How is the density of the material measured? Density of different materials
In many branches of industrial production, andAlso in construction and agriculture the concept of "material density" is used. This is the calculated value, which is the ratio of the mass of the substance to the volume occupied by it. Knowing such a parameter, for example, for concrete, builders can calculate the required number of it when pouring different reinforced concrete structures: building blocks, ceilings, monolithic walls, columns, protective sarcophagi, basins, locks and other objects.
How to determine the density
It is important to note that, by determining the densitybuilding materials, special reference tables can be used, where these values are given for various substances. Methods and calculation algorithms have also been developed that make it possible to obtain such data in practice if access to reference materials is not available.
The density is determined by y:
- liquid bodies with a device with a hydrometer (for example, the process of measuring the electrolyte parameters of a car battery known to everyone);
- solid and liquid substances using a formula with known initial mass and volume data.
All independent calculations, of course, will have inaccuracies, because it is difficult to reliably determine the volume if the body has an irregular shape.
Errors in density measurements
To accurately calculate the density of the material, the following should be considered:
- The error is systematic. It appears constantly, or it can change according to a certain law in the course of several measurements of the same parameter. It is connected with the error of the instrument scale, the low sensitivity of the device or the degree of accuracy of the calculation formulas. So, for example, by determining the body weight using weights and ignoring the effect of the buoyancy force, the data is approximate.
- Accuracy is random. Caused by the incoming causes and has a different effect on the reliability of the data being determined. Changes in ambient temperature, atmospheric pressure, indoor vibration, invisible radiation and air fluctuations all reflect the measurements. It is completely impossible to avoid such influence.
- Errors in the rounding of quantities. When obtaining intermediate data in calculating formulas, often numbers have a number of significant digits after the decimal point. The necessity of limiting the number of these signs and assumes the appearance of error. Part of this inaccuracy can be reduced, leaving in interim calculations by several orders of figures more than the final result requires.
- Inaccuracies of negligence (misses) arisedue to the erroneous calculations, incorrect inclusion of the measurement limits or the device as a whole, illegibility of the control records. The data obtained in this way can differ drastically from the calculations performed analogously. Therefore, they should be deleted, and the work must be performed anew.
Measurement of true density
Considering the density of the construction material,you need to take into account its true value. That is, when the structure of matter of a unit of volume does not contain shells, voids and foreign inclusions. In practice, there is no absolute uniformity, when, for example, concrete is poured into a mold. To determine its actual strength, which directly depends on the density of the material, the following operations are carried out:
- The structure is subjected to grinding to a powder state. At this stage get rid of the pores.
- Dry in a drying oven at a temperature of over 100 degrees, remove moisture from the sample.
- Cool to room temperature and pass through a fine screen with a mesh size of 0.20 x 0.20 mm, giving uniformity to the powder.
- The resulting sample is weighed on high-precision electronic scales. The volume is calculated in the volume by immersion in the liquid structure and measurement of the displaced liquid (pycnometric analysis).
The calculation is carried out according to the formula:
p = m / V
where m is the sample mass in g;
V is the volume in cm3.
Often the density measurement in kg / m3.
Average material density
To determine how the building community behavesmaterials in real operating conditions under the influence of moisture, positive and negative temperatures, mechanical loads, you need to use the average density. It characterizes the physical state of the materials.
If the true density is a constant anddepends only on the chemical composition and structure of the crystal lattice of matter, the average density is determined by the porosity of the structure. It is the ratio of the mass of a material in a homogeneous state to the volume of occupied space under natural conditions.
The average density gives an idea to the engineer about the mechanical strength, the degree of moisture absorption, the coefficient of thermal conductivity and other important factors used in the construction of elements.
The concept of bulk density
Introduced for analysis of bulk constructionmaterials (sand, gravel, expanded clay, etc.). The indicator is important for calculating the economical use of these or other components of the building mix. It shows the ratio of the mass of matter to the volume that it occupies in a state of loose structure.
For example, if the bulk densitymaterial of granular form and average density of grains, it is easy to determine the voidness parameter. When making concrete, it is more expedient to use filler (gravel, crushed stone, sand), which has a lower porosity of dry matter, since it will be filled with base cement material, which will increase the cost price.
Indicators of the density of some materials
If we take the calculated data of some tables, then in them:
- The density of stone materials, which contain oxides of calcium, silicon and aluminum, varies from 2400 to 3100 kg per m3.
- Wood species with a basis of cellulose - 1550 kg per m3.
- Organics (carbon, oxygen, hydrogen) - 800-1400 kg per m3.
- Metals: steel - 7850, aluminum - 2700, lead - 11300 kg per m3.
