In many sectors of industrial production, as well as in construction and agriculture, the concept of "material density" is used. This is a calculated quantity, 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 when pouring various reinforced concrete structures: building blocks, ceilings, monolithic walls, columns, protective sarcophagi, pools, locks and other objects.
How to determine the density
It is important to note that, when determining the density of building materials, you can use special look-up tables where these values are given for various substances. Calculation methods and algorithms have also been developed that make it possible to obtain such data in practice if there is no access to reference materials.
Density is determined by:
- liquid bodies with a hydrometer device (for example, the process of measuring the electrolyte parameters of a car battery known to everyone);
- solid and liquid substances using the formula with known initial data of mass and volume.
All independent calculations, of course, will have inaccuracies, because it is difficult to reliably determine the volume if the body has an irregular shape.
Density measurement errors
To accurately calculate the density of a material, the following must be considered:
- The error is systematic. It appears constantly or may change according to a certain law during several measurements of the same parameter. It is associated with the error of the instrument scale, low sensitivity of the device or the degree of accuracy of the calculation formulas. So, for example, by determining body mass using weights and ignoring the effect of buoyancy, the data are approximate.
- The error is random. It is caused by incoming causes and has a different effect on the reliability of the data being determined. Changes in ambient temperature, atmospheric pressure, room vibration, invisible radiation and air vibrations - all this is reflected in the measurements. To avoid such an influence is completely impossible.
- Error in rounding values. When obtaining intermediate data in the calculation of formulas, numbers often have many significant digits after the decimal point. The need to limit the number of these signs and suggests the appearance of an error. It is possible to partially reduce such inaccuracy, leaving in the intermediate calculations several orders of numbers more than the final result requires.
- Errors of negligence (misses) arise due to erroneous calculations, incorrect inclusion of measurement limits or the device as a whole, and illegibility of control records. The data obtained in this way can differ sharply from similar calculations. Therefore, they should be deleted, and the work performed again.
True Density Measurement
Considering the density of the material of construction, it is necessary to take into account its true indicator. That is, when the structure of the substance of a unit 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 real strength, which directly depends on the density of the material, carry out the following operations:
- The structure is subjected to grinding to a powder state. At this stage, get rid of the pores.
- It is dried in an oven at a temperature of over 100 degrees, and moisture residues are removed 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 a high precision electronic balance. The volume is calculated in the volume meter by immersion in the liquid structure and measurements of the displaced liquid (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 cm 3 .
A density measurement in kg / m 3 is often applicable.
The average density of the material
To determine how building materials behave under real operating conditions under the influence of moisture, positive and negative temperatures, and mechanical loads, you need to use the average density indicator. It characterizes the physical state of materials.
If the true density is a constant value and depends only on the chemical composition and structure of the crystal lattice of the substance, then the average density is determined by the porosity of the structure. It is the ratio of the mass of the material in a homogeneous state to the volume of occupied space in natural conditions.
The average density gives the engineer an idea of mechanical strength, degree of moisture absorption, thermal conductivity, and other important factors used in the construction of elements.
The concept of bulk density
Enter for the analysis of bulk building materials (sand, gravel, expanded clay, etc.). The indicator is important for calculating the cost-effective use of various components of the building mixture. It shows the ratio of the mass of a substance to the volume that it occupies in a state of loose structure.
For example, if the bulk density of a granular material and the average density of grains are known, then it is easy to determine the voidness parameter. 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 the base cement material will go to fill it, which will increase the cost.
Density indices 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 m 3.
- Wood with a base of cellulose - 1550 kg per m 3 .
- Organics (carbon, oxygen, hydrogen) - 800-1400 kg per m 3 .
- Metals: steel - 7850, aluminum - 2700, lead - 11300 kg per m 3 .
With modern building technologies, the density of the material is important from the point of view of the strength of the supporting structures. All heat-insulating and moisture-insulating functions are performed by low-density materials with a closed pore structure.