A proposed performance based approach for life cycle assessment of reinforced blended cement concrete

Abstract

The use of supplementary cementitious materials (e.g. fly ash and ground granulated blast furnace slag) as a partial replacement of ordinary Portland cement (OPC) in blended cement (BC) concrete has been established in recent years. However, an optimum mix design of BC concrete should not only achieve the targeted mechanical properties but also aim at minimizing the cost as well as environmental impacts. The first step towards an accurate estimate of BC concrete’s environmental impacts is to define an indicative functional unit. Unfortunately, most of the research that uses life cycle assessment (LCA) to compare OPC and BC concrete, selects a simple functional unit without taking into consideration the difference in mechanical properties and durability characteristics. Although several efforts were found integrating the durability characteristics in the environmental impact assessment over the whole life cycle, no consensus was found. In this study, a novel approach to quantifying the environmental impact of BC concrete compared to OPC concrete as a part of a decision making process on the type and mixing proportions of concrete to minimize its environmental impact. Using LCA, the method proposes that performance based parameters are defined: a targeted compressive strength and service life. Predictions should be made of these parameters based on generic user-input data like type of BC, water/binder ratios, binder content and OPC replacement rates. The comparative environmental impact is then quantified accordingly. It is believed that this novel approach allows the user to accurately select and proportion a blended cement concrete mix with the objective of minimizing its environmental impact.