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Ground-granulated blast-furnace slag and dolomite are by-products from the steel manufacturing and rock crushing industries, respectively. The addition of dolomite to a slag-based geopolymer matrix can improve its engineering properties and reduce disposal problems. This paper discusses the effect of alkali solution concentration, curing temperature and different proportions of slag and dolomite on the strength of geopolymer mortars. For maximum strength, the optimum ratio of slag and dolomite was found to be 70:30. Microstructural studies such as scanning electron microscopy and X-ray diffraction showed the co-existence of both calcium silicate hydrate and aluminosilicate gel in the slag–dolomite geopolymer matrix. Improved durability properties such as high resistance to water absorption, sorptivity and chemical attack can lead to the application of slag–dolomite geopolymer matrices in all types of structural elements.

This study analysed the condition of the surface layer of valve stems made of 317Ti steel after polishing and burnishing. Surface roughness, microhardness, and residual stress tests were carried out. The tests were carried out to determine the effect of the condition of the surface layer (especially non-standard parameters of surface roughness) of the stems on the durability of valves and to determine the possibility of obtaining a favourable state by means of sliding burnishing. Significant differences were observed in the values of the roughness parameters that determine the tribological properties of the surface, and higher surface microhardness and residual compressive stresses were obtained after burnishing. The durability of the stem-graphite seal in a reciprocating movement was tested, and the failure-free operation time of valves with burnished stems was approximately four times longer, which is the premise for recommending sliding diamond burnishing as a finishing treatment for valve stems.

Walnut shells can be used as fuels in power plants directly or as biochars obtained by pyrolysis or torrefaction. They are an example of clean waste biomass which shows a low ash content and a high Net Calorific Value, making them excellent for energy recovery in industrial and non-industrial applications, such as in bakeries, restaurants, and homes. Their main inconvenience is their low bulk density. Densification is a possible solution that reduces the costs of transportation, handling, and storage. In this work, after the characterization of the walnut shells, briquettes were obtained using a hydraulic piston press briquette machine under different conditions to find the best quality without the need for previous grinding for pelletizing. This method features easy operation and maintenance, and the briquette shape could be adapted as desired. The quality of the briquettes was measured through their density and durability. After fixing a compaction pressure to obtain acceptable briquettes, the factors affecting their quality were studied: operating temperature, moisture content, and the presence of small amounts of walnuts. Good quality briquettes were obtained with a compaction pressure of 66 MPa, with densities around 1040 kg/m3, and durabilities higher than 94% when the process was carried at 140 °C. The greatest increase in durability was observed between briquettes obtained at room temperature and those obtained at 80 °C. The presence of small amounts of walnuts, common after the shelling process, improved the durability. Although water is necessary, briquettes obtained from biomass with only 1% of moisture showed better durabilities. Therefore, walnut shells are suitable for obtaining good quality briquettes according to the specifications of solid biofuels established in the standards, without the need for any pretreatment. This research was funded by the Agencia Estatal de Investigación (Spain) [grant number AEI/10.13039/501100011033], by the University of Alicante [grant number UAUSTI21-03] and by the Spanish Ministerio de Economia y Competividad [Research Project CTQ2016-76608-R].

9 figures, 2 tables.-- Supplementary information available., Concern for the perpetuation of stone monuments is deeply ingrained in humans; however, despite the attempts made in this field, there is still a great deal of effort needed to bring about advancements in the conservation of ornamental stone. Erosive agents, such as rain, extreme temperatures, and chemical and biological agents, threaten our stone heritage and gradually wear away buildings, sculptures, and other monuments found all around the world. Limestone and dolostone have been widely used throughout history, given their ease of extraction and workability. Nevertheless, these properties make them particularly vulnerable to the aforementioned erosive agents, for which the main solution at present is costly and time-consuming restoration. Given the scarcity of effective and durable agents to prevent the deterioration of ornamental and heritage stones, and as graphene oxide (GO) has recently shown impressive effectiveness for this task, this work will further explore the viability of GO as a protective coating for monumental dolostone. For this purpose, GO is sprayed over dolostone surfaces by water dispersion with no adjuvants. The coating performance is assessed in terms of thermal stress, optical inspection (structured light 3D scanner), colorimetry, leachate analysis, and electron microscopy. The main results show that spray-coated GO over stone surfaces creates a highly protective and durable barrier without altering their aesthetic qualities., This research received funding from the University of León (ULE-PoC 2018) and Fundación General de la ULE y de la Empresa (FGULEM) under projects 2019/00149/001 and 2020. This research was also funded through an awarded MICINN project (PID2020-120439RA-I00). The authors are also thankful to the “Applied innovation against climate change and other aggressions on stone monuments (PRESERVARTE)” project of the Regional Ministry of Culture and Tourism of Castilla y León, which will be used to complement this research in the future.

This study investigated the effect of hollow 304 stainless-steel fiber on the corrosion resistance and mechanical properties of ultra-high-performance concrete (UHPC), and prepared copper-coated-fiber-reinforced UHPC as the control group. The electrochemical performance of the prepared UHPC was compared with the results of X-ray computed tomography (X-CT). The results reveal that cavitation can improve the distribution of steel fibers in the UHPC. Compared with solid steel fibers, the compressive strength of UHPC with hollow stainless-steel fibers did not exhibit significant change, but the maximum flexural strength increased by 45.2% (2 vol% content, length–diameter ratio of 60). Hollow stainless-steel fiber could better improve the durability of UHPC compared with copper-plated steel fiber, and the gap between the two continued to increase as the durability test progressed. After the dry–wet cycle test, the flexural strength of the copper-coated-fiber-reinforced UHPC was 26 MPa, marking a decrease of 21.9%, while the flexural strength of the UHPC mixed with hollow stainless-steel fibers was 40.1 MPa, marking a decrease of only 5.6%. When the salt spray test had run for seven days, the difference in the flexural strength between the two was 18.4%, but when the test ended (180 days), the difference increased to 34%. The electrochemical performance of the hollow stainless-steel fiber improved, owing to the small carrying capacity of the hollow structure, and more uniform distribution in the UHPC and lower interconnection probability were achieved. According to the AC impedance test results, the charge transfer impedance of the UHPC doped with solid steel fiber is 5.8 KΩ, while that of the UHPC doped with hollow stainless-steel fiber is 8.8 KΩ.

International audience; Anaerobic digestion, a renewable energy source, is the degradation of organic waste into biogas, mainly composed of CH4 and CO2. The sector is expanding rapidly due to its multiple environmental and economic benefits. This process is implemented industrially in concrete structures that are in direct contact with the biowaste being digested and the gas produced. Both phases can damage concrete through (i) the presence of volatile fatty acids, dissolved CO2, ammonium, and microbial biofilm in the liquid phase, and (ii) high concentrations of CO2 and various concentrations of H2S in the gas phase. In order to develop more sustainable concrete biogas units, long-term, in-situ experiments were carried out in a semi-industrial scale digester to provide new insights into the performance levels and deterioration mechanisms of various low-CO2 binders, including alkali-activated metakaolin (geopolymer), alkali-activated slag (AAS), and supersulfated cements (SSC), in comparison to calcium aluminate cement (CAC) and Portland cement based matrices. In the running conditions explored, carbonation of the cementitious matrices was predominant over other deterioration phenomena in both the digester liquid and the gas phases. Alkali-activated metakaolin and calcium aluminate cement performed better with few degradations observed. Supersulfated cements and alkali-activated slag showed an intermediate behaviour with good performance in the acidic liquid phase but low performance in the CO2-rich gas phase.

