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



and it is an observable fact that as soon as the wet-earth covering is 

 removed from the surface of the concrete it begins to dry out and, 

 necessarily, to shrink. The maximum. average shrinkage shown by 

 the concrete in any of the sections of different mixtures was approxi- 

 mately 0.0001 inch per inch of length, and this occurred about three 

 months after the pavement was laid. The temperature in this time, 

 however, had dropped 20°, and this fall in temperature accounts 

 almost exactly for the shrinkage. It has been shown by means 

 of laboratory specimens stored out of doors and subjected to all the 

 changes of the atmosphere that very little change in length takes place 

 under such conditions. It seems probable that the moisture content 

 of the concrete at Chevy Chase changed so little that the length of the 

 concrete was very little affected thereby. A hard rain, thoroughly 

 soaking the concrete, will have no immediate great effect upon its 

 length. It has been pointed out that moisture changes are rather slow 

 and progressive, and therefore it is unlikely that hard rains of even 

 several days' duration will have great effect on the expansion of the 

 concrete in the road. 



EXPANSION AND CONTRACTION OF OHIO POST ROAD.* 



These measurements were taken over three 300-foot experimental 

 sections of the concrete Ohio Post Road constructed in 1914 under 

 the supervision of the Office of Public Roads. The Ohio Post Road is 

 located partly in Muskingum County and partly in Licking County, 

 Ohio, and runs west from Zanesville, Ohio, for 24 miles over the old 

 Xational Pike to the Moscow Bridge over the South Fork of the 

 Licking River. This road was constructed on a sub-base composed 

 mainly of a stiff red clay. The total width of concrete surfacing is 

 16 feet, with a thickness of 6 inches at the edges and 8 inches at the 

 center. Expansion joints made of one thickness of 2-ply tar paper 

 were spaced 30 feet apart throughout the length of the road, with the 

 exception of the three experimental sections, on each of which the 

 spacing varied from 20 feet to 100 feet, intervening sections being 

 40. 00. and SO feet long. Expansion joints were placed at an angle 

 of 15° across the road. Both gravel and crushed stone were used 

 as coarse aggregate, the proportions in the former case being 1 : 1\ : 3 

 and in the latter 1:1:}: 3. Crushed stone used in the experimental 

 sections was obtained from limestone quarried on the Scioto River at 

 Marble Cliff. The sand and gravel were obtained from a washing 

 plant at Dresden, Ohio. 



As soon after laying as possible the concrete surface was covered 

 with canvas, which was removed when the concrete was 24 hours old 

 and replaced by a 2-inch earth covering. This was allowed to remain 



'Tin authors desire to acknowledge the assistance of the Ohio State Highway Depart- 

 ment in conducting the tests on this road. 



