The asphaltic bitumen consists of tiny carbon particles ap- 

 proximately of equal size called micelles, which might be imagined 

 as floating in an oily medium. The stability of the bitumen depends 

 on the ratio of micelles and medium.. Addition of a filler, i^e., 

 a finely ground non-hygroscopic product increases the stability of 

 the bitumen because, according to Professor Nellensteyn. the fjjiest 

 particles of the filler form new micelles, thus increasing the bind- 

 ing properties of the asphaltic bitumen . 



Dependent on the kind of work, the asphaltic bitumen must meet 

 certain standards, which are specified in the instructions for test- 

 ing bituminous construction materials (K.V.B.B.). One of the most 

 important points in the testing of asphaltic bitumen and asphalt 

 mixtures for hydraulic works is the de termination of the softness of 

 the material, which is measured by the degree of softness or the 

 penetration index. 



Asphalt mastic or asphalt cement is the name of the mixture of 

 asphaltic bitumen and filler. 



Asphalt mortar or sand asphalt is the name of the mixture of 

 asphalt mastic and sand. 



Asphalt concrete is the name of the mixture of asphalt mortar 

 with gravel or broken stone. 



In using asphalt mixtures which are to be transported over a 

 certain distance, one should take care to heat and preferably isolate 

 the containers, whereas for liquid mixtures the solid materials 

 should be kept in suspension by a special stirring device. 



Standards for asphaltic Bitume n an d Asphalt Mixtures 



For hydraulic works asphaltic bitumen and asphalt mixtures 

 should meet the following standards: 



1. Remain plastic, even after cooling down slightly 5 



2. Be sufficiently elastic, even at low temperatures, so 

 that the material will follow if the underlying base 

 settles unevenly; 



3. Remain stable upon a slope, even above the water sur- 

 face and at high temperatures 5 



4. Be proof against oxidation 3 



5. Stick to clean and dry surfaces; 



6. Be proof against aggressive water (salt water, swamp 

 water , etc . ) 3 



7. Be proof against abrasion by sand 3 



8. Be proof against wave action. 



The combination of elasticity and stability mentioned under 2 

 and 3 can hardly be expected in any material, but it has been 

 proven that a satisfactory compromise can be achieved. 



Of course it depends entirely on the kind of work for which 

 the material is to be used, x»rhich of the above mentioned properties 

 should be predominant 01 whether any other standards should be met. 



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