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In this study, SnO wrap on SnS was prepared and incorporated into carbon fiber/expanded graphite (CF/EG) cementitious composites by the coating process. The effects of different SnO wrap on SnS coating ratios and contents on the microstructures of CF/EG cementitious composites were investigated and discussed, and the thermoelectric properties of SnO wrap on SnS CF/EG cementitious composites were systematically investigated in the temperature range of 35–70 °C. The results show that the coating ratio and content of SnO wrap on SnS have a significant effect on the thermoelectric properties of CF/EG cementitious composites. It is noteworthy that when the SnO wrap on SnS is 2:1, the thermoelectric properties of its cementitious composites are greatly improved. For example, when it is added at 1.0 wt%, the conductivity is 2.27 S/cm, the Seebeck coefficient is 41.90 µV/°C and the power factor is 0.38 µW·m−1K−2. The addition of SnO wrap on SnS to CF/EG cementitious materials generates a large number of interfaces, and the presence of high-density interfaces hinders the motion of carriers, which leads to the scattering of carriers at the interfaces and enhances the Seebeck effect in cementitious composites. Therefore, SnO wrap on SnS has great potential for thermoelectric applications. [ABSTRACT FROM AUTHOR]

This paper explores the computational modeling of transient heat conduction in thermal energy storage (TES) systems for buildings made of cementitious composites with microencapsulated phase change materials (PCMs). Addressing solid ↔ liquid phase transitions, the study examines numerical approaches and homogenization techniques to define effective thermal properties. Discussion spans both numerical and analytical homogenization models, followed by a comprehensive exploration of approaches to incorporate phase change effects into the numerical solution of transient heat conduction problems. Challenges such as enthalpy-temperature hysteresis and supercooling phenomena are addressed, proposing alternative formulations for stable solutions and improved convergence. The paper highlights the complexities of phase change phenomena and emphasizes the need for ongoing research to enhance modeling techniques for practical applications. [ABSTRACT FROM AUTHOR]

Recently, numerous studies have been carried out with natural fibers in cementitious composites, due to the viability of using this type of fiber as a substitute for synthetic fibers. In this field of study, the present research aims to evaluate the feasibility of using corn straw fiber for the production of innovative cementitious composites. Mortars with a composition of 1:1:6:1.55 (cement/lime/sand/water) containing 0, 2.5 and 5% corn straw fiber were produced. The corn straw fibers were treated with three different alkaline products: sodium hydroxide (NaOH), potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)2). The compositions were evaluated by means of compressive strength, water absorption, density and porosity and consistency tests. Characterization tests were also carried out on the natural fibers subjected to the different treatments, where it was observed that chemical characterization revealed an increase in crystalline cellulose from 59.03% to 63.50% (NaOH), 62.41% (KOH) and 60.40% (Ca(OH)2), which enhances fiber strength. In the mortars, it was observed that the water absorption results were reduced when the alkaline treatments were used, reducing from 15.95% (composition without fibers) to 6.34% and 6.61% in the compositions with 2.5% and 5.0% of fibers treated with KOH, for example. The effects were also positive in the compositions with fibers treated in NaOH, where the water absorption values were 7.59% and 7.88% for the compositions containing 2.5% and 5.0% of treated fiber, respectively. Alkaline treatments also promote an increase in compressive strength when comparing the results of mortars with natural fibers and fibers treated with NaOH, for example. The result for mortars containing 5.0% untreated fibers was 0.22 MPa, while for the composition containing 5.0% fibers treated with NaOH, it was 3.79 MPa, an increase of more than 15x. This behavior is justified by the effect of the treatment, which, in addition to removing impurities from natural fibers, such as sugar, increases the crystalline cellulose content and the adhesion between fiber and matrix. Based on the results obtained, it is possible to conclude that (i) the treatment with NaOH increases the crystallinity and tensile strength of the fibers, promoting good properties for innovative cementitious composites; (ii) the treatment with KOH degrades the cellulose structure of the fiber, reducing the crystallinity and tensile strength; this promotes greater adhesion of the fiber to the matrix, reducing porosity and water absorption, but promotes a reduction in compressive strength when compared to composites with 2.5% natural fiber; and (iii) the treatment with Ca(OH)2 presents a reduction in water absorption and porosity, due to the impregnation of calcium in the fiber that improves the adhesion between fiber and matrix. [ABSTRACT FROM AUTHOR]

