Figure 17-2.—Wet sand.Figure 17-3.—Very wet sand.The procedure for adjusting the mixing watercaused by free surface moisture is as follows:. Determine the approximate FSM of the fineaggregate by the squeeze test.. Estimate the FSM of the coarse aggregate byobservation. Usually, 2-percent FSM is the maximumamount gravel will hold without actually dripping.. Multiply the percentages of FSM on theaggregates by their respective weights per cubic yard.This will yield the weight of the FSM on the aggregates.. Divide the total weight of the FSM by 8.33pounds per gallon to determine the number of gallonsof water. Subtract those gallons from the mixing waterrequirements in the original mix design.. If you are batching your concrete mix by weight,you need to account for the weight contributed by theFSM by increasing the total weights of the aggregatesper cubic yard by the weights of the FSM.Example Problem: Using the final mix proportionsas determined, adjust the design mix to account for6-percent FSM on the fine aggregate (FM = 2.70) and2-percent FSM on the coarse aggregate. Original mixdesign for a 1-cubic-yard trial batch wasCement:6.49 sacks (Type IA)Water:36.6 gallonsCoarse aggregate:1,735.0 poundsFine aggregate:1,153.0 poundsAir content:5.0 percentStep 1. Determine the amount of water (in gallons)on the coarse and fine aggregate.lllCoarse aggregate= 1,735 x 0.02 = 34.70 poundsFine aggregate= 1,153 x 0.06 = 69.18 poundsTotal weight of water= 103.88 poundsConverted to gallons= 12.47 gallonsStep 2. Adjust the original amount of mixing waterby subtracting the amount of water contributed by theaggregates. The adjusted water requirement then is24.13 gallons (36.6 - 12.47).Step 3. Adjust the weights of the aggregates by theamount contributed by the water.. Coarse aggregate= 1,735 + 34.7. Fine aggregate= 1,153 + 69.18= 1,770 pounds= 1,222 poundsStep 4. The adjusted mix design to account for theactual field conditions is nowCement:6.49 sacks (Type IA)Water:24.13 gallonsCoarse aggregate:1,770.0 poundsFine aggregate:1,122.0 poundsAir content:5.0 percentYou should check the moisture content of the aggregatesand make appropriate adjustments as conditions change(such as after rains, after periods of dryness, or when thenew material arrives). This quality control step assuresthat the desired concrete is produced throughout theconstruction phase.Materials EstimationAfter proportioning the mix, you must estimate thetotal amount of material needed for the job. This issimply done by computing the total volume of concrete17-9

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