Basic Requirements of Good Building Stones

 

No single stone can satisfy all the below mentioned quality requirements. For example, strength and durability requirement contradicts ease of dressing requirement. Hence it is necessary that site engineer looks into the properties required for the intended work and selects the stone accordingly. Some of the characteristics or properties of good building stones are as follows:

 

Weight

Building stones must be heavy.

 

Porosity

Stones with much pores are unsuitable because of water seeping into pores with acids and fumes destroy the stone. Water may freeze at colder climate and hence split the stone. Porosity of building stones depend upon the mineral constituent and structural formation of the parent rock. If stones used in building construction are porous then rain water can easily enter into the pore spaces and cause damage to the stones. Therefore building stone should not be porous.

 

Absorption

Water absorption of stone is directly proportional to the porosity of rock. If a stone is more porous then it will absorb more water and cause more damage to stone. In higher altitudes, the freezing of water in pores takes place and it results into the disintegration of the stone. Permissible limits of water absorption for some the commonly used building stones are as follow.

Type of Stone	Maximum limit of Water Absorption (%)
Sandstone	10
Limestone	10
Granite	1
Shale	10
Slate	1
Quartzite	3

 

Fineness of Grains

Fine grained are suitable for molding works.

 

 

 

 

Compactness

Stone’s durability is decided by its compactness.

 

Resistance to Fire

Stone should be homogenous in composition and free form calcium carbonate or oxide of iron.

Stones should be free from calcium carbonate, oxides of iron, and minerals having different coefficients of thermal expansion. Igneous rock show marked disintegration principally because of quartz which disintegrates into small particles at a temperature of about 575°C. Limestone, however, can withstand a little higher temperature; i.e. up to 800°C after which they disintegrate.

 

Electrical Resistance

The electrical resistance decreases when it gets wet. A stone should be non-absorbent to have steady and high electrical resistance.

 

Hardness and Toughness

A good building stone must be hard and tough. Hardness may be tested by scratching by pen knife and toughness by subjecting it to hammer action. Building stones should be capable to resist the adverse effects of natural forces like wind, rain and heat. It must be durable and should not deteriorate due to the adverse effects of the above natural forces. Toughness of stones means it ability to resist impact forces. Building stones should be tough enough to sustain stresses developed due to vibrations. The vibrations may be due to the machinery mounted over them or due to the loads moving over them. The stone aggregates used in the road constructions should be tough.

 

Strength

Building stones should be strong in compression. Generally most of the building stones have high strength to resist the load coming on it. Therefore it is not of prime concern when it comes to check the quality of stones. But when the stones are to be used in large structures, it becomes necessary to check the compressive strength of stones. Compressive strength of building stones generally fall within the range of 60 to 200N/mm2.

 

Durability

Compact, homogeneous stones having negligible water absorption are durable.

 

Seasoning

The stones after quarrying and dressing should be left for a period of 6 to 12 months.

Good stones should be free from the quarry sap. Lateritic stones should not be used for 6 to 12 months after quarrying. They are allowed to get rid of quarry sap by the action of nature. This process of removing quarry sap is called seasoning.

 

Specific Gravity

The more the specific gravity of stone, the more heavier and stronger the stone is. Therefore stones having higher specific gravity values should be used for the construction of dams, retaining walls, docks and harbors. The specific gravity of good building stone is between 2.4 and 2.8.

Workability

Stone should be workable. Stone is said to be workable when the work involved in stone working (such as cutting, dressing & shaping) is economical and easy to conduct.

 

Cost

Cost is an important consideration in selecting a building material. Proximity of the quarry to building site brings down the cost of transportation and hence the cost of stones comes down.

 

Dressing

Giving required shape to the stone is called dressing. It should be easy to dress so that the cost of dressing is reduced. However, the care should be taken so that, this is not be at the cost of the required strength and the durability.

 

Appearance and Color

Stones with much iron should be discouraged as the formation of iron oxides disfigures them and brings about disintegration. In case of the stones to be used for face works, where appearance is a primary requirement, its color and ability to receive polish is an important factor.

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Sources

civileblog.com/building-stones/

civilblog.org/2015/06/26/12-basic-quality-requirements-of-good-building-stones/