2 BULLETIN 532, U. S. DEPARTMENT OF AGRICULTURE. 



Aii extended series of laboratory and field tests was begun in 1010 

 by the Office of Public Eoads to make a close study of expansion and 

 contraction movements of concrete pavements. These included de- 

 tailed attention to the spacing, design, and movement of expansion 

 joints. It is the purpose of this bulletin to present the results of these 

 experiments in the hope that they will be of some value to those in- 

 terested in work of this nature. No attempt will be made herein to 

 apply the results obtained to the practical side of road construction, 

 although certain broad conclusions will be drawn from the results 

 which will be available for immediate application by the engineer. 



LABORATORY MEASUREMENTS OF EXPANSION AND CON- 

 TRACTION. 



It has been established by other investigators 1 that concrete ex- 

 pands on being heated and contracts on cooling by an amount differ- 

 ing very little from that of steel. A coefficient of 0.0000055 per de- 

 gree Fahrenheit seems to express accurately the effect of temperature. 

 Therefore, with change in temperature of 100° F., a 100-foot length 

 of concrete road, if unrestrained by friction at the base, would ex- 

 pand or contract 0.0000055 X100°X100 feet= +0.055 feet or 0.66 

 inch. This phenomenon alone, without considering any other influ- 

 ences, probably accounts in many instances for the cracking of con- 

 crete pavements. 



In view of the probable reliability of the already established tem- 

 perature coefficient of expansion, all efforts of the laboratory were 

 directed toward obtaining the change in length of concrete clue to 

 other causes. It has been shown, originally by Bauschinger and sub- 

 sequently by other investigators, that both neat cement and mortar 

 contract to a considerable degree upon hardening in air, while, on the 

 other hand, they show considerable expansion when placed in water. 

 Some of the values of contraction of neat cements and mortars, re- 

 ported by White in the 1911 Proceedings of The American Society 

 for Testing Materials, are as follows : 



Shrin kagc of neat cement kept in air. 



Per cent. 

 7 <lays (average of f; specimens) 0.109 



28 days (average of 6 specimens) .190 



6 months (average of 6 specimens) .236 



1 year (average of 5 specimens) . 270 



2 years (average of 5 specimens) . 2S9 



4 years (average of 5 specimens) . 322 



1 Eellar, " Volmnanderungen von Cementen verschiedener Mischung bei wechseldner 

 Temperatur and wechseldner Feuchtigheitsgrad," Tonind. Zeit. 19, 469 and 487, 1894 



Pence, W. D., "The Coefficient of Expansion of Concrete," Eng. News, 46,380 (1901) 



Norton, Chas. I., "Some Thermal Properties of Concrete," J. Am. Soc. Mech. Eng, 

 June, 1913, p. 1012. 



Budeloff and Xioglerschmidt, " Untersuchungen iiber die Langemlndcrungen von Beton 

 prismen beim EJrhartefi und in folge Temperaturwechsel," Deutsch. Auschuss fur Eisen 

 beton, Heft 23, 1913. 



