(1) Answer the following questions (it could be short answers): a) Briefly descr

Question

(1) Answer the following questions (it could be short answers):

a) Briefly describe what is meant by “breaking” of an asphalt emulsion?

b) Why is short-term oven aging important in the mix design process? Do the aging times always match up with the field aging times, and what difference does that make, if any?

c) Briefly list at least 4 improvements that the Superpave binder specification has brought to
the asphalt industry that were not possible under the old Viscosity or Penetration grading
systems:

d) In your own words, define Voids in the Mineral Aggregate (VMA) and tell why it is important?

Explanation / Answer

Q.1(a)

When an asphalt emulsion is applied on the aggregates, the asphalt must quickly separate from water so as to bind the aggregates. This process of separation is called breaking of an asphalt emulsion.

(b) Short term oven aging test is designed to simulate the field aging during the construction of hot mix asphalt (HMA) pavements. Aging is nothing but the hardening of the asphalt with time, which is classified in two categories, short term aging and long term aging. Short-term aging occurs during the construction phase and is primarily due to oxidation and to the loss of volatile components.

Using this test one can set the limits for the aging effects, such as the limit to stiffness achieved. Also limits are set for fatigue, thermal cracking and rutting. Generally short term aging is four 4 hours, but this time doesn't always match because of the variable field conditions.

There can be a number of reasons for the delay at the field, so in that case aging will be more, and that means the asphalt would become less suitable. Therefore one should design the mix for a longer delay or aging.

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