Port Kembla, High-Density Geopolymer Concrete

Port Kembla Harbor, located on the New South Wales coast of Australia, is a critical maritime gateway supporting regional industry, trade and port operations. Like many coastal facilities, the harbor’s breakwaters are exposed to continuous wave attack, saltwater corrosion and increasingly severe storm events associated with climate change. Rising sea levels and changing wave climates are expected to increase the forces acting on coastal protection structures, creating a need for stronger, more resilient and environmentally sustainable infrastructure solutions. Traditional breakwater upgrades typically require large quantities of quarried rock or conventional concrete armor units, materials that are associated with significant environmental impacts and carbon emissions.

To address these challenges, researchers from the University of New South Wales partnered with NSW Ports and several industry organizations to develop and trial an innovative high-density geopolymer concrete armor unit system for Port Kembla’s northern breakwater (Mahmood et al., 2018; Mahmood et al. 2020). The project formed part of broader efforts to improve climate resilience while reducing the environmental footprint of coastal infrastructure. Rather than relying on ordinary Portland cement concrete, the project utilized geopolymer concrete manufactured primarily from industrial by-products, including fly ash, ground granulated blast furnace slag and steel furnace slag aggregates.

A key aspect of the project was material selection and sourcing. Unlike conventional breakwater construction, which often depends on large volumes of quarried rock, the Port Kembla project sought to maximize the use of recycled and industrial waste materials. Steel furnace slag aggregates were sourced from slag produced by BlueScope Steel and processed by Australian Steel Mill Services at Port Kembla. The mix also included natural sand (Mahmood et al., 2018). The binder was created using low-calcium fly ash from the Vales Point Power Station and the ground granulated blast furnace slag sourced locally within the steel industry and supply chain. By selecting materials that were already available as industrial by-products, the project supported circular economy principles and reduced demand for virgin construction materials. Australia generates millions of tonnes of fly ash and metallurgical slag annually, making these by-products a valuable alternative resource for infrastructure projects Mahmood et al. (2020).

Environmental considerations played a significant role in the material strategy. Similar to examples in Pacific Island nations where environmental regulations restrict the extraction of local coral aggregate and natural coastal materials, the Port Kembla project demonstrates how alternative or manufactured materials can replace environmentally sensitive resources. The use of steel slag and fly ash reduced the reliance on quarrying. Furthermore, the geopolymer binder substantially reduced cement consumption, lowering the embodied carbon of the armor units compared with conventional concrete solutions.

The higher density of steel furnace slag aggregates provided an additional engineering advantage. The resulting geopolymer concrete achieved densities of approximately 2,570 to 2,630 kg/m3, higher than typical normal-weight concrete (Mahmood et al., 2018). Increased material density improves the stability of breakwater armor units, meaning smaller units can provide equivalent protection against wave forces. The 2018 paper estimated that armor unit size could be reduced by as much as 40 to 50 percent for equivalent stability (Mahmood et al., 2018). Size, volume and mass reductions are not interchangeable. Smaller units may reduce material and handling costs, but no cost data were reported.

As part of the field trial, 17.4 tonne Hanbar armor units were produced for the northern breakwater. Compressive strength varied by pour and age: 28-day strengths of 35.3, 46.8 and 47.8 MPa were reported for the three pours (Mahmood et al., 2018). Thirteen armor units were fabricated in August 2018, with one retained ashore. The three-year follow-up found no spalling in splash-zone units, but field-batched specimens air-cured in the laboratory showed strength loss and spalling. These differences underline the need to distinguish exposure conditions and maintain material quality control (Mahmood, Zahid and Foster, 2025). The Port Kembla trial is an example of how coastal projects can test lower-carbon armor materials, and of the quality-control lessons such trials provide.