UFC 3-260-02
30 June 2001
a. Reinforcing. Reinforcement may be added to concrete pavement to accomplish specific
purposes, but reinforcing is the exception rather than the rule for military airfield pavements. Reinforcing
concrete pavements usually adds cost and complicates construction so it is used only where its added
value balances these negative factors. Conventional reinforcing steel is added to keep cracks tightly
closed and to slow deterioration of the cracks. Therefore, it is useful wherever cracking cannot be
avoided (e.g., odd-shaped slabs, extra-large slabs, etc.). Because reinforcing slows the deterioration of
cracks, a relatively small empirical reduction in pavement design thickness is allowed by the material for
reinforcing up to 0.5 percent. Continuously reinforced concrete pavements use much more steel (0.6
percent and more) which added to resist deterioration in cracks developed from environmental stresses.
The steel is continuous, and the pavement has no joints. It provides a joint-free, smooth pavement, but
repairs to these pavements are often difficult. Fiber reinforcing products are actively marketed. Steel
fibers can significantly reduce the required pavement thickness, but there are concerns that the fibers
pose a foreign object damage (FOD) on military airfields with current finishing techniques. Plastic fibers
are of no particular value for military airfields. Their primary advantage for conventional concrete
appears at present to be resistance to plastic shrinkage cracking, but proper construction and curing
should handle this concern without adding plastic fibers at additional expense to the military. As noted
later, these fibers have been found useful in concrete exposed to exhaust from vertical and short take off
aircraft like the Harrier. Prestressed pavements are very efficient and produce the most structural
capacity for any given cross section of concrete pavement. The design and construction of prestressed
pavement is more sophisticated than conventional pavements, but prestressing construction technology
has been evolving and is more cost-effective today than in past years. More details on these various
reinforced pavements and their design is provided in subsequent chapters.
b. Constituents. Portland-cement concrete is composed of portland cement, aggregates, water,
and various additives. Portland cement must meet the requirements of ASTM C 150, and the various
types of portland cement are described in Table 9.1. Type I cement will be the most common cement,
although Type II, Type I/II, and more seldom Type V may be used in areas with sulfate exposures. Type
III cement might be encountered where its rapid strength gain is necessary or in cold weather concreting
where its higher heat of hydration is useful. Cements may be specified to be low alkali when problems
with alkali-aggregate reactions are anticipated, but such cements may not always be readily available
and may be expensive. Addition of fly ash is very common in modern concretes, and the addition of
ground granulated blast furnace slags is beginning to be used more often. Both may be used as
economical partial replacements for portland cement in the concrete mixture and can be used to provide
other desirable characteristics such as enhanced workability, lower permeability, sulfate resistance,
protection against alkali-aggregate reaction, etc. Aggregate quality requirements in TM 5-822-7/AFM
88-6, Chapter 8, for military airfield pavements are appreciably tighter than those used in ASTM C 33
which is the most commonly specified concrete aggregate requirement for the concrete industry. The
tighter requirements reflect the military's concern over potential FOD hazards to aircraft on airfield
pavements. These tighter restriction were adopted by the military in the 1950's after severe problems
with popouts developed on new airfield pavements at Selfridge AFB. Air entrainment is crucial for
protecting the concrete matrix against damage from freezing and thawing and will be used in all military
airfield pavements unless clearance not to do so is first obtained from the HQUSACE (CEMP-ET),
appropriate Air Force MAJCOM pavements engineer, or Naval Facilities Engineering Service Center.
Air entrainment causes some loss in strength, but it also enhances workability. Therefore, proper
mixture proportioning can use this enhanced workability to reduce the water-cement ratio and thereby
negate the strength loss from air entrainment. The proper dosage of air-entraining admixture to achieve
the targeted air content is affected by factors such as the amount of carbon (measured as loss on
ignition) in fly ash or the temperature. Therefore, all air entrainment for military airfield concrete will be
provided by liquid admixtures added at the plant. This allows the dosage to be adjusted to reflect
specific mixture characteristics and environmental fluctuations at the project site. Air entraining
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