Common Building Stones
The following are some of the commonly used stones:
Ø Basalt and Trap
Ø Granite
Ø Sandstone
Ø Slate
Ø Laterite
Ø Marble
Ø Gneiss
Ø Quartzite.
Their properties and uses are given below:
(i) Basalt and Trap: The structure is medium to fine grained and compact. Their color varies from dark brown to black. Fractures and joints are common. Their weight varies from 18 kN/m3 to 29 kN/m3. The compressive strength varies from 200 to 350 N/mm2. These are igneous rocks. They are used as aggregates for road metals, concrete. They are also used for rubble masonry work for bridge piers, river walls and dams. These are used as sidewalks.
(ii) Granite: Granite is also an igneous rock. The color varies from light brown to pink. Structure is crystalline, fine to coarse grained. They take polish well. They are tough durable. The specific gravity ranges from 2.6 to 2.7 and the compressive strength is 100 to 250 N/mm2. They are mainly used for bridge piers, river walls and dams. They are used as curbs and pedestals. The use of granite is common for monumental and institutional buildings. Polished granite is used as cladding for table tops, columns and walls. They are used as coarse aggregates in concrete.
(iii) Sandstone: These are sedimentary rocks, and hence stratified. These include quartz and feldspar. They are found in different colors like white, grey, red, buff, brown, yellow and even dark grey. The specific gravity varies from 1.85 to 2.7 and the compressive strength varies from 20 to 170 N/mm2. Its porosity varies from 5 to 25 percent. The weathering of rocks makes it unsuitable as a construction stone. For heavy structures it is desirable to use sand stones with silica cement if necessary. They are used for masonry work, for dams, bridge piers and river walls.
(iv) Slate: These are metamorphic rocks. They are composed of quartz, mica and clay minerals. The structure is fine grained. They split easily along the planes of the original bed. The color varies from dark brown, greenish brown, purple brown to black. The specific gravity is 2.6 to 2.7. The compressive strength ranges from 100 to 200 N/mm2. They are used as roofing tiles, slabs, pavements etc.
(v) Laterite: It is a metamorphic rock. It has a porous and sponge structure. It has a high percentage of iron oxide. Its color can be brown, red, yellow, brown and brown. Its specific gravity is 1.85 and compressive strength varies from 1.9 to 2.3 N/mm2. It can be easily excavated into blocks. With spices it gains strength. When used as a construction stone, its outer surface must be plastered.
(vi) Marble: It is a metamorphic rock. It can take a good polish. It is available in various pleasing colors like white and pink. Its specific gravity is 2.65 and compressive strength is 70–75 N/mm2. It is used for facing and decorative works. It is used for columns, flooring, steps, etc.
(vii) Gneiss: It is a metamorphic rock. It ranges from fine to coarse grains. Alternating dark and white bands are common. Light brown, pink, purple, greenish brown and dark brown varieties are available. These stones are not preferred because of the harmful elements present in it. They can be used in small constructions. Although hard varieties can be used for buildings. The specific gravity varies from 2.5 to 3.0 and the crushing strength varies from 50 to 200 N/mm2.
(viii) Quartzite: Quartzites are metamorphic rocks. The structure is coarse-grained and often grainy and branched. They are available in different colors like white, grey, yellow. Quartz is the main component, with small amounts of feldspar and mica. The specific gravity varies from 2.55 to 2.65. The crushing capacity varies from 50 to 300 N/mm2. They are used as building blocks and slabs. They are also used as aggregates for concrete.