Different civil engineering constructions use stone. It is necessary to find their suitability under different conditions. The following properties need to be examined before their use:
2.3.1 Appearance and Colour
Stones must look good in appearance and be of uniform colour. Such a quality is essential for stones to be used for decoration work. Light-coloured stones are preferred as they resist weathering action in a better way. Stones with iron oxide should not be used as the presence of iron oxide disfigures the stones and brings about disintegration.
2.3.2 Strength
Stones are used as a compression member and should have sufficient compressive strength. In general, all stones possess a reasonable degree of strength. The crushing strength of stone should be greater than 100 N/mm2. Igneous rocks have a strength of around 100 N/mm2 and some of the metamorphic rocks also possess these strengths. But sedimentary rocks have a lower strength.
2.3.3 Weight
In general, good building stones should have a high weight to resist higher compressive forces. Good building stones must have a specific gravity greater than 2.70. A heavy stone possesses more compactness and less porosity.
2.3.4 Hardness and Toughness
Stones must be hard and tough so that they can resist wear and tear. Hardness is assessed by scratching and toughness by hammering. A good building stone should have a wearing resistance less than 3%, and if it is more than 3% it is not satisfactory. Stones used for road work should be hard to resist wear and tear.
2.3.5 Porosity and Absorption
All stones possess porosity. Stones that have a porosity over a certain percentage are unsuitable for building purposes. The presence of a higher percentage of pores may absorb rain, which may deteriorate the stone. A good stone should not absorb water more than 0.6% by weight. It must be capable of withstanding effects of atmosphere. If stones in a cold climate absorb water, they may freeze and even split.
2.3.6 Compactness
A good stone must have a compact, fine, crystalline structure and must be strong. A compact stone is capable of withstanding the effects of external agencies effectively.
2.3.7 Fineness of Grain
Stones that are fine grained are suitable for moulding purposes. Such stones are easily carved and dressed. Non-crystalline structured stones are likely to disintegrate under the action of natural agencies.
2.3.8 Resistance to Fire
Stones must be fire resistant, i.e., they must retain their shape when subjected to fire. Limestone resists fire up to about 800°C. Sandstone can resist fire in a better way. Although argillaceous stones are poor in strength, they are highly fire resistant.
2.3.9 Durability
Stones must be durable. Basically, stones that have their natural bed perpendicular to the direction of pressure are durable. Durable stones are those which are compact, homogeneous, acid resistant and have negligible water absorption.
2.3.10 Dressing
Dressing is the act of shaping a stone for a decorative purpose or for other purposes. For this, the stone should possess uniform texture and softness so that they may be easily dressed. Hard stones can not be dressed.
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