Saturday, 25 November 2017

Determination of Particle Size Distribution of Coarse Aggregates

Grading refers to the determination of the particle-size distribution for aggregate. Grading limits and maximum aggregate size are specified because grading and size affect the amount of aggregate used as well as cement and water requirements, workability, pumpability, and durability of concrete. In general, if the water-cement ratio is chosen correctly, a wide range in grading can be used without a major effect on strength. When gap-graded aggregate is specified, certain particle sizes of aggregate are omitted from the size continuum. Gap-graded aggregate are used to obtain uniform textures in exposed aggregate concrete. Close control of mix proportions is necessary to avoid segregation.
AIM:
To determine particle size distribution of coarse aggregates by sieving or screening.
Apparatus:
·         Test Sieves conforming to IS: 460-1962
o   80 mm,
o   40 mm,
o   20 mm,
o   10 mm,
o   4.75 mm,
·         Balance,
·         Stop Watch.
FIGURE:
Procedure:
1.       Take a sample of coarse aggregate in pan and placed it in dry oven at a temperature of 100 – 110oC.
2.       Take the sample weight to nearest 0.1 gram.
3.     Place the set of sieves, with the largest opening on top, into a pan and pour the aggregate onto the top sieve.
4.       The use a mechanical sieve shaker is the preferred method for separating the materials into the specified sizes. If a mechanical shaker is not available, proceed with hand shaking.
5.       Establish a shaking time for different types of aggregates that will assure proper sieving of the material without degradation.
6.       When the required mechanical shaking time is complete, hand sieve by lateral and vertical motion of the sieves with a “jarring” action that keeps the material moving continuously over the surface of the sieves.
7.       Continue hand sieving until no material passes through the sieve.
8.       Brush particles clinging to each sieve into the next lower sieve with a bristle brush. Ensure no material is lost.
9.       Determine the individual weights to the nearest 0.1 g of aggregate retained on each sieve and record these weights.
10.    Report the percentages to the nearest 0.1% for each size of aggregate retained on each sieve.
OBSERVATION:
IS Sieve
Weight Retained on Sieve (gms)
Percentage of
Weight Retained (%)
Percentage of
Weight Passing (%)
Cumulative Percentage of
Passing (%)
Remark
80 mm





40 mm





20 mm





10 mm





4.75 mm





Total





CALCULATION:
The percent retained (%), Cumulative retained (%) & percent finer (%) is calculated.
Percent retained on each sieve = Weight of retained sample in each sieve / Total weight of sample
The cumulative percent retained is calculated by adding percent retained on each sieve as a cumulative procedure.
The percent finer is calculated by subtracting the cumulative percent retained from 100 percent.
Conclusion / Result:
The result of the sieve analysis is reported graphically on a semi log graph, taking sieve sizes on log scale and % finer in arithmetic scale.

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