Considerations of Sustainability in the Mixture Proportioning of Concrete for Strength and Durability

摘要

The mixture proportioning of concrete for sustainability should consider four aspects, without sacrificing affordability: the lowering of the carbon dioxide emissions; the minimization of raw materials required; reduction of energy demand during manufacturing and construction; and the longevity of the structure or other applications. Taking a set of concretes with different binders, including ordinary portland cement (OPC), fly ash (FA) and ground granulated blast furnace slag (GGBS), sustainability is assessed using different types of indicators including those that take into account the binder and clinker content, compressive strength, carbon footprint and energy demand. A new set of indicators called A-indices has been proposed for combining the influence of carbon dioxide emissions obtained from life cycle assessment (LCA) and durability parameter that relate to the service life of a structure. Here, this concept is illustrated by obtaining a parameter based on the chloride migration coefficient of the concrete. It is proposed that the decision-making process for sustainable concrete be made by minimizing both the A-index and the energy intensity, defined as the energy demand for a unit volume of concrete and unit performance parameter, such as 1 MPa of 1-year compressive strength. The best concretes considered here come out as those with ternary binders having 40% of the OPC replaced by a combination of GGBS and FA.