How Do Paving Materials Compare

What are your options for pathway surface materials and how do they stack up?

Organic-Lock™ is the result of more than 10 years of research with organic aggregate binders and their ability to create long-lasting surfaces that maintain a natural look and feel without continual maintenance. The result of this research is the strongest organic binder on the market.

Designed to be combined with crushed aggregate screenings to create stabilized, natural surfaces, Organic-Lock™ combines the toughness of traditional paving materials with all the benefits of a natural looking pathway.

Organic-Lock™ outperforms traditional paving materials on key metrics, such as permeability, environmental impact, and durability. It is often chosen where a natural looking permeable surface is desired.

Below, Organic-Lock™ will be directly compared to concrete, asphalt and traditional crushed stone to help you understand the difference.

Paving Material Comparison

Permeability

Permeability is a key consideration for new pavements. A permeable material can reduce the complexity and cost of drainage systems. New environmental standards also encourage the use of permeable paving materials over a wide range of commercial and residential surfaces.

Traditional concrete surface materials are considered to lack permeability. However, it is possible to use a scientifically engineered version of traditional concrete that allows water to drain through at an enhanced rate.

This material includes an alteration of the particle size distribution of the aggregate used in the concrete mixture. It is referred to as “porous” or “permeable” concrete, with the permeability rates varying based on the aggregate and sub-base used.

Similar to concrete, asphalt is considered to be lacking permeability, but there has been an evolution of permeable versions, which are termed “porous asphalt”. Porous asphalt is produced and placed using a similar method as conventional asphalt but it differs in that the fine particles in the aggregate are removed from the mixture.

The remaining larger, single-sized aggregate particles leave open spaces that give the material its porosity and permeability. Pollutants are a concern when using asphalt. Surface runoff with asphalt (including porous asphalt) is an environmental concern, as the pollutants cannot be filtered out through the normal filtration process and can be detrimental to the surrounding environment.

Studies have shown that standard asphalt installations can have concentrations of pollutants in surface runoff as high as 95 mg/l that end up in surface drainage systems [2].

Researchers have also found that porous concrete and asphalt mixtures will lose porosity if not cleaned regularly [1]. Complete clogging can occur in as little as three years without adequate cleaning. At this point, porosity cannot be recovered and replacement is necessary.

Given the importance of permeability and the limitations of traditional materials, Organic-Lock™ has been intentionally designed to maximize water flow.

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

Overall, these tests confirm an average infiltration rate of 1.20 inches/hour for Organic-Lock™ blended aggregate which is enough to cope with heavy rainfall, while still allowing for natural infiltration of water into the soil.

Rain on AsphaltRain on Organic-Lock Pathway

Durability

For anyone choosing material for a new paved area, durability is a key concern. Any material that cannot stand up to heavy sustained use will need to be replaced or repaired continually. Municipalities and businesses are increasingly budget conscious and are looking for materials with a low lifetime cost.

Although concrete is known as a durable material, it has a relatively low tensile strength. This comes into play when you consider the low thermal expansion coefficient, which causes concrete to shrink as it ages [3] [4].

Cracks in concrete will increase permeability, but this benefit is outweighed by safety concerns and the barriers this places on access to those with disabilities [5]. Repairing concrete paths with cracks also represents a significant cost. Effective repairs to concrete paths are difficult and replacement is often needed.

Asphalt is less durable than concrete, but is used due to a lower installation cost and the viability of repairs. As asphalt ages, the binders become increasingly brittle, reducing the tensile and compressive strength of the pavement [6].

This results in cracks in the asphalt which can limit accessibility and allow for weeds to grow through the pavement. Holes and cracks in asphalt can be repaired, but repairs cannot halt the overall deterioration.

Loose aggregates have traditionally been cheaper, and sometimes ideal to use to create a natural look and feel. However, they are far less durable than concrete or asphalt and can require a great deal of maintenance. One major problem with loose aggregates is water erosion.

Organic-Lock™ addresses this problem directly. Aggregate mixed with Organic-Lock™ creates a durable natural surface that incurs significantly less damage over time and requires less maintenance.

In a side by side comparison under laboratory conditions, using a rainfall simulation device, it was shown that the unstabilized aggregate washes out to completion after only 20 minutes of rainfall, where the aggregate blended with Organic-Lock™ only lost a total of 3% of its total material after 120 minutes on the rainfall simulator.

This rainfall erosion resistance is due to the expansion of the natural glue in Organic-Lock™ when it is exposed to water. This starts a chemical reaction that binds and locks in the loose aggregate preventing it from washing out. When wet, Organic-Lock™ increases firmness and stability, making it usable much more quickly in heavy rain events in comparison to regular saturated aggregate surfaces.

