gg EXPEEIMENT STATION KECORD. [Vol.35 



beginning i in. from tlie end, and the needle above the taper exactly 0.04 in. 

 in diameter." 



The use of hydrated lime in Oreg-on State concrete roads, R. S. Edwaeds 

 (Xat. Lime Manfrs. Assoc. Bui. IS {1915), pp. 15, figs. 2).— A review of con- 

 crete road practice in Oregon in 1914, especially in Jackson County, is given, 

 which, it is thought, has proved that the addition of hydrated lime in quantities 

 ranging from 5 to 10 per cent of the weight of the cement used in concrete pav- 

 ing work shows the following advantages : 



"(1) Decrease in labor cost in placing and surfacing the concrete. ... (2) 

 Tv.-enty per cent reduction of the transverse cracking of a 6-in. concrete road 

 slab under Jackson County climatic conditions, resulting in a saving of A ct. per 

 square yard, where asphalted felt joints were used, or 2 cts. per square yard, 

 where armored joints were used. There is also a future saving in maintenance 

 cost. ... (3) The concrete surface of a pavement in which hydrated lime was 

 used has actually shown a more uniform and dense finish and a more uniform 

 wear." 



In conclusion, the following suggestions are made : " In one-course concrete 

 pavements, which are not to be treated or surfaced with bitumen or oil, 8 per 

 cent of hydrated lime would seem sufficient to secure the stated results. In 

 concrete pavements which are to be treated with a bitumen wearing surface, 

 from 10 to 12 per cent of hydrated lime should prove sufficient and beneficial, 

 and in such cases an increase in the aggregate is justified. In two-course con- 

 crete pavement, the wearing surface of which is to take the traffic, it would 

 seem advisable to use 10 per cent hydrated lime in the base course with 5 per 

 cent in the top course. In rich surface mixtures, such as one cement, one sand, 

 and two crushed-rock screenings, the amount of cement per yard of concrete is 

 high, and a greater percentage of hydrated lime than 5 per cent is not neces- 

 sary and should not be used." 



See also a previous report by the author (E. S. R., 31, p. 387). 

 Loading of bridge floors {Cement Era, 14 {1916), No. 2, p. 60). — Tests by 

 the Ohio Highway Department on the distribution of concentrated loads on 

 highway-bridge floors are reported, the object of which was "to obtain a 

 sufficient knowledge of the distribution of loads through and by concrete floor 

 •slabs to enable the designer to rationally proportion the joists of a slab floor, 

 and also the slab itself, to carry concentrated loads. . . . 



" The following conclusions regarding the distribution of concentrated loads 

 on a reinforced concrete slab, to the floor joists, seem to be warranted by these 

 tests: (1) The percentage of reinforcement has little or no effect upon the load 

 distribution to the joists, so long as safe loads on the slab are not exceeded. 

 (2) The amount of load distributed by the slab to other joists than the one 

 immediately under the load increases the thickness of the slab. (3) The out- 

 side joists should be designed for the same total live load as the intermediate 

 joists, (4) The axle load of a truck may be considered as distributed uniformly 

 over 12 ft. in width of roadway. (5) If the slab has ample grip on the upper 

 ftinge of the I-beam and is continuous over the floor beams and the joists are 

 riveted to the web of the floor beams, the live load stress in the joist may be 

 but one-half as great as for a similar load on the bare I-beam supported at its 

 ends. (G) ru<ler these favorable conditions the axle load in a panel of not 

 moro than 20 ft. may be assumed as uniformly distributed over two-thirds of 

 the length of the joists considered as simple I-beams supported at the ends. 

 A\ ithout these conditions, the load may be assumed as uniformly distributed 

 over a length of at least 5 ft, 



" In a slab of a certain span and indefinite width, there is some width svm- 

 metrlcal with the load beyond which a single concentrated load will have no 



