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Soil stabilization technology has been applied for a long time in the infrastructure construction field. Currently, the use of waste materials as stabilizer is growing in attention, because it promises to develop green and high-performance soil stabilization efficiency. In this work, three common waste materials, including rice husk ash (RHA), steel slag (SS) and iron tailing (IT) powder, were selected and synergistically utilized with cement to prepare stabilized soil. The mechanical strength, hydration degree and microstructure of the stabilized soil samples were tested. The experimental results showed that the mechanical strengths of the samples were improved as the cement content increased. To be specific, RHA-blended samples exhibited the lowest strengths compared with those incorporating SS and IT, indicating the poor effect of RHA on stimulating strength improvement. Moreover, SS and IT showed a much more significant effect on enhancing the mechanical strength for the stabilized soil samples, and the strength increasing rates can reach up to 60% compared to the reference batch. In addition, microstructural analysis results further verified the benefits of cement and waste materials on improving the performance of stabilized soil samples, as the hydration reaction and pore structure were proven to be improved with the aid of waste materials. This work gives insights into environmentally friendly road construction with high utilization of selected common wastes. [ABSTRACT FROM AUTHOR]

As urbanisation and infrastructure development continue to drive rising cement demand, the imperative to significantly reduce emissions from this emissions-intensive sector has become increasingly urgent, especially in the context of global climate goals such as achieving net zero emissions by 2050. This review examines the status, challenges and prospects of low-carbon cement technologies and mitigation strategies through the lens of the U.K. cement industry. A mixed-methods approach was employed, combining structured literature searches across academic databases with analyses of industry reports, market data and technological roadmaps to ensure a comprehensive evaluation. Following an outline of cement production, resource flows and the sector's landscape in the U.K., the review delves into an array of decarbonisation pathways. This includes deploying the best available technologies (BATs), fuel switching, carbon capture utilisation and storage (CCUS), clinker substitution and low-carbon cement formulations. A critical assessment is provided on the technological readiness, costs, resource availability considerations and scalability aspects governing the widespread implementation prospects of these approaches within the U.K. cement industry. Furthermore, this study proposes a roadmap that considers priority avenues and policy needs essential for facilitating the transition towards sustainable cement production aligned with the U.K.'s net zero obligations by 2050. This evaluation contributes significantly to the ongoing decarbonisation discourse by holistically mapping technological solutions and strategic imperatives tailored to the unique challenges and opportunities presented by the U.K. cement sector. [ABSTRACT FROM AUTHOR]

The rapid expansion of photovoltaic (PV) technology as a source of renewable energy has resulted in a significant increase in PV panel waste, creating environmental and economic challenges. A promising strategy to address these challenges is the reuse of glass waste from decommissioned PV panels as a component of cementitious materials. This review explores the potential of integrating glass waste from PV panels into cementitious materials, focusing on its impact on their mechanical, thermal, and durability properties. This analysis includes various methods of processing PV glass waste, such as crushing and grinding, to obtain the desired particle size for cementitious applications. It goes on to analyze how advances in cementitious materials can facilitate the incorporation of PV glass waste, helping to improve properties such as compressive strength, workability, and setting time. In addition, this review makes a detailed analysis of the long-term sustainability and environmental benefits of PV glass waste, highlighting its potential to reduce the carbon footprint of cementitious materials. Incorporating PV glass waste can improve certain properties of cementitious materials, resulting in increased durability and improved thermal insulation, while contributing to waste reduction and resource conservation. This review highlights the importance of developing standardized recycling methods and integration processes and identifies areas for further research to optimize the use of PV glass waste in cement formulations. Ultimately, the sustainable integration of PV glass panel waste into cementitious materials is a viable approach to promote green building practices and support a circular economy in the construction industry. [ABSTRACT FROM AUTHOR]

The development of solid waste-derived activators for the preparation of alkali-activated systems is of great significance for further enhancing the environmental friendliness and sustainability of alkali-activated materials. In this review, the potential feasibility of applying solid waste-derived activators to prepare alkali-activated systems is explored. Through a discussion of alkali-activation mechanisms, the effect of activators on high-calcium and low-calcium systems is highlighted first. The properties and limitations of commonly used industrial-grade alkali activators are reviewed next. Finally, recent reports on waste-derived activators in alkaline activation systems are summarized, revealing the advantages and development trends of solid wastes with CaO, K2O/Na2O, and SiO2 as the main components of effective substitutes for alkaline industrial exciters. [ABSTRACT FROM AUTHOR]

Three-dimensional printing technology is transforming the construction industry, which is increasingly turning to advanced materials and techniques to meet environmental and economic challenges. This comprehensive literature review evaluated various binder materials, including cement, geopolymers, earthen materials, supplementary cementitious materials, polymers, and biopolymers, with a focus on their environmental impacts and rheological properties. The study revealed an increasing interest in cementitious binders, which deliver essential structural strength and exhibit a wide range of yield stress values (15 to 6500 Pa), influenced by binder type and supplementary materials such as nanoclay. However, the significant CO2 emissions associated with cement pose major sustainability challenges. As a sustainable alternative, geopolymers demonstrate lower yield stress values (800 to 3000 Pa) while ensuring adequate buildability for vertical printing and reducing environmental impact. These findings underscore the need to adopt sustainable binder matrices to align 3D printing construction practices with global sustainability goals. [ABSTRACT FROM AUTHOR]

Moisture is a critical factor leading to the deterioration of concrete structures. Hydrophobic cement-based materials, with their excellent waterproof performance, hold significant application value in humid, coastal, and cold environments. This study employed stearic acid (STA, CH3(CH2)16COOH) as a hydrophobic agent dissolved in anhydrous ethanol using ultrasonication to create an STA–ethanol solution. In addition, the ball-milling method was used to mix STA with tuff powder (TP) to prepare hydrophobic modified tuff powder (MTP). This study investigated the effects of the STA content, water–cement (w/c) ratio, cement–sand (c/s) ratio, the replacement rate, and addition method of TP and MTP on the wettability (contact angle and sorptivity) and compressive strength of the mortar. The effects of the STA on the cement hydration were explored by microanalysis techniques, such as SEM, XRD, and FTIR, and the modification method with the best effect was recommended based on a gray correlation degree analysis. The results indicate that the STA could be successfully grafted into the mortar without affecting the types of cement hydration products. When using the STA–ethanol solution for hydrophobic modification, adding 0.9% STA by weight increased the mortar contact angle to 69.5° and reduced the sorptivity by 22%, while the 28-day compressive strength was decreased. When the w/c ratio was 0.5, the contact angle rose with the increase in the replacement rate of MTP, while the sorptivity and compressive strength decreased. The grey relational analysis showed that at a w/c ratio of 0.4, the STA–ethanol solution was a more effective modification method in terms of reducing the mortar sorptivity. [ABSTRACT FROM AUTHOR]

