Overview & Technical Significance
Particle size distribution is the single most critical parameter governing blast cleaning performance. The gradation of abrasive media directly determines achievable anchor profile depth, coverage rate, cleaning efficiency, and dust generation. Abrasives that are too coarse produce rough, irregular profiles exceeding coating specifications; abrasives that are too fine fail to achieve adequate anchor profile depth, compromising mechanical adhesion.
Sieve analysis performed per ASTM E11 (sieve specification) and ASTM C136 (test method) provides quantitative characterization of particle size distribution as a cumulative percent passing or retained on each sieve size. Results are compared against the abrasive manufacturer's specification or project quality plan acceptance criteria.
ASTM E11 — Sieve Specification
ASTM E11 specifies the dimensional requirements for woven wire mesh cloth and test sieve frames used in particle size analysis. All sieves used for abrasive testing must comply with ASTM E11 or equivalent international standard (ISO 565).
Key Sieve Parameters
| Sieve No. | Aperture (mm) | Aperture (µm) | Wire Diameter (mm) | Typical Abrasive Use |
|---|---|---|---|---|
| No. 7 | 2.80 | 2800 | 0.800 | Very coarse steel grit/shot |
| No. 10 | 2.00 | 2000 | 0.710 | Coarse steel grit G10 |
| No. 12 | 1.70 | 1700 | 0.630 | Steel grit G12 |
| No. 14 | 1.40 | 1400 | 0.560 | Steel grit G14 |
| No. 16 | 1.18 | 1180 | 0.500 | Steel grit G16 |
| No. 18 | 1.00 | 1000 | 0.450 | Steel grit G18 / Shot S330 |
| No. 25 | 0.710 | 710 | 0.355 | Steel grit G25 / Shot S230 |
| No. 30 | 0.600 | 600 | 0.315 | Garnet #30 |
| No. 40 | 0.425 | 425 | 0.224 | Steel shot S110 / Garnet #40 |
| No. 50 | 0.300 | 300 | 0.180 | Copper slag, fine abrasives |
| No. 70 | 0.212 | 212 | 0.125 | Fine garnet, staurolite |
| No. 80 | 0.180 | 180 | 0.120 | Fine mineral abrasives |
| No. 100 | 0.150 | 150 | 0.107 | Very fine abrasives |
Sieve Verification Requirements
Per ASTM E11, test sieves must be verified against NIST-traceable reference standards at intervals not exceeding 12 months, or immediately after any impact, dropping, or suspected damage. Verification records must be maintained and available for inspection.
Maximum aperture size < 1.25× nominal aperture designation
Minimum aperture size > 0.75× nominal aperture designation
Wire diameter tolerance: ± 15% of specified value
Frame: No distortion, no holes, secure mount to frame
REJECT IF: Any aperture exceeds 1.25× nominal | Frame distorted | Holes or breaks in mesh
Sieve Analysis Test Procedure (ASTM C136)
Sample Preparation
Obtain a representative sample per the project sampling plan. Minimum sample mass: 300 g for fine abrasives (all passing No. 16 sieve), 500 g for coarse abrasives. Dry sample at 110°C ± 5°C for 2 hours minimum if moisture content exceeds 0.5%. Cool to room temperature in desiccator before weighing.
Balance Verification
Verify analytical balance calibration with NIST-traceable weights before each test session. Minimum balance resolution: 0.1 g for samples > 200 g; 0.01 g for smaller sub-samples. Record balance ID and calibration date in test record.
Sieve Stack Assembly
Inspect each sieve for damage before use. Assemble sieve stack in descending order of aperture size (largest on top, smallest on bottom), with pan at base. Brush each sieve clean before use — do not use wire brushes on No. 100 or finer. Record sieve IDs and verify calibration dates are current.
Initial Weighing
Weigh each empty sieve + pan to 0.1 g resolution. Record tare weights. Weigh total sample to 0.1 g and record as W₀ (initial sample mass). Transfer entire sample to top sieve.
Mechanical Shaking
Place sieve stack on mechanical shaker. Shaking time: minimum 10 minutes at amplitude per shaker manufacturer specification. After shaking, perform 1-minute additional hand shake check: if any sieve retains > 0.1% of total sample mass in additional pass, continue shaking in 5-minute increments until complete.
