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.-�'�� ' - . ��y�� i• �....' ... " � � . ='r lk s,' z '�Y6+w�� ,� �� f,4 _.,., . �:� �'ie., `r� �` �� „�� F LL _� �� Y ° ,. �� ,.� �� _ r, �� , ?�. w � ' s�; �t %'. • *�. , �Y�� �:-. i.��il�tF _l��Z°' �. �� �` ,� e a_ � � .. � � , �i �Y.� � ♦ 1 �� "�# ,� ��,��c b�; � ;'t � .� � d t �-�� 1 `��Z a ,'�� n� �I�r . y ,p j .I ` _ ; w . � ^ •, L'kt` F-1 L- F i� . . P- � f I`-•_ _ .. � Liquid asphalt cement is a complex mixture of hydrocarbons. It may also be referred to as "binder" or bitumen (term commonly used outside North America�. Some asphalt comes from natural asphalt lakes such as the La Brea Tar Pits. Most of the asphalt used in road building is actually a by-product of crude oil refining. Asphalt is IeR over aRer the lighter grades of oil are drawn off at the refinery. It can be further processed for use in paving mixtures or other industries such as roofing. Asphalt is a thermoplastic, which means it is hard at normal highway temperatures, but thick and sticky when heated. It is the material in pavement that coats aggregate and glues (or binds� the mix together. Eighty percent of asphalt used in the United States is for paving mixtures. f `� , � � 'i �� , ', . . . "��. . 6 f ��," E� `� . r No. Tar is a black or brown liquid derived from the destructive distillation of organic matter. Though it can be produced from petroleum, it is most often from coal as a by-product of coke production. It was once used to seal roadways, roofing shingles, and wooden ship hulls. However, since the 1970s, asphalt has completely replaced the use of tar in paving mixtures. � . i i ! . , � . .'!�" I . . � �� E � Pavement is a highly controlled mixture consisting of liquid asphalt cement and aggregate. Before being placed on a roadway, this mixture is referred to as hot mix asphalt (HMA�, asphaltic concrete, or bituminous concrete. An HMA pavement mixture is about 95% aggregate and 5% asphalt cement. <<� .i �, �, _ , _ t : � �.� � �"r,�°i�� .[��' ' i I I �'�_'� �� _ � � � � °. No. Asphalt is insoluble and does not react with water. In fact, hot mix asphalt (HMA) has been used to line surfaces of Fish hatchery ponds and community water reservoirs. For example, the Metropolitan Water District of Southern California has used hot mix asphalt liners in its reservoirs for over four decades. Asphalt is also used to seal potable water supply pipes. Another important use of hot mix asphalt is industrial retention ponds and landfill liners. Asphalt liners prevent harmful substances from leaching into the soil and possibly contami- �' nating ground water. �-- ._. _ _ _ _ - �, �� ,,..� - . _ . .. _ _ _ ., _. _ . . : _. . _ ` �.�,;t ^�� .� *