Användning av mer och grövre ballast för att reducera klimatpåverkan i grova betongkonstruktioner : En studie ur ett livscykelperspektiv

Sammanfattning

This thesis investigates how the use of more and coarser aggregate can reduce climate change in massive concrete structures, when examined from a life cycle perspective. Three construction methods were analyzed; 1) ready-mix concrete, with a maximum aggregate size, Dmax, of 16, 32 and 64 mm, 2) pre-placed aggregate concrete, using two different cement types, and 3) concrete with plum stones, combined with ready-mix concrete using maximum aggregate size Dmax 32 mm. Both the pre-placed aggregate and the plum stone material were assumed to be locally sourced. A life cycle assessment (LCA) was conducted, using climate impact measured by Global Warming Potential (GWP) in kg CO2e and a commuter ferry as a reference object. Qualitative interviews with industry representatives complemented the quantitative life cycle analysis. Using ready-mix concrete with Dmax 16 mm as reference, results show that an increase in maximum aggregate size to Dmax 32 mm reduced GWP with up to 8%, and a reduction of up to 16% when increased to Dmax 64 mm. While pre-placed aggregate concrete using CEM I resulted in a higher GWP compared to the reference, a substitution to CEM II reduced GWP with 23.6%. Concrete with 20% of the concrete volume replaced with plum stones, resulted in the greatest reduction of GWP among the studied cases, up to 26.4% for the concrete element. Decreased concrete volumes and use of locally sourced aggregate resulted in a reduction both in production and in transport-related emissions. A sensitivity analysis confirmed that logistical operation is dependent on the concrete type and that increased transport distances impact ready-mix concrete the most. Practical feasibility of coarse aggregate in concrete was found to be constrained by reinforcement density, pumpability limitations and aggregate fractions available locally. A trend toward self-compacting concrete was further limiting the use of coarse aggregate. The use of alternative construction methods was thought to be context dependent, but suitable for massive constructions when combined with local aggregate sources. The study concluded that the use of more and coarser aggregate in mass concrete structures show potential to reduce climate impact, but that additional research on necessary technology development is needed for the industry to realize the potential in actual construction, which is suggested for further research.