Question

Consider the Marshall method of mix design for bituminous mix. With the increase in bitumen content, which of the following statements is/are TRUE?

• A. The stability decreases initially and then increases
• B. The flow increases monotonically
• C. The air voids ($V_A$) increases initially and then decreases
• D. The voids filled with bitumen ($V_{FB}$) increases monotonically

Hint:

In Marshall mix design, bitumen content affects various parameters like stability, flow, and voids. Typically, stability decreases after a peak, while flow and $V_{FB}$ increase monotonically.

Answer 1

The Correct Option is B, D

Statement (A): The stability initially increases with bitumen content, reaches a maximum, and then decreases with further increase in bitumen content. Therefore, Statement (A) is False.
Statement (B): With an increase in bitumen content, the flow increases monotonically because the more bitumen there is, the more it flows and spreads in the mix. Hence, Statement (B) is True.
Statement (C): The air voids ($V_A$) decrease initially with increasing bitumen content, reach a minimum, and then start increasing. Hence, Statement (C) is False.
Statement (D): The voids filled with bitumen ($V_{FB}$) increases monotonically with an increase in bitumen content, as more bitumen fills the voids in the mixture. Hence, Statement (D) is True.
\[ \boxed{\text{Correct Statements: (B) and (D)}} \]