28 
BULLETIN 532, U. S. DEPARTMENT OF AGRICULTURE. 
greatly by the temperature expansion and contraction. It seems 
that the concrete in the road, when subjected to actual weather condi- 
tions, does not suffer the prolonged extreme ranges of moisture con- 
tent suffered by the laboratory concrete specimens kept indoors in 
the dry air of the laboratory and therefore does not expand or con- 
tract because of moisture changes to the extent that the laboratory 
specimens change. Undoubtedly in warm, dry weather there will 
be some slight contraction just after the moisture is allowed to dry 
out from the concrete, particularly in a well-drained sub-base. It 
seems that enough of the water absorbed by the concrete, due to rains 
or to capillarity, remains in the concrete during the dry weather to 
prevent much change in length. There may be conditions of pro- 
longed extremes of wetness and dryness in the road which will affect 
the expansion and contraction to an appreciable extent. Thus in the 
spring of the year the prolonged moisture of the previous winter 
might so aid the expansion occurring during the first day of high 
temperature that the road will heave where proper allowance has not 
been made for this expansion. There are also conditions of poor 
drainage in the sub-base, particularly in a low section in the road, 
where the concrete will be practically constantly saturated, in which 
case the expanding effect of the moisture will be in evidence. 
(2) Effect of variations in temperature — -field measurements. — It 
has been pointed out that, as a rule, the concrete in a road expands 
and contracts as the temperature rises and falls. It will be interest- 
ing to compare the actual measurements of the expansion and con- 
traction of the concrete in the road with the calculated change, as- 
suming no friction at the base and assuming a coefficient of expansion 
of 0.0000055 per degree F. Table I shows a comparison of the 
actual with the theoretical unit changes in the concrete of the Ohio 
Post Boad, 
Table I. — Change in length of concrete in Ohio Post Road. 
Section I. 
Section II. 
Oct. 31. 
Mar. 4. 
June 19. 
Feb. 25. 
Nov. 2. 
Mar. 3. 
Chantre in temperature 
—32 
-0. 00017 
-0. 000176 
-52 
-0.00031 
-0. 00029 
-14 
-0.0000(54 
-0. 000077 
-48 ; -22 
-0.00023 , -0.000076 
-0.00026 -0.000121 
-45 
-0.000227 
Calculated temperature change 
-0.000248 
Section II. 
Section III. 
June 17. 
Feb. 25. 
Nov. 7. 
Mar. 6. 
June 15. 
Feb. 22. 
Change in temporal ure 
+3 
+0.00002* 
+ 0.000017 
oo 
— 0.0001(58 
-0.00021 
4-3 
+ 0.0000096 
+0. 0000165 
-14 
-0. 000109 
-0. 000077 
+ 24 
-10.00014S 
+ 0.000132 
-10 
J 0. 000072 
Calculated temperature change 
-0.000055 
