APPENDIX C-Continued 



APPENDIX 3— LABORATORY TESTS 



A3.1 — Selection of concrete mix proportions can be 

 accomplished effectively from results of laboratory 

 tests which determine basic physical properties of 

 materials to be used, establish relationships between 

 water-cement ratio, air content, cement content, and 

 strength, and which furnish information on the work- 

 ability characteristics of various combinations of in- 

 gredient materials. The extent of investigation desirable 

 for any given job will depend on its size and im- 

 portance and on the service conditions involved. De- 

 tails of the laboratory program will also vary, depend- 

 ing on facilities available and on individual preferences. 

 A3.2 — Properties of cement 



A3.^.1 Physical and chemical characteristics of ce- 

 ment influence the properties of hardened concrete. 

 However, the only propwrty of cement used directly 

 in computation of concrete mix proportions is specific 

 gravity. The specific gravity of portland cements of 

 the types covered by ASTM C 150 and C 175 may 

 usually be assumed to be 3.15 without introducing 

 appreciable error in mix_ computations. For other 

 types such as the blended hydraulic cements of ASTM 

 C 595, the specific gravity for use in volume calcula- 

 tions should be determined by test. 



A3.2.2 A sample of cement should be obtained 

 from the mill which will supply the job, or preferably 

 from the concrete supplier. The sample should be ample 

 for tests contemplated with a liberal margin for 

 additional tests that might later be considered desirable. 

 Cement samples should be shipped in airtight con- 

 tainers, or at least in moisture-proof packages. 

 A3. 3 — Properties of aggregate 



A3.3.1 Sieve analysis, specific gravity, absorp- 

 tion, and moisture content of both fine and coarse ag- 

 gregate and dry-rodded unit weight of coarse aggre- 

 gate are physical properties useful for mix computa- 

 tions. Other tests which may be desirable for large or 

 special types of work include petrographic examination 

 and tests for chemical reactivity, soundness, durability, 

 resistance to abrasion, and various deleterious sub- 

 stances. Such tests yield information of value in judg- 

 ing the long-range serviceability of concrete. 



A3.3.2 Aggregate gradation as measured by the 

 sieve analysis is a major factor in determining unit 

 water requirement, proportions of coarse aggregate 

 and sand, and cement content for satisfactory work- 

 ability. Numeroiis "ideal" aggregate grading curves 

 have been proposed, and these, tempered by practical 

 considerations, have formed the basis for typical sieve 

 analysis requirements in concrete standards. ASTM 

 C 33, "Specification for Concrete Aggregates," provides 

 a selection of sizes and gradings suitable for most 

 concrete. Additional workability realized by use of 

 air-entrainment permits, to some extent, the use of 

 less restrictive aggregate gradations. 



A3. 3.3 Samples for concrete mix tests should be 

 representative of aggregate available for use in the 

 work. For laboratory tests, the coarse aggregates 

 should be separated into required size fractions and 

 reconstituted at the time of mixing to assure represen- 

 tative grading for the small test batch^'S. Under some 

 conditions, for work of important magnitude, labora- 

 tory investigation may involve efforts to overcome 

 grading deficiencies of the available aggregates. Un- 

 desirable sand grading may be corrected by: (1) separa- 

 tion of the sand into two or more size fractions and 

 recombining in suitable proportions; (2) increasing or 

 decreasing the quantity of certain sizes to balance the 

 grading; or (3) reducing excess coarse material by 

 giinding or crushing. Undesirable coarse-aggregate 

 gradings may be corrected by: (1) crushing excess 

 coarser fractions; (2) wasting sizes that occur in 

 excess; (3) supplementing deficient sizes from other 

 sources; or (4) a combination of these methods. What- 

 ever grading adjustments are made in the laboratory 

 should be practical and economically justified from the 

 standpoint of job operation. Usually, required aggre- 

 gate grading should be consistent with that of eco- 

 nomically available materials. 

 A3.4 — Trial batch series 



A3. 4.1 The tabulated relationships in the body of 

 this report may be used to make rough estimates of 

 batch quantities for a trial mix. However, they are 

 too generalized to apply with a high degree of ac- 

 curacy to a specific set of materials. If facilities are 

 available, therefore, it is advisable to make a series 

 of concrete tests to establish quantitative relationships 

 for the materials to be used. An illustration of such a 

 test program is shown in Table A3.4.1. 



A3.4.2 First, a batch of medium cement content 

 and usable consistency is proportioned by the described 

 methods. In preparing Mix No. 1, an amount of water 

 is used which will produce the desired slump even if 

 this differs from the estimated requirement. The fresh 

 concrete is tested for slump and unit weight and ob- 

 served tflosely for workability and finishing character- 

 istics. In the example, the yield is too high and the 

 concrete is judged to contain an excess of sand. 



A3.4.3 Mix No. 2 is prepared, adjusted to cor- 

 rect the errors in Mix No. 1. and the testing and 

 evaluation repeated. In this case, the desired prop- 

 erties are achieved within close tolerances and cylinders 

 are molded to check the compressive strength. The 

 information derived so far can now be used to select 

 proportions for a series of additional mixes, No. 3 to 

 6, with cement contents above and below that of Mix 

 No. 2, encompassing the range likely to be needed. 

 Reasonable refinement in these batch weights can be 

 achieved with the help of corrections given in the notes 

 to Table 5.3.7.1. 



A3.4.4 Mix No. 2 to 6 provide the background, in- 

 cluding the relationship of strength to water-cement 



TABLE A3.4. 1— TYPICAL TEST PROGRAM TO ESTABLISH CONCRETE-MAKING 

 PROPERTIES OF LOCAL MATERIALS 



Cubic yard b«tch quanUtlM. lb 



Concrete characteristics 



Mix 



No. 



Cement 



Sand 



Coarse 

 ABSregate 



Water 



Total 

 used 



Slump. 



Unit wt., 

 lb per 

 cult 



Yield, 

 cult 



28-day 

 Compressive, 

 strength, psl 



Work- 

 ability 



Estimated 



Used 





MO 



1375 



1810 



325 



350 



4035 



4 



147.0 



27.45 



■ _ 



Oversanded 





WO 



12S0 



1B7S 



345 



340 



3M5 



3 



147.0 



28.B7 



3330 



o.k. 





400 



13M 



1875 



345 



345 



3855 



4.5 



145.5 



27.18 



2130 



oJt. 





4U 



I2M 



1875 



345 



345 



3H0 



4 



148.2 



27.08 



2810 



oJc. 





HO 



1210 



1875 



345 



345 



3880 



3 



147J 



28.88 



3800 



oX 





•00 



iiae 



1875 



345 



345 



3889 



3.1 



148.S 



28.87 



4380 



oX 



ACI STANDARD 



335 



