536 EXPERIMENT STATION RECOED. 



ance to traffic. ... (3) They produce practically no dust and may be easfly 

 cleaned. (4) They can be maintained at comparatively small cost until 

 renewals become necessary. (5) They may be made to serve as an excellent 

 base for some other type of surface when resurfacing becomes desirable. (6) 

 They present a pleasing appearance." The principal disadvantages are "(1) 

 They are somewhat noisy under horse traffic. (2) There is no method of con- 

 structing necessary joints in the pavements which will entirely prevent exces- 

 sive wear in their vicinity. Furthermore, joints do not altogether eliminate 

 cracking, and wherever a crack develops it must be given frequent attention 

 in order to prevent rapid deterioration of the pavement. (3) They can not 

 be as readily and effectively repaired as many other types of pavements. . . . 

 " The one-course type of concrete pavement is greatly to be preferred to the 

 two-course tj'pe, but there are conditions under which the adoption of the two- 

 course type of construction may be justified. The proportion of cement to 

 the sand and coarse aggregate combined should not be less than about 1 : 5, and 

 the proportion of sand to coarse aggregate should not be less than li : 3, nor 

 greater than 2 : 3. Ordinarily, when gravel is used as coarse aggregate, the 

 proportions may be made 1 part of cement to li parts of sand to 3 parts of 

 gravel, and when crushed stone is used as coarse aggregate 1 part of cement 

 to IJ parts of sand to 3 parts of crushed stone. 



" All types of contraction joints which have yet been devised require careful 

 and frequent attention in order to prevent rapid deterioration of the pavement 

 in their vicinity. It appears that better results are obtained by spacing the 

 joints at an angle of about 75° to the center line of the road than when they 

 are placed at an angle of 90°. Thin bituminous wearing surfaces for concrete 

 pavements can not be economically justified at present. . . . 



" Intelligent angineering supervision is absolutely essential in concrete pave- 

 ment construction, because defective materials or workmanship can not be 

 readily repaired after the pavement is completed, and they are not usually 

 apparent until the pavement has been in use for some time." 



Specifications are given which are believed to typify the best practice which 

 has been developed in concrete pavement construction. 



Vitrified brick pavements for county roads, V. M. Peirce and C. H. jNIooee- 

 riELD {U. S. D«fi. Agr. Bui. 2J,6 (1015), pp. 38, pis. 10, figs. 3).— This is a 

 revision of Department Bulletin 23 (E. S. R., 30, p. 86). 



Notes on the width, alig'nment, grade, and drainage features of the 

 designing of country roads, R. A. Meeker {Engin. and Contract., ^2 (1914), ^o 

 15, pp. 346, 347). — This is a brief summary of important details connected with 

 the preparation of plans for rural road improvements under New Jersey con- 

 ditions. 



It is stated as axiomatic that the width of roads should be in multiples of 8 

 ft, and that in order to obtain a roadway of sufficient width to accommodate 

 travel passing in both directions 24 ft. may well be taken as the minimum allow- 

 able width. The important considerations in alignment are pointed out as 

 direct distance, grades, and the economic features of grading. Grade is con- 

 sidered to be the most important economic feature in road design. As regards 

 drainage, it is thought that for earth roads a fall of 1 in. per foot from the 

 center to the gutters, for water-bound macadam f in. per foot, and for bitumin- 

 ous concrete i in. per foot is sufficient. For country roads gravel or plain 

 macadam is thought to be sufficient for surfacing. 



Progress reports of experiments in dust prevention and road preserva- 

 tion, 1914 (U. S. Dept. Agr. Bui. 257 {1915), pp. .4/,).— This bulletin reports 

 the results from a number of experiments in dust prevention and road preser- 

 vation conducted by the Office of Public Roads in 1914, a similar report for 1913 



