BITUMINOUS MIX DESIGN BY MARSHALL METHOD
(As per ASTM D 1559 – 62 T )
One of the method of designing of bituminous mix is Marshall Method. Objective To determine the stability and flow properties of bituminous mixes and to design the mix at optimum bitumen content.
i) I.S sieve
ii) Weighing machine
iii) Mixing tray with heating arrangement
iv) Moulds assembly including hammer, pedestal, sample extractor.
v) Marshall stability machine
1) Grading of the aggregate to be used in the mix to be selected first.
2) The proportion of each aggregate is determined to achieve at desired grading within
limit specified in MoRT&H specification, 5th revisions.
3) The Sp. Gravity of each aggregate and the Sp. Gravity of Bitumen determined.
4) The quantity of each aggregate (in kg) as per desired proportion with respect to total quantity of 1200 gm dry aggregate is determined for preparation of each sample. The quantity of bitumen to be mixed is also determined in gm.
5) 2% filler (Lime, Cement etc.) material is added to aggregates and the mix heated to 150
to 170 °C and the bitumen (VG30) is heated to 150 to 165 °C , so that the difference in temperature should be maintained to 15 °C .
6) The aggregates and Bitumen is thoroughly mixed with trowel.
7) Mould assembly & rammer are preheated to a temp, of 100 to 145 °C.
8) Mixing temp. is maintained at 150-165° C for VG30 bitumen.
9) After mixing mixed materials is placed in the mould assembly and compacted by
rammer with 75 blows in each face.(Rammer weight = 4.50kg and height of drop=45.7 cm)
10) 2 such samples for each bitumen percentage are prepared.
11) At least four sets of such trial specimens are prepared generally with 0.25% increment
in bitumen content, so that total no of specimens to be prepared for testing is 2 x 4 = 8 nos.
12) The specimens are left in room temp. for cooling for at least 24 hours.
13) The weight, average thickness and diameter of each specimen is recorded. There is a
correction of volume, considering the height of specimen should be 63.5mm.
14) Theoretical Sp. Gravity & Bulk density of each sample determined
15) Air voids, VMA, VFB value are determined.
16) The samples to be tested fully immersed under water during 30 to 40 minutes in
controlled water bath so that temp. can be maintained 60±1 °C.
17) Finally the stability and flow value for each sample is observed by Marshall stability
18) Following graphs are plotted from the test results : i) Marshal stability vs. bitumen % ,
ii) Bulk density vs. bitumen %, iii) % Air void vs bitumen %, iv) Flow vs bitumen %, v) VMA vs bitumen %, vi) VFB vs bitumen %.
19) The optimization in bitumen design is obtained from first three curves ( against 4 % air void)
20) Prepare specimens (usually 3 sets) with the actual bitumen obtained from design and
check the value of density, flow, voids ,VMA, VFB, stability for confirmation with
Bulk Density by physical measurement method:
Marshall Stability & Flow test: