UNIT III

 Material used for engineering purpose can be divided into three group those required for their  1) Mineral Characteristics 2) Structural Properties 3) Water Any investigation for these materials should include an assessment of their quality as well as their volume.

 Building stones,aggregate are included in the second group and their suitability would be assessed by their volume, general quality and rock mass properties like size and shape of the block  Water is important due to its ability to mix with Cement.  The chemical characteristics of the supply would therefore be considered as well as the volume available.

 Aggregate:- Concrete is of grate importance as a structural material and special attendance has to be paid to the nature aggregate employed.  Aggregate includes gravel crushed stone, sand and other material which are mixed with cement and water in making concrete.  The selection of suitable aggregate is important because ¾ volume of concrete is aggregate.  There are different rocks which can be used as aggregate. Some of them are Basalt, Gabbro Granite,Quartzite etc.

 Porosity:- The porosity of a rock is the ratio of the volume occupied by pores to the total volume of the rock sample.  It is generally expressed in percentage of the volume of the sample.  If W1 is the weight of the dry rock sample.  W2 is the weight of the sample when it is made saturated with water and  V is its total volume,  Porosity can be determined as follows  P= (W2-W1)/V x 100

 The strength of rock is determined by knowing its crushing strength,shearing and resistance to abrasion.  The crushing strength is the resistance offered by a stone to pressure.  The resistance called shearing strength.  The stones which are to be put in the foundation of civil engineering structure must have high crushing and shearing strength.  For making road metal the rock having high crushing strength are selected  The resistance of a stone to scratching or rubbing action is called its resistance to abrasion  The stone used for paving and flooring purpose must have high resistance to abrasion.

 Permeability is the capacity of a rock to transmit water. It indicate the also with which the water can percolate through the opening of rock.  The Permeability of rock is perpendicular important in number of engineering problems such as those connected with dams,reservoirs,water supply,sanitary engineering and other structure.  The permeable rock are considered harmful because they cause seepage of water which may even lead to the destruction of the structure.

 The durability of a stone is it’s capacity to retain it’s capacity to retain its original size,strength and appearance throughout a long period.  Some rock which do not resist weathering,decay and loose strength early.  The durability of a rock is directly to it’s mineral composition and texture.  Building stones in big cities are severely affected by Co2 and So2 gases which are released into the atmosphere by various industries.  During continues rain the pores in stone may be filled with a saturated salt solution. Then the crystallization of sault occurs which cause disintegration of stones

 When rock are heated to high temperature and the cooled, they may get damaged.  This is particularly the case if they rich in mineral like calcite and feldspar.  The rocks in the order of decreasing resistance to damage by fire are sand stone,granite,limestone,gneiss and marble.

 It is the resistance of a rock to tensile stresses.  Test rock cylinder diametrically in such a way that applied load would develop tensile rupturing along the plane of the specimen.  Loads are gradually increased till the cylinder fracture