Reviewed by Er. Inderjit Sharma (Retd.), Punjab PWD
What is the Ten Percent Fines Value (TFV)? It is the load (in kN) needed to crush the aggregate so that 10% of it turns into fines (passing the 2.36 mm sieve).
Higher TFV = stronger stone. A stone needing 200 kN to make 10% fines is much stronger than one that needs only 60 kN.
Why use it? For weaker aggregates (crushing value above about 30%), the standard crushing test is not sensitive enough; TFV gives a better comparison. This guide follows IS 2386 (Part 4) and BS 812 (Part 111).
The Idea in One Picture
Apparatus Required
Compression testing machine
Applies a steadily increasing load (up to about 400 kN) in 10 minutes.
Cylinder, plunger & base plate
Hardened steel cylinder, 150 mm inside diameter.
Cylindrical measure
Fixes the amount of sample: 3 layers × 25 tamps.
Tamping rod
Rounded end; compacts each layer.
Sieves 12.5, 10, 2.36 mm
Prepare the sample and separate the fines after crushing.
Balance (1 g) & oven
Weigh to 1 g; dry at 105–110 °C.
Test Setup
Procedure
- Sieve the aggregate and take material passing 12.5 mm and retained on 10 mm (BS 812 uses 14–10 mm). Dry it in the oven at 105–110 °C (or soak it for 24 hours if a soaked TFV is required).
- Fill the cylindrical measure (115 × 180 mm) in 3 equal layers, tamping each layer 25 times. Level the top. This sets the sample size; weigh it (m1).
- Put the steel cylinder on the base plate and add the sample in 3 layers × 25 tamps. Level the surface and insert the plunger so it sits flat.
- Place it in the compression machine. Apply load at a steady rate so the plunger goes down in 10 minutes by about:
• 15 mm for rounded aggregate (gravel)
• 20 mm for normal crushed aggregate
• 24 mm for honeycombed aggregate (some slags)
Note the maximum load reached (x, kN). - Release the load, take out all the material and sieve it on the 2.36 mm sieve. Weigh the fines passing (m2). Fines % = m2 ÷ m1 × 100.
- The fines must be between 7.5% and 12.5%. If not, repeat at an adjusted load. Do two tests at the load that gives fines in this range.
Calculation
x = maximum load applied (kN); y = mean percentage fines from the two tests at load x (must be between 7.5% and 12.5%). Report to the nearest whole number (10 kN or more) or to the nearest 0.5 kN below 10 kN.
📝 Worked example
x = 180 kN; fines from two tests = 9.6% and 10.4% → y = 10.0%
TFV = 14 × 180 ÷ (10.0 + 4) = 180 kN
📈 Graph method
The BS method also lets you plot load against % fines for several tests and read the load at 10% fines from the best-fit line.
Try It: TFV Calculator
Enter the maximum load and the weights from two tests at that load. The values filled in are the worked example.
Precautions
🔩 Plunger must not jam
Check that the plunger moves freely inside the cylinder throughout loading.
⏱️ Steady 10-minute loading
Apply the load evenly so the target penetration is reached in about 10 minutes.
🧹 Don’t lose fines
Empty the cylinder over a clean tray; if m2 + m3 differs from m1 by more than 10 g, repeat the test.
🦺 Safety
Keep hands clear of the platens and use a guard; aggregate can burst out under high load.
Practical Tips for Site Engineers
1. Typical Minimum TFV
| Use | Minimum TFV |
|---|---|
| Concrete for wearing surfaces | 50 kN |
| Other concrete | 30 kN |
| Granular sub-base (soaked, MoRTH) | 50 kN |
Always follow your contract specification.
2. Good Site Habits
- Use TFV for weaker material: for soft stone, moorum, laterite or slag, TFV shows differences that the crushing value test misses.
- Soaked vs dry: many stones lose strength when wet. A large drop between dry and soaked TFV warns that the material may weaken in the monsoon. Test soaked where specified (e.g. GSB).
- Save time with AIV: estimate the first trial load from the impact value (4000 ÷ AIV) to reach the 7.5–12.5% range in fewer trials.
- Test at source approval and again when the quarry face or material changes.
- Read it with other tests: TFV, AIV, abrasion value, shape and water absorption together decide whether a source is acceptable.
Key Takeaways
- TFV = load (kN) that produces 10% fines (passing 2.36 mm); higher means stronger.
- Sample 12.5–10 mm in a 150 mm cylinder, 3 layers × 25 tamps; load so the plunger goes 15/20/24 mm in 10 minutes.
- Fines must fall between 7.5% and 12.5%; TFV = 14x ÷ (y + 4).
- Typical minimums: 50 kN for wearing surfaces, 30 kN for other concrete, and 50 kN for soaked GSB.
- On site: best test for weaker aggregates; compare soaked and dry values; estimate the first load from AIV.
References: IS 2386 (Part 4): Methods of Test for Aggregates – Mechanical Properties; BS 812 (Part 111): Methods for Determination of Ten Per Cent Fines Value; IS 383: Coarse and Fine Aggregate for Concrete; MoRTH Specifications for Road and Bridge Works (Section 400).