Concrete is responsible for 8–10% of total anthropogenic CO2 emissions, with cement production accounting for over 60% of this contribution. Considering this environmental impact, the integration of sustainable and alternative materials as replacements for cement represents a promising strategy for emission reduction. Alkali-activated materials and/or geopolymers can be used as an alternative construction material and are formed by activating aluminosilicates such as fly ash, granulated blast furnace slag, and/or clays with alkaline solutions. The selection of precursors for geopolymer synthesis is strictly related to their local availability. Among these, activated clays have gained considerable attention, offering great potential for geopolymer production due to their widespread availability and composition. Albania has a great potential due to the weathering conditions, but very limited information is available. In this preliminary study case, different clays were collected from different areas across Albania and investigated for their reactivity and suitability as precursors for geopolymers after thermal treatment. These clays were subject to characterization, and their reactivity was assessed according to R3-bound water methods. Calcination of clays was performed at temperatures of 650 and 750 ℃ for 1 h. The results indicated that calcined clays from Albania can have potential to be suitable source materials in geopolymerization reactions and/or as supplementary cementitious materials.

In recent years, substantial progress has been achieved in the development of multifunctional cement-based composites, targeting improved energy efficiency and environmental sustainability while minimizing material depletion. Leveraging the high thermal capacity of these materials facilitates controlled heat storage and release, providing versatile applications in renewable energy management and heat regulation, influencing structural integrity and long-term resistance. Recent research has integrated phase change materials (PCMs) into these composites to harness their superior thermal energy density. This comprehensive review examines the latest experimental research findings on these hybrid materials, emphasizing their thermo-physical behaviour and influence on structural properties and durability. Furthermore, it provides an overview of PCM characteristics and their integration into cement-based matrices. It critically analyses the interaction between PCMs and the cement matrix, explaining effects on structural performance, hydration processes, and freeze–thaw mechanisms. Furthermore, the paper explores recent experimental techniques and protocols for measuring and assessing the structural and thermo-physical properties of these composites. By identifying key trends, the review aims to provide valuable insights into the design and optimization of cement-based composites with PCMs, ultimately enhancing energy efficiency and resource conservation.

Inverkan av betongens tidsberoende deformationer på basala egenskaper hos anläggningskonstruktioner är ansenlig.  Lastberoende deformationer (krypning) och lastoberoende (krympning) spelar stor roll. Betongens krypning och krympning kan därför inte förbises vid t ex analys och dimensionering med hänsyn till spännkrafter, andra ordningens beteenden hos slanka konstruktioner och vid uppkomst av egenspänningar och sprickrisker.

Information/data är begränsade för moderna betongers beteende m a p de tidsberoende deformationerna. Försöksdata, t ex beträffande tidig krympning av självuttorkning, är knapphändiga och det finns i Sverige i stort sett inga försöksresultat angående långtidseffekter under flera år, speciellt för krypning men även för krympning.

Skillnader finns i beräknade spännkraftsförluster mellan tillgängliga modeller. Detta är naturligt med hänsyn till de erfarenheter som framkommit vid litteraturstudien beträffande materialeffekter.

Concrete's ability to auto-repair the cracks reduces the need for maintenance and repair. Autogenous self-healing is an intrinsic property of concrete highly dependent on the binder composition. The urgent necessity to decrease CO2 emissions of concrete by replacing cement with “greener” materials provides challenges and opportunities for self-healing cementitious materials. This research aims to verify the self-healing behavior of environmentally friendly multi-component binders. An experimental study is conducted to test the effect of binder composition-related parameters (e.g., phase composition, porosity) and crack geometry on the self-healing efficiency of the “green” mortars. Cementitious materials with 50 wt.%cement replacement with limestone powder blended with fly ash, blast furnace slag, and silica fume are investigated. Sorptivity change, compressive strength regains, and crack closure after self-healing are used to quantify the self-healing efficiency. Quantitative analysis and correlations between chemical composition/microstructural features, geometrical crack characteristics, and self-healing measures are investigated. The results indicate that “green” binder composition affects the self-healing mechanism leading to different levels of performance recovery. Some SCMs-limestone binder formulations enable a better self-healing efficiency than pure OPC or OPC/limestone cementitious materials, presumably due to a synergistic effect between the limestone and the mineral additions. Correlation analysis indicated that geometrical complexity characterized by fractal dimension and tortuosity of the crack does not affect the external crack closure, whereas the fractal dimension and maximum crack width are correlated with the internal crack healing.

