taken into account in the total amount of mixing water.

 The ductility of the obtained concrete mixtures was evaluated by the standard cone draft, the strength of concrete by testing specimen cubes with a rib size of 10 cm, solidified under normal conditions.

Table 1 shows the test results of the properties of the complex modifier, concrete mixtures and concrete. The compositions and parameters of the obtained modifiers are given in table. 1, from which it can be seen that samples N 5-10 have low humidity and, accordingly, low freezing point. Samples N 4 and 11, having a humidity of more than 8% and prone to freezing at a higher temperature (-5 and -8 ^o C), do not allow to solve the problem and can be excluded from subsequent tests.

 The effectiveness of the products obtained (N 1-3 and 5-10, table 1) was evaluated on concretes of the same composition (see table 2). The introduction of MK and chemical additives in the form of a complex powdery modifier (samples 5,6,7,9,10, table 1) leads to an increase in concrete strength from 7 to 13%, and the plasticity of concrete mixtures is practically not lost after 120 minutes (compositions 4, 5,6,8,9 tab. 2). In mixtures (compositions N 1, 2,3, Table 2), prepared with silica fume and chemical additives in the form of a suspension (pulp) of 50% concentration (samples N 1,2,3, Table 1), a sharp drop is observed ductility, which in 120 minutes almost reaches OK 0 cm.

 The use of a complex powdery concrete modifier with a granule size of more than 500 microns (sample No. 8, Table 1), while maintaining the plasticity of concrete mixtures after 120 minutes, leads to a decrease in concrete strength by 19% (composition 7, table 2), which is obviously due with an insufficient degree of disaggregation of relatively large particles of the modifier.

 Thus, from the table. Figures 1 and 2 show that the proposed method for preparing concrete mixtures using a complex powder modifier has the following advantages.

 Concrete mixtures of the same composition have higher ductility and practically do not lose it during storage for 2 hours.

 Concretes of the same composition have a higher (by 7-13%) compressive strength.

 The technology of preparing concrete mixtures with a complex modifier has been simplified, since there is no need for several processing lines for introducing silica fume and other chemical additives into the mixer and insulation of containers with liquid chemical additives of the paths for their supply to the concrete mixer is not required.

Claims (1)

 1. A method of preparing a concrete mixture, including mixing cement, aggregates, water and an aqueous suspension of a complex modifier containing silica fume and chemical additives, characterized in that the aqueous suspension of a complex modifier of the following composition, wt. Silica fume 40 70
Chemical additives 2 10
Water Else
before mixing, it is dried in an air stream at 160 - 150 ^o C to obtain a powder consisting of granules up to 500 microns in size and a moisture content of 1 8%
2. The method according to claim 1, characterized in that the minimum mixing time of cement, aggregates, water and a complex powdery modifier is 3 minutes

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