CHOOSE THE STONE
PROPERTIES
Real volume mass
It is the ratio between the mass of the dry specimen and its real volume and provides a rough indication of the compactness of a material. Generally a greater volumetric mass corresponds to high mechanical properties. It is therefore particularly useful for calculating the loads on artifacts, load-bearing structures or covering panels, when it is necessary to design stone walls for sea and rivers protection or to contain the land. Furthermore, a high compactness means that dust, odours, smoke, germs and pollen do not penetrate the surface layer of the material.
Unit of measurement: Kg/m3
Reference standard: UNI EN 1936
Thermal conductivity
The rocks are generally discrete conductors of heat, the specific conductivity of marble is about 3 W/m°K and this identifies a material with lower thermal resistance than insulating materials specifically conceived (having conductivity of 0.04 W/m°K). For wall covering uses, stone proves to be thermally useful and with a building inertia regulator function, mitigating the transmission of thermal shocks at the change of environmental conditions between inside and outside, and acting as a thermal insulator. However, the values depend on the structure, texture and mineralogical composition of the material: they are higher in compact and fine-grained rocks, smaller in porous and coarse-grained rocks. In general, a stone material not subjected to heat exchange remains cold but if heated it retains heat and it gradually releases the energy stored. This is why stone materials are considered particularly suitable for use in pavings with integrated heating.
Unit of measurement: Watt / meter per Kelvin degree.
Elastic modulus
It is the ratio between the value of the compression exerted on a rocky body and the value of the dimensional decrease that it undergoes. The test is particularly significant for covering products as it allows to carry out specific stability and safety checks following mechanical stresses. The elastic modulus is therefore defined as the ratio between the variation of longitudinal tension and the unitary deformation in the longitudinal direction produced.
Unit of measurement: MPa
Reference standard: UNI EN 14146
Coefficient of water absorption at atmospheric pressure
It indicates the ability to absorb water at atmospheric temperature and pressure and is expressed as the ratio between the specimen imbued with water mass and the dried specimen mass. It is directly proportional to the porosity of the material and provides indications on compactness and durability under normal environmental conditions and in cases of prolonged contact with rainwater or wet soils. The infiltration of water in a rocky material is one of its main degradation factors and this occurs in close connection with its exposure to freezing. The absorption in stone materials is generally expressed as an increase in mass percentage compared to the initial value and is quantified as a percentage.
Unit of measurement: %
Reference standard: UNI EN 13755
 | Resistance to imbibition |
Flexural strength under concentrated load
The test defines the bending breaking load and is a fundamental parameter for the mechanical strength of natural stone. A typical example of bending stress is the thrust exerted by the wind on wall slab coverings, this action is one of the most dangerous because it is fatiguing and its evaluation is one of the key problems for designing external coverings, especially when the thickness of the stone material used is very thin.
Unit of measurement: MPa
Reference standard: UNI EN 12372
| Flexural strength |
Compressive strength
The compressive strength of a rock is the resistance opposed to stresses that tend to crush it by uniaxial crushing. It is given by the ratio between the breaking load and the area of the bearing surface on which the load is exercised. Among the many factors that influence the compressive strength (texture, alteration status, duration of application of the loads, etc.), the structure, i.e. the cohesion of the rock, which generally guarantees greater resistance as it increases, for example in materials with fine grains and crystalline structure, is particularly important. Differently the stratified or oriented materials generally have a preferential direction along which they have less strength.
Unit of measurement: MPa
Reference standard: UNI EN 1926
| Compressive strength |
Compressive strength after freezing cycles
It identifies the ability of a stone to withstand harsh climates and frost, in fact the water that penetrates into the porosities of a stone material, due to the effect of frost, will increase by volume passing from the liquid to the solid state and this will affect the solidity of the material. The test consists in evaluating the specimen conditions after 48 freezing (-12 °C) and thawing (20 °C) cycles considering the surface variations, including the presence of possible cracks or signs of deterioration, as well as the decrease of the compressive strength absolute value. The factors that negatively affect freezing are flake structure, porosity, imbibition coefficient and presence of clay. Rocks that offer poor frost resistance, showing a reduction in compressive strength of more than 20%, are called freezable.
Unit of measurement: MPa
Reference standard:UNI EN 12371
| Frost resistance |
Wear resistance due to sliding friction, abrasion, friction in relation to San Fedelino granite
It allows to evaluate the behaviour of a material when it is subjected to rubbing, walking over, transit of people, vehicles or objects. It is therefore an abrasion that, in a more or less long time, changes the original surface characteristics of the material.
There are different test methods:
Wear due to sliding friction
The measurement is carried out using the Amsler-Laffon tribometer, which requires the specimen of material fastening to the abrasive plate on which it is then rotated at a speed of 1 m/s for a number of turns equivalent to the length of 1 km. The loss of thickness of the material is then registered, expressed in mm and therefore in absolute terms.
Unit of measurement: mm
Reference standard: R.D.2234 of 1939
Frictional wear in relation to San Fedelino granite
The data resulting from the test carried out at the Amsler-Laffon tribometer is compared to the behaviour of the San Fedelino granite, whose abrasion is considered equal to the unit. It therefore identifies a relative abrasion coefficient in relation to the heights of the abraded layers in the material under test compared to those of the reference material. The rocks that are more resistant than the San Fedelino granite have an index greater than 1, those less resistant an index lower than the unit.
Unit of measurement: units or tenths of absolute numerical unit
Reference standard: UNI EN 1097-1
Abrasion wear
An abrasive wheel is rotated on the natural stone specimen: at the completion of 75 laps made in a time frame of 60 +/- 3 seconds, the size of the impression made on the material is measured. The higher the measurement value, the lower the abrasion resistance.
Unit of measurement: mm
Reference standard: UNI EN 14157 / UNI EN 1341
| Wear resistance |
Knoop Micro-hardness
It is the ability of a rock to be engraved or marked, the test is obtained by evaluating the size of the impression left by a diamond penetrator in relation to the load impressed.
Unit of measurement: Kg/mm2
Reference standard: UNI EN 14205
The following can be distinguished
Impact resistance
It defines the tenacity or in contrast the fragility of a natural stone, i.e. the resistance to breakage due to the action of a direct blow provided by a blunt instrument. It allows evaluating the behaviour of stone materials in all those frequent accidental situations such as heavy objects falling. The test is carried out by dropping a steel sphere weighing 1.02 kg and 6.3 cm in diameter on a flat slab placed on a bed of sand with a thickness of 10 cm. The minimum fall height required to break the slab is therefore calculated.
Unit of measurement: cm
Reference standard: UNI U32.07.248.0
Reaction to fire
Natural stones are inert to flames, they do not emit toxic substances and ensure effective protection of the covered structures, they therefore fall within the A1 category. This property is of particular interest for furnishing projects, fireplaces and hobs.
Unit of measurement: six classes A1, A2, B, C, D, E, F
Reference standard: EN 13501-1