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Recent decades have witnessed the increasing use of soil mixing technology to construct cut-off walls for groundwater control or underground pollutant containment. The strength and permeability of soil mix columns deteriorate considerably when subjected to chemical, mechanical and environmental stresses, leading to the need for repair of crack-originated damage. The development of self-healing grouts could provide more resilient and sustainable soil mix cut-off walls. In this study, for the first time, self-healing soil mix columns incorporating reactive magnesium oxide pellets were developed. The magnesium oxide-based cementitious grout was mixed with a sand soil using a laboratory-scale auger, and the embedded magnesium oxide pellets were ruptured upon cracking, producing expansive healing products due to hydration and carbonation, which can significantly fill the crack volume. The effects of magnesium oxide on the grout and soil mix samples were investigated in terms of both fresh and hardened properties. In addition, the self-healing performance was evaluated by examining permeability recovery and crack closure, and the microstructure and morphology of the magnesium oxide pellets and healing products were analysed. The results demonstrate the great potential of reactive magnesium oxide pellets as a self-healing agent for soil mix cut-off wall materials. [ABSTRACT FROM AUTHOR]

The construction industry has been increasingly concerned with the environment and sustainability, and one solution is engineered cementitious composites (ECC), which have self-healing, ductility, and strength properties. Researchers have been working to make ECC greener by creating synergistic mechanical interactions between fibers, matrices, and fiber–matrix interfaces. This study developed ECC using local river sand, silica fume, moderate to high-volume fly ash (FA), and bulky PVA fibers, evaluating workability and compressive strength at various testing ages (1, 7, 28, 60, and 180 days). According to the test findings, fresh ECC mortar mixtures exhibit an increase in workability with increasing FA content due to the spherical and glossy form of FA particles. All ECC samples have a compressive strength of over 20 MPa after 1 day, making them high-early compressive strength composites. The sample with the highest compressive strength after 28 days was 111.28 MPa. PVA fibers, FA, and SF contribute to increasing strength while using local river sand as an ingredient in composite mixtures is also beneficial. The samples experienced a bulging process during failure due to the use of oiled PVA fibers. The maximum load before the collapse was attained after a longer period of time where smeared cracks were visible on the samples' surface. Based on the analysis of the compressive strength over a period of more than 28 days, it is clear that both ECC mortar and bulky PVA-ECC samples exhibit sufficient strength stability. It is worth mentioning that as the curing age of ECC increases, there is a gradual increase in strength, although the level of increase is relatively slow. [ABSTRACT FROM AUTHOR]

Cement-based cementitious materials occupy a central position in the construction industry, but the problem of high carbon dioxide(CO2) emissions from cement production has attracted global attention. To meet this challenge, finding low-carbon alternative materials has become a top priority in the research of new building materials. At the same time, the problem of large amounts of lithium slag piling up needs to be solved, and resource utilization has become its potential way out. In this study, the volcanic ash activity of lithium slag was activated by composite activation means of high-temperature calcination and sodium silicate, and it was used as an alternative mix to cement. The Box–Behnken design and response surface method (BBD-RSM) was utilized to optimize the ratio of activated lithium slag composite cement-based cementitious materials, and high-performance new solid waste cementitious materials were prepared. The results show that activated lithium slag composite cementitious materials activated lithium slag exhibit excellent performance when activated lithium slag mass fraction is 7.3%, the sodium silicate dosage is 8.8%, and water–solid ratio is 0.6:1. The composite cementitious material under this ratio shows excellent performance, with fluidity 235.69 mm, gelation time 73.54 s, water evolution rate 1.123%, 3d and 28d compressive strengths, respectively, are 11.54 MPa and 22.9 MPa. Compared with ordinary Portland-cement-based cementing materials, the uniaxial compressive strength, modulus of elasticity, and tensile strength at break of activated lithium slag cementitious material solidified body were increased by 34.33%, 36.43%, and 34.98%, and the compressive deformation and tensile deformation were enhanced by 37.78% and 40%. This study not only provides a theoretical basis and experimental foundation for the preparation of new solid waste cementitious materials, but also provides a new solution for the reinforcement of crushed rock bodies in engineering practice, which is of great significance for promoting the low-carbon development of the construction industry. [ABSTRACT FROM AUTHOR]

The hydration reaction of mass concrete seriously endangers the structural safety. At present, the concrete production relies excessively on fly ash due to hydration reaction. In view of the problem that the demand of fly ash exceeds the supply, this paper proposes to use dacite powder to partially replace fly ash as the raw material for preparing cementitious materials. Through comprehensive tests and microstructure tests, various properties of dacite powder and fly ash composite cementitious materials are studied. The results show that: 1. The dacite powder with a specific surface area of 650 m²/kg, a fineness of 15% under laser particle size and a ball-milling time of 1.0 h has the best performance. 2. It is advisable to mix dacite powder and fly ash. The total amount of dacite powder should not exceed 30% of the cementitious material. It has the best performance when the amount of dacite powder and fly ash is the same. 3. The alkali activity of aggregate can hardly be inhibited by mixing dacite powder alone. The recommended measures to inhibit the alkali activity of aggregate are: i) mixing more than 20% fly ash alone. ii) mixed with 25% dacite powder and more than 15% fly ash. [ABSTRACT FROM AUTHOR]

Sugarcane vinasse wastewater (SVW) is one of the most voluminous waste generated in the ethanol industry and usually applied in fertigation. It is characterized by presenting high COD and BOD; thus, continued disposal of vinasse results in negative environmental impacts. In this paper, we investigated the potential of SVW in replacement of water in mortar, rethinking about reuse of effluent, reduction of pollutants in the environment, and water consumption in civil construction. Mortar composites with 0, 20, 40, 60, 80, and 100% of water replaced by SVW were studied in order to determine the optimum content. Mortars with 60 to 100% of SVW result in improved workability and reduction in water demand. The mortars with 20, 40, and 60% SVW resulted in satisfactory mechanical properties, i.e., similar to the control mortar. However, XRD analysis of cement pastes showed that the SVW causes a delay in CH formation, reaching mechanical strength after 28 days. Durability tests results showed that SVW contributes to the mortar becoming more impermeable; therefore, less susceptible to weathering. This study provides an important evaluation of the potential of SVW for application in civil construction, indicating relevant results for replacement of water by liquid wastes in cementitious composites and reduction the use of natural resources. [ABSTRACT FROM AUTHOR]

This paper investigates the properties and durability of cementitious composites incorporating solid-solid phase change materials (SS-PCM), an innovative heat storage material. Mortars with varying SS-PCM contents (0%, 5%, 10%, 15%) were formulated and characterized for rheological, structural, mechanical, and thermal properties. Durability assessment focused on volume stability (shrinkage), chemical stability (carbonation), and mechanical stability (over thermal cycles). Mortars with SS-PCM exhibited significant porosity and decreased mechanical strength with higher SS-PCM content. However, thermal insulation capacity increased proportionally. Notably, the material's shrinkage resistance rose with SS-PCM content, mitigating cracking issues. Despite faster carbonation kinetics in SS-PCM mortars, attributed to high porosity, carbonation appeared to enhance long-term mechanical performance by increasing compressive strength. Additionally, SS-PCM composites demonstrated superior stability over thermal cycles compared to reference mortars. [ABSTRACT FROM AUTHOR]

