RU2319681C1 - Method of manufacture of concrete and reinforced concrete articles - Google Patents

Abstract

FIELD: construction engineering; manufacture of concrete and reinforced concrete articles.

SUBSTANCE: method of manufacture of concrete and reinforced concrete articles includes preparation of concrete mix, placing the mix in form, holding it in form and heat and moisture treatment. During preparation of concrete mix, complex additive is introduced in it in the amount of 0.1-0.85 of cement mass which contains the following components, mass-%: sodium nitrite, 10-21; C-3, 14-32; micro-silica, 47-75. Heat and moisture treatment is carried out by steaming by the following mode: raising the temperature to 40-70 C for 1-3 hours, holding at this temperature for 2-6 hours and cooling for 1-3 hours. For manufacture of precast reinforced concrete products, curing of concrete mix before heat and moisture treatment is carried out at temperature of 8-28 C continued for 0.5-3.5 hours.

EFFECT: enhanced strength of concrete at early hardening terms at retained high final strength.

2 cl, 1 tbl, 13 ex

Description

The invention relates to the construction, namely to the manufacture of concrete and reinforced concrete products.

Known methods for the manufacture of concrete and reinforced concrete products by preparing concrete mixtures, laying them in molds and holding in molds to set concrete with the required strength [1].

The disadvantage of this method is the slow rate of curing with concrete.

To accelerate the rate of curing of concrete, hardening concrete is treated by treating it. Various methods of such processing are known. For example, a method of caring for hardening concrete by its heat-moisture treatment in steaming chambers at a relative humidity of 100% and a temperature of +80 ... 95 ° С [2].

The disadvantage of this method is the reduction in the final strength of hardened concrete.

Known methods for increasing the strength of concrete in the later stages of hardening by introducing various additives into its composition. One of such methods is the introduction of finely ground additives-fillers into the concrete mixture, which increase the density and, consequently, the strength of hardened concrete [3]. However, this method, slightly increasing the final strength of concrete in the later stages of hardening, does not allow to obtain high strength of concrete in the early stages of hardening.

Closest to the invention, the technical essence is a method of manufacturing precast concrete products, including preparing a concrete mixture, introducing into its composition a complex additive containing a finely ground component, holding the mixture at a temperature of minus 10 ... 15 ° C for 24 hours and heat and moisture treatment by steaming at a temperature of +80 ... 95 ° С according to the 3 + 12 + 4 hours regime [4]. He is taken as a prototype.

The disadvantage of this method is the impossibility of obtaining high strength concrete in the early stages of hardening and the associated reduced speed of turnover of molds or formwork (at least 43 hours), resulting in reduced productivity of reinforced concrete plants.

In addition, at such a heat treatment temperature, significant thermal stresses occur in the hardening concrete in the initial stages, exceeding its strength and causing cracking, leading to a decrease in the final strength and durability of the manufactured structures.

These disadvantages are eliminated in the proposed method for the manufacture of reinforced concrete products.

The technical result of the claimed invention is to increase the strength of concrete reinforced concrete products in the early stages of hardening while maintaining their high final strength.

The essence of the invention lies in the fact that in the known method of manufacturing concrete and reinforced concrete products, including preparing a concrete mixture, laying it in a mold, holding the mixture in mold and heat and moisture treatment, a complex fine-mixed additive is added to it in the amount of 0.1 when preparing the concrete mixture. .. 8.0% of the mass of cement, including silica fume, superplasticizer C-3 and sodium nitrite in the following ratio, wt.%: Sodium nitrite - 10 ... 21, C-3 - 14 ... 32, silica fume - 47 ... 75, and heat-moisture treatment is carried out by prop arivings according to the regime: temperature rise to 40 ... 70 ° С - 1 ... 3 hours, holding at the indicated temperature - 2 ... 6 hours, cooling - 1 ... 3 hours, while for the manufacture of precast concrete products exposure of the concrete mixture to heat and moisture treatment is carried out at a temperature of 8 ... 28 ° C for 0.5 ... 3.5 hours.

