MARSHALL STABILITY AND FLOW VALUES OF BITUMINOUS MIX SPECIMEN

The specimens to be tested are kept immersed under water in a thermostatically controlled water bath maintained at 60⁰ ± 1⁰C for 30 to 40 minutes. The specimens are taken out one by one, placed in the Marshall test head and the Marshall stability value (maximum load carried in kg. before failure) and the flow value (the deformation the specimen undergoes during loading up to the maximum load in 0.01 mm units) are noted. The corrected Marshall stability value of each specimen is determined by applying the appropriate correction factor, if the average height of the specimen is not exactly 63.5 mm. The correction factors are given in Table.

Correction Factors for Stability and Flow Value

Volume of Specimen  in Cubic Centimeters	Approximate Thickness of Specimen in mm	Correction Factors
457-470	57.1	1.19
471-482	58.7	1.14
483-495	60.3	1.09
496-508	61.9	1.04
509-522	63.5	1.00
523-535	65.1	0.96
536-546	66.7	0.93
547-559	68.3	0.89
560-573	69.9	0.86

OBJECTS OF BITUMINOUS PAVING MIX DESIGN

According to Asphalt institute design manual, the over all objective for the design of the bituminous paving mixes, to determine an economical blend and grading of aggregates and a corresponding bitumen content which would yield a mix having the following characteristics.

• Mix should exhibit sufficient stability to satisfy the service requirements of the pavement and the traffic conditions, without undue displacements.

• It should have sufficient bitumen content to ensure a durable pavement by coating the aggregates and bonding them together and also by water-proofing the mix.

• Bitumen mix should have sufficient voids in the total compacted mix as to provide a reservoir space for a slight amount of additional compaction due to traffic to avoid flushing, bleeding and loss of stability.

• It should have sufficient flexibility even in the coldest season to prevent cracking due to repeated application of traffic loads.

• The mix should have sufficient workability while placing and compacting the mix. 

• The mix should be the most economical one that would produce a stable, durable and skid resistant pavement.