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September 16, 2024
Tim Walker, Managing Director of CoGri Limited (New Zealand), shares his views on the difficulties the commercial flooring industry may face from the introduction of Low-Carbon Concrete and how a systematic approach is the best way forward.
The construction industry is undergoing a significant transformation as the need for sustainability drives the adoption of Low-Carbon Concrete (LCC) in new building projects. While the benefits of reducing carbon emissions in concrete production are clear, this shift has introduced several challenges that affect construction quality, particularly in surface finishes.
In my practice (predominantly in New Zealand and Australia), we have observed an increase in surface delamination and other finishing issues, likely related to the increased use of LCC mixes.
The American Society for Concrete Contractors has documented challenges with finishing mixes using Portland/limestone cement concrete – one of the current strategies employed in LCC concrete in New Zealand.
I believe the risks and challenges with LCC mixes can be managed and overcome systematically.
By aligning finishing and curing techniques with the specific characteristics of local LCC mix designs, project teams can deliver high-quality results while supporting the industry’s commitment to sustainability.
Low-carbon concrete typically replaces a portion of traditional Portland cement with supplementary cementitious materials (SCMs) such as fly ash, slag, or silica fume and/or uses a Portland/limestone cement blend.
While these replacements can significantly reduce the embodied carbon, they also alter the performance characteristics of the concrete.
In New Zealand and Australia, we’ve seen several key issues arise, including:
Delamination occurs when the surface layer of concrete separates from the underlying structure. With LCC, this risk is heightened due to slower setting times and altered bleed water characteristics. Surface crusting, which traps bleed water, can exacerbate the problem, especially if finishing techniques aren’t adapted to the slower-setting concrete.
Many cement replacements, while reducing carbon emissions, can slow down the strength gain of the concrete. While this isn’t always an issue, it can become problematic if the construction programme requires early access or loading. To avoid potential delays, early strength gain requirements must be carefully evaluated during the planning stages.
Contractors have also reported challenges in achieving high-quality surface finishes. Sticky mixes and variable setting times complicate the finishing process, and achieving a uniform appearance—particularly in burnished or polished finishes—can be difficult without adjusting both the concrete mix and the finishing method.
Using SCMs affects the bleed water profile, which can lead to an increased risk of plastic shrinkage cracking. Without the use of anti-evaporative sprays, these cracks can form during the critical early hours of concrete setting, undermining the structural integrity and aesthetics of the final surface.
We have also seen that with certain SCM mixes, abrasion resistance can be particularly sensitive to poor curing practices. This is especially important for high-performance floors where durability and long-term wear resistance are critical.
The key to successfully working with Low-Carbon Concrete is to take a systematic approach, tailoring the mix design and construction process to the specific challenges LCC poses.
Here are several best practices to help mitigate these risks:
Different LCC mixes perform differently, and finishing techniques must be adjusted accordingly.
Early collaboration with suppliers and mix designers ensures that finishing methods are matched to the specific behaviour of the LCC mix being used.
This alignment is critical to avoid issues like floor delamination and surface finish inconsistencies.
Proper curing is crucial for Low-Carbon Concrete, particularly for mixes with high proportions of SCMs. Best practices include:
For more technical guidance, FACE Consultants recommend referencing The Concrete Society’s TR74, which provides further insight into curing practices to optimise performance, particularly concerning abrasion resistance.
To ensure smooth project execution, test pours and mock-ups are highly recommended. These allow the project team to evaluate the performance of the mix under real-world conditions and trial the necessary finishing and curing techniques. Identifying potential issues early allows contractors to adjust their approach before moving to full-scale pours. This ensures both the structural integrity and aesthetic quality of the concrete.
Where early strength gain is essential, planning for the slower strength development associated with some SCM replacements is crucial. In some cases, programme adjustments may be necessary to meet early loading or access requirements.
FACE Consultants have a deep understanding of the challenges and opportunities associated with Low-Carbon Concrete.
Over the years, we have worked with clients across Australia and globally to run trials that de-risk the use of LCC in demanding environments.
One example is our recent commission with a major listed industrial property fund in Australia where the trials we conducted on green concrete slabs provided valuable insights into how supplementary cementitious materials can be used successfully in high-performance flooring.
By combining specialist contractor involvement, comprehensive testing, and an evidence-based approach, we help clients optimise mix designs and finishing processes. This ensures that both sustainability goals and construction quality are met, even in time-critical or technically challenging projects.
Low-carbon concrete represents the future of sustainable construction, but it brings with it a new set of challenges.
The risks of concrete delamination, poor surface finishes, and slower strength gain can be mitigated through a carefully structured approach. By tailoring finishing and curing techniques to the specific properties of LCC mixes, contractors can overcome these issues and deliver superior results.
At FACE Consultants, we are committed to helping clients navigate these challenges while reaping the benefits of sustainable construction practices. Through our expertise and proactive risk management strategies, we ensure your projects meet both sustainability objectives and the highest standards of construction quality.
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