Master's thesis maritime engineering
The construction of infrastructure must not only be evaluated in terms of construction costs and technical solutions, but also considering the overall environmental impacts, including greenhouse gas emissions, of the infrastructure’s construction and long-term use.
The master's thesis examined how high are the CO2 emissions relating to the construction of a quay structure. Three different methods of quay construction – sheet piling, caisson structure and elevated pier slab – were compared on the basis of an environmental lifecycle assessment. For this purpose, the lifecycle phases relating to the production of the construction materials and the structure’s construction process were examined (see phases A1 to A5 in Figure 1). The three structure types were pre-designed and evaluated considering the same conditions in terms of service life, subsoil conditions, dimensions, location and so on.
"The master's thesis opened my eyes to the topic of carbon footprints in the construction industry and how much there is still to do!” Kai-Julian Hendler, former student trainee
Evaluation
The analysis showed that the sheet piling structure has the lowest CO2 emissions, with a value of approx. 45 tonnes of CO2-equivalent (t CO2-eq) per linear metre of berth. The caisson structure and the pier slab have CO2 emissions of approx. 61 and 86 t CO2-eq per metre, respectively. For comparison: About one tonne of CO2 is emitted per person flying from London to New York and back. Furthermore, it could be shown that the largest proportion of greenhouse gases (about 80 %) is emitted during the production of the construction materials – especially Portland cement and steel. The mobilisation and demobilisation of construction equipment and site facilities, together with the transport of construction materials, contributes approx. 6% to 11% towards the total greenhouse gas emissions. A similar value is contributed by the quay structure’s construction phase.
The sensitivity analysis showed how innovative measures such as adapting the concrete mix design (reducing the proportion of Portland cement, replacing it with fly ash or blast furnace slag) and increasing the proportion of recycled steel can reduce the CO2 footprint by approx. 26% to 40%.
Limiting aspects
According to ArcelorMittal (2019), the availability of steel scrap can currently only cover around 22% of global demand for steel, but the proportion is expected to increase to around 40% to 50% by 2050. A proportion of 85% recycled steel was used in the sensitivity analysis of this study. However, given the limited supply of steel scrap, it is perhaps not realistic to assume such a high value. The relatively low availability of steel scrap emphasises the importance of the recovery/recycling of steel elements (lifecycle phase D) as the benefit can be partially or fully allocated to an existing project (Hammond & Jones, 2011). Among other things, it was investigated how a changed composition of the binder affects the concrete. For this purpose, the fly ash content and the blast furnace slag content of the binder were increased to 35% and 65% respectively. Concrete with a higher proportion of fly ash or blast furnace slag has lower early strength than concrete containing only Portland cement (The Concrete Centre, 2020). This can affect the construction schedule as it can increase the time required for the concrete to harden enough for the formwork to be removed. It is therefore important that designers and project managers work together with suppliers and contractors before the start of the project or in its early stages, in order to be able to evaluate the possible benefits and limitations of CO2 reduction in the concrete production.
