FEATURES OF CONCRETE STANDARDIZATION

Let's consider the features of these designations: 

1. The main indicator of the quality of concrete is the ultimate strength in uniaxial compression of a sample-a cube with an edge 15 cm long with their division into classes (B) or the ultimate strength in compression of cylindrical samples measuring 15x30 cm with the division of concrete into classes (C). Quality indicators of both classes are accepted according to the standard withguaranteed security. In total, there are 19 classes of compressive strength when testing cubes (from B1 to B60, from C0.8 to C55), the strength value is expressed in MPa. 

2. The grade of concrete is normalized according to the average value of the compressive strength index: M50, 75, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700 and 800; it is expressed in kg/ cm2 : from 15 (for cellular concrete) to 600 and above (for heavy concrete). 

The marking of concrete, in addition to strength, is established by frost resistance and water resistance. 

According to frost resistance, concrete is marked: F50, 75, 100, 150, 200, 300, 400, 500. To those who have not maintained the number of cycles of freezing at a temperature of -15 – -20 ° C and thawing at a temperature set by the brand +15 – +20 °C refers to concrete samples that lose more than 5% by weight during testing from the initial value. 

The following brands are accepted for water resistance: W2, W4, W6, W8, W10 and W12. Waterproofness is checked by applying water pressure to a sample of cylindrical shape and 15 cm thick at various hydrostatic pressures expressed in Pa (from 2∙105 to 12∙105). 

Depending on the purpose, concrete is divided into structural, hydraulic, road, special, etc. 

To obtain a test of normal density from construction gypsum, it is necessary to take 50-70% of water from its mass, for production in production conditions — 60-80%. Gypsum, depending on the setting time, can be of the following types: fast–hardening (the beginning of setting no earlier than 2 minutes, the end — no later than 15 minutes), normal-hardening (the beginning of setting no earlier than 6 minutes, the end — no later than 30 minutes), slowhardening (the beginning of setting no earlier than 20 minutes, the end is not normalized). 1.5 hours after the samples are made, they are divided into 12 grades according to the compressive strength: G-2, G-3, G-4, G-5, G-6, G-7, G-10, G-13, G-16, G-19, G-22, G-25 (the numbers indicate the lower tensile strength in MPa). 

The bending strength of the samples is calculated as the arithmetic mean of the two largest test results of three samples. 

The compressive strength of the samples is calculated by the formula: 

Rс= F/A (MPа), 

where F — destructive load; 

А — the surface area of the sample in contact with the plate. 

The compressive strength of the sample is calculated as the arithmetic mean of the four maximum values according to the test results of six samples.

Regulatory documentation is the main guide for employees of the standardization system. Accordingly, a thorough study and proper understanding of the standards is an important requirement for specialized specialists. 

Dovranguly MAMMEDOV, 

Lecturer at the Institute of Engineering, Technical 

and Transport Communications, 

Deputy of the Mejlis of Turkmenistan.