For a mix design requiring 1200 lb of fine aggregate at SSD with 2.5% free moisture, what amount needs to be weighed?

To determine the appropriate amount of fine aggregate to weigh for this mix design, it's essential to account for the moisture content of the fine aggregate. When dealing with aggregates in a saturated surface-dry (SSD) condition, any additional moisture content must be considered to ensure that the final weight of the aggregate includes an adjustment for the moisture that is free.

In this case, the provided weight of the fine aggregate in SSD condition is 1200 lb, but it contains 2.5% free moisture. To calculate the amount of fine aggregate to weigh, you can use the following formula:

Desired aggregate weight at SSD = Actual weight of aggregate to be weighed - (Moisture percentage x Actual weight of aggregate to be weighed)

Rearranging this gives:

Actual weight of aggregate to be weighed = Desired aggregate weight at SSD / (1 - Moisture percentage)

In this case, the moisture percentage is 2.5%, or 0.025 in decimal form. The calculation will be:

Actual weight of aggregate to be weighed = 1200 lb / (1 - 0.025)

= 1200 lb / 0.975

≈ 1230 lb

Thus, to achieve the required 1200 lb of fine