In order to achieve the resourceful, large-scale and high-value utilization of bulk industrial solid wastes such as flue gas desulfurization gypsum (FGDG), fly ash (FA) and ground blast furnace slag (GGBS), and to reduce the dosage of cementitious materials, orthogonal experimental methods were used to prepare composite cementitious materials based on the principle of synergistic coupling and reconstruction of multi-solid wastes. Through the method of extreme difference and ANOVA, the influence law of different factor levels on the performance of the cementitious materials was studied, and the maximum compressive strength of cementitious materials was reached when the ordinary Portland cement (OPC) dosage was 20%, the FGDG dosage was 56%, the FA dosage was 19.2% and the slag dosage was 4.8%, and the W/B was 0.55. The hydration products and microscopic morphology of the cementitious materials were analyzed by means of XRD, SEM and MIP techniques, so as to elucidate the complex synergistic hydration mechanism, and then to determine the more optimal group distribution ratio. The results show that the hydration reaction between FGDG and OPC can be synergistic with each other, and C-A-H further generates AFt under the action of SO42−, and at the same time, it plays the role of alkali-salt joint excitation for FA–GGBS, generates a large amount of cementitious materials, fills up the pores of the gypsum crystal structure, and forms a dense microstructure. [ABSTRACT FROM AUTHOR]

The urgent need for sustainable construction that corresponds to the three pillars of sustainable development is obvious and continuously requires innovative solutions. Cementitious composites with TiO2 nanoparticles (NT) addition show potential due to their improved durability, physico–mechanical characteristics, and self-cleaning capacity. This study aimed to evaluate the influence of NT on cementitious composites by comparing those with 2%–5% nanoparticles with a similar control sample without nanoparticles, as well as an analysis of cost growth. The experimental results showed an increase in bulk density of the material (4.7%–7.4%), reduction in large pore sizes by min. 12.5%, together with an increase in cumulative volume and cumulative specific surface area of small pore sizes, indicating densification of the material, also supported by SEM, EDS, and XRD analyses indicating acceleration of cement hydration processes with formation of specific products. The changes at microstructural level support the experimental results obtained at macrostructural level, i.e., modest but existent increases in flexural strength (0.6%–7.9%) and compressive strength (0.2%–2.6%) or more significant improvements in abrasion resistance (8.2%–58%) and reduction in water absorption coefficient (37.5%–81.3%). Following the cost–benefit analysis, it was concluded that, for the example case considered of a pedestrian pavement with a surface area of 100 m2, using 100 mm thick slabs, if these slabs were to be made with two layers, the lower layer made of cementitious composite as a reference and the upper layer with a thickness of 10 mm made of cementitious composite with 3% NT or 4% NT, the increase in cost would be acceptable, representing less than 15% compared to the cost for the exclusive use of cementitious composite without NT. [ABSTRACT FROM AUTHOR]

Carbon-based nanomaterials such as graphene oxide sheet)reinforced cementitious composites have attracted extensive interest owing to their improved post-fire mechanical properties. However, the role of graphene in anti-thermal detriment is still unclear. In the current study, the mechanical characteristics, pore structure, and interface evolution of graphene-toughened cement based materials under high temperatures are investigated. Scanning electron microscope analysis showed that graphene implanted in the cement matrix had out-of-plane deformation at elevated temperature. The deformation caused the evolution of the interface between graphene and the cement-based material with respect to temperature. Correspondingly, the toughening effect of graphene on cement-based materials decreased first and then increased. The reinforced domain of graphene switched from mesopores to capillary pores when the temperature was beyond 400°C, contributing to the enhanced reinforcement efficiency of the cement mortar. The interfacial evolution process with an in-depth analysis based on multiple scales would benefit from optimizing the design of graphene composites at high temperatures. [ABSTRACT FROM AUTHOR]

The present study explores the feasibility of using recycled materials from display glass electronic waste (DGE-waste) in the production of cementitious mortars as a granular corrector for dune sand and as a cementitious addition. The effects of the DGE-waste replacement ratio (5–20% with 5% steps by weight of three types of dune sand from three different regions) on the engineering properties of reinforced cementitious composite were experimentally investigated to assess the performance of dune sand mortar. The results show that the incorporation of DGE-waste in dune sand mortar can increase the mechanical strengths (flexural and compressive) by up to 35% and 43%, respectively, and improve the dynamic modulus of elasticity by at most 12% as compared with the control mortar, as well as decrease open porosity by up to 28%, which reduces micro-cracks and voids. When cement is replaced with 15% recycled DGE-waste, the mechanical strength and dynamic modulus of elasticity, as well as open porosity and absorption, are decreased by 4–7% and 17–20%, respectively. Considering the environmental impact and engineering properties, the optimal percentage of DGE-waste incorporation is 15% for cement replacement and 20% for dune sand replacement. [ABSTRACT FROM AUTHOR]

This article deals with the study of hazardous chromium leaching, stabilized/solidified by cement CEM II after 28 days of curing, in an acidic environment. The mortars subjected to this study were investigated by X-ray diffraction (XRD) characterization to evaluate the influence of chromium waste on their mineralogical structure. In the study range (0.6–1.2%), increasing the mass percentage of Cr2O3 in the mortars indicates that chromium accelerates the hydration process and setting of the mortar and increases the mechanical strength of the mortars compared to the control sample. It was observed that the release of chromium during the Toxicity Characteristic Leaching Procedure (TCLP) test and the efficiency of the stabilization/solidification process depended on the initial Cr concentration and the leaching time. The use of XRD allowed the identification of new crystallized phases in the cement matrices, namely, CaCrO4·2H2O and chromium–ettringite Ca6Cr2(SO4)3(OH)12·26H2O, which confirms the immobilization of chromium and the efficiency of the stabilization/solidification process. In this research, the release mechanism was found to be primarily a surface phenomenon by modeling the experimental data (dissolution or precipitation). [ABSTRACT FROM AUTHOR]

The structural performance of buried drainage pipes is gradually deteriorating under the influence of external loads and chemical and microbial corrosion. It is crucial to reinforce them and improve their bearing capacity for safe use. One of the important technologies used to extend the service life of deteriorated pipes is the use of fiber-reinforced cementitious composites (FRCC) for spray repair. Combined with the current situation of drainage pipes, this article introduces the basic properties of FRCC, briefly describes the requirements for material performance for drainage pipe spraying rehabilitation, reviews the structural bearing capacity of drainage pipes repaired by spraying with FRCC, and discusses the relevant research and engineering applications of the spraying method. Studies show that FRCC has high strength and corrosion resistance, and excellent sprayability. The structural performance of the host pipe is significantly improved after repair, but measures should be taken to enhance the interfacial bonding performance during the repair. In the design of the liner wall thickness, there is no unified calculation theory, and the existing methods have not considered the influence of secondary load on the structure. It is recommended to combine the type of pipe defects and the degree of deterioration in further study. [ABSTRACT FROM AUTHOR]

The need for cementation constructions and material usage has increased tremendously. However, finding the optimum mix and designing the required construction is challenging. Hence, the present research work has planned to design a novel fruit fly-based mix selection (FFbMS) for designing the carbon nanotube (CNT). Here, the mixes that have been considered to design the single-walled CNT are polyvinyl alcohol (PVA) microfibre, carbon nanofibre (CNF) and cement paste (CP). Initially, the mixes are selected based on the ASTM C 305 standard, and the casting process has been performed. Then, several optimization iterations were executed to find the optimal state by valuing the mechanical properties in each iteration. Moreover, based on the gained compressive rate, tensile strength and crack rate, the optimal value has been set, and the mix range has been noted. The temperature range for testing Thermal characteristics varied from 100 to 1000 °C. The gained maximum compressive strength by a novel FFbMS is 24 GPA, and the flexural strength is 6.9 MPa at 600 °C and 4.8 at 1000 °C, which is quite better than the conventional mixes. Finally, the performance score has been measured in five ways: CP, CP + CNF, CP + PVA, CP + CNF + PVA and optimal CP + CNF + PVA. Here, the optimal CP + CNF + PVA have recorded the finest performance outcome. The gained maximum compressive strength by a novel FFbMS is 24 GPA, and the flexural strength is 6.9 MPa at 600 °C and 4.8 at 1000 °C, which is quite better than the conventional mixes. [ABSTRACT FROM AUTHOR]

