Building Design and Construction Handbook - Merritt - Ventech!

9.6 SECTION NINE
9.5 YIELD CALCULATION
Questions often arise between concrete suppliers and buyers regarding ‘‘yield,’’ or
volume of concrete supplied. A major reason for this is that often the actual yield
may be less than the yield calculated from the volumes of ingredients. For example,
if the mix temperature varies, less air may be entrained; or if the sand becomes
drier and no corrections in batch weights are made, the yield will be under that
calculated.
If the specific gravity (sp. gr.) and absorption (abs.) of the aggregates have been
determined in advance, accurate, yield calculations can be performed as often as
necessary to adjust the yield for control of the concrete.
Example
Yield of Non-Air-Entrained Concrete. The following material properties were
recorded for materials used in trial batches: fine aggregate (sand) sp. gr. � 2.65,
abs. � 1%; coarse aggregate (gravel) sp. gr. � 2.70, abs. � 0.5%; and cement, sp.
gr. � 3.15 (typical). These properties are not expected to change significantly as
long as the aggregates used are from the same source. The basic mix proportions
for 1 yd3 of concrete, selected from the trial batches are
Cement: 564 lb (6 bags)
Surface-dry sand: 1170 lb
Surface-dry gravel: 2000 lb
Free water: 300 lb/yd 3 (36 gal/yd 3 )
Check the yield:
564 3
Cement volume � � 2.87 ft
3.15 � 62.4
3
Water volume � 300/62.4 � 4.81 ft
1170 3
Sand volume � � 7.08 ft
2.65 � 62.4
2000 3
Gravel volume � � 11.87 ft
2.70 � 62.4
3
Total volume of solid constituents � 26.63 ft
Volume of entrapped air � 27 � 26.63 � 0.37 ft 3 (1.4%)
Total weight, lb/yd 3 � 564 � 300 � 1170 � 2000 � 4034
Total weight, lb/ft 3 � 4034/27 � 149.4
Weight of standard 6 � 12 in cylinder (0.1963 ft 3 ) � 29.3 lb
These results indicate that some rapid field checks should be made. Total weight,
lb, divided by the total volume, yd 3 , reported on the trip tickets for truck mixers
should be about 4000 on this project, unless a different slump was ordered and the