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In Situ Density Test- Part 1 (Core Cutter Method)

In soil mechanics, No matter what you are calculating whether it's bearing capacity of soil or stresses in soil, you encounter with a term 'Density of soil'. The density of soil is used in calculating the stresses in soil, Earth pressure beyond the Retaining wall, Dam, Embankment and Estimation of soil settlement under structural loads. It is also used in Field Compaction of soil and in many other method.
In simple language, we can defined Density of soil as ratio of Mass of soil to Volume of that soil (Mass per unit volume of soil).

                                             Density, γ= W/V

            γ= mass density of soil
           W= weight of soil 
            V= volume of soil

For dry density we know, 

   where w= water content

For calculating the density of soil, there are number of field test. From which, we are going to discuss Core Cutter method.


Apparatus
Cylindrical core cutter (height=12.7 cm & internal dia= 10 cm)Steel RammerSteel dolly (height= 2.5 cm & d…

Workability and Slump test for Concrete

 

The term Workability of concrete  is used to describe the ease or difficulty with which the concrete is handled, transported and placed .The loss of homogeneity is minimum. 
       As a physical property of concrete can be defined as amount of useful work done to produce full compaction.
 Workability is mainly affected on  following reasons:
  •    Water content,water cement ratio and aggregate cement ratio.
  •  Grading,shape,texture and maximum size of coarse aggregate used in mixture.
The concrete mixture for one work may prove to be too stiff or wet for another work.
The strength  of concrete is not to be affected,the degree of workability can be obtained: 
  •  By changing slighty proportions of fine and coarse aggregate in case of concrete mixture is too wet.
  •   By adding a small quantity of water cement paste in the proportion of mixture.
The workability of concrete is measure by various test but slump test is quite common 
SLUMP TEST: In the slump test, standard cone whose length is 300mm,one diameter is 100mm and other diameter is 200mm.

3
   The concrete is filled about one fourth portionand then rammed
Then it is completely filled with concrete such that cone is full of concrete and then cone is raised vertically and removed.
  The concrete is allowed to subside and the height of concrete is measured. The  slump is obtained by deducting height of concrete after subside from 30 cm.
The main advantage of slump test is that apparatus is cheap,portable and convenient of same indentical mix.
But major disadvantage is that it is not used for concrete in which maximum size of aggregate exceeds 40mm
   Classification of concrete :
   
    Slump               nature of concrete mix
   No slump          stiff and extra stiff mix
   10 -20mm         poorly mobile mix
   40-150mm        mobile mix
   Over 150mm    cast mix
 
Type of concrete                        slump
For road construction                20-40mm
For mass concrete                       25-50mm
Canal linings                                70-80mm
Arch and side walls                    90-100mm


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