This paper presents the results of experiments conducted on the flotation separation of cyclone dust particles. The flotation process was conducted using a laboratory flotation apparatus comprising three chambers. Experimental tests supported theoretical results of the theoretical reasoning and justification for the choice of parameters that the flotation process should have in order to extract particles of such small sizes. Furthermore, this work elucidates the concept of "nanobubbles" and substantiates their viability for use in the flotation of nanoparticles, given that bubbles of such a magnitude are firmly affixed to the hydrophobic surface of particles. Bubbles of a larger size than nanoparticles will float both hydrophobic and hydrophilic particles. The effective flotation of cyclone dust from the gas cleaning of silicon and ferroalloy production provided two materials as a result. The experiments yielded insights into the rational technological parameters of the flotation mode for obtaining new products. These insights were gleaned from the preliminary conditioning (conditioning time from 0.5 to 1.5 h) of wet cyclone dust (dry dust weight of 4 kg) with liquid glass (1.4 g per 1 dm3 of pulp) in a cavitation unit at a pH value of 8.5. The flotation process was conducted in a three-chamber flotation apparatus with a volume of 0.02 m3 for a duration of 90 min, utilizing a pneumohydraulic aerator with air suction from the atmosphere. In this instance, the pulp was conveyed via a pump at a pressure of 0.4 MPa from the initial cleansing chamber into the aerator. During the flotation process, kerosene (1 mg per 1 dm3 of pulp) and pine oil (2 mg per 1 dm3 of pulp) were added as additives. The resulting products were silicon dioxide (95%) and carbon nanoparticles (94%). [ABSTRACT FROM AUTHOR]

The article presents the findings of a study conducted on a range of microsilicon grades selected at the Bratsk Ferroalloy Plant. The following analytical techniques were employed: X-ray fluorescence analysis, X-ray diffraction analysis, a granulometric composition study, and pozzolanic properties. The grades of the investigated microsilicon are compared with the furnace grade and the grade of the produced ferrosilicon. The findings of the research conducted at the Bratsk Ferroalloy Plant indicate that the microsilicon produced at the facility is suitable for use as an additive in the production of tires, artificial irregularities, and other rubber products intended for use on roads. In such applications, the quality and durability of the material are determined by its ability to withstand abrasion and wear. Therefore, it is essential to utilize the purest, most amorphous, and most finely dispersed silicon dioxide. The gas cleaning device GCD-4 FeSi-75 exhibits the greatest number of these parameters among the samples presented. Different samples of microsilica have a color from white to dark gray. The chemical and granulometric compositions were determined. The pozzolan activity was investigated. Based on the conducted analyses, it is possible to draw conclusions about the properties of materials and the potential for use in the construction industry for concretes of various values. The results of the analyses indicate that silicon dioxide with GCD-4 FeSi-75 is suitable for use in critical concrete structures. The quality of the silicon dioxide with GCD-4 FeSi-75 can be compared with that of Elkem 971. It is recommended that all the studied samples be employed as modifiers for cast iron, with the GCD-4 FeSi-75 sample being the optimal choice for testing in steels. The utilization of this modifier enables a reduction in the consumption of FeSi, exerting both an alloying and modifying effect on the melt. However, it is essential to emphasize the necessity for technological selection of the method of administration, as the powder, in its pure form, is susceptible to combustion and is not readily digestible. The quality of such a modifier, with a stable guaranteed effect, is comparable to the use of FeSi. Silicon dioxide plays an essential role in the production of refractories. The primary criteria for this industry are purity, the minimum content of the crystalline phase, and the activity of the material. It is recommended that the material from GCD-4 FeSi-75 be used in the production of refractories. [ABSTRACT FROM AUTHOR]

The activation product chlorine-36 (36Cl) is an important radionuclide within the context of the disposal of nuclear wastes, due to its long half-life and environmental mobility. Its behaviour in a range of potential cementitious encapsulants and backfill materials was studied by evaluating its uptake by pure cement hydration phases and hardened cement pastes (HCP). Limited uptake of chloride was observed on calcium silicate hydrates (C-S-H) by electrostatic sorption and by calcium monosulphoferroaluminate hydrate (AFm) phases, due to anion exchange/solid solution formation. Diffusion of 36Cl through cured monolithic HCP samples, representative of cementitious materials considered for use in deep geological repositories across Europe, revealed a markedly diverse migration behaviour. Two of the matrices, a ground granulated blast furnace slag/ordinary Portland cement blend (GGBS–OPC) and an ordinary Portland cement (CEM I) effectively retarded 36Cl migration, retaining the radionuclide in narrow, reactive zones. The migration behaviour of 36Cl within the cementitious matrices is not strictly correlated to the measured sorption distribution ratios (Rd-values), suggesting that physical factors related to the microstructure can also have a distinct effect on diffusion behaviour. The findings have implications when selecting cementitious grouts and/or backfill materials for 36Cl-bearing radioactive wastes. [ABSTRACT FROM AUTHOR]

Cement-based construction materials, commonly known as "cement concrete", result from the hydration reaction of cement, which releases heat. Numerous studies have examined the heat of cement hydration and other thermal properties of these materials. However, a significant gap in the literature is the assessment of the impact of the hydration temperature on the material's strength, particularly compressive strength. This work presents an experimental methodology that consistently estimates the temperature evolution of a mixture used to manufacture concrete or mortar during the first hours of Portland cement hydration. The methodology aims to ensure results that correspond to an infinite medium (adiabatic conditions), where there are no heat losses to the surroundings. Results obtained under adiabatic conditions (simulating an infinite medium) indicate that a ready-made mortar (Portland cement: sand: water; 1:2.5:0.5) can reach temperatures of approximately 100 °C after 48 h of hydration. Under these conditions, compressive strength decreases by up to 20%. [ABSTRACT FROM AUTHOR]

