191S] 



EURAL ENGINEERING. 



291 



Frictional resistance of concrete on variov.s sub-hases {suh-hases thorottgJily 

 saturated with tvater and surrounding ground exceedinylij soft; iceight of 

 specimen, 870 lbs.). 



Kiii'i or base. 



Level clay 



Uneven clay . . 



Loam 



Level ssnrl 



3-in. cravel 



?-in. broken 

 stone 



3-in. broken 

 stone 



Oiled clay 



Clay and cob- 

 ble stones . . . 



Concrete base. 



Sand, oile;! 



Concrete, oiled 



Move- 

 ment. 



o.oni 



.001 

 .001 

 .001 

 .001 



.001 



.001 

 .001 



.001 

 .000 

 .001 



Force. 



120 

 200 

 150 

 140 

 510 



240 

 150 



140 



2, 500+ 



180 



.000 2,:.00+ 



Coeffi- 

 cient. 



0.14 

 .23 

 .17 

 .16 

 .58 



.46 



.28 

 .17 



.16 



2.9 + 



.21 



2.9-1- 



Move- 

 ment. 



0.01 

 .01 

 .01 

 .01 

 .01 



.01 



.01 

 .01 



.01 

 .00 

 .01 

 .00 



Force. 



300 

 460 

 260 

 280 

 640 



660 



630 

 410 



410 



2. 500+ 



'280 

 2, 500+ 



Coeffi- 

 cient. 



0.35 

 .53 

 .30 

 .32 

 .73 



.76 



.73 

 .47 



.47 

 2.9 + 



.32 

 2.9 + 



Move- 

 ment. 



0.05 

 .05 

 .05 

 .05 

 .05 



.05 



.05 

 .05 



.05 

 .00 

 .05 



.00 



500 

 620 

 410 

 400 

 950 



900 

 850 



710 



2, 500+ 



4SC 

 2,500+ 



Coeffi- 

 cient. 



0.58 

 .71 

 .47 

 .46 



1.10 



1.08 



.82 

 2.9 + 



.55 

 2.9 + 



Move- 

 ment. 



1.500 



1.400 



.750 



.750 



.500 



2.000 



Force. 



950 

 925 

 925 

 875 

 1,050 



1,160 



.875 1,625 

 1.250 'l,425 



1.750 

 .000 

 .375 

 000 



1,260 

 2,500+ 



800 

 2,500+ 



Coeffi- 

 cient. 



1.09 

 1.06 

 1.00 

 1.00 

 1.20 



1.33 



1.87 

 1.G4 



1.45 

 2.9 + 



.92 

 2.9 -f- 



These results, v.-lien compared with the previous results, " show very clearly 

 that much depends upon the moisture condition of the sub-base. A wet sub- 

 base permits the concrete to slide very much easier than does a dry sub- 

 base. This apparently al.so applies to the specimens mounted on broken stone 

 and gravel base, particularly when the movements are small. 



" The formation of transverse cracks in concrete bases can readily be 

 ascribed to direct tension due to frictional resistance at a time when the 

 concrete is contracting, whether this is caused by decrease in temperature, 

 or by drying out of the moisture. The test results show that the coefficient 

 of friction can readily vary from almost to something over 2 or more, 

 depending upon the movement of the concrete and the character of the sub- 

 base. The distance between transverse cracks is dependent upon the coefficient 

 of friction, and the total force of friction must extend over this distance. 



" Calling the coefficient of friction /, the distance between cracks D, the 

 weight of the pavement per square foot w, we may write the equation : 



/ X ?c X D = tensile strength of concrete per foot of width." 



Farm concrete, K. J. T. Ekblaw {New York: The Macmillan Co., 1917, pp. 

 XI +295, pis. 16, figs. 71). — This is a nontechnical treatise on the subject, con- 

 sisting of the following chapters : Cement ; concrete ; foundations and walls ; 

 pavements, floors, sidewalks, steps ; concrete building blocks ; concrete fence 

 posts ; tanks, troughs, and cisterns : drain tile, culverts, and bridges ; concrete 

 silos ; concrete surfaces and stucco ; concrete in residences ; and approximate 

 cement tests, with an appendix giving standard specifications and tests for 

 Portland cement. 



Tests of fuel for agricultural steam eng'ines (Bui. Dir. Gen. Agr., Com. et 

 Colon. Twiis, 20 {1916), No. S7, pp. 49-55; abs. in Intcrnat. Inst. Agr. [Rome], 

 Internat. Rev. Sci. and Pract. Agr., 7 {1916), No. 7, pp. 1012, lOlS) .—Tests of 

 seven kinds of wood and of lignite and coal briquettes in a 24-horsepower 

 steam engine driving a hay baler working at a rate of 40 to 50 bales per 

 hour are reported. 



It was found that wood could be used for running the engine, two and a 

 half to three times as much wood as coal being required. Slightly better 

 results were obtained with dry wood than with green wood, and also with the 

 larger sized branches than with the smaller ones. The resinous wood gave 

 about medium results. Lignite gave about twice as good results as wood. 



