This study investigates the mechanical properties and microstructural characteristics of five concrete mixtures specifically designed for application in low and intermediate-level nuclear waste repositories. These repositories necessitate construction materials that not only offer durability and strength but also maintain a long service-life under the underground environmental conditions over extended period. The concrete mix design was formulated with a focus on optimizing durability and sustainability, incorporating supplementary cementitious materials such as silica fume and slag to enhance the concrete durability. Comprehensive microstructural analyses using petrographic analysis and Micro x-ray fluorescence (μ-XRF) provided insights into the hydrate phases and pore structure evolution, revealing that the concrete exhibits dense microstructures and low permeability, essential for reducing leaching and sulfate attack risks. Mechanical testing demonstrated high compressive strength and modulus of elasticity, showing the suitability of concrete mixtures for structural components in repository environment. Overall, the findings highlight the potential of this designed concrete mixture in meeting the demands of low and intermediate level nuclear waste storage, ensuring safety and stability while also supporting environmental sustainability using eco-friendly materials.
Chloride binding plays a major role with respect to chloride ingress. On one hand, engineering models often rely on "apparent" diffusion coefficients, which account for both the diffusion of chlorides in the pore solution and chloride binding. On the other hand, mechanistic models intend to consider the two phenomena separately. However, the inputs to model chloride binding are quite complex to acquire, because they require dedicated experiments that are usually only conducted for research purposes.In this paper, an approach is proposed to estimate binding parameters from chloride ingress profiles. First, the effective diffusion coefficient is measured with a chloride migration test. Then, a chloride profile from a diffusion test is fitted with a model where transport of free chlorides follows Fick's second law, and free and bound chlorides are linked by a Freundlich equation. Finally, the surface concentration and the Freundlich parameters are adjusted to obtain the best possible fit. The derived Freundlich parameters are fairly close to the ones measured in dedicated chloride binding experiments. A case study applying this approach to concrete elements exposed to seawater in a Danish harbour is also presented.
This study examines the benefits and limitations of different supply chain models for recycled concrete aggregates (RCA), a highly resource- and CO2-intensive material. Focusing on Sweden, it combines material science insights with policy analysis and logistics modelling to assess the potential of RCA in construction. RCA demonstrate strong reuse potential in both bound (new concrete) and unbound (road and backfilling) applications, with life cycle assessments indicating lower climate impacts than virgin aggregates. However, barriers to achieve circularity persist, including fragmented regulations, limited infrastructure, and weak market demand. Using qualitative data from industry actors and quantitative modelling, three scenarios are developed: high-utility reuse of elements, consolidated recycling into bound and unbound applications, and low-utility recycling for backfilling. Results highlight the importance of selective demolition, traceability, procurement models, and strategic placement of concrete material terminals. The study concludes that coordinated policy, logistics planning, and procurement practices are critical to scaling RCA adoption.
Calcium Sulfo-Aluminate (CSA) clinkers are predominantly tailored for specialized markets that require distinct properties such as accelerated strength development and shrinkage compensation, both of which are primarily associated with the presence of the ye’elimite phase. The commercial CSA clinkers constitute a high ye’elimite content from the use of raw materials such as pure alumina or bauxite, which is listed as a critical raw material by the European commission and therefore significantly increasing the production costs. This economic limitation renders CSA cement substantially more expensive than Ordinary Portland cement (OPC), thereby confining its use to small-scale application. These challenges may be addressed by exploring alternative alumina-rich industrial by-products or Al-rich residues characterized by Fe2O3 and SiO2 contents below 5% and Al2O3 content above 60 %, which hold the potential to fully substitute pure alumina or bauxite. Therefore, maintaining the high ye’elimite content of the CSA clinkers without the use of pure alumina or bauxite. However, incorporating Al-rich residues from the aluminium industry may pose a risk to the human health during clinker production due to its high dioxin content of ~ 35 ng TEQ kg−1, higher than the limit proposed by SINTEF of 10 ng TEQ kg−1. Therefore, future research direction should focus on initially the degradation technologies for dioxin removal from the raw material followed by evaluating the feasibility of using Al-rich industrial residues as the sole source of alumina in CSA clinker production, aiming to optimize their processing and performance while minimizing reliance on pure alumina or bauxite.
The simplest way to reduce global CO2 emissions linked to cement productions is to reduce the amount of clinker by partially replacing it with supplementary cementitious materials (SCMs). The availability of the most common used SCMs (e.g. fly ash), is, however, expected to decrease in the coming years. Extensive research is conducted to find new alternatives and ensuring long-term durability of concrete incorporating new materials is crucial for implementation. The impact of novel SCMs from Nordic countries on fresh and hardened properties as well as durability performance in mortar and concrete was studied. The composite cements analysed had a composition of 78 wt.% Portland cement, 18 wt.% SCM and 4 wt.% limestone. The investigated SCMs include natural materials such as clays and volcanic rocks (rhyolite and hyaloclastite), and industrial products such as fly ash, slag, oil shale ash, bio-fuel ash or bio-coal fly ash. All SCMs except oil shale ash had comparable performance to fly ash in terms of resistance to carbonation and chloride ingress, resistance to freeze-thaw scaling and mitigation of ASR. Concretes prepared with oil shale ash had considerably higher chloride ingress and no mitigating effect on ASR expansion.
