OFFICE OF PUBLIC EG ADS. . 737 



The work was begun on September 12, 1910, and continued until November 

 10, 1910, when bad weather prevented its completion. It was again taken up 

 on July 10, 1911, and the field work was completed on August 12, 1911, and 

 will be described in detail at a later time. Of the nine experiments mentioned 

 above, one was with refined water-gas tar, one with asphalt block, five with oil 

 asphalt, one with a refined asphaltlc pi'eparation, and one with a semisolid re- 

 fined semiasphaltic oil. In these experiments various methods of applying the 

 bituminous binder were tried, including the penetration and mixing methods 

 and the prepared-filler method. The sections treated were rather short, and 

 most of them did not exceed 300 feet, which made the unit costs rather high. 

 The cost per square yard for the wearing surface varied from 82.18 cents to 

 49.73 cents. The highest cost was for a section 300 feet in length of oil asphalt, 

 laid by the mixing method, and the lowest cost was for an oil-asphalt section 

 300 feet long, treated by the penetration method. 



IKSPECTION OF OBJECT-LESSON ROADS. 



During the past fiscal year inspections were made of nine object- 

 lesson roads previously built under the direction of this office. These 

 were located at the following places : Dodge City, Kans. ; Palatka, 

 Fla. ; Bowling Green, Ky. ; Newton, Mass.; Williamston, N. C. ; Car- 

 negie, Okla.; Greenville, S. C. ; Knoxville, Tenn. ; and Mexia, Tex. 



All of these roads were found in good condition, some in excellent 

 condition. The road built at Bowling Green, Ky., with rock asphalt 

 presents an especially satisfactory appearance and is significant as a 

 result of construction with locally obtained rock asphalt. 



At Greenville, S. C, the contrasting appearance of portions of the 

 same macadam road, built in 1909 and 1910, was striking. The por- 

 tion finished with bitumen was in excellent shape, whereas the water- 

 bound macadam showed a wear of from 1 to 2 inches. 



HIGHWAY BRIDGES AND CULVERTS. 



In the report of this office for 1910 mention was made of the need 

 for better highway bridges and culverts. The need still exists and is 

 becoming more apparent each year. 



Daring the year a division of bridge and culvert engineering was 

 established in this office, and an experienced bridge engineer was 

 employed for the purpose of collecting and preparing usefrl data on 

 this subject and preparing it suitably for distribution. Bulletin No. 

 39, entitled " Highway Bi-idges and Culverts," was issued, and other 

 bulletins dealing more in detail with the different types of bridges 

 and culverts, are in preparation. 



Upon proper application a bridge engineer will be sent, if deemed 

 practicable, to make inspection, surve}^, and estimate for proposed 

 bridges and culverts, to prepare plans, and to superintend the erec- 

 tion of such structures. It is intended, hoAvever, that this assistance 

 shall be limited to object-lesson work. 



Under the direction of the bridge engineer of the office, there were 

 built at Bennettsville, S. C, between November 12, 1910, and Decem- 

 ber 16, 1910, three reinforced concrete culverts at a cost of $332.50 for 

 labor alone. Culvert No. 1 was a IG-foot span, 30 feet Avide to the 

 outer side of the parapets, with side walls 4 feet high and the cover 

 of the steel I-beam type incased in concrete. Culvert No. 2 was a 

 7-foot span, 30 feet wide to the outer side of the parapets with side 

 walls 5 feet high and the cover of reinforced concrete slab. Culvert 



23165°— AGB 1911 47 



