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



Section III. Cement concrete, surface treated with bituminous materials. 

 Section IV. Oil-cement concrete. 

 Section V. Cement concrete. 

 Section VI. Vitrified brick. 



Some of the above sections were not built in continuous lengths. 



Because of unfavorable weather, work was stopped on this road, 

 on December 15, after the concrete of Section III had been poured. 

 Work was resumed in the following spring and carried to comple- 

 tion. On the bottom of figure 13 will be found a partial layout of 

 the various sections of the road as constructed, giving the dates of 

 construction and the character of the coarse aggregate. A complete 

 description of the road and method of construction may be found in 

 other publications of this office. 1 



During the construction of the cement concrete sections bronze 

 plugs of the type previously described were inserted in the road sur- 

 face, spaced 10 feet apart in a line 5 feet from the east side of the 

 road. At every fifth plug there was placed also a transverse plug- 

 offset 10 feet from the line of plugs paralleling the road. The layout 

 of the sections of the road measured is shown in figure 13. 



The first set of measurements was taken as soon as practicable 

 after the concrete had hardened. The dates and temperatures arc 

 given on this plate just above the road layout. Kef erring to the 

 second set of readings, it will be seen that in general, when the tem- 

 perature is lower than the initial temperature, the uncracked portions 

 of concrete show contraction, and when the temperature is higher 

 than the initial temperature, expansion occurs. Cracks are indicated 

 by dotted lines and are seen at various intervals throughout the 

 length of the road, in practically all the different sections except 

 that containing limestone aggregate. In the cold weather, during 

 which this set of readings was taken, the cracks opened up, as shown 

 by the expansion readings. The shrinkage of the concrete naturally 

 would cause an opening of the cracks. 



In the spring of 1913 a bituminous carpet coat was placed over 

 the concrete up to the end of the oil-cement gravel-aggregate section 

 (station No. 210), and expansion measurements were made in the 

 hot weather of the spring, summer, and fall. It is interesting to 

 note that the readings taken on July 3, 1913, all showed expansion, 

 even those taken over the cracks. Expansion at the cracks as well 

 as in the concrete is rather difficult to account for with certainty. 

 However, during the previous winter the cracks undoubtedly opened 

 up very wide during the coldest weather, owing to low tempera- 

 ture contraction, aided perhaps by the freezing of water in the cracks, 

 and became filled with material from the road which prevented 



1 Office of Public Roads Circular No. 99. U. S. Department of Agriculture Bulletin 

 No. 105. 



