THE 



SOUTH AFRICAN JOURNAL 

 OF SCIENCE 



COMPRISING THE REPORT OP THE 



SOUTH AFRICAN ASSOCIATION FOR THE 

 ADVANCEMENT OF SCIENCE 



(1921, DURBAN.) 



Vol. XVIII. JUNE, 1922. Nos. 3 and 4. 



ASPHALT IN RELATION TO ROAD CONSTRUCTION. 



BY 



D. Basil W. Alexander, 

 Borough Engineer's Office, Durban. 



Read Jul ii 13, 1921. 



In this paper the writer proposes to treat the subject of 

 Asphalt Construction under two main beads, viz., Asphalt and 

 Construction. First, then, Asphalt will be considered. This will 

 be sub-divided into Natural and Artificial. The former will be 

 further divided into Rock Asphalt and Lake Asphalt, and the 

 latter will treat of Oil Asphalt. 



As a general introduction to this subject it will be germane 

 to define asphalt in order to give a clearer understanding of terms 

 concerning which there is a good deal of confusion. It may be defined 

 as a more or less plastic solid formed by the mixture of mineral 

 matter in varying proportions with a naturally occurring bitumen. 

 The term "naturally occurring" is introduced in order to dis- 

 tinguish them from the bitumens derived from coal and shales. 

 Some critics may contend that it will exclude oil asphalts, which 

 are merely an accelerated form derived from the basis of all true 

 asphalts, viz., asphaltic petroleum. 



Clifford Richardson says : — 



"Asphalt may be defined as a mineral plastic, found in nature 

 in a more or less solid state, or recovered as such from an 

 asphaltic petroleum in which it occurs in solution, consisting of a 

 homogeneous fixture of hydrocarbons of the asphaltic type with a 

 small proportion of their sulphur and nitrogen derivatives, melt- 

 ing on the application of heat, and miscible in all proportions with 

 heavy asphaltic oils, or flux, to form a viscous cementing material 

 which is used in the construction of pavements and roads, and 

 for other industrial purposes." 

 This definition, while very comprehensive, takes no cognizance of 

 the asphalt formed in the still at high temperatures by polymeriza- 

 tion or the molecular condensation of lighter forms to a solid form. 

 That this does occur has been often noted by the writer during 

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