This paper examines the effect on mechanical properties such as compressive strength, flexural strength, and dynamic modulus of elasticity (DYE) of different proportions of wollastonite (β-CaSiO3) and colloidal nano-silica (n-SiO2) partially replacing cement. Durability indicators (water absorption, sorptivity and sulphate treatment test) were also examined to ascertain the quality of hardened paste mixes with respect to the control mix. The regression models were found for mechanical properties using different parameters from the results obtained, and statistical relations were established and validated. Regression analysis shows the significance of every parameter considered and model for the prediction of mechanical strengths. Finally, the results were substantiated by the microstructural characterization by FESEM. β-CaSiO3 and colloidal n-SiO2 replaced cement by 15%, and 1.5%-6% with an offset of 1.5%, respectively at low (0.25), medium (0.40) and high (0.55) water/binder (w/b) ratio. FESEM micrographs showed dense Calcium-silicate-hydrate (CSH) gel and stratlingite (CASH) was formed by blended cement paste mixes containing β-CaSiO3 and n-SiO2. n-SiO2 at 3% and CaSiO3 at 15% replacements of cement (NS3 mix) was the optimum replacement level for the cement paste mix. Analysed regression model suggests that the models and parameters were found significant and can also be used for prediction (based on R2 values and p-value)., Este artículo examina el efecto sobre propiedades mecánicas como la resistencia a la compresión, la resistencia a la flexión y el módulo dinámico de elasticidad (DYE) de diferentes proporciones de wollastonita (β-CaSiO3) y nanosílice coloidal (n-SiO2) que reemplazan parcialmente al cemento. También se examinaron indicadores de durabilidad (absorción de agua, sorción y prueba de tratamiento con sulfato) para determinar la calidad de las mezclas de pasta endurecida con respecto a la mezcla de control. Se encontraron los modelos de regresión para las propiedades mecánicas utilizando diferentes parámetros a partir de los resultados obtenidos, y se establecieron y validaron relaciones estadísticas. El análisis de regresión muestra la importancia de cada parámetro y modelo considerados para la predicción de las resistencias mecánicas. Finalmente, los resultados fueron corroborados mediante la caracterización microestructural realizada por FESEM. El β-CaSiO3 y el n-SiO2 coloidal reemplazaron al cemento en un 15 % y entre un 1.5 % y un 6 % con una compensación del 1.5 %, respectivamente, en relación peso/peso baja (0.25), media (0.40) y alta (0.55). Las micrografías FESEM mostraron un gel denso de calcio-silicato-hidrato (CSH) y la estratlingita (CASH) formada por mezclas de pasta de cemento combinadas que contenían β-CaSiO3 y n-SiO2. Los reemplazos de n-SiO2 al 3% y CaSiO3 al 15% de cemento (mezcla NS3) fueron el nivel de reemplazo óptimo para la mezcla de pasta de cemento. El modelo de regresión analizado sugiere que los modelos y parámetros se encontraron significativos y también se pueden usar para la predicción (basado en los valores R2 y el valor p).

Along the Portuguese coastline, several military fortifications were built with the intention to protect the territory from the constant military threat from the sea. These constructions have been subjected, during centuries, to a very aggressive environment; the renders, whose main function is the protection of walls, are particularly exposed to such actions. Nossa Senhora dos Anjos de Paimogo’s Fort, better known as the Paimogo’s Fort, is one of these fortifications, built in 1674 and classified of public interest since 1957. Within the scope of the “Coast Memory Fort” Project of EEA Grants Culture Programme 2014–2021, promoted by the Municipality of Lourinhã, repair mortars are being developed for the preservation of the Fort, considering the physical–mechanical and chemical characteristics of the pre-existing mortars and of the substrate, as well as the aggressive environmental conditions. In this work, several mortar compositions, compatible with the original mortars and designed to resist the aggressive environment, are briefly described and their main physical and mechanical characteristics are analysed and compared in successive ages. Different binder mixes were used, and a fine-tuning of the aggregate was carried out. Assessment of sequential wetting/drying cycles’ effect on the mortar’s behaviour is also presented. The laboratory results reveal that mortars with additions of 30% of quicklime present the best behaviour (with the lowest water absorption and highest strength). Moreover, the substitution of part of the siliceous sand by limestone aggregate, in general, increases the mortars’ mechanical strength; however, the drying occurs slower, which could compromise the durability of these mortars if a good balance is not achieved.

Alkali-activated binders for concrete composites are emerging as the available low-embodied-carbon alternatives to ordinary Portland cement (OPC). Despite decades of research, the durability of alkali-activated concrete remains a concern, especially the issues related to chloride penetration and the potential for chloride-induced corrosion of embedded steel bars. In this study, a multi-phase, multi-component ionic numerical model is developed to investigate the chloride transport in alkali-activated fly ash/slag (AAFS) concretes. The model framework considers the porosity of concrete, the chloride binding, and the electrochemical coupling between multi-species. Based on the proposed model, the parametric studies of a series of influencing factors on both chloride transport and initiation time of reinforcement corrosion are performed and discussed. The results indicate that the slag content and the water to binder ratio are the dominant factors affecting chloride penetration and corrosion initiation time of steel bars in AAFS concretes due to their greater contributions to reduce the porosity, while the aggregate volume fraction presents a limited effect compared with other factors. The transport model proposed in this study brings insights to the prediction of the service life of alkali-activated reinforced concrete structures. ISSN:0008-8846

An effective pathway to achieve the sustainable development of resources and environmental protection is to utilize shale ceramsite (SC), which is processed from shale spoil to produce high-strength lightweight concrete (HSLWC). Furthermore, the urgent demand for better performance of HSLWC has stimulated active research on graphene oxide (GO) in strengthening mechanical properties and durability. This study was an effort to investigate the effect of different contents of GO on HSLWC manufactured from SC. For this purpose, six mixtures containing GO in the range of 0–0.08% (by weight of cement) were systematically designed to test the mechanical properties (compressive strength, flexural strength, and splitting tensile strength), durability (chloride penetration resistance, freezing–thawing resistance, and sulfate attack resistance), and microstructure. The experimental results showed that the optimum amount of 0.05% GO can maximize the compressive strength, flexural strength, and splitting tensile strength by 20.1%, 34.3%, and 24.2%, respectively, and exhibited excellent chloride penetration resistance, freezing–thawing resistance, and sulfate attack resistance. Note that when the addition of GO was relatively high, the performance improvement in HSLWC as attenuated instead. Therefore, based on the comprehensive analysis of microstructure, the optimal addition level of GO to achieve the best mechanical properties and durability of HSLWC is considered to be 0.05%. These findings can provide a new method for the use of SC in engineering.

