How the Use of Geogrid Helps Reduce Truck Loads and CO2 Emissions

Laying the path for sustainability

How the use of geosynthetic materials reduces CO₂ emissions and the overall carbon footprint of highway construction

Looked at from a sustainability standpoint, the National Highway System in Canada could be considered a 38,021 km conduit for pollutants.  The transportation sector accounted for 24% (173Mt CO 2 eq) of the greenhouse gas emissions produced by all of Canada’s industry contributors in 2015 according to Canadian government data.  But it isn’t just cars and trucks traversing the highway system that creates the problem.  Constructing and repairing those roads is also a major culprit.

That’s where geosynthetic materials come in to play. These synthetic, polymeric products allow highways to be built using less asphalt and aggregate which reduces CO2 producing truck trips to and from construction sites.  Geosynthetics also prolong the lifetime of roadways, which reduces long-term maintenance costs and saves owners time and money while additionally limiting GHG contribution.

Geosynthetics have been around since the early days of roadway construction. Even the Romans experimented with various materials to stabilize roadways and embankments, with varying degrees of success. Where they incorporated natural materials with soil to build the world’s first transportation networks, modern engineers transformed the use of geosynthetics and roadway longevity with the advent of polymers, not subject to biodegradation. With evolving technology, applications of geosynthetics are enabling owners to significantly increase the lifespan of transportation resources, which is great for their bottom line, but is that all geosynthetics do in the broad world of sustainability?

Testing

Tensar Corporation, a leading producer of proprietary geosynthetic materials used in a variety of soil stabilization applications, utilizes road construction software to evaluate pavement design options and optimize pavement performance using Tensar Geogrids. The SpectraPave4-PRO™ Software (SP4-PRO) is a comprehensive, systems-based pavement design software suite that offers the full benefits of Tensar’s knowledge and experience in analyzing both subgrade stabilization and pavement optimization applications. Tensar offers the software at no cost to designers.

Tensar recently used the SP4-PRO software to demonstrate pavement performance of typical pavement sections in comparison to its own Geogrids. The results, which are illustrated below, demonstrate initial cost savings of 15.8%-16.4% when using Tensar geogrids over asphalt and aggregate base. The number of trucks travelling over existing infrastructure to service a project can be reduced by 25%.  The pavement life can be improved from 19-25%.  And the amount of time to construct a project can be significantly decreased by approximately 8 days per lane km.  This translates into additional benefits and costs such as reduced safety concerns, user costs and environmental costs.

Lower Construction Costs and Material Quantity Savings

Here is a scenario to compare and contrast material savings and help lower construction costs by using less aggregate. As you can see the performance on the road is improved with the geogrid layer.

Fifty mm of asphalt with 200 mm of aggregate base can support 833,333 cars, 161 buses and 90 dump trucks.

Seventy-five mm of asphalt with 200 mm of aggregate base can support 4,166,667 cars, 803 buses and 45 dump trucks

But, a 50 mm of asphalt coupled with 200 mm of aggregate base on a Tensar TriAx Geogrid, can support 37,500,000 cars, 7,229 buses and 4,056 dump trucks.

The Tensar Mechanically Stabilized Layer (MSL) was reduced from 200mm to 150mm in the stabilized sections, the estimation of construction costs savings would be around 10%. The construction cost savings could come in many variables, like the decrease use of aggregate base, but also savings through less use of equipment like dump trucks that visit the site with the aggregate.

Expedited Construction Time

Another cost savings is the reduction of time required to place and compact less aggregate base and asphalt, which helps to reduce the time to build the road.

Minimized Carbon Emissions

Using public sources for standard values, a fully-laden articulated truck emits 1.09kgCO₂e/km of travel. Based on this data, Tensar has evaluated the environmental benefit of saving granular layer thickness in pavement projects.

The reduction in layer thickness by incorporating a Tensar MSL will typically have a positive environmental benefit in terms of the “carbon footprint” of the finished road construction. Although Tensar TriAx geogrids are manufactured from carbon-rich polymers, incorporating the geogrid in a granular base reduces the requirement for aggregate and asphalt where embodied energy is very high, and a saving on CO2e emissions can be quantified. Reducing material quantities also reduces the number of vehicle movements required to construct the road and so further CO2e savings can be made.

Reduction in Construction Vehicle Traffic

Although local and federal regulations require that trucks cover their loads while in operation. These laws were put in to place to prevent debris from unexpectedly falling onto roadways and injuring nearby motorists. However, these covers – often tarps – do not always stay in place in windy conditions. As a result, many construction trucks still spill gravel, sand, rocks, trash and building materials onto roadways causing safety hazards for other drivers.

The CAA Foundation for Traffic Safety estimates that vehicle parts and cargo unintentionally discharged onto roadways in Canada and the United States account for 25,000 vehicle accidents and 90 fatalities each year. Passenger vehicles and construction traffic both account for these incidents, as small debris can have catastrophic consequences when moving at high speeds on congested roadways. Construction traffic continues to increase in major urban areas to provide the community infrastructure required to sustain population growth.

The use of geosynthetic materials may not prevent your neighbour from poorly securing a mattress to the roof of his car, but it can reduce maintenance needs for the highway he traverses. Tensar’s proprietary TriAx Geogrid, have been found to increase highway infrastructure lifespan, thus minimizing long-term maintenance costs and reducing the volume of construction truck traffic for roadway construction projects. Fewer trucks on the roadways equate to less opportunities for falling debris that inadvertently threaten motorists across the country.

The future of geosynthetics

Engineers continue to utilize evolving technology to achieve sustainability across multiple industries domestically and worldwide. In the construction industry, geosynthetic materials offer multiple sustainable benefits to prolong infrastructure longevity and reduce maintenance requirements. Increased infrastructure lifespans eliminate related construction traffic, which results in reduced carbon emissions and public safety incidents. As projects utilizing geosynthetics require less overall stabilizing materials and emit less CO₂ emissions, owners benefit from improved project schedules, reduced impacts on the environment and lower materials costs to save both time and money. Ultimately, geosynthetic materials improve infrastructure assets, increase returns on owner investments, help owners do their part to combat greenhouse gases, and protect the safety of our family and friends on the road.

Written By Paul Hewgill, C.E.T. | Regional Sales Manager, Eastern Canada
Tensar International Corporation

If you have any questions, Paul can be reached at PHewgill@tensarcorp.com