Specimen size effects on the diametrical mechanical testing of cylindrical asphalt mixes: Fid-Bau Portal

Specimen size effects on the diametrical mechanical testing of cylindrical asphalt mixes

Lim, C.T. / Tan, S.A. / Fwa, T.F.

Specimens, 101.6 mm (1), 127.0 mm (2), and 152.4 mm (3) in diameter, of asphalt mixtures were prepared to test for the specimen size effect on the resilient modulus test, the indirect tension test, and the Marshall test. Four asphalt mixtures with different top stone sizes ranging from 15.8 mm to 31.5 mm were used. They are B1 mix (base course), Airport, W3, and W6 mixes (wearing course). The specimens had the same level of compaction. The stability ratios (stability of specimens 3/2, 3/1 and 2/1) were analyzed. The were close to the theoretical values reported by Kandhal 1990. Detailed comparison of flow values for the W3 and B1 mixes were made. The B1 mix gave an unacceptable flow/diameter ratio caused by the effect of large stones. The value was too low in the case of the specimen 1 for the B1 mix. However, acceptable values were found for all sizes tested using the W3 mix, which had a top stone size less than 25.4 mm. Hence, large stones (greater than 25.4 mm) in specimens 1 tend to produce lower deformation under loading, which also accounts for the higher modulus measured in the resilient modulus test. The influence of the ratios of the diameter of specimens to top stone size were determined for the resilient modulus and the indirect tension test. A general trend of reduction in resilient modulus and indirect tensile strength was observed. The trend suggested that the specimens 2 and 3 would give more realistic values of tensile strength and stiffness for mixes using larger stones (larger than 25.4 mm). When larger diameter specimens are used, the results obtained from the resilient modulus and the indirect tension test are more representative of the behavior of mixtures.