Three-dimensional printing of cementitious materials for construction has been extensively investigated in recent years, with several demonstration projects successfully carried out. These efforts aim to leverage the printing process to achieve more efficient production of components compared to conventional concrete technologies. This includes both the process itself (eliminating the formwork stage) and the flexibility in producing complexly shaped elements. To maximize the potential of 3D printing in the construction industry, additional steps must be taken, grounded in a holistic view of the entire process. This involves integration of the production chain, including design, materials, and manufacturing of components, to create elements with optimal performance, encompassing structural, environmental, and architectural aspects. Such multi-functionality requires the viewing of 3D printing not just as a production technology but as a platform enabling the integration of all these components. To advance this approach, quantitative tools are developed to optimize the following three key components: material composition; manufacturing parameters to ensure buildability; and design tools to optimize multiple performance criteria, particularly structural and architectural shape. A demonstration component, namely a post-tensioned beam, featuring two multi-functional characteristics—structural and architectural—is designed, produced, and evaluated. The scientific concepts and research tools used to develop these quantitative design tools are multidisciplinary, including rheological characterization, control of the internal structure and composition of granular materials, simulation of the mechanical behavior of green material during printing, and the hardened properties of the components, all utilizing structural optimization to enhance performance. [ABSTRACT FROM AUTHOR]

One of the most important hydration phases of Portland cement is ettringite, a calcium sulfo-aluminate mineral ( C a 6 A l 2 (O H) 12 (SO 4) 3 · 26 H 2 O ) showing a great capacity of adsorbing radionuclides and other contaminant cationic and anionic species, or incorporating them into its crystal structure. In this work, the X-ray diffraction pattern and infrared spectra of a synthetized ettringite sample are recorded and simulated, employing theoretical methods based on Density Functional Theory. Despite the complexity of this phase, the calculated structure, X-ray diffraction pattern and infrared spectrum are in excellent agreement with their experimental counterparts. Since the calculated and experimental spectra are consistent, the main infrared bands are assigned using a normal coordinate analysis, some of them being completely reassigned with respect to other experimental works. The good agreement found provides strong support for the computational methods employed towards their use for studying the surface adsorption properties and the incorporation of contaminations in its structure. The density of reactive groups at the surfaces of ettringite is reported, and the surface adsorption of water molecules is studied. These surfaces appear to be highly hydrophilic, in agreement with the experimental finding that the ettringite structure may include more water molecules, at least up to 27, one more than in its standard formula. [ABSTRACT FROM AUTHOR]

In this study, comprehensive investigation of the shrinkage compensation mechanisms of calcium-based expansive agents (CEAs), their effects on the properties of (ultra) high-strength concrete (HSC/UHSC), and the existing problems in applying this methodology was conducted. Analyses showed that the rational use of CEAs under certain conditions could greatly or completely inhibit the development of autogenous shrinkage of HSC/UHSC and significantly reduce the risk of associated cracking. However, it was found that the hydration of the CEAs affected the hydration process of other binders, thereby altering the microstructure of concrete. This, in turn, led to a reduction in mechanical properties such as compressive strength, flexural strength, and elastic modulus, with the rate of reduction increasing as the amount of CEA used increased. Moreover, when attempting to improve the shrinkage compensation effects, increasing the amount of CEA presented a risk of delayed expansion cracking of the HSC/UHSC. Neither the expansion mechanism, expansion conditions, nor the inhibition methods have yet been fully clarified in the current stage. Lastly, newly proposed Ca–Mg composite EAs were outlined, and the research prospects of Ca–Mg composite EAs in HSC/UHSC were explored. [ABSTRACT FROM AUTHOR]

The use of industrial solid waste to capture and fix CO2 is a promising technology for CO2 sequestration. A thermogravimetric analyzer and CO2 cement hydration mixing device were used to study the effects of mixing method, curing system, temperature, CO2 concentration and other factors on the carbon fixation amount and performance of the circulating fluidized bed fly ash cement-based material system. The results showed that the carbon fixation and early strength of the cementitious materials could be improved by adding CO2 in the stirring process and making CO2 directly participate in the process reaction. The cementing materials samples prepared with CO2 were cured in a standard curing box for 2 days and a carbon atmosphere for 1 day, the carbon fixation amount of the cementing material was increased by 33% and the compressive strength of the cementing material was also improved. This is because under the combined action of carbon mixing and carbon curing, the prepared binding materials produced more Ca(OH)2 in the early stage, and it reacts with the introduced CO2 to form CaCO3. The strength of the calcium carbonate crystals is higher than the strength of the earlier stage of cement, and at the same time, the samples would solidify more CO2. Considering the carbon fixation amount, sample performance and solid waste utilization rate, the best conditions for the cementing materials are as follows: the content of the circulating fluidized bed fly ash (CFA) was 35%, the concentration of carbon curing was 30%, the curing temperature was 40 ℃, the water-binder ratio was 0.4, and the carbon fixation amount of the cementing material could reach about 20%. The use of CFBFA to solidify and storge CO2 is not only a new way to utilize high value-added fly ash resources, but also beneficial for reducing industrial carbon dioxide emissions. [ABSTRACT FROM AUTHOR]

