TYPES OF STONES

Stones can be either artificial or natural.

ARTIFICIAL STONES

It also called the engineered stone. They are made from crushed natural stones bonded with the Portland cement in very low water/cement ratio of less than 0.32.

Manufacturing of artificial stones by use of  the natural stones:

1)    Calcareous stone materials such as marble, limestone or dolomite.

2)    Siliceous stone materials such as granite, quartzite, sand, porphyry.

The nature, colour, quality of the aggregate used as well as the bonding paste can vary the aesthetic appearances of the artificial stones. 

Manufacturing process

1)    A mixture of the raw materials which are crushed stones and the bonding agent( cement) is compacted by vibration under vacuum to produce

Ø Slab tiles where thin monolayer tiles of the required sizes are produced

Ø Large-size block which these block are then sawn into slabs to be transformed into finished products with the required sized

The figure below refer to the process take place in the manufacturing of artificial stone 
                                                      

                                                   

NATURAL STONES

Stones used in the building materials which taking from the earth and cutting them into the size and shapes required for the construction.

3 types of rocks are quarried to produce building stones:

·        Igneous rock that deposited in a molten state such as granite and basalt

·        Sedimentary rock that deposited by the action of water, wind and ice such as sandstone, limestone, dolomite

·        Metamorphic rock that is formerly either igneous or sedimentary. Its properties changed according to heat and pressure. These rocks such as slates, marble, quartzites.

The natural stones are generally extremely durable. However, deterioration may result due to wrong choice of stone being exposed to the weather elements, faulty design and workmanship, atmospheric pollution, soluble salt action, frost, wetting and drying, rusting of ferrous metals and vegetation growth.

Igneous stones

Granite is using for most building purpose. It is a mosaic of mineral crystals such as feldspar, mica and quartz. It can be obtained in gray, black, pink, red, brown and green.

                                              

Properties of granites:

1) High compressive strength up to 335 N/mm²

2) Nonporous

3) Hard and durable which able to withstand hard knocks and abrasion,

4) Resistant to ordinary chemicals,

5) High density of between 2460-3200kgandm2,

6)  Impermeable which making it a very good material for damp-proof courses or bases in contact with the ground.

Sedimentary stones

A)Limestones is composed of either calcium carbonate or of a mixture of calcium and magnesium carbonates.

                                          

Properties of limetones

1)    porous

2)    vary in hardness

3)    soluble in water containing carbon dioxide

4)    Attacked by acid

B) Sandstones consist of fine and coarse particles of quartz with particles of         feldspar or mica bonded together by natural cement. The natural cement is deciding the strength, durability and colour of the sandstone.

                                                       

Sandstone are classified according to the types of the natural cement    

1.     Siliceous sandstones are cemented by compound of silicate. They are good in resistance of acid and are durable. However, it is difficult to work with

2.     Calcareous sandstones are cemented with calcite crystals of calcium carbonate. The stone is more easily worked compared with siliceous sandstone. However, it is less durable and used in the rural areas.

C) Dolomite stone are bonded with calcium carbonate and magnesium carbonate which are white-bluff colour.

Metamorphic stones

A)  Slates are made by immense earth pressure acting upon clay which are dense hard stone with closely spaced planed of cleavage, along which easily split into sheets.

                                                     

Properties of good slates:

Ø Durable

Ø Acid and alkali resistant

Ø Strong in tension and compression compared with other stones

Ø Very hard and denser than granite

Ø No allow moisture movement

Ø Negligible moisture absorption and good impervious

Ø Good electrical insulator

Ø Interesting appearances with textures

B)   Marbles is recrystallised form of limestone which have a consistent parttern throughout the thickness of a block. Pure marble is very fine crystallized.

                                                           

Properties of marbles:

Ø Very hard, dense and resistant to abrasion

Ø Varying in colour and vein

Ø Impervious but discoloration can result in damp conditions

Ø Sugaring can occur on exposed surface and highly marbles tend to fade

Ø Excellent self-polish which greatly enhance its appearance,

Ø Susceptible to acid attacks, thus polished surface is not retained for long if used externally in a polluted atmosphere,

THE DIFFERENT FORMS IN  WHICH STONES ARE USED

The construction industry used stones in the following form:

·        Fieldstone which is rough stones obtained from river beds and fields.

·        Rubble which is irregular quarried fragments that have at least one good face.

·        Dimension stone which is quarried and cut into rectangle form.

·        Cut stone ,this is quarried and cut into large slabs.

·        Ashlar which is small rectangular blocks.

·        Flagstone which it is thin slabs of stone used for flooring and paving; either regular or irregular shape

·        Crushed stone which is useful in site work as freely draining fill material, paving, surfacing materials and aggregates.