(c) Asphalt Injection . Asphalt injection is the subsurface 

 application of asphalt pumped under pressure through pipes. The method is 

 used to reduce leakage of a hydraulic structure through underground cracks, 

 fissures, and cavities. Injection of asphalt into the subsurface has been 

 done to prevent leaching of soils through rock reveted embankments at 

 commercially developed sites to prevent surface subsidence behind the 

 embankment . 



The hot, fluid asphalt is usually pumped through heated perforated pipes 

 dropped into drilled holes at the leakage strata levels. Once in the 

 leakage channel, the asphalt spreads out and hardens into a tight plug or 

 water stop. With sufficient pumping pressure, the asphalt will do this even 

 in fissures filled with water. These asphalt plugs can adapt to slight 

 movements in the formation and changes in water pressure. 



(d) Asphalt Mattresses . Asphalt mattresses are precast sections 

 or blankets of asphalt mastic reinforced with wire mesh and steel cables or 

 fiber netting and lines. Generally they vary in thickness from 25 to 50 

 millimeters (1 to 2 inches). Their length and width are limited only by the 

 size of the molding platform and the cababilities of the equipment used to 

 manipulate and place them. 



The reinforced asphalt mattress was developed by the U.S. Army Corps of 

 Engineers in 1932-34 for use on underwater revetments on the banks of the 

 lower Mississippi River. Continuous asphalt mattresses were cast on a 

 special barge pulled into the water. Mattresses have since been adapted for 

 use in European hydraulic structures and in Japan. Their principal function 

 is to protect the surface on which they rest from erosion or scour by waves 

 and currents. They are often used at the toe of a revetment or lining. 

 After a short period, the edge of the mattress settles into the scour zone, 

 thus stabilizing the erosive process. Asphalt mattresses are also used as 

 linings and as protective blankets for hydraulic structures. 



2. Preplaced Aggregate Concrete. 



Preplaced aggregate (PA) concrete derives its name from the unique 

 placement method by which it is made. Intrusion and grouted concretes are 

 other common names used for this type of concrete. In this method of 

 construction, forms are first filled with clean, well-graded coarse aggre- 

 gate. Structural quality grout is then injected into the voids of the 

 aggregate mass to produce concrete. 



This method of placing concrete is especially adaptable to underwater 

 construction, to concrete and masonry repairs, and, in general to new 

 structures, where placement by conventional means is unusually difficult or 

 where concrete of low volume change is required (U.S. Bureau of Reclamation, 

 1963) . This method of placing concrete has been used in the construction of 

 bridge piers, atomic reactor shielding, plugs for outlet works in dams and 

 tunnels, in mine workings, and for embedment of penstocks and turbine scroll 

 cases, as well as a great variety of repair work. Recently this process has 

 been used for exposed aggregate and other architectural treatments. Inasmuch 

 as preplaced aggregate concrete construction is a relatively specialized 

 type, it is essential that the work be undertaken by well-qualified personnel, 

 experienced in this method of concrete construction. 



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