Figure 2-7. Very wet sand.
The percentage of FSM determined by this method approximates the amount of water by the weight of the sand.
Use these estimates to adjust the mix design.
Fine aggregates have a tendency to bulk (expand in volume) when wetted and when the mass is disturbed. This
factor becomes very important if the concrete is being batched at a mixer by volume; the initial mix design must
be adjusted. The procedure for adjusting the mixing water and sand bulking due to free surface moisture is as
Determine the approximate FSM of the fine aggregate by the squeeze test.
Estimate the FSM of the coarse-aggregate by observation. Usually, 2 percent FSM is the maximum
amount gravel will hod without actually dripping.
Multiply the percentages of FSM on the aggregates by their respective weights per cubic yard. This will
yield the weight of the FSM on the aggregates. If the aggregate has an absorption factor rather than FSM
the weight of water needs to be subtracted rather than added.
Divide the total weight of the FSM by 8.33 pounds or gallons to determine the number of gallons of
water. Subtract those gallons from the mixing water requirements in the original mix design.
Batch the concrete mix by weight. Account for the weight contributed by the FSM by increasing the total
weights of the aggregates per cubic yard by the weights of the FSM.
Batch the concrete by volume. Increase the volume of the fine aggregate by the bulking factor determined
from Figure 2-8 on page 2-22. The formula for volume increase is--
Vwet = Vdry x (1 + BF). (V = volume, BF = bulking factor.)
Coarse aggregates do not bulk; therefore, no adjustment is necessary.