Soft to medium clay soil possesses major sources of damages to the pavement layers overlying them because of their potential failure under moisture changes and external heavy traffic load. In such situations, soil stabilization methods can be used to improve the soil properties and satisfy the desired engineering requirements. This study presents the use of sugarcane bagasse ash (SBA) and lime as chemical stabilizers for a clay soil subbase. Sugarcane bagasse ash and lime are used individually and as mixtures at varying percentages to stabilize a clay soil from Taxila, Pakistan. Various geotechnical laboratory tests such as Atterberg limits, compaction test, and California Bearing Ratio (CBR) are carried out on both pure and stabilized soils. These tests are performed at 2.5%, 5%, and 7.5% of either SBA or lime by weight of dry soil. In addition, mixtures of lime and SBA in ratios of 1:1, 2:1, 3:1, 1:2, and 1:3 are used in 5%, 7.5%, and 10% of dry soil weight, respectively. Results indicate that soil improved with 7.5% SBA showed a 28% increase in the liquid limit, while soil mixed with 2.5% lime in combination with 7.5% SBA showed an increase of 40% in the plastic limit. For the plasticity index, the soil mixed with 7.5% SBA showed an increase of 42%. Moreover, 2.5% lime in combination with 2.5% SBA showed the best improvement in soil consistency as this mixture reduced the soil plasticity from high to low according to the plasticity chart. Furthermore, 2.5% SBA in combination with 5% lime demonstrated the largest improvement on the CBR value, which is about a 69% increase above that of the pure soil. Finally, the cost analysis indicates a promising improvement method that reduces pavement cost, increases design life, and mitigates issues of energy consumption and pollution related to SBA as a solid waste material. [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]

In the realm of cementitious materials, integrating nanoclay shows promise in enhancing properties relevant to additive manufacturing. This paper presents a novel mathematical model that combines simple empirical dissolution/nucleation Avrami-like kinetics with a thixotropic kinetics equation. To analyze the initial exothermic peak, two sets of the calculation parameter function are built to describe the exothermic rate as a function of time, following an exponential pattern. This allows for the prediction of the changes in cumulative heat and heat rate during hydration, considering different concentrations of nanoclay. In the rheological aspect, the relationship between shear stress, shear rate, and time is modeled as a combination of exponential dependencies. This enables the prediction of the variations in shear stress with one variable while holding the other constant (either time or shear rate). By integrating these aspects, this model effectively describes both the first exothermal peak and the rheological behavior during cement hydration with the inclusion of nanoclay. Validated against experimental results, these models demonstrate good accuracy (overall below 3% error), reliability, and applicability. The findings offer valuable insights into the thermal and rheological aspects of concrete printing, enabling informed design decisions for both scientific and industrial applications. [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]

This paper presents two original methods for monitoring and evaluating concrete specimens/structures affected by external sulfate attack (ESA). The first is a drying method developed to assess the penetration depth of sulfate ions in a concrete structure, as this parameter is a relevant indicator of the progress of the ESA. This method has been specifically designed for on-site investigations. The second experimental method involves the use of optical fibers capable of measuring the swelling response of specimens to ESA in real time. According to the results obtained, these two new methods seem likely to be used to complement or replace traditional methods such as inductively coupled plasma (ICP) for determining the penetration depth of sulfate ions or as extensometers for measuring swelling. These traditional methods (ICP and extensometers) are generally considered painful and time-consuming, whereas, because of its simplicity, the proposed drying method will enable experts to regularly inspect concrete structures and make informed decisions on the measures to be taken to repair or prevent further damage induced by ESA, while the second method appears promising for experimental studies involving the monitoring of a large number of ESA-affected specimens. [ABSTRACT FROM AUTHOR]

The article presents research results regarding the possibility of modifying pre-stressed concrete railway sleepers to improve their durability. The cracks that appear in these elements are one of the reasons for shortening the period of safe use. They do not have a significant impact on the load-bearing capacity of these elements, but on their durability. The resulting scratches become an easy way for the external environment to migrate inside the element, including the reinforcement area. Despite efforts to eliminate the possibility of cracking, this phenomenon still occurs in railway sleepers. In order to reduce the negative effects of cracking the cement matrix, a technology for modifying a prefabricated concrete element with resin-filled tubes towards its autonomous self-healing was developed and tested. The tests were divided into three stages, including laboratory tests carried out on cement mortar beams, semi-technical tests carried out on reinforced concrete beams, and industrial tests carried out on pre-stressed concrete and prefabricated railway sleepers. All research conducted on a laboratory and semi-technical scale, preceding the target stage, was intended to ultimately enable the development of tube application technology on an industrial scale while verifying the effectiveness of self-healing at the laboratory level. The use of self-healing cementitious materials potentially reduces the negative effects of cracking railway sleepers, as shown by observations conducted during the research. [ABSTRACT FROM AUTHOR]

Copper smelting slag discharged from mining and high-aluminum fly ash generated during the combustion of coal for energy production are two typical bulk solid wastes, which are necessary to carry out harmless and resourceful treatment. This research proposed an eco-friendly and economical method for the co-consumption of copper smelting slag and high-aluminum fly ash. Cementitious materials were compounded with copper smelting slag and high-aluminum fly ash as the main materials were successfully prepared, with a 28-d compressive strength up to 31.22 MPa, and the heavy metal leaching toxicity was below the limits of the relevant standards. The optimum mechanical properties of the cementitious materials were obtained by altering the material proportion, ball mill rotation speed, and CaO dosage. Under the combined effect of mechanical ball milling at a suitable speed and chemical activation with a certain alkali concentration, the prepared cementitious materials had an initial activation. The pastes of the cementitious materials generated a gel system during the subsequent hydration process. The two steps together improved the mechanical strength of the cured products. The preparation was simple to operate and offered a high stability of heavy metals. The heavy metal contaminants were kept at a low content throughout the process from raw materials to the prepared cured specimens, which was suitable for application in practical environmental remediation projects and could provide effective solutions for ecological environment construction. [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]

The wet carbonation process of steel slag (SS) is envisaged to be an effective way to sequestrate CO2 and improve the properties of SS as a supplementary cementitious material. However, the carbonation process still struggles with having a low carbonation efficiency. This paper studied the effect of glycine on the accelerated carbonation of SS. The phase composition change of carbonated SS was analyzed via XRD, FT-IR, and TG–DTG. The carbonation process of SS is facilitated by the assistance of glycine, with which the carbonation degree is increased. After 60 min of carbonation, SS with glycine obtained a CO2 sequestration rate of 9.42%. Meanwhile, the carbonation reaction could decrease the content of free calcium oxide in SS. This significantly improves the soundness of SS–cement cementitious material, and the compressive strength of cementitious materials that contain carbonated SS with glycine is improved. Additionally, the cycling performance of glycine in the successive wet carbonation process of SS was investigated. Multicycle experiments via solvent recovery demonstrated that although the promotion effect of glycine was reduced after each cycle, compared with the SS–water system, the carbonation process could still be facilitated, demonstrating that successive wet carbonation via solvent recovery has considerable potential. Herein, we provide a new idea to facilitate the wet carbonation process of SS and improve the properties of SS–cement cementitious material. [ABSTRACT FROM AUTHOR]

