How is material density measured? Density of various materials

In many branches of industrial production, andalso in construction and agriculture, the concept of "density of the material." This is a calculated value, which is the ratio of the mass of a substance to the volume it occupies. Knowing such a parameter, for example, in concrete, builders can calculate the required amount of it when pouring various reinforced concrete structures: building blocks, floors, monolithic walls, columns, protective sarcophagi, pools, locks and other objects.

How to determine the density

It is important to note that by determining the densitybuilding materials, you can use special reference tables, where these values ​​are given for various substances. Methods and calculation algorithms have also been developed that allow such data to be obtained in practice if there is no access to reference materials.

The density is determined by:

• liquid bodies using a hydrometer device (for example, the process of measuring electrolyte parameters of a car battery) known to all;
• solids and liquids 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.

Error in the density measurements

To accurately calculate the density of a material, consider the following:

• Погрешность систематическую.It appears constantly or can change according to a certain law in the process of several measurements of the same parameter. Associated with the accuracy of the instrument scale, low sensitivity of the device or the degree of accuracy of the calculation formulas. So, for example, determining the body mass with the help of weights and ignoring the impact of the buoyancy force, the data are approximate.
• The error is random.Caused by incoming reasons and has a different impact on the reliability of the data being determined. Changes in ambient temperature, atmospheric pressure, vibration in the room, invisible radiation, and fluctuations in the air all reflect on the measurements. To avoid such influence is completely impossible.

• Error in rounding values.When receiving intermediate data in the calculation of formulas, often the numbers have many significant digits after the decimal point. The need to limit the number of these signs implies the appearance of an error. Partially to reduce such inaccuracy is possible, leaving in intermediate calculations several orders of magnitude more than the final result requires.
• Negligence errors (misses) occurdue to the erroneous calculations, the incorrectness of the inclusion of the limits of measurement or of the device as a whole, the illegibility of the control records. The data thus obtained may differ sharply from similarly performed calculations. Therefore, they should be deleted and the work done anew.

True Density Measurement

Considering the density of the construction material,you need to take into account its true indicator. That is, when the structure of the substance of a unit of volume does not contain shells, voids and foreign inclusions. In practice, there is no absolute uniformity, for example, when concrete is poured into a mold. To determine its real strength, which directly depends on the density of the material, carry out the following operations:

• The structure is subjected to grinding to a state of powder. At this stage, get rid of pores.
• Dry in a drying oven at a temperature above 100 degrees, remove residual moisture from the sample.
• Cool to room temperature and pass through a fine sieve 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 meter by immersion in a liquid structure and measuring the displaced fluid (pycnometric analysis).

The calculation is carried out according to the formula:

p = m / V

where m is the mass of the sample in g;

V is the volume in cm³.

Frequently applicable density measurement in kg / m³.

Average material density

To determine how construction behavematerials in real conditions of operation under the influence of moisture, positive and negative temperatures, mechanical loads, you need to use the average density. It characterizes the physical state of materials.

If true density is constant anddepends only on the chemical composition and structure of the crystal lattice of the substance, the average density is determined by the porosity of the structure. It is the ratio of the mass of the material in a uniform state to the volume of occupied space in natural conditions.

The average density gives the engineer an idea of ​​the mechanical strength, degree of moisture absorption, thermal conductivity and other important factors used in the construction of elements.

The concept of bulk density

Вводят для анализа сыпучих строительных materials (sand, gravel, expanded clay, etc.). The indicator is important for calculating the cost-effective use of certain components of the building mixture. It shows the ratio of the mass of the substance to the volume, which it occupies in a state of loose structure.

For example, if the bulk density is knownmaterial granular form and the average density of grains, it is easy to determine the parameter of hollowness. In the manufacture of concrete, it is more expedient to use a filler (gravel, crushed stone, sand), which has a lower porosity of dry matter, since basic cement material will be used to fill it, which will increase the cost.

Density of some materials

If we take the calculated data of some tables, then in them:

• The density of stone materials containing oxides of calcium, silicon and aluminum varies from 2,400 to 3,100 kg per m^3.
• Timbers with a base of cellulose - 1550 kg per m³.
• Organic (carbon, oxygen, hydrogen) - 800-1400 kg per m³.
• Metals: steel - 7850, aluminum - 2700, lead - 11300 kg per m³.