Brooklyn Bridge Park

Gravel stabilized with Organic-Lock used in Brooklyn Bridge Park in NYC

 

Using Stabilized Gravels in Landscaping

 

The use of stabilizers such as Organic-Lock™ has made gravels one of the most well rounded solutions for those looking to strike a balance between price, durability and environmental impact.

Stabilized gravels are increasingly replacing concrete, pavers and asphalt as the go to material for landscape designers. This is in large part due to tightening environmental regulations and generous subsidies for using more environmentally friendly hardscaping materials [1].

Using gravels is a natural solution that requires far less complex drainage and maintains natural infiltration due to their porosity. This, combined with the ability to source these materials locally allows you to satisfy many of the requirements for LEED certification [2].

Stabilized gravel is also a great way to lower project costs, both initially and in the long term due to its low installation and maintenance cost.

There are a lot of different types of gravel out there though, so which one should you use? Below, you will get a brief overview of the most commonly used gravels and how to choose the best one for your next project.

 

The Most Commonly Used Types of Gravel

 

The gravels commonly used in landscaping are naturally occurring. Each type has its own unique characteristics which make it more suitable for some purposes than others.

Here are the most frequently used gravels with their major characteristics and best uses explained.

 

Decomposed Granite

 

Granite is the most commonly occurring igneous rocks on the planet and can be found almost anywhere, making it a good way to ensure you are using local materials for your project.

Decomposed granite is a naturally occurring derivative of granite and is found in a wide range of colours. Through natural weathering, smaller pieces of granite flake away from the main outcrop [3].

This natural process results in a natural aggregate of various sizes, ranging from small pebbles to a sand like consistency. These are separated out to form decomposed granite of different consistencies for landscaping use [4].

One of the main characteristics of decomposed granite is its strength, particularly when it is tightly compacted with a stabilizer. When laid in this manner it has close to the durability of concrete, but with the high levels of filtration of a natural aggregate [5].

 

Limestone Chips

 

Limestone is a naturally occuring sedimentary rock that is also found over a wide geographic area.

This stone is quarried for a variety of purposes outside of landscaping, including as an aggregate in concrete [6]. This means there are a variety of sizes available.

Limestone chips are typically used for driveways and paths, but tends to have more jagged edges and larger individual pieces than other gravels.

Like other gravels, limestone chips allow for higher levels of filtration, but can not always be compacted as tightly as smaller aggregates such as decomposed granite which can impact its erosion resistant properties.

 

Crushed Granite

 

The main difference between this and decomposed granite is that it is solid granite that has been crushed, rather than relying on natural weathering [9].

This results in a cost effective option that is perfect for covering large areas, however the crushing process does result in more jagged edges than decomposed granite.

This material fits in well with natural landscapes and drains well, negating the need for elaborate and expensive drainage systems.

 

Extraction of gravel taking place in an open-pit mine

 

The Importance of Stabilizers

 

Just as important as choosing the right gravel for your next project is understanding the role a stabilizer such as Organic-lock™ plays.

Even when damage does occur, repairing a stabilized gravel path is simple. The affected area can be dug up and recompacted using simple hand tools, with no or minimal use of new materials.

Combined with the low installation cost, this hassle free maintenance reduces the lifetime cost of this material well below comparable materials [10].

 

Improved Durability and Easy Maintenance

 

Stabilizers have made loose aggregates a much more compelling material choice for hardscapes because of how well they stop wear and erosion.

Organic-Lock is an all natural compound that is mixed with a loose aggregate when it is laid. When wet, Organic-Lock expands, locking the gravel in place and preventing any erosion or washouts.

Before stabilizers, paths made of gravel would require frequent maintenance and a constant renewal of the aggregate due to erosion. Now, a well compacted, stabilized gravel path can endure even heavy downpours without any adverse effects.

Under laboratory conditions, aggregate stabilized with Organic-Lock lost only 3% of its total material after 120 minutes on the rainfall simulator compared to a 97% loss of unstabilized aggregate over the same period of time. It is hard to find an all natural, permeable material that can match this low erosion rate while still giving you a hard and durable surface.

 

Improve Infiltration and Manage Runoff

 

In addition to the durability and cost savings stabilized gravel can offer, it is also a big positive for the natural environment. Even with the use of Organic-Lock as a stabilizer, gravel paths retain their naturally high levels of infiltration.

Natural infiltration recharges aquifers and prevents harmful runoff into local waterways. More traditional hardscaping surfaces such as concrete or asphalt are impervious and prevent this natural process [11].

Environmental standards now recognize the damage impervious surfaces can cause. In particular, LEED certification specifies the use of materials that lower runoff and allow for infiltration [12].

Under laboratory conditions, aggregate mixed with Organic-Lock TM displayed infiltration as high as 1.90 inches/hour when dry. This did not drop significantly after 360 minutes of exposure to water, falling to only 1.13 inches/hour.

As you can see gravel stabilized with Organic-Lock is the perfect way to meet these standards without compromising on the usability of your hard surfaces.

 

Choosing the Right Gravel for Your Next Project

 

The best thing you can do to ensure the ideal aggregate/gravel for your project needs, is to contact the supplier of the aggregate binder and get guidance from them.  Company’s like Envirobond (makers of Organic-Lock) have a team that will guide you to achieving the ideal aggregate for optimal performance on your project.12].

The aesthetic choice (i.e. color etc..) of the aggregate will be up to you, but it’s always best to go into a decision like this with your eyes wide open in terms of performance expectations.  Most often the physical make-up of the aggregate should be a well-graded material, meaning that it has an even amount of particles at each size of the aggregate profile.12].

Aside from that, any aggregate that has a strong compaction track record will typically perform the best when mixed with an aggregate binder.12].

 

References

 

[1] [2] [12] Abel, K. (2016). Trends in LEED Buildings and their Effects on Urban Permeability. GIS For Water Resources. Accessed: 24 Feb 2019. Available from: https://www.caee.utexas.edu/prof/maidment/giswr2016/Papers/Abel.pdf

 

[3] [4] Jenkins, E (2018). Hardscaping 101: Decomposed Granite. Gardenista. https://www.gardenista.com/posts/hardscaping-101-decomposed-granite/

 

[5] Kafka Granite (2019). A Short Guide to What You Need to Know about Decomposed Granite. https://www.kafkagranite.com/short-guide-need-know-decomposed-granite

 

[6] [9] Holmes, K. (2019). 10 Things Your Landscape Designer Wishes You Knew About Gravel (But Is Too Polite to Tell You). Gardenista. https://www.gardenista.com/posts/10-things-designer-wishes-knew-gravel-landscapes-polite-tell/

 

[7] [8] Christensen, J. (2017). A Guide to Pea Gravel, Gravel, Crushed Stone, River Rocks and Decomposed Granite for Landscaping. Gardening Channel. https://www.gardeningchannel.com/a-guide-to-pea-gravel-gravel-crushed-stone-river-rocks-and-decomposed-granite-for-landscaping/

 

[10] Babashamsi, P., Yusoff, N.I., Ceylan, H., Ghani, N., Jenatabadi, H.S. (2016). Evaluation of pavement life cycle cost analysis: Review and analysis. International Journal of Pavement Research and Technology, 9(4), pp. 241-254/ DOI: https://doi.org/10.1016/j.ijprt.2016.08.004.

 

[11] Northern Virginia Soil and Water Conservation District (2019). Control Heavy Runoff – Solving Drainage and Erosion Problems. Accessed: 07 Mar 2019. Available from: https://www.fairfaxcounty.gov/soil-water-conservation/drainage-problem-control-runoff