Anyone in the construction industry knows that before you can build - whether it’s a skyscraper, an airport, or a humble residential driveway - you need a strong, well-compacted foundation. Fewer, though, know which roller is best. Static roller vs vibratory roller - which one should you choose?
Let’s talk about why compaction is so important, demystify a few of the technical terms you might hear from compaction professionals, and compare which types of rollers are typically used in construction.
Why do I need to use the right roller?
There are five principal reasons rollers are used in soil compaction and to compact asphalt finishes:
- Increase the load-bearing capacity
- Reduce the settling and shrinkage over time
- Ensure a reduction in water seepage/ingress into substrate
- Reduce swelling and contraction
- Provide better overall stability
If a building or road is constructed on a loose substrate, or the finish has cracks as a result of sticking, the weight of a structure or passing traffic will slowly compact the material downward. As a result, the structure or road will slowly change in shape – causing cracks, expensive structural damage or a cracked pavement that is unusable or unsafe.
There are many different types of compaction rollers on the market, all designed to suit a particular type of construction project or worksite. They vary by size, weight, compaction output and drum type.
What kind of roller should I use?
To choose the right type of roller for your project, you need to consider the soil, project, and site.
Different types of soil will require different construction equipment. For example, padfoot rollers deliver a better performance on clay, while sand, gravel, and mixed soils are better suited for a smooth drum roller.
Then, the specifications of the project and conditions of the site will also have an impact on the roller that will be used to compact the soil. For example, if you need to cover a big area, larger rollers will be better.
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Common compaction terms explained
Let’s get a bit more detailed by looking at some compaction jargon that isn’t always well-understood, such as frequency, amplitude, centrifugal force and static linear load.
Frequency
Frequency describes the number of hits of the drum onto the surface of the material being compacted per second. It’s measured in hertz – 1 hertz is equal to 1 cycle per second. The optimal frequency is different for each material. For soil the compaction frequency is a range between 20 hertz (rockfill) and 45 hertz (clay). For asphalt compaction it’s 35-55 hertz.
Amplitude
Amplitude is the distance between the ‘up and down’ (or top and bottom) position of the drum per hit. Higher amplitudes are recommended when you’re compacting non-cohesive material, whereas lower amplitudes are suggested for the compaction of semi-cohesive and cohesive materials. For soil, aim for an amplitude range between 2.5 mm (rockfill) and 0.8 mm (clay) – and for asphalt compaction it’s best to land somewhere between 0.25-0.8 mm.
Centrifugal Force
Centrifugal force depends on the frequency and eccentric mass of your drum/vibrating system. Higher centrifugal forces allow for a bigger depth effect of compaction, therefore higher compaction outputs. For harder-to-compact materials such as boulders, rocks, clay, or sand, you’ll need a higher centrifugal force.
Static Linear Load
Static linear load is the value of applied linear pressure only by a drum load, generated from the machine weight itself. This factor is one of the most important technological parameters of a compaction roller and is also considered in other standardised equations and in several compaction formulas. The static linear load generally has higher compactive parameters.
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Static vs. vibratory rollers
Another big decision you’ll have to make when compacting is whether to use a static or a vibrating roller. Most models, including our multi-tyred rollers, are available in either static or vibratory configurations.
How does a static roller work?
Static machines rely purely on a high static linear load for overall compaction performance. This means that the weight of the roller and the width of the drums are critical to the compactive effort.
How does a vibratory roller work?
Vibratory drums can be adjusted to vary the frequency and sometimes amplitude of the vibratory action. As such, vibratory rollers (like the ones on our tandem smooth drum rollers) offer an ideal combination of static weight and centrifugal forces along with varying frequency and amplitudes.
Operators can turn the vibrations on or off, meaning a vibratory roller can also be used as a static roller, and can also control the amplitude and frequency to suit the project.
The drums’ vibration adds a dynamic load to the static roller weight, which in turn creates a greater total compactive effort. Drum vibration also reduces friction and aggregate interlock during the compaction process, allowing aggregate particles to move naturally into final positions. This creates greater friction and interlock that would not be achieved without vibration, which in turn equates to a great finish.
Which Type of Roller is Best for Compaction?
In most cases, a vibrating roller is a great option – especially considering you can switch off the vibrating function if it’s not needed. On the other hand, in tight, residential areas or environments near bridges, static rollers are better suited.
Whatever you’re building – from a city tower block to a backyard shed – we hope these tips and concepts will help you create the right foundation.
Frequently Asked Questions
A static roller is used for soil compaction near residential areas or bridges where vibrations can be potentially dangerous.
Static compaction uses high static linear load while vibratory compaction uses a combination of static weight and centrifugal forces for soil compaction.
A road roller typically has 2 or 3 heavy drums that are used for compaction during road construction, while a vibratory roller uses vibrating drums in addition to static weight to compact the material.
The key benefits of using a vibratory roller for compaction is their versatility, cost-efficiency, and ease of use. These rollers are able to cover a big area of soil, whether it’s granular, mixed, or semi-cohesive, with fewer passes. As they require minimal setup, vibratory rollers are great for road construction, building foundations, and a number of other applications.
As both a static roller and smooth drum vibratory roller operating without vibration use the same principle, you need to consider factors like the soil type and compaction requirements to decide which roller is best based on the static linear load and overall weight (sometimes a vibe roller is used without vibration to finish a surface).
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