Merchant vessels' performance on brash ice plays an important role in navigation in fast ice conditions in Northern Baltic ports. Among many parameters, the piece size distribution and macroporosity of the brash ice influence the accuracy of the model simulations of ship performance in brash ice. These properties also govern the brash ice accumulation and consolidation in ship channels. The current work presents analyses of macroporosity and piece size distribution from three full-scale brash ice channels investigated during winters 2020–21 and 2021–22. The results provide insights into brash ice macroporosity and piece size distribution. Smaller brash ice pieces exhibited higher porosity. On each measured cross-section, the average macroporosity ranged from 1.4% to 23%, with standard deviations of 3.8% and 16%, respectively. Porosity variations were observed in relation to equivalent brash ice thickness, the number of ship passages, and cumulative freezing air temperatures. Total porosity and the channel's brash ice porosity initially increased with breaking events and then stabilized at approximately 23% and 30%, respectively, after 9 passages. In contrast, side ridge porosity increased initially (up to 23%) and subsequently decreased. The initial total, brash ice and side ridge maximal porosities after the breaking event were estimated equal to 25%, 35% and 30%, respectively. The first two channels, which were navigated a total of 9 and 10 times, had an average degree of brash ice consolidation equal to 0.84 and 0.76, and an average degree of side ridge consolidation equal to 1.1 and 1.0, respectively. The third channel, characterized by frequent navigation, exhibited a consolidation degree of 0.82 for brash ice and 1.35 in the side ridges. The average vertical piece size across all cross-sections ranged from 0.28 m to 0.52 m with standard deviations of 0.16 m and 0.25 m. The average horizontal piece size ranged from 0.33 m to 0.4 m with standard deviations between 0.2 m and 0.34 m. The horizontal piece size distribution of brash ice was best described by the probability density function of a three-parameter lognormal distribution.

Carpet fibres have demonstrated the potential to mitigate early-age cracking and improve tensile properties in concrete. However, a detailed analysis of the varied types of standard carpet fibres in reinforced concrete has been lacking. This study aims to bridge this gap by investigating the performance of concrete reinforced with widely used waste carpet fibres, namely Nylon, Polypropylene, Polytrimethylene terephthalate, and Polyester. The study employs fibres at 0.3 % and 0.5 % volume fractions with a 12 mm length. The research examines mechanical properties, shrinkage and cracking behaviour, pore structure, microstructure, and the ITZ. Results show that 0.3 % fibre volume yielded optimal performance based on GRA analysis. All fibre types reduced shrinkage compared to the control with no fibres. Nylon T1 at 0.3 % achieved a 22.3 % reduction at 90 days. Furthermore, fibre inclusion enhanced flexural and splitting tensile strengths up to 12 % and 39 % respectively due to fibre bridging, pore refinement, and reduced porosity. Notably, individual fibre mechanical properties influenced concrete performance significantly. Hydrophilic fibres exhibited a thinner 10 µm ITZ compared to 15 µm for hydrophobic fibres, contributing to denser interfacial regions and improved bonding. This study demonstrates the potential of carpet fibre-reinforced concrete as a sustainable solution, offering enhanced mechanical properties, shrinkage mitigation, and effective utilization of carpet waste, addressing critical issues in construction and waste management sectors.

Frost durability, a critical parameter for concrete, especially in harsh exposure regions, has been extensively researched, with almost four thousand papers published since the 1970s. However, a systematic mapping of this research is yet to be explored. This paper presents a novel approach based on Natural Language Processing (NLP) and machine learning to semi-automatically analyze the existing literature on frost durability of cementitious materials. The aim is to identify research gaps and provide insights for future work, offering a comprehensive understanding of the freeze and thaw (FT) research area. Data sets containing academic abstracts on FT tests have been created, and the identified articles are topically structured using a latent Dirichlet allocation (LDA) topic modeling approach. The publication volume associated with each topic over time has been quantified, providing an overview of the research landscape. The results show that NLP and t-SNE effectively review large volumes of technical text data, identifying 12 dominant themes in FT research, such as mechanical properties and material composition. Over recent decades, there has been a shift from focusing on structural performance to emerging topics like cracking and Supplementary Cementitious Materials (SCMs). Additionally, t-SNE and K-means clustering revealed four main clusters, suggesting future research should focus on the FT durability of eco-friendly materials, accelerated testing, and enhanced FT durability materials. These findings not only facilitate the identification of gaps and opportunities for future work but also have practical implications for developing more durable and sustainable concrete.

The study investigates the influence of multi-walled carbon nanotubes (MWCNTs) on the macro- and microstructure of cement paste (CP) subjected to thermal shock conditions. CPs with 0–0.3 % MWCNTs content, exposed to a sudden temperature load in a range 50–600 °C, were analyzed in terms of mechanical properties, chemical and phase composition, air pore structure, and microstructure of cement hydration products (Si/Ca, Al/Ca, portlandite, unhydrated part of cement). The research found the optimum MWCNT range to be 0.05–0.1 %, enhancing CP's thermal performance by strengthening cement hydration products and their cohesion, by more the nucleation effect than bridging effect. With the application of MWCNTs, the density of the solid cement phase increased, and the amount of the unhydrated part of cement decreased by up to 21.5 %, at 0.1 % MWCNTs content. Unfortunately, the increase in the MWCNTs content resulted in an increase in the pore volume in the worst case, up to 12.7 %, but it did not negatively affect the strength parameters. The MWCNTs effect caused an increase in tensile strength (fcf) by up to 41.0 % at temperatures above 400 °C, where in the most favorable case improvement in compressive strength reached 16.7 %. The study showed that MWCNTs as an admixture to cement composites is suitable for environments where there is a high variability in terms of thermal loads.

