How to test stone? PART 4 – Volumetric density and open porosity
In previous issues of the magazine Kurier Kamieniarski we discussed mechanical properties of stone materials: compressive strength, bending strength and resistance to tearing in the pin hole. In this article we will describe the way of determining the density and porosity of materials in accordance with the PN-EN 1936:2010-05P norm “Testing methods for natural stone. Determination of density and volumetric density and total and open porosity”.
Two types of density appear in the standard: volumetric and ordinary density, and two types of porosity: open and total porosity. Volumetric density (ρb) is the ratio of the weight of the dried sample to its volume, i.e. the volume of the sample under test is taken into account together with the volume of voids (open and closed pores). Density (ρr) is the ratio of the weight of the dried sample to its volume of solid matter, i.e. the volume of voids is not taken into account. Open porosity is the ratio, expressed as a percentage, of the volume of open pores (those into which new fluid can enter) to the volume of the sample to be tested. Total porosity is the ratio, expressed as a percentage, of the volume of open and closed pores to the volume to be tested.
Volumetric density and open porosity
For all stoneware products, this test is carried out every 2 years – usually using samples prepared for compressive strength testing (a cube with a side of 50 mm). The samples are dried at 70°C to a constant weight. Then, after cooling in a exsiccator, they are weighed (md). Placing in an exsiccator is necessary in order to protect the samples from absorbing moisture from the air. The next stage of the test involves forcing water into the pores of the stone. This is done in a vacuum vessel. First, the samples are held for 120 minutes at a pressure reduced to about 2 kPa (0.2% of average atmospheric pressure) to remove air from the open pores of the stone. Then, while maintaining the vacuum, demineralised water is slowly introduced into the vessel until the samples are completely submerged. Atmospheric pressure is then restored and the samples remain under water for a further 24 hours.
After this time, the samples are weighed in water (mh) and in air (ms). From the measurements, using Archimedes’ law, the exact volume of the samples is determined.
Volume of the sample in cm³:
Volume of open pores in cm³:
Volumetric density of stone in kg / m³:
Open porosity in per cent:
Source: Kurier kamieniarski
Author: Michał Firlej | Published: 25.8.2015