The incorporation of graphene-based materials into cement composites is one of many interesting nano-reinforcement techniques. However, the conventional production of graphene materials usually requires large quantities of solvent with energy-intensive mixing, which in turn restricts their commercial viability in cement and concrete applications. In this study, an approach for production of flash graphene (FG) from motor oil soot and diesel particulate using a Joule heating system was developed. A high-quality FG was obtained, as evident from Raman spectroscopy analysis. The FG product was added to a mixture to reinforce its microstructure. The results of the mechanical tests conducted on the cement mortar reinforced by admixing 0.1 wt % FG showed an increase in compressive, tensile, and flexural strengths and modulus of elasticity by 38%, 27%, 27%, and 34%, respectively, after curing for 28 days. The durability characteristics in terms of water absorption showed a slightly higher resistance of the FG-reinforced mortar to water penetration. The drying shrinkage of the FG-reinforced mortar was like that of the control mixture. A molecular dynamics simulation was performed on the cured FG-reinforced cement mortar to find that the Ca–Si interactions in the hydrated cement phase were boosted by the presence of FG, in addition to the strong interaction between the Ca and FG sheets. This study could contribute toward developing strong and sustainable nano-reinforced cementitious composites using graphene materials derived from inexpensive carbon and waste sources. [ABSTRACT FROM AUTHOR]

This research investigated the properties of modified cementitious composites including water purification from heavy metal—zinc. A new method for characterizing the immobilization properties of tested modifiers was established. Several additions had their properties investigated: biochar (BC), active carbon (AC), nanoparticulate silica (NS), copper slag (CS), iron slag (EAFIS), crushed hazelnut shells (CHS), and lightweight sintered fly ash aggregate (LSFAA). The impact of modifiers on the mechanical and rheological properties of cementitious composites was also studied. It was found that considered additions had a significantly different influence over the investigated properties. The addition of crushed hazelnut shells, although determined as an effective immobilization modifier, significantly deteriorated the mechanical performance of the composite as well as its rheological properties. Modification by iron slag allowed for a significant increase in immobilization properties (five-fold compared to the reference series) without a substantial impact on other properties. The negative effect on immobilization efficiency was observed for nanoparticulate silica modification due to its sealing effect on the pore network of the cement matrix. The capillary pore content in the cement matrix was identified as a parameter significantly influencing the immobilization potential of most considered modifications, except biochar and active carbon. [ABSTRACT FROM AUTHOR]

This study investigates crack growth and propagation in Engineered Cementitious Composite (ECC) beams reinforced with polyvinyl alcohol (PVA) fibers through numerical analysis. The research evaluates numerical findings alongside experimental data from a prior stage. Similar to the experimental phase, the numerical procedure models eight ECC beam specimens, comprising four with 2% and four with 1.5% PVA fibers, utilizing the extended finite element method (XFEM) in Abaqus software. Force-displacement and force-crack mouth opening displacement (CMOD) graphs are generated and compared with experimental results. The study demonstrates XFEM's high accuracy in numerically solving fracture problems and predicting structural behavior, as well as determining parameters assessing ECC behavior during crack growth. Findings reveal that ECC beams with 2% fibers exhibit lower loading capacity and higher displacement values, displaying greater CMOD and ductility compared to those with 1.5% fibers. Additionally, a slight impact on flexural capacity is observed with increasing PVA fiber percentages. [ABSTRACT FROM AUTHOR]

Poultry litter (PL) disposal is a major concern for poultry farms around the world, it is estimated that millions of metric tons of this waste are generated globally and as consumption rates increase so does the associated waste; the usual means of disposal include soil fertilization and livestock feeding, however, these disposal strategies are linked with hazardous environmental consequences: eutrophication, ammonia (NH3) emissions and leaching of heavy metals. New environmentally friendly processes have been developed in order to reduce the impact of poultry litter and provide new means of revalorization: proper management and selection, elemental recovery (P, K and N) and its use as biomass for energy generation. One of the most promising revalorization opportunities for this ash residue lies in the development of greener cementitious composites in the pursuit of net-zero energy projects by reducing the carbon footprint of the modified concrete by replacing cement or aggregates, given the typical chemical composition (> 40% CaO) of poultry litter ash (PLA). The present review deals with PLA potential to replace cement or fine aggregates in cementitious composites, how this substitution affects the transport properties of the resultant composite and the effects on strength development and future considerations to be further investigated. [ABSTRACT FROM AUTHOR]

A multiscale micromechanics-based progressive damage model is developed to investigate the overall mechanical behavior and the interfacial microcrack evolutions of the cementitious composites featuring superabsorbent polymer (SAP) under uniaxial tension. Elastic properties, progressive damage process, and homogenization procedure of cementitious composites are systematically integrated in this model. The effective elastic moduli of the composites are determined based on a multiscale micromechanical framework. According to the small strain assumption, the total strain tensor and the elastic-damage compliance tensor are additively decomposed into elastic and damage-induced components. The damage-induced strains and compliances are then deduced from micromechanics. To characterize the progressive elastic-damage induced by microcracks, stages of microcrack propagation are identified from the interface contact stress and the matrix cleavage stress. The complex potentials and stress intensity factors for kinked interface cracks are derived from the distributed dislocations method. By implementing the homogenization process, the macroscopic mechanical behavior is obtained from the micro/mesoscale. The results indicate that the material parameters have clear mechanical significance. Different parameters, such as the SAP addition ratio, aggregate content, initial interfacial crack size, and initial interfacial crack location, are revealed to be influential in the overall mechanical behavior of the composites. The proposed model can be generalized to other particle-reinforced composites with different constituent properties, which can potentially contribute to the design and optimization of durable composites.

