Which statement about SSD conditioning is true?

• A. The sample is covered with water either by complete immersion or by adding approximately 6 % moisture.
• B. The specified time period for the sand to soak in the water is 24-48 hours.
• C. A current of warm air may be used to assist getting the sand to an SSD condition.
• D. When performing the cone test to check the condition of the sand, permit the tamper to fall freely from 50 mm over the top of the sand.

Answer: (C)

SSD conditioning means bringing the aggregate to a saturated surface-dry state: all pores are filled with water, but there is no free moisture on the surface. The reason a current of warm air is used is that it speeds up the removal of surface moisture so you reach that surface-dry condition reliably and efficiently without drying out the internal pore water. The warm air dries the top layer evenly and quickly, helping you avoid prolonged soaking or inconsistent surface wetness, which could affect how the material behaves in subsequent tests.

Other methods described—immersing the sample fully, using a fixed moisture addition, or soaking for a set time—don’t consistently produce the SSD state across different sands and conditions. The cone-test detail relates to a different procedure (density testing) and not to achieving SSD, so it isn’t the method used for conditioning.