APPENDIX C-Continued 



Solid volume 





of coarse 1719 



nt'gregate =2-:6r^62:4" 



= 10.28 cu ft 



Volume of 

 air = 0.05 x 27 



= 1.35 cu ft 



Total volume 

 of ingredi- 

 ents except 

 sand 



= 18.71 cu ft 



Solid volume 

 of sand 

 required = 27 - 18.71 



= 8.29 cu ft 



Required 

 weight of 

 dry sand =8.29 x 2.64 x 62.4= 1366 lb 



6.3.7.3 Batch weights per cubic yard of 

 concrete calculated on the two bases are com- 

 pared below: 





Based on 



Based on 





estimated 



absolute 





concrete 



volume 





weight, 



of ingredients. 





lb 



lb 



Water (net mixing) 



270 



270 



Cement 



540 



540 



Coarse aggregate 







(dry) 



1719 



1719 



Sand (dry) 



1371 



1366 



6.3.8 Step S. Tests indicate total moisture of 

 3 percent in the coarse aggregate and 5 percent 

 in the fine aggregate. If the trial batch propor- 

 tions based on assumed concrete weight are used, 

 the adjusted aggregate weights become 



1719(1.03) =1771 lb 

 1371(1.05) = 14401b 



Coarse aggregate (wet) 

 Fine aggregate (wet) 



Absorbed water does not become part of the 

 mixing water and must be excluded from the 

 adjustment in added water. Thus, surface water 

 contributed by the coarse aggregate amounts to 

 3 — 0.5 = 2.5 percent; ■ by the fine aggregate 

 5 — 0.7 = 4.3 percent. The estimated requirement 

 for added water, therefore, becomes 



270 - 1719(0.025) - 1371 (0.043) = 168 lb 



The estimated batch weights for a cubic yard of 

 concrete are: 



Water (to be added) 



168 lb 



Cement 



540 lb 



Coarse aggregate (wet) 



1771 lb 



Fine aggregate (wet) 



1440 lb 



ToUl 



3919 lb 



6.3.9 Step 9. For the laboratory trial batch, the 

 weights are scaled down to produce 0.03 cu yd or 

 0.81 cu ft of concrete. Although the calculated 

 quantity of water to be added was 5.04 lb the 

 amount actually used is in an effort to obtain 

 the desired 1 to 2-in. slump is 4.50 lb. The batch 

 as mixed, therefore, consists of 



Water (added) 



Cement 



Coarse aggregate (wet) 



Fine aggregate (wet) 



Total 



4.50 lb 

 16.20 lb 

 53.13 lb 

 43.20 lb 

 117.03 lb 



The concrete has a measured slump of 2 in., unit 

 weight of 141.8 lb per cu ft, and air content of 

 6.5 percent. It is judged to be slightly oversanded 

 for the easy placement condition involved. To 

 provide proper yield and other characteristics for 

 future batches, the following adjustments are 

 made: 



6.3.9.1 Since the yield of the trial batch 

 was 



117.03/141.8 = 0.825 cu ft 

 and the mixing water content was 4.50 (added) 

 -f 1.29 on coarse aggregate -|- 1.77 on fine aggre- 

 g"ate = 7.56 lb the mixing water required for a 

 cubic yard of concrete with the same slump as 

 the trial batch should be 



7.56 X 27 

 0.825 



= 247 lb 



The slump was satisfactory but, since the air 

 content was too high by 1.5 "percent, more water 

 will be needed for proper slump when the air 

 content is corrected. As indicated in Paragraph 

 5.3.9.2, the mixing water should be increased 

 roughly 5x1-5 or about 8 lb, bringing the new 

 estimate to 255 lb per cu yd. 



6.3.9.2 With the decreased mixing water, 

 less cement will be required to provide the de- 

 sired water-cement ratio of 0.5. The new cement 

 content becomes 



255/0.5 = 510 lb 



6.3.9.3 Since the concrete was found to be 

 oversanded, the quantity of coarse aggregate per 

 unit volume will be increased 10 percent, to 0.74, 

 in an effort to correct the condition. The amount 

 of coarse aggregate per cubic yard becomes 



0.74 X 27 X 95 = 1898 lb dry 

 or 



1898 X 103 = 1955 lb wet 



1898 X 1.005 



1907 lb SSD* 



6.3.9.4 The new estimate for the weight of 

 the concrete with 1.5 percent less air is 141.8/0.985 

 = 144.0 lb per cu ft or 144.0-x 27 = 3888 lb per 

 cu yd. The weight of sand, therefore, is 



3888 - (255 -f 510 + 1907) = 1216 lb SSD* 

 or 



1216/1.007 = 1208 lb dry 



'Saturated-surface -dry 



ACI STANDARD 



329 



