The Risks of Low-Carbon Concrete in Construction

Jul 9
3 min read

This CQA article examines the potential risks of using low-carbon concrete in construction projects, incorporating insights from the broader discussion on green concrete - we are not advocating restrictions on low-carbon concrete - we are suggesting that specifiers and contractors approach it carefully - and understand that it may not behave in the same way as traditional concrete.

we are not advocating restrictions on low-carbon concrete - we are suggesting that specifiers and contractors approach it carefully - and understand that it may not behave in the same way as traditional concrete

Concrete has been the backbone of modern construction for decades, providing unmatched versatility and durability. However, its production comes at a significant environmental cost, with traditional cement—an essential component—contributing approximately 8% of global carbon dioxide emissions. To mitigate this impact, the construction industry has turned to low-carbon and green concrete as a sustainable alternative.

While these innovations offer significant benefits for reducing emissions and promoting sustainability, they also present challenges and risks that must be carefully considered.

Performance Variability of Low-Carbon Concrete

Low-carbon concrete often incorporates supplementary cementitious materials (SCMs) such as fly ash, slag, or silica fume. While these materials can enhance specific properties like durability, their performance can vary based on their source and mix proportions.

This variability may cause:

inconsistent concrete strength,
extended setting times, and
durability issues,

which may impact buildability in unintended ways particularly in projects where precise performance characteristics are critical.

For instance, in green concrete applications, the use of industrial by-products like fly ash or slag can result in varying performance characteristics. These differences necessitate additional testing and tailored finishing techniques, which can increase time and costs.

Key Risks/Challanges of Low-Carbon Concrete

Floor Delamination in Specific Applications

One notable risk of low-carbon concrete, particularly in warehouse or industrial settings, is the potential for floor delamination. This issue arises due to slower setting times and altered bleed water characteristics in low-carbon concrete, which can make it more susceptible to separation between layers if finishing techniques are not adapted.

For large-scale, high-traffic applications, this risk could compromise the durability and functionality of the surface.

Slower Strength Development

Traditional concrete gains a significant portion of its strength in the first 28 days. Low-carbon concrete, which often substitutes Portland cement with SCMs, typically exhibits slower strength development. This delay can affect construction schedules, especially in projects requiring rapid construction or early loading of structural elements. Builders may need to extend timelines or adopt specific curing methods to ensure proper strength development.

Material Availability

The production of low-carbon concrete relies on industrial by-products like fly ash and ground granulated blast furnace slag (GGBS). However, the availability of these materials is not guaranteed, especially as industries such as coal-fired power plants and steel manufacturing adopt decarbonisation measures. Limited supply can lead to material shortages, increased costs, and challenges in scaling up low-carbon concrete production for widespread use.

Lack of Universal Standards and Definitions

A significant challenge with low-carbon concrete is the absence of universally accepted definitions and standards. Terms such as "low-carbon" or "green concrete" are often used interchangeably, leading to confusion and inconsistencies in their application. This lack of clarity can make it difficult for clients, designers, head contractors, subcontractors, and regulators to assess and specify appropriate materials, potentially delaying project approvals.

Compatibility with Existing Construction Practices

Many construction practices, equipment, and standards have been optimised for traditional concrete. The introduction of low-carbon concrete often requires adjustments to these methods, including changes in formwork design, curing techniques, and material handling. For example, the slower setting times of green concrete may necessitate retraining construction crews to avoid improper finishing, which could lead to defects like cracking or delamination.

Uncertain Long-Term Performance

While low-carbon concrete offers promising performance in laboratory settings, its long-term behaviour in real-world conditions remains less understood compared to traditional concrete. Concerns such as water resistance, carbonation depth, and durability in chemically aggressive environments need further research and validation. For example, magnesium oxychloride cement (MOC), a potential alternative to traditional cement, has historically suffered from poor water resistance, although ongoing research aims to address this issue.

Conclusion

Low-carbon and green concrete are critical innovations in the push for sustainable construction. These materials offer significant environmental benefits by reducing carbon emissions, conserving natural resources, and repurposing industrial waste. However, their adoption is not without risks. Issues such as performance variability, material availability, regulatory challenges, and market acceptance must be addressed to ensure their successful integration into construction practices.

The construction industry must adopt a balanced approach, combining rigorous testing, updated standards, and ongoing research to mitigate these risks. By doing so, low-carbon concrete can play a pivotal role in creating sustainable, durable, and environmentally friendly infrastructure for future generations.