This study proposed wavelet-based approaches to characterise random vibration road excitations for durability prediction of coil springs. Conventional strain-life approaches require long computational time, while the accuracy of the vibration fatigue methods is unsatisfactory. It is therefore a necessity to establish an accurate fatigue life prediction model based on vibrational features. Wavelet-based methods were applied to determine the low-frequency energy and multifractality of road excitations. Strain-life models were applied for fatigue life evaluation from strain histories. ANFIS modelling was subsequently adopted to associate the vibration features with the fatigue life of coil springs. Results showed that the proposed wavelet-based methods were effective to determine the signal energy and multifractality of vibration signals. The established vibration-based models showed good fatigue life conservativity with a data survivability of more than 90%. The highest Pearson coefficient of 0.955 associated with the lowest RMSE of 0.660 was obtained by the Morrow-based model. It is suggested that the low-frequency energy and multifractality of the vibration signals can be used as fatigue-related features in life predictions of coil springs under random loading. Finally, the proposed model is an acceptable fatigue life prediction method based on vibration features, and it can reduce the dependency on strain data measurement.

The durability assessment of additively manufactured parts needs to account for both surface-breaking material discontinuities and surface-breaking porosity and how these material discontinuities interact with parts that have been left in the as-built state. Furthermore, to be consistent with the airworthiness standards associated with the certification of metallic parts on military aircraft the durability analysis must be able to predict crack growth, as distinct from using a crack growth analysis in which parameters are adjusted so as to match measured data. To partially address this, the authors recently showed how the durability of wire arc additively manufactured (WAAM) 18Ni-250 maraging steel specimens, where failure was due to the interaction of small surface-breaking cracks with surface roughness, could be predicted using the Hartman–Schijve variant of the NASGRO crack growth equation. This paper illustrates how the same equation, with the same material parameters, can be used to predict the durability of a specimen where failure is due to surface-breaking porosity.

The combination of glass powder (GP) with pozzolanic additions to replace clinker can develop new types of binders (ternary cement) with improved physical and mechanical properties, thereby enabling a reduction in consumption of clinker and natural resources, and the minimisation of the carbon dioxide emissions. In this context, the present work is an attempt to study the influence of GP with two different specific surface areas (Blaine) GP30 = 300 m2/kg and GP45 = 450 m2/kg, combined with slag, on the mechanical behaviour and durability of mortars. The mechanical properties were investigated using compressive and flexural strength tests. Aspects related to durability were examined as well by water-accessible porosity, capillary absorption and sorptivity tests. The replacement rate of cement by GP varied from 10 to 20% and the proportion of slag was fixed at 10%. The results showed that a binary mortar made with 20% GP45 replacement showed increases in 90 day compressive strength, while ternary mortar with 20% GP45 + 10% slag replacement gave the best result. The same trend is also valid for durability properties examined in this study. The combined use of GP and slag at 30% replacement levels seemed to perform better compared with using GP alone.

Cement-based composites reinforced with steel bars are the primary material in the construction of infrastructure. Their durability in the service environment is thus a crucial topic. The application of bio-mineralisation technology shows great prospects in improving the properties of cement-based materials (CBMs). In this study, the underlying mechanism was explored by investigating the effects of various factors on the mineralisation gradient at the surface layer of CBMs. Four factors were studied to investigate the process of bacterial action: the absorption of carbon dioxide from the air, the transformation of carbon dioxide into HCO3−, the adsorption of Ca2+ from the pore solution of CBMs and the formation of calcium carbonate in pores, which results in a decrease in porosity. The results of calcium carbonate content and porosity indicated that bacteria could regulate the mineralisation gradient at the surface of CBMs. Numerical calculations and experimental measurements were also conducted for further verification.

The durability of ultra-high-performance concrete (UHPC) exposed to freezing–thawing (F–T) is closely associated with its micromechanical properties. In this study, the nanoindentation technique is employed to characterise the micromechanical properties of UHPC at different F–T cycles. It is observed that the indentation moduli of low-density calcium silicate hydrate, high-density calcium silicate hydrate, and calcium hydroxide in the studied UHPC decrease moderately with the decreasing ranges of 11.58, 14.56 and 3.3%, respectively, after undergoing 1500 F–T cycles. More micropores gradually form, converge and connect, and the volume fraction of micropores increases up to about 120%. The interfacial transition zone (ITZ) between steel fibre and cement paste is more prone to act as the weakest zone than that between fine sand and cement paste. The thickness of ITZ enlarges from 22 μm of the unconditioned stage to 60 μm at 1500 F–T cycles. Based on the micromechanical properties obtained from the nanoindentation test, the modulus of elasticity values of UHPC under different F–T cycles are predicted using the multiscale homogenisation model. It is proved that the combined micromechanical characterisation and multiscale homogenisation technique is capable of predicting the macromechanical properties of UHPC and their changes under F–T action.

Graphical abstract CDs are utilized as crucial structure-directing agents to elaborately design 3D cross-linked rod-like structured Bi2Se3/CDs composites. Computational simulations combined with experiments demonstrate that such robust 3D framework and the existence of interface Bi-O-C bond can simultaneously enhance the intrinsic sluggish kinetics and structural stability, endowing Bi2Se3/CDs anode with fast-charging capability and durable cycling life. Download : Download high-res image (205KB) Download : Download full-size image Advanced electrode materials for fast-charging lithium-ion batteries are of great significance to next-generation energy-storage systems. Herein, three-dimensional (3D) hierarchical rod-structured Bi2Se3/carbon dots (Bi2Se3/CDs) composite is elaborately designed for fast-kinetics lithium storage. It is proposed that CDs-induced self-assembly growth and site-selective ion-exchange transform nanosheets into cross-linked architecture. Such robust 3D framework provides efficient channels for electron/ion transport and sufficient inner space for volume variation as confirmed by theoretical prediction. Notably, the existence of interface Bi-O-C bond would effectively enhance its inherent bulk electronic conductivity and accelerate ionic transportation by narrowing the bandgap and reducing the Li+ migration energy barriers. Consequently, intrinsic sluggish kinetics and structural stability are simultaneously improved, endowing Bi2Se3/CDs composite electrode fast charging/discharging capability of 165 mAh g−1 at 20 A g−1 (corresponding to charge in ≈27 s) and excellent long-term durability with the capacity of 502 mAh g−1 over 950 cycles at 1 A g−1. Moreover, the intercalation-conversion-alloying type lithium storage mechanism of Bi2Se3/CDs is revealed by in-situ XRD. This work provides a train of thoughts for other CDs-tailored composites with tunable morphology and structure.

Carbonation has been proven to be a promising way to improve the mechanism properties and durability of steel slag products. Carbonic anhydrase (CA) bacteria can promote the early-age carbonation process of γ-dicalcium silicate (γ-C2S), which is one of the main mineral phases of steel slag. In this study, one kind of alkali-resistant CA bacteria was chosen to investigate its effects on the carbonation process of γ-C2S. Results showed that the bacteria could increase the compressive strength of carbonated γ-C2S by 19.0% when compared with carbonated samples without bacteria. The main products of carbonated γ-C2S were vaterite, calcite and silicon dioxide gel. The addition of bacteria could only accelerate the deposition of calcium carbonate, while hardly changing the types and properties of the carbonation products. The accelerated carbonation was found to reduce the inward diffusion of carbon dioxide. In addition, reasons for the decline of the accelerating carbonation effect were explained by X-ray computed tomography testing results. However, CA bacteria could change the morphology of calcium carbonated during the carbonation process of β-C2S and further accelerate the hydration process of β-C2S. The pore structure could also be refined with the incorporation of bacteria.

