Harnessing timber residue for earth-friendly concrete

The Next Big Thing: Harnessing timber residue for earth-friendly concrete

The notorious environmental impact of traditional concrete is now widely recognised. The urgent need for a sustainable shift is paramount.

The substantial carbon emissions from its production demand innovative solutions. Yet concrete remains a stalwart in construction due to its affordability and structural reliability. It’s within this paradox that my associates and I are exploring a paradigm shift, picturing a construction landscape where timber residue not only mitigates environmental concerns but also redefines the essence of sustainable building materials.

Even though our research is predominantly focused on the structural advantages of this new composite element, it also reveals positive implications for resource management, including economic viability and sustainability within the construction domain. Expanding on my ongoing research at Macquarie University – after my previous work at the University of Adelaide, and KU Leuven in Belgium – the synergy between timber and concrete not only complements but also enhances various benefits of this composite element. So, let’s unlock the untapped potential of timber residue, paving the way for a future where sustainable construction takes root from the heart of our forests.

Why minimise the use of concrete in construction? And why incorporate timber residue? Data sheds light on these questions.

Australia is predicted to have around 5.6 million tonnes of log harvest residues resulting from the processing of 28.6 million cubic metres of log harvest available for further utilisation in 2050. This amount is expected to be higher for the sawmill residue – 5.6 million tonnes for every 11.3 million cubic metres of sawlogs. In Europe, the numbers above are obviously much higher. According to the Global Forest Sector Outlook 2050, the maximum volume of wood industry residues in Europe may amount to 873 million cubic metres in 2050.

Concrete pole with wood chips visible in cross-section
Timber waste incorporated into concrete for a more sustainable future. Credit: Tohid Ghanbari-Ghazijahani

My goal is to capture the attention of the engineering community and environmentalists, encompassing researchers, practitioners and stakeholders. This will be achieved by evaluating the underutilisation of significant amounts of timber residue and emphasising its potential integration into concrete for two reasons. Firstly, it tackles a substantial economic issue, where timber residue is underused and often sold for burning, making this option less economically viable. Secondly, the integration aligns with addressing the growing environmental concerns associated with conventional concrete usage.

Beyond the well-known issue of CO2 emissions, our research sheds light on less-recognised yet critical factors contributing to resource depletion, especially the extraction of sand and gravel. This not only results in material stock reduction but also disrupts ecosystem balance, causing habitat fragmentation, and leading to issues such as erosion, sedimentation, and water quality impacts due to sediment runoff.

Now, let’s get structural! Concrete and timber emerge as allies, sharing a remarkable quality – a high compressive strength that, in most cases, forms the backbone of structural engineering. When compared to steel and concrete, structural timber exhibits a strength-to-weight ratio that surpasses structural steel by 20% and exceeds non-reinforced concrete by 4-5 times in compression. As we explore the synergy of concrete and timber, the integration of timber chips into concrete structures takes centre stage, propelled by the power of their combined features.

Picture this: lower weight, optimised utilisation of timber residue, minimised concrete volume, and enhanced ductility stand as the driving forces behind this groundbreaking idea.

Let’s unlock the untapped potential of timber residue.

Using timber in concrete decreases the overall weight of the structure, which (a) improves safety and (b) yields economic benefits. But how? In general, lighter structures exhibit increased resilience against earthquakes. The amount of sideways forces generated by earthquakes depends on the mass of the structure. As a result, lighter structures undergo less stress during seismic events, which helps them better withstand the impact of earthquakes. You might ask: what if a structure is located in an area invulnerable to seismic activity? Well, resilience is not the only benefit of the new composite. The timber-concrete composite necessitates a lower amount of material in both columns and foundations, thanks to the reduced self-weight of the stories above. This directly enhances economic efficiency by minimising construction materials.

Our future research is expected to focus on elaborating possible manufacturing processes, and different sizes of timber particles, which leads to optimal concrete mix designs to enhance the composite’s mechanical properties. A thorough life cycle assessment is expected to measure the environmental advantages throughout the lifespan of structures, considering embodied energy and end-of-life and recycling considerations.

Collaboration with industry partners is deemed necessary to enhance the production of timber-concrete composites and incorporate them into real-world projects in the construction sector, which will, in turn, allow us to evaluate long-term performance and durability. Engaging with stakeholders, including contractors and policymakers, is crucial to encourage the adoption of this environmentally friendly alternative in the construction industry.

The Next Big Thing will take place not by shutting down the concrete industry but by strategically reducing the concrete from construction and substituting it with greener alternatives.

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