158 Bulletin 86 



costly at the outset and cost nothing at all for maintenance. Cul- 

 verts of 15 to 24 inches capacity have been installed for ditch 

 crossings with only a few inches of earth over them. Usually they 

 support the loaded farm wagons that pass over them, but not 

 always. It is safer to give them a good cover, even though the 

 road grade has to be raised. 



During the past few years most of the culverts built in Arizona 

 have been of corrugated iron, usually the so-called ingot-iron cul- 

 verts. Ingot-iron is said to be nearly pure iron and to resist cor- 

 rosion as well as wrought iron. A comparison of the merits of 

 ingot-iron and cement pipe is presented in the hope that it may be 

 of value, especially to state and county officials. 



1. Portability: Here the ingot-iron culverts have some advantage 

 in case the cement pipe must be hauled a long distance. If the ce- 

 ment pipe can be made in the vicinity it may be easier to transport 

 it on a short haul than to haul the iron culverts from a distant rail- 

 way station. 



2. Strength: The crushing strength of eleven 12-inch corrugated 

 iron pipes were tested at the University of Maine*. The actual in- 

 side diameters varied from 10 to 12}^ inches. The crushing loads 

 per lineal foot for five lap rivetted pipes averaged 4470 pounds. 

 This is somewhat more than the average for 12-inch cement pipe 

 as given on page 125. Instances have been observed on Arizona 

 state highways where ingot-iron culverts, placed too near the grade 

 line, have been flattened, crushed, and broken through by freight 

 wagons. Cement pipe culverts have failed when placed too near 

 the surface. Both classes of pipe are safe if buried their own depth. 



Yuma County has employed McCracken cement pipe culverts 

 for the extensive bond-built highways of that county. The specifi- 

 cations called for 12, 18, and 24-inch diameters, and mortar propor- 

 tions of 1 to 3>1 An interesting test was made of this pipe by the 

 county engineer. He statesf : 



"Before we used the pipe, a test was made at the factory, on 12- 

 inch pipe covered with one foot of dirt. A wagon was loaded at 

 about approximately three tons on the rear wheels. A 6 by 6 was 

 laid across the driveway just before the wagon was driven over the 

 pipe, thus throwing the load six inches higher and dropped from 

 this height onto the ground just above the pipe. The load was run 

 across and dropped onto the pipe repeatedly. Upon taking up the 

 pipe, no defects whatever could be found. This machine-made pipe 



•T^niv. Me. Technol. Exp. Sta., Bui. II, 1, (191fi). » ^ 



tFrom a private communication from C. M. Hindman, County Engmeer, August 

 10, 1916. 