Various properties of sodium ion batteries deteriorate severely when dropping to subzero temperature. Herein, we reveal an accelerated charge-transfer mechanism for high-voltage Na3V2(PO4)2F3 cathode through constructing weakly-solvating architecture, which endows it with superior temperature adaptability (capacity retention of C − 25 ∘ C / C 25 ∘ C reaches 90.8%). The resulting weak solvation effects synergistically lower the activation energy barrier for charge-transfer reactions, thus accelerating the kinetics at low temperature and increasing the energy density by ∼75 Wh Kg−1. Ab initio molecular dynamics calculations show that a weakly-solvating structure forms spontaneously in a low-concentration electrolyte (merely 0.3 M) and thereby facilitates Na+ desolvation process. Besides, visual TOF-SIMS confirms the construction of a dense and uniform cathode/electrolyte interface layer, which optimizes the interface chemistry and improves the interfacial kinetics. In-situ and ex-situ XRD also evidence a smaller degree of structural evolution of the Na3V2(PO4)2F3 cathode, which contributes to long-term durability (attaining a high capacity retention of 93.4% after 1000 cycles at −25 °C). Furthermore, it is demonstrated that under such extreme conditions the Na3V2(PO4)2F3||hard-carbon full cell functions well for over 300 h. These findings elucidate the roles of weak solvation construction in realizing faster kinetics for high-voltage cathodes and provide a feasible pathway for achieving more practical sodium ion batteries.

Socks, being a necessary item of clothing, must be comfortable and maintain their quality throughout their life. Since the applicability of modal fibers and microfibers, as well as yarns produced using unconventional processes, in sock knitting has been insufficiently researched, this paper evaluated three groups of medium sized socks knitted in a plain single jersey pattern produced with the highest percentage of ring, rotor and air-jet spun modal or micro modal yarns of the same linear density in full plating with different textured polyamide 6.6 yarns compared to conventional cotton socks. The sock quality was evaluated through an investigation of the physical properties, wear resistance and dimensional stability, as well as the water vapor absorption, air permeability and thermal resistance using the thermal foot model before and after five repeated washing and drying cycles, according to the proposed methodology. The results showed that the fiber fineness, the structure of the differently spun yarns and the sock plain knits, the polyamide content and the implementation of the pretreatment of the socks had an influence on the obtained results. The socks made from modal and micro modal yarns differed in their properties. Compared to cotton socks, they have better comfort properties, a generally better pilling resistance and, after pretreatment, a comparable abrasion resistance.

The effects of Nano-CaCO3 on the physical, mechanical properties and durability of cement-based materials were investigated in this paper. The mechanical property, durability and SEM microscopic tests of test blocks with different Nano-CaCO3 content were carried out. Results showed that Nano-CaCO3 could improve the flexural strength, compressive strength and impermeability of cement-based materials. When the content of Nano-CaCO3 is 2.0%, the strengthening effect of Nano-CaCO3 on the cement-based materials was optimized, and the flexural strength of cement-based materials after 3 d, 7 d and 28 d increased by 12.6%, 18% and 32.4%, respectively, compared with the reference group. When the content of Nano-CaCO3 exceeded 2.0%, the flexural strength of cement-based materials begins to decline with the increase of Nano-CaCO3 content. Similarly, when the content of Nano-CaCO3 reached 2.0%, the impermeability of the cement-based materials was also optimized, and the permeability height of the base group could be increases by 41.4%. At the early stage of hydration, the exothermic rate of cement with 2.0% Nano-CaCO3 content was higher than that of other contents. When the content of Nano-CaCO3 increased from 0 to 2.0%, the hydration exothermic rate increased gradually with the increase of Nano-CaCO3 content.

The chloride diffusion coefficient (Dcl) is one of the most important characteristics of concrete durability. This study aimed to develop a prediction model for the Dcl of concrete incorporating supplemental cementitious material. The datasets of concrete containing supplemental cementitious materials (SCMs) such as tricalcium aluminate (C3A), ground granulated blast furnace slag (GGBFS), and fly ash were used in developing the model. Five machine learning (ML) algorithms including adaptive neuro-fuzzy inference system (ANFIS), artificial neural network (ANN), support vector machine (SVM), and extreme learning machine (ELM) were used in the model development. The performance of the developed models was tested using five evaluation metrics, namely, normalized reference index (RI), coefficient of determination (R2), mean absolute error (MAE), and root mean square error (RMSE). The SVM models demonstrated the highest prediction accuracy with R2 values of 0.955 and 0.951 at the training and testing stage, respectively. The prediction accuracy of the machine learning (ML) algorithm was checked using the Taylor diagram and Boxplot, which confirmed that SVM is the best ML algorithm for estimating Dcl, thus, helpful in establishing reliable tools in concrete durability design.

Carbonation is a key mechanism for deterioration of reinforced concrete structures. In design for resistance to carbonation, the performance of mixes is often specified and measured in laboratory carbonation tests where initial carbonation is sometimes present in specimens. The coherent interpretation of results from carbonation tests is vital as they enable a more accurate prediction of the performance of concrete structures in situ. This paper assesses two different approaches to considering the initial carbonation depth when extracting the carbonation coefficient from results of carbonation testing. Experimental data is compared to models for either approach using least squares regression. Both linear and non-linear representations of the initial carbonation depth are shown to fit the data well. The non-linear approach gives a larger estimate of carbonation coefficient than the linear approach, and is more consistent with the mathematical derivation of the carbonation equation. The ramifications of this difference will be most significant when the initial carbonation depth is large relative to the depth of the carbonation front. The accurate modelling of carbonation progression underpins performance-based design of new concrete structures and the assessment of existing concrete infrastructure.

This research aims to improve the quality of recycled concrete fine aggregates (RFA) by using diammonium hydrogen phosphate (DAP). We aimed to understand the effect of DAP treatment on durability performance due to the carbonation action of mortars with the partial and total substitution of treated RFA. The results showed a maximum reduction in the RFA water absorption of up to 33% using a minimum DAP concentration due to a pore refinement as a consequence of the formation of calcium phosphates such as hydroxyapatite (HAP). The carbonation phenomenon did not have a significant effect on the durability of mortars with DAP-treated RFA, as we did not find a decrease in the compressive strength; the carbonation depth of the mortars with 100% treated RFA decreased up to 90% and 63% for a w/c of 0.45 and 0.50, in comparison with mortars with 0% treated RFA. An inversely proportional relationship was found between the accelerate carbonation and the compressive strength, showing that higher percentages of treated RFAs in the mortar promoted an increase in compressive strength and a decrease in the carbonation rate, which is behavior associated with a lower permeability of the cement matrix as one of the consequences of the microstructural densification by DAP treatment.

Most reinforced concrete structures serve under windy environments, and the carbonation resistance under that circumstance exhibits significant difference from that under the steady (no wind) environment. In this study, a windy environment was simulated using one self-developed wind tunnel, and alkali-activated slag/fly ash paste specimens were adopted for the carbonation under variant windy environments. Meanwhile, to reveal the effect of inner humidity on the carbonation, sliced alkali-activated materials (AAM) were mass-balanced first to variant humidity, and were then carbonated under a 2.5 m/s windy environment. With the assistance of computed tomography (CT), the structure of AAM at variant carbonation ages was rendered. The experimental result showed that wind is capable of promoting the exchange of moisture between the sample inside and the outer atmosphere, leading to faster carbonation as compared to that under no wind environment. When preconditioned to lower inner humidity, the carbonation rate of AAM was faster because the larger gaseous space benefited the intrusion of both CO2 and moisture. Furthermore, when preconditioned to lower humidity, the cracking extent of AAM was severer, which also contributed to the faster carbonation. Moreover, compared with ordinary Portland cement (OPC), the carbonation front on each instant 1D gray-scale value profile was broader, which suggested that the carbonation progress of AAM under windy environments was no longer controlled solely by diffusion. In addition, the gray-scale value on instant 1D profile fluctuated drastically, which verified cracking in AAM carbonated under windy environments. The current work not only deepens the understanding of the carbonation mechanism in-site (mostly under windy environments), but also helps to develop more environment-friendly construction material, with better durability performance.

