CS211565B1 - Method of determination of the rigidity characters of the concrete mixture - Google Patents

Description

The invention solves a method for quickly determining the strength characteristics of a concrete mixture. Using the method, the strength of the concrete after heat treatment and subsequent treatment for 28 days is sufficiently accurately estimated. Using the solved method, the suitability of the concrete mixture for strengthening the concrete by heating to a temperature of 45 to 95 ° C is also determined.

The current methods of checking concrete mix and concrete do not meet the needs of operational control. In terms of strength, the suitability of the concrete mixture is generally checked by testing the strength of test specimens made of the controlled mixture and treated in a constant manner for 28 days. The test results are obtained at a time when the manufacturing conditions are usually changed so much, for example as regards the raw materials used, ev. on the function of the production equipment, that the correction of the composition of the concrete mixture according to test results is no longer justified. The analysis of fresh concrete does not describe the variability of the properties of the supplied cement. Sufficiently accurate accelerated testing of cement properties has not yet been resolved. The solved accelerated strength tests of the test specimens are not fully satisfactory because of their unsuitability when changing the type and class of cement or its supplier. Their duration is not fully satisfactory either.

The results are usually obtained after a period of more than 24 hours and therefore the control does not allow a possible correction in the next shift. This duration is also not suitable for work difficulties arising from the necessary laboratory work on a public holiday following the last working day of the week. It is also known to derive a 28-day strength from accelerated concrete post-warming tests with alternatively 2 and 6 hours of isothermal heating. Also, this test is unsuitable for a test duration that is longer than a shift and longer because of the inadequate test accuracy. Similar disadvantages have the known test, which is based on the withdrawal of strength from tests of concrete after 1.3 and 7 days. These disadvantages are overcome by the solution according to the invention, wherein the determination of the strength characteristics of the concrete mixture, in particular the estimation of the 28-day strength of the concrete made therefrom and its suitability for reinforcing the concrete by heating to 45 to 95 ° C is carried out by test specimens, which have been thermally bonded for a period of tau (h) of less than 7 h and longer than 3 at an average surface temperature of t (° C) = 60 (α-lntau), where α is a constant greater than 2,65; less than 2.85. Next, the strength characteristics of cement R _CA are determined using test specimens made of a mixture of stable composition and aggregate of stable properties.

These test bodies are heat-treated in the same way as test concrete bodies to determine the strength R R of the concrete. The strength characteristics shall be determined from the regression relationship calculated from the results of conclusive tests, which shall contain as independent variables at least R ^ concrete and the strength characteristics of cement ^E CA ·

The advantage of the solution according to the invention lies mainly in the fact that all the determined strength characteristics are found out during one working shift and therefore the method of their determination satisfies the requirements for effective operative control. In the production of concrete test pieces using accelerated hardening of concrete Whether any deviations from the required structural strengths of the building components are due to the properties of the concrete mixture or the component manufacturing method, mainly the compaction and the heat treatment method used.

According to the tests according to the invention, it is therefore possible to carry out the necessary corrections in the composition of the concrete mixture or even the correction of the production process and the modification of the equipment. In this way, the. achieves less variability in strength. The required statistically guaranteed prescribed strength is therefore achieved with reduced consumption of energy-intensive cement.

Examples of use:

In order to verify the suitability of the method of operative control of the concrete according to the invention under the conditions of a component production plant with a wide range of raw materials supplied, verification tests were performed. 39 concrete mixtures with temperatures from 14.5 to 24 ° C were tested.

Sets of 150 mm edge test cubes were made from each of the concrete mixes to determine the strengths R _A , R _c , Rg and Rp> where

R ^ strength (MPa) to standard heating according to the invention. The test cubes are manufactured in a standard test equipment, ensuring all operations from creation to warming. The average temperature of the heated mold and hence the surface of the test cubes was t = 64 ° C, the maximum temperature was 66 ° C. The total warming time was tau = 5.5 h.

R _c strength (MPa) of non-heat-treated concrete treated for 28 days in a humid environment according to ČSN 731311: temperature 20 ± 3 ° C, relative humidity over 90%.