Carbon fibre, steel fibre and graphite were used as conductive fillers to prepare cementitious materials with excellent electrothermal properties. The electrically conductive cementitious materials with different volume dosages were analysed through compressive and flexural strength, electrochemical impedance spectroscopy and temperature rise tests. An equivalent circuit model was established to study the electrically conductive heat generation mechanism in the electrically conductive cementitious composites. The results indicate that the mechanical properties of cementitious composite materials with a ternary conductive phase are better than those of pristine cementitious materials because the fibrous filler improves their mechanical properties. However, the incorporation of graphite in the material reduces its strength. Introducing fibrous and point-like conductive phase materials into the cementitious material enhances the overall conductive pathway and considerably reduces the electrical resistance of the cementitious material, enhancing its conductive properties. The volume ratios of carbon fibre, steel fibre and graphite that achieve an optimal complex doping in the cementitious material were 0.35%, 0.6% and 6%, respectively. This was determined using the mutation point of each circuit element parameter as the percolation threshold. In addition, at a certain safety voltage, there is a uniform change between the internal and surface temperatures of the conductive cementitious material, and the heating effect in this materialis is considerably better than that in the pristine cementitious material. [ABSTRACT FROM AUTHOR]

Ferrocement is a type of thin wall‐reinforced concrete composed of hydraulic cement mortar reinforced with several layers of steel wire mesh. The material is used as a low‐cost construction and retrofit solution and allows the creation of very thin elements. In the past, the material was also used to build some structural engineering masterpieces that currently face preservation challenges. Despite the use of the material, few studies have analyzed its durability with respect to corrosion and its evaluation for preservation purposes. The paper presents the results of a testing campaign on ferrocement replica specimens subjected to a corrosive environment. After an aggressive aging procedure, where the specimens are exposed to chloride ingress, the specimens are tested through a four‐point bending test to compare their performances. Results of the mechanical behavior are compared to the results from the half‐cell potential monitoring carried out during the aging process and optical microscope acquisitions regarding the cross‐sectional corrosion‐loss area in the wires. The aim is to assess the performance of historical ferrocement exposed to degradation due to corrosion; this can be useful in identifying the best procedures to protect and preserve it, as well as in evaluating its performance over time. [ABSTRACT FROM AUTHOR]

Textile-reinforced cementitious composites have great potential to offer novel design opportunities for thin-section structures thanks to their superior material capabilities. In this work, new cementitious composites with novel reinforcement configurations are developed, which have superior mechanical properties. The cementitious composites contain inclined through-the-thickness reinforcements, and their enhanced performance on thin-section material hardening under flexural loading is demonstrated. Furthermore, a new practical FE modeling approach is proposed that involves the combined use of multiple cohesive regions and 1D reinforcement elements that pass through these regions with a bilinear material law. This approach provides a new computationally efficient modelling framework whereby reinforcement pull-out during hardening is readily captured without resorting to computationally demanding interface laws between the reinforcement and the cementititous matrix. The model can model enhanced hardening of new configurations and provides comparable results with the experimental findings. The model can be used in the modelling and design of novel cementitious composites with engineered reinforcement configurations. Overall, this study aims to open up new avenues for the smart material design of cementitious composites with novel structural reinforcements. [ABSTRACT FROM AUTHOR]

Copyright of Materiały Budowlane is the property of Wydawnictwo SIGMA-NOT and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study systematically investigates modification methods for recycled aggregate, including acid modification, abrasion testing, and triple-mixing improvement. Recycled aggregate from a single source replaced 50% and 100% of natural aggregate in concrete mixes, which were compared to controls using natural aggregate and unmodified recycled aggregate. Simultaneously, recycled aggregate and recycled waste tire steel fibers were employed to enhance sustainability. Modification effects on properties were isolated by adjusting aggregate gradations and using superplasticizer to control water-binder ratios. Key quantitative findings include a 10% reduction in compressive strength with 50% recycled aggregate and a 15.7% reduction with 100%, due to lower density, increased porosity, and cracks. Modification methods improved strength by 4–9.5% for 50% recycled aggregate and 2–5% for 100% replacement. The triple-mixing method notably enhanced 50% recycled concrete, while acid modification was most effective for 100% recycled concrete. Unit weight decreased by 5% with 50% and 3.6% with 100% recycled aggregate. Workability reduction was observed with recycled fiber addition, while modified recycled aggregate mitigated this effect. Axial stiffness decreased by 21.76% with 100% recycled aggregate, with modification methods showing varied effects. Energy absorption decreased by 19.5% with 50% and 24.3% with 100% recycled aggregate, minimally impacted by modification. [ABSTRACT FROM AUTHOR]

