Developing ECO2: a performance based ecological and economic framework and tool for sustainability assessment of concrete

Hafez, Hisham Tarek (2021) Developing ECO2: a performance based ecological and economic framework and tool for sustainability assessment of concrete. Doctoral thesis, Northumbria University.

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The use of concrete is associated with immense negative environmental impacts. More than 50 billion tonnes of aggregates are extracted annually for use in concrete, which presents high risks of depleting natural resources. Moreover, concrete has an embodied carbon footprint of 350 kg eq CO2/m3 on average of which 90% is attributable to the production of ordinary Portland cement (OPC). Although this is less than that of steel and most polymers per unit mass, the intensive use of concrete results in an alarming 7% share of the global carbon emissions. Therefore, increasing interest is being directed towards producing sustainable concrete. Conducting a Life cycle assessment (LCA) is a widely accepted tool to assess and compare the acclaimed environmental gains of these sustainable concrete types, while calculating the base line cost of each of these mixes could suffice for economic comparisons. However, sustainability is a multifaceted concept and in order to validate the sustainable of a concrete mix, multi criteria sustainability frameworks are needed. The critical examination of the only two frameworks found in the literature that fits this description, MARS-SC and CONCRETop, showed the need to develop a new one that covers their gaps, which inspired the main contribution in this PhD project.

A novel ECOnomic and ECOlogical assessment framework for concrete (hence the name ECO2 which also refers to the symbolic carbon dioxide formula) was created with the following distinguishing features:

1. The scope specified for the LCA study is selected as Cradle-to-Grave in order to account for the whole life cycle of concrete. Therefore, the LCA inventory data, for which sitespecific primary data is prioritized, would include upstream data such as the impact allocation from previous processes from which the raw materials originated and downstream data such as the demolition and disposal impact of concrete.
2. The ECO2 framework considers the amount of carbon sequestration, which is the term used to describe how much carbon dioxide is absorbed by concrete from the environment. The accurate calculation of the carbon footprint of a concrete mix is vital for its absolute environmental impact assessment, but would soon in the near future also affect its economic impact when carbon taxation becomes a normal practice.

Aside from filling the technical gaps of the sustainability assessment method, the main contribution the ECO2 framework brings is a shift in the philosophy related to the inclusion of the concrete performance in the process. In both reviewed frameworks (MARS-SC and CONCRETop), concrete performance is assessed as a separate pillar of sustainability perpetuating that the higher performance is rewarded with a higher sustainability index value. Instead, the ECO2 framework brings forward a two layered performance based methodology that promotes a value of resource efficiency. First, the user sets a minimum requirement for the workability and strength depending on the project specifications. The second layer is to correlate the expected service life of each qualifying concrete mix to the required service life of the concrete application within the project through a factor N. This factor, for which the minimum value is 1, is then multiplied by the functional unit used for the LCA to ensure that the economic and ecological assessment are not only accurate but also truly reflective of sustainability. An MS excel tool was also developed to self-validate the ECO2 framework in what could be labelled as a methodical contribution. Finally, three case studies were conducted using the newly developed ECO2 framework as follows:

1. The first case study was experimental using electric arc furnace slag as a precursor for alkali activated concrete and comparing its ECO2 sustainability index to a basic alkali activated concrete mix based on fly ash as a precursor. The case study showed that the deterioration in the mechanical properties of the novel alkali activated slag concrete largely overshadow the ecological and economic merits of recycling it.
2. The second case study was analytical using a database of more than 2500 data points to predict and hence optimize the functional, environmental and economic performance of blended cement concrete using the ECO2 framework. The mixes included varying combinations of five different types of SCMs based on plain and reinforced concrete scenarios of different strength and service life requirements.
3. The final case study was prepared to investigate an issue facing the UK Green concrete market which is the need to shut down all coal operated electrical power plants by 2022 and the subsequent absence of fly ash. The case study used the ECO2 framework to compare between importing fly ash from China, Germany and recycling locally existing stockpiled fly ash in the UK. The vital parameter in the comparison was the environmental and economic impact resulting from the transportation of fly ash from its source to the location of the concrete batch plant in the UK.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: Life Cycle Assessment, Sustainable concrete, Service life prediction, concrete durability, blended cement concrete
Subjects: H900 Others in Engineering
Department: Faculties > Engineering and Environment > Mechanical and Construction Engineering
University Services > Graduate School > Doctor of Philosophy
Depositing User: John Coen
Date Deposited: 26 Oct 2021 07:32
Last Modified: 26 Oct 2021 08:00

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