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Organisationseinheit der BAM
Balancing the Mechanical Performance and Environmental Sustainability of Fiber-Reinforced Concrete
(2025)
Fiber-reinforced concrete (FRC) can have improved durability and tensile properties, potentially enabling the more efficient use of concrete and lowering greenhouse gas (GHG) emissions. Yet, systematic quantifications of the environmental impacts of FRC, particularly when paired with changes to mechanical properties and the implications for material longevity, are limited. Herein, an assessment following the life-cycle assessment methodology for four common FRCs was performed, namely, those reinforced with polyvinyl alcohol (PVA), steel (ST), polypropylene (PP), and polyethylene terephthalate (PET). The analysis was bound to a cradle-to-gate scope, and solely virgin fiber material production was considered for the environmental impacts. Coupled changes in compressive and tensile strength, environmental impacts, and the role of material longevity and cost relative to unreinforced concrete were examined. Findings from this work show that, similar to unreinforced concrete, cement remains a key source of GHG emissions in FRC production. However, in FRCs fibers can drive additional emissions by up to 55%. Notably, PVA and ST led to the highest impacts and costs, which were minimal for inclusions of PP and PET. Yet ST contributed to the greatest benefits in flexural and compressive strengths. When the effects of longevity were integrated, FRC with PP reinforcement could offer desired emissions reductions with minimal increase in use period and cost, but the other fiber reinforcements considered may need to offer longer service life extension to reduce emissions compared with conventional concrete. These results indicate that FRC can enhance mechanical performance, but fiber type selections should be informed by the design life to achieve actual GHG emissions reductions.
Industrial sectors, especially those with significant global CO2 emissions like the cement and concrete industries, are striving to achieve net-zero emissions by 2050. It is anticipated that carbon dioxide removal will be required to meet these goals. Hydrated cement in concrete can react with atmospheric CO2 to form carbonate minerals (i.e. carbonation), and in doing so, act as a carbon uptake mechanism. This carbonation process can be accelerated via various engineering interventions, such as crushing concrete after demolition. In this literature review, we examine key parameters, including porosity, exposure conditions, CO2 concentration, curing methods, coatings, and the use of supplementary cementitious materials, that affect CO2 uptake in concrete to inform better quantification of life cycle emissions. These findings can inform the feasibility of implementing carbonation as a method for reducing emissions from cement-based materials and identify data limitations that need further study for future modeling efforts. Presently, it has been estimated that 9%–17% of concrete production emissions could be re-adsorbed during use and end of life. However, such estimates of uptake have only considered limited data sets, without fully addressing the comingled effects of the parameters impacting carbonation. Further, some carbon uptake modeling efforts may require input values that are not readily available, or may be challenging to repeat, and do not accurately account for carbon fluxes over the life cycle. Findings from this review highlight the importance of development of systematic approaches to assess cradle-to-grave life cycle assessments using dynamic carbon accounting when measuring concrete carbonation.
The Influence of Biochar on the Flow Properties, Early Hydration, and Strength Evolution of Paste
(2023)
In order to reduce the carbon footprint, biochar can be used as CO2 negative concrete constituent.The paper shows results of experiments with cement paste and mortar mixtures with 5%, 15% and 30% of cement volume replaced by biochar. The density of the char is measured with a pycnometer I dried and wet conditions, workability is assessed using a spread flow test, and hydration characteristics are measured using isothermal heat flow calorimetry. In addition strength results are presented. The results show that char does not interfere with the cement hydration at early ages, but the water entrapped in the particles can have a slight retarding effect. In general workability and strength were negatively affected by the presence of biochar. However, small amounts of biochar can even have a positive effect on strength without negatively affecting the other properties of the material. The fact that at dosages above 5% the performance specifications of paste and mortar deteriorated has a detrimental effect on the use of biochar as carbon sink in structural concrete.
