Unit i
- 1. UNIT I STONES – BRICKS – CONCRETE BLOCKS
- 2. STONE AS BUILDING MATERIAL Stone is one of the oldest building material. Our ancient people used to live in small homes or caves made of stones. Researches from Archaeologists shows that stone is used as building material in India starting from 3200 BC. Many ancient monuments like Ajantha temple, Taj Mahal etc., were completely made of stone. Many ancient civilizations like Indus valley civilization, Mesopotamian civilization used stone as building material.
- 3. Stones are derived from rocks which form the earth’s crust and have no definite shape or chemical composition but are mixture of two or more minerals.
- 4. CLASSIFICATION OF STONE Stones are classified in following four ways i)Geological ii)Physical iii)Chemical iv)Practical i)Geological o Geologically the rocks are classified as a)Igneous rocks - Formed by cooling the molten lava on or inside the earth’s surface during the volcanic eruption.
- 5. - The portion of lava which comes outside the surface, cools quickly and forms the rock of non- crystalline nature such as Trap or Basalt. - The portion which remains inside the earth undergoes cooling at slow rate and results in formation of crystalline variety known as granite.
- 7. b)Sedimentary rocks - Formed by gradual deposition of disintegrated rocks, vegetable matter and clay at the bottom of rivers, lakes or sea. - Eg: Limestone, Sandstone. c)Metamorphic rocks - When sedimentary rocks or igneous rocks are subjected to great heat and pressure inside the earth, a new variety of rock is formed known as metamorphic rocks. - The change of structure is called metamorphism. - Eg: Limestone changes to marble, Slate changes to gneiss etc.,
- 8. ii)Physical classification a)Stratified rocks b)Unstratified rocks a)Stratified rocks - Exhibit distinct layers which can be separated. - Plane along which separation can be carried is called clevage plane. - Eg: limestone, slate, sandstone.
- 10. b)Unstratified rock - Do not show any sign of strata and cannot be easily split in to slabs. - Eg: Granite, trap. iii)Chemical classification a)Silicious rocks Eg: Sandstone, Quartzite b)Argillaceous rocks Eg: Slate, laterite, kaolin c)Calcarious rocks Eg: Limestone and marble
- 11. iv)Practical Classification - Classified based on usage - Stones have been classified as granite, marble, slate, limestone etc.,
- 12. CRITERIA FOR SELECTION OF STONE Appearance and Colour - Uniform and appealing colour if used for decoration. - Free from flaws and clay holes. - Stones with high iron content should not be used since it will disfigure and brings detoriation to stones. - Able to receive good polish. Weight - Weight should be high as heavier stones can resist high force. - Heavy stone possesses more compactness and less porosity.
- 13. Porosity and absorption - If porosity is high the stone is unsuitable for construction because during rain water will seep in to pores and destroy the stone. - When climate is cold, water entering pores may freeze and split the stone. Fineness of grain - Fine grained stones are suitable for moulding works. - Non-crystalline stones will disintegrate under the action of natural agencies. Compactness - Stones durability is decided by their compactness or density of compaction. - Compact stone can withstand the effects of external agencies effectively.
- 14. Resistance to fire - For resistance against fire, the stone i)should have homogeneous composition and ii)should be free from calcium carbonate or oxide of iron. Electrical resistance - The electrical resistance of a stone decreases when it gets wet. - Stone must be non-absorbent to have steady and high electrical resistance. Hardness and toughness - Stone must be hard and tough to resist wear and tear. - Hardness is tested by scratching with a pen knife. - Toughness is tested by subjecting it to hammering action.
- 15. Strength - Stones used in buildings are subjected to compression. - Hence they should have sufficient strength to meet the requirements. Durability - A stone is more durable if it is i)compact ii)homogeneous iii)free from any material affected by HCL and H2So4. - It should have negligible water absorption. Dressing - The art of shaping a stone is known as dressing. - Stones should possess uniform texture and softness for easily dressing.
