Producing concrete with the correct yield and be-ing able to ve rify that yield is extremely impor-tant to eve ry ready mix producer and to eve ryc o n t ra c t o r. Many times questions of yield areraised by a contractor who believes he has not receivedall of the concrete that the ready mix producer is cert a i nhe has delive red. If such questions are to be re s o l ve ds a t i s f a c t o rily the ready mix producer has to be able toc o n f i rm that the cubic yard batch weights he is using re-ally do yield 27 cubic feet of concrete. Many yield com-plaints are traceable to spillage and waste of concre t ed u ring the pour, inaccuracy of grading or of measure-mentanddeflectionoftheform s.Becausesomeofthese causes are difficult to confirm, especially after thep o u r, confirmation of the volume of concrete yielded bythe cubic yard batch weights is a ve ry important start i n gpoint.Yi el d measurementbased on a uni twei ghtt estThe common method for measuring yield is based ona simple unit weight test, usually using a 12- c u b i c - f o o tc o n t a i n e r. Pro c e d u res used for determining unit we i g h ta re described in ASTM C 138, the standard test methodfor unit weight. A sample is taken from each of three dif-f e rent truckloads in accordance with ASTM C 172, thes t a n d a rdmethodforsamplingconcre t e,andaunitConsistent yield leadsto consistent qualityYield of concreteCalculating yield accurately isimportant to quality, economy andjobsite controlBY JERRY G. ROSEASSOCIATE PROFESSORDEPARTMENT OF CIVIL ENGINEERINGUNIVERSITY OF KENTUCKYLEXINGTON, KENTUCKYBATCH WEIGHTS FOR ONE CUBIC YARD (27 CUBIC FEET)SSD* Design Adjustment for Free Adjusted**(lbs/cu yd) Moisture in Aggregate Batch Wei ghtsWater 253 -49 (38 + 11) 204Cement 564 564Sand 1250 +38 (0.03 x 1250) 1288Coarse aggregate 1877 +11 (0.006 x 1877) 18886% air entrainment ______Total 3944 3944* SSD (saturated surface dry) means that the aggre-gate particles have absorbed all of the moisturepossible, and that their surface is dry. They will nei-ther absorb water from the mix nor add water tothe mix.** In the field, aggregates can be expected to con-tain some free surface moisture. In this example itis assumed that the sand contains 3 percent sur-face moisture and the coarse aggregate 0.6 per-cent surface moisture. Because the free surfacemoisture becomes a part of the mix water, andbecause the batch weights of the sand and thecoarse aggregate include the weight of the sur-face moisture, the batch weights of all three mustbe adjusted. The total cubic yard batch weight of3944 pounds remains the same. The 49 pounds ofthe mix water being batched as part of the aggre-gates is deducted from the water to be batchedseparately.weighttestisrunoneachsample.Anave rageunitweight is calculated. Total weight of the batch is then di-vided by the ave rage unit weight to determine the vo l-ume (or yield) of freshly mixed concrete in the batch.This pro c e d u re is illustrated in the shown example.For this example the adjusted weights we re batchedout. Three unit weight tests we re perf o rmed on the fre s hc o n c rete and the ave rage unit weight was calculated asf o l l ow s :Since the cubic yard yield is greater than 27.0 cubicfeet, the ove ryield is 0.28 cubic foot or about 1 perc e n t .The unit weight test must be run ve ry carefully becauseof the effect that discrepancies in the unit weight willh a ve on the result. That is the reason that an ave rage ofat least three tests is needed.Yi el d cal cul at i on based on absol ut e vol umeCo n c rete mixes are designed by the absolute vo l u m et e c h n i q u e. In a batch ofconcre t e, the sum of the ab-solute volumes of cement, aggregate and water plus thevolume of air isequal to the volume of concretepro-ducedperbatch.Weightsoftheva riousingre d i e n t smust be chosen to yield a design volume (usually onecubic yard) of concrete with the desired cement content,w a t e r-cement ratio and air content.To calculate the absolute volume of a material for ag i ven weight, the specific gravity of the material mustbe known. Specific gravity is the weight of a material di-vided by the weight of an equal volume of water. For ex-a m p l e, the specific gravity of cement is 3.15. Thus, onecubic foot absolute volume of cement weighs 3.15 times62.4(theweightof1cubicfootofwater)or196.6p o u n d s. With this information we can calculate the vo l-ume that any weight of cement will occu-py in the concrete by dividing the cementweight by196.6. A similar calculation ismade for the other concrete ingre d i e n t s.The