According to this article, the novel, highly absorbent, resin microcapsules prepared by the sharp hole-bath method, together with the polypropylene fibers, were used in the cementitious materials, with an aim to study the impacts of the dosage of polypropylene fibers, the mass fraction of microcapsules and the curing age on the strength of mortar and its self-repair effect. The uniaxial compression test and the permeability test were also applied to evaluate the mechanical properties of specimens and the self-repair effect of cracks. The results showed that when the amount of microcapsules is 1.5% and the amount of polypropylene fibers is 0.17%, the specimen reaches its peak strength, meanwhile the microcapsules have no negative effect on its initial compressive strength. When the amount of microcapsules is 0.75% and the amount of polypropylene fibers is 0.17%, the strength repair rate and the seepage repair rate of cement-based materials reach the best. In addition, the strength repair rates showed that, compared with the single addition of microcapsules, the 'bridging effect' of polypropylene fibers could help microcapsules better complete the crack self-repair work. [ABSTRACT FROM AUTHOR]

Cement-based materials (CBM) are used for several applications in radioactive waste underground repositories as engineered barriers. Thaumasite sulfate attack (TSA) is a type of cement-based materials' corrosion, which has been investigated in regard to civil engineering structures, but very little research has been made on TSA in the environment of rad-waste repositories. The paper introduces types of rad-waste repositories and thaumasite characterization; summarizes mechanisms of TSA corrosion and its impact on CBM properties and durability; and defines the specifics of underground repositories in relation to TSA. High relative humidity is typical for underground disposal sites, cold temperatures (below 15 °C) are characteristic for near-surface repositories, while in deep geological repositories the temperatures may reach 80–100 °C which allows the decomposition and recrystallization of ettringite and eventually thaumasite. Sites located in clay rock, salt rock, limestone, dolomite etc., but also some waste forms itself may be rich in sulfates and carbonates. All these are conditions favoring TSA on CBM and thus research in this area should not be underestimated. [ABSTRACT FROM AUTHOR]

Magnesium slag (MS) discharged from the magnesium alloy industry exhibits very low hydration activity in cementitious materials. The surface characteristics of particles subjected to acidic medium treatment can enhance the hydraulic ability. Acid modification pre-treatment (AMP) represents a promising and viable approach. The feasibility of acid modification pre-treatment to enhance the activity of MS was investigated in this work, by studying the property evolution of MS pre-treated by three types of acids (formic acid, acetic acid, and phosphoric acid) and its hydration behavior with ordinary Portland cement paste. Experimental findings reveal that MS particles undergo corrosion during acid modification, resulting in a rough microstructure and smaller particle size. In comparison with cement blended with raw MS, the 28-day compressive strength of cement blended with modified MS increased by 17.51 % and 22.56 % for formic acid and acetic acid modification, respectively. Although organic acid modification did not alter the types of hydration products in cement blended with MS paste, the efficient modification by organic acids was attributed to both a significant increase in specific surface area (275 % for formic acid modification and 325 % for acetic acid modification) and the bonding of carboxyl groups to Ca2+ ions on the surface of MS. The substantial surface area of acetic acid-mediated MS enhanced the early hydration rate and notably reduced the induction period. The presence of carboxyl groups attached to the surface of MS particles facilitated hydration and the formation of C-S-H gels due to the nucleation site effect. Hence, organic acid modification offers promising strategies for utilizing silicate-based solid waste such as magnesium slag in cementitious materials. • Acid-modification pre-treatment increases the specific surface area of magnesium slag particles. • Rough microstructure of acid modified-MS enhances its hydration activity. • MS-Cement modified with formic acid exhibits 22.56 % strength improvements at 28 days. [ABSTRACT FROM AUTHOR]

This paper delves into the innovative realm of vascularization within concrete, a technique that embeds channel networks into the concrete matrix, mirroring the vascular systems found in living organisms. This approach facilitates the flow of diverse substances throughout the material, significantly expanding the functionalities of concrete beyond its traditional use. The work studies the core principles behind optimizing vascular networks in cementitious materials, from established methods like Constructal Law and Murray's Law to computational approaches and lesser-known theories like Percolation Theory and Darcy's Law. The discussion extends to fundamental fluid dynamics principles - Hagen-Poiseuille, Bernoulli's, Continuity, and Navier-Stokes Equations - and their significance in vascular network design. Additionally, the paper outlines various strategies to construct these vascular networks, addressing the evolution of fabrication methods over time and the challenges encountered. While most existing research focuses on self-healing and thermal regulation capabilities, this paper also explores the potential of vascular networks for a broad spectrum of applications. Through this review, the paper underscores vascularization's transformative potential in shaping concrete technology's future. • An innovative realm of nature-inspired vascularization within concrete was reviewed. • Core principles behind optimizing vascular networks in cementitious materials were summarized. • Fundamental fluid dynamics principles and their significance in vascular network design were reviewed. • Various strategies to construct vascular networks and the challenges encountered were reviewed. • Applications of vascularization in concrete such as self-healing and thermal regulation were discussed. [ABSTRACT FROM AUTHOR]

Copper slag (CS) is a kind of non-ferrous solid waste with low content of aluminosilicate and relatively high content of iron oxide. In this paper, the feasibility and mechanism of CS as the mineral admixture and precursor of alkali activated cementitious material were studied. The effects of CS on mechanical properties were studied and the hydration products were determined by several characterization methods. Scanning Electron Microscopy (SEM) and Mercury Injection Porosimetry (MIP) were performed to characterize the microstructure. The results show that CS composite fly ash (FA) has more advantages than CS alone, but its application as a mineral admixture is limited by the low activity. The alkali activated cementitious material prepared by CS and FA as precursor has excellent mechanical properties. The compressive strength of specimen at 28 days age can reach the maximum of 81.3 MPa when the dosage of CS is 30 %. The 3d and 28d compressive strength of the specimen contained 60 % CS obtained 57.7 MPa and 70.7 MPa, respectively. The research exhibits great potential for the future utilization of CS. • The effects of copper slag (CS) as mineral admixture and the precursor of alkali activated cementitious material are compared. • Compressive strength of the binders are improved due to the synergistic of fly ash (FA) and CS. • Mixing 30 % CS in GBFS-based alkali activated cementitious materials improved the mechanical performance. • The impact and potential of CS as a component of the cementitious materials are evaluated. [ABSTRACT FROM AUTHOR]

The CO2 emissions from the cement industry and the production of waste wood chips are increasing with the rapid growth of the construction industry. In order to develop a green environmental protection building material with low thermal conductivity and up to standard mechanical properties, in this study, pine waste wood chips were mixed into cement-based materials as fine aggregate, and three different kinds of cementitious binders were used, including sulfur aluminate cement (SAC), ordinary Portland cement (OPC), and granulated blast furnace slag (GBFS), to prepare a recycled light cementitious composite material. The mechanical, thermal conductivity, shrinkage, water absorption, and pore structure of a wood chip light cementitious composite material were studied by changing the Ch/B (the mass ratio of wood chip to binder). The results showed that the strength, dry density, and thermal conductivity of the specimens decreased significantly with the increase in the Ch/B, while the shrinkage, water absorption, and pore size increased with the increase in the Ch/B. By comparing three different kinds of cementitious binders, the dry density of the material prepared with OPC was 942 kg/m3, the compressive strength of the material prepared with SAC was 13.5 MPa, and the thermal conductivity of the material prepared with slag was the lowest at 0.15 W/m/K. From the perspective of low-cost and low-carbon emissions, it was determined that the best way to prepare a light cementitious composite with waste wood chips is to use granulated blast furnace slag (GBFS) as the cementitious binder. [ABSTRACT FROM AUTHOR]

