To determine the Marshall stability of bituminous mixture as per ASTM D 1559.
Marshall stability is the resistance to plastic flow of cylindrical specimens of a bituminous mixture loaded on the lateral surface. It is the load carrying capacity of the mix at 60oC and is measured in kg.
i) Marshall stability apparatus
ii) Balance and water bath
From Marshall stability graph, select proportions of coarse aggregates, fine aggregates and filler in such a way, so as to fulfill the required specification. The total weight of the mix should be 1200g.
i) Heat the weighed aggregates and the bitumen separately upto 170oC and 163oC respectively.
ii) Mix them thoroughly, transfer the mixed material to the compaction mould arranged on the compaction pedestal.
iii) Give 75 blows on the top side of the specimen mix with a standard hammer (45cm, 4.86kg). Reverse the specimen and give 75 blows again. Take the mould with the specimen and cool it for a few minutes.
iv) Remove the specimen from the mould by gentle pushing. Mark the specimen and cure it at room temperature, overnight.
v) A series of specimens are prepared by a similar method with varying quantities of bitumen content, with an increment of 0.5% (3 specimens) or 1 bitumen content.
vi) Before testing of the mould, keep the mould in the water bath having a temperature of 60oC for half an hour.
vii) Check the stability of the mould on the Marshall stability apparatus.
Plot % of bitumen content on the X-axis and stability in kg on the Y-axis to get maximum Marshall stability of the bitumen mix. A sample plot is given below
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