1¾ strength (MPa) of concrete immediately after operationally used heat treatment, lasting a total of 5 hours. The temperature rise time to 80 ° C was 3.5 hours, the maximum concrete temperature reached 85 ° C.

Rp strength (MPa) of concrete after operationally used heat treatment according to the previous point and treated to the age of .28 days in a humid environment according to ČSN 731311

Among other tests of materials and concrete mixtures were also found: strength characteristics of cement ^R CA ^and workability of concrete mixture K, where ^R CA strength (MPa) of test specimens, made of a mixture of stable composition and aggregate of constant properties, reshaped as well as test concrete for measuring the strength R _and concrete.

For workability of concrete mixture (with VeBe) determined according to ČSN 731312. Determination of workability of concrete mixture.

211569

Six different cements were used in the tests to verify the regression relationships listed below in the wider field of concrete mixes: three Portland class 400, two slag class-t and land class 325 and one slag class port 250. The cement dosage was 280, 360 and 440 kg. / nr finished concrete, workability K was 5, 12 and over 30 s VeBe. Different types of aggregates were used. Test series with accelerating and plasticizing additive were included in the evaluation tests.

From the main test results, the following relations, their estimates of the standard bending S, the standard relative errors S _R and the selection coefficients of multiple correlation B were determined. '

He did

Estimated strength Rp>> as dependent variables is used as determined strength Rp.

RPY = 12.64 + 2.326 R _and - 0.539 R - 0.01155 r | · - 0.0219 ^R A · ^R CA S = 1.40 MPa, S _R = 4.21%, R = 0.9875

Example 2

Estimation of strength immediately after the heat Egy; The determined strengths Rg are used as dependent variables. Relationship 2a) not utilizing the determined workability of the concrete mixture:

Rgy = -2.59 + 1.145 R _a + 0.176 R _CA + 0.0069 R _A - 0.02346 R _A. R ^,

W = 0.99 MPa, _R = 6.80%, R = 0.9899

Relation 2b) using the determined workability of the concrete mixture:

Rg _V = 0.38 + 1.272 R _A - 0.134 R _CA - 1.94 ln K - 0.0232 fi _A. H _CA. + 0.169 R _CA. .ln £

S = 0.81 MPa, S _r = 6.14%, R = 0.9934.

Thus, relationship 2b) is more accurate than relationship 2a).

Example 3

Estimation of strength of non-heat-treated concrete Rq ^; the determined strengths Rq are used as dependent variables.

R _cv = 2.06 + 3.277 R _A + 0.345 Rq _A - 0.0813 R _A '. R _CA

S = 2.46 MPa, S _r = 5.84%, R = 0.9727 Note for further use:

In order to specify the relationships for conditions other than the verified field, the tests of strength R _A , R R, Rg and Rp of concrete will be carried out as well as tests of characteristics of used cements Rq _A , workability of concrete mixture K and possibly other characteristics.

The above regression relationships will be refined from the test results. If the strength characteristics of the concrete mixture, as determined by the specified or specified regression relationships, are lower than the corresponding prescribed strengths, the cement dose is increased, otherwise the cement dose can be reduced,

Claims (1)

SUBJECT OF THE INVENTION. Method for determining the strength characteristics of a concrete mixture, in particular estimation of the 28-day strength of the concrete made therefrom and its suitability for reinforcing the concrete by heating to 45 to 95 ° C, characterized in that the strength R _{A of} concrete tau (h) which is less than 7 hours and more than 3 hours, with an average surface temperature of t (° C) = 60 (a - ln tau) where a is a constant greater than 2,65 and less than 2, 85, where the strength characteristics of the cement are determined » Rq _A using test specimens made from a mixture of fixed composition and aggregates of constant properties, heat-treated as well as test concrete specimens to determine the strength R bet of concrete, the strength characteristics determined from the regression relationship calculated from the test results containing at least strength as independent variables R _{A of} concrete and strength characteristics of cement R _CA ·