SU894568A1 - Method of determining strength properties of concrete - Google Patents

Description

(54) METHOD FOR DETERMINING THE STRENGTH PROPERTIES OF CONCRETE

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The invention relates to the study of the properties of concrete, mainly to the study of the properties of fine-grained high-strength concrete.

There is a known method for controlling cracking in concrete during its loading, including the registration of a change in the speed of ultrasound through a test specimen 1.

The known method is distinguished by the complexity of the apparatus used, the insufficient accuracy of the measurements and the limited field of use.

Closest to the present invention is a method for determining the strength properties of concrete, including the manufacture of a concrete sample and the measurement of its electrical characteristics during the loading process. In this case, conductive coatings in the form of strips are applied to the sample surface and their rupture is fixed upon the cessation of current in the measuring circuit 2.

The disadvantage of this method is also low measurement accuracy.

The purpose of the invention is to improve the accuracy of determining the onset of microcracking in concrete.

The goal is achieved by the fact that in the method of determining the strength properties of concrete, including the manufacture of a concrete sample and measurement of its electrical characteristics during the loading process, a constant electric current is passed through the sample during the manufacturing process, the voltage of the electric current in the sample is measured during its loading the dependence of the stress on the magnitude of the load is judged on the beginning of microcracking.

The drawing shows the dependence of the change in electric current on the level of mechanical voltage in a concrete sample — where N is the load at the time of the readout from the instruments; NP is the destructive load of the concrete prism; R ° is the boundary of the onset of crack formation; U is the electric current.

Concrete samples are manufactured in forms, the two opposite sides of which are electrically isolated from each other. In the process of hardening of the concrete prism (immediately after the laying of the concrete and before the window 20 of its setting), a constant current of 20-30 V is passed through the sample. After the concrete has cured

direct current is disconnected, then the operations required by the concrete processing technology are performed.

Before testing, the end faces of the prisms are imposed by metal plates which, when tested, serve as electrodes, and dielectric elastic gaskets insulating the metal plates from the press plates. Then, the concrete prism was tested by compressive load with the test specimen brought to destruction. In the process of testing, a concrete prism with electrodes is included in an electrical circuit consisting of a concrete prism with electrodes and a galvanometer, for example of the type of a type of open circuit. Depending on the level of mechanical stress in the concrete prism during the testing process, the software on the scale of the lvanometer gauge removes readings. In this case, the process of loading in a concrete prism on opposite faces creates a potential difference. The readings of the galvanometer increase in proportion to the level of mechanical stress in the prism. With the formation of microcracks in the body of concrete, the increase in the voltage of the electric current decreases. In place

variations in linear stress versus load value determine the onset of microcracking in concrete R.

Claims (2)

1. USSR author's certificate number 408208, cl. G 01 N 33/38, 1972. 2. USSR author's certificate number 675363, cl. G 01 N33 / 38, 1978. L. L //.