following mix designis pro p o s e dfor a cubic yard of concre t e. The we i g h t sa re based on the aggregates being in a SSDcondition. The SSD specific gravities areg i ven, from which the weight of a cubicfoot absolute volume is calculated.The total yield is 26.81 cubic feet and themix underyields by 0.19ofa cubic foot.The logical way to make up the additionalvolume needed would be by adding 0.19 ofa cubic foot of sand or coarse aggregate ora combination of the two. For example, ifsand we re added, the amount wouldbe0.19 x 164.1 = 31 pounds. The mix wouldthen yield exactly 27.00 cubic feet. If it didnot appear that the workability of the mixwould benefit from more sand, the addi-tion could be made with 0.19 cubic foot ofcoarse aggregate which would weigh 0.19 x168.5 or 32 pounds.If either the weight or specific gravity ofan ingredient is changed, the yield will beaffected. Also, a 1percentchangein airvolume will result in a yield change of 0.27cubic foot (1 percent of 27 = 0.27).Total weight of the 12-cubic-foot containerfilled with concrete (average of three) 92.4 poundsEmpty weight of the container 20.1 poundsWeight of 12 cubic foot of concrete(92.4 - 20.1) 72.3 poundsUnit weight of the concrete in pounds percubic foot (72.3 x 2) 144.6 poundsThe yield is then calculated as follows:weight per cubic yardyield in cubic feet = -weight per cubic foot3944yield = = 27.28 cubic feet144.6SSD Batch Specific Pounds per cubic footweight gravity absolute volumewater 240 1.00 1.00 x 62.4 = 62.4cement 564 3.15 3.15 x 62.4 = 196.6sand 1229 2.63 2.63 x 62.4 = 164.1coarse aggregate 1850 2.70 2.70 x 62.4 = 168.5Add enough air entraining admixture to produce 6 percent air content.The absolute volume calculations would then be:Batch Weight Absolute Volume(pounds) (cubic feet per cubic yard)water 240 240 = 3.8562.4cement 564 564- = 2.87196.6sand 1229 1229- = 7.49164.1coarse aggregate 1850 1850- = 10.98168.56 percent air 0.06 x 27 =1.62______Total volume cubic feet per cubic yard 26.81SummaryThe expected yield for a proposed mixture of materi-als can be calculated by using established absolute vo l-ume calculation pro c e d u re s. The weights and specificg ravities of each material and the air percentage must bek n ow n .The common method for adjusting the yield is to in-c rease or decrease the weight of one or more of the ma-t e rials to produce the re q u i red volume change. Ty p i c a l-ly the fine aggregate is adjusted if the mix appears to beundersanded. If additional sand is not needed, the ad-justment may be made in the coarse aggregate alone orin a combination of the fine and the coarse.Air contents are assumed for calculation purposes,but have to be checked after the mix is made and the ad-m i x t u re dosage va ried as re q u i red to provide the speci-fied air content.The common measurement for yield invo l ves a unitweighttestonthefreshconcre t e.Providedtheunitweight test is conducted properly and the total we i g h t sof the mix ingredients are known, the yield value re p re-sents the actual volume of concrete being pro d u c e d .When a mix undery i e l d s, the purchaser is not re c e i v-ing a sufficient volume of concre t e. This results in ove r-payment to the producer and increased constru c t i o nc o s t s. If the underyield is due to low air content or lowcement content the mix quality may be adversely affect-ed. The importance of maintaining the re q u i red air con-tent, cement content, and water-cement ratio cannotbe ove re m p h a s i ze d .Whenamixove ry i e l d s,thepurchaserre c e i vesag reater volume of concrete than was specified. This re p-resents a loss for the pro d u c e r. Howe ve r, if the cementcontent is not increased accord i n g l y, the cement is usedwith a larger volume of concrete than intended, decre a s-ing thecement content and possibly resulting in de-c reasedstrengthandqualityoftheconcre t e.Iftheove ryield is due to increased volume of water the con-c rete quality is reduced. A higher than designed air vo l-ume will increase yield, but may reduce stre n g t h .A consistent yield, as reflected by a consistent unitweight, is one of the best indicators of mix quality. Avarying yield is indicative of varying proportions of mixi n g redients which will result in va rying quality of thefinished product. Mixes that show a consistent yield arem o re likely to meet quality re q u i re m e n t s. Yield checksshould be routinely conducted aspart of the qualitycontrol plan. P U B L I C AT I O N# C 8 6 0 3 1 3Copyright 1986, The Aberdeen Gro u pAll rights re s e r v e d