AASHTO T 99-21 PDF Download

The AASHTO T 99-21 standard is a method of testing the moisture-density relations of soils using a 2.5-kg (5.5-lb) rammer and a 305-mm (12-in.) drop. This standard provides four alternate procedures, labeled as Methods A, B, C, and D. Method A and B use a 101.60-mm (4-in.) mold, while Method C and D use a 152.40-mm (6-in.) mold. All methods require the soil material to pass through either a 4.75-mm (No. 4) sieve or a 19.0-mm (3/4-in.) sieve, depending on the method being used.

The standard applies to soil mixtures with 40% or less retained on the 4.75-mm sieve for Methods A and B, and 30% or less retained on the 19.0-mm sieve for Methods C and D. If the test specimen contains oversized particles, adjustments must be made for dry density and moisture in accordance with Annex A1 of the standard. If the specified maximum tolerances for oversized particles are exceeded, alternate methods of compaction control must be used.

It is worth noting that one approach for compacting such soils is to use a test fill to determine the required degree of compaction and a method to achieve that level of compaction. A method specification is then used to control compaction by specifying the type and size of compaction equipment, lift thickness, and the number of passes. This standard serves as a guideline for carrying out these testing procedures to ensure the desired moisture-density relationship of the soil.