Mortar beams incorporating carbon nanofibers (CNFs), which were synthesized in situ on Portland cement particles, were used to produce nanomodified Portland cement sensors (SmartCem sensors). SmartCem sensors exhibited an electrical response comparable to a thermistor with a temperature coefficient of resistivity of − 0.0152/ °C. The highest temperature sensing was obtained for the SmartCem sensor, which contained ~ 0.271 wt.% of CNFs. The calculated temperature sensitivity was approximately 11.76% higher in comparison with the mortar beam containing only unmodified Portland cement. SmartCem sensors were used to monitor the cement hydration in large-scale self-compacting concrete beams. The measurements were conducted after casting for 7 days. Additionally, commercially available thermocouple and humidity sensors were used as references. The results showed that changes in electrical resistivity measured by the SmartCem sensor were well aligned with the ongoing hydration processes.

Mortar sensors were fabricated as beams incorporating different amounts of carbon nanofibers (CNFs) synthesized in-situ on cement particles. Changes in electrical resistivity were measured and compared to recorded changes in compressive stress, temperature, and humidity. Sensing mechanisms and corresponding models were developed. The findings of the study indicate that the piezoresistive effect is influenced by the critical concentration of CNFs inside the composite matrix and the tunneling effect. In addition, water absorption and desorption, as well as the amount of chemically bound water played an important role in humidity sensing. Thermal fluctuation-induced tunneling conduction was dominant for the temperature sensitivity.

Brash ice formation and accumulation occur at a faster rate in ship channels, harbours and turning areas compared to the surrounding level ice. Accurate prediction of brash ice thickness plays an important role in addressing operational challenges and optimisation of ice management strategies. This study enhances existing brash ice growth models by considering the effects of snow and accounting for brash ice expulsion towards the sides of ship channels at each passage. To validate the influence of these critical factors on brash ice thickness, three distinct ship channels located in the Bay of Bothnia, Luleå, Sweden, were investigated. For two test channels formed for study purposes, the slower growth rate of brash ice caused by snow insulation was more prominent than the brash ice growth acceleration caused by the snow–slush–snow ice transformation. In the third channel characterised by frequent navigation, the transformation of slush into snow ice played a more substantial role than snow insulation. In both test channels, the brash ice growth model performed optimally, assuming a 10% expulsion of brash ice sideways at each vessel passage. In the third, wider and more frequently navigated channel, a 1.2% brash ice expelling coefficient predicted well the measured brash ice thicknesses.

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.

Autogenous self-healing of post-fire damaged concrete enables structure performance auto-recovery leading to reduced repair costs, less generated waste, and lower CO2 emissions. In this paper, to improve the efficiency of this process and understand the underlying mechanism, the self-healing of 0.1 wt% MWCNT-modified and pure cement paste subjected to novel environmental stimulators was tested. High-temperature damage was induced at 200 °C and 400 °C, followed by a self-healing cyclic treatment with water, a mixture of water with phosphate-based retarding admixture, and limewater. The self-healing efficiency of the proposed solutions were compared based on crack closure, strength regains, porosity, and chemical composition changes. The surface crack closure after 200 °C varied between 33% and 60%, whereas for 400 °C, only retarding admixture exposure obtained over 50% crack closure and the most considerable decrease in average crack width of 33% for MWCNT-modified paste. The highest values of compressive strength recovery, equal to 18% and 14%, exceeding the intact specimen's compressive strength, were observed for the MWCNT-modified paste healed in water and limewater. Water exposure with an extended wetting phase enhanced the compressive strength recovery of the MWCNT-modified materials. Strong (r = 0.87) and moderate (r = 0.52) positive correlations were observed between temperature loading and compressive and flexural strength recovery parameters, respectively. Higher porosity and interconnected crack network, caused by high temperature, facilitated the self-healing process. Porosity changes before and after healing were pronounced in contrast to the amount of unhydrated cement, which did not exhibit noticeable changes. The healing mechanism included three processes: calcite formation, further hydration inside the cracks, and rehydration of the bulk cement paste.Previous article in issue

This study determined how replacing sodium nitrate-based antifreeze admixture (AF) with belite-calcium sulfoaluminate (belite-CSA) cement affects the early age properties of ecological concretes based on ordinary Portland cement (OPC) and ground granulated blast-furnace slag (GGBFS). Concrete specimens were cured at −15 °C and treated in various ways before testing, i.e., no treatment, stored at 20 °C for 12 and 24 h. Generally, the addition of belite-CSA cement shortened the setting time due to the rapid formation of ettringite. The incorporation of 25 wt% of antifreeze admixture (AF) to the OPC-GGBFS concrete cured at −15 °C partially inhibited ice formation and enabled the continuation of hydration processes. This trend was observed for all samples, independent of the applied AF after freezing curing. On the contrary, the addition of 20 wt% of CSA failed to inhibit the ice formation and increased the risk of frost damage for concretes despite the treatment after freezing. These concrete specimens had lower hydration, lower strength, and a more porous binder matrix. The microstructure of the binder matrix was significantly affected by the amount of CSA and extreme negative curing, followed by no notable recovery post-curing at room temperature. Therefore, pre-curing at room temperature for at least 6 h has the potential to avoid frost damage. Concrete containing 25 wt% AF combined with 12 h and 24 h of curing at 20 °C after removal from freezing and prior to testing could enhance the compressive strengths of all concretes. The renewed hydration was indicated as the main influencing factor.