In this paper, a novel core@shell nanosphere (TiO2@CoAl-LDH) based on layered double hydroxide (LDH) combined with a nano-TiO2 semiconductor was synthesized and introduced to cementitious materials via spraying technology and a smearing method. The compatibility with a cementitious matrix and the effects of TiO2@CoAl-LDH on cement hydration, surface microstructure, and the microscopic mechanical properties of mortar were investigated by AFM, microhardness testing, FESEM, and BET analysis. Meanwhile, the effects of TiO2@CoAl-LDH introduction methods on the photocatalytic performance and durability of the photocatalyst were systematically evaluated by methylene blue (MB) removal ratio and wear testing. The results show that TiO2@CoAl-LDH exhibits enhanced compatibility with cementitious matrices and a higher photocatalytic capacity than individual CoAl-LDH and nano-TiO2. The photocatalytic mortar prepared via spraying technology (CM-C) displays a higher photocatalytic capacity than that prepared via the smearing method (CM-S). Among them, the mortar with two layers of photocatalytic coatings (CM-C2) has the highest MB removal ratio, which reached 95.1% within 120 min of UV-visible light irradiation. While on the other hand, the wear test revealed that the smeared mortar has a higher photocatalytic capacity and better photocatalyst durability than the sprayed mortar. This work is expected to contribute to the development of multifunctional sustainable building materials. [ABSTRACT FROM AUTHOR]

Photoinduced processes governed by light activated TiO2 have been studied in many ways. One of the most active areas is the development of TiO2 photocatalysis technologies on their application for reducing environmental impacts. The immobilization of TiO2 on solid support, such as cementitious materials, greatly enhances its use in practical applications. In this review, a wide range of applications for achieving eco-efficient building using cementitious composite materials containing TiO2 photocatalyst was presented. The basic mechanism of photocatalysis, such as electron excitation, charge transfer process, reactive oxygen species (ROS) generation, and its role to oxidize the pollutant and microorganisms were extensively discussed. Unlike self-cleaning and air purification systems, the study on the antibacterial function of a cement-based surface containing TiO2 is very limited. In photocatalytic cementitious materials, the key element affecting the photocatalytic performance is the accessible active surface area. However, microstructure of cementitious materials changes with age due to hydration and surface carbonation. Hence, surface area reduction and mass transfer limitation become the main drawbacks of incorporating TiO2 in cementitious materials. This review, therefore, provides the state of the art in photocatalytic cement-based composite materials and identifies the areas in which future improvement is needed. [ABSTRACT FROM AUTHOR]

Epoxy resin, CFRP (Carbon Fiber Reinforced Polymer) sheet, and concrete flexural specimens are selected to study the durability of carbon fiber strengthened cementitious materials in a cold region. Two exposure environments, chloride immersion and salt-freeze coupling, are set up, and the mechanical deterioration is discussed utilizing a microscopic observation mechanical test and finite element analysis. The damage to the epoxy resin, CFRP sheet, and concrete exerts a more severe performance degradation in the salt-freeze coupling environment when compared with the chlorine salt immersion environment. The freeze–thaw action destroys the bonding surface of CFRP and concrete based on the microscope observation. The flexural strength of the specimens strengthened with CFRP is 3.6 times higher than that of the specimens without CFRP, while the degradation rate is only 50%. These observations show that the strengthened CFRP effectively improves the cementitious material's flexural performance in the cold region. The finite element model of epoxy and CFRP subjected to chloride immersion and salt-freeze coupling environment is established. The degradation formula of bond performance between CFRP and concrete is proposed. In addition, the flexural mechanical numerical model is established with and without CFRP strengthened concrete, respectively. Research results provide a technical reference for applying CFRP reinforced cementitious materials in a cold region. [ABSTRACT FROM AUTHOR]

In this paper, for the first time, we investigate the inherent ionic conductivity of seawater-based cementitious composites containing marine sand aggregates, when air cured over 28 days with the objective of uncovering new functionalities. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and density functional theory (DFT) were employed to elucidate the ionic conduction mechanisms in this material system and characterize its stress self-sensing and electrochemical charge retention capabilities. The results revealed that the marine aggregates are not ionic conductive materials; however, they facilitate improved electrochemical response through enhanced formation of highly ion-exchanging calcium-silicate-hydrate (C-S-H) phases, coupled with integrated porous channels that enable sustained ion mobility despite drying. This synergistic ion transport yielded a bulk ionic resistivity around 25 kΩ⊡cm at room temperature, which lies in typical ranges seen in solid-state electrolytes for battery systems. Controlled compressive loading indicates appreciable self-sensing capacity at low-stress levels, suggesting applicability to detect the onset of mechanical damage. Negligible charge leakage upon 28 days of curing further demonstrates the electrical energy storage potential of the sea-based cement. By harnessing locally available seawater and marine sand resources to develop ionic conductive cementitious composites, this work provides the framework to optimize durable multifunctionality for sensing and electrical energy storage in reinforced concrete infrastructure. This in return improves the sustainability and energy efficiency of the built environment. • A new approach to induce self-sensing and energy storage in cementitious composites using marine sand. • Marine sand enhances ionic conductivity, electroactivity, charge storage capacity, and self-sensing composites. • Coupling between self-monitoring and energy storage enables multifunctional structural materials. • Marine sand valorizes this abundant waste for advanced cement composites. [ABSTRACT FROM AUTHOR]

There is currently an increased need for associating construction material properties and behavior with the nature of their microstructure. One of the major issues in this context is the need for understanding the curing process in freshly poured cement-based materials. This is particularly important when nanoreinforcement materials, such as carbon nanotubes, are used to enhance the mechanical behavior and multifunctionality of the final structure. The solidification point, at which the state of liquid suspension transmutes to the solid state, is of particular interest since it greatly influences the load-bearing capacity of the cement-based material and its structural behavior at the long term. The main purpose of the present work is to develop a reliable method for monitoring the hydration process during the early stages of freshly poured cementitious composites enhanced with carbon nanotubes. This methodology is based on the use of nonlinear elastic waves. To achieve this goal, a combination of contact ultrasonics with noncontact optical detection was used. The detection method for evaluating the setting process is based on the assessment of higher-harmonic amplitudes of an ultrasonic wave, with a given frequency, propagating through the cementitious material. It was observed that the material nonlinearity changes significantly during the hardening process, compared to velocity or attenuation measurements which are based on linear acoustics. These changes were more noticeable as the concentration of carbon nanotubes in the cement matrix increases, indicating that higher harmonics are more susceptible to minute microstructural changes. [ABSTRACT FROM AUTHOR]