The effects of a partial replacement of Ordinary Portland cement (OPC) with three types of calcium sulfoaluminate (CSA) cements (40 wt% and 20 wt%) were investigated. The obtained results were generally in agreement with previously published data but with few interesting exceptions. Setting times were shortened due to the formation of ettringite. The maximum hydration temperature increased for concretes containing 40 wt% of CSA but decreased when 20 wt% replacement was used. The decrease was related to the deficiency of the available sulfates, which limited the formation of ettringite. The presence of extra anhydrite and calcium oxide was associated to the delayed establishment of the second temperature peak in contrast to OPC-based concretes. Their surplus delayed calcium aluminate and belite reactions, and triggered renewed formation of ettringite, C-S-H and portlandite. Effects of aluminum hydroxide were also indicated as possibly important, although not proved experimentally in this research. The slightly lower compressive strength measured for mixes containing 40 wt% of CSA were linked with more formed ettringite. The same factor was indicated as the key to the reduction of the total shrinkage in mixes containing 40 wt% of CSA and increased for the lower CSA replacement level. In that case, the insufficient amount of formed ettringite caused too small expansion, which could not efficiently mitigate or compensate the developed shrinkage.

Replacement of cement with supplementary cementitious materials (SCMs) is a proven method to reduce clinker in cement and contribute to decreased CO₂ emissions. Natural clays are commonly occurring materials that do not possess pozzolanic activity in their original state. Mechanochemical activation (MCA) can be an alternative and sustainable method to enhance their reactivity. In this study, the pozzolanic reactivity of three natural clays, originating from Sweden, was analyzed after the application of MCA in a planetary ball mill. Strength activity index (SAI), Frattini test, and conductivity test were used to evaluate the pozzolanic reactivity. All processed clays by MCA have achieved a SAI greater than 100%, while the Frattini test indicated an improved pozzolanic activity of samples containing a higher amount of clay minerals. The obtained results show that MCA could improve the pozzolanic reactivity, but the effect depends on the mineralogical composition and particle size of the clays.

The latest report from the Intergovernmental Panel on Climate Change made once again clear the urge to take immediate actions to reduce the emissions of carbon dioxide and other greenhouse gases. Among the UN Sustainable Development Goals (SDGs), Nr. 12 (“Ensure sustainable consumption and production of raw materials”) aims to improve the industrial sector and to ensure a high quality of life. Concrete is the second most used material after water and in its traditional form utilizes cement clinker, whose production contributes to 8-10% of the anthropogenic CO₂ emissions. Among the strategies to diminish the CO₂ footprint, use of supplementary cementitious materials (SCM) and alkali-activated materials (AAM) are currently considered the most efficient countermeasures.  

Within this framework, revalorization of poorly reactive sources by mechanochemical activation can contribute to the development of novel binders with decreased CO₂ footprint that can be utilized as partial or full replacement of Portland cement in concrete. Natural clays, mine tailings and air-cooled blast furnace slags (ACBFS), were activated in this study. Their applicability to be used in concretes as SCMs or/and AAMs was assessed. Natural clays are a mixture of various phases, whose compositions depends on weathering conditions. Naturally, they do not possess sufficient chemical reactivity to be utilized as SCMs. Similar properties possess mine tailings generated after extraction of precious elements, and slags produced in  blast furnaces of traditional steel plants.  

