Reviewed by Er. Inderjit Sharma (Retd.), Punjab PWD
What is this test? It finds the specific gravity and water absorption of fine aggregate and small coarse aggregate (below 10 mm), such as sand, stone dust and grit. Pieces this small can’t be weighed in a wire basket, so we use a pycnometer (a glass jar with a cone-shaped cap).
Specific gravity = how heavy the aggregate is compared with the same volume of water. Water absorption = how much water it soaks up, as a % of its dry weight.
Why it matters: needed for concrete and bituminous mix design and for correcting the mixing water. This guide follows IS 2386 (Part 3).
The Pycnometer
The Idea Behind the Test
We weigh the pycnometer full of water, and then with the sample plus water. The sample pushes out its own volume of water. From the difference we get the volume of the aggregate, and so its specific gravity.
Apparatus Required
Pycnometer (1 litre)
Glass jar with a brass cone cap that has a small hole at the top.
Balance (0.5 g)
5 kg capacity; weighs the pycnometer and the sample.
Oven
Dries the sample at 105–110 °C.
Warm air (hair dryer)
Gently dries the soaked sand to the surface-dry state.
Sieves (10 & 4.75 mm)
Separate the size range to be tested.
Trays, filter paper, airtight container
For draining, spreading and cooling the sample.
Procedure
Step 1: Soak the Sample
- Take about 1000 g of aggregate passing the 10 mm sieve and retained on 4.75 mm. For finer material (sand), take about 500 g.
- Put it in a tray and cover it with distilled water at 22–32 °C. Stir gently to remove air bubbles.
- Soak for 24 ± ½ hours.
Step 2: Bring to Saturated Surface-Dry (SSD)
- Drain the water through filter paper, putting back any fine particles caught on the paper.
- Spread the sample and dry it with a gentle stream of warm air, stirring often, until the surface moisture disappears and the aggregate becomes free-running (grains no longer stick together).
- Weigh it straight away: this is A (SSD weight).
Step 3: Pycnometer Weighings
- Put the SSD sample into the pycnometer and fill it with distilled water. Roll and shake it gently (with the hole covered by a finger) to remove trapped air.
- Top up with water to the hole in the cone, dry the outside and weigh it: B.
- Empty the contents into a tray, making sure all the aggregate comes out.
- Refill the pycnometer with distilled water to the same level, dry the outside and weigh it: C. The water temperature must be within 2 °C of the first weighing.
Step 4: Oven-Dry
- Drain the sample, then dry it in the oven at 105–110 °C for 24 ± ½ hours.
- Cool it in an airtight container and weigh it: D.
- Do at least two tests and report the mean.
Calculation
A
Weight of saturated surface-dry sample
B
Pycnometer + sample + water
C
Pycnometer + water only
D
Weight of oven-dry sample
Try It: Specific Gravity Calculator
Enter your weights in grams. The values filled in are a worked example.
Bonus: correct the mixing water for wet sand
Precautions
🫧 Remove all air
Roll and shake the pycnometer until no more bubbles rise. Trapped air makes the specific gravity come out low.
🌬️ Don’t over-dry
Stop warm-air drying as soon as the grains flow freely. Over-drying gives low absorption and wrong values.
🌡️ Same temperature
Keep the water temperature within 2 °C for weighings B and C.
🧹 Don’t lose fines
Return fines from the filter paper and rinse every grain out of the pycnometer. Lost material gives wrong results.
Practical Tips for Site Engineers
1. Typical Values
| Material | Specific gravity | Water absorption |
|---|---|---|
| Natural river sand | 2.6–2.7 | 0.5–1.5% |
| Crushed stone sand (M-sand) | 2.6–2.8 | 1–3% |
| Stone dust / grit (4.75–10 mm) | 2.6–2.8 | 0.5–2% |
Typical ranges only; actual values depend on the source.
2. Good Site Habits
- Sand moisture changes the mix the most: sand on site often holds 3–8% water, much more than coarse aggregate. Check it daily (more often after rain) and correct both the water and the sand weight. The calculator above does this.
- Volume batching? Allow for bulking: damp sand swells in volume (up to 20–40%), so a box of damp sand holds less sand. Prefer weigh batching; if using boxes, increase the sand volume as per a bulking test.
- Test each source: river sand and M-sand from different sources have different values. Retest when the source changes.
- Low SG is a warning: it may mean silt, clay, mica or light particles. Check silt content (wash test) and grading too.
- Quick SSD check: fill a small cone with the drying sand, tamp it lightly and lift the cone. If the sand slumps slightly, it is close to SSD (this cone check comes from ASTM C128 and is not part of IS 2386).
- Cover sand stockpiles so their moisture stays steady; drain the base so the bottom layer isn’t waterlogged.
Key Takeaways
- For aggregate below 10 mm: use a pycnometer instead of a wire basket.
- Soak 24 h, dry with warm air to free-running SSD (A), then weigh pycnometer + sample + water (B), pycnometer + water (C), and oven-dry sample (D).
- Bulk SG = D ÷ [A − (B − C)]; SSD SG = A ÷ [A − (B − C)]; apparent SG = D ÷ [D − (B − C)].
- Water absorption = (A − D) ÷ D × 100.
- On site: correct the water and sand weight for sand moisture every day; watch for bulking and silt.
References: IS 2386 (Part 3): Methods of Test for Aggregates – Specific Gravity, Density, Voids, Absorption and Bulking; IS 383:2016: Coarse and Fine Aggregate for Concrete; IS 10262: Concrete Mix Proportioning.