Importance:
This experiment is carried out to find and check the gradation of coarse aggregate i.e. crush. The concrete’s main bulky material is crush, it is used to increase the volume of the concrete along with its strength giving property. The gradation of other two materials of crush is checked by the experiment no 1 and experiment no 2, but here the purpose of finding the fineness modulus is not the same as in previous experiments. Instead here its fineness modulus is calculated for finding the water ratio to be used, along with the value of specific gravity of crush and its maximum grain size.
In this experiment the maximum size of coarse aggregate will be calculated from the table of fineness of modulus. For example if its maximum size is ¾ inches, then it means that it contain all the grain size less than and equal to ¾ inches. This can also be expressed by writing it as a: ¾ inch Down crush.
Sieves Used:
The sieve used for this gradation are 1 ½ in, 1 in, ¾ in, ½ in, 3/8 in, and #4 sieve. The difference is that #4 sieve means that there are four holes in one linear inch of the sieve, whereas 1 ½ inch sieve means that the one side dimension of the sieve hole is 1 ½ inches (not that, there are one and a half inch in one linear inch of the sieve). The sieves are stacked in ascending order of their dimensions. In this the crush sample is of 3000 g.
The procedure of taking reading is same as in the previous experiment except that we have to find out the maximum grain size as well from the same table.