Highway Materials Testing Questions and Answers

Answer: D

The aggregate impact test measures the toughness of aggregates, their resistance to failure by sudden shock or impact: a standard hammer is dropped on a sample in a mould and the fines produced are weighed. The crushing strength test gives the resistance to a slowly applied compressive load, the Los Angeles test gives resistance to wear (abrasion) by steel balls, and the angularity number test is a measure of the shape (angularity) of the particles. They measure strength, hardness and shape, and not toughness.

Answer: C

The key marks both statements as correct. The first limits the liquid limit of the fines used in the wearing course of an earth road in a seasonally wet tropical climate to 40 percent, so that the surface does not become sticky and weak when wet. The second limits the wet aggregate impact value to 40 for aggregate in the base and 30 in the surfacing. I could not check the figures in the code text, so this explanation follows the official key.

Answer: B

The mix is a Gap-graded mix.

A gap-graded bituminous mix leaves out some aggregate sizes in the gradation. The larger aggregate particles float in a rich mortar of fines and binder, which gives the mix good fatigue resistance and tensile strength, as in stone matrix and rolled asphalt types.

A well-graded mix contains all sizes in a continuous gradation, an open-graded mix has few fines and many voids for drainage, and 'unbound' material has no binder at all.

Answer: B

The maximum water content in bitumen is 0.2% by weight.

Bitumen should be practically free of water, because water causes foaming when the bitumen is heated and weakens its bond with aggregate. The specifications limit water content to 0.2 percent by weight, tested by the Dean and Stark distillation method.

0.1 percent is stricter than the limit, and 1 and 2 percent would allow enough water to cause foaming in heating.

Answer: B

The least count of the penetrometer is 0.1 mm.

In the penetration test, a standard needle under a 100 g load is allowed to penetrate a bitumen sample at 25°C for 5 seconds. Penetration is reported in units of 0.1 mm (1/10 mm), so the dial reads to 0.1 mm; a bitumen of grade 80/100 penetrates 8 to 10 mm.

1 mm would be too coarse to distinguish grades, while 0.01 mm and 0.001 mm are finer than the test reports.