PSI - Issue 2_B

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Lee Leon et al. / Procedia Structural Integrity 2 (2016) 2913–2920 Author name / Structural Integrity Procedia 00 (2016) 000–000

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The friction value was average to be 50 0 which is just about that of crushed rock. The angle is higher because of the adhesion behaviour of the binder within the mix. This is sufficient since the mixes were made of crushed limestone. Since this relationship can be represented by the Mohr-Coulomb Failure Criteria, the failure mode is in fact shear failure. We can also say that the test method used (uniaxial unconfined compression test) does in fact give representative results for an asphalt concrete layer in compression.

Table 2. The shear failure and friction angles of asphalt concrete mixes. Mix type Average measured failure angle

Calculated friction angle

HMA 2 HMA 3 SMA 3

69 o 70 o 68 o

50 o 51 o 48 o

3.2. Failure mode of asphalt concrete Experimental results will deviate more and more away from this idealized model as more properties are changed that affect the elastoplastic and frictional characteristics of the specimen. This is proven in Fig. 5 showing the discretized graph of stress vs. strain of a 100mm sample, where the shape of the graph varies greatly from the theoretical model in Fig. 2. This variation is due to the change in mode of failure from a pure shear failure to a forced shear combination failure caused by the relatively small height of those samples. This smaller height changes the interaction of frictional forces within the macrostructure and so the graph and ultimately the mode of failure will also change.

a

b

Fig. 5. (a) Stress-strain curve for 100 mm height sample (b) Stress-strain curve for 150 mm height sample

a

b

100 mm sample 150 mm sample

100 mm sample 150 mm sample

Fig. 6. (a) Stress-strain curve for HMA 2 at 27 o C (b) Stress-strain curve for HMA 2 at 45 o C