The application of carbon fiber in cement matrix has some disadvantages, such as poor dispersion and poor interfacial adhesion. In order to improve the interaction between carbon fiber and cement matrix and improve the properties of cement-based composites, carbon fiber was modified by electrophoretic deposition of nano-graphene oxide (GO). In this paper, the effects of doping CF into the cement matrix before and after GO modification are studied comparatively in terms of electrical conductivity, electrothermal warming effect, and pressure-sensitive properties of the cement matrix. It was found that the GO-modified CF reduces both the electrical resistivity of cementitious composites and the required level of fiber incorporation compared to CF. The percolation threshold is 0.7 wt% for CF and 0.5 wt% for GO-CF. The GO-modified CF is more effective than CF as a conductive filler to enhance the electrothermal warming performance of the cement matrix. When the GO-CF doping rate is 0.5%, the specimen temperature increases most rapidly, and the temperature rise value reaches a maximum of up to 30.45 °C, which is twice that of the CF group. When the fiber content is 0.7%, the pressure sensitivity of the sample was the best. When the fiber content is 0.5%, GO-CF can improve the pressure sensitivity of cement mortar specimens, and increase the resistance change rate of the cement mortar specimens by 5.7%. [ABSTRACT FROM AUTHOR]

The aim of this paper was to examine the effects of adding TiO2 nanoparticles to cementitious compositions and partially substituting natural aggregates with recycled aggregates consisting of glass, brick, slag, or textolite, and to examine the material's ability to resist corrosion under the action of chloride ions existent in the environment that attack the steel reinforcement. The results show that the changes in the cementitious composite when it comes to the composition and microstructure influence the formation of the oxide passivating layer of the reinforcement. The addition of TiO2 nanoparticles and recycled aggregates impacts the kinetics and corrosion mechanism of the reinforcement. An addition of 3% TiO2 was found to be optimal for reinforcement protection. Electrochemical impedance spectroscopy confirmed the results obtained by open-circuit potential and linear polarization tests. The classification of favorable conditions indicates that compositions with recycled aggregates and 3% TiO2 are the most effective, with compositions in which the natural aggregates were partially substituted with slag being the most effective. [ABSTRACT FROM AUTHOR]

Emission of greenhouse gases and increasing global warming have posed serious threats to the environment and survival of mankind. Construction industry is amongst the leading polluters and currently traditional materials are being used at large scale to meet the increasing demand to construct new facilities. Concrete is a widely used material in construction industry and steel bars are often used as reinforcement. Cement being the main constituent of concrete and steel bars used in it require greater amount of energy. During the fabrication of concrete, an intensive amount of carbon dioxide (CO2) is emitted to the environment. The utilization of industrial waste (by-products) as a replacement of cement and textile waste as a reinforcement for cementitious composites represent one of the promising solutions. Use of industrial by-products not only address the waste disposal problem but also help in reducing energy demand for concrete production. This paper describes an over review on the efforts done in reducing dependence of traditional materials used in cementitious composites. [ABSTRACT FROM AUTHOR]

Abstract One of the major challenges in the civil engineering sector is the durability of reinforced concrete structures against carbonation during the physico-chemical process of interaction of hydrated cementitious composites with carbon dioxide. This aggressive process causes carbon penetration into the reinforcement part, which affects the behavior of the structure during its lifetime due to corrosion risk. A countermeasure is using alternative cementitious materials to improve concrete texture and resist increased carbonation depth (CD). Considering that the CD test requires a long time and a skilled technician, this study strives to provide an alternative approach by moving from traditional laboratory-based methods towards artificial intelligence (AI) techniques for modeling the CD of sustainable concrete containing fly ash (CCFA). Despite the development of single AI models so far, it is undeniable that utilizing metaheuristic optimization techniques in the form of hybrid models can improve their performance. To this end, a new hybrid model from the integration of biogeography-based optimization (BBO) technique with artificial neural network (ANN) is developed for the first time to estimate the CD of CCFA. The error distribution results revealed that 59% of the ANN predictions had errors within the range of (− 1 mm, 1 mm], while the corresponding percentage for the ANN-BBO predictions was 70%, indicating an 11% reduction in the prediction errors by the proposed hybrid model. Furthermore, A10-index highlighted a performance improvement of 78% for the hybrid model, which met the closeness of the predicted values to the observed ones, so that the value of this index for models of ANN and ANN-BBO was 0.5019 and 0.8947, respectively. Analyzing the cross-validation confirmed the reliability and generalizability of the developed model. Also, the three most influential variables in estimating the CD were exposure time (27%), carbon dioxide concentration (22%), and water/binder (18%), respectively. Finally, the superiority of the ANN-BBO model was verified by comparing it with previous studies’ models.

