1919] 



RURAL ENCINI.I'.RING. 787 



per ecu! of hydrated Hme may be added t<> cemenl mortars without seriously 

 Impairing the strength. A large number <>f contractors use i<» per cent lime. 

 Averages of the value of tensile Btrength Cor the various ages give 10 per cent 

 as the best value for air and water storage, 7.5 pet cent for soil storage, ami 



B per cent as the best value for all three kinds of storage. The real value of 

 the addition of lime to cement mortars is the increase in plasticity or work- 

 ability, which is very desirable from the contractors' point >>f view." 



Effect of salt in warm climate on reinforced concrete, J. C. Foss, jr. (Con- 

 orete [Detroit, Mich.], 13 (WIS), No. 5, pp. 11,9, 150, figs. 1,).— From observa- 

 tions made on concrete structures built in the Hawaiian Islands under his su- 

 pervision, the author concludes "that salt water should never be used in rein- 

 forced concrete; that all possibility that salt might be present must be elimi- 

 nated; that reinforced concrete, where used in places having warm salt atmos- 

 pheric conditions, requires exceptionally careful construction. Some engineers 

 contend that the action is no greater in a warm climate than in a cold one. 

 It is, in the writer's opinion, many times greater, for in observing structures 

 which show failures we find on the Islands that every one of them was ex- 

 posed to salt influence, though in many cases a very small amount, and that 

 disintegration has been abnormally fast." 



Reinforced draintile tested, W. J. Sciii.ick {Concrete [Detroit, Mich.], 1] 

 (1918), No. -}, pp. 1-19, 11,0, fig. 1). — A summary of the results of tests at the 

 Iowa Engineering Experiment Station of 278 concrete (1:3) draintile from 

 -2 to .'{it in. in diameter is reported. The tile were reinforced witli two con- 

 centric hoops, usiim the 6-tie and bridge type tie bracing between hoops. 



"The manner of failure was the same, in general, for all the reinforced tile. 

 The first cracks developed were those at the four quarter points, as in unrein- 

 forced tile. These were followed by a varying number of circumferential 

 cracks along the reinforcing hoops. At failure the reinforcing hoops usually 

 pulled out on the inside at the top and bottom of the tile, or the circumferential 

 cracks opened along one or more hoops. In many cases the section of the tile 

 beyond the end hoops broke loose at least a part of the way around the tile. 

 In a few cases the behavior of the tile under test indicated that one or more 

 of the main hoop wires in the reinforcing had broken. In other, and more 

 numerous cases, the weld between the tie wires and the hoop wires was broken 

 at some points. The circumferential cracks and breaks were much more notice- 

 able in the tile in which the 'bridge' type reinforcing was used. . . . 



"Careful consideration of all facts seems to warrant the selection of the 

 cracking strength of a reinforced concrete draintile as iis safe supporting 

 Strength, in the ditch, and even then a factor of safety of 1$ should be applied 

 to the predetermined probable loads, as for other draintile. . . . 



"In these tests the increases in maximum supporting strengths as larger 

 hoops of bridge type reinforcing were used were much more uniform than were 

 the increases in cracking strengths. Also, the increases in both cracking and 

 maximum strengths were more uniform in those tile which had wall thickness 

 nearer normal. This latter fact indicates that if standard reinforcing is to be 

 used considerable care should be taken to keep the forms true to the normal 

 dimensions. 



Mixtures and mixing for draintile (Concrete [Detroit, Mich.}. 7? (WIS). 

 No. 8, pp. 85. 86, 107). — This is an abstract of a paper on proportioning of 

 cement concrete in draintile, by R. W. Cram, in which it is pointed out that 

 draintile manufacture with relatively dry mixtures necessitates special study 

 as involving conditions that do not apply in the use of plastic mixtures. It is 

 also pointed out that thorough mixing is necessary, that within certain limits 



