This study examines climate-optimised reinforcement piling in weak soils, focusing on how the environmental impact of precast concrete piles can be reduced through partial cement replacement with fly ash. Cement production accounts for a large proportion of carbon dioxide emissions associated with the construction sector, while the need for deep foundations in soft clay soils is increasing as construction expands to areas with poorer ground conditions.The aim of the study is to investigate how fly ash concrete affects the dimensioning material properties of precast concrete piles and how changes in material parameters influence long-term deformation, deformation behaviour and long-term deformation capacity in soft clays. The study also examines the potential climate savings that can be achieved without reducing bearing capacity or long-term deformation behaviour.The work is based on an analytical and comparative approach using calculation models according to Eurocode 2 and Eurocode 7 together with material data obtained from previous research, standards and technical reports. A conventional reference concrete is compared with a climate-optimised concrete in which 30 % of the cement is replaced by fly ash.The theoretical part addresses concrete material properties, pozzolanic reactions in fly ash, soil–pile interaction and the geotechnical characteristics of soft clay. The calculations comprise axial capacity, deformation, creep effects and simplified life-cycle calculations of carbon dioxide emissions. The results show that fly ash concrete can reduce climate impact by approximately 30 % per pile through a reduced cement content, while the dimensioning bearing capacity is largely maintained. However, fly ash concrete exhibits greater creep, resulting in increased long-term deformation and indicating that deformation behaviour may become more critical in serviceability limit state design.The findings indicate that climate-optimised concrete mixtures can be used in precast concrete piles provided that changes in deformation behaviour and long-term effects are considered in the design process. Material optimisation therefore needs to be combined with geotechnical analyses to assess how altered deformation properties may influence pile behaviour over time.In conclusion, partial cement replacement with fly ash has the potential to reduce the climate impact of concrete piles in soft clay soils. However, careful design and consideration of long-term properties are necessary for practical implementation in precast concrete piles.