Nanomaterials integration within construction materials could promote the generation of more sophisticated structural materials, as it imbues reinforcement at the nanoscale. This research adopted experimental approaches to assess the influence of metallic nanomaterials on the performance of cementitious composites with various ratios of boric acid (1%, 3%, and 5% by sand's weight) and lime (0.5%, 1.5%, and 2.5% by sand's weight), respectively, for use in construction infrastructure facilities. This research provides valuable insight into the potential of using boric acid and lime as well as metallic nanomaterials to strengthen cement-based composites. Initial curing stages revealed a notable decrease in compressive strength attributed to the inhibitory effects of boric acid and lime on cement hydration. However, the introduction of TiO2 nanoparticles demonstrated significant enhancements in compressive strength and durability. Statistical analysis emphasized the significance of nanomaterials in augmenting compressive strength, with implications for long-term performance. This study has shown that the addition of nano-titanium dioxide TiO2 can significantly enhance the compressive strength of Portland cement mortars, particularly when used in conjunction with appropriate ratios of boric acid and lime. The results of the 7 days test indicated that the inclusion of boric acid and lime in the cement mortars significantly decreased the compressive strength. However, the addition of nano-TiO2 to cement mortars containing 1% boric acid and 0.5% lime resulted in a 31-fold increase in compressive strength compared to cementitious composites without nano-TiO2. In contrast, the compressive strength significantly increased by 1.2 times, 85.3 times, and 65.1 times, respectively, after 56 days for the addition of boric acid (1%, 3%, and 5%) with lime (0.5%, 1.5%, and 2.5%), respectively, in the presence of nano-TiO2, compared to the 7 days strength. The results also illustrated that, in general, the incorporation of various types of nano-TiO2 into cementitious composites containing boric acid and lime increases their compressive strength as the ratios of boric acid and lime increase, as long as sufficient curing time is allowed.

In cold climates, concrete structures confront durability challenges due to harsh conditions. This study evaluates the effects of incorporating natural fibers, such as hemp and flax fibers (at 1 vol%), and partially replacing cement with fly ash (at 25 and 50 wt%) on the properties of cementitious composites subjected to accelerated aging under freeze-thaw cycles and deicing salts.Findings reveal that natural fibers enhance the freeze-thaw resistance, reducing deterioration (scaling) to 5–8% after 56 cycles. When mortars were subjected to accelerated freeze-thaw cycles, the compressive strength of plain mortar significantly decreased (up to 57%). However, adding natural fibers to the matrix substantially reduced its compressive strength loss. In the case of flexural strength, plain mortars experienced 33% loss, while hemp, flax, and polypropylene fiber mortars showed only 13%, 23%, and 10% losses, respectively. Furthermore, mortars experience a notable enhancement in their energy absorption capacity when reinforced with natural fibers, particularly with hemp fibers (up to 348% higher than plain mortar).Under harsh conditions, hemp and flax-reinforced mortars, with 25 wt% fly ash replacement, lose the compressive strength significantly however still demonstrate an alternative to synthetic fibers in terms of flexural strength. Even with 25 wt% of fly ash, mortars with natural fiber reinforcement display significantly superior energy absorption capacities compared to plain mortars (up to 48%).

In fabric-cement composites, the limited impregnation of cementitious matrix products due to thick and twisted yarns leads to premature failure due to poor bonding strength. In addition, cellulosic textile reinforcements have many challenges about durability, appearance of voids at mortar-fiber interface, and rise of microcracks. Textile performances were evaluated in different conditions: coated with micro-silica powder, pretreated, and without any treatment. This study also assessed how textile weave structure and yarn geometry configuration affect the interactions of two different jute textiles (Close Weave Jute Fabric – CJF and Open Weave Jute Fabric - OJT) when used as reinforcement in mortar matrix. Textile characterization and composite analysis (by four-point bending tests, SEM/EDS, and physical tests) were conducted to assess the different textile reinforcements, the mechanical behavior of produced composites, and visual and chemical compounds analysis of the interfacial transition zone between textile and mortar matrix after silica coating. Micro silica powder coating was deemed necessary to address limited impregnation and to avoid telescope pull-off. Weave structure determined the difference between jute fabrics to reinforce mortar matrix, being only OJF (larger interstices in the weave structure) with micro silica coating allowed a better matrix interaction and stood out from the other textiles and achieved the best specific energy of all samples, (4.28 ± 0.91) kJ.m-2. Calcium and silicon inside the yarn interstices and textile-matrix interface indicate the formation of strong bonds by calcium-silicate-hydrate products. The silica coating treatment enhanced formation of strong bonds, which demonstrated future promise for natural fiber application. [ABSTRACT FROM AUTHOR]

