Figure 2-2. Appearance of concrete mixes containing correct and incorrect amounts of mortar.
(continued)
Determine and note the slump, air content, workability, and unit weight of the concrete as shown. To find the
most economical proportions, make more trial batches, varying the percentage of fine aggregate. In each batch
keep the w/c ratio, aggregate graduations, air content, and slump approximately the same Table 2-5 on page 2-12
summarizes the results of four trial batches made in the laboratory. Figure 2-3 on page 2-13 plots the percentage
of fine aggregate used in these mixes against the cement factor. The minimum cement factor (538 pounds per
cubic yard) occurs at a fine-aggregate content of about 32 percent of the total aggregate. Since the w/c ratio is
0.46 by weight and the unit weight of the concrete for an air content of 5 percent is about 144 pounds per cubic
foot, the final quantities for the mix propositions (per cubic yard) are as follows:
2-11
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