Featured Application: Superabsorbent polymers of novel structure have been used in cementitious-based composite materials improving their self-healing behavior by an index of 60%. Cementitious structures have prevailed worldwide and are expected to exhibit further growth in the future. Nevertheless, cement cracking is an issue that needs to be addressed in order to enhance structure durability and sustainability especially when exposed to aggressive environments. The purpose of this work was to examine the impact of the Superabsorbent Polymers (SAPs) incorporation into cementitious composite materials (mortars) with respect to their structure (hybrid structure consisting of organic core—inorganic shell) and evaluate the microstructure and self-healing properties of the obtained mortars. The applied SAPs were tailored to maintain their functionality in the cementitious environment. Control and mortar/SAPs specimens with two different SAPs concentrations (1 and 2% bwoc) were molded and their mechanical properties were determined according to EN 196-1, while their microstructure and self-healing behavior were evaluated via microCT. Compressive strength, a key property for mortars, which often degrades with SAPs incorporation, in this work, practically remained intact for all specimens. This is coherent with the porosity reduction and the narrower range of pore size distribution for the mortar/SAPs specimens as determined via microCT. Moreover, the self-healing behavior of mortar-SAPs specimens was enhanced up to 60% compared to control specimens. Conclusively, the overall SAPs functionality in cementitious-based materials was optimized. [ABSTRACT FROM AUTHOR]

This article presents a study on crack mode classification in cementitious materials under uniaxial compression using gaussian mixture modeling (GMM) of acoustic emissions approach. To implement a retrofitting method to an in-service concrete structure, a prior knowledge about the type of crack developed in the concrete structure is useful. Because, occurrence of AE events during fracture process in solids is random, a probabilsitc method has been required to classify the AE sources related to different types of cracks. In this study, a monotonically increasing unconfined uniaxial compressive load has been applied on different cylindrical specimens of plain cement concrete cast with maximum coarse aggregate size of 20 mm, 12.5 mm and cement mortar to study crack classification. It has been observed that the slope of the line separating the AE data clusters belonging to tensile and shear cracks is more steep for the concrete specimen containing 20 mm maximum coarse aggregate when compared to the concrete specimen containing 12.5 mm maximum coarse aggregate and cement mortar. This indicated that as the coarse aggregate size in concrete increased, the generated AE events related to shear cracking decreased. Also, the AE based b-value has reached minimum at the peak load. At the time of failure, AE related to shear cracking has increased sharply. [ABSTRACT FROM AUTHOR]

The present research investigates the feasibility of manufacturing masonry mortars with recycled sand. The primary aim is to study the effect of fine recycled aggregates on fresh and hardened states with properties. Two series of mortars were designed by substituting natural sand with recycled sand, with variable sand replacement ratios ranging from 0% to 100%. One series, named variable workability series, has variable workability with constant water to cement ratio (W/C), while the other series, called constant workability series, has a constant workability with variable W/C. The density, air content, and slump of mortars in fresh state were measured with a special attention devoted to the effect of pre-saturation of recycled sand on the slump. In the hardened state, the microstructure was studied by means of water accessible porosity test and mercury intrusion porosimetry test. Flexural and compressive strength as well as the dynamic modulus of elasticity were also examined and the correlations between these properties and the microstructure have been established. It was found that the properties of mortars with recycled sand are lower than those obtained for the natural sand mortar (−20% for variable workability series and −45% for constant workability series at the age of 28 days). For the series with variable workability, mechanical properties decrease to a step starting from 30% replacement ratio, while linearly decrease for the mortars with constant workability. The difference between the two series lies in the difference in total porosities and the pore size distribution. [ABSTRACT FROM AUTHOR]

Nanomaterials have made significant progress in the field of cementitious materials, but suffer from primary problems of high cost and poor dispersity. Carbon dots (CDs) as a novel low-cost and high-dispersity nanomaterial preliminarily demonstrate their potential for cement. Nevertheless, it lacks systematic research on their effects on cement properties. For the first time, this work comprehensively investigates the effects of CDs on the hydration, mechanics, and chloride binding of cement composites. More importantly, the relevant mechanisms are revealed in depth. Specifically, cost-efficient ($0.013/g) and well-dispersed (dispersed in simulated concrete pore solution for 7 d) CDs are directly prepared by a facile microwave approach. The CDs dramatically retard the early hydration, improve later mechanical performance, and obviously enhance chloride binding. In detail, 0.2 wt% CDs reduce the second exothermic peak value by 75%, but improve the chloride binding capacity of paste by 51%. And 0.1 wt% CDs enhance the compressive/flexural strength of mortar by 17%/21%. Crucially, related influence mechanisms are uncovered. Namely, CDs create a protective barrier to retard hydration through the complexation of their abundant surface groups with Ca2+; While CDs exert the nucleation effect to boost the formation of C–S–H and Friedel's salt, thereby playing a positive impact on chloride binding; Meanwhile, CDs with suitable dosages carry out nucleation effect to counteract their air-entraining effect, thus improving later mechanical properties of cement composites. This study is expected to provide a novel low-cost and high-dispersity CDs nanomaterial to advance the development of high-performance cementitious materials. [Display omitted] • Low-cost and high-dispersity CDs are prepared by simple and eco-friendly microwave way. • Effects of CDs on properties of cement matrices are comprehensively investigated. • Influence mechanisms of CDs on properties of cement composites are firstly revealed. [ABSTRACT FROM AUTHOR]

Surface protective coatings are prone to cracking and failure due to the deformation of concrete structure itself and harsh service environment factors such as UV, ion erosion, and large temperature differences during the period of service. It is urgently required to develop new types of self-healing coatings to provide long-lasting protection for concrete structures and extend their service life. In this investigation, a lignin-based self-healing agent was prepared using aniline and lignin as raw materials. Its characterization was analyzed by SEM and FT-IR. By introducing the lignin-based healing agent and dynamic disulfide bonds, a new kind of self-healing polyurethane coating was prepared, and its self-healing ability was qualitatively and quantitatively evaluated, indicating that it had excellent self-healing performance. After self-healing process, the crack could withstand bending force. Moreover, with the increased temperature, the self-healing efficiency of tensile strength gradually increased, reaching a maximum of 86.42% at 60 ℃. Meanwhile, the self-healing efficiency of its elongation at break firstly increased and then gradually decreased, reaching a maximum of 93.77% at 40 ℃. This self-healing polyurethane coating had high hydrophobicity (139.4°) and excellent abrasion resistance. After 40 friction cycles, its hydrophobicity only decreased by 10.9% to 124.2°. In addition, this self-healing protective coating also showed excellent resistance to chloride ions, effectively protecting cementitious materials with the damaged surface. This work provides a new method for long-term protection of concrete structures. • Self-healing polyurethane coating had excellent self-healing performance. • Self-healing polyurethane coating had high hydrophobicity and good abrasion resistance. • Self-healing polyurethane coating had positive protective effects on cement-based materials. [ABSTRACT FROM AUTHOR]

This study focused on the modification of a mixture of a lime-based composite cementitious material (LCM) by using chemical admixtures to increase the mechanical performance of the LCM. The different types and amounts of chemical admixtures including NaOH and Na 2 SO 4 were used as activators to prepare the novel modified LCM. The mechanical strength, hydration kinetics, assemblage of hydrates and microstructure of the modified LCM were systemically explored and compared to conventional LCM. The experimental results indicated that Na 2 SO 4 had better effects on the improvement of LCM strength compared to NaOH when used alone as the activator. The composite activator that was composed of Na 2 SO 4 and NaOH showed the optimal effects on the increase of the LCM strength. The composite activator effectively increased the hydration rate of the LCM, and more hydrates were formed during the hydration process of the LCM. Furthermore, the U-phase was formed only in the hydration products of the LCM containing the composite activator. A large amount of U-phase as crystals effectively occupied and filled the space in the LCM paste and led to the formation of a compact microstructure with fewer macro-pores. Thus, the presence of U-phase in the paste increased the strength of the LCM. [ABSTRACT FROM AUTHOR]