A novel fiber reinforced cementitious composites was developed by incorporating microencapsulated phase change materials (PCMs) and nanographene oxide (NGO) to enhance the composites' thermal properties without compromising the compressive strength. Regarding the thermo-mechanical properties, with the addition of NGO, while mechanical properties improve, thermal mass increases and the heat storage ability of the produced composite material enhances. In this situation; it can be interpreted that it will be possible to benefit more from the energy stored by PCMs, as the energy required to change the temperature of the unit mass of the material will decrease. The environmental impact assessment has also revealed that CO 2 emissions from production increase with the use of PCMs. However, it has been determined that the addition of NGOs will make a positive contribution to the life cycle, as CO 2 emissions resulting from cement will decrease. In conclusion, a novel fiber reinforced composite with enhanced thermal and mechanical properties by combining PCMs and NGO has shown a great potential for environmentally friendly buildings with the integration of structure, energy conservation and long term durability. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

One of the major challenges in the civil engineering sector is the durability of reinforced concrete structures against carbonation during the physico-chemical process of interaction of hydrated cementitious composites with carbon dioxide. This aggressive process causes carbon penetration into the reinforcement part, which affects the behavior of the structure during its lifetime due to corrosion risk. A countermeasure is using alternative cementitious materials to improve concrete texture and resist increased carbonation depth (CD). Considering that the CD test requires a long time and a skilled technician, this study strives to provide an alternative approach by moving from traditional laboratory-based methods towards artificial intelligence (AI) techniques for modeling the CD of sustainable concrete containing fly ash (CCFA). Despite the development of single AI models so far, it is undeniable that utilizing metaheuristic optimization techniques in the form of hybrid models can improve their performance. To this end, a new hybrid model from the integration of biogeography-based optimization (BBO) technique with artificial neural network (ANN) is developed for the first time to estimate the CD of CCFA. The error distribution results revealed that 59% of the ANN predictions had errors within the range of (− 1 mm, 1 mm], while the corresponding percentage for the ANN-BBO predictions was 70%, indicating an 11% reduction in the prediction errors by the proposed hybrid model. Furthermore, A10-index highlighted a performance improvement of 78% for the hybrid model, which met the closeness of the predicted values to the observed ones, so that the value of this index for models of ANN and ANN-BBO was 0.5019 and 0.8947, respectively. Analyzing the cross-validation confirmed the reliability and generalizability of the developed model. Also, the three most influential variables in estimating the CD were exposure time (27%), carbon dioxide concentration (22%), and water/binder (18%), respectively. Finally, the superiority of the ANN-BBO model was verified by comparing it with previous studies' models. [ABSTRACT FROM AUTHOR]

Cementitious composites are ubiquitous in construction, and more and more research is focused on improving mechanical properties and environmental effects. However, the jury is still out on which material can achieve low-carbon and high-performance cementitious composites. This article compares the mechanical and environmental performance of zero-dimensional fullerenes, one-dimensional carbon nanotubes (CNTs), two-dimensional graphene oxide (GO), and three-dimensional nano-graphite platelets (NGPs) on cementitious composites. The literature review shows that two-dimensional (2D) GO has the best mechanical and environmental performance, followed by 3D NGPs, 1D CNTs, and 0D fullerenes. Specifically, GO stands out for its lower energy consumption (120–140 MJ/kg) and CO2 emissions (0.17 kg/kg). When the optimal dosage (0.01–0.05 wt%) of GO is selected, due to its high specific surface area and strong adhesion to the matrix, the compressive strength of the cementitious composites is improved by nearly 50%. This study will help engineers and researchers better utilize carbon-based nanomaterials and provide guidance and direction for future research in related fields. [ABSTRACT FROM AUTHOR]

