Practically all stones are injured if exposed to such high temperatures 

 as may be encountered in fires, and particularly if exposed to the combined 

 action of fire and water. The cause of disintegration is usually attributed 

 to internal stresses resulting from unequal expansion of unequally heated 

 parts of the material. Experience has shown that granites have a particu- 

 larly poor resistance to fire and are susceptible to cracking and spalling. 

 This is probably due to the irregularity of the stone structure and the 

 complexity of the mineral composition. The coarse-grained granites are 

 most susceptible to the action of fire and water, and the gneisses often 

 suffer even more severely because of their banded structure. 



Limestones suffer little from heat until a temperature somewhat above 

 o o 



100 Celsius (212 Fahrenheit) is reached; at this point the decomposition 



of the stone begins, due to the driving out of carbon dioxide. The stone 



then tends to crumble, because of the flaking of the quicklime formed. 



Marble, due to the coarseness of the texture and the purity of the material, 



suffers more than limestone. The cracking is irregular, and the surface 



spalls off similar to that experienced by granites. 



Sandstones, especially if of a dense, nonporous structure, suffer from 

 high temperature and sudden cooling less than most other stones. The 

 cracking of sandstones that does occur appears mostly in the planes of the 

 laminations. Sandstones in which the cementing ingredient is silica or 

 lime carbonate are better fire resistants than those in which the grains 

 are bound by iron oxide or clay. 



8. Uses In Coastal Construction . 



a. Offshore Structures . 



(1) Breakwaters. Stone is one of the principal materials used in 

 breakwater building. Itf is used from the core to the armor in various 

 lifts and layers each having a different gradation. Not all cores are made 

 of stone but when a stone core is used it usually is made of impermeable 

 quarry run stone. The core is covered by a blanket of filter material 

 graded to protect the core from eroding away due to the action of waves and 

 currents and to allow changes of hydrostatic pressure in the core without 

 loss of core material. The next layer is usually the underlayer graded to 

 be stable against the anticipated surge and current action. The final 

 layer of armor stone is placed in the area where waves impinge on the 

 breakwater. Armor stone is graded and sized to remain stable under the 

 impact of unbroken, breaking, and broken waves. Where storm waves may 

 overtop the breakwater, armor stone must be placed on the backslope as well 

 as the seaward face. The elevations and width of crest will depend on the 

 desired use as well as the degree of porosity. Porosity or void ratio is 

 important in dispersing the wave energy and reducing the impact load of the 

 waves striking the breakwaters. 



The design size of armor rock for a breakwater is a function of slope, 

 density, and wave height (U.S. Army, Corps of Engineers, 1971a). Hence, the 

 primary concern in the selection of armor stone is density, durability, and 

 available size. Armor stone may be required in pieces varying from about 9 

 to 270 kilonewtons (1 to 30 short tons). It is usually difficult to 

 quarry, transport, and place stones larger than 270 kilonewtons in size. 



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