Polymer concrete, which contains silica fume powder and vinyl ester resin as two replacements for Portland cement, has improved mechanical properties and durability compared to ordinary concrete. Thus, this kind of concrete is considered to be a high-strength concrete that is resistant to corrosion and chemical attacks. In this paper, the effects of the combination of silica fume powder and vinyl ester resin as two Portland cement replacements on the workability and slump value, initial and final water absorption, compressive and tensile strength, and failure and fracture paths of the polymer concrete have been investigated. All investigations have been based on 16 different polymer concrete mixture designs. The results indicate that the optimum percentages for a combination of silica fume and vinyl ester resin, which has the maximum compressive strength (34.26 MPa) and the maximum tensile strength (4.92 MPa), are a combination of 10% silica fume and 5% vinyl ester resin. To evaluate the durability of polymer concrete, the water absorption of all mixture designs has also been measured. Accordingly, the mixture design, which includes a combination of 15% vinyl ester resin and 5% silica fume, has a minimum initial and final water absorption equal to 0.62% and 1.95%, respectively.

Carbon nanotubes (CNTs) are extremely conductive and flexible, making them ideal for applications such as flexible electronics and nanoelectromechanical systems. However, in order to properly apply them in such devices, their long-term durability must be assessed. In the present study, we demonstrate cyclic loading of a thick MWCNT (175 nm) under axial compression, observed in situ under a transmission electron microscope (TEM). The force was applied via controlled displacement, while real-time TEM videos of the deformation process were gathered to produce the morphological data. The in situ observations combined with force–displacement curves revealed the onset of buckling instabilities, and the elastic limits of the tube were assessed. The MWCNT retained its original structure even after 68 loading–unloading cycles, despite observed clues for structural distortions. The stiffness of the tube, calculated after each loading cycle, was in a 0.15 to 0.28 TPa range—comparable to the literature, which further validates the measurement set-up. These in situ tests demonstrate the resilience of CNTs to fatigue which can be correlated with the CNTs’ structure. Such correlations can help tailoring CNTs’ properties to specific applications.

Both the discrete and continuous particle packing models are used to design UHPC, but the influences of a water film covering the particle surfaces on the compactness of the particle system were not considered in these models. In fact, the water film results in a certain distance between solid particles (DSP), which affects the compactness of the particle system, especially for cementitious materials with small particle sizes. In the present study, the mixture design method for UHPC was proposed based on the Fuller distribution model modified using the DSP. Then, the components of cementitious materials and aggregates were optimized, and the UHPC matrices with high solid concentrations were obtained. The results showed that the solid concentration, slump flow, and compressive strength of the UHPC matrix reached 77.1 vol.%, 810 mm, and 162.0 MPa, respectively. By replacing granulated blast furnace slag (GBFS) with quartz powder (QP), the flexural strength of the UHPC matrix was increased without reducing its compressive strength. When the steel fiber with a volume fraction of 1.5% was used, the slump flow, compressive strength, tensile strength, and flexural strength of the UHPC reached 740 mm, 175.6 MPa, 9.7 MPa, and 22.8 MPa, respectively. After 500 freeze–thaw cycles or 60 dry–wet cycles under sulfate erosion, the mechanical properties did not deteriorate. The chloride diffusion coefficients in UHPCs were lower than 3.0 × 10−14 m2/s, and the carbonation depth of each UHPC was 0 mm after carbonization for 28 days. The UHPCs presented ideal workability, mechanical properties, and durability, demonstrating the validity of the method proposed for UHPC design.

The article presents durability results for cement mortars made with the addition of slag from municipal waste incineration plants as a replacement for natural aggregate. The undertaken durability tests included frost resistance tests and evaluation of strength, microstructure, water absorption and abrasiveness before and after 150 freeze–thaw cycles. The work reveals that MSWI slag in amounts up to 50 vol. % caused deterioration in the workability and water absorption of cement mortars, regardless of the type of cement used. This, in turn, resulted in a reduction in the compressive and flexural strengths of the composites compared to mortars made with sand alone. Nevertheless, the use of a higher grade of cement, CEM I 52.5 R, resulted in an increase in compressive strength and thus increased the mortars’ frost and abrasion resistance. In addition, after the induced freeze–thaw cycles, mortars made with MSWI slag showed comparable or higher frost and abrasion resistance than those made using natural aggregate.

Manufactured sand is one of the effective ways to alleviate the extreme shortage of natural sand in the construction industry. This paper uses granite and limestone manufactured sand to study the effect of high fines content on the durability of high-strength manufactured sand concrete, and analyzes its influence mechanism by combining macro and micro test methods. The results show that the carbonation depth of manufactured sand concrete is the smallest when the fines content is 10%. When the fines content is less than 15%, the chloride and sulfate impermeability of concrete are improved effectively. Through macroscopic and microscopic tests, it is found that the main reason why fines can improve the durability of concrete is the filling effect. Too much fines will inhibit the hydration of cement and adversely affect the durability of concrete. Therefore, the fines content of high-strength manufactured sand concrete should be controlled within 5~15%, and the durability is the best when the fines content is 10%.

Long transport distances and extended storage of biomass pellets especially in humid environments provide a suitable setting for enhanced degradation in the form of moisture sorption, cracking and attrition. We developed an optically transparent, low-cost and environmentally friendly coating to reduce moisture sorption and storage degradation of pellets. The developed coating is a hybrid sol–gel, based on tetraethoxysilane (TEOS) and 3-glycidoxypropyl-trimethoxysilane (GPTMS) precursors. We coated two types of untreated and one type of torrefied wood pellets and stored them in a climate chamber during 1 month simulating a ship's hold, at a constant condition of 40 °C and 85% relative humidity. After 1 month of storage, the mean water contact angle increased by a factor of two compared to the uncoated ones. The lower wettability of the sol-gel coated untreated pellets compared to the non-coated torrefied pellets might provide an alternative to torrefaction.

