3. Analyze Volumetrics Suppose you are conducting a Superpave mix design for an
ID: 1713381 • Letter: 3
Question
3. Analyze Volumetrics Suppose you are conducting a Superpave mix design for an interstate pavement with 25 million design ESALs, using a 19-mm nominal maximum aggregate size blend. Suppose also that you find three aggregate blends that pass the Superpave criteria, and the bulk specific gravities (Gsb) are 2.704, 2.701, and 2.696, respectively Based upon local experience, you select 4.5% by wt. of mix as the estimated optimum asphalt content for all three mixes. Your lab has compacted two specimens of each of the three blends at 45% ac to 100 gyrations, plus two Gmm samples, and the following results are obtained. Use Gb -1.023 Blend 1 Blend 2 Blend 3 Rep 1Rep 2 Rep 1 Rep 2 Gmb Specimen dry wt 4699.44704.2 4709.6 4711.54698.1 4695.1 27891 2793.1 4699.8 Rep 2 Gmb submerged wt 27 2787.5 Gmb SSD wt Gmm 2.565 2.568 2.559 Determine the most promising blend.Explanation / Answer
Ans:
Given- Aggregate size- 19mm
Bulk specific gravity of 3 aggregatesGsb is 2.704, 2.701, and 2.696 respectively
Percentage of asphalt content=Pb=4.5
Asphalt binder specific gravity(Gb=1.023)
Bulk specific gravity of blends (Gmb)= (Wd) / (WSSD - WSUB)
Blend 1= (4699.4+4704.2)/((4706.2+4705.8)-(2775+2774.8))= 2.427
Simillarly for Blend 2=2.441
Blemd 3=2.458
AIr voids= (1- Gmb / Gmm)*100
Blend 1= 5.38
Blend 2=4.94
Blend 3=3.94
Voids in mineral aggregate=(1-(Gmb (1-Pb)/Gsb)*100
Blend 1= 13.78
Blend 2= 13.69
Blend 3=13.57
Voids filled with asphalt= voids in mineral aggregate- percentage void air
Blend1=8.32
Blend 2= 8.75
Blend 3= 9.63
Air voids should be maintained between 3-7 percent.
The amount of voids filled with asphalt should be minimum,to maintain the effective asphalt content.
Therefore,
The most promising blend is BLEND 1
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