APPENDIX C-Continued 



bearing soils; or aggregate free of excessive soft 

 particles where resistance to surface abrasion is 

 required. Use of a low water-cement ratio will 

 prolong the life of concrete by reducing the 

 penetration of aggressive liquids. Resistance to 

 severe weathering, particularly freezing and 

 thawing, and to salts used for ice removal is 

 greatly improved by incorporation of a proper 

 distribution of entrained air. Entrained air should 

 be used in all exposed concrete in climates where 

 freezing occurs.* 



3.6 — Density. For certain applications concrete 

 may be used primarily for its weight characteris- 

 tic. Examples of applications are counterweights 

 on lift bridges, weights for sinking oil pipelines 

 under water, shielding from radiation, and for 

 insulation from sound. By using special aggre- 

 gates, placeable concrete of densities as high as 

 350 lb per cu ft can be obtained— see Appendix 4. 



4. BACKGROUND DATA 



4.1 — To the extent possible, selection of con- 

 crete proportions should be based on test data or 

 experience with the materials actually to be 

 used. Where such background is limited or not 

 available, estimates given in this recommended 

 practice may be employed. 



4.2 — The following information for available 

 materials will be useful: 



4.2.1 Sieve analyses of fine and coarse ag- 

 gregates 



4.2.2 Unit height of coarse aggregate 



4.2.3 Bulk specific gravities and absorptions 

 of aggregates 



4.2.4 Mixing water requirements of concrete 

 developed from experience with available aggre- 

 gates 



4.2.5 Relationships between strength and wa- 

 ter-cement ratio for available combinations of 

 cement and aggregate 



4.3 — Estimates from Tables 5.3.3 and 5.3.4, re- 

 spectively, may be used when the last two items 

 of information are not available. As will be 

 shown, proportions, can be estimated without the 

 knowledge of aggregate specific gravity and ab- 

 sorption. Item 4.2.3. 



5. PROCEDURE 



5.1 — The procedure for selection of mix propor- 

 tions given in this section is applicable to normal 

 weight concrete. Although the same basic data 

 and procedures can be used in proportioning 

 heavyweight concrete, additienal information as 

 well as sample computations for this type of con- 

 crete are given in Appendix 4. 



5.2 — Estimating the required batch weights for 

 the concrete involves a sequence of logical, 



PROPORTIONS FOR NORMAL AND HEAVYWEIGHT CONCRETE 



straightforward steps which, in effect, fit the 

 characteristics of the available materials into a 

 mixture suitable for the work. The question of 

 suitability is frequently not left to the individ- 

 ual selecting the proportions. The job specifica- 

 tions may dictate some or all of the following: 



5.2.1 Maximum water-cement ratio 



5.2.2 Minimum cement content 



5.2.3 Air content 



5.2.4 Slump 



5.2.5 Maximum size of aggregate 



5.2.6 Strength 



5.2.7 Other requirements relating to such 

 things as strength overdesign, admixtures, and 

 special types of cement or aggregate. 



5.3 — Regardless of whether the concrete char- 

 acteristics are prescribed by the specifications or 

 are left to the individual selecting the propor- 

 tions, establishment of batch weights per cubic 

 yard of concrete can best be accomplished in the 

 following sequence: 



5.3.1 Step I. Choice o/ slump. If slump is not 

 specified, a value appropriate for the work can 

 be selected from Table 5.3.1. The slump ranges 

 shown apply when vibration is used to consoli- 

 date the concrete. Mixes of the stiffest consistency 

 that can be placed efficiently should be used. 



TABLE 5.3.1— RECOMMENDED SLUMPS 

 FOR VARIOUS TYPES OF CONSTRUCTION 





Slump 



m. 



Types of construction 



Maximum* 



Minimum 



Reinforced foundation walls and footings 



3 



1 



Plajn footings, caissons, and 







substructure walls 







Beams and reinforced walls 



4 





Building columns 



4 





Pavements and slabs 







Mass concrete 



3 





*May b« Increased 1 



for methods of consolidation other 



5.3.2 Step 2. Choice oj maximum size of ag- 

 gregate. Large maximum sizes of well graded 

 aggregates have less voids than smaller sizes. 

 Hence, concretes with the larger-sized aggre- 

 gates require less mortar per unit volume of 

 concrete. Generally, the maximum size of ag- 

 gregate should be the largest that is economically 

 available and consistent with dimensions of the 

 structure. In no event should the maximum size 

 exceed one-fifth of the narrowest dimension be- 

 tween sides of forms, one-third the depth of slabs, 

 nor three-fourths of the minimum clear spacing 

 between individual reinforcing bars, bundles of 

 bars, or pretensioning strands. These limitations 

 are sometimes waived if workability and methods 

 of consolidation are such that the concrete can be 



•For further details, see ACI Committee 201. "DurablUtj of 

 Concrete In Service." ACI Journal. Proccedlnfff V. W. No. It. 

 Dec. ISO. pp. lT;i-I8a>. 



322 



