How to Assess the Quality of Fine Aggregate at Site?Posted in Student Corner | Email This Post |
There are lots of methods and test, that we can use for assessing the quality of construction sand or Common sand. But when it comes to the case of site practices, the methods like bulk density, bulkage, specific gravity test etc, become difficult or up to an extent impossible. There comes the importance of Sieve test on fine aggregates.
Sieve testing is one of the very fast methods of checking the quality of construction sand. Even though, the result of sieve test cannot be considered as the final result to ensure the quality of sand.
Arrange the sieve sets as per IS 383:1970 as follows and sieve a representative sample of known weight through the sieve set.
|Is sieve size||Weight of sand retained||Percentage retained||Cumulative percentage retained||Cumulative Percentage passed|
Fineness modulus (F.M) = Total Cumulative percentage retained/100
3. Result Analysis:
3.1. Based on grading Zones
The result of the sieve analysis is analysed based on the Zones of aggregate described on IS 383: 1970. By drawing the grading curve (semi log curve) for the obtained values of percentage retained on each sieve, but in the case of site practice it might be difficult to plot the curve. Hence the gradation of aggregate is assessed by the range of values for each sieve sizes. While going through the analysis we may face the issue that the values of percentage retained may be overlapping with all the four zones.
It should be noted that the values of 600 microns Sieve size are not over lapping in any zone. Hence it can be considered as one reference point for assessing that to which zone the aggregate belongs.
The gradation can be indicated as,
|Percentage Passing||15 to 34||34 to 59||60 to 79||80 to 100|
|Zone of Aggregate||Zone 1||Zone 2||Zone 3||Zone 4|
3.2. Based on Fineness Modulus
As per IS 1542: 1992 – clause 5.2, the fineness modulus of sand shall be not less than 1.4 in case of crushed stone sands and crushed gravel sand and not less than 1.5 in case of naturally occurring sands. Lower FM indicates fine sand and higher FM indicates courser sand.
4. Result interpretation
4.1. Based on gradation Curve:
|Zones||Zone 1||Zone 2||Zone 3||Zone 4|
4.2. Based on Fineness Modulus:
The fineness modulus is also considered as the indication of quality of aggregate. According to IS recommendations the aggregate should posses the F.M to the range of 2.6 to 3.2. Greater than 3.2 should be rejected.
The Classification of sand based on Fineness modulus is as follows,
Fine Sand – 2.2 to 2.6
Medium sand – 2.6 to 2.9
Coarse Sand – 2.9 to 3.2
• IS 383 : 1970
• IS 1542 : 1992
• IS 456 : 2000
This article is submitted to us by Vaishnav C R Nair. We are thankful to him for submitting this very useful article to us.