- 16. Cost - Cost is an important factor for selecting building stone. - The cost of stone depends upon the ease with which it can be quarried out, proximity of quarry to place of use and transportation facilities available. - Dressing cost should also be low. Seasoning - Good stone must be free from quarry sap. - Stones after quarrying and dressing should be left for a period of 6 to 12 months for proper seasoning before use in construction work.
- 17. USES OF STONES AND THEIR SELECTION USE NAME OF STONE REASON Construction of building exposed to high wind particles Granite and sand stone Hardness due to presence of silica General building work (i.e walls, foundation and super structure) Sand stone Hard and durable Heavy engineering works (docks, bridges and light houses) Granite and gneiss Strong, durable, capable of resisting thrust Building exposed to fire Compact sand stone Fire resisting property Building in industrial town Granite and Sand stone Acids and smoke proof Road metal and railway ballast Granite and basalt Hard, tough and abrasion resistance
- 18. TESTS ON STONES 1)Hardness Test: o Tested by a pen knife. o Determined with aid of Moh’s scale of hardness. o If a pocket knife makes a mark on fresh surface of limestone, the hardness of it may be taken as H = 3. o Hard silicious rock has a hardness of H=7 since it cannot be scratched easily with knife. o Coefficient of hardness is found as follows i)A cylinder of dia 25mm and height 25mm is taken and filled with stone to be tested. ii)It is then weighed. iii)Placed in Dorry’s testing machine and pressed with a load of 1250 gm.
- 19. iv) Annular disc of the machine is rotated at a speed of 28 r.p.m. v)During rotation, coarse sand of standard specification is sprinkled on top of disc. vi)After 1000 revolutions, the specimen is taken out and weighed. Coefficient of hardness = 20 – (loss in weight in gm/3) 2)Crushing Test o Tested to find out compressive strength of stone. o Needed for stones used at bottom of heavy structure. o The test is carried out as follows i)Stone is cut in to cubes of size 40mmX40mmX40mm and sides of cube are finely dresses and finished.
- 20. ii) Specimen are placed in water for 72 hours prior to test and tested in saturated condition. iii)Load bearing surface is covered with plywood and load is applied axially on the cube at the rate of 13.7 N/mm2 per minute with crushing testing machine. iv)Crushing strength per unit area is maximum load at which sample crushes divided by area of bearing face of specimen. Name Compressive strength(N/mm2) Laterite 2 to 3 sandstone 70 Granite 70 to 130 Trap 300 to 400
- 21. 3) Impact test: o Carried out in an impact testing machine. o The test is carried out as follows i)Cylinder of dia 25mm and height 25mm is taken and filled with sample stone. ii)Sample is placed on the machine. iii)A steel hammer of 20N is allowed to fall axially in vertical direction. iv)Height of first blow is 1cm, that of second blow is 2cm and so on. v)The blow at which specimen breaks is noted. If it is nth blow, n represents the toughness index of the stone.
- 22. 4) Fire resistance test o Stone which is free from calcium carbonate can resist fire. o Presence of calcium carbonate in the stone can be detected by dropping few drops of dilute sulphuric acid which will produce bubbles. 5)Attrition test o To determine the rate of wear of stones employed for construction of road. o Carried out in Deval’s attrition testing machine. o Test is carried out as follows i)Sample of stone is broken in to pieces of 60mm size. ii)Samples are taken in cylinders of dia 200mm and length 340mm respectively.
- 23. iii)Cylinders are rotated about the horizontal axis for 5 hours at the rate of 30 r.p.m. iv)Contents are taken out from the cylinder and passed through a size of 1.5mm mesh. v)Retained material is weighed. % wear = (loss in wt/initial wt)X100. 6)Acid Test o Stone is kept for one week in the solution of sulphuric acid and hydrochloric acid. o Corners of stones will turn roundish and loose particles will get deposited on surface if alkaline content is high. o Stone having