In 2008, the International Zinc Association (IZA) sponsored a study of the life-cycle inventory (LCI) and life-cycle assessment (LCA) of hot-dip galvanized steel. IZA hired world-renown environmental firms Five Winds International and PE International to conduct the study. Five Winds and PE International collected worldwide galvanizing data from the American Galvanizers Association (AGA), the European General Galvanizing Association (EGGA), Galvanizers Association of Australia (GAA), and Hot Dip Galvanizers Association of South Africa (HDGASA) to conduct the study.
The goal of the study was to provide a life-cycle inventory (LCI) for 1 kg of hot-dip galvanized steel product, and then using the LCI information, conduct a life-cycle assessment (LCA) to understand the full environmental impact of galvanized steel from production through use and end-of-life. The LCA is intended to not only provide an accurate picture of where galvanizing stands currently, but also to highlight opportunities for minimizing environmental impact in the future.
LCI & LCA Overview
The LCI study examines the environmental impact of producing 1 kg of hot-dip galvanized steel. The LCI of the hot-dip galvanizing process is a gate-to-gate study, which means it only examines the environmental impact generated from the time the product arrives at the galvanizer’s facility up to the point when it is ready to be shipped to the job site. However, in order to really gauge the impact of producing 1 kg of hot-dip galvanized steel, the impact of producing steel and zinc must also be analyzed. Combining the LCI’s of all three (steel, zinc, and the galvanizing process), a cradle-to-gate study, provides the true impact of producing 1 kg of hot-dip galvanized steel, which is the same as the production phase of the LCA.
The LCA study examines the full environmental impact of hot-dip galvanized steel from production to end-of-life. LCA is considered a cradle-to-grave study, as it considers initial impact of production, impact during use due to maintenance and/or emissions generated, and the end-of-life impact or credit. For hot-dip galvanized steel, a more accurate term would be cradle-to-cradle, as the zinc and steel are both 100% recyclable at the end-of-life.The LCA study conducted by Five Winds and PE International examined a hot-dip galvanized structural beam (16 m, 940 kg) and a utility pole (10.7 m, 184 kg). Each hot-dip galvanized product will yield slightly different results, but the figures provided here can be used as a guideline. Figure 5 is a visual representation of hot-dip galvanized steel’s LCA.
LCI & LCA Terminology
Throughout the LCI and LCA, a number of environmental criteria were measured. Before revealing the results of the study, it is important to define the following criteria:
- Primary Energy Demand (PED) measured in mega Joules (MJ), is the sum of the total primary energy consumed in the manufacture and supply of products.
- Joule (J) the SI unit of work or energy, equal to the work done by a force of one newton when its point of application moves through a distance of one meter in the direction of the force. A mega Joule (MJ) is one million Joules.
- Global Warming Potential (GWP) measured in kilograms CO 2 equivalent (100 years), is the potential to gradually increase over time the average temperature of Earth’s atmosphere and oceans that induce changes to Earth’s climate.
- Acidification Potential (AP) measured in kilograms SO 2 equivalent, is the amount of hydrogen ions created when a substance is converted into an acid, known as acid rain.
- Photochemical Ozone Creation Potential (POCP) measured in kilograms ethene (C 2 H 2) equivalent, is the creation of summer smog, or increased levels of ozone at ground level.