28 



BULLETIN 532, IT. 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 Eoad. 



Table I. — Chancre in length of concrete in Ohio Post Pioa<l. 





Section I. 



Section TI. 





Oct. 31. 



Mar. 4. 



.Tunc 19. 



Feb. 25. 



Nov. 2. 



Mar. 3. 



Change in temperature 



—32 



-0. 00017 

 -0.000170 



-52 

 -0.00031 

 -0. 00029 



-14 

 -0.000065 



-0.000077 



-48 

 -0. 00023 

 -0. 00026 



22 



-0. 000076 

 -0.000121 



-45 



-0. 000227 



Calculated temperature change 



-0. 000248 





Section II. 



Section III. 





.Tunc 17. 



Fob. 25. 



Nov. 7. 



Mar. 6. 



June 15. 



Feb. 22. 



Change in temperature 



+3 



+ 0. 01)0(12 1 

 + 0.000017 



go 



-0.000168 



-0.00021 



+3 

 +0. 0000096 

 +0. 0000165 



-14 

 -0.000109 



-0. 000077 



+ 24 

 J 0. 000148 

 -| 0.000132 



-10 



+ 0.000072 



Calculated temperature change 



-0.000055 