Thermal damage assessment of cementitious composites is essential for evaluating post-fire health conditions of the engineering structures, as well as the basis for reinforcement and repair after fires. Fibers and fly ash are widely used in cementitious composites due to their excellent properties. However, quantifying and predicting the thermal damage of hybrid fibers reinforced cementitious composites blended with fly ash at high temperatures is still inexplicit. Hence, this study aims to realize multiscale prediction of thermal damage for hybrid fibers reinforced cementitious composites blended with fly ash at high temperatures. First, the volumes of the phase compositions during hydration and dehydration are calculated by the hydration of cement and fly ash and the dehydration of hydration products. Then, a multiscale model is established to predict the thermal damage of hybrid fibers reinforced cementitious composites and verified by the experimental data. At last, the temperature field of tunnel lining structure in fires is obtained by numerical modeling and employing it to predict thermal damage at different thicknesses and moments. Results show that the heating rate determines the dehydration degree of hydration products and the volumes of the phase composites at high temperatures. The proposed multiscale model can reflect the thermal microcracking of cement paste, the interfacial thermal damage between aggregates and the cement paste, and the deterioration of elastic modulus of fibers. After three hours of exposure to fires, serious damage appears at the surface and the thickness of 2 cm and 5 cm of the lining, while there is nearly no damage at a thickness of 30 cm or more. [ABSTRACT FROM AUTHOR]

The aim of this study is to analyze the effect of the addition of TiO2 nanoparticles (NTs) on the physical and mechanical properties, as well as the microstructural changes, of cementitious composites containing partially substituted natural aggregates (NAs) with aggregates derived from the following four recycled materials: glass (RGA), brick (RGB), blast-furnace slag (GBA), and recycled textolite waste with WEEE (waste from electrical and electronic equipment) as the primary source (RTA), in line with sustainable construction practices. The research methodology included the following phases: selection and characterization of raw materials, formulation design, experimental preparation and testing of specimens using standardized methods specific to cementitious composite mortars (including determination of apparent density in the hardened state, mechanical strength in compression, flexure, and abrasion, and water absorption by capillarity), and structural analysis using specialized techniques (scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS)). The analysis and interpretation of the results focused primarily on identifying the effects of NT addition on the composites. Results show a decrease in density resulting from replacing NAs with recycled aggregates, particularly in the case of RGB and RTA. Conversely, the introduction of TiO2 nanoparticles resulted in a slight increase in density, ranging from 0.2% for RTA to 7.4% for samples containing NAs. Additionally, the introduction of TiO2 contributes to improved compressive strength, especially in samples containing RTA, while flexural strength benefits from a 3–4% TiO2 addition in all composites. The compressive strength ranged from 35.19 to 70.13 N/mm2, while the flexural strength ranged from 8.4 to 10.47 N/mm2. The abrasion loss varied between 2.4% and 5.71%, and the water absorption coefficient varied between 0.03 and 0.37 kg/m2m0.5, the variations being influenced by both the nature of the aggregates and the amount of NTs added. Scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS) analysis showed that TiO2 nanoparticles are uniformly distributed in the cementitious composites, mainly forming CSH gel. TiO2 nanoparticles act as nucleating agents during early hydration, as confirmed by EDS spectra after curing. [ABSTRACT FROM AUTHOR]

Nanomaterials integration within construction materials could promote the generation of more sophisticated structural materials, as it imbues reinforcement at the nanoscale. This research adopted experimental approaches to assess the influence of metallic nanomaterials on the performance of cementitious composites with various ratios of boric acid (1%, 3%, and 5% by sand's weight) and lime (0.5%, 1.5%, and 2.5% by sand's weight), respectively, for use in construction infrastructure facilities. This research provides valuable insight into the potential of using boric acid and lime as well as metallic nanomaterials to strengthen cement-based composites. Initial curing stages revealed a notable decrease in compressive strength attributed to the inhibitory effects of boric acid and lime on cement hydration. However, the introduction of TiO2 nanoparticles demonstrated significant enhancements in compressive strength and durability. Statistical analysis emphasized the significance of nanomaterials in augmenting compressive strength, with implications for long-term performance. This study has shown that the addition of nano-titanium dioxide TiO2 can significantly enhance the compressive strength of Portland cement mortars, particularly when used in conjunction with appropriate ratios of boric acid and lime. The results of the 7 days test indicated that the inclusion of boric acid and lime in the cement mortars significantly decreased the compressive strength. However, the addition of nano-TiO2 to cement mortars containing 1% boric acid and 0.5% lime resulted in a 31-fold increase in compressive strength compared to cementitious composites without nano-TiO2 In contrast, the compressive strength significantly increased by 1.2 times, 85.3 times, and 65.1 times, respectively, after 56 days for the addition of boric acid (1%, 3%, and 5%) with lime (0.5%, 1.5%, and 2.5%), respectively, in the presence of nano-TiO2, compared to the 7 days strength. The results also illustrated that, in general, the incorporation of various types of nano-TiO2 into cementitious composites containing boric acid and lime increases their compressive strength as the ratios of boric acid and lime increase, as long as sufficient curing time is allowed. [ABSTRACT FROM AUTHOR]

