Building Stone(1)

Durability

Durability of rock will be depend on its capacity  to stand the attack of the agents of weathering . Resistance to weathering will be determined by the chemical stability of constituent mineral which varies within wide limit.

Some minerals being more easily decomposed than others. The common rock forming minerals when arranged in the order of increasing resistance to weathering . ( nepheline, lecute, olivine , augite hornblende, plagioclase, orthoclase, biotite , muscovite, quartz,.)  Acid rocks are more durable than the basic rocks.

Porosity

The shape , size, nature of packing of the grains of a rock give  rise to the property of porosity. It is expressed as ratio between the total volume of pores spaces and total volume of rock sample. It expressed in percentage.

Porosity is an important  engineering property in the sense that it accounts for absorption values of stones. i. e. capacity of stone to absorb moisture when immersed in water for 72 hours.

Presence of interlocking crystals angular grains abundant cementing material are responsible for low porosity of stone .highly porous if composed of spherical or rounded grains

eg. granite quartzite basalts       .1 to .5 percent

Sand stone , lime stone               5 to 25 percent

   Density

Weight per unit volume of substance  1) Dry density 2) bulk density 3) saturated density 4) true density

Engineering significance of this is denser rock are stronger than lighter rock of same composition. Density of stone being known , load imposed by it at any level in the stone.  Granite     2.7 Basalt     2.9   Sandstone   2.6  Limestone 2.6

Abrasive Resistance

It is more qualitative than quantitative property. It is defined as resistance which a stone offers to rubbing action. This test is carried for stones used in along paving  road, in flooring, in building and as lining in tunnels. The safe value for coefficient of wear is 20 .  Abrasive resistance is determined with the help of Dorrys Abrasion testing machine.

Frost and Fire resistance

Many building stones shows quick disintegration when used in situation involving frost formation or heating. Frost causes disintegration by expansion of water , on freezing within the rock pores.

 In case of fire it is unequal expansion in different minerals and also at different depth from surface inward. This effect becomes more pronounced when rock is first heated and then suddenly cooled by water. Stone may crumble to pieces under such a treatment. Rock which are found porous and weak in strength are easily affected in cold climates by frost action.