Abstract Although steel is one of the most common and useful reinforcing materials worldwide, it has always had a major disadvantage: it rusts. This study proposes the utilization of high performance cementitious mortar (HPCM) as a repairing material for corroded RC elements. The experimental study was executed in two phases. Phase one evaluated the physical properties and corrosion resistance of the HPCM layer and compared the recorded results with those of conventional concrete. Different tests and measurements were conducted (XRF, XRD, SEM images, stereoscopic images, and half-cell readings) for this purpose. Phase two studied the structural behavior of corroded RC beams that were repaired with an HPCM layer. The investigated parameter was the effect of adding HPCM layers with different thicknesses to the bottom chord of specimens subjected to different corrosion levels. Six corroded specimens were tested under three-point loading with different corrosion levels (10%, 15%, and 20% of mass loss) and different HPCM layer thicknesses (0, 50, and 80 mm), in addition to three non-corroded control specimens with different HPCM layer thicknesses (0, 50, and 80 mm). From the results, the specimens with the HPCM layer material confirmed the effective behavior of this material to reduce corrosion. Moreover, the HPCM layer showed a significant positive impact on the ultimate capacity and cracking pattern of the tested RC specimens. [ABSTRACT FROM AUTHOR]

• Within the elastic regime, the resistivity drops as the compression increasing. • The resistivity reaction can match well with the damage developing process. • The damage calculated with resistivity can arrive 0.8 at last. Pilot researches prove that graphene nanoplatelets (GNPs) are promising nano-sized additives to improve the smartness of cementitious materials. This work aims to reveal the explicit correlation between the damage development and the resistivity reaction of cementitious composites infilled with GNPs. A weight content of 4.5% (GNPs/cement) is used to cast two groups of concrete samples, named as C20 and C30 (according to their designed compressive strength), whose volume fractions of GNPs are 0.43% and 0.61%, respectively. Investigations shows different failure patterns during compression loading and their piezoresistive characteristics are probed systematically. Additionally, damages determined by strain-stress curves and ultrasonic pulse velocity penetrations in the middle section are also studied for comparing. The damage evolution process illustrated by resistivity reactions contains a slight decrease of resistivity within the elastic regime, a moderate damage developing stage before the peak force, an expeditive damage section just after the peak force and a relaxed damage expanding when the stress drops to less than 50% of the strength. At last, the damages obtained with resistivities increase to 0.8. This indicates that the piezoresistivity of smart concrete containing GNPs can be a promising tool to detect damages detailedly. [ABSTRACT FROM AUTHOR]

The structural performance of reinforced concrete (RC) beams strengthened with fabric-reinforced cementitious matrix (FRCM) was investigated. Fourteen unstrengthened and strengthened beams were tested in flexure under four-point load configuration. Test parameters included the internal reinforcement ratios (0.5% representing flexure-deficient beams and 0.72 or 1.27% representing typical under-reinforced beams), the type of FRCM fabric (carbon and polyparaphenylene benzobisoxazole [PBO]), the number of fabric plies (one and two plies), and the strengthening scheme (straight at soffit or U-wrap). Test results revealed that the gain in flexural strength was inversely proportional to the internal reinforcement ratio of the beams regardless of the fabric type, scheme, or number of plies used. U-wrap strengthening scheme provided an inherent anchorage that limited the premature delamination of the fabric, which was a common mode of failure in the soffit-strengthening scheme. Beams strengthened with U-wrap single-ply of carbon- and PBO-FRCM showed an average gain in strength of 70% and 51%, respectively, compared to 28% and 20% for their counterparts strengthened with the soffit scheme. Moreover, the use of U-wrap double-ply of PBO fabric resulted in an average gain in strength of 72%. The theoretical formulations of ACI 549 satisfactorily predicted the load-carrying capacities of the soffit and U-wrap strengthened beams with an average ratio of Pu/Pu Th of 1.07 and a standard deviation of 11%. [ABSTRACT FROM AUTHOR]

Encapsulation‐based self‐healing technology is an effective method for healing the crack‐deteriorated cementitious material. Encapsulation‐based self‐healing initiates by crack occurrence and progresses by chemical reaction of released self‐healing agents in the cracks, which are contained in capsules. In this paper, a review has been conducted on various healing agents, encapsulation techniques, as well as experimental approaches, basing on existing substantial studies. Recently, there is no consistent agreement on the effective criteria for evaluating encapsulation‐based self‐healing and mature solution for increasing the survival ratio of capsules during mixing. However, the polyurethane‐based healing agents filled in glass or ceramic tubes are popularly applied for self‐healing cementitious materials. Besides, the polymer capsules present promising attractions for engineering application. Mechanical strength and durability are the most widely used self‐healing efficiency assessment indexes. On the other hand, nondestructive technique and numerical modeling have also extensively adopted to visualize and evaluate the self‐healing behavior of cementitious materials. However, there are still some challenges, which require further investigations, such as behavior of crack propagation, kinetics of healing agent in discrete crack surfaces, effect of inserted capsules on the mechanical properties of self‐healed cementitious materials. [ABSTRACT FROM AUTHOR]

Abstract Cracking occurrence due to shrinkage related effects is a widely recognised issue which is frequently evaluated with the shrinkage restraining ring test. This paper provides a state-of-the-art review of the ring test method, which has been used for the last four decades. The last review on such matter was conducted only in early 2000s; however, a significant amount of studies has been conducted since then and considerable advancements or modifications in this testing method have taken place over the last decade. Studies on the traditional ring test, i.e. a circular concrete ring cast around a steel ring, are identified and the history, tendencies, practices and quantitative methods are analysed thoroughly. Furthermore, any modifications/advancements in the testing method with respect to their purpose, applications and capabilities based on current knowledge, are addressed. Finally, an insight on the challenges that the developers of testing methods for restrained shrinkage are faced with is given together with perspectives for their future potential improvement. [ABSTRACT FROM AUTHOR]

Self-healing cementitious materials are regarded as an effective choice to increase the sustainability of the resource and environment. In this study, an alkali-responsive mineral self-healing agent (AMS) was prepared inspired by bone repair. The healing component, phosphate, was loaded into the halloysite nanotubes (HNTs) and encapsulated by the layer-by-layer (LbL) self-assembly method. The structure and alkali-responsive behavior of AMS, the effect of AMS on the mechanical properties of cement pastes, the stability of AMS before cement cracking, and its effect on the self-healing efficiency of the cement pastes were investigated with a range of analytical techniques. Results showed that AMS was successfully encapsulated and endowed with excellent alkali responsiveness. The incorporation of AMS was effective in reinforcing the mechanical performances of cement pastes. XRD analysis showed that the phosphate encapsulated in AMS can be mostly retained until cracks appear. When cracks occurred, the B-type carbonated calcium-deficient hydroxyapatite was found as the main product in the crack environment. The surface crack around 130 μm in the damaged specimens containing 5% AMS was fully sealed and healed, and its damaged compressive strength was almost completely recovered after curing for 28 days. The synergistic effect of autonomous healing triggered by AMS and autogenous healing behavior promotes the self-healing process and improves the self-healing efficiency of the hardened cement pastes. [Display omitted] • Alkali-responsive mineral self-healing agent (AMS) was prepared by LbL self-assembly. • LbL self-assembly endows AMS with excellent alkali responsive behavior. • The incorporation of AMS improved the mechanical properties of cement pastes. • AMS accelerated self-healing process and improved healing efficiency of cement. • Healing products in the cracks consisted of B-type carbonated CdHAP, CH, and calcite. [ABSTRACT FROM AUTHOR]