Concrete, the ubiquitous cementitious composite though immensely versatile, is crack-susceptible. Cracks let in deleterious substances causing durability issues. Superseding conventional crack-repair methods, the innovative application of microbially induced calcium carbonate precipitation (MICCP) stands prominent, being based on the natural phenomenon of carbonate precipitation. It is eco-friendly, self-activated, economical, and simplistic. Bacteria inside concrete get activated by contacting the environment upon the crack opening and filling the cracks with calcium carbonate—their metabolic waste. This work systematizes MICCP's intricacies and reviews state-of-the-art literature on practical technicalities in its materialization and testing. Explored are the latest advances in various aspects of MICCP, such as bacteria species, calcium sources, encapsulations, aggregates, and the techniques of bio-calcification and curing. Furthermore, methodologies for crack formation, crack observation, property analysis of healed test subject, and present techno-economic limitations are examined. The work serves as a succinct, implementation-ready, and latest review for MICCP's application, giving tailorable control over the enormous variations in this bio-mimetic technique. [ABSTRACT FROM AUTHOR]

This study investigates the mechanical properties of cementitious composites with 3D-printed auxetic lattices, featuring negative Poisson’s ratios (auxetic behavior) in multiple directions. These lattices were fabricated using vat photopolymerization 3D printing, and three base materials with varying stiffness and deformation capacities were analyzed to determine their impact on the composites’ mechanical behavior. To unravel the reinforcing mechanisms of multidirectional auxetic lattices, which exhibit auxetic behavior in both planar and out-of-plane directions, X-ray computed tomography (X-ray CT) was utilized to analyze composite damage evolutions under different strain levels. The micro-CT characterization reveals that auxetic lattices more effectively constrain crack growth and dissipate energy by distributing stress evenly within the cement matrix. In contrast, due to lack of lateral confinement, the non-auxetic lattice reinforced composites primarily dissipate energy through extensive crack propagation and interfacial damage, leading to lower peak strength. When strain exceeding 5%, although the confinement from the auxetic behavior diminished with crack propagation, the lattice can still maintain the composite’s structural integrity, resulting in 1.7 times higher densification energy than conventional cement-based materials. These findings provide valuable insights for designing auxetic lattice-reinforced cementitious composites with enhanced load-bearing capacity and improved dissipation capabilities.

Abstract The use of natural fibers in cementitious composites has been gaining prominence in engineering. The natural lignocellulosic fibers (NLFs) used in these composites have advantages such as reduced density, reduced fragmentation and concrete cracking, thus improving flexural performance and durability. Coconut-fiber is one of those natural fibers and its use presents technical, ecological, social and economic benefits, as it is improperly disposed of, representing a large waste of natural resources, in addition to causing environmental pollution.. Thus, composites reinforced with natural fibers are promising materials for the construction industry, as in addition to meeting the sustainability of buildings, there will also be a reduction in urban solid waste generated and gains for structures with the use of environmentally friendly materials that meet to active efforts and with greater durability. This work aims to evaluate the tensile behavior of green coconut-fibers subjected to different drying temperatures through chemical, thermal (TG/DSC), morphological, visual and mechanical analysis. Drying temperatures of 70 °C, 100 °C and 130 °C were analyzed and the results indicated that the drying temperature at 70 °C was satisfactory, providing fiber-reinforced composites with good tensile strength, combined with good ductility.

The safety and durability of concrete structures are prone to damage and result in significant harm to human society. Hence, monitoring and estimating the states of concrete structures is of great significance to protecting human safety. Graphene nanoplatelets (GNPs) and carbon nanotubes (CNTs) are promising candidates to endow cementitious composites with piezoresistivity for the health monitoring of concrete structures. Therefore, the aim of this article is to explore the effect of the hybrid GNPs and CNTs on behavior of cementitious composites with cooperation effects. The cementitious composites containing the hybrid GNPs and CNTs with simplified manufacturing methods are developed first. And then, the mechanical behaviors, electrical conductivities, and piezoresistive performances of the composites are investigated systematically. Finally, the modification mechanisms are also discussed. The results proved that the electrical resistivity of the composites with the hybrid GNPs and CNT concentration of 5.0 wt% is reduced by three orders of magnitudes, and the FCR and sensitivities are reached at 36.0% and 1.1% MPa−1/177.9, respectively. Its compressive strength/elastic modulus is achieved at 73.3 MPa/16.9 GPa. Therefore, the hybrid GNPs and CNTs modified cementitious composite present great potential application in monitoring and evaluating service states of civil infrastructures.