Highway Research Record

Laboratory Study to Determine the Impact of Flakiness and Elongation Indices on Performance of Dense Bituminous Macadam

Date of Start: September 2004 to February 2005
(i) Central Road Research Institute, New Delhi (R I)
(ii) National Highways Authority of India (S)

Scope and Objectives
(i) To determine the impact of Flakiness and Elongation indices on the Engineering properties of DBM mixes.
(ii) To study the extent to which Flakiness and Elongation indices can be allowed in DBM mixes without affecting the mix      properties.
(iii) To study the effect of only Flakiness index on DBM mixes.
(iv) To study the performance of DBM mixes in the laboratory at varying Flakiness and Elongation indices


(i) Preparation of DBM Mixes at Flakiness and Elongation indices of 30, 40, 50 and 60 percent and at flakiness index of 15, 25,     30 and 35 percent.
(ii) Testing for Mix properties like Marshall Stability, Density, Air-voids etc.
(iii) Laboratory Performance Tests like Permanent Deformation, Tensile Strength Ratio and Indirect tensile strength.


Based on the results obtained through the extensive laboratory studies undertaken for the aggregates used for production of DBM mixes with varying combined flakiness and elongation indices and varying flakiness index alone, the following major conclusions can be drawn:
(i) The stability of bituminous mix decreases with increase in combined indices from 30 to 60%. The value of stability in all the     cases is beyond 900 kg (MoRTH Specified), which may be due to reorientation of aggregates resisting the plastic     deformation. (ii) DBM mixes with 30 and 35% flakiness index have poor resistance to water damage as the indirect tensile     strength ratio values were less than the specified value of 80%.
(iii) Mixes with combined indices of 50 and 60% and flakiness index of 30 and 35% showed poor resistance to permanent      deformation, as can be inferred from creep results
(iv) The mixes with combined indices of 50 and 60% had lower resilient modulus (2000MPa). Similarly, DBM mixes with       flakiness index of 35% had resilient modulus nearer to 60% as that of combined indices.
(v) The flakiness index plays a vital role in the performance of DBM mixes. Increase in combined flakiness and elongation indices       from 30 to 60% resulted in a poor mix in terms of its volumetric properties and also laboratory performance studies.
(vi) Mixes with flakiness index upto 25 % resulted in a durable mix.

Significance/ Utilisation potential

The findings can be used to rationalize values of Flakiness and Elongation indices for conditions prevailing in India, which has been a point of major debate for some time, by the profession.

It is recommended that full scale field trials should be conducted to support/ supplement laboratory performance data.

Reports/ Publications

A technical report on the study has been submitted to NHAI