In many industries, as well as in construction and agriculture, the concept of "material density" is used. 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, for concrete, builders can calculate the required amount of it when pouring various reinforced concrete structures: building blocks, ceilings, monolithic walls, columns, protective sarcophagi, pools, sluices 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 reference 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 determined from:
- liquid bodies with a hydrometer device (for example, the well-known process of measuring the parameters of the electrolyte of a car battery);
- solid and liquid substances using the formula with known initial mass data andvolume.
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
In order to accurately calculate the density of the material, the following must be taken into account:
- The error is systematic. It appears constantly or can change according to a certain law in the process of 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, determining body weight using weights and ignoring the effect of buoyancy, the data is approximate.
- The error is random. It is caused by incoming reasons and has a different effect on the reliability of the data being determined. Changes in ambient temperature, atmospheric pressure, vibrations in the room, invisible radiation and air vibrations - all this is reflected in the measurements. It is completely impossible to avoid such influence.
- 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 characters implies the appearance of an error. This inaccuracy can be partially reduced by leaving in intermediate calculations several orders of magnitude more than the final result requires.
- Careless errors (misses) are due to erroneouscalculations, incorrect inclusion of measurement limits or the device as a whole, illegibility of control records. The data obtained in this way can differ sharply from similar calculations. Therefore, they should be deleted and the work done again.
True Density Measurement
Considering the density of the building material, you need to take into account its true value. 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, the following operations are carried out:
- The structure is subjected to grinding to a powder state. At this stage, get rid of pores.
- Dry in an oven at a temperature of over 100 degrees, the remaining moisture is 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 a volumetric meter by immersing in a liquid structure and measuring 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 – volume in cm3.
Density measurement in kg/m is often applicable3.
Average material density
Toto determine how building materials behave 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 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 represents the ratio of the mass of the material in a homogeneous state to the volume of space occupied in natural conditions.
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
Introduced for the analysis of bulk building 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 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 voidage parameter. In the manufacture of concrete, it is more expedient to use a filler (gravel, crushed stone, sand), which has a lower porosity of the dry matter, since the base cement material will be used to fill it, which will increase the cost.
Indicatorsdensities 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.
- Timber with cellulose backing - 1550 kg per m3.
- Organics (carbon, oxygen, hydrogen) - 800-1400 kg per m3.
- Metals: steel - 7850, aluminum - 2700, lead - 11300 kg per m3.
With modern building construction technologies, the material density index is important from the point of view of the strength of load-bearing structures. All heat-insulating and moisture-proofing functions are performed by low-density materials with a closed-cell structure.
