54 
BULLETIN 126, U. S. DEPARTMENT OF AGRICULTURE. 
Except for 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 volumetrically 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 pas? 
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 : 
Pro-portions of materials used in making concrete slabs. 
Mixture. 
Number of slab. 
1 
2 
3 
By volume: 
1 
3 
5 
100 
118 
319 
552 
1 
2 
4 
72 
99 
203 
441 
Sand 
3 
Gravel 
5 
By weight: 
Water 
75 
79 
244 
Gravel 
431 
