Method of concrete strength growth monitoring during heat treatment

FIELD: construction.

SUBSTANCE: method involves measurement of hardening concrete temperature at given time moments and calculation of concrete strength over three days for hardening in standard conditions by the formula: where R, % is concrete strength gained in time τ, days, Kt is temperature factor depending on concrete hardening temperature and three-day strength.

EFFECT: reduced labour consumption of monitoring.

1 tbl, 2 dwg

 

The invention relates to the construction and can be used when carrying out heat treatment of concrete structures.

The known method of monitoring the increase of concrete strength by heat treatment, comprising determining the temperature of curing of concrete at specific points in time and determining the time of achievement of concrete 25%strength in normal conditions used in the calculations of strength of concrete (copyright certificate №1734013 A1, MCP G01N 33/38, 15.05.92)

The disadvantage of the method is based on the assumption that 100% of the strength of concrete under normal conditions is achieved in 28 days, this strength is vintage, although many of the concrete further hardening, which is obtained by this method the strength is not sufficiently accurate. In addition, the proposed method is time-consuming, because the timing of achievement of concrete 25%strength involves the implementation of measurement strength (test samples) throughout the period of hardening.

The invention solves the problem of reducing the complexity of control over the strength of concrete by determining the value of a three-day concrete strength under normal conditions and use in the calculation of the correction factor that takes into account the increase in the time of curing when the deviation from normal is s conditions temperature curing of concrete.

To obtain the desired technical effect in the known method of monitoring the increase of concrete strength by heat treatment, comprising determining the temperature of curing of concrete at specific points in time and strength, it is proposed to define a three-day concrete strength under normal conditions, and concrete strength to be calculated by the formula:where R, % - strength concrete, accumulated within time τ, d, Kt- temperature coefficient, which is determined depending on the temperature of the curing concrete and three-day concrete strength under normal conditions.

On the above chart shows:

figure 1 - dependence dialed strength of concrete of different grades depending on the time when the temperature setting 20°C; R, % - typed concrete strength at time τ, d;

figure 2 - dependence of the temperature coefficient from a three-day strength R3concrete and temperature curing; Kt- temperature coefficient, t,°C - temperature hardening.

The method is as follows.

Make samples of concrete 10×10×10 cm Place the samples in the chamber normal storage and incubated for 28 days.

Sample test for compressive strength after 3 days and after 28 days. Then define a three-day concrete strength R3as p is ocent of nominal strength R 28adopted by over 100%.

Studies have shown that the dependence of curing the concrete stamps, a three-day strength of which R3is in the range of 30÷60% of nominal strength R28concrete, at a temperature of 80°C are almost equal (see figure 1, the deviation of the set of specified strength is less than 5%). Thus, the time a set of concrete specified strength at a temperature of 80°C can be based, without taking into account three-day strength characterizing mark of concrete. The time during which the concrete used brand reaches the required strength shall be determined by multiplication of the time achieve this concrete strength at a temperature of 80°C by a factor of Ktdependent three-day concrete strength and temperature of the curing concrete. For each used in the production of concrete brand pre-experimentally determine the coefficients Ktat different temperatures of concrete hardening, for example, with an interval of 10°C, as shown in the table:

t=80°Ct=70°Ct=60°Ct=50°Ct=40°Ct=30°Ct=20°C t=10°C
R3=30%1,2441,7192,4663,7145,95910,42420,664
R3=35%between 1,3031,7552,4493,5725,5259,25317,394
R3=40%1,3071,7272,3603,3625,0598,20014,814
R3=45%11,2701,6552,2253,1114,5817,24212,683
R3=50%1,2051,5522,059 2,8364,1066,36010,865
R3=55%1,1181,4261,872to 2.5483,6375,5419,277
R3=60%1,0161,2861,6722,2543,1804,7787,864

According to the experimental data, construct graphs of the temperature coefficient of the Ktfrom a three-day strength R3concrete and temperature of curing concrete t°C. Intermediate values are determined by interpolation.

In the process of heat treatment of concrete structures or products in the production of first define the concrete temperature t°C at a given point in time. Then on a three-day concrete strength R3and measured the temperature of the concrete is determined by pre-established the dependency of the temperature coefficient of Ktdetermining the increase in time of curing ecosmarte concrete relative to the time set of the same strength at temperature, equal to 80°C. the Strength of concrete, dialed within a certain time, determined by the formula:

,

where R, % - strength concrete, collected at time τ;

Kt- temperature coefficient, which is determined depending on the temperature of the curing concrete and three-day concrete strength under normal conditions.

A specific example of the method.

For example, it is necessary to determine the strength, which is gaining concrete grade 200 Portland cement grade 300 for 45 hours at 50°C.

Make samples of concrete 10×10×10 cm Place the samples in the chamber normal storage and incubated for 28 days. Test specimens for compressive strength after 3 days and after 28 days define a three-day concrete strength R3=40%.

From the above table, or the graphs in figure 2 determine the temperature coefficient of Kt=2,360.

According to the formula determine the strength of this brand of concrete when the temperature setting of 50°C, which he scored for 45 h:

K=100-82,09*e^(-0,961*45/24*1/2,36)=61.7 per cent.

The proposed calculation of the strength of concrete is much easier than described in the nearest analogue, in addition, it has been experimentally confirmed by the increase in the accuracy of determination of concrete strength by approximately 10%, compared with the nearest equivalent.

The control method for Nuristani the feet of concrete strength by heat treatment, includes determining the temperature of curing concrete, specific points in time, and strength, characterized in that the determined three-day strength of concrete during hardening under normal conditions, and the strength of concrete is determined by the formula

where R, % - strength concrete, accumulated within time τ, d;
Kt- temperature coefficient, which is determined depending on the temperature of the curing concrete and three-day strength.



 

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3 dwg, 1 tbl

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FIELD: technologies for testing properties of materials.

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FIELD: technologies for testing properties of materials.

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EFFECT: higher efficiency, broader range of functional capabilities.

8 ex

FIELD: technologies for testing properties of materials.

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EFFECT: higher precision, lower laboriousness.

4 ex

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1 dwg, 1 ex

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EFFECT: decreased labor consumption.

1 dwg, 1 ex

FIELD: building, particularly to perform nondestructive testing of structure concrete strength.

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EFFECT: possibility to determine physical and mechanical concrete characteristics directly in structure body.

1 dwg

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