UFC 3-260-02
30 June 2001
admixtures that are interground with the cement and designated as Type IA, Type IIA, etc. are not
suitable for this use as they do not provide the flexibility of adjusting admixture dosage to reflect
changing mixture and site conditions. A number of other admixtures besides those for air-entrainment
are available to accomplish specific tasks (primarily retarders, accelerators, and those for enhanced
workability at a given water-cement ratio). Use of these is generally at the discretion of the engineer
doing the mixture proportioning for a specific project or of the contractor who must deal with a specific
site problem. The engineer responsible for the mixture proportioning is responsible for selection of
admixtures and concrete materials that are compatible and cause no adverse interactions. If the
contractor elects to use an admixture ( e.g., a retarder because of lengthy haul times), then he or she is
responsible for selecting an admixture compatible with the concrete mixture and which has no adverse
effect on the fresh or hardened concrete mixture.
c. Special Air Force Requirement. During the 1980s and 1990s, newly placed concrete airfield
pavement on Air Force bases had widespread problems with excessive spalling derived primarily from
construction related problems, part of which sprung from the common use of concrete mixtures with poor
workability. To partially address these problems, the Air Force now requires a well-graded concrete
aggregate be used for all their airfield pavements with specific limitations depending on anticipated
placement methods (i.e., slipform, with form-riding equipment, or by hand). Specific requirements and
details are contained in the Air Force Concrete Mix Design Handbook and will be conformed to for all Air
Force pavements unless a waiver is obtained from the Air Force MAJCOM pavements engineer.
d. Durability. Properly proportioned and placed, portland-cement concrete is a highly durable
material. Protection against freezing and thawing is achieved by ensuring adequate strength gain before
the concrete is first allowed to freeze (crucial issue in cold-weather concreting), using aggregates that
are resistant to freezing effects (avoiding aggregates that are prone to produce popouts and D-cracking),
and providing adequate air entrainment to protect the concrete matrix. Special precautions are needed
when concrete will be exposed to sulfates or if the concrete mixture contains certain aggregates
susceptible to reactions between the portland cement alkalis and some aggregate minerals (most
commonly certain specific forms of silica and more rarely certain dolomitic materials). Details on these
durability issues and guidelines on selecting appropriate levels of air entrainment are provided in TM 5-
822-7/AFM 88-6, Chapter 8. The water-cement ratio in military airfield paving mixtures is limited to a
maximum of 0.45. This requirement enhances durability by keeping the concrete permeability low as
well as improves strength when compared to using higher water to cement ratios in the concrete mixture.
e. Design Strength.
(1) Test Method. Military airfield pavements are designed on the basis of the third point,
flexural beam test (ASTM C 78). Thickness design is based on fatigue relationships from full-scale field
tests that characterized the test pavement with the flexural test determined in this manner. Other test
methods (e.g., center-point flexural beam or splitting tensile test) give numerically different values from
this test and are therefore not suitable substitutes. Pavement thickness design is based on classical
fatigue analysis, and the results are very sensitive to the specific value of flexural strength used in the
design. Consequently, it is important that military airfield pavement design define the concrete strength
consistently with the fatigue relationship used in the design procedure. Consequently, all military airfield
design will be based on the ASTM C 78 flexural strength.
(2) Correlations. There are no unique relationships between different concrete strength tests
(third-point flexural beam, center-point flexural beam, compressive, splitting tensile, etc.), and all such
tests are indices of strength rather than an inherent material property. There are many published
relationships that allow estimation of one strength test result as a function of another test (e.g., estimate
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