22,6 Nelson: The Solid Bitumens of Leyte 627 



The above table shows that the mineral aggregate is essen- 

 tially composed of calcium carbonate. The Leyte impregnated 

 rock is thus found to be a bituminous limestone, and it remains 

 to see what kind of pavement can be made of this material as 

 compared with the pavements made from bituminous sandstone. 



It is a well-known fact that in the United States roads are 

 made of artificial mixtures of bitumen, silicious sand, and lime- 

 stone, whereas in Europe natural bituminous limestones are 

 used. The latter are principally obtained from deposits at Val- 

 de-Travers, Switzerland; at Seyssel, France; at Ragusa, Sicily; 

 and at Limmer and at Vorwohle in Germany. The bituminous 

 content of these natural rocks averages 10 per cent, and the 

 material is mostly used without the addition of fluxes or fillers 

 by merely heating it and spreading the softened mass on an 

 appropriate foundation. The roads thus obtained in Europe 

 are of excellent quality. 



According to A. Danby 5 experiments were carried out by 

 Messrs. Durand-Clay and Debray to determine the resistance to 

 crushing stress of artificially made bituminous limestone and 

 bituminous sandstone. He states: 



Blocks of equal sizes were made of the two materials, and though 

 that comprised of the bituminous limestone broke under an average pressure 

 of 328 kgs. per square centimeter, that made with the bituminous sandstone 

 only resisted up to a pressure of 217 kgs. per square centimeter. 



These experiments show that bituminous limestone is con- 

 siderably more resistant to traffic than bituminous sandstone and 

 that we therefore have a very important point in favor of the 

 Leyte rock. 



When we come, however, to consider the action of atmospheric 

 erosive agents on pavements, we find that calcarious pavements 

 weather out a great deal more rapidly than do those made of 

 bituminous sandstone. The reason is that rain water always 

 carries a non-negligible proportion of carbonic acid ; this reacts 

 with calcium carbonate forming calcium bicarbonate which dis- 

 solves in water leaving behind the bituminous cement, and the 

 latter, deprived of a portion of its mineral aggregate, softens and 

 becomes inutilizable for traffic. This action of rain water is 

 fortunately slow; but in a rainy country, like the Philippines, 

 the damage resulting to the pavement is not inconsiderable. 

 This condition could be remedied by the introduction of a certain 

 proportion of silicious fillers. 



•Natural Rock Asphalts and Bitumen. London (1913) 160. 



