Features of Kashkarov hammers

In construction, it is often necessary to determine the strength of concrete. This is especially true for the supporting structures of buildings. The strength of the concrete guarantees not only the durability of the structure. The maximum mass with which an object can be loaded also depends on it. One of the ways to determine this indicator is to use the Kashkarov hammer. What this tool is, as well as how to use it correctly, will be discussed in the article.

Kashkarov's hammer is a measuring device that is able to determine an indicator that indicates the compressive strength of concrete by plastic deformation. Despite the fact that this device gives rather inaccurate indicators, it is often used on construction sites where monolithic work is performed, as well as in reinforced concrete factories.

The device of Kashkarov's hammer is regulated in GOST 22690-88. It consists of:

• metal body, which guarantees the durability of the tool;
• handle (metal frame);
• head (working part of the hammer);
• a spring that dampens the impact force from the hammer;
• glasses, where the reference rod and ball are placed;
• a reference rod, with the help of which the study is carried out;
• a steel ball that hits the rod;
• rubberized grip that prevents the tool from sliding in the hand.

The reference rods are made from hot rolled steel, from which the rebar is made. Used VstZsp and VstZps, which correspond to GOST 380. Samples have temporary tensile strength. The rods are tested at the factory.

The main indicator for determining the strength of concrete is its compressive limit. In order to determine the strength of the material, the test piece must be hit with a hammer. The blow is applied strictly at an angle of 90 degrees. In order for the result to be as close to real indicators as possible, at least five blows should be applied. Please note that only 4 marks can be applied to one reference rod. The distance between blows must be at least 1.2 cm.

The diameter of the prints is measured with a magnifying glass. Instead of a magnifying glass, you can also use a caliper here. Then you need to add the dimensions of the imprint on the standard and on the concrete, divide the resulting number by two. The final result will show what the strength of the concrete sample is. In this case, the resulting indicator should be in the range of 50-500 kg / cu. cm. When determining the strength of concrete using Kashkarov's hammer, tables compiled by an experimental method are used.

Each Kashkarov hammer is sold complete with instructions for use, which clearly describe how to use this measuring tool correctly.To test the strength of concrete with a Kashkarov hammer, you need to select a 10x10 cm section of a concrete object. It must be flat, without grooves and bumps, and there must be no visible pores. The distance from the edge of the product should be more than 5 cm.

You need to take Kashkarov's hammer, insert the reference rod into the corresponding groove with the sharp end inward. A clean sheet of paper and a piece of carbon copy should be laid on the selected area of ​​concrete. Then you need to hit the workpiece with a hammer, as described above. After each impact, the standard should be advanced to a new area and the sheet of paper should be replaced. The next blow should fall on a new place (at a distance of more than 3 cm from the previous one).

The next step is to measure the prints. If the difference in the obtained indicators is more than 12%, all studies should be repeated anew. Based on the obtained indicators, the class of concrete is determined, while the smallest of the resulting indicators is selected.

Low air temperatures have practically no effect on the result of the study. Therefore, it is allowed to use this measuring tool at ambient temperatures down to -20 degrees. However, in this case, the temperature indicators of concrete and reference rods must be the same. This means that the reference rods must be left outside for at least 12 hours before testing in freezing temperatures.

Kashkarov's hammer has both pros and cons. The advantages of using this tool include, first of all, the ease of measurement. Even a beginner in the construction business can cope with such a study.

For testing, it is not necessary to destroy the sample, that is, the study can be carried out directly on the finished product. This is especially important if the research items are bulky. Also, the pluses include the cost of the device. Such a tool can be purchased for use in everyday life, for example, erecting a monolithic house for yourself.

But Kashkarov's hammer also has significant drawbacks. The error of the device is 12 to 20 percent, which is quite a lot. Modern electrical sclerometers provide more accurate results. The strength of concrete is determined only in the surface layers (1 cm deep). As you know, these layers are often susceptible to destruction due to carbonization. In addition, the device is practically insensitive to the strength of the coarse aggregate and its grain size composition.

You can buy a Kashkarov hammer in one of the specialized stores selling various measuring instruments. It can also be ordered in an online store of a similar focus. The cost of this device is from 2500 rubles. At the same time, in addition to the tool, you will need to purchase reference rods, a set of ten pieces of which will cost you 2,000 rubles.

For more information on Kashkarov's hammers, see the video below.