لخّصلي

STONES
1.0 Introduction:
All the building structures are composed of different
types of materials. These materials are either called building
materials or materials of construction. It is very essential for a
builder, may be an architecture or engineer or contractor, to
become conversant thoroughly with these building materials.
The knowledge of different types of material, their properties
and uses for different purposes provides and important tool in
the hands of the builders in achieving economy in material
cost. The material cost in a building ranges 30 to 50 percent
cost of total cost construction. In addition to material
economy, the correct use of material results in better
structural strength, functional efficiency and esthetic
appearance
1.1 Classification of Rocks:
Building stones are obtained from rocks occurring in
nature and classified in three ways.

1. Geological classification


2. Physical classification


3. Chemical classification
   I. Geological Classification:
   According to this classification, the rocks are of the
   following types.
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   a. Igneous rocks: Rocks that are formed by cooling of Magana
   (molten or pasty rocky material) are known as igneous rocks.
   Eg: Granite, Basalt and Dolerite etc.
   b. Sedimentary rocks: these rocks are formed by the deposition
   of production of weathering on the pre-existing rocks.
   Examples: gravel, sandstone, limestone, gypsum, lignite etc.
   c. Metamorphic rocks. These rocks are formed by the change
   in character of the pre-existing rocks. Igneous as well as
   sedimentary rocks are changed in character when they are
   subject to great heat and pressure. Known as metamorphism.
   Examples: Quartzite, Schist, Slate, Marble and Gneisses.
   II. Physical Classification:
   This classification based on general structure of rocks.
   According to this, the rocks are classified into three types
   a. Stratified Rocks: These rocks posses planes of stratification
   or cleavage and such rocks can be easily split along these
   planes
   Ex: sedimentary rocks
   b. An stratified rocks: The structure may be crystalline
   granular or compact granular. Examples: Igneous rocks and
   Sedimentary rocks affected by movements of the earth.
   c. Foliated Rocks: These rocks have a tendency to split up in a
   definite direction only. Ex: Metamorphic rocks.
   III. Chemical Classification:
   According to this classification rocks are classified into three
   types.
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   a. Siliceous rocks: In these rocks, silica is predominates. The
   rocks are hard; durable and not easily effected by weathering
   agencies. Ex: Granite, Quartzite, etc.
   b. Argillaceous Rocks: In these rocks, clay predominates. The
   rocks may be dense and compact or may be soft.
   Ex: slates, Laterites etc.
   c. Calcareous rocks: In these rocks, calcium carbonate
   predominates. The durability to these rocks will depend upon the
   constituents present in surrounding atmosphere. Ex: Lime Stone,
   marble etc.
   1.2 Uses of stones:


4. Structure: Stones are used for foundations, walls, columns,
   lintels, arches, roofs, floors, damp proof course etc.
   2.Face works. Stones are adopted to give massive appearance
   to the structure. Wall are of bricks and facing is done in stones
   of desired shades. This is known as composite masonry.


5. Paving stones: These are used to cover floor of building of
   various types such as residential, commercial, industrial etc.
   They are also adopted to form paving of roads, foot paths etc.


6. Basic material: Stones are disintegrated and converted to
   form a basic material for cement concrete, morum of roads,
   calcareous cements, artificial stones, hallow blocks etc.
   5.Misalliances: Stones are also used for (i) ballast for
   railways (ii) flux in blast furnace (iii) Blocks in the
   construction of bridges, piers, abutments, retaining walls,
   light houses, dams etc.
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   1.3 Qualities of a good building stone:
   The following are the qualities or requirements of a good building
   stone.


7. Crushing strength: For a good building stone, the crushing
   strength should be greater than l000kg per cm2
   .


8. Appearance: Good building stone should be a uniform
   colour, and free from clay holes, spots of other colour bands
   etc capable of preserving the colour for longtime.


9. Durability: A good building stone should be durable. The
   factors like heat and cold alternative wet and dry, dissolved
   gases in rain, high wind velocity etc affect the durability.


10. Fracture: For good building stone its fracture should be
    sharp, even and clear.


11. Hardness: The hardness greater than 17, treated as hard used
    in road works. It is between 14 to 17, medium hardness, less
    14 said be poor hardness.


