The co-calcination of bauxite residue (BR) with kaolinitic clay for use as a supplementary cementitious material (SCM) has shown to be a promising processing route to enable the incorporation of > 20 wt.% of BR in cement formulations. Previous research showed that, among several other improvements, the co-calcination process leads to a reduction in the content of soluble alkali, enhancing workability and maintaining the mechanical performance of mortars up to day 28. Building upon previous results, this work focuses on the strength development of blended cement mortars containing co-calcined BR 28, 56 and 90 days after mixing. Two different SCMs are included in the investigation: one produced using high-purity kaolin and another one produced under the same conditions but using a clay containing 40 wt.% kaolin, which is more advantageous from an economic perspective. The cement replacement ratio with SCM is 30 wt.%, but further replacement of cement with other mineral admixtures, e.g., blast furnace slag, limestone filler, and set regulator, is also explored. The results of this work show that the strength development of mortars containing co-calcined BR with kaolin continues up to day 90. Moreover, it is demonstrated that the use of lower grade kaolin to produce the SCM does not impair mechanical properties when the BR:kaolin weight ratio is maintained.

Adequate supplementary cementitious materials (SCMs) with an interesting influence on the strength of cement mortars can be obtained by co-calcining bauxite residue (BR) with kaolin clay. The process has proven its technical feasibility in lab scale for a variety of BRs and different grades of kaolin clays, under the EC funded ReActiv project and has been presented in ICSOBA 2022. In the present paper the co-calcination of BR with kaolin clay in an industrial pilot plant is reported. Using a 6 m long indirect heated rotary kiln located at MYTILINEOS, several tons of BR have been mixed with clay in a 70%-30% weight mix and calcined at temperatures between 700-800 C, in the length of the kiln. Heat of hydration obtained by R3 test using calorimetry at VITO confirms the activity of the calcined material, while further laboratory testing at Holcim validates its potential as a new SCM material that can replace part of the clinker used in cement formulations.

In emerging countries, Portland cement plays an extremely significant role in the expansion of infrastructure. Global cement production is expected to grow considerably in the next decades, heavily contributing to the global anthropogenic CO2 emissions, if the way of producing cement will not change. The use of supplementary cementitious materials (SCM) as a partial replacement of clinker in Portland cement is one of the main strategies adopted to reduce CO2 emissions by global cement industries. However, the availability of conventional SCM like blast furnace slag and fly ash is regional and globally limited compared to the demand for Portland cement. In Brazil, a country of continental dimensions with great regional differences, the same mitigation actions will not necessarily be applied in all regions and nowadays, in regions where slag and fly ash are not available, such as the Amazon, pozzolanic and Portland-composite cements are manufactured with up to 30 % calcined clays or 25 % limestone filler. An alternative for these regions would be the manufacture of cement with active or inert SCM from mining by-products. Some materials like the gibbsite-kaolinite waste (GKW) and the bauxite residue (BR) have demonstrated their potential use in previous studies. In this experimental investigation, blended cements were produced with clinker replacement levels of 50% by a combination of metakaolin produced from the calcination of GWK and bauxite residue. The results demonstrated the high mechanical efficiency of these binders compared to ordinary Portland cement. The incorporation of metakaolin provided very high compressive strengths, while the bauxite residue accelerated the clinker hydration and pozzolanic reactions. The combination of the two by-products from the aluminum chain resulted in an increase in both initial and long-term strength, allowing clinker replacements of up to 50% and reductions of 35% in greenhouse gas emissions and 50% in the consumption of non-renewable natural resources (NR2). The results are promising and noteworthy with respect to early-age compressive strengths, as they increase construction productivity, but also in minimizing the use of NR2. However, more in-depth studies on durability and dimensional stability are essential.

Most (estimated > 90%) of the world's concrete exhibits compressive strength of up to 50 MPa, with the remaining percentage divided between high- and ultra-high-strength concretes. These different compositions find applications in monolithic floors, paving blocks, ordinary concrete for columns and beams, urban furniture, and more, and are of great practical interest. It's important to note that a solution designed for a specific application and using certain raw materials may not be suitable for another purpose, particularly in highly demanding situations. Therefore, development efforts must be driven by the requirements of both fresh (before hardening) and hardened (aged) state properties. The combination of bauxite residue (BR) with Portland cement (PC) is closely linked to the key sustainability challenges facing the aluminium and cement industries. This integration is in line with the roadmap outlined by the International Aluminium Institute, which recognizes it as one of the most impactful applications for this residue. The focus of this project is to develop large-scale and low-cost applications for BR without the need for additional treatments, such as energy-intensive calcination or environmentally harmful additives. The research presented here, explores alternatives for incorporating a significant amount of BR into cementitious compositions (up to 116 kg/m³ of concrete, equivalent to 5.4% of total solid mass or 27% of cement mass) with compressive strengths in the range of 30 to 50 MPa. These compositions are intended to produce paving or monolithic concrete, suitable for various cementitious building components. In particular, the study used raw materials from the northern region of Brazil, considering logistical considerations. The material was easy to mould, showed satisfactory fresh and hardened (aged at 28 days) performance, and, as a considerable amount of residue was incorporated without compromising performance, it resulted in more environmentally friendly products.