Atech Center - Hydrometer Procedure

The test sample for this procedure should be prepared using either dry prep or wet prep methods (AASHTO T87, AASHTO T146).

The sample mass used for the sieve analysis is dependent on nominal maximum size of particles (Figure 2). The sieve analysis is performed on particles larger than the 2 mm (#10) sieve in accordance with AASHTO T27, Sieve Analysis of Fine and Coarse Particles.

Nominal Maximum Size of Particles, mm (in)	Approximate Minimum Mass of Sample, kg (lb)
75 (3)	5 (11.02)
50 (2)	4 (8.82)
25 (1)	2 (4.41)
9.5 (3/8)	0.5 (1.10)

Figure 2. Mass required for sieve analysis

AASHTO also stipulates alternate procedures for separating the larger particles from the finer particles using either a 4.75 mm (#4) or 0.425 mm (#40) sieve in lieu of the usual 2 mm (#10) sieve. Local specifications may dictate which sieve to use for the separation, but normally the 2 mm (#10) sieve is used and therefore this text will discuss the procedure using only the 2mm (#10) sieve.

Figure 3. Separation of the finer particles to be placed in suspension using a 2mm sieve.

Make the separation on the 2mm (#10) sieve and obtain sub-samples from the portion passing the 2mm (#10) sieve (Figure 3) for hygroscopic moisture and hydrometer analysis. Sample mass for the hydrometer portion of the test should be approximately 100 grams for sandy soils and approximately 50 grams for silty or clayey soils. Sample masses should be determined immediately or placed in air-tight containers until tested.