The evolution of construction engineering depends on the development of cementitious materials with optimized properties and lower environmental impacts, such as the preparation of mortars with higher mechanical resistance and durability. Nanotechnology is a promising tool for industrial innovation, enhancing material properties like durability and mechanical performance. Thus, herein, we prepared mortars incorporating ZnO nanoparticles and evaluated their properties. The results showed that smaller percentages of ZnO presented better performance in consistency tests, and all samples containing ZnO showed higher mechanical resistance than the reference, thus suggesting the great potential of nanoparticles in optimizing the mechanical properties of mortars. [ABSTRACT FROM AUTHOR]

The integration of nanotechnology across various industries has significantly enhanced product quality and manufacturing technologies for diverse materials. Within the construction sector, the adoption of nanomaterials has sparked the advent of innovative construction methods. Extensive studies have been conducted on various nanomaterials, particularly micro- and nanosilica, exploring their use as partial substitutes for cement in concrete formulations. This study aimed to furnish a comprehensive overview of silica's impact on concrete properties in civil engineering and road construction. Environmental concerns and potential hazards necessitate the development of strategies for managing industrial by-products. Metallurgical processes generate several such by-products, among which is silica fume—a residue from smelting in the silicon and ferrosilicon industries. Waste silica dust and slurries have proven highly effective in creating high-strength, high-performance concrete. The study presents a literature review focusing on micro- and nanosilica derived from production waste at ferroalloy and silicon plants. It includes a comparative analysis of the primary characteristics of microsilica from various sources and examines the extensive use of microsilica as a modifying additive in building materials. Analyzing different concrete compositions with and without fumed silica determined the ranges of results for each indicator. The incorporation of micro- and nanosilica into the concrete mix demonstrated its efficacy. The morphology of waste silica particles, characterized by the smooth and spherical surfaces of micro- and nanosilica particles, significantly influences the workability properties of the concrete. [ABSTRACT FROM AUTHOR]

This research aims to analyze the distribution and evolution of pores within the planar structure of cement-based materials. Utilizing digital imaging methods, a model for pore plane distribution was established, and the evolutionary patterns of both total pore numbers and varying pore sizes in cement-based materials were investigated. The research introduced an innovative experimental method for analyzing pore distribution within cement-based planar structures. Additionally, a hybrid method was proposed, combining automated image binarization thresholding with manual comparative analysis, thereby enhancing the feasibility of comparative research. Pores were categorized into four distinct sizes: tiny pores (5–200 μm), small pores (200–500 μm), medium pores (500–1000 μm), and large pores (>1000 μm). Areas with apertures <5 μm were classified as dense areas. The findings indicated that the overall number of pores in cement-based materials increased due to the influence of styrene butadiene latex additives. However, at a 15% dosage, the rate of pore formation reached an inflection point, confirming that various factors, such as styrene butadiene latex, air bubbles, and the cement-based material itself, collectively influenced pore formation. The research also demonstrated that styrene butadiene latex affected the four categorized pore sizes differently. Importantly, a higher latex dosage did not necessarily lead to a proportional increase in pore content. Pore content was influenced by multiple factors and exhibited different distribution patterns. The number of micropores, although relatively small, gradually increased with higher latex dosages, while small and medium pores generally showed an upward trend. At a 10% latex dosage, both small and medium pores reached a turning point in their rate of increase. Large pores also exhibited a general increase, peaking at a latex dosage of 10%. It was confirmed that both the total pore volume and the content of micropores were critical factors in determining the mechanical properties of cementitious materials. Higher porosity and micropore content generally weakened mechanical performance. However, at a small latex dosage, there was an improvement in flexural strength. When the latex dosage reached 15%, the total pore and micropore content declined, resulting in a balanced increase in flexural strength and a mitigated decline in compressive strength. This study offers valuable insights into the evolution of total pore volume and the content of pores of various sizes, providing a theoretical basis for the meticulous selection of additive types and dosages from a microscopic perspective. [ABSTRACT FROM AUTHOR]

The effectiveness of 3D concrete printing (3DCP) relies on understanding the rheological properties of cementitious materials and their time-dependent evolution. These materials exhibit shear-thinning viscosity, an elastic region, and both static and dynamic yield stress, which are challenging to balance in 3DCP. Layer deformation can be caused by factors such as self-weight, the weight of subsequently deposited layers, and the stress induced by the nozzle pressing. Starting at the level of a single filament, the final geometrical conformity of a 3D-printed object is the sum of individual filament conformities. Hence, the control of layer deformation during the printing process is critical. The failure of 3D-printed objects can occur due to two primary mechanisms: material failure, which occurs when the material's strength is exceeded, resulting in fracture or uncontrolled deformation; and stability failure, where the object cannot retain equilibrium of forces. These mechanisms often interact; extensive deformations resulting from material failure can lead to stability loss, or conversely, stability loss generates local excessive stresses leading to material failure. The governing mechanism depends on various factors, including material and process characteristics, as well as the transient nature of material properties, print strategy, and object design. With this in mind, this research aimed to broaden the understanding of the connection between rheological material properties—primarily yield stress—and the geometric conformability of printed objects. Experimental tests were conducted on pastes using a rheometer, and correlated mortars, allowing for the evaluation of realistic extrusion properties. [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]

This paper deals with the characterisation of cementitious materials from selected cultural heritage structures in Slovenia. The mineralogical–petrographic compositions of an aggregate, a type of binder and secondary minerals were studied via electron microscopy and X-ray powder diffraction. The porosity and pore network were determined using a mercury porosimeter. The results show that the aggregate of the samples was highly diverse, ranging from limestone, dolomite, quartz, feldspar and mica. The binder of the investigated samples was cementitious; either ordinary Portland cement was used, or ordinary Portland cement blended with ground granulated blast furnace slag was used. Some samples consisted of cement–lime binders. The investigated examples entailing cement materials for their construction contribute to a better understanding of the technology used to prepare historical cementitious and cement–lime mixtures. [ABSTRACT FROM AUTHOR]