Should damage occur to an Organic-Lock™ aggregate surface, it can be simply repaired by wetting and reworking the aggregate and compacting it again. The repair process is simple and does not require a large investment of equipment or manpower.

As you can see, Organic-Lock™ has successfully found a way to combine the flexibility and permeability of loose aggregate with the durability of traditional pavement materials.

If you need durability without compromising on the aesthetic value, then it is hard to look past this product. The fact that it’s made from a renewable plant resource is a significant benefit that puts it into a class of its own.

Environmental Impact

Environmental impact is an increasing concern with municipal authorities when making pavement material choices.

It has been known for some time that concrete is not an environmentally sustainable choice. Globally, concrete accounts for 7% of greenhouse emissions [7]. Although efforts are being made to limit this, they are in their infancy.

Asphalt is not much better. Bitumen is a by-product of fossil fuel production, which has a well known impact on the natural environment. The use of non-petroleum substitutes is theoretically possible, but uneconomical and research suggests that substitute materials result in less durability [8].

In addition to a significant impact on C02 emissions, excessive use of concrete and asphalt in urban areas can have a heat sink effect [9] and limit the replenishment of the water table due to low permeability [10].

Organic-Lock™’s natural plant based formulation avoids any undue impact on the environment with no harsh chemicals used in its production.

Water can easily permeate through the aggregate without eroding it, which helps maintain natural drainage, without the common damage incurred by traditional aggregate surfaces. Organic-Lock™ looks and feels like a natural surface, but behaves like a scientifically engineered surface.

The composition and production of Organic-Lock™ qualifies it for LEED points. The key ingredient is renewable, and creates a permeable surface that uses local materials. Just by using Organic-Lock™ for your travelled surfaces, you will qualify for LEED points.

Why paving material choice matters

With an increasing focus on environmental sustainability in urban environments, paving material choice is no longer a straightforward one.

Traditionally concrete or asphalt were the default choices for pavements, but their shortcomings are becoming increasingly evident. Not only are these materials damaging to the environment, their lifetime cost can be high when repair and replacement is considered.

Organic-Lock™ has been designed from the ground up to address the shortcomings of these traditional pavement materials. It is simple to maintain, sustainable, durable and has a pleasing natural aesthetic.

If you are considering Organic-Lock™ for your next project, then contact us for support, tips or access to project case studies.

Sources

[1][2][10] Scholz, M., Grabowiecki, P. (2007). Review of permeable pavement systems.
Building and Environment, 42(11), 3830-3836. https://doi.org/10.1016/j.buildenv.2006.11.016.

[3] Gaio-Graef, A., Pilakoutas, K., Neocleous, K., Vania, M  Peres, N.N. (2012). Fatigue resistance and cracking mechanism of concrete pavements reinforced with recycled steel fibres recovered from post-consumer tyres. Engineering Structures, 45, 385-395. https://doi.org/10.1016/j.engstruct.2012.06.030.

[4] Hiltunen, D.R, Roque, R. (1994). A MECHANICS-BASED PREDICTION MODEL FOR THERMAL CRACKING OF ASPHALTIC CONCRETE PAVEMENTS (WITH DISCUSSION). Journal of the Association of Asphalt Paving Technologists, 63, 81-117. http://worldcat.org/issn/02702932

[5] US Department of Transportation (2013). A Guide for Maintaining Pedestrian Facilities for Enhanced Safety. Available from: https://safety.fhwa.dot.gov/ped_bike/tools_solve/fhwasa13037/chap3.cfm

[6] Cui, S., Blackman, B., Kinloch, A.J., Taylor, A. (2014). Durability of asphalt mixtures: Effect of aggregate type and adhesion promoters. International Journal of Adhesion and Adhesives, 54, 100-111.
https://doi.org/10.1016/j.ijadhadh.2014.05.009.

[7] Mehta, P.K. (2009). Global Concrete Industry Sustainability. Concrete International, 31(2), 45-48. https://www.concrete.org/publications/internationalconcreteabstractsportal/m/details/id/56323

[8] Hesp, Simon A.M.; Herbert F. Shurvell (2010). X-ray fluorescence detection of waste engine oil residue in asphalt and its effect on cracking in service. International Journal of Pavement Engineering. 11(6), 541–553. https://doi.org/10.1080/10298436.2010.488729

[9] Hawes, D.W., Feldman, D., Banu, D. (1993). Latent heat storage in building materials. Energy and Buildings, 20(1), 77-86. https://doi.org/10.1016/0378-7788(93)90040-2.