8. Determine the quantities for the first trial batch. Let’s assume that the size of ourlaboratory trial batch is 1 cubic yard. For a batch of this size, you need the followingquantitieslllllof the ingredients:Cement Type IA= 610 pounds 94 pounds per sack= 6.49 sacksWater= 305 pounds 8.33 pounds per gallon= 36.6 gallonsCoarse aggregate = 1,735 poundsFine aggregate = 1,152 poundsAir content = 5.0 percentIf needed, more trial batches should be mixed to obtain the desired slump and air contentwhile you keep the water-cement ratio constant.Variation in MixturesThe proportions at which you arrive in determiningmixtures will vary somewhat depending upon whichmethod you use. The variation is the result of theempirical nature of the methods and does not necessarilyimply that one method is better than another. You starteach method by assuming certain needs or requirementsand then proceed to determine the other variables. Sincethe methods begin differently and use differentprocedures, the final proportions vary slightly. This is tobe expected and points out further the necessity of trialmixtures in determining the final mixture proportions.Adjustments for Moisture in AggregatesThe initial mix design assumes that the aggregatesare saturated, surface dry (SSD); that is, neither the fineaggregates nor the coarse aggregates have any freewater on the surface that would be available as mixingwater. This is a laboratory condition and seldom occursin the field. The actual amount of water on the sand andgravel can be determined only from the material at themixing site. Furthermore, the moisture content of theaggregates will change over a short period of time;therefore, their condition must be monitored andappropriate adjustments made as required. Coarseaggregates are free draining and rarely hold more than2 percent (by weight) of free surface moisture (FSM)even after heavy rains. A good field test for estimatingthe FSM on fine aggregates is the squeeze test describedbelow.l The squeeze test.1. Take samples for the squeeze test from a depthof 6 to 8 inches below the surface of the piled sand. Thisnegates the effect of evaporation at the surface of thepile.2. Squeeze a sample of the sand in your hand. Thenopen your hand and observe the sample. The amount ofFSM can be estimated using the following criteria:a. Damp sand (0- to 2-percent FSM). Thesample will tend to fall apart (fig. 17-1). The damper thesand, the more it tends to cling together.b. Wet sand (2- to 4-percent FSM). The sampleclings together without excess water (fig. 17-2).c. Very wet sand (5- to 8-percent FSM). Thesand will ball and glisten or sparkle with water (fig.17-3). The hand will have moisture on it and may evendrip.Figure 17-1.—Damp sand.17-8

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