Maria Jose Valdebenito
Master of Advanced Studies in Architecture Candidate
University of British Columbia - School of Architecture and Landscape Architecture

 

J. Dahmen
Assistant Professor
University of British Columbia - School of Architecture and Landscape Architecture

 

 

FULL ARTICLE PDF


 

EXECUTIVE SUMMARY

This paper provides a preliminary assessment of the environmental impacts of a novel noise barrier produced by Walls Systems Northwest, Inc (WSNW). The proposed noise barrier, referred to as a vegetative sound structure (VSS), is constructed of a combination of precast concrete elements and compacted soil. The system is intended to provide a freestanding vegetative sound barrier for use along highways. The analysis employs Life Cycle Assessment (LCA) screening techniques to characterize the environmental impacts of the noise barrier and compare them to a base case consisting of a popular panelized concrete conventional noise barrier (CNB). The objective of the research is to provide information on the environmental impacts of the novel vegetated barrier, measured in the Global Warning Potential (GWP) and other factors, as it compares with the conventional barrier.

 

Goal and Scope

A rigorous Life Cycle Assessment requires a significant amount of effort and resources to collect, verify, inventory, and analyze data from numerous sources, as well as a peer review to ensure impartiality. While a full-fledged peer-reviewed LCA study is beyond the scope of this research, our aim is to provide preliminary information on the environmental performance of the vegetative sound structure. At the same time, the information presented in this report can be used as a useful point should a full-fledged peer-reviewed LCA be undertaken in the future. Such a study would provide valuable data to key transportation and infrastructure decision-makers so they can make informed decisions about the environmental impacts of this type of acoustical barrier.

 

Methodology

LCA studies are intended to be comparative rather than absolute, providing information about the environmental impacts of the product as they compare to the impacts produced by a functionally equivalent base case. The impacts of the VSS are compared to a typical CNB that produces an equivalent amount of acoustical protection. Acoustical analysis modeling is conducted on the VSS as well as the CNB used in the study. The acoustical modeling ensures that the comparison of the two cases is based on equivalent acoustical performance that takes into account the different physical characteristics affecting the acoustical performance of the barriers. These factors include overall dimensions (thickness, length and height), the absorptive capacity of the faces, and position of the barrier, source, and receiver. The results of this study suggest that the VSS can achieve the same acoustical performance as the CNB with slightly lower overall height. This initial acoustical comparison together enables the calculation of overall material quantity required for the test and the base case. The study the uses a leading LCA software tool called the Athena Impact Estimator to calculate and compare 3 Valdebenito and Dahmen Screening Life Cycle Assessment of Vegetated Noise Barrier the environmental impacts of the materials used in the VSS against those of the CNB base case.

Based on information provided by the manufacturer, the VSS utilizes a lower strength concrete than the CNB. Accordingly, the VSS is modeled in the software using 21MPa (3,000 psi) concrete strength containing 35% fly ash, a post consumer substitute for ordinary Portland cement (OPC). In contrast, the CNB base case is modeled using a 28MPa (4,000 psi) concrete strength containing 9% fly ash. Although these figures differ slightly from the composition of actual materials used for each barrier due to the limitations of the modeling software, they are still capable of producing a meaningful comparison between the two barriers. The same type of reinforcing steel used in both barriers, but the VSS requires 94% less reinforcing steel than the CNB base case, which has a significant effect on their respective environmental performance.

 

Impact Assessment & Results

The study indicates that the overall environmental impacts of the VSS are 54% lower than those of the CNB base case. This represents significantly improved environmental performance over the base case. Each 33-metre section of VSS constructed will save 50,000 MJ of energy and emit 5 tonnes less CO2 to the atmosphere than the CNB base case. The VSS outperforms the CNB by more than 50% across all impact categories, including acidification potential, respiratory effect on human health, and smog potential.

The two primary factors influencing the environmental impacts of the two noise barriers are the concrete and reinforcing steel used in construction. Concrete varies in quantity and type between the two systems; steel varies in quantity only, but both have a pronounced effect on the overall environmental impacts. The concrete strength required by the VSS members is lower than the concrete strength of the CNB panels. Lower strength concrete requires less energy-intensive cement than higher strength concrete, resulting in lower environmental impacts. The VSS further reduces the environmental impacts of concrete by substituting 30% of the cement content with a post-consumer supplementary cementitious material. Finally, the VSS design requires only a small fraction of the reinforcing steel required by the CNB. The reduced amount of cement and steel in the VSS translates to significantly environmental benefits over the CNB base case.

Additional improvements to the environmental performance of the VSS are also possible if structural members are optimized to further reduce material use, although this has not been modeled as part of the study. The VSS also has the potential to create positive aesthetic and ecological effects that are beyond the scope of the study. A vegetative barrier could have positive aesthetic effects on the surrounding context, whether along transit corridors or residential areas, due to the plants on its vertical faces. The vegetated surface of the VSS could also have positive ecological benefits due to the 4 Valdebenito and Dahmen Screening Life Cycle Assessment of Vegetated Noise Barrier potential ability to increase biodiversity in where it is deployed. Quantifying the effects merit further research, as its benefits are difficult to measure with current existing technologies.

 

Conclusion

This paper provides a preliminary assessment of the environmental impacts of a novel sound barrier system produced by Walls Systems Northwest. The study provides a transparent communication of the environmental benefits of a vegetative noise barrier compared to a conventional noise barrier. The report provides the groundwork for future scholars to conduct a full-fledged environmental assessment of the VSS. The Life Cycle Assessment (LCA) screening techniques strongly suggest that the individual and overall environmental impacts of the VSS are significantly lower than the effects of a conventional concrete panel barrier providing the same level of acoustic protection. The improved environmental performance is attributable primarily to the reduction of cement and steel in the design of the vegetative barrier. Finally, the VSS offers potential environmental benefits in the areas of biodiversity, carbon sequestration and aesthetic beauty that are currently not accounted for in the analysis. The positive results of the screening LCA suggest that the company proceeds with development and commission a full-fledged peer reviewed LCA study to establish environmental performance.