Objective

For determination of elongation index of coarse aggregate, where the        size of the coarse aggregate are larger than 6.3 mm. 

Reference Standards

IS: 2386 (Part I) – 1963 – Method of test for aggregates for concrete (Part I) Particle size and shape.

Equipment & Apparatus

• Length gauge
• Sieves (63mm,50mm,40mm,31.5mm,25mm,20mm,16mm,12.5mm,10mm)
• Balance (0-10kg)
•  Oven (300⁰c)

  

Test Sample Preparation

Surface dry samples is used for the test. A minimum number of 200 pieces of any specified fraction is required to do the test. 

Procedure

1. The sample is sieved through IS sieve specified in Table shown below.

   

2. A minimum of 200 pieces of each fraction is taken and weighed.
3. In order to separate elongated materials, each fraction is then gauged individually for length in the length gauge.
4. The pieces of aggregate from each fraction tested which could not pass through the specified gauge length with its long sides elongated are collected separately to find the total weight of aggregate retained on the length gauge from each fraction.
5. The total amount of elongated material retained by the length gauge is weighed to an accuracy of 0.1% of the weight of sample. 

Calculation

In order to calculate the elongation index of the entire sample of aggregates, first the weight of each fraction of aggregate passing and retained on the specified set of sieves is noted (Y1, Y2, Y3, Y4…..etc). Each piece of these are tried to be passed through specified length of the gauge length with its longest side and those elongated pieces which do not pass the gauge are separated and weighed (y1, y2, y3, y4…etc). Then the elongated index is the total weight of the material retained on the various length gauges, expressed as a percentage of the total weight of the sample gauged.

Reports

Elongation index is reported in percentage to the nearest whole number. 

Safety & Precautions

• Use hand gloves while removing containers from oven after switching off the oven.
• Use safety shoes, mask & aprons at the time of test.
• Thoroughly clean & dry the container before testing.
• Special care should be taken that no outer air enters when using the balance.
• All parts of the equipment should always be kept clean.
• After the end of the test sieve should be clean by smooth brush.