APPENDIX C-Continued 



Since the yield was 0.819 cu ft, the air content 

 was 



0.819-0.817 



0.819 



— 0.2 percent 



With the proportions of all components except 

 fine aggregate established, the determination of 

 adjusted cubic yard batch quantities can be com- 

 pleted as follows: 



Volume of 





343 



= 5.50 cu ft 



water 



— 



62.4 



Volume of 





553 



= 2.81 cu ft 



cement 



= 



3.15 X 62.4 



Volume of 











= 



0.002 X 27 



= 0.05 cu ft 



Volume of 









coarse 





1896 



= 11.34 cu ft 



aggregate 



= 



2.68 X 62.4 



Total volume exclusive of 





fine aggregate 





= 19.70 cu ft 



Volume of 









fine ag- 









gregate 









required 



= 



27 - 19.70 



= 7.30 cu ft 



Weight of 









fine ag- 









gregate 









(dry 









basis) 



= ' 



7.30x2.64x62.4 



= 12031b 



Tlie adjusted basic batch, weights per cubic yard 

 of concrete, then, are: 



Water (net mixing) 



Cement 



Coarse aggregate (dry) 



Fine aggregate (dry) 



343 lb 



553 lb 

 1896 lb 

 1203 lb 



These differ only slightly from those given in 

 Paragraph 6.2.9.4 for the method of assumed 

 concrete weight. Further trials or experience 

 might indicate small additional adjustments for 

 either .method. 



6.3— Example 2., Concrete is required for a 

 heavy bridge pier which will be exposed to fresh 

 water in a severe climate. An average 28-day 

 compressive strength of 3000 psi will be re- 

 quired. Placement conditions permit a slump of 

 1 to 2 in. and the use of large aggregate, but 

 the only economically available coarse aggregate 

 of satisfactory quality is graded from No. 4 to 1 

 in. and this will be used. Its dry-rodded weight is 

 found to be 95 lb per cu ft. Other characteristics 

 are as indicated in Section 6.1. 



The calculations will be shown in skeleton form 

 only. Note that confusion is avoided if all steps 

 of Section 5 are followed even when they appear 

 repetitive of specified requirements. 



6.3.1 Step 1. The desired slump is 1 to 2 in. 



6.3.2 Step 2. The locally available aggregate, 

 graded from No. 4 to 1 in., will be used. 



PROPORTIONS FOR NORMAL AND HEAVYWEIGHT CONCRHE 



6.3.3 Step 3. Since the structure will be ex- 

 posed to severe weathering, air-entrained con- 

 crete will be used. The approximate amount of 

 mixing water to produce a 1 to 2-in. slump in air- 

 entrained concrete with 1-in. aggregate is found 

 from Table 5.3.3 to be 270 lb per cu yd. The 

 recommended air content is 5 percent. 



6.3.4 Step 4. From Table 5 3.4(a), the water- 

 cement ratio needed to produce a strength of 

 3000 psi in air-entrained concrete is estimated to 

 be about 0.59. However, reference to Table 

 5.3.4 (b) reveals that, for the severe weathering 

 exposure anticipated, the water-cemei^t ratio 

 should not exceed 0.50. This lower figure must 

 govern and will be used in the calculations. 



6.3.5 Step 5. From the information derived in 

 Steps 3 and 4, the required cement content is 

 found to be 270/0.50 = 540 lb per cu yd. 



6.3.6. Step 6. The quantity of coarse aggregate 

 is estimated from Table 5.3.6. With a fine aggre- 

 gate having a fineness modulus of 2.8 and a 

 1 in. maximum size of coarse aggregate, the table 

 indicates that 0.67 cu ft of coarse aggregate, on 

 a dry-rodded basis, may be used in each cubic 

 foot of concrete. For a cubic yard, therefore, the 

 coarse aggregate will be 27 x 0.67 = 18.09 cu ft 

 Since it weighs 95 lb per cu ft, the dry weight of 

 coarse aggregate is 18.09 X 95 = 1719 lb. 



6.3.7 Step 7. With the quantities of water, 

 cement and coarse aggregate established, the re- 

 maining material comprising the cubic yard of 

 concrete must consist of sand and air. The re- 

 quired sand may be determined on the basis of 

 either weight or absolute volume as shown below. 

 6.3.7.1 Weight basis. From Table 5.3.7.1, the 

 weight of a cubic yard of air-entrained concrete 

 made with aggregate of 1 in. maximum size is 

 estimated to be 3900 lb. (For a first trial batch, 

 exact adjustments of this value for differences 

 in slump, cement factor, and aggregate specific 

 gravity are not critical.) Weights already known 

 are: 



Water (net mixing) 



Cement 



Coarse aggregate (dry) 



Total 



270 lb 

 540 lb 

 1719 lb 

 2529 lb 



The weight of sand, therefore, is estimated to be 

 * 3900 - 2529 = 1371 lb (dry) 

 6.3.7.2 Absolute volume basis. With the 

 quantities of cement, water, air, and coarse ag- 

 gregate established, the sand content can be cal- 

 culated as follows: 



= 4.33 cu ft 



328 



