Example Using Absolute Volume MethodDetermine the mix proportions for a retaining wall, using the following specificationsand conditions:Required 28-day compressive strength (f´_{c})Maximum size aggregateExposure conditionFineness modulus of fine aggregateSpecific gravity of portland cementSpecific gravity of fine aggregateSpecific gravity of coarse aggregateDry-rodded unit weight of coarse aggregateDry-rodded unit weight of fine aggregateSlumpCement3,000 psi3/4 in.Moderate freeze-thaw exposure—exposure to air2.703.152.652.60102 lb/cu ft100 lb/cu ft3 in.Type IATo determine the mix proportions, proceed as follows:1. Estimate the air content. From table 17-3, the air content should be 5 percent(3/4-inch aggregate, air-entrained concrete, moderate exposure).2. Estimate the mixing water content. From table 17-3, you should use 305 poundsof mixing water per cubic yard of concrete (3-inch slump, 3/4-inch aggregate, air-entrainedconcrete).3. Determine the water-cement ratio. From table 17-2, a water-cement ratio of 0.59will satisfy the strength requirement for 3,000 psi concrete. From table 17-1, you find that awater-cement ratio of 0.50 will satisfy the exposure conditions. Since 0.50 is the smaller ofthe ratios, that is what you should use.4. Calculate the cement content. By using the weight of the mixing water content(Step 2) and the water-cement ratio (Step 3), you can determine the cement content asfollows:5. Calculate the coarse aggregate content. By using table 17-5 and interpolatingbetween fineness moduli of 2.6 and 2.8, you find that for 3/4-inch aggregate having a finenessmodulus of 2.7, the volume of dry-rodded aggregate per unit volume of concrete is 0.63.Therefore, the volume of coarse aggregate needed for 1 cubic yard of concrete is0.63 x 27 = 17.01 cubic feet. Since the dry-rodded weight of the coarse aggregate is 102pounds per cubic foot, then the weight of the coarse aggregate for a cubic yard of the concreteis 17.01 x 102= 1,735 pounds.17-6

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