The field of 3D printing is in rapid evolution. The 3D printing technology applied to civil engineering is a promising advancement. From equipment and mixture design to testing methods, new developments are popping up to respond to specific demands either for the fresh or hardened state. Standardizing methods are still at an early age. For this reason, there is a multitude of 3D printers with different capabilities to print cementitious materials. In addition, norms are not applicable in 3D printing material science. Advances are being made to create new methods of testing. The key parameters of this new 3D printing process based on stratification, multiple uses of binders, and measurement at fresh and hardened states are being perfected to achieve an industrial application. This article gives an overview of how 3D-printed structures are made along with critical parameters that influence their performances. Our review suggests that the quality of the 3D prints is determined by the printing method, key printing parameters, and the mix design. We list different tests to help characterize these 3D-printed cementitious materials at the fresh state and to assess their performances at the hardened state. We aim throughout this work to give a state-of-the-art of recent advances in 3D printing technology. This could help for a better understanding of cementitious materials 3D printing for current and future related research work. [ABSTRACT FROM AUTHOR]

A novel approach for describing the acoustic activity in brittle structural materials while they are loaded mechanically at levels close to those causing macroscopic fracture is proposed. It is based on the analysis of the rate of acoustic emissions in terms of the Natural Time concept. Experimental data from protocols with either intact or notched beams, made of cementitious materials, subjected to three-point bending are analyzed. It is concluded that in case the acoustic activity is described with the aid of the F-function in the Natural Time domain, its evolution is governed by a power law, independently of geometrical details and the type of the loading scheme. It appears that the onset of validity of this law provides an interesting pre-failure indicator. [ABSTRACT FROM AUTHOR]

One of the key problems that affect the durability of reinforced concrete structures is the corrosion of rebar induced by chloride. Despite the complicated transport mechanism of chloride ions in cementitious materials, diffusion is still the key mechanism of chloride ingress. The determination of the chloride diffusion coefficient will help to predict the chloride profile inside the cementitious materials and estimate the service life with regard to chloride-induced corrosion. However, this paper shows that the chloride diffusion coefficient in the literature is sometimes misunderstood. Such a misunderstanding results in the overestimation of the chloride resistance of cementitious materials. To clarify the chloride diffusion coefficient, this paper first presents the steady- and non-steady-state diffusion equations in cementitious materials. The factors that influence the diffusive flux are identified. The effective and apparent diffusion coefficients are then clearly explained and properly defined. We also point out the obscure definitions of the effective diffusion coefficient in the literature. The varied definitions of the effective diffusion coefficient are the result of the consideration of different factors affecting the diffusion process. Subsequently, this paper discusses two natural diffusion test methods that are frequently employed in cementitious materials to measure the chloride diffusion coefficient. The influencing factors considered by the measured diffusion coefficients are analyzed in detail. Then, the diffusion coefficients determined in some of the studies are reviewed. It is shown that three typical errors could occur when numerically determining the diffusion coefficients. [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]

There have been efforts to use building demolition waste as an alternative aggregate in concrete to decrease the use of natural resources for construction. The World Green Building Council estimates that the construction industry is responsible for more than 50% of all material extracted globally and that construction and demolition waste makes up 35% of global landfills. As a result, incorporating recycled aggregate (RA) in concrete production is a prudent course of action to reduce the environmental impact. This study reviews prior research on using recycled aggregate instead of conventional ingredients in concrete. The composition and morphology of different types of RA, the behavior of RA in fresh and hardened states, keyword co-occurrence and evolution analysis, and the various additives used to enhance the inferior properties of RA are discussed. The RA showed different physical properties when compared with natural aggregate. However, the addition of pozzolanic materials and various pretreatment techniques is desirable for improving the inferior properties of RA. While building waste has been utilized as a substitute for fine and coarse aggregate, prior research has demonstrated that a modified mixing approach, an adequate mixing proportion, and the optimum replacement of cementitious materials are necessary. Based on the review, the recommendation is to use RA at a replacement level of up to 30% and the addition of precoated and pozzolanic materials as a treatment to provide concrete with adequate workability, strength, and durability for structural applications. [ABSTRACT FROM AUTHOR]

Modeling the meso-scale behavior of a material allows one to answer many problems in an inductive reasoning approach. By simulating the behavior of the sample, researchers can correct the overall behavior of the material. The purpose of this article was to gather the main information linking the issue of tomographic imaging to the modeling of damage mechanisms. This paper addresses the topic of meso-scale modeling of cementitious materials. The authors have mapped the interconnectedness of the issues of cementitious materials and X-ray computed tomography (µCT) according to the Web of Science database. The main interconnecting threads are indicated. The authors focused on the use of µCT. The theoretical basis for conducting tomographic measurements is presented. Reference was made to the basics of physics and mathematics in X-ray projection and data reconstruction. Tools and analyses for data processing are indicated. The benefits of in situ µCT are indicated with reference to the practical application of the method. In addition, the main developments of recent years in the most widely used computational methods for meso-scale models are presented. [ABSTRACT FROM AUTHOR]

The 3D cementitious material printing method is an extrusion-based additive manufacturing strategy in which cementitious materials are extruded through a dynamic nozzle system to form filaments. Despite its ability to fabricate structures with high complexity and efficiency, the uneven material distribution during the extrusion and deposition process is often encountered when a radial toolpath is introduced. This limits the design freedom and printing parameters that can be utilized during radial toolpath printing. Here, we report a facile strategy to overcome the existing challenges of cementitious material non-homogeneity by rationally developing new nozzle geometries that passively compensate the differential deposition rate encountered in conventional rectangular nozzles. Using two-phase numerical study, we showed that our strategy has the potential of achieving a homogeneous mass distribution even when the nozzle travel speed is unfavorably high, while filament from a rectangular nozzle remains highly non-homogenous. The material distribution unevenness can be reduced from 1.35 to 1.23 and to 0.98 after adopting trapezoid and gaussian nozzles, indicating improvements of 34.3% and 94.2%, respectively. This work not only outlines the methodology for improving the quality of corner/curved features in 3DCMP, but also introduces a new strategy which can be adopted for other extrusion-based fabrication techniques with high material inertia. [ABSTRACT FROM AUTHOR]

