Are Aggregate Driveways Slippery? (A Helpful Guide With Reasons!)
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Are Aggregate Driveways Slippery?
Exposed aggregate driveways are not as slippery as many other types of concrete finishes. In addition to the unique looks, high skid resistance is a major advantage of an exposed aggregate driveway.
An exposed aggregate driveway has high skid resistance due to its texture. A wide range of textures is possible. Texture depends on the aggregate size & profile and the exposure level.
The exposed aggregate surface is created by removing a part of the top layer of the concrete driveway, while it still has its plasticity. A “deactivator” (aka retarder) is sprayed onto the freshly poured concrete surface.
Reputed manufacturers, such as Deco-crete Supply, make deactivators with predetermined exposure depths. This ensures that you wash off exactly the right thickness of the top layer. While most of the concrete slab sets in normal time, the top layer sets at a slower predetermined rate.
The top layer is then removed using a combination of a pressure washer and a buffer with a medium stiff brush.
The timing has to be just right. The slab should be set firm, so that it holds on tight to the aggregates. But the top layer should still be soft so that the brush can remove the cement & sand layer.
Generally speaking an exposed aggregate that has smaller, sharper aggregates with relatively higher exposure depth will be more skid resistant. Such texture is best for driveways.
Exposed aggregate slabs with larger, rounded aggregates and relatively lower exposure depth are less skid resistant. But they are more aesthetically appealing and softer on bare feet. Such texture is best for patios and decks.
Is Aggregate Driveways Slippery When Wet?
An exposed aggregate driveway is less likely to become more slippery when wet due to its texture. On the other hand, smooth driveways become more slippery when wet due to hydroplaning (aka aquaplaning).
Hydroplaning occurs when a thin water film between the tires and the driveway causes the car to lose traction. It is a bit like being on a surfboard, but with no control. Needless to mention it can be dangerous at high speeds or on curves.
All concrete driveways must be sealed to protect the concrete slab from water penetration. Topical sealers make the concrete surface smooth and more slippery. The risk of hydroplaning increases.
Topical sealer must be applied on exposed aggregate driveways too, to protect it from water penetration. Fortunately, topical sealers do not make an exposed aggregate driveway smooth.
The dry film thickness (DFT) of the sealer is much lower than the texture profile of the exposed aggregate driveway.
A topical sealer on an exposed aggregate driveway adds gloss, color and beauty along with water impermeability but without any significant decrease in skid resistance.
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What Is Meant by Skid Resistance?
Skid resistance is the force required to move a tire that has locked and is no longer able to rotate. A driveway or road surface with low skid resistance results in the tire having little or no traction. Instead of coming to a quick halt the tire slides and skids.
A driveway or road has micro texture and macrotexture.
Micro texture refers to the small-scale texture of the pavement aggregate component (which controls contact between the tire rubber and the pavement surface) while macrotexture refers to the large-scale texture of the pavement as a whole due to the aggregate particle arrangement (which controls the escape of water from under the tire and hence the loss of skid resistance with increased speed).
pavement interactive
Skid Resistance is measured using the sand patch test. A calculated measurement of sand is placed on the surface and spread in an even circle; as the sand is spread it fills each crack and crevice of the surface.
The diameter of the sand circle is then used to calculate the average surface texture depth. Higher the depth, higher is the skid resistance.
Exposed Aggregate has a much higher average surface texture depth as compared to other concrete slab finishes such as smooth, honed, broomed or stamped.
Thank you very much for reading this post. I do hope you found it informative and helpful.
