supported by an open-graded asphalt drainage layer with an asphalt mastic 

 placed with a screed over the compacted subsurface. The drainage layer 

 serves to prevent damage to the watertight outer layer by draining away any 

 seepage through the outer layer or any ground water intrusion. 



The physical properties of asphalt alone are considered in its use in 

 coastal structures in addition to its adhesive properties as a binder and its 

 viscous properties under service conditions. The manner of asphalt placement 

 as well as the service conditions will require certain minimum and maximum 

 viscosities . 



(b) Use in Coastal Structures . Engineers have made consider- 

 able use of asphaltic materials in the construction of many structures for 

 coastal protection. Asphalt concrete is used to pave or revet the slopes and 

 tops of earth or sand seawalls. It may also be used to pave, or cap, the top 

 surfaces of quarrystone jetties, breakwaters, groins, and cellular steel 

 breakwaters. Asphalt mastic mixtures are also used for grouting to fill-in 

 the voids of quarry stone jetties and groins, and of the riprap facings of 

 seawalls and revetted slopes. In foreign countries special equipment has 

 been designed to place a sand-asphalt mastic under water in a continuous 

 operation. The blanket is designed to prevent scour of large areas of the 

 seabed. As more and more emphasis is placed on pollution control, engineers 

 are finding that asphalt offers an economical and effective means of lining 

 dredge disposal sites and waste storage areas that are sometimes necessary in 

 the construction of coastal structures. Asphalt has an excellent history of 

 performance in its use in coastal structures when properly designed and used 

 in accordance with its physical properties and capabilities. 



(2) Preplaced Aggregate and Grout . Portland cement grout poured in 

 the voids of preplaced aggregate is a specialized construction method. It 

 generally uses large stone with the voids filled with grout. It is a type of 

 mass concrete used as a seawall or bulkhead. The physical properties as to 

 durability, resistance to abrasion etc. are much the same as those of the 

 stone and concrete components. One difference is in the cement grout mix 

 design. Pozzolons and fluidizers are added to improve handling during 

 placement and bonding to rock or old concrete. 



(3) Portland Cement Grout . Portland cement grout will have the same 

 physical properties as Portland cement concrete of similar mix design. 

 Grout, however, is usually modified in its mix design because of its intended 

 use and placement methods. This results usually in a grout mix of cement and 

 water with sand. Very small gravel and clay, used as inert fillers, or even 

 bentonite used as a stabilizer, may be added when it is placed under water. 

 Grout is easily placed by pouring, pumping or injecting into place. In 

 filling joints or narrow cracks it can usually be poured into place. In 

 filling large voids or holes, pumping is a common procedure. When stabilizing 

 ground beds for foundations or the area behind bulkheads to prevent leaching 

 of the soil it may be injected into the ground or structure. This injection 

 procedure may be the same as pumping but at relatively high pressure. 



(4) Soil Cement . Soil cement is a mixture of pulverized soil and 

 measured amounts of Portland cement and water compacted to a high density. 

 The physical properties of soil cement are its high density as compared to 

 uncemented soil and its rigidity, resulting in a structural slablike, material 



378 



