The research, published in the journal Construction and Building Materials, examined whether red mud, a highly alkaline residue generated in enormous quantities by aluminum refining, could be combined with dredged sediment to replace a substantial portion of conventional Portland cement in concrete formulations. The team, led by Faber Chaparro and Mohamed Osman, both MSc and PhD graduates of 2026 respectively, along with their colleague Mohammad Almakhadmeh and supervised by Ahmed Soliman, associate professor in Concordia’s Department of Building, Civil and Environmental Engineering, estimated that the substitution could reduce greenhouse-gas emissions by anywhere from 25 to 50 per cent, depending on how the mixture is formulated. That range is significant because it suggests the approach is not a marginal improvement but a potentially transformative one for an industry under intense pressure to shrink its environmental impact.

The logic behind the study rests on a class of materials known as limestone calcined clay cements, often abbreviated as LC3, which have emerged in recent years as one of the most promising routes to lower-carbon concrete. Rather than relying almost entirely on clinker, LC3 blends combine clinker with calcined clay and limestone powder, allowing a large fraction of the traditional binder to be replaced while retaining most of the mechanical performance. The catch is that the clay must be of reasonable quality, rich in the reactive minerals that participate in the pozzolanic reactions responsible for strength development. Low-grade clays and dredged sediments, which are abundant and cheap, often fall short of that standard because they contain impurities and lack the reactive phases that make calcined clays useful binders.

This is where red mud enters the picture. Red mud is the caustic slurry left behind when bauxite ore is processed with sodium hydroxide to extract alumina, the feedstock for aluminum metal. It is produced at a rate of well over 150 million tonnes per year worldwide, and it accumulates in vast holding ponds that pose both environmental hazards and disposal costs for the aluminum industry. Chemically, however, red mud contains oxides of iron, aluminum, and silicon, along with residual alkaline compounds, several of which are precisely the kinds of constituents that can contribute to cementitious reactions if the material is properly activated. The Concordia researchers hypothesized that red mud could compensate for the deficiencies of low-quality dredged sediment, supplying the reactive components that the sediment lacks.

To test that hypothesis, the team first subjected both the red mud and the dredged sediment to a thermal treatment, heating them at 800 degrees Celsius. Calcination at this temperature drives off bound water and restructures the mineral phases, breaking down crystalline structures and creating amorphous, chemically hungry material that can dissolve and react in the alkaline environment of a hydrating cement paste. The researchers varied the duration of the heating and found that one hour produced the best overall results, maximizing the reactivity of the two materials without wasting energy on longer treatment. That finding matters for practical deployment, because the energy cost of the calcination step directly affects both the economics and the carbon accounting of the final cement.

With the activated materials in hand, the team prepared a series of blended cement formulations in which the treated red mud and dredged sediment replaced varying proportions of Portland cement. The mixtures were then evaluated for their physico-chemical performance, including the formation of hydration products and the mechanical strength of the resulting pastes and mortars. The results revealed a clear synergistic effect: red mud could offset some of the inherent limitations of the dredged sediment, promoting the formation of the compounds that give cement its strength. In several formulations, the combination of the two waste materials produced stronger products than mixtures containing the dredged sediment on its own, demonstrating that the pairing is more than the sum of its parts.

Equally important was the finding that dosage matters. The researchers observed that excessive amounts of red mud could reduce strength in some mixtures, a consequence likely tied to the material’s iron-rich composition and its residual alkalinity, which can interfere with normal hydration chemistry when present in high concentrations. At moderate levels, however, the red mud improved the structure and performance of the blended binder, refining the microstructure and supporting the development of strength-giving phases. This dose-response behaviour underscores a recurring theme in cement chemistry: supplementary cementitious materials are not interchangeable fillers but reactive components whose optimal proportions must be carefully calibrated for each combination of source materials.

The implications extend beyond the laboratory. Dredged sediment is generated continuously by ports, waterways, and harbours around the world, and disposing of it is a persistent logistical and environmental challenge, since contaminated sediments cannot simply be dumped back into ecosystems. Red mud, meanwhile, sits in accumulating stockpiles that occupy land and carry risks of alkaline leaching. If even a fraction of these two streams could be diverted into cement production, the construction industry would gain a low-cost, locally available source of binder materials while two waste-management problems would be partially solved at once. The emissions benefit compounds the appeal: because the waste materials displace both clinker and virgin raw materials, the approach attacks the carbon problem from two directions simultaneously, reducing the need for limestone calcination and for quarrying fresh clay.

The study, titled “Physico-chemical performance of red mud/dredged-based LC3,” was published on 12 September 2026 and received funding from the Natural Sciences and Engineering Research Council of Canada, the Fonds de Recherche du Québec – Nature et Technologies, and the Canadian Standards Association. The authors declared no known competing financial interests. As with any experimental cement research, the path from laboratory formulations to structural concrete will require further validation, including long-term durability testing, work on workability and setting behaviour, and assessment of how variability in waste-stream composition affects performance at industrial scale. But the core result stands: materials that industries currently pay to dispose of can be transformed, with a modest input of heat, into ingredients that make cement both stronger and substantially cleaner. In a sector where even single-digit percentage reductions in emissions are celebrated, a formulation capable of cutting greenhouse gases by up to half represents the kind of advance that could reshape how the world builds.

Subject of Research: Using red mud and dredged sediment as supplementary materials in low-carbon limestone calcined clay cement

Article Title: Research: Industrial waste can be a key ingredient in low-carbon cement, new Concordia study shows

Article References: Research: Industrial waste can be a key ingredient in low-carbon cement, new Concordia study shows. (n.d.). Original publication

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Keywords: cement, red mud, dredged sediment, LC3, clinker, carbon emissions, Concordia University, construction materials, aluminum industry, waste valorization, calcination, sustainable building