The problem asks which factors would increase the effective specific gravity of aggregates in asphalt concrete. We need to select at least two correct answers from the options provided. The options are: A. Presence of unreacted cement particles B. Complete removal of surface moisture C. Partial asphalt absorption in pores D. High water-permeable voids E. Use of hydrophobic coatings

1. Problem Description

The problem asks which factors would increase the effective specific gravity of aggregates in asphalt concrete. We need to select at least two correct answers from the options provided. The options are:

A. Presence of unreacted cement particles

B. Complete removal of surface moisture

C. Partial asphalt absorption in pores

D. High water-permeable voids

E. Use of hydrophobic coatings

2. Solution Steps

The effective specific gravity $G_{se}$ is defined as:

$G_{se} = \frac{W_{dry}}{W_{dry} - (W_{sat} - W_{dry})}$

Where:

$W_{dry}$ is the oven-dry weight of the aggregate

$W_{sat}$ is the saturated surface-dry weight of the aggregate

The effective specific gravity is affected by the volume of permeable voids within the aggregate particles. Factors that reduce the volume occupied by water or increase the mass of the aggregate will tend to increase the effective specific gravity.

A. Presence of unreacted cement particles: Unreacted cement particles will be denser than typical aggregate material. This increases the overall mass, thus increasing the effective specific gravity. This is a correct answer.

B. Complete removal of surface moisture: Removing surface moisture decreases $W_{sat}$. This reduces $W_{sat} - W_{dry}$, which results in an increase in the denominator of the $G_{se}$ equation.

Since $G_{se} = \frac{W_{dry}}{W_{dry} - (W_{sat} - W_{dry})} = \frac{W_{dry}}{2W_{dry}-W_{sat}}$, decreasing $W_{sat}$ will increase $G_{se}$. This is incorrect.

C. Partial asphalt absorption in pores: If asphalt is absorbed into the pores, it increases the mass of the aggregates and reduces the volume of voids accessible to water. Since asphalt generally has a lower density than aggregate solids, it will decrease the effective specific gravity, not increase it.

D. High water-permeable voids: High water-permeable voids would mean $W_{sat}$ increases substantially. The term $W_{sat} - W_{dry}$ in the denominator becomes large, which reduces the effective specific gravity. This is an incorrect answer.

E. Use of hydrophobic coatings: If the coating is hydrophobic, it prevents water from entering the pores of the aggregate. This keeps $W_{sat}$ close to $W_{dry}$. So, $W_{sat}-W_{dry}$ becomes smaller and the value of $G_{se}$ becomes larger. Thus, this increases the effective specific gravity.

Therefore, options A and E increase the effective specific gravity.

3. Final Answer

A. Presence of unreacted cement particles

E. Use of hydrophobic coatings