12. Percentage wear: For a good building stone, the percentage
    wear should be equal to or less then 3 percent.


13. Resistance to fire: A good building stone be fire proof.
    Sandstone, Argillaceous stone resists fire quite well


14. Specific gravity: For a good building stone the specific
    gravity should be greater then 8.7 or so.


15. Texture: A good building stone should have compact fine
    crystalline structure should be free from cavities, cracks or
    patches of stuff or loose material.
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    Stones Page 5


16. Water absorption: For a good building stone, the percentage
    absorption by weight after 24 hours should not exceed 0.60.


17. Seasoning: Stones should be well seasoned before putting
    into use. A period of about 6 to 12 months is considered to be
    sufficient for proper seasoning.


18. Toughness Index: Impact test, the value of toughness less
    than 13 – Not tough, between 13 and 19 – Moderate, greater
    than 19- high
    1.4 Characteristics of stones
    In order to ensure suitable selection of stone of
    particular work, one must be conversant with its composition,
    characteristics, uses and place of availability.
    1.4.1 Granite


19. Igneous rock


20. Composed of quart, felspar and mica and minerals


21. Available in grey, green, brown and pink and red


22. Hard and durable


23. High resistance to weathering


24. The texture varies with its quality


25. Specify gravity 2.7 and compressive strength 700 to 1300
    kg/cm2


26. Used for ornamental, road metal, railway ballast, aggregate
    for concrete; for construction of bridges, piers and marine
    works etc.
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    1.4.2 Balast


27. Igneous rock


28. It is compact, hard and heavy
    3.Available in red, yellow grey, blue and greenish black
    colour


29. Specific gravity is 3 and compressive strength varies 1530
    to 1890 kg/cm2.


30. Used for ornamental, rail road ballast, aggregates for
    concrete etc.
    1.4.3 Sand Stone:


31. Sedimentary rock


32. It is available in variety of formations fine grained, coarse
    grained compact or porous


33. Available in white, green, blue, black, red and yellow.


34. Specific gravity 2.65 to 2.95


35. Compressive strength is 650kgs / cm2


36. Used for ashlar works
    1.4.4 Lime Stone:


37. Sedimentary rock: It is available in a variety of forms
    which differ from one another in colour Compaction, texture,
    hardness and durable
    a. Compact lime stone
    b. Granular lime stone
    c. Magnesia lime stone
    d. Kanker lime stone
    f. Used for paving, road metal, etc
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    1.4.5 Marble


38. Metamorphic rock


39. Available in white, blue, green, yellow black and red colour


40. High compactness,


41. Suitable for decorative works, wall lining columns, pile,
    table slabs, hearths, tiled floors, steps of stair case etc.
    1.4.6 Slate:


42. Metamorphic rock


43. Non absorbent, compact fine grained and produce metallic
    ringing sound when struck


44. Available in black, dark blue, grey, reddish brown etc.


45. Used for providing damp proof course, paving dados etc
    1.5. Selection of stones
    In contemplating the use of stone for various
    engineering works, the selection of the nature and quality of
    stone is governed by the purpose in view, cost of stone, its
    ornamental value and durability Suitability various types of
    stones for different purposes and situation is briefly discussed
    below
    a. For face work, in general marble, granite and close-grained
    sand stone are used in the form of thin slabs (veneers) where
    the structure subjected to adverse weather effects.
    b. For pillars, balustrade, pedestals, columns statues and door
    and window sill and paving stone, granite marble and
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    Page 8 Building Materials & Construction
    compact lime stone can be recommend because they can take
    good polish.
    c. For ornamental works such as moulding and carvings, finegrained sand stone, fine grained marble and fine grained
    granite are used.
    d. For bridges, piers, docks, break-waters and other marine
    structures the stone should be very hard, heavy, strong and
    durable granite and gneiss are recommended for this purpose
    e. For road metal, stones should be hard, tough, resistant to
    abrasion and durable. Basalt and course-grained granite are
    generally recommended for this purpose.
    f. For railway ballast, the stone should be hard, dense, durable,
    tough and easily workable sandstone, compact lime stone,
    trap and quartzite are commonly used
    g. In situation like steps, doors sills, pavings etc where there is a
    regular flow of traffic, stone should be hard, dense, easily
    workable and durable. Marble, slates and sand stones are
    commonly use in such places.
    h. In fire proof construction, compact sand stone should always
    be prefferred.
    1.6 Artificial stones: These are also known as cast stones or
    reconstructed stones. Artificial stones may take up various
    forms such as
    a. Cement concrete: This is the mixture of cement, fine
    aggregates, coarse aggregates and water. It may be cast in site
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    Stones Page 9
    or pre-cast if steel is used with cement concrete, it is known as
    reinforced cement concrete.
    b. Mosaic tiles: Pre-Cast concrete tiles with marble chips at
    top surface are known as tiles. They are available in different
    shades and widely adopted at present.
    c. Terrazo : This is a mixture of marble chips and cement. It
    is used for bathrooms residential buildings, temples etc.
    Advantages of artificial stones:


