In 2012, the Canadian Precast Prestressed Concrete Institute (CPCI) published an ISO compliant Life Cycle Assessment (LCA) study of a five-storey precast concrete building, led by a team of consultants including Morrison Hershfield and the Athena Sustainable Materials Institute (ASMI). The study represents the cornerstone of the precast industry’s sustainable strategy and its commitment to a sustainable future

The peer reviewed ISO compliant study evaluates the impacts throughout the life of a precast concrete structure — from extraction, production and transport of raw materials, through the manufacturing processes and transport of the product to the project site, the assembly on site, customer use, occupancy, maintenance of the structure during its function life, and finally to its end of life recycling or disposal.

Highlights of the precast concrete study

For a five-storey commercial building with cradle to grave boundaries, the operating energy contributed up to 89 per cent of the global warming potential (GWP) for Toronto, and 50 per cent for Vancouver.

The constituent materials themselves represented 9 per cent and 38 per cent of the total GWP impact in Toronto and Vancouver respectively.

When comparing a total precast building with precast envelope, to alternatives such as a brick and steel stud, or curtain wall envelopes, the study revealed that buildings with precast structures had the lowest operating energy in both Toronto and Vancouver.

CPCI also engaged the consultants in a sensitivity analysis, evaluating the same building with a variety of reuse strategies at the end of life, and evaluating the same building with higher RSI values typically associated with insulated precast wall panels in Canadian applications.

Ten “end of life” reuse scenarios were evaluated, of which two are cited here: Reusing 50 per cent of hollow-core slabs for another 60 years on another building (scenario five in the study) further reduces GWP by 169 tonnes (carbon dioxide equivalent), total primary energy (TPE) by 2 million megajoule (MJ), and solid waste by 26 tonnes. Reusing 60 per cent of all precast elements for another 40 years (scenario ten) further reduces GWP by 315 tonnes (carbon dioxide equivalent), TPE by 3.7 million MJ and solid waste by 50 tonnes.

The sensitivity analysis on insulated precast wall panels compared the results with the minimum ASHRAE thermal performance (R-13.2 at the time of the study) to more commonly used R-20 insulated precast wall panels. The increase in overall effective wall R-value demonstrated a further 7 per cent decrease in annual heating energy, 1 per cent decrease in fan use, 2 per cent decrease in annual energy use, 2 per cent decrease in electricity use, and a 1–2 per cent decrease in natural gas use. Conversely, the increase did not affect cooling energy use, and did not affect interior loads such as lights and equipment.

The LCA study has been the impetus for the recently implemented CPCI sustainable plant program. The program’s aim is to decrease the industry’s impact on the environment in the areas of global warming, energy, water use, waste, dust and noise generation. Through the program, CPCI is providing the tools for its member plants to measure and implement improvements that will have a measurable impact on their environmental performance using a unique software tracking program, developed exclusively for CPCI.

The software program, developed for CPCI by ASMI, enables a manufacturer to measure their “cradle to gate” environmental footprint. Once a manufacturing facility enters their raw material usage, electricity, natural gas, gas, diesel, heavy fuel oil and liquefied propane gas usage, the software uses the ASMI database to calculate the GWP, TPE and water usage for the plant. Architects and engineers can now request this in their contract specifications for precast projects.

The next step, utilizing the complete LCA study, is the completion of product category rules (PCR) for precast concrete in North America and development of Environmental Product Declarations (EPDs). EPDs are third-party verified reports published by product manufacturers that provide quality assured and comparable information regarding environmental performance of their products or system.

The LEED v4 rating system and Architecture 2030 are emphasizing the demand for EPDs by addressing transparency in environmental lifecycle impacts and the selection of building products with improved lifecycles. North American precast concrete associations are working together with ASTM International to achieve a third-party verified EPD; providing comprehensive, uniform, and transparent details about the product’s composition and environmental impact throughout its lifecycle to be released in the fall.

Robert Burak, P.Eng., is president of CPCI. Learn more about CPCI’s commitment to transparency through its Life Cycle Assessment of Precast Commercial Buildings and the CPCI sustainable plant program.