Factors Affecting Strength, Hardness and Toughness of Stones
- Hardness or softness of the components
- Proportions of the hard and soft minerals
- Size and shape of the minerals
- Cementing material
a) Hardness or softness of the components:
The composition of the compounds determines its hardness or softness. Stones containing Si, Na, K are poor while that containing Mg, Ca, and Fe are good, as they are harder. If the stone is composed of soft and unhardened materials it will result in a soft materials and vice versa.
b) Proportion of hard and soft materials:
The amount of soft and hard material in a specific sample of stone also matters. Greater the amount of hard materials more will be the resistance to weathering.
c) Size and shape of the minerals in stones:
Crystalline solids are hard and compact, thus superior to non-crystalline. Finer the crystals, stronger the stones and vice versa, This property i.e fineness reduces the pores in the stone.
It is the property of atoms or particles to attract each other. The fine grains have more cohesive power than the coarser grains. Greater the cohesion in stone causes increase in the hardness, strength and toughness of stones. The property of compactness also depends deeply on cohesion.
Stones in wet conditions and having pores in them allow a lower crushing strength than normal. Porosity can reduce the strength upto 30 - 40% e.g limestone and sandstone are affected by this property. Porosity is the property of a substance in which it contains pores i it. It also reduces the resistance to a concentrated (point) load.
If a stone is compact, dense, it would also be non-porous and strong , thus toughness also depends upon density.
g) Cementing material:
Stones with silicates as cementing material will be resistant to weathering than those with calcareous or ferruginous binding material. So, cementing material also affects the choice of stone selection.