Spanish
Russian
Arabic
In road engineering, the preparation of asphalt mixture specimens is a key step in evaluating pavement performance. Different compaction methods directly affect the density, air voids, and subsequent performance indicators of the specimens.Currently, the two most widely used methods are the Marshall Impact Compaction Method and the Gyratory Compaction Method (SGC method).
So, what are the differences between these two methods? And how should engineers choose between them in practical applications? This article will provide a comprehensive explanation.
I. Comparison of Methods and Principles
1. Marshall Compaction Method:
The Marshall compaction method is a traditional specimen molding method that uses a vertically falling hammer to impact and compact the mixture. Specifically, a mold containing asphalt mixture is fixed on a compaction table, and the hammer is allowed to fall freely from a height of 457mm, compacting the specimen bidirectionally (each side is compacted a certain number of times, such as 75 times).
In short: vertical impact, similar to rammed earth.
2. Superpave Gyratory Compactor (SGC)
Superpave Gyratory Compactor: A more modern compaction method that combines vertical pressure with rotary shearing to compact the mixture. While the specimen is subjected to vertical pressure, the mold base rotates at a fixed angle and speed, causing the mixture particles to rearrange, more closely resembling the actual road surface compaction process.
In short: kneading and compressing, similar to a road roller.
II. Comparison of Technical Parameters
Comparison Item | Marshall Impact Compaction Method | Gyratory Compaction Method |
Compaction Principle | Vertical hammer impact (tamping) | Vertical pressure + rotational shear (kneading) |
Specimen Size | Φ101.6 mm × 63.5 mm (standard) | Φ100 mm or 150 mm, adjustable height |
Control Parameters | Number of blows (e.g., 75 blows per face) | Number of gyrations (e.g., 100 cycles), vertical pressure, gyration angle |
Temperature Requirements | Compaction temperature: 120–150°C (for asphalt cement mixtures) | Similar to Marshall method; requires strict temperature control |
Equipment Cost | Lower, simple operation | Higher, more precise and advanced equipment |
III. Comparison of Volumetric Properties and Road Performance
The results show that the two molding methods have significantly different effects on the performance of asphalt mixtures:
1. Density and Porosity: Specimens formed by rotary compaction have higher density and lower porosity. This is because the shearing action during rotary compaction allows the aggregate particles to be better interlocked, eliminating most of the air voids.
2. High-Temperature Stability: In terms of high-temperature rutting resistance, the mixture formed by rotary compaction (100 cycles) performed best, while the mixture formed by standard Marshall compaction had relatively poor high-temperature performance. This is related to the fact that rotary compaction is closer to the compaction state of actual road surfaces.
3. Water Stability: The opposite is true regarding water stability—the Marshall compaction method produces the best water stability, while the rotatable compaction method (125 cycles) produces the worst. This indicates that excessive rotatable compaction may damage the asphalt film on the aggregate surface, reducing its resistance to water damage.
4. Fatigue Resistance: In terms of fatigue resistance, rotatable compaction (100 cycles) yields the best results, while the Marshall compaction method produces the worst.
5. Internal structural uniformity: CT scans revealed that the specimens formed by rotary compaction had a more uniform internal void distribution, a greater thickness of asphalt mortar, and better contact and interlocking between coarse aggregates.
IV. Engineering Application Recommendations
1. When to Choose the Marshall Compaction Method?
Mix design for conventional road engineering
Limited laboratory conditions and insufficient equipment budget
Large amounts of historical data requiring comparison
Projects with particularly high requirements for water stability
2. When to Choose Rotary Compaction?
Highway and Heavy-Traffic Road Design
Application of Superpave Design System
Skeleton-Compacted (SAC) Mixture Design
New Materials such as Cold-Recycled Mixtures and Warm-Mix Mixtures
Studies Requiring Evaluation of Long-Term Pavement Performance
3. Research Recommendations
For dense-structure asphalt mixtures, studies have shown that a design using 100 rotary compaction cycles can achieve better overall road performance. For conventional mixture mix design, both methods can be used in combination for mutual verification.
V. Conclusion
While both compaction and rotary compaction are methods for molding asphalt mixture specimens, they represent different stages of development:
Compaction = Traditional standard method (hammering)
Rotary compaction = Modern method simulating real rolling (pressure + rotation)
With the development of road engineering technology, rotary compaction is gradually becoming the international mainstream, while compaction continues to play an important role in traditional specifications and teaching.