46. Cavities may be kept in artificial stones to convey pipes,
    electric wires etc.


47. Grooves can be kept in artificial stone while it is being cast
    which are useful for fixing various fittings.


48. It can cast in desired shape


49. It can be made in a single piece and hence trouble of getting
    large blocks of stone for lintels, beams etc is avoided.


50. It can be made stronger than natural stone


51. It is cheap and economical


52. It is more durable than natural stone


53. Natural bed is absent in artificial stones and hence, the
    question of taking precautions with respect to the natural bed
    of stones does not arise.
    1.7 Aggregates - Grading: Aggregates is derived from igneous,
    sedimentary and metamorphic rocks or is manufacture from
    clays, slag etc. The properties of concrete are directly related
    to those of its constituents and should be hard, strong,
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    durable, and free from clay, loam, vegetables and other such
    foreign matters. The presence of clay or dirt coating prevents
    the adhesion of cement on the surface of aggregates and
    ultimately retards the setting and hardening of cement and
    reduces the strength, durability and soundness of concrete.
    Depending upon their size, the aggregates are classified as (i)
    Fine Aggregative (ii) coarse aggregates.
    (i) Fine Aggregates: The material, most of when passes through
    4.75mm I.S. sieve size, is termed as fine aggregates. It should
    not contain more than 1 to 8% of fine particles, which may be
    obtained from sea, river, lake or pit may be used as fine
    aggregates but care should be taken all its impurities must be
    removed
    (ii) Coarse Aggregates: The material whose particles are of such
    size as are retained on 4.75mm, I.S sieve are called coarse
    aggregates. The size of the coarse aggregates used depends
    upon the nature of work. The maximum size may be 23mm
    for mass concrete such as dams etc. and 63mm for plain
    concrete. Crushed hard stone and gravel is the common
    materials used as coarse aggregates for structural concretes.
    Coarse aggregates usually obtained by crashing granite,
    gneiss, crystalline lime stone and good variety of sandstone
    etc.
    Grading of Aggregates:
    Grading of aggregates consists of proportionating the
    fine and coarse aggregates in such a ratio, so as to get
    strongest and densest mix with the least amount of cement.
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    Stones Page 11
    Grading the aggregates is so graded as to have minimum
    voids when mixed with all ingredients, and water should
    render a concrete mass of easy workability.
    The grading of aggregates are done by the following methods
    (i) By trail – In this method, proportionating of aggregates
    as to give heaviest weight for same volume, yield the
    densest concrete
    (ii) By finesse modules method (sieve analysis method): in
    this method, the samples of both coarse and fine
    aggregates are passed through a set of nine standard sieve
    and the percentage of sample retained on each of the said
    sieves is determined. The total of these percentages
    divided by 100 gives the finesses modulus of sample
    (iii) By minimum voids method: This method is based on the
    fact, that so obtain dense concrete the quantity of cement
    should also be slightly in excess of voids more that the
    fine aggregates. In this method the voids in the fine and
    coarse aggregates are separately found out with the help of
    graduated cylinder and water. The percentage of voids I
    aggregate, “X” given by the equation.
    X = (V1 – V2) x 100
    V2
    Where v1, volume of water filled
    Where v2, volume of aggregates.
    (iv) By arbitrary standards: It is a commonly adopted
    method of propitiating the aggregates in a concrete mix
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    for small works of moderate importance. This method is
    not recommended for large works or important works in
    this method, the volume of cement, sand and coarse
    aggregates are taken in the proportion of 1:n:2n
    respectively. The quantity of water to be used a varied suit
    the workability descried.