Digital fabrication methods with concrete have been rapidly developing, with many problems related to component production and material control being solved in recent years. These processes produce inherently layered cementitious components that are anisotropic, and in many cases, produces a weak interface between layers, which are generally referred to as cold joints. While material strength at these interfaces has been well studied in recent years, durability has received less attention, even though cold joints can function as channels for aggressive agents, such as chlorides. This work presents a method using micro-X-ray fluorescence (μXRF) to image chloride ingress into layer interfaces of 3D printed fine-grained concrete specimens produced with varying layer deposition time intervals, and also compares it to neutron imaging of moisture uptake. The results show that cold joints formed after a 1 day time interval are highly susceptible to chloride ingress, and that curing conditions play a major role in how quickly interfacial transport can take place. The μXRF method is also shown to be useful for study of transport of chlorides in cold joints, due to its spatial resolution and direct analysis of an aggressive species of interest., Materials and Structures, 56 (3), ISSN:1359-5997, ISSN:0025-5432, ISSN:1871-6873

Three industrial aluminosilicate wastes were studied as precursors to produce alkali-activated concrete: (i) electric arc furnace slag, (ii) municipal solid waste incineration bottom ashes, and (iii) waste glass rejects. These were characterized via X-ray diffraction and fluorescence, laser particle size distribution, thermogravimetric, and Fourier-transform infrared analyses. Distinctive combinations of anhydrous sodium hydroxide and sodium silicate solution were tried by varying the Na2O/binder ratio (8%, 10%, 12%, 14%) and SiO2/Na2O ratio (0, 0.5, 1.0, 1.5) to find the optimum solution for maximized mechanical performance. Specimens were produced and subjected to a three-step curing process: (1) 24 h thermal curing (70 °C), (2) followed by 21 days of dry curing in a climatic chamber (~21 °C, 65% RH), and (3) ending with a 7-day carbonation curing stage (5 ± 0.2% CO2; 65 ± 10% RH). Compressive and flexural strength tests were performed, to ascertain the mix with the best mechanical performance. The precursors showed reasonable bonding capabilities, thus suggesting some reactivity when alkali-activated due to the presence of amorphous phases. Mixes with slag and glass showed compressive strengths of almost 40 MPa. Most mixes required a higher Na2O/binder ratio for maximized performance, even though, contrary to expectations, the opposite was observed for the SiO2/Na2O ratio.

The increase in concrete structures’ durability is a milestone to improve the sustainability of buildings and infrastructures. In order to ensure a prolonged service life, it is necessary to detect the deterioration of materials by means of monitoring systems aimed at evaluating not only the penetration of aggressive substances into concrete but also the corrosion of carbon-steel reinforcement. Therefore, proper data collection makes it possible to plan suitable restoration works which can be carried out with traditional or innovative techniques and materials. This work focuses on building heritage and it highlights the most recent findings for the conservation and restoration of reinforced concrete structures and masonry buildings.

International audience; This paper studies the behavior of four different calcined clay-based geopolymers under sulfuric acid attack and gives insights into their degradation mechanisms. Pastes were cast using metakaolin and meta-illite and were activated by two different alkaline solutions. Mineralogical and microscopic characterizations were performed on pastes before and after attack. Results indicated that all pastes were affected by low leaching of alkali cations, and thus by a linkage disequilibrium of the geopolymer network. Meta-illite based geopolymers, which had not been addressed in the literature until now, hold promise for improving the durability of materials in aggressive environments.

The attempt to face the limitations of wood-based materials, especially concerning the relationship with water, is still a considerable gap in research on this subject. The present work proposes the accomplishment of thermal treatment in fiberboard-type hardboard, using different temperatures and times, to evaluate the effect on the physical-mechanical properties. The parameters of the heat treatment were temperatures of 120 and 160 °C and times of 20 and 40 min. The hardboards were individually heat treated in a kiln. The characterization was performed from physical tests such as bulk density, moisture content, water absorption (2 and 24 h), thickness swelling (2 and 24 h); and mechanical properties of flexural strength. The treatment with a temperature of 160 °C for 40 min showed the lowest values of water absorption in 24 h (34%). Thickness swelling was lower compared to control, for all the treatments applied. Regarding flexural strength, the treatment that adopted the 160 °C for 20 min showed the highest MOR value (26.3 MPa). In general, the performance of heat treatments positively influenced the physical and mechanical properties of the hardboards, being an interesting alternative in the development of products for applications in internal environments.

Identification and rapid characterization of novel supplementary cementitious materials (SCMs) is a critical need, driven by shortfalls in conventional SCMs. In this study, we present a discussion of recently developed reactivity tests – the R3 test, the modified R3 test, the lime strength test, and the bulk resistivity index test. These tests measure reactivity parameters such as heat release, bound water, calcium hydroxide consumption, strength, and bulk resistivity. All tests can screen inert from reactive materials. To additionally differentiate pozzolanic and latent hydraulic materials, two parameters, for example, calcium hydroxide consumption and heat release, are needed. The influences of SCM bulk chemistry, amorphous content, and fineness on measured reactivity are outlined. Reactivity test outputs can predict strength and durability of cement paste/mortar/concrete; however, caution must be exercised as these properties are influenced by a variety of other factors independent of reactivity. Thoughts are provided on using reactivity tests to screen materials for concrete durability.

Corrosion is among the most observed phenomena that threaten the profitability of concentrated solar thermal power plants and constitutes a real risk factor for metallic materials. Solar reflectors are between the impacted materials by corrosion because they are composed of metallic reflective layers that can easily be oxidized in air. To avoid this, paint systems could be applied in the back of the reflective layers as a barrier, that prevents the diffusion of corrosive elements to the metal layer. Metallic structures that support those reflectors can also be easily corroded and are replaced with composite structures that are not affected by corrosion. However, the durability of the paint protection systems and the composite structures must be inspected to ensure their effectiveness in protecting solar mirrors against corrosion, since they are found in sites that are often characterized by arid conditions, which affects corrosion protection solutions. This work is devoted to study the corrosion aspects and the parameters that affect the resistance of the protection systems of glass solar mirrors and solar mirrors fixed on composite structures by the use of a real outdoor exposure facility on a coastal site. The results show the important role of the paint coating layers number on the protection against corrosion. Also, the role of edge protection and shape were highlighted. Solar mirrors fixed on composite structures show a weak resistance because of the degradation of the fixing glue which creates areas of retention of salts and moisture that cause an aggressive corrosion of the metal layers.

Nano-zeolite was used in the present study as a substitute for a part of lime and then inclusion polypropylene fiber in stabilized soil matrix to develop the soil stabilization method with lime and to improve the efficiency of this technique. In so doing, specimens of soft soil with 5, 10 and 15% of modifier L (lime), LZ (lime-nano-zeolite) and LZF (lime-nano-zeolite-fiber) were prepared, and were subjected to 1–7 wet-dry cycles. Then, microstructure and macrostructure tests were performed on the specimens. The results of the analyses, indicated that the optimal replacement of lime with nano-zeolite would be 40%, and the optimal amount of polypropylene fibers inclusion would be 1% in the stabilized soil matrix. Major reduction in lime consumption would yield a 40% increase in compressive strength and a 21% improvement in durability. The results also showed that the specimen containing 15%LZF would have excellent durability against environmental conditions and very good performance in terms of unconfined compressive strength (UCS), tensile strength and weight loss. Before and after applying 7 wet-dry cycles, the UCS increased by 39% and 16%, respectively. The results of this study indicate that LZF modifier is a suitable option for lime-based stabilization in areas under wet-dry cycles.

