RU2486488C1 - Method to determine concrete strength - Google Patents

Abstract

FIELD: testing equipment.

SUBSTANCE: method to determine concrete strength with non-destructive method according to a preset dependence, consists in the fact that liquid drops are applied onto the surface of the tested item. Further angles of sample contact are measured θ. Then the curve of functional dependence is built, cos θ-1 =f(1/σ_l), where σ_l - surface tension of liquid, the tangent of inclination angle is determined for this functional dependence α, and on the basis of the previously built dependence, the strength of concrete samples is calculated.

EFFECT: reduced time for determination of object strength, expansion of range of non-destructive check methods application.

2 cl, 2 dwg

Description

The invention relates to methods for testing building materials made of concrete, and in particular to determining their mechanical properties, in particular strength, both during the intermediate inspection of products at the stage of formation of physical and mechanical properties, and during the inspection of structures of already constructed buildings and structures.

There are destructive and non-destructive methods of control.

Non-destructive evaluation methods include methods of plastic deformation, elastic rebound, ultrasonic method, wave shock method and others [GOST 22690-88. Concretes, determination of strength by mechanical methods of non-destructive testing].

The known method of non-destructive determination of concrete strength using a Kashkarov standard hammer [Recommendations for determining the strength of concrete with a Kashkarov standard hammer according to GOST 22690.2-77]. In accordance with GOST 22690-88, the method is based on the relationship between the strength of concrete R and the value of the indirect strength characteristics of concrete N, defined as the ratio of the diameter of the imprint on concrete to the diameter of the imprint on a reference steel bar.

There is a method of determining the strength of concrete by non-destructive testing and a device for its implementation, which allows to determine the strength of concrete by a non-destructive method by measuring the print of a hammer on a sample and comparing it with a measuring scale on a ruler [RU, patent 2145070, G01N 3/00, 3/02, 3/32, G01B 3/02, 2000]. This method is adopted as a prototype.

The objective of the invention is to reduce the time to determine the strength of objects and expand the range of application of non-destructive testing methods.

The definition is as follows. Solutions of a standard liquid are prepared, in our case, water-alcohol solutions of ethanol of various concentrations. A drop of wetting liquid is applied to the sample. According to the parameters of the droplet, the surface wetting angle θ is measured. Formulate dependence cosθ-1 = f (1 / σ _x) determine the slope of the functional relationship as well. According to the previously obtained dependence, the strength of concrete samples is calculated.

The surface tension of a standard fluid σ _{W is} established by any known method: the Rebinder method, the method of counting drops, etc. [Surface phenomena and surfactants: Handbook / A.A. Abrmzon, L.E. Bobrova, L.P. Zaichenko et al. - L .: Chemistry, 1984-392 p., Ill.]. In our case, the hanging drop method was used, implemented on the EasyDrop setup, designed to measure surface tension, interfacial tension between two liquids, and also to measure the contact angle between the liquid and a solid surface. The results of measurements of the surface tension of the liquid of various aqueous-alcoholic solutions of ethanol are shown in table 1.

The wetting angle of the surface of the test material is determined by any known method (digital photography, observation under a microscope), in this case, the EasyDrop laboratory setup was used, the measurement principle of which is based on highlighting the drop on one side of the lift table and recording it with a video camera and transferring the image of the drop to a computer (Fig. .one). Using the DSA1 software, the droplet shape is analyzed and the contact angle determined. The cosine of the wetting angle is calculated, and the strength of concrete samples is determined from the previously constructed calibration dependence.

The calibration dependence is obtained as follows. Beams with a size of 40 × 40 × 160 mm are made from a solution of cement and sand at a temperature of 20 ° C using vibration for 3 minutes at a site with an amplitude of 0.35 mm and an oscillation frequency of 3000 in 1 min [GOST 310.1-76 Cements. Test methods. General provisions and GOST 310.4-81 (2003) Cements. Methods for determining the tensile strength in bending and compression]. The strength characteristics of standard samples are determined by the non-destructive testing method using a concrete strength meter IPS-MG4.03 after 28 days of exposure of the samples. To conduct parallel measurements, three standard samples of six different mixtures of sand, cement and water are produced. For all samples, the compressive strength is determined by the method for determining the strength with a Kashkarov hammer; among the three samples of the mixture, the average value of strength is determined.

The wetting angle is determined on the installation Easy Drop water-alcohol solution.

The surface tension of water-alcohol solutions is determined by the hanging drop method. In tests, the physical parameters of the drop were selected experimentally, the diameter of the capillary was 1.821 mm. Table 1 presents the obtained results of the surface tension values of water-ethanol solutions σ _g . All experiments were carried out at 22 ± 1 ° C.

Table 1 No. p / p The water content, vol.% (σ _w ± 0.02) × 10 ³ , H / m one 0 24.74 2 10 26.61 3 twenty 27.34 four thirty 28.11 5 40 28.42 6 fifty 31.31

Based on the obtained values, a graph of the functional dependence cosθ-1 = f (1 / σ _W ) is plotted. This dependence is described by the equation of a straight line (figure 2).

Table 2 shows the coefficients a and b of the equation cosθ-1 = a × (1 / σ _W ) + b, the reliability of the approximation (R ² ) for each series of experiments.

table 2 Strength, MPa Odds a × 10 ² b 31.5 1.98 -0.81 21.8 1.79 -0.73 14.6 1.22 -0.51 12.6 1.17 -0.49 8.2 1,11 -0.46

Comparing the strength of concrete samples with the value of the slope of the straight line a , we can distinguish a linear relationship. The functional dependence of the slope of the straight line cosθ-1 = a × (1 / σ _W ) + b on the strength parameter of the standard sample (P) is linear in nature with a satisfactory value of the approximation reliability (R ² = 0.92). Strength is determined by the following relationship:

, $$P=\frac{a-0.0068}{\mathrm{0,0004}}$$

,

Where

and - the tangent of the slope of the dependence cosθ-1 = f (1 / σ _W ).

The application of the method for determining the strength of concrete will reduce the duration of the measurement by reducing the operations performed. The proposed method allows to determine the strength at any stage of the set of structural strength, as well as in existing buildings and structures.

Claims (2)

1. A method for determining the strength of concrete by a non-destructive method according to a pre-established dependence, including applying marks on the surface of the test object, characterized in that the marks are applied with droplets of liquid, the wetting angles of the samples are measured, θ, a graph of the functional dependence cosθ-1 = f (1 / σ _w ) determine the tangent of the angle of inclination of this functional dependence a, where σ _w is the surface tension of the liquid, and the strength of the test object is determined from the previously established dependence. 2. The method according to claim 1, characterized in that the liquid is a water-alcohol solution.

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