Finding viable replacements for cement in the drive towards developing sustainable concrete

By Dr Lee Yeong Huei

Reducing the carbon footprint within the construction industry has emerged as a critical focus for numerous researchers globally. Their efforts are primarily directed towards demonstrating the sustainability of various materials, technologies, systems, and concepts through life cycle assessments when applied within the industry.

These innovations encompass various aspects ranging from construction materials to methodologies. One noteworthy innovation involves the development of sustainable concrete, where numerous studies and reviews have aimed to identify various industrial waste materials as potential substitutes for cement or aggregate.

However, it’s imperative to recognise that the transition towards sustainable concrete cannot remain in the confines of academic research. Rather, it necessitates a concerted effort by both academia and industry to actively promote the exploration and implementation of sustainable concrete applications within the construction industry.

By embracing sustainable practices and prioritising the development and implementation of eco-friendly alternatives like sustainable concrete, the construction industry can play a pivotal role in mitigating environmental impact, reducing carbon emissions, and fostering a more sustainable built environment for future generations.

Moreover, beyond its environmental benefits, the adoption of sustainable concrete can also yield economic advantages such as cost savings over the long term, improved resource efficiency, and enhanced resilience to regulatory changes and market fluctuations. Therefore, it is paramount to initiate a comprehensive study of the potential applications of sustainable concrete and actively promote its adoption within the construction industry.

Ordinary Portland Cement (OPC), a key component of concrete responsible for binding aggregates together, is notorious for its significant environmental impact, particularly in terms of carbon dioxide emissions and energy demand during manufacturing. The cement production process emits a substantial amount of carbon dioxide into the atmosphere, contributing to approximately 6 per cent of global human-made carbon emissions.

This alarming rate of emissions poses a severe threat to the environment, highlighting the urgent need for alternative approaches in concrete production. Research efforts focused on the development and application of sustainable concrete have thus become a critical scientific and policy priority on a global scale. By exploring alternative materials and manufacturing processes, researchers aim to create concrete formulations that minimise carbon emissions while maintaining structural integrity and performance standards.

Recognising the environmental consequences associated with OPC, there is a growing imperative to develop sustainable alternatives that reduce or eliminate its use. One promising avenue involves the utilisation of truly green OPC-less concrete binders and supplementary cementitious materials (SCMs) to partially substitute OPC in concrete mixes. This approach aims to mitigate the environmental footprint of concrete production by reducing the reliance on OPC and incorporating environmentally-friendly substitutes.

SCMs, which can replace a portion of the cement in concrete mixes, include waste products from various industries such as the metallurgical, agro-industrial, and food processing sectors. By repurposing these waste materials as SCM substitutes for cement, concrete producers can significantly lower or even eliminate net carbon dioxide emissions associated with concrete production.

The chemical effect of industrial waste materials plays a pivotal role in their suitability as cement replacements. Materials such as rice husk ash (RHA), palm oil fuel ash (POFA), ground granulated blast furnace slag (GGBS), and fly ash (FA) are classified as pozzolanic materials due to their high silica dioxide content, which enables them to react with calcium hydroxide present in cement.

This reaction generates additional hydration products within the concrete matrix, thereby enhancing its strength. However, the strength development in concrete mixes utilising these industrial waste materials may not strictly follow conventional trends, primarily due to the filler effect.

The particle size distribution of the waste materials significantly influences the concrete’s strength. Finer particles lead to denser packing within the concrete matrix, resulting in improved strength. Conversely, larger particle sizes fail to adequately densify the concrete, leading to reduced strength performance. Therefore, the observed decrease in concrete strength beyond a certain replacement level can be attributed to larger particle sizes that do not contribute effectively to densification.

Moreover, the drop in strength beyond the optimum replacement level can be attributed to the dilution effect. As the replacement level increases, there is a corresponding decrease in the amount of cement present in the mix, leading to a shortage of hydration products essential for concrete strength development. This dilution effect becomes more pronounced as the replacement level surpasses the optimal threshold, resulting in diminishing returns in terms of concrete strength.

The exploration of industrial waste materials as potential replacements for cement in concrete mixes has garnered significant attention from researchers worldwide. Numerous reviews and studies have been conducted to identify the optimal range of replacement for various industrial waste materials. As discussed earlier, industrial wastes possessing similar chemical composition and particle size distribution to cement exhibit promising potential for cement replacement in concrete mixes.

However, before these industrial waste materials can be widely adopted in the construction industry, it is essential to conduct comprehensive evaluations of their mechanical properties and durability. This thorough examination ensures that the resulting concrete meets the requisite performance standards and can withstand the rigours of real-world applications.

At Curtin Malaysia, a steadfast commitment to sustainability underscores its endeavours to make meaningful contributions to the industry. Central to this commitment is its researchers’ ongoing exploration of innovative approaches to repurpose industrial wastes, thereby mitigating environmental impact and promoting resource conservation.

Through interdisciplinary research initiatives, researchers at Curtin Malaysia and partner institutions collaborate to identify viable pathways for the utilisation of industrial waste in construction materials.

This involves comprehensive investigations into the chemical, physical, and mechanical properties of various waste streams to ascertain their suitability and performance in construction applications. The researchers at Curtin Malaysia actively engage with industry stakeholders, government agencies, and community partners to foster collaboration and knowledge exchange in the pursuit of sustainable construction practices.

Through the exploration of industrial waste second life applications, they endeavour to reduce local industrial waste, promote resource efficiency, and create a more sustainable future for generations to come.

Concrete casting and testing

Dr. Lee Yeong Huei is a senior lecturer in the Department of Civil and Construction Engineering and Head of the Structures and Materials Research Cluster at Curtin Malaysia’s Faculty of Engineering and Science. He is actively involved in various research activities in the fields of numerical analysis, structural analysis, concrete materials, interlocking blocks, fire engineering, sustainable construction and engineering education. Sustainable concrete is one of his research focus areas. In addition, he has jointly published more than 50 journals, conference papers and book chapters related to his research. Dr. Lee can be contacted by email to yeong.huei@curtin.edu.my.