54 



BULLETIN 126, U. S. DEPARTMENT OF AGEICULTUEE. 



Except fur a roller placed under one end, each slab was lying on 

 ground composed mostly of loose gravel. 



The slabs were 12 inches wide, 6 inches deep, and 11 feet long. 

 The steel pins inserted vertically in the top were spaced 10 feet apart, 

 thus leaving 6 inches length of slab beyond the pin at each end. A 

 wet hand-mixed concrete mixture was used for each slab, numbered 

 1 and 2, and volumetric ally proportioned 1:3:5 and 1:2:4, respec- 

 tively. Each slab was of rectangular cross section throughout. 



The general average coefficient of expansion measured was 0.0000043 

 for slab 1 and 0.0000042 for slab 2. 



LABORATORY TESTS AT THE STATE UNIVERSITY OF IOWA. 



In the fall and winter of 1913-14 the experimental work initiated 

 at Logan, Utah, was continued in the laboratory of the State Univer- 

 sity of Iowa under the same supervision as before. 



The sand and gravel used were taken from the bed of Iowa River. 

 This raw material was screened through a 1-inch mesh screen and 

 again through a |-inch mesh screen. The material failing to pass 

 the latter screen was considered gravel. The sand was unscreened, 

 but it was fine and clean. 



Three horizontal slabs were cast with the same dimensions as those 

 made at Logan. The apparatus and equipment were practically 

 the same, except that the laboratory permitted a somewhat careful 

 control of influencing conditions not possible in the open-air work. 

 In addition, a specially devised apparatus permitted the making of 

 observations for change of length within 30 minutes after water had 

 been added to the dry materials used in making the concrete. Brass 

 pins with their upper ends highly polished were used instead of steel 

 pins. The methods employed for temperature determination and 

 control were quite satisfactory and it is believed gave results fully as 

 accurate as the investigations warranted. 



Two slabs of seasoned concrete were used for determining the 

 coefficient of expansion. A third one was used to determine the 

 influence on change of length due to setting. Each slab was made 

 of hand-mixed concrete, using the materials composing the concrete 

 in the following proportions : 





Proportions of materials used in making concrete s 



labs . 









Mixture. 



Number of slab. 





1 



2 



3 



By volume: 



Cement 



1 

 3 



5 



100 

 118 

 319 

 552 



1 

 2 



4 



72 



99 



203 



441 



1 



Sand 



3 



Gravel 



5 



By weight: 



Water 



75 



Cement 



79 



Sand 



244 



Gravel 



431 