Developing accurate and interpretable models to forecast concrete's self-healing behavior is of interest to material engineers, scientists, and civil engineering contractors. Machine learning (ML) and artificial intelligence are powerful tools that allow constructing high-precision predictions, yet often considered "black box" methods due to their complexity. Those approaches are commonly used for the modeling of mechanical properties of concrete with exceptional accuracy; however, there are few studies dealing with the application of ML for the self-healing of cementitious materials. This paper proposes a pioneering study on the utilization of ML for predicting post-fire self-healing of concrete. A large database is constructed based on the literature studies. Twelve input variables are analyzed: w/c, age of concrete, amount of cement, fine aggregate, coarse aggregate, peak loading temperature, duration of peak loading temperature, cooling regime, duration of cooling, curing regime, duration of curing, and specimen volume. The output of the model is the compressive strength recovery, being one of the self-healing efficiency indicators. Four ML methods are optimized and compared based on their performance error: Support Vector Machines (SVM), Regression Trees (RT), Artificial Neural Networks (ANN), and Ensemble of Regression Trees (ET). Monte Carlo analysis is conducted to verify the stability of the selected model. All ML approaches demonstrate satisfying precision, twice as good as linear regression. The ET model is found to be the most optimal with the highest prediction accuracy and sufficient robustness. Model interpretation is performed using Partial Dependence Plots and Individual Conditional Expectation Plots. Temperature, curing regime, and amounts of aggregates are identified as the most significant predictors. [ABSTRACT FROM AUTHOR]

The significance of ion activity in transport through a porous concrete material sample with steel rebar in its center and bathing solution is presented. For the first time, different conventions and models of ion activity are compared in their significance and influence on the ion fluxes. The study closes an interpretational gap between ion activity in a stand-alone (stagnant) electrolyte solution and ion transport (dynamic) through concrete pores. Ionic activity models developed in stationary systems, namely, the Debye–Hückel (DH), extended DH, Davies, Truesdell–Jones, and Pitzer models, were used for modeling the transport of ions driven through the activity gradient. The activities of ions are incorporated into a frame of the Nernst–Planck–Poisson (NPP) equations. Calculations were done with COMSOL software for a real concrete microstructure determined by X-ray computed tomography. The concentration profiles of four ions (Na+, Cl−, K+, OH−), the ionic strength, and the electric potential in mortar (with pores) and concrete samples (with aggregates and pores) are presented and compared. The Pitzer equation gave the most reliable results for all systems studied. The difference between the concentration profiles calculated with this equation and with the assumption of the ideality of the solution is negligible while the potential profiles are clearly distinguishable. [ABSTRACT FROM AUTHOR]

By introducing probabilistic modeling approaches, the interface transition zone (ITZ) and the bulk paste (BP) of concrete are investigated on the basis of the nanoindentation results, especially with respect to the relationship between the microstructure and mechanical properties of cementitious materials. The investigation of the probability density function (PDF) of the random field for nanoindentation properties revealed that the same properties of the ITZ and the BP usually yield the same PDF, which was elaborated from different points of view. Specifically, a log-normal distribution was best for nanoindentation hardness, whereas the Weibull distribution and gamma distribution were much more suitable for the nanoindentation modulus of both the ITZ and the BP. According to the comparative study of the correlation structure, both the ITZ and BP obeyed the exponential correlation structure associated with a first-order autoregressive process, and basically exhibited a similar scale of fluctuation. Furthermore, the scales of fluctuation were found to be directly related to the clinker size and the distance between clinkers. Our work provides a new approach to stochastically modeling cementitious materials, where the content of hydration products controls the mean values of nano-properties, the indentation property dominates the PDF, and the nano-topological structure governs the correlation structure. [ABSTRACT FROM AUTHOR]

Incorporating geopolymeric recycled brick aggregate concrete into steel tubes provides a promising solution to reduce environmental impact of construction and demolition waste. In this paper, geopolymeric recycled brick aggregate concrete-filled steel tubular column (GRBACFST) was developed to improve the environmental sustainability of composite column. Considering the replacement ratio of recycled brick aggregate (RBA), the thickness of the steel tube, type of cementitious materials and the axial compression ratio as the variation parameters, experimental research was performed to explore the cyclic behavior of GRBACFST columns, including the failure mode, bearing capacity, hysteresis curve, ductility and degradation characteristics. Results demonstrated that the failure of GRBACFST columns occurred in the region at column bottom, with the bulge of steel tube and crush of geopolymeric recycled brick aggregate concrete. The proposed GRBACFST columns exhibited favorable hysteretic behaviors with desired bearing capacity, excellent ductility, and energy dissipation behavior, which were enhanced by the increased thickness of the steel tube. The bearing capacity and ductility were reduced with the increase of axial compression ratio, while enhanced with thicker steel tube. Moreover, the degradation of stiffness and strength was more obvious under larger axial compression ratio. The increase of replacement ratio of RBA caused a significant reduction of bearing capacity, while it had few effect on the hysteretic index. It was concluded that the hysteretic behavior of proposed GRBACFST column was not sensitive to the types of cementitious material and geopolymers could serve as an eco-friendly binder for concrete. [ABSTRACT FROM AUTHOR]

Obtained natural sands can present different particle size distributions (PSD), although they have the same mineralogical origin. These differences directly influence the physical and mechanical behavior of mortars and, therefore, the performance of mortar and ceramic renderings. Standardizing the particle size of sands based on pre-established requirements in normative standards (NBR 7214 or ASTM C778) is one way to minimize these effects. However, these standards do not consider the optimization of the granular skeleton through the analysis of bulk density and PSD, which may be insufficient to obtain satisfactory results. Therefore, this paper analyzes the effects of using different particle size ranges on the physical and mechanical behavior of cement and hydrated lime mortars. The properties of consistency index, bulk density, air content, capillary water absorption, water absorption by immersion, flexural strength, compressive strength, and dynamic modulus of elasticity were evaluated. For this purpose, standardized sands of the same mineralogical origin were made with different particle size ranges, being: (i) standardized sand constituted by 25% of coarse and fine fractions (S25-control), (ii) standardized sand constituted by 30% of coarse fraction and 20% of fine fraction (S30-20), and (iii) standardized sand composed by 40% of coarse fraction, and 10% of fine fraction (S40-10), respectively. The results indicated that variations in the particle size composition of the standardized sands are necessary to obtain mixtures with higher compactness and, therefore, mortars with better physical and mechanical performance. Thus, the dosage of the particle size fractions of standardized sand should consider the optimization of the granular skeleton, being the unit mass and the granulometric composition as important parameters to meet this premise. [ABSTRACT FROM AUTHOR]

