The fine aggregate particle size distribution test is an important inspection item in hydraulic concrete testing. It is used to evaluate the particle size distribution characteristics and grading rationality of fine aggregates, thereby ensuring that the workability and mechanical properties of concrete meet design requirements. This test is carried out in accordance with relevant hydraulic engineering testing standards and mainly includes the test scope, required equipment, testing procedures, and result analysis. Through a standardized testing process, an accurate particle size distribution curve of fine aggregate can be obtained, providing a reliable basis for mix design and quality control in engineering applications.

1. Scope

1. 1This test is used to determine the particle size distribution of fine aggregates and to calculate the fineness modulus or the mean particle size of fine sand and very fine sand.

2. Apparatus and Equipment

2.1 Balance

A balance with a readability not greater than 0.1 g.

2.2 Test Sieves

Square-hole sieves with aperture sizes of 10 mm, 5 mm, 2.5 mm, 1.25 mm, 0.63 mm, 0.315 mm, and 0.16 mm (ISO C series), including a pan and lid. Alternatively, square-hole sieves ranging from 9.5 mm to 0.15 mm (ISO B series) may also be used. The test sieves shall comply with the requirements of SL 126.

2.3 Drying Oven

A drying oven capable of maintaining a temperature of (105 ± 5) °C.

2.4 Auxiliary Equipment

Sieve shaker, metal trays, brushes, and other necessary tools.

3. Test Procedure

3.1 The fine aggregate used for the particle size distribution test shall have a maximum particle size not greater than 10 mm. A representative sample of fine aggregate in its natural state shall be taken and thoroughly mixed. Then, using the quartering method, the sample shall be reduced into two test portions, each not less than 550 g. The samples shall be dried in an oven at (105 ± 5) °C to constant mass, then cooled to room temperature for testing. If any lumps form after drying, they shall be broken up by hand before testing.

Note: In this standard, constant mass refers to the condition where, during drying, the difference between two successive weighings taken at an interval of more than 1 hour does not exceed 0.1% of the latter weighing result.

3.2 Arrange the sieves in order of decreasing aperture size and number them as i = 1–6, where the top 5 mm sieve is No. 1 and the bottom 0.16 mm sieve is No. 6. Stack all sieves and the pan tightly together. Weigh the oven-dried fine aggregate sample (G₀, accurate to 0.1 g). Pour the entire dried sample into the top No. 1 sieve, cover it, and mount the complete sieve stack on a sieve shaker. Operate the machine for 10 minutes.

After shaking, remove the sieve stack and manually sieve each sieve in sequence from larger to smaller aperture on a clean metal tray. Continue sieving until the amount passing per minute does not exceed 0.1% of the total sample mass. The particles passing through each sieve are transferred to the next lower sieve and sieved together with the material already retained on that sieve.Repeat the procedure sequentially until all sieves have been completed.

3.3 When the retained mass of the sample on any sieve exceeds 200 g, the sample on that sieve shall be divided into two portions for sieving. The sum of the two results shall be taken as the retained mass for that sieve size.

3.4 After sieving, the particles retained on each sieve shall be carefully removed and gently brushed clean using a soft brush. The retained mass on each sieve (ai, accurate to 0.1 g) shall then be weighed and recorded.

3.5 If the fine aggregate is very fine sand, each test portion may be reduced to 250 g after oven drying. During sieving, an additional 0.080 mm square-hole sieve shall be placed below the smallest sieve. The retained mass and partial retained percentage on the 0.08 mm sieve shall be recorded and calculated.

3.6 When a sieve shaker is not available, manual sieving may be performed. During manual sieving, place the complete sieve stack containing the sample on the test bench. Hold the lid firmly with the right hand and support the side of the sieve stack with the left hand. Lift one side of the sieve stack (tilting it at an angle of 30°–35°) so that the bottom of the sieve makes point contact with the bench surface. Rotate the sieve stack clockwise for 3 minutes for rolling sieving.Then, sieve each sieve individually until the required sieving condition is achieved.

4. Experimental Results

4.1 The percentage of residue on each sieve was calculated according to formula (1.4-1):

Pi=ai/G0×100%(1.4-1)

Where: P——Percentage of residue on sieve i, i=1～6;

ai——Residue on sieve i, g;

G₀——Total sample, g.

4.2 The cumulative sieve residue percentage of each sieve is calculated according to formula (1.4-2) (rounded to the nearest 0.1%):

Ai=P₁+…+Pi(1.4-2)

Where Ai is the cumulative sieve residue percentage of sieve i, i=1～6.

4.3 The fineness modulus is calculated according to formula (1.4-3):

FM=［(A2+A3+A4+A5+A6)-5A1］/(1-A1)(1.4-3)

Where FM is the fineness modulus;

A1~A6 are the cumulative percentage of residue on each sieve.

4.4 The fineness modulus is taken as the average of two measurements (rounded to the nearest 0.1). If the sum of the residue on each sieve and the mass of powder in the pan differs from the original mass of the sample by more than 1% of the sample mass, or if the difference in the fineness modulus between the two tests exceeds 0.2, the test should be repeated.

4.5 If necessary, a sieving curve can be plotted with the sieve aperture size of each sieve as the x-axis and the corresponding cumulative sieve residue percentage as the y-axis.

4.6 For fine sand (FM: 2.2～1.6) or extra-fine sand (FM: 1.5～0.7), the average particle size can be calculated according to formula (1.4-4) (rounded to 0.01mm interval) based on the sieving results.

dm=0.5×［(a2+a3+a4+a5+a6)/(0.0024a2+0.02a3+0.17a4+1.3a5+11a6)］1/3(1.4-4)

Where dm——average particle size of fine aggregate, mm; a₂～a₆——sieve residue of sieves 2～6, g.