Facts & Figures Book - KPI-JCI

100SIEVE ANALYSIS ENVELOPEPercent passing by weight80604020Nos 100-4 sievesNos 4-1.5 in. sieves0100 50 30 16 8 4 3 /8 1 /2 3 /4 1 1 / 2Standard sizes of square-mesh sievesCurves indicate the limits specified in ASTM for fine and coarse aggregateFIGURE NO. 2EXAMPLE OF ALLOWABLE GRADATION ZONEIMPORTANCE OF GRADATION—CONCRETETo improve workability of concrete, either the amount ofwater or the amount of fine particles must be increased.Since the water-to-cement ratio is governed by thestrength required in the final cured concrete, any increasein the amount of water would increase the amount ofcement in the mix. Since cement costs are much greaterthan aggregate, it is evident that varying the gradation ismore economical. Most of the formula used for proportioningthe components of the concrete have been worked outas the results of actual experimentation. They are based,however, on two fundamentals.1. To obtain a sound concrete, all voids must be filledeither with fine aggregates or cement paste.2. To obtain a sound concrete, the surface of eachaggregate particle should be covered with cementpaste.An ideal mix is a balance between saving on cementpaste by using fine aggregates to fill the voids, and theadded paste required to cover the surfaces of these additionalaggregate particles.12