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

With the rapid development of urbanization, the construction industry consumes a lot of cement and produces a large amount of construction waste. To overcome this situation, the rational use of recycled aggregate produced from waste concrete is one of solutions. In some countries, the building industry has approved the use of recycled coarse aggregates in concrete, with some limits. However, practically all existing standards and regulations prohibit the use of recycled fine aggregate (RFA) in concrete. Therefore, study on improving the performance of RFA concrete is vital. In this study, the effects of fly ash and GGBS on concrete with RFA were investigated. Compressive strength, pore structure, drying shrinkage and accelerated carbonation were tested. The correlation between the pore structure and properties of concrete was analyzed. The results show that adding fly ash and GGBS to RFA concrete increased its compressive strength, modified pore structure, reduced drying shrinkage, and even achieved higher compressive strength and lower drying shrinkage than normal concrete. The compressive strength was mainly affected by the capillary pores, and the carbonation was mainly affected by the gel pores. [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]

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]

Concrete structures are increasingly becoming exposed to organic acid attack conditions, such as those found in agriculture and food-related industries. This paper aims to experimentally verify the thermodynamic modeling of cement pastes under acetic acid attack. For this, a modeling approach implemented in IPHREEQC via Matlab is described, and results are compared with measured pH and compositions of equilibrated solutions (MP-AES) as well as unreacted/precipitated solids (XRF, XRD and STA) for a wide range of acid concentrations. The 11% replacement of cement by silica fume (SF) led to a 60 or 70% reduction (measured or modeled, respectively) of Portlandite content in the hardened cement paste due to the pozzolanic reaction resulting in higher content of CSH phases, which has effects on the progression of dissolution processes and a resulting pH with increased acid concentrations. Considering that no fitting parameter was used, the model predictions showed good agreement with measured values of pH, dissolved ion concentrations and composition of the remaining (degraded) solids overall. The discrepancies here were more pronounced at very high acid concentrations (equilibrium pH < ~4), i.e., after the full dissolution of hydrate phases due to limitations in the model used to describe Al-, Si- and Fe-gel phases and/or identified experimental challenges in precipitation of calcium and aluminum acetate hydrates. [ABSTRACT FROM AUTHOR]

Civil construction is essential for the world economy and the largest generator of construction and demolition waste (CDW), mainly due to a lack of planning, technological control, and restoration execution, among other factors. While efforts are made to minimize this waste generation, one possible application for CDW is its incorporation into Portland cement-based materials as recycled aggregates, in partial or total replacement of natural aggregates. However, for CDW use to be feasible, the structure performance and safety must be assured, and the adherence between concrete and reinforcement bars, in this context, is a fundamental mechanism. With this perspective, this paper aims to investigate the influence of recycled aggregate on steel–concrete bonding. To this end, the SREE (Systematic Review for Engineering and Experiments) method was employed as a novelty, including a methodology quality analysis, to search and analyze relevant scientific articles published in the last ten years. The results revealed that the use of CDW as recycled aggregates in concrete worsens the steel–concrete bonding, and that ribbed steel bar seems to be the best option when employed in RC structures built with CDW-concrete, although the bar diameter and the anchorage length still need further investigations, and that CDW-concrete's use can significantly contribute to reducing the emission of greenhouse gases and to capturing CO2 from the atmosphere. Therefore, further investigations should focus on the real influence of recycled aggregate type and replacement content, bar diameter, anchorage length, and CDW's potential to capture CO2. [ABSTRACT FROM AUTHOR]

The physical meaning and calculating process of the rheological parameters of two nonlinear rheological models, the parabolic model and the modified Bingham model, were compared. The fluidity test and a rheological experiment on cementitious materials were performed. The Couette inverse problem is a key issue in measuring and solving the rheological parameters of fresh cementitious materials. The solution of the Couette inverse problem based on the modified Bingham model is discontinuous when the coefficient of the quadratic term is equal to zero, resulting in a large deviation between the fitting curve and the rheological experimental data. The credibility of the rheological parameters of the pastes calculated based on the modified Bingham model is low. The formulas for calculating yield stress, fiducial differential viscosity and the degree of shear thickening or shear thinning of the parabolic model have been developed. The credibility of the rheological parameters of the pastes calculated based on the parabolic model is high. The flow performance of the paste can be clearly characterized by the rheological parameters calculated with the parabolic model. [ABSTRACT FROM AUTHOR]

The hybrid optimization of modern cementitious materials requires concrete to meet many competing objectives (e.g., mechanical properties, cost, workability, environmental requirements, and durability). This paper reviews the current literature on optimizing mixing ratios using machine learning and metaheuristic optimization algorithms based on past studies on varying methods. In this review, we first discuss the conventional methods for mixing optimization of cementitious materials. Then, the problem expression of hybrid optimization is discussed, including decision variables, constraints, machine learning algorithms for modeling objectives, and metaheuristic optimization algorithms for searching the best mixture ratio. Finally, we explore the development prospects of this field, including, expanding the database by combining field data, considering more influencing variables, and considering more competitive targets in the production of functional cemented materials. In addition, to overcome the limitation of the swarm intelligence-based multi-objective optimization (MOO) algorithm in hybrid optimization, this paper proposes a new MOO algorithm based on individual intelligence (multi-objective beetle antenna search algorithm). The development of computationally efficient robust MOO models will continue to make progress in the field of hybrid optimization. This review is adapted for engineers and researchers who want to optimize the mixture proportions of cementitious materials using machine learning and metaheuristic algorithms. [ABSTRACT FROM AUTHOR]