PART 4 – DENSITY AND POROSITY

Total density and porosity

It is a test that is done every 10 years. The norm determines the possibility of doing the test in two ways: method A (pycnometer) and method B (Le Chatelier volumetric flask). The first method is more precise. This is why it is used more often and will be described below.

Samples from the previous volume test of density and open porosity are then separately ground to dust that will allow for individual dust grains to pass through a sieve with the size of the openings 0.063 mm. It is then dried to a constant weight and separated into approximately 10 g of stone dust (m_e).

Deionized water is poured into the pycnometer until it is filled up to half of its volume. Weighed stone dust is then poured off and mixed with water to disperse in the liquid. Pycnometer is then exposed to vacuum (2 kPa) until there are visible bubbles. The pycnometer is then filled with water and the process of sedimentation occurs until the stone dust settles at the bottom and water above the sample is not clear. The rest of the water is then poured in, the pycnometer is closed with a stopper and dried (wiped off) from the outside. The whole unit is then weighed and written down as m₁.

Emptying and cleaning the pycnometer is the next phase. After that it is filled with deionized water. Next, it is sealed off and wiped. The pycnometer is weighed again, and the value written down as m. Calculation 2 is done according to the following formulae.

Density is expressed by the following formula:

Total porosity is expressed by this formula:

This is how you can determine the basic characteristics, density and porosity, of rock. Knowledge of density of the material is important for construction works. Designers need to know the weight of the element so that they can design constructions with enough load bearing capacity. The results should be similar in repeated tests of the material. If there are changes of the volume weight of natural stone in subsequent tests, it can signify changes in mineral composition of the rock delivered for the test. High porosity can also influence other characteristics of the material. The influence does not always have to be direct. There can be differences in liquid absorption, frost resistance, and durability of the material to temperature shocks. In other words, these are parameters that show the durability of material in different conditions of use.

Source: Kurier kamieniarski

Author: Michał Firlej   |   Published: 25.08.2015