30 June 2001
b. Material Requirements. Suitable materials for aggregate base courses include natural,
processed, manufactured, and stabilized materials which meet ASTM D 2940. These are the most
common types of base course materials. Select local materials if possible, and consider local
experience and practices when selecting a base material.
c. Gradation. To provide adequate drainage, the base course must contain little or no fines
(material that passes the 0.075-millimeter (No. 200) sieve). Gradation requirements assure adequate
stability and drainage by the base course under repeated loads. Crushed aggregates have greater
stability than round-grained materials.
d. Wear Resistance. Aggregates suitable for base-course material must have the ability to
withstand abrasion and/or crushing. Do not use soft aggregates for base course material because they
may break down into fines which will inhibit drainage. Use the Los Angeles abrasion test (ASTM C 131)
for determining aggregate abrasion resistance. Aggregates suitable for base course shall have a
percentage loss in the Los Angeles abrasion test less than or equal to 40 percent.
e. Lean Concrete Bases. Lean concrete mixtures may be used as base material to provide
increased support and reduce pumping. They may also be more economical than stabilized bases.
Lean concrete refers to a mixture composed of low-cost, locally available aggregates that may not meet
specifications for normal concrete mixtures and an amount of portland cement that is usually less than
for normal concrete mixtures. Local aggregates, substandard aggregates, and recycled materials may
all be used in lean concrete mixtures for base materials. When properly designed, these materials can
provide a strong and erosion-resistant base.
(1) Material specifications and gradation requirements for aggregates used in lean concrete
mixtures are not as restrictive as those for aggregates used in normal concrete. Aggregate gradations
should conform to one of the gradations given in Table 8-2. The aggregate materials should be free
from any elongated or soft pieces and dirt. Mix design for lean concrete bases is discussed in
Gradations for Lean Concrete Base Materials
Percentage by Weight Passing Sieve
(square opening) mm (in.)
4.75 (No. 4)
0.425 (No. 40)
0.075 (No. 200)