Pavements and Roads; Their Construction and Maintenance

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER III. ASPHALT PAVEMENTS. THE NATURE AND USES OF ASPHALT. Asphalt is a variety of bitumen, found in a native condition and not manufactured, and in a solid form is commercially known as glance pitch. Glance pitch is found in limited quantities in various parts of the Rocky Mountains and in Texas. It is very pure and is used to make a high grade of varnish, but its brittleness makes it useless for paving or roofing compounds. Occurrence. The asphalt of Trinidad is found in a so-called lake about 130 feet above the sea-level, on the island of that name. The lake is a level tract, about 114 acres in area, of brownish material of an earthy appearance. It is sufficiently hard to bear the weight of carts and animals, and yet its consistency is such that excavations fifteen feet in depth are filled up by the flow of adjacent material in a few months. It is estimated that the amount of asphalt in the lake is upwards of six million tons. On partial analysis it yields approximately 40 per cent, of pure bitumen, 40 per cent, of earthy and vegetable matter, and 20 per cent, of water. The material is heated in large tanks at a temperature of about 300 Fahr., to drive off the water and let the larger portions of the earthy matter settle and the vegetable matter to be skimmed off the surface. This refined asphalt contains about 60 per cent, of pure bitumen and 40 per cent, of finely divided earthy matter invisible to the eye. This material is too brittle for commercial use, and it is therefore mixed with a heavy, dark oil, known as the residuum of petroleum, in the proportion of six parts of asphalt to one of residuum. This is the material so largely used in paving and roofing compositions. On the coast of California, near Santa Barbara, and also in certain portions of...