Center for Earth Systems Engineering and Management

Hemcrete is an alternative, environmentally‐friendly building material gaining adherents in Great Britain and other European countries. It is an attractive choice as a building material because it is made from a renewable resource, hemp, a hardy plant that is a close, but non‐hallucinogenic relative of marijuana. This plant is relatively easy to cultivate, requires little in the way of pesticides or fertilizers, and almost all parts can be used for various products from paper to textiles to food.

Hemcrete is made from a mixture of lime, water, and the fibrous outer portion of the hemp plant called the “hurd” or “shive”. When mixed, it is worked and placed much like conventional concrete ‐ hence the name. However, that is where the similarities with concrete end. Hemcrete is not comparable to concrete on a strength basis, and is better described as an alternative insulation product. When built into walls of sufficient thickness, Hemcrete offers high thermal efficiency, and has strong claims to being carbon negative. The purpose of this study
was to evaluate this claim of carbon negativity, and to compare these environmentally friendly qualities against conventional fiberglass batt insulation.

Our model was constructed using two identically sized “walls” measuring eight feet square by one foot in depth, one insulated using Hemcrete, and the other using fiberglass. Our study focused on three areas: water usage, cost, and carbon dioxide emissions. We chose water
usage because we wanted to determine the feasibility of using Hemcrete in the Phoenix metropolitan region where water is a troubled resource. Secondly, we wished to evaluate the claim on carbon negativity, so CO2 equivalents throughout the production process were measured. Finally, we wished to know whether Hemcrete could compete on a cost basis with more conventional insulation methods, so we also built in a price comparison.

Since the cultivation of hemp is currently unlawful in the United States, this study can help determine whether these restrictions should be relaxed in order to allow the construction of buildings insulated with Hemcrete.

The current study conducts a comparative LCA of two alternative structural retrofit/ strengthening techniques - steel jacketing, and the carbon fiber reinforced polymer (CFRP) retrofit. A cradle-to-gate system boundary is used for both techniques. The results indicated that the CFRP retrofit technique has merits over the conventional steel jacketing in all three impact categories covered by this study. This is primarily attribute to the much less material consumption for CFRP retrofit as compared to steel jacketing for achieving the same load carrying capability of the retrofitted bridge structures. Even though the transoceanic transportation of carbon fiber has been taken into account in this study, the energy consumption and environmental impacts of CFRP transportation is still much smaller than steel due to it light weight property. The impacts of CFRP retrofit are mainly focused in the material manufacturing phase, which implies that the improvements in the carbon fiber manufacturing technology could potentially further reduce the environmental impacts of CFRP retrofit.

Results are available here. 

The environmental life cycle assessment of electric rail public transit modes requires an assessment of electricity generation mixes. The provision of electricity to a region does not usually adhere to geopolitical boundaries. Electricity is governed based on lowest cost marginal dispatch and reliability principles. Additionally, there are times when a public transit agency may purchase wholesale electricity from a particular service provider. Such is the case with electric rail modes in the San Francisco Bay Area.

An environmental life cycle assessment of San Francisco Bay Area public transit systems was developed by Chester and Horvath (2009) and includes vehicle manufacturing/maintenance, infrastructure construction/operation/maintenance, energy production, and supply chains, in addition to vehicle propulsion. For electric rail modes, vehicle propulsion was based on an average electricity mix for the region. Since 2009, new electricity contract information and renewable electricity goals have been established. As such, updated life cycle results should be produced.

Using recent wholesale electricity mix and renewable electricity goal data from the transit agencies, updated electricity precombustion, generation, transmission, and distribution environmental impacts of vehicle propulsion are estimated. In summary, SFMTA Muni light rail is currently purchasing 100% hydro electricity from the Hetch Hetchy region of California and the Bay Area Rapid Transit (BART) system is purchasing 22% natural gas, 9% coal, 2% nuclear, 66% hydro, and 1% other renewables from the Pacific Northwest . Furthermore, the BART system has set a goal of 20% renewables by 2016. Using the GREET1 2012 electricity pathway, a life cycle assessment of wholesale and renewable electricity generation for these systems is calculated.

Chester and Horvath (2009)

Building energy assessment often focuses on the use of electricity and natural gas during the use phase of a structure while ignoring the energy investments necessary to construct the facility. This research develops a methodology for quantifying the “embedded” energy and greenhouse gases (GHG) in the building infrastructure of an entire metropolitan region. “Embedded” energy and GHGs refer to the energy necessary to manufacture materials and construct the infrastructure. Using these methods, a case study is developed for Los Angeles County.