Flakiness and Elongation Index (Shape Test) of Aggregates as per IS: 2386 (Part I)
Objective:
To determine the flakiness index and,
To determine the elongation index of given aggregates sample.
To assess suitability of aggregates for use in different types of road pavements
Introduction:
The particle shape of aggregates is determined by the percentages of flaky and elongated particle contained in it. In the case of gravel it is determined by its angularity number. For base course and construction of bituminous and cement concrete types, the presence of flaky and elongated particles are considered undesirable as they may cause inherent weakness with possibilities of breaking down under heavy loads.
Rounded aggregates are preferred in cement concrete road construction as the work ability concrete improves. Angular shapes of particles are desirable for granular base course due to increase stability divided from the better interlocking. When the shape of aggregates deviates more from the spherical shape, as in the case of angular, flaky and elongated aggregate, the void content in aggregate of any specified size increases and hence the grain size distribution of a graded aggregate has to be suitable altered in order to obtain minimum voids in the dry mix of the highest dry density.
The angularity number denotes the void content of single sized aggregates in excess of that obtained with spherical aggregates of the same size. Thus angularity number has considerable importance in the gradation requirements of various types of mixes such as bituminous concrete and soil-aggregate mixes.
The evaluation of shape of the particles, particularly with reference to flakiness, elongation an angularity is necessary.
Apparatus:
The apparatus consists of;
- A standard Thickness & Length Gauge
- I.S. Sieves of sizes 63, 50, 40, 31.5,25, 20, 16, 12.5, 10 and 6.3 mm.
- A balance of cap 5 kg to weigh the samples.
Detailed test procedure is attached below.
Objective:
To determine the flakiness index and,
To determine the elongation index of given aggregates sample.
To assess suitability of aggregates for use in different types of road pavements
Introduction:
The particle shape of aggregates is determined by the percentages of flaky and elongated particle contained in it. In the case of gravel it is determined by its angularity number. For base course and construction of bituminous and cement concrete types, the presence of flaky and elongated particles are considered undesirable as they may cause inherent weakness with possibilities of breaking down under heavy loads.
Rounded aggregates are preferred in cement concrete road construction as the work ability concrete improves. Angular shapes of particles are desirable for granular base course due to increase stability divided from the better interlocking. When the shape of aggregates deviates more from the spherical shape, as in the case of angular, flaky and elongated aggregate, the void content in aggregate of any specified size increases and hence the grain size distribution of a graded aggregate has to be suitable altered in order to obtain minimum voids in the dry mix of the highest dry density.
The angularity number denotes the void content of single sized aggregates in excess of that obtained with spherical aggregates of the same size. Thus angularity number has considerable importance in the gradation requirements of various types of mixes such as bituminous concrete and soil-aggregate mixes.
The evaluation of shape of the particles, particularly with reference to flakiness, elongation an angularity is necessary.
Apparatus:
The apparatus consists of;
- A standard Thickness & Length Gauge
- I.S. Sieves of sizes 63, 50, 40, 31.5,25, 20, 16, 12.5, 10 and 6.3 mm.
- A balance of cap 5 kg to weigh the samples.
Detailed test procedure is attached below.