Abstract Novel techniques such as power ultrasound (PUS) are currently under consideration to improve the hydration of cementitious materials and to promote the effectiveness of replacing supplementary cementitious materials; SCMs, in terms of mechanical, microstructural and transport properties. This could enhance the properties of cementitious composites, reduce the quantity of waste materials, as well as decreasing the CO 2 footprint of cementitious materials. A handful of studies have investigated this promising field and little is known about the mechanisms by which the ultrasound acts in cement-based systems. This paper outlines the possible mechanisms involved on the effects of PUS as a method to promote cement hydration kinetics of Portland cement and binary blends. It also reviews and analyses previous research conducted mostly on the dispersing effects of PUS on the enhancement of pozzolanic reactivity of SCMs in cementitious systems. This review concludes with some perspectives on research needed to gain a fundamental understanding of this emerging field. Graphical abstract Unlabelled Image Highlights • Effect of acoustic cavitation on sonocrystallisation and its application in cementitious materials have been discussed. • It has been hypothesized that power ultrasound has a potential to enhance cement hydration due to the proposed mechanisms. • Scarce current studies show that the PUS can improve the mechanical and microstructural properties of cementitious composites. • Potential research needed to obtain a better understanding of the PUS interaction in cementitious materials have been suggested. [ABSTRACT FROM AUTHOR]

Highlights • Specimens for all methods were prepared from the same cement paste cylinder. • Permeabilities determined by various methods were used in a moisture transport model. • Permeability determined by beam bending can provide closer results to measured ones. • Katz–Thompson and Kozeny-Carman equations largely overestimate permeability. • The effect of choosing an appropriate method is more important than the batch effect. Abstract Values of water permeability for cementitious materials reported in the literature show a large scatter. This is partially attributed to the fact that materials used in these studies are different. To eliminate the effects of cements, specimen preparation, curing conditions and other batch effects, this study employs a single cement paste to prepare all specimens for a variety of permeability determination methods, such as beam-bending, sorptivity, Katz–Thompson and Kozeny-Carman equations. Permeabilities determined by these methods are then used in a moisture transport model. Compared with the measured mass loss curves, we found that permeability determined by the beam-bending method is more suitable for the moisture transport model than the other methods. The difference results from the use of a saturated specimen in the beam-bending method, while specimens in the other methods are dried (or rewetted). As already shown in the literature, the microstructure of the dried or rewetted specimens is altered and different to the original microstructure of the water saturated specimens. In addition, we found that drying tests for the inverse analysis method must be done at high RHs (63% in this study) to reduce the effect of vapor diffusion on the determination of water permeability. [ABSTRACT FROM AUTHOR]

Highlights • Influence of nanoparticles on the properties of cement-based materials is discussed. • Nanoparticles can significantly alter the hydration mechanism of cement paste. • Research needs are identified based on the gaps in the current state of knowledge. Abstract This review paper intends to synthesise the data published in the literature on the uses of different types of nanomaterials in cementitious materials. According to ASTM, depending on types, the size of nanoparticles varies from 1 nm to 100 nm. Application of nanomaterials in different sectors has shown that the properties of conventional materials can be significantly improved when nanoparticles are included. The addition of nanoparticles in cementitious materials can act as a filler agent, producing a dense matrix and reduce the growth of micro pores. Some nanoparticles also help in the secondary reactions forming cement composite and contribute to the strength development. Moreover, this paper summarises the current knowledge of the microstructure, mechanical strength and durability of cementitious materials when incorporating different types of nanoparticles. In addition, research needs are identified based on the gaps in the current state of knowledge on using nanoparticles in cement-based construction materials. [ABSTRACT FROM AUTHOR]

Abstract The quaternary system Ca(II)–Pu(III/IV)–OH–ISA was investigated in a series of solubility experiments where equilibrium conditions were reached from undersaturation conditions with PuO 2 (ncr,hyd) at T = (22 ± 2) °C under Ar atmosphere. Experiments were performed in 0.1 m NaCl–NaOH–NaISA–CaCl 2 solutions at 8 ≤ pH m ≤ 12.5 (pH m = –log [H+], in molal units), 10−5 m ≤ m(ISA) tot ≤ 10−2 m and 10−3.5 m ≤ m(Ca) tot ≤ 0.02 m. Reducing conditions were adjusted and buffered with hydroquinone (HQ) or Sn(II), which allowed us to work in the (pe + pH m) region ≈ 9 and ≈ 1.5, respectively. Solid phase characterization (in-situ XRD, XANES and EXAFS) and analogy with the ternary system Pu–OH–ISA previously studied by our group indicate that PuO 2 (ncr,hyd) remains unaltered in the course of the solubility experiments at pH m ≤ 12 and controls the solubility of Pu under reducing conditions in the presence of ISA and Ca(II). In HQ-systems, the impact of ISA on the solubility of PuO 2 (ncr,hyd) is clearly enhanced compared to Ca(II)-free solutions of analogous composition, thus indicating the formation of quaternary complexes of the type Ca(II)–Pu(IV)–OH–ISA in the aqueous phase. The combination of slope analysis of the solubility data and DFT calculations support the predominance of the two aqueous quaternary complexes Ca(II)Pu(IV)(OH) 3 ISA –H + and Ca(II)Pu(IV)(OH) 3 ISA –2H (aq) below and above pH m ≈ 11, respectively. The same speciation scheme explains properly the solubility of Pu in Sn(II)-buffered systems at pH m > 11. Below this pH m , solubility data under these very reducing conditions suggest the possible formation of ternary Pu(III)–OH–ISA aqueous complexes, although the scatter of the data does not allow a definitive conclusion to be drawn. The presence of Ca(II) in solution destabilizes Pu–ISA colloids, which significantly enhance Pu solubility in comparable, Ca-free systems. Based on these experimental and theoretical results, a thermodynamic model for the system Ca2+–Pu4+–OH––Cl––ISA––H 2 O(l) is derived. This study provides quantitative tools to evaluate the solubility behavior of Pu in reducing cementitious environments containing ISA, as expected in underground repositories for low- and intermediate-level radioactive waste (L/ILW) due to the degradation of cellulosic materials. Highlights • The presence of Ca(II) and ISA increases Pu solubility up to 2.5 log 10 -units. • Formation of Ca(II)–Pu(IV)–OH–ISA complexes confirmed in alkaline, reducing systems. • Ca(II) ions contribute to the agglomeration of "Pu–ISA" colloids. • DFT provides relevant insights on the structures of Ca(II)–Pu(IV)–OH–ISA complexes. • A thermodynamic model is derived for the system Ca2+–Pu4+–OH––Cl––ISA––H 2 O(l). [ABSTRACT FROM AUTHOR]

The chemical and physical processes associated with alkali–aggregate reaction and delayed ettringite formation, otherwise known as internal swelling reactions (ISRs), have been the subject of considerable research spanning several decades, yet the implications for affected structures are still open to debate. A major knowledge gap currently exists between the diagnosis and prognosis of ISR mechanisms, and the quantification and management of risk associated with ISR expansion in structures. This lack of understanding of the effects of ISRs on structural behaviour may be attributed to the fact that parameters such as confinement, boundary conditions, anisotropy and loading conditions are complex and vary greatly in existing structures. Furthermore, the correlation between the results of microscopic/macroscopic analyses on concrete core samples and the in situ performance of large-scale structures is still not well understood, even at a fundamental level. The aim of this paper is to summarise current knowledge of the structural implications of ISR mechanisms in concrete structures and stimulate a discussion of the importance of pursuing multi-scale experimental testing programs for the assessment of ageing infrastructure. A parametric analysis is included using the software VecTor2. [ABSTRACT FROM AUTHOR]