The present study aims to enhance the reactivity of these resources through mechanochemical activation (MCA) in a planetary ball mill. The process is considered a clean technology able to enhance the reactivity of crystalline materials without resorting to high processing temperatures or additional chemicals. MCA can induce amorphization, destroying the structure and breaking the bonds within the aluminosilicates and other minerals structure. The chosen parameters in the ball mill, as i.e. the filling amount, time of grinding, or speed of rotation, are strictly related to the degree of amorphization. Longer time of grinding, higher ball to processed powder (B/P) ratio, and higher grinding speeds generally increased the degree of the obtained amorphization. In such regard, an optimized process was chosen and further utilized to process all the poorly reactive resources. After MCA, the potential of clays and tailings as a SCM was investigated, while ACBFS was investigated as a precursor for alkali-activated materials. The achieved mechanical properties indicated a direct correlation between the enhanced amorphization degree of the mechanically activated clay and the increased strength values. The evaluation of SCMs was done by testing of their pozzolanic reactivity, enhanced after the mechanochemical activation. The reactivity was assessed by the strength activity index (SAI) and the Frattini test. Clays with higher content of clay minerals and tailings from the Kiruna mine deposit in Sweden showed increased pozzolanic reactivity and a great potential to be utilized as partial replacement of cement in concrete production. Furthermore, preliminary tests have shown that the alkali activation of the processed ACBFS produced solidified matrixes with considerable mechanical properties.   

Fine-grained soils often show a low bearing capacity as well as a high frost susceptibility. These aspects are a challenge for the needs of infrastructure. The addition of hydraulic binder to fine-grained soils is common worldwide to improve the soil properties for engineering purposes. The classical hydraulic binders are lime and cement, but nowadays more and more by-producs are used as well like e. g. fly ash, slag or filter dust. The binders are called “hydraulic” because they react with water. By this reaction new minerals are formed, connecting the soil particles together. This improves the properties of the soil: A strength increase is even visible when the curing takes place in cold environment or after freezing and thawing cycles. Another challenge that occurs in fine-grained sulfidic soils is their possible acidification, when aerated due to e. g. excavation or drainage. Sulfide minerals in contact with oxygen produce sulfuric acid. The low pH caused by this oxidation can mobilize metals from the soil minerals, with harmful consequences for the environment. The addition of lime or calcite is one possible action to improve acid sulphate soils for agricultural and aqua-cultural purposes. The high pH of the lime and calcite increases the buffer capacity of the soil. However, the addition of hydraulic binder to a fine-grained sulfide soil in order to improve both the engineering properties and to buffer the potential acidification is sparsely investigated. In the present publication a field investigation is described where a cement mixture with cement kiln dust (CKD) is used alone and in combination with a calcite-rich by-product from the paper industry to improve a fine-grained sulfide soil for possible usage in earthworks. Samples taken from the surface after one year show a buffering of the potential acidification. Additionally, a strength increase can be seen in the stabilized soil when compressed and stored in a tube in field conditions.

An efficient solution to increase the sustainability of building materials is to replace Portland cement with alkali-activated materials (AAM). Precursors for those systems are often based on water-cooled ground granulated blast furnace slags (GGBFS). Quenching of blast furnace slag can be done also by air but in that case, the final product is crystalline and with a very low reactivity. The present study aimed to evaluate the cementitious properties of a mechanically activated (MCA) air-cooled blast furnace slag (ACBFS) used as a precursor in sodium silicate alkali-activated systems. The unreactive ACBFS was processed in a planetary ball mill and its cementing performances were compared with an alkali-activated water-cooled GGBFS. Mixes based on mechanically activated ACBFS reached the 7-days compressive strength of 35 MPa and the 28-days compressive strength 45 MPa. The GGBFS-based samples showed generally higher compressive strength values.

Excavation and removal of unstable clayey soils before construction works, e.g., in infrastructure, residential or commercial buildings, etc., can generate vast amounts of waste clay deposits. Treatment of those clays to achieve suitable supplementary cementitious materials (SCMs) for use in concrete production can extensively contribute to a circular economy. Mechanical activation (MC) by ball milling has shown suitability to be an alternative and sustainable method to process clays and to obtain dehydroxylation at reduced temperatures and without the addition of chemicals. Furthermore, BM can induce amorphization, increased chemical reactivity, and improved pozzolanic properties. Amorphization of crystalline phases can be achieved also for poorly reactive materials such as air-cooled blast furnace slags (ACBFS), which can be further utilized as a precursor in sodium silicate alkali-activated systems. This study shows how mechanical activation is promoting the reactivity of clay and ACBFS, and their potential to be used as a replacement for cement in concrete production. Evaluation of the pozzolanic activity before and after treatment was performed for the treated clay, suggesting increased pozzolanic properties. While alkali-activated systems based on mechanically treated ACBFS reached, after 28 days, comparable compressive strength values with the commonly used ground granulated blast furnace slag (GGBFS)