Sustainability assessment of potentially 'green' concrete types using life cycle assessment

Nowadays, numerous introduction sections of scientific articles and books publishedon potentially “green” concrete with high cement replacement levels includeoften nothing more than a rather vague general justification for the researchconducted. Usually, their authors state that because at least 50% of the ordinaryPortland cement (OPC) is replaced with by-products from other industries, cementrelatedgreenhouse gas emissions can be reduced substantially. However, thisacclaimed environmental benefit is almost never quantified in an objective way. Oreven worse, it is roughly estimated that the reduction in environmental burden interms of percentage should more or less resemble the cement replacement level.The lacking of an objectively quantified environmental score for these low-cementconcrete types is in a way rather surprising because the required assessment toolto achieve this goal is certainly available and quite generally accepted under thename life cycle assessment (LCA). True, LCA was originally not developed for theconstruction industry. Moreover, at the start it was far from a well-developedmethodology. The study of environmental impact of consumer products began inthe late 1960s and early 1970s when environmental issues like resource and energyefficiency, pollution control, and solid waste became issues of broad public concern.1,2 Initially, those studies were not much more than simple comparisonsbetween products to see which one was better. Soon it was recognized that formany of these products the largest portion of the environmental impact was notcaused by its use, but by its production, transportation, or disposal.1 One of the firstpublished examples of system analysis quantifying the resource requirements, emissionloadings and waste flows of a production chain from “cradle-to-grave,” datesfrom 1974. The study was conducted by the Midwest Research Institute for the USEnvironmental Protection Agency.3 In fact, it was a follow-up of a study performedby the same institute for the Coca Cola Company in 1969 already, to enable anenvironmental comparison between different beverage containers. In the subsequentyears, extensive efforts were done to harmonize and standardize LCA. It resultedin the publication of the ISO standards on LCA4,5 and the development ofsome important impact methods (e.g., Center of Environmental Science (CML)6,Sustainable and Nonconventional Construction Materials using Inorganic Bonded Fiber Composites.As such, the whole methodology had gained substantialimportance by the first decade of the 21st century. It is also in this period that theLCA approach drew the attention of the construction sector.8 Moreover, environmentalpolicy all over the world started to become more and more life cycle based,especially with respect to carbon footprinting. These specific circumstances convincedthe Concrete & Environment Research Group of the Magnel Laboratory forConcrete Research of Ghent University to dedicate more research efforts to quantifyingthe environmental impacts related to cement and concrete production using LCA.It resulted in a thorough understanding of the actual sustainability of concrete withhigh volumes of the cement replaced with fly ash (FA), an industrial by-product ofcoal-fired electricity production.913 The functional unit (FU) choice and allocationof impacts approach related to industrial by-products were identified as very importantissues when performing an LCA study on concrete. They have been addressedthoroughly in the first two case studies included in this book chapter (Section 9.4 and9.5). Studying the high-volume FA concrete, also helped to gradually fine-tune theLCA methodology for other novel concrete types. As such, a third case study couldbe included in which the environmental impacts related to the incorporation of naturalflax fibers in concrete are assessed (Section 9.6). Prior to the actual case studies, thenecessary background on LCA of concrete, the studied concrete compositions, andthe natural flax fiber are provided (Sections 9.2 and 9.3).Nowadays, numerous introduction sections of scientific articles and books publishedon potentially “green” concrete with high cement replacement levels includeoften nothing more than a rather vague general justification for the researchconducted. Usually, their authors state that because at least 50% of the ordinaryPortland cement (OPC) is replaced with by-products from other industries, cementrelatedgreenhouse gas emissions can be reduced substantially. However, thisacclaimed environmental benefit is almost never quantified in an objective way. Oreven worse, it is roughly estimated that the reduction in environmental burden interms of percentage should more or less resemble the cement replacement level.The lacking of an objectively quantified environmental score for these low-cementconcrete types is in a way rather surprising because the required assessment toolto achieve this goal is certainly available and quite generally accepted under thename life cycle assessment (LCA). True, LCA was originally not developed for theconstruction industry. Moreover, at the start it was far from a well-developedmethodology. The study of environmental impact of consumer products began inthe late 1960s and early 1970s when environmental issues like resource and energyefficiency, pollution control, and solid waste became issues of broad public concern.1,2 Initially, those studies were not much more than simple comparisonsbetween products to see which one was better. Soon it was recognized that formany of these products the largest portion of the environmental impact was notcaused by its use, but by its production, transportation, or disposal.1 One of the firstpublished examples of system analysis quantifying the resource requirements, emissionloadings and waste flows of a production chain from “cradle-to-grave,” datesfrom 1974. The study was conducted by the Midwest Research Institute for the USEnvironmental Protection Agency.3 In fact, it was a follow-up of a study performedby the same institute for the Coca Cola Company in 1969 already, to enable anenvironmental comparison between different beverage containers. In the subsequentyears, extensive efforts were done to harmonize and standardize LCA. It resultedin the publication of the ISO standards on LCA4,5 and the development ofsome important impact methods (e.g., Center of Environmental Science (CML)6,Sustainable and Nonconventional Construction Materials using Inorganic Bonded Fiber Composites.As such, the whole methodology had gained substantialimportance by the first decade of the 21st century. It is also in this period that theLCA approach drew the attention of the construction sector.8 Moreover, environmentalpolicy all over the world started to become more and more life cycle based,especially with respect to carbon footprinting. These specific circumstances convincedthe Concrete & Environment Research Group of the Magnel Laboratory forConcrete Research of Ghent University to dedicate more research efforts to quantifyingthe environmental impacts related to cement and concrete production using LCA.It resulted in a thorough understanding of the actual sustainability of concrete withhigh volumes of the cement replaced with fly ash (FA), an industrial by-product ofcoal-fired electricity production.913 The functional unit (FU) choice and allocationof impacts approach related to industrial by-products were identified as very importantissues when performing an LCA study on concrete. They have been addressedthoroughly in the first two case studies included in this book chapter (Section 9.4 and9.5). Studying the high-volume FA concrete, also helped to gradually fine-tune theLCA methodology for other novel concrete types. As such, a third case study couldbe included in which the environmental impacts related to the incorporation of naturalflax fibers in concrete are assessed (Section 9.6). Prior to the actual case studies, thenecessary background on LCA of concrete, the studied concrete compositions, andthe natural flax fiber are provided (Sections 9.2 and 9.3).B