Step 3. Adjust the weights of the aggregates by the amount contributed by the water.
CA 1,768 lb/cy + 35.4 lb/cy
= 1,803.4 lb/cy
FA 1,083.4 lb/y + 64.98 lb/cy
= 1,148.38 lb/cy
Step 4. Adjust the volume of the fine aggregate to reflect the "bulking".
Given FM = 2.70. From Figure 2-8, the FA is considered a medium sand. Select the appropriate
moisture content across the bottom of the figure, read up to the appropriate sand curve, and read the
correct bulking factor on the left edge. For this example, FSM equals 6 percent and the bulking factor is
0.28.
The increase in FA volume is then--Vwet = Vdry (1 + BF) = 10.5 cf (1 + .28) = 13.44 cf
Gravel will not bulk de to its shape and size.
Step 5. The adjusted mix design to account for the actual field conditions is now--
Cement
= 7.05 sacks (Type IA)
Water
= 26.6 gallons
CA
= 17.0 cf or 1,804 lb/cy
FA
= 13.44 c for 1,148 lb/cy
Air content
= 5 percent
It is important to check the moisture content of the aggregates and make appropriate adjustments as conditions
change (after rains or periods of dryness or when the new material arrives). This quality-control step assures that
the desired concrete is produced throughout the construction phase.
Materials Estimation
After designing the mix, it is necessary to estimate the total amounts of material needed for the job. This is
simply done by computing the total volume of concrete to be poured, adding a water factor, and multiplying this
volume times the amount of each component in the 1-cubic yard mix design. The mix design is the original based
on SSD aggregate condition. The procedure follows:
Step 1. Determine the total volume (in cubic yards) of concrete to be poured.
Step 2. Add an extra amount for waste. If your total volume is 200 cubic yards or less, then add 10 percent. If
the total volume is greater than 200 cubic yards, then add 5 percent.
Step 3. Determine the total amount of cement, fine aggregate, and coarse-aggregate by multiplying the amounts
of these components needed for 1 cubic yard by the adjusted total volume. Order cement in sacks and sand and
gravel in tons.
Step 4. Determine the required amount of water needed for the job. Water is required on concrete projects not
only for mixing but for wetting the forms, tool clean up, and curing. A planning factor of 8 gallons of water for
each sack of cement is usually sufficient. The reader is cautioned, however, that not all of this water will be used
for concrete.
2-23
EN5466
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