Mat 28, 1915] 



SCIENCE 



801 



pared was closed for twenty-four hours, after 

 which traffic was admitted. 



This thin bituminous coating acts in four ca- 

 pacities: First, it waterproofs the surface; sec- 

 ond, it acts as a carpet and deadens the noise of 

 traffic; third, it affords good foothold for horses, 

 and fourth, it prevents abrasion of the concrete, 

 thus prolonging its life. 



TopeJca Biturmnous Concrete Pavements Con- 

 structed with Tar Cement: Philip P. Shaeples. 

 The Topeka bituminous concrete is shown to be 



a revival of types of pavements laid with coal-tar 



cement twenty-five years or more ago. 



The vulcanite pavements' of Pittsburgh and tar 



concrete pavements of New England are described 



and compared mth Topeka specifications. 



The precautions necessary to secure successful 



work with the Topeka specification using coal tar 



cement are given. 



Bituminous Pavements with Two or More Layers 

 of Bituminous Concrete: Arthur H. Blanch- 



ARD. 



In cases where one product of a stone-crushing 

 plant is used for the aggregate of the wearing 

 course of a bituminous concrete pavement and this 

 product is composed of broken stone varying but 

 little in size, let us say from f in. to IJ in., it will 

 be advisable to use two layers of bituminous con- 

 crete. If the above product was used for the first 

 layer and was constructed with a compacted 

 thickness of from If to 2 inches, the second layer 

 might properly be composed of broken stone from 

 J to J in. in size and spread about i in. to f in. 

 in thickness. After the second layer had been 

 rolled the pavement could be finished with or 

 without a seal coat of bituminous cement and a 

 dressing of uncoated stone chips. This method is 

 suggested in order to secure with the above type 

 of broken-stone product a surface of the wear- 

 ing course which will be as dense as when a 

 product ranging in size from i inch to IJ inch is 

 used and the pavement finished with a seal coat of 

 bituminous cement and stone chips. 



From a historical standpoint it is of value to 

 note that an English bituminous pavement of 

 similar type was described in the Engineering 

 Becord of July 23, 1898. The fundamental prin- 

 ciples involved have been made use of in the many 

 successful 'bituminous concrete pavements con- 

 structed in England during the past fifteen years 

 under the trade names of Tarmac and Quarrite. 



Bituminous Macadam Pavements {Penetration 

 Method) : Frederick Steele Strong. 



In determining the quantity per square yard of 

 bituminous material to be used in construction of 

 a bituminous macadam pavement there are four 

 paramount functions to be considered: First, the 

 nature and consistency of the bituminous mate- 

 rial; second, the quality of the stone; third, the 

 depth and sizes of the course; fourth, the kind of 

 traffic and severity of climatic conditions. 



With this data, the following equation has been 

 deduced for the proper amount of binder to be 

 used in eases where the stone is of low crushing 

 and abrasive strength, this classification not to 

 include any stone which is so poor as to be ques- 

 tionable or worthless. Let Y represent the num- 

 ber of gallons to be used per square yard. Let 

 X represent the depth of the top course in inches. 

 Then T = 9/10 X. For instance, with stone of 

 low test, and depth of stone of 2 in., we deter- 

 mine that the quantity of binder should be ap- 

 proximately 1.8 gals, per square yard; and by 

 using this equation again, it is found that for a 

 depth of 3 in. the amount of bituminous mate- 

 rial should be 2.7 gallons per square yard. 



This binder is to be applied in two applications, 

 the first to be two thirds the full amount and the 

 second the balance, and the application is made 

 by pressure machine. I believe no top course for 

 a road of this type should be less than 3 in. in 

 depth. The best stone available should be used 

 even if its cost would entail the use of cheaper 

 material in bottom course, but by this I do not 

 depreciate the importance of a foundation, as 

 without this any road is worthless. 

 Some Ways to Differentiate between Bitumens: 



George P. Hemstreet. 



The Present Status of Adhesive and Cohesive 

 Tests of Bituminous Materials: John S. Cran- 



DELL. 



During the past year the writer has made a series 

 of tests to determine the binding values of a num- 

 ber of bituminous binders. The first tests were 

 made as follows: Cylindrical briquets 25 mm. 

 high X 25 mm. diameter, composed of stone, sand, 

 filler and binder were molded under a pressure of 

 500 kilos per square inch, or 750 kilos per square 

 inch, and were then allowed to season. They 

 were then tested in the small Page Impact Ma- 

 chine that is used for the cementation test of 

 stone. The number of blows required to break or 

 crush each briquet was recorded. Different per- 

 centages of the ingredients were tried. It was 

 found that pieces of crushed stone were cracked 

 while in the molding machine. Other mechanical 



