8 



BULLETIX lOTT, r. S. DEPAP.TilEXT OF AGRICULTURE. 



poimds per square inch. Pavements composed of concrete of less 

 strength have generally proved unsatisfactory. 



In practice it is generally not feasible to follow strictly any of 

 the theories in the proportioning of the materials. The aggregates 

 must usually be obtained fi'om commercial sources and the specified 

 grading of these aggregates must be such that they can be supplied 

 TTithout excessive expense or decreased output. The maximum size 

 usually specified ranges from 1^ to 2^ inches. When the *2|^-inch 

 size is permitted it is usually provided that 90 to 95 per cent of the 

 aggregate shall pass a 2-inch circular opening. For sand graded as 

 described on page 4 and a coarse aggregate, well graded from i inch 

 to If inches, the proper proportions for concrete pavements would 

 l3e 1 part of cement to 2 parts of fine aggregate to 3 parts of coarse 

 aggregate. For coarse aggregate from ^ inch to 2^ inches in size. 

 a projx)rtion of 1:2:S^ or even 1:2:4 may be used provided there 

 is sufficient mortar to finish the concrete properly. These propor- 

 tions may have to be altered slightly, but for good commercial ag- 

 gregate graded as descril^ed on page 5 the proportions given will 

 prove satisfactory. Where it is not possible to obtain commercially 

 gi'aded aggregates of the sizes mentioned, different proportions of 

 aggregate should be used. The following table .^ which gives a 

 large number of pro|x>rtions designed to produce concrete of ap- 

 proximately 3.000 pounds compressive strength at 28 days when 

 mixed with the water necessary to give a workable consistency, 

 indicates the great variety of combinations that can be used. 



Ahram^^s table of iiroportioni^ and quantilies Jar one euhic yard of concrete. 



[Bssed Tipon labor 



wocEanepiad 



Cement in harrds, aggregates in eubic yards. 



inv^csti^atioiis, nacg approved material;, compressive stroigth, 2S dars, with 

 ! plastiaty, 6 by 12-iDch cylinders, .1,000 pounds per <3qoare indi.) 



Coaise aggregates. 



Fine aggnc^ies, screen openings per inrh. 



O-S 



0-i 



Sine, indies. 



o 



~ 











3 



3 i 



s 









L> 



o 1 



^ 



2.4 



. 1 



L6 



.fi9l 



I.SS|I 



•^ 



2.7 



1 



1.6 



.75 



L77 



.42 



f=« Xi -^ 



=- r- O 



e> I 1^ 



Xo. 4 scref-a to J: 



Proportions.... 



Qoan titles 



Ko. 4 sfTieien xc 1: 



Proportions.... 



Qiiarinties. 



Xo- 4 screen toll: 



Proportions.... 



Qoantities. 



Xo. 4 screen to 2: 



PnqM»rtiOBs._. 



Qoantities 



1 

 1.96 



1-3 

 .37 



1 

 1.90 



.66 1.8! .43 .62 



1.3 



.3^ 



LS^ .33. 



1.2 

 i.7^ .31 



.S4 L6S! 



3.5 

 .90i 1.6S 



LS , Z3 



1 



I.S3| 



2.0 



.521 



1.8 i 2.6 



2.0 

 .46 .66 1.67 .50 



2.3 

 .59 



2.5 



.62j 



1 2.7 

 L79I 



L7 3.1 1 ! 2. 

 .41 .75 1.61 



s.n 3.0 



.471 .72 



1 1 2.6 



L72 .66 



2.4 

 1.62! .57 



11 1.6 3.7 1 L9 3l6 

 3 1.55 .36 .85j L52 .43; .81 



1 

 1.53! 



2.2 

 .30 



1.5 

 .40 



1-8 

 .46 



24 



.57 



3.1 



.70 



5 Table prepared by A. N. Johnson, 

 Abrams, Stractural Materials Research 



based on ivsnlts of investigations by Prof. D. 

 Laboratory, Lewis Institute, Chicago, 111. 