Recently, flexible electronic device technology has evolved beyond curved devices with the development of flexible/stretchable devices that can be crumpled or stretched. Both elasticity and durability are essential for these devices, which should have high-conductivity for antennas and repeatability for sensors. In addition, electronic-skins, which can have a direct impact on the human-body, should be harmless to the human-body and should not be deformed by contact with sweat or organic matter. In this study, PDMS substrates were used to satisfy the above conditions. PDMS is used to fabricate human-friendly, flexible/stretchable substrates, and it has excellent repeat durability characteristics. To improve the adhesion of these PDMS films and electrodes, conductive paste was produced based on PDMS resins of the same properties. In addition, two types of Ag particles were selected as conductive fillers because the electrode characteristics of the antenna application requires excellent conductivity, and conductive paste were produced using flake Ag, which could affect conductivity, and Ag nanoparticles that affect stretchability and repeatability. The paste was applied using a high-efficiency printing technique. The printed electrodes were cured in a thermal oven. For higher conductivity, photonic-sintering was carried out during post-processing. As a result, 1.1117×106 (S/m) had excellent conductivity, performed well in repeated tensile-durability experiments of 30% to 100 times, and produced a bow-tie antenna for the above electrodes. As a result of tensing up to 35% through a Network-Analyzer, there was no performance change in the resonance-frequency or return-loss values, and excellent electrodes were developed that would achieve excellent performance even if they are applied in the sub-frequency area of 5G-antennas in the future.

Novel multi-effect diffusion solar distiller (MED) was developed to improve the performance and reliability of conventional MED. Conventional MED consists of several flat metal plates (effect plates), each one equipped with a wick that serves as both an evaporation surface and a seawater feeding medium. However, the wick-plate structure has several problems such as higher manufacturing cost, lower performance, and durability deterioration. The new wick-free plates (WFPs) have many horizontally patterned grooves on an evaporation surface of a flat plate and can evenly spread and retain the feed saline water on the surface like as fabric wick. Experimental results showed that the performance of the proposed novel MED equipped with WFP (WFP-MED) is similar to that of conventional MED with wick-plate and even better productivity up to 7 % due to lower thermal resistance of WFP. Production stability with respect to the fluctuation of feed flow rate of WFP-MED is better than that of conventional MED. Moreover, WFP-MED is more effective in increasing productivity by increasing the number of effects. The 3-effect diffusion distiller with WFP has 0.84 of distillation efficiency under 10.8 MJ/m2 of solar insolation.

Poor durability of reinforced concrete structures can lead to serious structural failures. An accurate model to observe the effects of aggressive agents like carbonation, sulfate ingress, and seawater solutions on the solid phase assemblage will help designers and specifiers better understand how cement behaves in these environments. This paper presents the first steps in developing such a model using the PHREEQC geochemical software by accounting for alkali binding and dissolution. It also presents the use of discrete solid phases (DSPs) to account for the solid-solution behaviour of siliceous hydrogarnet and magnesium silicate hydrate (M-S-H). A new thermodynamic description of the vaterite phase has also been developed for this work using the cemdata18 thermodynamic database. The predicted phase assemblages of cements in these environments here agree with previously published findings using a different thermodynamic model supported with experimental data.

Sulfate attack in concrete structures significantly reduces their durability. This article reports the experimental findings on the effects of sodium sulfate on limestone calcined clay cement (LC3) in an alternate wet and dry media. The samples underwent wet–dry conditions of 28 cycles. Two types of LC3 were studied, one made from clay (LC3-CL) and the other made from fired rejected clay bricks (LC3-FR). The composition of each LC3 blend by weight was 50% clinker, 30% calcined clay, 15% limestone, and 5% gypsum. The reference compressive strength was evaluated at 2, 7, and 28 days of age. Then, ordinary Portland cement (OPC) and LC3-CL blends were subjected to alternate wet–dry cycle tests, immersion in a 5% sodium sulfate solution, or in water. For all exposed samples, sorptivity tests and compressive strength were done. The results showed that LC3 blends met the requirements for KS-EAS 18-1:2017 standard, which specifies the composition and conformity criteria for common cements in Kenya. The LC3 blend also had a lower rate of initial absorption compared to OPC. Additionally, LC3 blend also showed good resistance to sodium sulfate when exposed to alternating wetting and drying environment. OPC showed higher compressive strength than LC3 blends for testing ages of 2, 7, and 28 days. However, the LC3 samples utilized in the sodium sulfate attack experiment, which were later tested after 84 days, exhibited higher compressive strengths than OPC tested after the same period.

Ternary Portland cement usage with a high amount of cement constituents different from clinker can afford great climate change advantages by lowering the Portland cement clinker content in the final product. This will contribute to cutting greenhouse gas emissions to close to zero by 2050. Such ternary Portland cements can be composed of different amounts of ground granulated blast-furnace slag (GBFS), coal fly ash (CFA), and clinker (K). Cements made with GGBFS, or CFA boast pozzolanic characteristics. Therefore, they would improve both the concrete compressive strength at later ages and durability. The 28- and 90-days mechanical strength test, non-steady state chloride migration test, described in NT BUILD 492, and natural chloride diffusion test (NT BUILD 443) were performed in concrete. Ternary cements made with GBFS and/or CFA presented better chloride diffusion resistance than concrete made with plain Portland cements. Furthermore, the development of compressive strength was delayed. The service life study was developed for concretes made with ternary cements with regard to the chloride penetration case.

RESUMO O estado de Minas Gerais é o maior produtor de minério de ferro e, consequentemente, de rejeito de minério de ferro (RMF) do Brasil. Esta atividade de grande impacto ambiental está no centro das discussões políticas e sociais atuais devido aos desastres com rompimento de barragens ocorridos nas cidades de Mariana (2015) e de Brumadinho (2019), ambas mineiras. Estes eventos põem em discussão os métodos de descarte do RMF e coloca em destaque a possibilidade de um uso mais sustentável para este resíduo. Uma das alternativas é a utilização do RMF como insumo na fabricação de componentes da construção civil. Este trabalho avaliou a viabilidade do uso de RMF como agregado miúdo em microconcretos para a produção de elementos vazados. Para isso, o RMF foi caracterizado por meio de ensaios físicos e químicos. A dosagem do microconcreto foi realizada com base no método ABCP com fc28 = 25 MPa e abatimento do tronco de cone entre 80 e 100 mm. Para a análise mecânica do microconcreto, foram moldados corpos de prova (10x20 cm) cilíndricos e realizados ensaios de resistência à compressão, absorção e índice de vazios, após 28 dias de cura. Para obter parâmetros de durabilidade, foram realizados ensaios de carbonatação natural aos 60, 120 e 180 dias, carbonatação acelerada aos 28 e 56 dias (teor de CO2 = 5%; Umidade Relativa = 65%), além de ensaio de ataque ácido (solução H2SO4 a 5%). O estudo apontou para a viabilidade da substituição do agregado miúdo por RMF na produção de microconcretos para elementos vazados, sem prejuízo para a sua durabilidade. ABSTRACT The Minas Gerais state is the largest producer of iron ore and, as a result, iron ore tailings (IOT) of Brazil. This activity has a great environmental impact and it is currently the subject of political and social discussions in Brazil, due to disasters with disruption of mining dams that occurred in the cities of Mariana (2015) and Brumadinho (2019), both cities of Minas Gerais. These events bring into discussion the currents methods of IOT disposal and highlight the possibility of a more sustainable use of mining tailings. One of the sustainable alternatives is the use of IOT as an input in the manufacture of civil construction components. In this way, this paper aimed to evaluate the feasibility of using iron ore tailing as fine aggregate in microconcretes for the production of hollow elements (brick vents). Thus, the IOT was characterized through physical and chemical tests. The dosage of microconcrete was performed based on ABCP method with fc28= 25 MPa and the slump test between 80 e 100mm. For the mechanical analysis of the microconcrete, cylindrical specimens (10x20cm) were molded and tests were executed on them, such as compression and flexure strength, water absorption and void ratio. after 28 days curing. To obtain durability parameters, was performed natural carbonation tests at 60, 120 and 180 days, accelerated carbonation tests at 28 and 56 days (CO2 content = 5%; relative humidity (RH) = 65%), and acid attack test (H2SO4 solution content = 5%). The research indicates the feasibility of replacing of the fine aggregate by IOT in the production of microconcretes for hollow elements (brick vents) confection without prejudice to its durability.