Graphene oxide has recently been considered as an ideal candidate for enhancing the mechanical properties of the cement due to its good dispersion property and high surface area. Much of work has been done on experimentally investigating the mechanical properties of graphene oxide-cementitious composites; but there are currently no models for accurate estimation of their mechanical properties, making proper analysis and design of graphene oxide-cement-based materials a major challenge. This paper attempts to develop a novel multi-scale analytical model for predicting the elastic modulus of graphene oxide-cement taking into account the graphene oxide/cement ratio, porosity and mechanical properties of different phases. This model employs Eshelby tensor and Mori-Tanaka solution in the process of upscaling the elastic properties of graphene oxide-cement through different length scales. In-situ micro-bending tests were conducted to elucidate the behaviour of the graphene oxide-cement composites and verify the proposed model. The obtained results showed that the addition of graphene oxide can change the morphology and enhance the mechanical properties of the cement. The developed model can be used as a tool to determine the elastic properties of graphene oxide-cement through different length scales. [ABSTRACT FROM AUTHOR]

Concrete structures are often subjected to drying in the natural environment. To simulate moisture transport in concrete during drying, a continuum model is commonly used, which generally requires the measured water vapor desorption isotherm as input data to address the equilibrium between liquid phase and water vapor at a given temperature. The main problem in measuring desorption isotherms is that the sample needs very long time to reach mass equilibrium at a certain relative humidity. To improve the method of measurement of sorption isotherms, we proposed to use Weibull equation to determine the mass loss at the infinite time. However, Weibull equation does not work well with the anomalous drying kinetics that were recently reported in the literature. In this paper, based on the theory of dual-porosity, a new equation is proposed by separating the moisture transport in the large and small pores to estimate the drying kinetics for cementitious materials. Fitting the drying kinetics measured by the dynamic vapor sorption analyzer shows that the newly developed equation has a very high capability for a large range of relative humidities, especially for the anomalous drying kinetics. This paper also demonstrates that using the proposed equation can reduce the duration of measuring desorption isotherms. [ABSTRACT FROM AUTHOR]

Various systems for simulating particulate matter are developed and used in concrete technology for producing virtual cementitious materials on the different levels of the microstructure. Basically, the systems can be classified as two distinct families, namely random sequential addition systems (RSAs) and discrete element methods (DEMs). The first type is hardly being used for this purpose outside concrete technology, but became popular among concrete technologists. Hence, it is of utmost relevance to compare the two families in their capabilities, so that the reliability of produced data can be estimated. This paper pursues to do this on the basis of earlier published material of work performed by a succession of PhD students in the group of the second author. Limited references will be given to external sources. [ABSTRACT FROM AUTHOR]

We employ a numerical methodology to predict the freeze-thaw performance of cementitious composites containing lightweight aggregates (LWAs) impregnated with phase change material (PCM) as thermal energy storage (TES) agent. The governing equation for heat transfer is combined with homogenization techniques to predict the temperature and associated heat flow for cementitious materials during the phase transition of the PCM. The material properties of the cementitious composite and heat dissipation behavior during thermal cycling were characterized using a small-scale longitudinal guarded comparative calorimeter (LGCC) test. Phase transitions associated with freezing/melting of PCM occurs gradually over a narrow temperature range. Pore size effect of LWA on freezing and melting behavior of PCM was found to be relatively small. This approach is extended to the prediction of the thermal energy storage capacity of PCM on improving the freeze-thaw performance of concrete specimens exposed to realistic thermal conditions at various locations in the United States. [ABSTRACT FROM AUTHOR]

Cementitious Repair Materials (CRMs) in the construction industry have been used for many decades now and has become a very important part of activities in cement world. The performance of some of these CRMs when applied to retrofitting concrete structural elements is also well documented. However, the characterization of some of the CRMs at the micro- and nano level is not fully documented. The first step to studying materials at the microscopic level is to be able to fabricate proper specimens for microscopy. In this study, a special and newly developed class of CRM was selected and fabricated by Focused Ion Beam (FIB) using well-known “Lift-out” technique. The prepared specimen was later examined using various analytical techniques such as energy dispersive x-ray analysis using one of the highest and most stable Scanning Transmission Electron Holography Microscopy (STEHM) around the world. This process enabled understanding of the composition, morphology, and spatial distribution of various phases of the CRM. It was observed that the microstructure consisted of a very fine, compact, and homogenous amorphous structure. X-ray analysis indicated that there was considerable deviation between the Si/Ca ratios for the hydrated product. [ABSTRACT FROM AUTHOR]

This work makes the link between the experimental technique of x-ray tomography and the reliable representation of the heterogeneities of a cementitious material at the meso-scale (aggregates, mortar matrix and macro-porosity). An image analysis procedure and its validation are presented. Images coming from x-rays scans are treated to finally obtain a trinary 3D image, where each phase of the material's meso-structure is separated. The separation of the aggregates from the mortar matrix is the technical challenge, due to the physics of x-ray interaction with matter, addressed on this work. Validation of the proposed method is made by comparing the grain size distribution curves computed from images of the same set of aggregates coming from x-rays and neutron scans. The reliably obtained morphology can be used as a basis for direct physical simulations, as well as data to improve morphological models of any type. [ABSTRACT FROM AUTHOR]

Among the many possible strategies for reducing anthropogenic greenhouse gas (GHG) emissions is reduction of emissions associated with the production of concrete, which is responsible for 8–9% of global anthropognic GHG emissions. Using supplementary cementitious materials (SCMs) in concrete to offset demand for clinker in cement is a commonly proposed method to cut GHG emissions from concrete production. The most commonly used SCMs are industrial byproducts, such as fly ash and ground granulated blast furnace slag, but the extent to which these SCMs should be used in individual concrete mixtures is not well examined. This research examines the contribution of fly ash and ground granulated blast furnace slag to compressive strength, the role of allocation in the assessment of environmental impacts, and the impacts of transportation. Quantitative analyses are developed using environmental impact assessments and comparisons are drawn based on changes in GHG emissions for concrete production. The findings of this research show that these three factors can outweigh benefits associated with use of SCMs: depending on SCM type and use of allocation or changes in transportation, high levels of SCM replacement do not consistently result in lower GHG emissions for the production of concrete per unit strength. Limited supplies of these popular byproduct SCMs amplifies the necessity to efficiently use these materials. Within the limitations of this study, this work shows strategic use of SCMs to cut GHG emissions based on regional availability and based on application should be a priority. [ABSTRACT FROM AUTHOR]

Storing healing agents in capsules is one of the most promising self-healing methods in cementitious materials. Because of the considerable advantage of microencapsulation, it has become more interested as compared to the other encapsulation methods. The sodium silicate, which has many advantages as a healing agent in cementitious materials, can be encapsulated through the interfacial polymerization of shell-forming monomer on the aqueous sodium silicate droplets. This study, which is a part of comprehensive project, aimed to produce these microcapsules by optimization of the monomer. The microcapsules were characterized by the yield, SEM, EDS, FTIR, TGA, and XRD analyses. In addition, the fracture behavior of the optimized microcapsule was examined in a cement paste matrix. It was observed that most of the microcapsules seem to be spherical shaped and free-flowing powder. Fracture behavior of optimized microcapsules revealed a sufficient shell-matrix interfacial bond strength which is essential for releasing healing agent into cracks. [ABSTRACT FROM AUTHOR]