ASPHALT PAVEMENTS. 97 
BNGINEERING., 
ASPHALT PAVEMENTS. 
GEN. Q. A. GILLMORE, U. S. A. 
Within the last twenty-five years bitumen, in some of its many forms, has 
been employed to a considerable extent, as the binding material or matrix for 
road and street coverings laid in continuous sheets without joints. They are all 
comprised under the general head of asphalt paveinents. The city of Paris 
took the lead in this innovation upon the former methods of paving with stone, 
the reasons assigned for the change being, (1) the want of connection and homo- 
geneity, in the elements of which the stone paving is composed, (2) the incess- 
ant noise produced by them, (3) the imperfect surface drainage which they se- 
cure, by reason of which the foul waters are not carried off but filter into the 
joints, and (4) the ease with which they can be displaced, and used for the con- 
struction of barricades, breastworks and rifle pits in time of civil war. 
The forms of bitumen most extensively employed for pavements are mineral 
tar; asphalt rock, which is an amorphous carbonate of lime impregnated with 
mineral tar, and known in commerce as Jdituminous limestone ; asphaltuu ; heavy 
petroleum ous \ike those from West Virginia, or others not volatile under 212 Fah., 
or the residuum of refined petroleum containing no water, and so refined as not 
. to be volatile at 212 Fah. 
The principal sources of the natural mineral tar of commerce are in France, 
at Bastenne (Landes) and at Pyrimont Seyssel (Ain), and in Switzerland at Val 
de Travers, in the canton of Neuchatel. At Bastenne as well as at Gaujac, in 
the south of France, it flows frome sevral springs mixed withwater. 
Asphaltum is a variety of bitumen generally found in a solid state. At ro- 
_ dinary temperature it is brittle, and too hard to be impressed with the finger nail. 
It is black or brownish in color, opaque, slightly translucent at the edge of a 
new fracture, of smooth fracture, and has little odor unless rubbed or heated. It 
melts easily, burns with very little if any residue, and is very inflammable. 
It is found floating on the Dead Sea, and in many places in Europe. Many 
localities in Mexico supply it, and it abounds in the islands of Barbadoes, Trini- 
dad and Cuba, and in Ritchie county, West Virginia, and in New Brunswick, 
Dominion of Canada. 
A capital distinction must be made between pavements of asphalt hereafter 
described, made either with natural asphalt rock, or with the refined asphaltum 
as a cement, combined with suitable calcareous powder, and all or nearly all 
of those attempted imitations of it, produced by mixing crude mineral tar, or 
manufactured tar, with one or more pulverized minerals or earths. And more 
especially must we exclude from the category of asphalt pavements, all those 
