PREPARATION OF TEST SPECIMEN FOR MARSHALL METHOD

The coarse aggregates, fine aggregates and the filter materials should be proportioned and mixed specified gradation of mineral aggregates and bitumen binder as per IRG: 29–1968 are given in Table. The aggregates and filler are mix together in the desired proportion as per the design requirements and fulfilling the specified gradation. The required quantity of the mix is taken so as to produce a compacted bituminous mix specimen of thickness 63.5mm, approximately.

Approximately 1200g of aggregates and filler are taken and heated to a temperature of 175⁰ to 190⁰C. The compaction mould assembly and rammer are cleaned and kept pre-heated to a temperature of 100⁰C to 145⁰C. The bitumen is heated to temperature of 121⁰C to 138⁰C and the required quantity of first trial percentage of bitumen (say, 3.5% by weight of mineral aggregates) is added to the heated aggregate and thoroughly mixed using a mechanical mixer or by hand mixing with trowel. The mixing temperature for 80/100grade bitumen may be around 154⁰C and that for 60/70grade, about 160⁰C.The mix is placed in a mould and compacted by rammer, with 50 blows on either side. The compacting temperatures may be about 138⁰C for 80/100grade bitumen and 149⁰C for 60/70grade. The compacted specimen should have thickness of 63.5mm. The weight of the aggregate taken may be may be suitably altered to obtain a thickness of 63.5±3.0 mm.  At least two specimens, but preferably three or four specimens should be prepared at each trial bitumen content which may be varied at 0.5 percent increments up to about 7.5 or 8.0 percent.

 

Specified Grading of Aggregates for Bituminous Concrete

Passing Sieve size	Retained Sieve size	Weight of Aggregate (gm)
20 mm	12.5 mm	120
12.5 mm	9.5 mm	120
9.5 mm	4.75 mm	240
4.75 mm	2.36 mm	216
2.36 mm	600 micron	216
600 micron	300 micron	72
300 micron	150 micron	72
150 micron	75 micron	84
75 micron	Filler	60
Total =		1200 gm

FLASH AND FIRE POINT TEST OF BITUMINOUS MATERIAL

Bituminous materials leave out volatiles at high temperatures depending upon their grade. These volatile vapors catch fire causing a flash. This condition is very hazardous and it is therefore essential to determine this temperature for each bitumen grade, so that the paving engineers may restrict the mixing or application temperatures well within the limits. The flash point is the lowest temperatures at which flash occurs due to the ignition of the volatile vapors when a small flame is brought in con tact with the vapors a bituminous product, gradually heated under standardized conditions. As mentioned above, this test is an indication of the critical temperature at and above which suitable precautions should be taken to prevent fire hazards during application. When the bituminous material is further heated to a higher temperature, the material itself catches fire and continues to burn; the lowest temperature causing this condition is the fire point. The fire point is always higher than the flash point of a material. ISI vide specifications I.S: 1209-1258 gives the following definitions.

Flash point-“The flash point of a material is the lowest temperature at which the vapor of substance momentarily takes fire in the form of a flash under specified condition of test.” 

Fire point –“The fire point is the lowest temperature at which the material gets ignited and burns under specified condition of test.”