FEMA P55 Coastal Construction Manual, Fourth Edition - Mad Cad

13 CONSTRUCTING THE BUILDING Volume II
Figure 13-6.
Open masonry foundation
13.1.4 Concrete Foundation Construction
Concrete foundation or superstructure elements in coastal construction almost always require steel
reinforcement. Figure 13-7 shows a concrete foundation, and Figure 13-8 shows a house being constructed
with concrete. Completed cast-in-place exterior concrete elements should generally provide 1-1/2 inches or
more of concrete cover over the reinforcing bars. Minimum cover values vary according to bar size and
exposure to earth or weather per ACI 318-08. This thickness of concrete cover serves to protect the reinforcing
bars from corrosion, as does an epoxy coating. The bars are also protected by the natural alkalinity of the
concrete. However, if saltwater penetrates the concrete cover and reaches the reinforcing steel, the concrete
alkalinity will be reduced by the salt chloride and the steel can corrode if it is not otherwise protected.
As the corrosion forms, it expands and cracks the concrete, allowing the additional entry of water and
further corrosion. Eventually, the corrosion of the reinforcement and the cracking of the concrete weaken
the concrete structural element, making it less able to resist loads caused by natural hazards.
During placement, concrete normally requires vibration to eliminate air pockets and voids in the finished
surface. The vibration must be sufficient to eliminate the air without separating the concrete or water from
the mix.
13-10 COASTAL CONSTRUCTION MANUAL