Asphalt Retexturing:
Waterblasting or Shotblasting?
Waterblasting is often the better method for asphalt when the loss of texture is caused by excess bitumen, flushing, rubber deposits, oil, or traffic film. In that situation, the aim is to uncover the existing aggregate—not aggressively abrade the pavement.
Shotblasting is more appropriate when the aggregate itself has become polished and must be mechanically roughened.
Technical Insight
Why waterblasting is often preferable
1. It removes the material causing the problem
High-pressure water removes excess binder and contaminants from between and over the aggregate particles, reopening the surface texture and drainage paths. Queensland’s current bituminous-retexturing specification defines waterblasting specifically as the removal of excess binder, while Irish guidance recommends high-pressure water jetting for mature “fatted-up” wheel tracks.
2. It is more selective and usually less aggressive
The pressure can be adjusted so that exposed binder and road film are removed without unnecessarily attacking the asphalt matrix. In a documented ultra-high-pressure watercutting process, the binder underneath the aggregate remained undisturbed and the aggregate was not displaced. By comparison, shotblasting deliberately fires steel pellets at high velocity to pit and abrade the pavement’s superficial layer and the aggregate surface.
This makes correctly calibrated waterblasting particularly attractive where the aggregate is still sound but covered by binder, where treatment is limited to wheel paths or isolated flushed areas, where preserving aggregate embedment is important, and where only a small amount of material should be removed.
3. It can clean and retexture in one operation
A vacuum-recovery waterblasting machine removes binder, rubber, dirt and other deposits while recovering the water and dislodged material. It therefore restores the original texture rather than adding a new coating or removing a continuous layer of asphalt.
4. There is no steel blast media to manage
Waterblasting replaces steel shot and dry abrasive fines with a recovered wet slurry. Shotblasting equipment can also be closed-cycle, but it must collect and separate the steel shot, control dust, and ensure that escaped shot is removed from the carriageway. Waterblasting is therefore generally preferable where airborne dust or residual metallic media are concerns though it still produces contaminated liquid and solid waste that must be properly collected and disposed of.
5. It is well suited to binder flushing
TRL testing1 found that water jetting can improve skid resistance where a binder film covers the aggregate. The same research noted that shotblasting is not effective where there is a serious excess of binder, such as a heavily fatted-up surface dressing.
1. Roe, P. G., and Hartshorne, S. A. (1998). Mechanical retexturing of roads: a study of processes and early-life performance. TRL Report 298. Transport Research Laboratory, prepared for the Highways Agency.
Important Limitation:
Not All Waterblasting Is the Same
Conventional high-pressure waterblasting mainly cleans the aggregate and restores macrotexture—the visible spaces that allow water to escape beneath the tyre. If the aggregate itself is highly polished, ordinary waterblasting may produce only a temporary improvement because it does not expose a fresh stone face.
A properly calibrated ultra-high-pressure watercutting system can also rejuvenate the aggregate’s fine microtexture, but it is substantially more aggressive and needs careful control. Excessive pressure or slow travel speed can remove too much binder, strip aggregate, or scour the underlying material. Current specifications therefore require trial areas, adjustable pressure, and checks for aggregate stripping and pavement damage.
Shotblasting Is Still a Valid Treatment
Shotblasting should not be considered an inferior process in every situation. It can improve both macrotexture and microtexture by removing surface material and pitting polished aggregate.
Bottom Line
For a sound asphalt road affected by flushing or surface contamination, waterblasting is usually better because it removes the substance masking the aggregate while minimizing unnecessary abrasion of the pavement. Shotblasting is better when the stone itself must be mechanically roughened.
A defensible specification would require a representative trial section and acceptance testing for friction, texture depth, and aggregate loss rather than selecting the method solely from visual appearance.
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