The method is as follows. The production of concrete and reinforced concrete products is carried out according to a new technology: a complex fine-milled additive in the amount of 0.1 ... 8.0% of the mass of cement is introduced into the concrete mixture, including binder, fine and coarse aggregates and mixing water, the prepared mixture is laid in molds, then carry out its exposure at a temperature of +8 ... 28 ° C for 0.5 ... 3.5 hours, then carry out its steaming at a temperature of +40 ... 70 ° C according to the mode (1.0 ... 3) + (4 ... 6) + (1 ... 3) hours.

The invention is illustrated by the following examples.

13 series of samples were made measuring 15 × 15 × 15 cm in size from concrete mixtures of various quantitative and qualitative compositions with various exposure times and subsequent processing methods (table).

Portland cement used was made by Portland cement of the Maltsov plant of the ПЦ М500 DO brand, as fine aggregate - quartz sand of the Vyazemsky opencast mine with a particle size module of 2.56, and granular crushed stone of Orsk plant fraction 10 ... 20 as a large aggregate. The additive was introduced in an amount of 0.5 ... 10.0% of the mass of cement. The composition of the additive is as follows: sodium nitrite - 15%, C-3 - 25%, silica fume - 60%.

After manufacturing, concrete samples of series Nos. 2, 5, 6, 9 were kept for 1.0 hour at a temperature of + 20 ° С, and then they were steamed at a temperature of + 60 ° С according to the 3 + 6 + 2 hours regime. Samples of the 7th series were kept for 3.6 hours before TVO. Samples of the 8th series were kept for 0.9 hours at a temperature of 23 ° C, and then they were steamed at a temperature of + 70 ° C according to the regime of 2 + 5 + 3 hours. Samples of the 13th series were steamed at a temperature of + 90 ° C. Samples of series No. 3 and 11 were not subjected to TVO, samples of series No. 4 and 12 were not kept before TVO, and samples of series No. 10 were not kept and were not subjected to TVO.

Samples were tested for compression at the age of 0.5; 1.0; 4.0; 28 and 56 days of hardening (table). As follows from the results obtained, concretes made by the proposed method (compositions No. 5 ... 9) are actively gaining strength both in the early and subsequent curing periods. The strength of concrete at the age of 0.5 days is 20 ... 42 MPa, and at the age of 1.0 days - 25.0 ... 47.0 MPa, while the strength of concrete according to the prototype at the age of 1.0 days is only 0.1 MPa.

The data presented indicate that a high rate of curing is achieved by concrete only if the specified manufacturing technology of concrete is observed and with the optimum amount of additive. Deviation from these parameters (compositions No. 2, 3, 9) leads to a decrease in the rate of curing during all periods of hardening and does not allow to obtain the required results. At the same time, an increase in the amount of added additive compared to the optimal content (compositions No. 5 and 6) does not significantly affect the results, and a decrease in the amount of added additive (composition No. 9) sharply reduces the strength of concrete in the early stages of hardening. At the same time, from the point of view of strength, the content of the additive in the amount of 0.1 ... 8.0% of the mass of cement is optimal.

As can be seen from the data obtained, when using individual technological methods of the claimed invention (compositions No. 10, 11, 12) or if not incomplete combination (compositions No. 2, 3, 4) the claimed effect is not achieved.

Lowering the temperature of the moisture-humid treatment to + 60 ° С (compositions No. 2, ..., 10) compared with the known regime (composition No. 13) avoids the decrease in the final strength of concrete that occurs during high-temperature processing, due to a decrease in the initial period of hardening of completeness hydration of Portland cement clinker, caused by accelerated formation in the early stages of hardening on the surface of cement grains of durable, dense shells of hydration products that impede further hydration of the cement, and therefore high final strength of concrete.

Sufficient concrete holding time before the start of the temperature rise and a relatively low processing temperature will allow the particles of the finely ground additives to become crystallization centers, to which the growth and attachment of cement stone tumors will take place. This leads to the formation of a strong, finely porous structure of hardened cement stone, an increase in the density and strength of concrete in the early stages of hardening.

Achieving the set result is carried out only with the mandatory integrated application of all these technological methods, because their separate use does not allow to obtain the desired effect in connection with the following.

