Several times I came across the waterproofing brand W4, W6 for concrete and waterproofing. What do these abbreviations stand for? How to understand them?
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Several times I came across the waterproofing brand W4, W6 for concrete and waterproofing. What do these abbreviations stand for? How to understand them?
Water resistance is the ability of concrete (or waterproofing) not to allow water to pass under pressure. W2, W4, ... W20 indicate the grade of concrete, and the numbers 2, 4, ... 20 indicate the pressure value in Pascals (though I forgot in kilos and megas).
Water resistance is the ability of concrete not to allow water to pass through under pressure that gradually increases to a certain value.
The following grades of concrete are distinguished by water resistance: W2, W4, W6, W8, W10, W12, W14, W16, W18, W20. Numbers 2-20 indicate the maximum pressure in atmospheres at which water infiltration through a 150 mm high cylinder sample has not yet been observed under standard test conditions (for example, for concrete grade W2, the water resistance of samples is 0.2 MPa = 2 atm).
As a rule, ordinary concrete has a water resistance grade lower than W2.
Cement waterproofing materials have a water resistance grade of W2-W16.
In the technical data sheets of waterproofing products manufactured in Europe, water resistance is determined based on the maximum pressure measured in Bars . For example, for waterproofing Nanodefense Eco (manufacturer Kerakoll) waterproofness ≥ 3 bar.
Can you write in more detail what pressure is in atmospheres and bars? How many atmospheres are there in 1 bar? I do not understand.
Pressure measurement units (ST SEV 1052-89) are determined in one of two ways:
In the International System of Units (SI), adopted in 1960, the unit of force is N (newton) and the unit of area is m2. From here the unit of pressure is determined: pascal Pa=1 n/m2 and its derivatives, for example, kilopascal (1 kPa=10 3 Pa), megapascal (1 MPa=10 3 kPa=10 6 Pa). Along with the SI system, units of other, earlier systems, as well as non-systemic units, continue to be used in the field of pressure measurement. In the technical system of units MKGSS (meter, kilogram-force, second), force is measured in kilograms of force (1 kgf≈9.8 N). Pressure units in MGKSS are kgf/m2 and kgf/cm2; The unit kgf/cm2 is called the technical or metric atmosphere (at). When measuring excess pressure in technical atmosphere units, the designation “ati” is used. In the physical system of units CGS (centimeter, gram, second), the unit of force is the dyne (1 dyne = 10 –5 N). Within the framework of the GHS, the unit of pressure bar was introduced (1 bar = 1 dyne/cm2). There is an off-system meteorological unit of the same name, bar, or standard atmosphere (1 bar = 10 6 dynes/cm2; 1 mbar = 10 –3 bar = 10 3 dynes/cm2), which sometimes, out of context, causes confusion. In addition to the indicated units, in practice such a non-systemic unit is used as the physical or normal atmosphere (atm), which is equivalent to a balancing column of 760 mm Hg. Art. Occasionally, a pressure unit from the MTS system of units (meter, ton, second) is used: piezo (1 pz = 1 cn/m2, where 1 cn = 10 8 dynes is a force of 1 wall, imparting an acceleration of 1 m/s2 to a body weighing 1 ton ). In English-speaking countries, the widely used unit of pressure is psi (psi = lbf/in2) - pound force per square inch (1 lb = 0.4536 kg). When measuring absolute and excess pressure, the designations psia (absolute) and psig (gage) are used respectively.
For approximate estimates and calculations of pressure with a relative error of no more than 0.5%, it is useful to use the following relationships: 1 at = 1 kgf/cm2 = 10 4 kgf/m2 = 0.97 atm = 0.98 × 10 3 mbar = 0.98 bar = 10 4 mm water column = 10 m water column = 735 mm Hg. = 0.98×10 5 Pa = 98 kPa = 0.098 MPa. With an error of 2%, we can neglect the difference between the technical atmosphere, the standard atmosphere (bar) and a tenth of a megapascal (1 atm = 1 bar = 0.1 MPa), and with an error of 3%, the difference between the technical and physical atmospheres (1 atm = 1 atm).
Denis , thank you very much for your detailed answer. I admit that from the first reading much was not clear, but after reading it three or four times, understanding came. It’s good that this material will be saved on the forum; you can return to it, if necessary.
Since the conversation went in such a detailed direction about pressure, I think that it is necessary to consider the types of measured pressures. For example, in the literature there are such concepts as barometric pressure, absolute pressure, excess pressure, etc. I don’t have time for this myself, I ask my colleagues to join in, it will be educational for many.
In practice, the pressures of gaseous and liquid media can be measured relative to two different levels (see figure):
Pressure measured relative to vacuum is called absolute pressure (AP) . Barometric pressure (BP) is the absolute pressure of the earth's atmosphere. It depends on the specific measurement conditions: air temperature and altitude. Pressure that is greater or less than atmospheric, but measured relative to atmospheric pressure, is called, respectively, excess pressure (DI) or vacuum pressure, vacuum pressure (DV) . Obviously, YES=DB+DI or YES=DB–DV. When measuring the pressure difference between media in two different processes or two points of one process, such that none of the pressures is atmospheric, such a difference is called differential pressure (DP) .
I believe this material can complete the discussion of pressure, since the forum thread relates to waterproofness.
Do I understand correctly that if the water resistance grade W4 is indicated for concrete, then at atmospheric pressure a sample cylinder 150 mm high from such concrete will not allow water to pass through from a water column 30 m high (1 atm is equivalent to a balanced column of 10 m of water column. )? And if this concrete sample is at a pressure of 3.8 amt, then the height of the water column should not exceed 2 m?
Yes, you get the essence of the phenomenon. The total pressure for waterproof grade W4 should not exceed 4 atm. Similar reasoning applies to waterproofing. Here, however, it should be understood that some types of waterproofing can work both on pressing (positive pressure) and on tearing (negative pressure). As a rule, the water resistance of the clamp is greater than the water resistance of the pull. The manufacturer indicates specific values in the technical data sheets. They should be followed.