Stones and Aggregates
Stones and Aggregates
Stones are naturally available material for building and are obtained from rocks.
Quarrying
Stones are obtained from rocks by quarrying. Quarrying is done at some depth below the earth level, where weathering effects are not found. Quarrying is done, either by hand tools or by blasting. Dense and compact rocks are blasted, while soft rocks are channeled.
Dressing of stones
The stones are dressed to get regularity in shape and uniform size. The stone are dressed to have a hammer dressed surface, tooled surface, cut stone and rubbed surface. Dressing is done also for easy transportation.
Different types of rocks
Rocks are classified in to igneous rocks. Sedimentary rock and metamorphic rocks, Rocks are formed from minerals like quartz, feldspar, mica, horn blends, dolomite, calcite and agnate.
(a) Igneous Rocks:
These rocks are formed by cooling of molten rocky material called Magma. They have a grained, crystalline structure and they are siliceous. E.g.: Granite, basalt, dolerite.
(b) Sedimentary Rocks:
These rocks are formed due to hardening of products of weathering on pre-existing rock. They are stratified and can be easily split. E.g.:- Sandstone, lime stone, laterite, gypsum.
(c) Metamorphic Rocks:
These are formed by character change of existing rocks. They are foliated in nature and can be split at a definite direction. E.G:- Slate and Marble.
Types of stone
(a) Granite:
It is obtained from igneous rocks. It is hard and durable. It is highly resistant to weathering. It is used for construction of walls, column and bridge piers. It is used also as ballast for rail track, road and course aggregate for concrete.
(b) Trap and Basalt:
They are hard, rough and durable. They are used for paving works as road metal and also for decoration purposes.
(c) Sand stones:
It belongs to sedimentary variety. It’s strength is low. It can be worked easily and is moderately stratified. It is used for facing works, carving works etc.
(d) Laterite:
It is of sedimentary origin. It is porous and contains high percentage of calcium carbonate. It is used in manufacture of lime and cement.
(f) Marble :
It is metamorphic and calcareous. It has crystalline structure. It is used for construction of monuments, column facing, wall lining and flooring in the form of slabs.
Qualities of a good building stone
Stones used for walls, piers, dams etc must be tough and hard. The color of the stone should not be easily affected by weathering agents. It should be durable. A good building stone should allow easy dressing. It should have low water absorption. It should be fire resistant. It should have a uniform structure and close texture. It should have a uniform structure and close texture. It should posse’s good crushing strength.
Aggregates
Aggregates are important ingredients in concrete. It occupies 70% to 80% by volume of concrete. Aggregates are considered to be chemically inert materials.
Classification based on size
Fine aggregates (sand):- Passes through 4.75 mm and retained on 150µm. I.S sieve size.
Course aggregates:- Passes through 20 mm and retained on 4.7 mm I.S sieve size.
Bulking of sand
Increase in the volume of sand due to the addition of moisture content is termed as bulking of sand. Bulking increases with the increase in moisture content up to 8 to 9 percent moisture content. Fine sand bulks more than the coarse sand.
Quality of fine Aggregates (sand)
It should be free from clay content. It should not contain inorganic matter and dirt. Sand should satisfy the grading requirement depending on the type of work. It should not be smooth and round. It should be irregular and rough.
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