Proctor Compaction Test: Standard vs Modified
Published November 2025 · 6 min read · Elipslab Technical Team
What Is the Proctor Compaction Test?
The Proctor compaction test determines the optimum moisture content (OMC) at which a given soil achieves its maximum dry density (MDD) when compacted under specific energy. This relationship is fundamental to earthwork quality control — compacting soil at OMC maximises bearing capacity and minimises future settlement.
Two versions exist: Standard Proctor (ASTM D698) for light to moderate construction loads, and Modified Proctor (ASTM D1557) which uses 4.5× more compaction energy, suitable for highway subgrades and airfield pavements.
Required Equipment
- Compaction Mold: 101.6 mm (4 in) or 152.4 mm (6 in) diameter cylinder with base plate and collar.
- Proctor Hammer: Standard — 2.49 kg mass, 305 mm drop. Modified — 4.54 kg mass, 457 mm drop.
- Extruder: To push compacted specimens out of the mold without damage.
- Balance: ±1 g accuracy for moisture content determination.
- Drying Oven: Maintained at 110°C ± 5°C.
- Sieves: 4.75 mm and 19 mm for material preparation.
Standard vs Modified: Key Differences
| Parameter | Standard (ASTM D698) | Modified (ASTM D1557) |
|---|---|---|
| Hammer mass | 2.49 kg (5.5 lb) | 4.54 kg (10 lb) |
| Drop height | 305 mm (12 in) | 457 mm (18 in) |
| Layers | 3 | 5 |
| Blows per layer (4-in mold) | 25 | 25 |
| Compaction energy | 600 kN·m/m³ | 2700 kN·m/m³ |
| Typical application | Embankments, fill | Highway subgrade, airfields |
Test Procedure
- Prepare soil at 4–6 different moisture contents bracketing the expected OMC.
- Compact each sample into the mold in the specified number of layers, each receiving the required number of hammer blows.
- Trim the collar and measure the total wet mass of mold + soil.
- Take a representative moisture sample and dry in oven at 110°C for 24 hours.
- Calculate dry density for each moisture content and plot the compaction curve.
- Read OMC and MDD from the peak of the compaction curve.
Field Compaction Control
The Proctor MDD and OMC serve as the target for field compaction. Field density is measured by sand cone test (ASTM D1556) or nuclear gauge (ASTM D6938). A minimum relative compaction of 95% of MDD is typically specified for road subgrades.
Proctor Compaction Equipment from Elipslab
Elipslab supplies Standard and Modified Proctor sets including mechanical hammers, 4-inch and 6-inch molds, extruders, and complete test kits compliant with ASTM D698 and D1557. Manufactured in Ankara, Turkey — available worldwide.