Abrasion resistance of stone

Abrasion resistance of stone refers to the stone’s resistance to abrasion and scratches. Abrasion resistance of stone depends on the state of granulation and hardness of the constituent minerals.

Some rocks undergo irregular erosion due to the different hardness of minerals and other constituents (such as: granite) and in this sense, it may be less than rocks that have a low but uniform hardness (such as: lime stone) should be considered. Abrasion resistance of stone is important when it is subjected to abrasion. Staircases, pavements and floors of buildings are among the places that are subject to constant wear and tear.

Additionally, in arid areas where wind erosion is significant or along beaches where the presence of sand and wind can cause abrasion, the wear resistance of the rock must be considered. Testing the wear resistance of stones can be done in different ways, including frictional wear and sand throwing.

Frictional wear

Through this test, the amount of weight or volume of the worn layer is determined from a flat sample placed in the vicinity of a rotating plate with a certain speed and worn by standard abrasive materials. This test is done for floor stones, steps, sidewalks and similar things. The test method is according to the national standard of Iran No. 619.

Sand throwing test

This method is suitable for checking the wear resistance of rubble stones or coarse aggregates that are exposed to wind and storm erosion. Another common method for the wear resistance of stones is the Los Angeles test, which must be performed according to Iran’s national standard No. 448.

Abrasion resistance is classified according to the ASTM C-170 standard based on the table below:

The most important factors affecting the wear resistance of stone are:

• Mineralogical composition

• The shape of seeds and their size

• Intergranular cement material

• Hardness of constituent minerals

• Physical properties of stone such as resistance, hardness and durability

Mineralogical composition

The most important feature of the stone that affects its wear resistance is the mineralogical composition of the stone. It is obvious that by increasing the amount of harder minerals in the mineralogical composition of the rock, its wear resistance also increases.

The presence of high hardness minerals such as quartz, sphene and orthoclase feldspars in the mineralogical composition of stones can greatly increase the wear resistance of these stones.

On the other hand, stones that are composed of minerals with a lower degree of hardness, such as: muscovite and biotite, will have less wear resistance. In fact, stones such as: granite and hornfels with a high percentage of quartz and feldspar have more wear resistance than stones such as: shale and schist.

The shape of the seeds

The shape variables of seeds have been investigated by different researchers. Researchers have used two dimensionless variables to describe the shape of seeds. These two dimensionless variables are sphericity and roundness.

Sphericity defined by Wadell (Wadell, 1934) is the ratio of seed volume to the volume of the sphere surrounding the seeds. The roundness defined by Wadell (Wadell, 1934) is also obtained from the sum of the radius of the circles that are placed in the corners of the particle as the number of circles in the corners of the particle.

According to the studies of Rostami et al. (Rostami et al., 2012), grain shape variables (sphericity and roundness) have a significant effect on the wear resistance of stone, so that with the increase of roundness, the wear resistance decreases significantly.

Wear resistance application

Paying attention to the abrasion resistance of building stones in different applications is very important. The use of inappropriate stones in high-traffic areas that are subject to high wear and tear will cause wear of the stone surface in a short period of time and increase its slipperiness.

Stones such as Limestone with the dominant mineral calcite, due to their low hardness, are not suitable for high-traffic environments such as the staircase of crowded buildings and will suffer asymmetric wear.