Carbonation of cement-based materials may lead to durability problems, so that it is necessary to find a way to reduce the effect of carbonation on concrete durability. This study investigated the effects of cellulose nanofibrils (CNFs) on the durability of carbonated cement-based materials. Two dosages of CNFs were used to prepare cement pastes and mortars. Before and after accelerated carbonation (4 % CO2 concentration and 57 % relative humidity), their microstructure, mineralogical composition, moisture retention capacity, drying kinetics, and water absorption were measured. Results show that the contents of hydration products (CH, C-S-H, and ettringite) slightly decrease with the increase of CNFs dosage. After carbonation, the carbonation ratios of hydration products decrease with CNFs dosage so that more hydration products remain in the carbonated materials. The calcite content was found to increase with the dosage of CNFs which may help the transformation of other metastable calcium carbonates to calcite. The coarsening effect of carbonation on pore structure was clearly observed in measured pore size distribution for all materials, while our results show that this effect is weakened by CNFs. Moisture transport is clearly accelerated by carbonation, but the acceleration rate is diminished with the increasing dosage of CNFs, suggesting that CNFs are able to reduce the microstructural damage by carbonation., Cement and Concrete Research, 162, ISSN:0008-8846

Strain localization is a significant issue that poses interesting research challenges in viscoelastic materials because it is difficult to accurately predict the damage evolution behavior. Over time, the damage mechanism in the amorphous structure of viscoelastic materials leads to subsequent localization into a shear band, gradually jeopardizing the materials’ elastic sustainability. The primary goal of this study is to further understand the morphological effects and the role of shear bands in viscoelastic materials precipitated by strain localization. The current study aims to consolidate the various failure mechanisms of a sample and its geometry (surface-to-volume ratio) used in torsional testing, as well as to understand their effects on stress relaxation durability performance. A torsional shear load stress relaxation durability test was performed within the elastic region on an isotropic viscoelastic sample made of silicon rubber and a 70% weight fraction of micron-sized carbonyl iron particles. Degradation was caused by a shear band of localized plasticity that developed microscopically due to stress relaxation durability. The failure pattern deteriorated as the surface-to-volume ratio decreased. A field-emission scanning electron microscope (FESEM) and a tapping-mode atomic force microscope (AFM) were used for further observation and investigation of the sample. After at least 7500 cycles of continuous shearing, the elastic sustainability of the viscoelastic materials microstructurally degraded, as indicated by a decline in stress performance over time. Factors influencing the formation of shear bands were observed in postmortem, which was affected by simple micromanipulation of the sample geometry, making it applicable for practical implementation to accommodate any desired performance and micromechanical design applications.

In the field of space mechanical lubrication, to improve the reliability and life of space lubrication, solid lubricating film-liquid lubricant composite lubrication has been used in recent years. This lubrication method can improve the durability of sliding friction mating surfaces, reduce equipment wear, and extend the service life of motion mechanisms. However, due to unstable factors such as volatilization and creeping of liquid lubricants in microgravity and ultra-high-vacuum environments, the solid lubricating film wears out after long-term use and produces wear debris and other unfavorable factors. To solve the above problems, this study proposes a novel composite lubrication system constituting a MoS2 film in combination with a supramolecular gel. The tribological performance of this lubrication system establishes an extended service life with a lower wear rate compared to the MoS2 film, regardless of functioning in vacuum or atmospheric conditions. More importantly, the results of the irradiation experiment demonstrate that MoS2-gel exhibits better anticreep performance as compared to MoS2-oil when exposed to atomic oxygen and ultraviolet light for 4 h. The analysis of this composite lubrication mechanism also reveals the formation of a continuous transfer film on the surface of the friction pairs by virtue of the outstanding synergistic effect between the MoS2 film and the gel. MoS2 debris is present in the gel as an additive, and the gel is capable of replenishing automatically once the MoS2 film is depleted. Moreover, the strong anticreep properties of the gel are attributable to the multialkylated cyclopentane oil being trapped by the intricate reassembling of the gelator network. It is firmly believed that this novel MoS2-gel composite lubrication system may have good prospective applications in space and special machinery domains.

The self-consolidating concrete (SCC) become the material of choice by concrete industry due to its superior properties. However, these properties need to be verified under hot weather conditions. The paper investigates the behavior of SCC under hot weather. Six SCC mixtures were prepared under high temperatures. The SCC mixtures incorporated polycarboxylate admixture at different dosages and prolonged mixed for up to 2 hours at 30 °C and 40 °C. The cement paste was replaced with 20% of fly ash (FA). The fresh properties were investigated using slump flow, T50, and VSI tests. The compressive strength was measured at 3, 7, and 28 days. The durability of SCC mixtures was evaluated by conducting rapid chloride penetration and water absorption tests.

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) bring new opportunities for portable power generation due to their outstanding advantages such as high tolerance to fuel/air impurities and simplified heat/water management. However, carbon-supported nanostructured Pt-based catalysts running at temperatures over 150°C are challenged by the severe aggregation and carbon corrosion, thus leading to poor durability. Herein, we demonstrate that dendritic Pt-Ni nanoparticles supported on fluorinated carbon black (white carbon black) could significantly enhance the performance and durability of HT-PEMFCs as the cathode catalysts running at 160°C due to the strong interaction of the F and Ni atoms to form a NixFy interface on Pt-Ni nanoparticles. With the formation of a stable NixFy interface, this integrated HT-PEMFC reached peak power densities of 906 mW cm−2 and demonstrated excellent durability at 160°C under anhydrous H2/O2 conditions. This mitigation strategy was applied to Pt-alloy/C electrocatalysts and resulted in the elimination of Pt dissolution in practical fuel cells.

The effect of quarry dust-based geopolymer cement on the compressive strength, erodibility, and durability potential of expansive soils has been studied under laboratory conditions. The particular interest was on the geopolymer cement treatment of soils subgrade under hydraulically bound environments. Lateritic soils, which form the compacted foundation of pavements, tend to swell upon contact with moisture and shrink during the drying periods. These two factors affect the response and overtime performance of foundation infrastructure. On the other hand, underground and side rail surface flows affect badly constructed pavements by eroding dislodged foundation materials. However, the need to study the erodibility response of the foundation materials exposed to moisture movements has given rise to the present study. The soils classified as A-7–6, A-7–5, and A-7–5 soils according to AASHTO classification, which are highly plastic and expansive were treated with 10–120% by dry weight of soil and the effect on the compressive strength and durability was studied. Conversely, 10–150% by dry weight was used to study the erodibility response of the treated soils. Both treated frequencies were done at the rate of 10%. The treatment protocol showed that the geopolymer cement (GPC) consistently improved the compressive strength, erodibility, and durability of the treated soils. The results have shown that the green cement has improved the properties of the compacted earth utilized under moisture-bound environment and show the potential to be used as an alternative and sustainable binder for earthworks.