A simple decrease in the temperature of the thermal moisture treatment to +40 ... 70 ° C does not allow to obtain the necessary strength in the early stages and high final strength of concrete.

Exposure of concrete to heat-moisture treatment, in particular, at a temperature of 8 ... 28 ° C for 0.5 ... 3.5 hours, leads to an increase in final strength, but does not allow to obtain high strength in the early stages.

The mere introduction of finely ground additives, increasing the final strength of concrete, does not allow to obtain high strength at an early age.

Thus, the proposed method of manufacturing concrete and reinforced concrete products has undoubted advantages in comparison with known methods. It can be used in the manufacture of various concrete and reinforced concrete products and structures, for example, railway sleepers, tubing tunnels, piles, racks, lintels, crossbars, floor slabs, etc.

Information sources

1. Sheikin A.E. Construction Materials. Textbook for high schools. - M .: Stroyizdat, 1978. - C.186 ... 190.

2. Chaus and others. Technology of production of building materials, products and structures. - M .: Stroyizdat, 1988 .-- P.128 ... 129.

3. A.S. 1172902 USSR. Concrete mix / A.E. Sheikin, L.M. Dobshits. - MIIT (USSR). - Discoveries. Inventions 1985. - No. 30.

4. A.S. 2036188 Russian Federation. A method of manufacturing prefabricated reinforced concrete products / L.M. Dobshits, D.M. Prudovsky, M.S. Goodis and others - MIIT (RF). - Discoveries. Inventions 1995. - No. 15. (prototype).

Table Composition number Technological methods for preparing concrete Compressive strength, MPa in age, days The amount of finely ground additives,% of the mass of cement Shutter speed Moisture treatment mode 0.5 1,0 4.0 28.0 56.0 ° C Time, hour. ° C Time, hour. 1 (prototype) 15.1 -10 24.0 +90 3 + 12 + 4 - 0.1 22.0 40,0 41.3 2 - +20 1,0 +60 3 + 6 + 2 6.5 10.3 18.7 39,4 45.1 3 2,5 +20 1,0 - - 13.1 16.8 30,0 51.0 53.1 four 2,5 - - +60 3 + 6 + 2 18.3 25.1 37.3 48.1 48,2 5* 10.0 +20 1,0 +60 3 + 6 + 2 42.0 43.7 45.0 58.9 59.0 b * 8.0 +20 1,0 +60 3 + 6 + 2 41.5 43.9 45.1 59.0 59.2 7 2,5 +20 3.6 +60 3 + 6 + 2 41.0 42,4 45.0 57.1 58.0 8* 0.5 +23 0.9 +70 2 + 5 + 3 40,0 43.0 43,2 55.0 57.1 9 0.05 +20 1,0 +60 3 + 6 + 2 20.3 25.3 30,4 41.6 43,2 10 2.0 - - - - 9.8 16.5 25.7 43.7 50.1 eleven - +20 1,0 - - 2.9 4.9 20,0 40,0 40.9 12 - - - +60 3 + 6 + 2 5.3 18,4 22.2 38.7 40.3 13 2,5 +20 1,0 +90 3 + 6 + 2 41.3 43.1 45.3 45.1 38,0 * The specified concrete is used in the manufacture of precast concrete products.

Claims (2)

1. A method of manufacturing concrete and reinforced concrete products, including preparing a concrete mixture, laying it in a mold, holding the mixture in mold and heat and moisture treatment, characterized in that when preparing the concrete mixture, a complex additive is introduced into it in an amount of 0.1-8% of the mass of cement including silica fume, superplasticizer C-3 and sodium nitrite in the following ratio, wt.%: sodium nitrite 10-21 S-3 14-32 silica fume 47-75 and thermal moisture treatment is carried out by steaming according to the mode: raising the temperature to 40-70 ° C for 1-3 hours, holding at the indicated temperature for 2-6 hours, cooling for 1-3 hours. 2. The method according to claim 1, characterized in that for the manufacture of precast concrete products, the exposure of the concrete mixture to heat and moisture treatment is carried out at a temperature of 8-28 ° C for 0.5-3.5 hours