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FIELD TESTS FOR CEMENT

Following four field tests may be carried out to ascertain roughly the quality of cement colour : colour of cement should be uniform i.e. grey colour  with a light greenish shade   Physical Properties : cement should fell smooth when touched or rubbed in between gingers  if it is felt rough ,it indicates adulteration with sand  if hand is inserted in a beg or heap of cement , it should  feel cool and not warm  if small quantity of cement is thrown  in a bucket of water , it should sink and should not float on the surface  A thin paste of cement with water should feel sticky between the fingers  if the cement contains too much of pounded clay and silt as an adulterant , the paste will give an earthy smell         3 :Persence of lumps : cement should be free form any hard lumps . such lumps are formed by                  the absorption of moisture form the atmosphere              . Any bag of cement containing such lumps should be rejected .         4: Strengt
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COMPRESSIVE STRENGTH TEST

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Cement, fine aggregate and coarse aggregate (up to 38) to be used for making concrete are weighed in the ratio to be used in the field and are of hand mixing or by machine mixing             Now water is added and the entir batch mixed until the concrete appears to be homogeneous and has the desired consistency test specimens recommend are 150×150×150 mm cubes or cylinders of 150 diameter and 150 mm height  Mixed concrete is filled into the  mould in layers of 50 mm and each layer is tamped with 16 mm in diameter and 600 mm long 35 times or with a vibrator   Test specimens are stored at a temperature 27+-3 °c at 90% humidity for 24+_1/2 hour form the time of addition of water to the dry ingredients  the After this time specimens are removed  from the moulds and placed in water and kept there until taken  out just before the test                      • usually specimens are tested for 7 day  or 28 day  strength but IS code only suggest 28                         days stre
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FACTORS AFFECTING WORKABILITY

1 - water content:  Fluidity of concrete increases with water content because addition of water enhance interpartical lubrication  At site it is normal practice to increase the water content to make the concrete warkable which lowers the strength  In controlled concrete this cannot be resorted and even in uncontrolled concrete this should be the last choice  But in case if more water is added due to any reason the cement content should be proportional increased    2- mix proportions :  Aggregate cement ratio influences the workability to a large extent . The higher the ratio leaner will be the concrete. Lean concrete paste available for lubrication of per unit surface area of aggregates will be less and hence the warkability is reduced    3- shape of aggregates :      Big size aggregate  the total surface area to be wetted is less paste is required for lubricating the surface to reduce internal friction .for a given water content big size aggregate give high warkab
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WARKABILITY

Warkability is defined as the property of concrete which determines the amount of useful internal wark necessary to produce full compaction  In simple words it can also be defined as the ease with which concrete can be compt 100% with regard to made of compaction and place of deposition  A concrete which can be readily compacted is said to be workable , but to merely say that warkability determines the ease of placement and the resistance to segregation is to loose a description of this vital property of concrete  Desired warkability in any particular case would depend on the means of compaction available likewise ,a warkability suitable for mass concrete is not necessary sufficient frothing , inaccessible ,or heavily reinforced section  It should be noted at warkability is different form consistency . consistency indicates fluidity or mobility  Concrete with high consistency may not be workable for a particular job and concrete having same consistency many very in warkability
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BRICK MASONARY

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1 . Stretcher :  Stretcher is the longer face of the brick ( i.e. 19 cm × 9 cm ) A course of bricks in which all the bricks are laid as stretches on facing is known as a stretcher course or stretching course  2. Header :  Header is the shorter face of the brick ( i.e. 9 cm × 9 cm ) . A course of bricks in which all the bricks are laid as headers on the facing is known as header course or heading course .  3. Lap :  Lap is the horizontal distance between the vertical joints of successive bricks courses  4 . Prepand :  Perpend  is an imaginary vertical line which includes the vertical joint separating two adjoining brick  5 . Bed :  Bed is the lower surface ( 19 cm × 9 cm ) of the brick when laid flat  6 . Closer :  closer may be of various types  closer it is a portion of a bricks with the cut made longitudinally, and is used to close up bond at the end of course  it helps in preventing the joints of successive sources ( higher or lower )
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WHAT IS SLUMP TEST

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Slump test is one of most extensively used test all over the world  Slump test does not measure workability of concrete , although it gives a measure of consistency , but is very useful in detecting variation in uniformity of mix of given nominal proportions  Dimensions of the mould are, bottom diameter =200 mm top diameter =100mm and hight = 300 mm  Mould is filled in with fresh concrete in four layers , each layers of approximately one - quarter of the height of the mould and tamped with 25 strokes of the rounded end of the tamping rod ( dia 16 mm and length 600 mm)  Strokes are distributed in a uniform manner over the cross section and for the second and subsequent layers should penetrate into the underlying layer  After the top layer has been rodded, the concrete is struck off level with a trowel or the tamping rod such that the mould is exactly filled .  Mould is removed immediately by raising il slowly and carefully in a vertical direction   It allows the concrete to sub
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REBOUND HAMMER TEST (SACHMIDT HAMMER TEST )

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It is a surface hardness tester for which an empirical correlation has been established between strength and rebound number It is based on the principal that the rebound of elastic mass depends on the hardness of surface against which the mass impinges  For this test, a rebound hammer also called Sachmidt hammer ,which weight about 1.8 kg and is suitable for both laboratory and field work  Is has a spring controlled hummer mass that slids on plunger with in a tubular casing . Hammer is forced against the surface of concrete bt the spring and the distance of rebound is measured on a scale which give indication of concrete strength  This test is suitable for the concrete having strength in the range of 20-26 MPa  Results are affected by facters sach as smoothness of surface size and shape of specimen , moisture condition of the concrete ,type of cement and coarse aggregate and extent of extent of carbonation of surface 
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