Open Access

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.

Admixtures are important constituents to enhance the performance of concrete. They allow for more efficient use of binders which can mitigate negative environmental impacts from producing cement-based materials. Commonly used rheology modifying agents like polycarboxylate ethers or cellulose ethers are synthetic or semi-synthetic, respectively. This requires additional energy consumption for their production and global supply chains particularly for many developing regions, which will be large consumers of concrete in the future. However, many locally available bio-based polysaccharides could be effectively used instead. These polymers are often overlooked by engineers and scientists due to their limited distribution and inherent complexity, yet they represent an underleveraged source of precursors for admixtures. This study investigates the action mechanisms of some bio-based rheology modifying agents, i.e., acacia gum and miscanthus gum, and provides a comparison to a conventionally modified starch. The results show that the mechanism of action of these polymers is closely related to the composition of the mixture, mixing regime, and the composition of the aqueous phase. Depending on the agent, either plasticizing or stabilizing effects on rheology can be revealed.

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.

As future populations are projected to boom, cement and concrete consumption in Africa is expected to explode. With increasing interest in the socio-economic development of this region tied to recent investment in production capacity by development banks, we investigate the current state of production, consumption and the related environmental impacts for cement in Africa. Trade and production statistics are used to map the source of production and understand regional material fluxes. A harmonized environmental impact model is assembled that represents the technology and energy sources of each area to model the production emissions from each unit of material. Herein, greenhouse gas (GHG) emissions as well as water demands, water consumption, particulate matter, and other notable air pollutants are modeled to provide information on climate related impacts as well as those directly related to human health. Median 2022 import reliance by country or area was ~37% with 15 areas fully reliant on imports. While GHG-related impacts are similar, there were shifts in particulate matter and water related impacts between imported and domestically produced materials. Together this model enables the exploration of potential impact shifting and raises important question about material sovereignty and the ability for local areas to regulate the embodied environmental impacts of the building material that are critical to future socio-economic development in their regions.

Chemical admixtures are an integral component of modern concrete and enable the careful tailoring of fresh and hardening properties. Herein we investigate candidate materials from the bioeconomy in idealized system and discuss the methodology as a possible rapid evaluation technique to categories the role of the candidate biopolymers at selected dosages.