Weighing Individual Fractions
Remove each sieve and weigh with retained material to 0.1 g. Calculate retained mass by subtracting tare. Record retained mass for each sieve size. Sum all retained masses including pan and compare to W₀ — total material recovery must be within ± 0.3% of W₀. Masses outside this tolerance indicate contaminated sieves or loss, and test must be repeated.
Calculation & Reporting
Calculate percent retained on each sieve: %Retained = (Mass retained ÷ W₀) × 100. Calculate cumulative percent retained and cumulative percent passing. Record and compare results to acceptance criteria. Generate test report per laboratory format.
Gradation Requirements by Abrasive Type
Gradation requirements vary by abrasive type, trade designation, and service application. The following table provides typical requirements for common abrasives. Always verify against the applicable product standard (SAE J444 for steel shot/grit, project specification for mineral abrasives).
| Abrasive Type | Designation | Nominal Sieve Range | Min. % Retained on Upper Sieve | Max. % Passing Lowest Sieve |
|---|---|---|---|---|
| Steel Grit | G-10 | No. 7 / No. 16 | 85% retained on No. 7 | ≤ 10% passing No. 16 |
| Steel Grit | G-16 | No. 12 / No. 25 | 85% retained on No. 12 | ≤ 10% passing No. 25 |
| Steel Grit | G-25 | No. 16 / No. 40 | 85% retained on No. 16 | ≤ 10% passing No. 40 |
| Steel Shot | S-330 | No. 16 / No. 35 | 85% retained on No. 16 | ≤ 10% passing No. 35 |
| Steel Shot | S-230 | No. 25 / No. 50 | 85% retained on No. 25 | ≤ 10% passing No. 50 |
| Garnet | #30/60 | No. 30 / No. 60 | 90% retained on No. 30 | ≤ 5% passing No. 60 |
| Copper Slag | Coarse | No. 16 / No. 50 | Min. 80% retained on No. 16 | ≤ 5% passing No. 50 |
| Aluminum Oxide | 36 Grit | No. 25 / No. 60 | Per ANSI B74.12 | Per ANSI B74.12 |
Sampling Procedures
Representative sampling is foundational to valid particle size testing. ASTM D75 (Standard Practice for Sampling Aggregates) provides the general framework; the following guidance is specific to blast abrasives.
Sample Sources & Minimum Quantities
| Sample Source | Sampling Method | Minimum Increments | Min. Total Mass |
|---|---|---|---|
| Bulk bag (1 tonne) | Trier or probe sampler | 5 points (top, middle, 3 sides) | 500 g |
| 25 kg sack | Divide lot; sample selected sacks | 1 sack per 10 in lot | 300 g per sack |
| Blast pot (in-service) | Catch at nozzle during operation | 3 catches per test event | 200 g combined |
| Wheel blast machine | Catch from separator output | 3 timed catches | 300 g combined |
| Storage hopper | Incremental sampler at discharge | 5 timed increments | 500 g |
Equipment Specification
Mechanical Sieve Shaker
Rotary or vibrating type. Must accept standard 200 mm or 8-inch diameter sieve stack. Amplitude and frequency per manufacturer. Timer minimum: 60-minute range. Annual calibration verification required.
Analytical Balance
Minimum capacity 2000 g; resolution 0.1 g. Calibration with NIST-traceable weights. Level indicator required. Shield from drafts. Monthly internal verification; annual external calibration.
Drying Oven
Forced-air convection oven. Temperature range: ambient to 150°C. Accuracy ±5°C at 110°C. Temperature uniformity verified with calibrated thermocouple.
Sieve Set
ASTM E11-compliant woven wire sieves, 200 mm diameter, stainless steel. Brass or stainless frames. Annual verification against NIST standards. Maintain complete chain-of-custody and verification records.
Calculation Methodology
STEP 2 — Recovery Check: Σmᵢ / W₀ × 100 must be 99.7% to 100.3%
STEP 3 — % Retained: %Retᵢ = mᵢ / W₀ × 100
STEP 4 — Cumul. % Retained: Sum all %Ret from largest sieve to sieve i
STEP 5 — % Passing: %Passᵢ = 100 − Cumulative %Retained at sieve i
REPORT TO: Nearest 0.1% for individual fractions; 0.1% for cumulative