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This study investigated the inclusion of magnesium silicate monohydrate (MSMH) crystal in MgO–SiO 2 mixes designed for extrusion-based 3D printing. Considering the adjustment and optimization of rheological properties are fundamental for the printability of cement pastes, the dynamic rheology, thixotropy and strength development of the prepared mixes were analyzed to characterize their fresh properties, workability, buildability, and mechanical performance. Furthermore, isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis (TG/DTG), and scanning electron microscopy (SEM) were employed to investigate the phase composition and microstructural evolution of the pastes, with and without the presence of MSMH. Addition of MSMH at 2 % of the binder component significantly enhanced the plastic viscosity, dynamic yield stress and thixotropy. Pastes incorporating 2 % MSMH exhibited excellent structural build-up without affecting extrudability, with a minimal strain deformation in the printed structure. The compressive strength of all pastes exceeded 20 MPa after 3 days, reaching ∼50 MPa at 28 days with 2 % MSMH inclusion. The introduction of MSMH improved the peak heat flow measured by isothermal calorimetry and enhanced the formation and growth of hydration products after 7 days of curing, resulting in a more compact microstructure. [ABSTRACT FROM AUTHOR]

Sustainable structures are an important area of research, particularly for anticipated extended human presence on the Moon or Mars. Persistent human presence on the Moon will require building materials that are already present at the site to construct bases. The high cost associated with reinforcing metal (rebar) in mission payloads necessitates the exploration of alternative reinforcement methods for sustained lunar bases. Human hair is strong in tensile strength and will become available in any long-term mission. By using otherwise wasted hair instead of heavy metal, mission payloads and costs could be lowered. Concrete workability, compressive strength, and porosity were measured for a series of different cement compositions. These compositions consisted of combinations of Ordinary Portland Cement (OPC), lunar regolith, deionized (DI) water and human hair. Increased workability and porosity were found for increasing hair concentrations. Compressive strength slightly decreased with increased hair concentration. [ABSTRACT FROM AUTHOR]

AbstractThe potential of microbially induced carbonate precipitation (MICP) for soil bio-improvement has been widely studied as an alternative to the traditional cementation by Portland cement. While multiple-phase injection techniques are commonly used for MICP treatment, they impose complexities and require a high number of injections. One of the latest developments in biocementation research area is using one-phase-low-pH MICP method as a more effective and efficient alternative to the traditional two-phase method. However, the one-phase-low-pH method has its challenges. The main challenge is delaying the start of carbonate precipitation to produce a homogenous distribution of cementation in soil matrixes. This study has tried to expand the lag phase with magnesium substitution for 20% calcium cations and decrease the initial temperature of reagents. These actions prolonged the lag phase by about five times, improved the crystal structure of carbonate precipitation and enhanced the transportability of bacteria in a 1 m length sand column. A modified injection strategy for all-in-one solution was introduced, and its capabilities were investigated in long sand columns. This new injection strategy provided a more uniform urea conversion, carbonate precipitation, and strength. It also decreased the required bacteria by 75% and minimized the necessity of pH adjustment and the initial low temperature of reagents. [ABSTRACT FROM AUTHOR]

The longevity of waste asphalt can be considerably improved through cold recycling techniques combined with various additives. This research investigates the cold regeneration of aged asphalt concrete using Reclaimed Asphalt Pavement (RAP), Portland cement, cationic bitumen emulsion, and additional aggregates. The primary goal is to evaluate the performance enhancements in terms of average density, compressive strength, water resistance, and swelling across different mix compositions. Three distinct mixtures were formulated and assessed. Mix No. 1, composed solely of RAP, showed the lowest average density and highest swelling, indicating poor performance due to the lack of binding agents. Mix No. 2, which incorporated RAP, Portland cement, and water, exhibited the highest density and compressive strength, highlighting the crucial role of Portland cement in improving structural integrity. Mix No. 3, a more complex mixture including RAP, aggregates, Portland cement, water, and bitumen emulsion, displayed balanced properties with enhanced moisture resistance and reduced swelling. The experimental findings emphasize the effectiveness of adding Portland cement and bitumen emulsion to improve the mechanical and durability characteristics of recycled asphalt mixtures. Specifically, Mix No. 2 and Mix No. 3 demonstrated significant performance improvements, making them suitable for road maintenance applications. This study advocates for the widespread use of cold recycling methods with additive integration to achieve sustainable and cost-effective pavement restoration solutions. [ABSTRACT FROM AUTHOR]

The main cause of corrosion of reinforcing steel, especially in infrastructure structures, is the penetration of chlorides, which can lead to high corrosion rates at the reinforcement steel. A frequently used accelerated test method to evaluate the chloride penetration resistance of concrete and mortars is the rapid chloride migration (RCM) test. The test was initially developed for ordinary Portland cement (OPC) based materials and involves spraying an indicator solution onto split test specimens to determine the penetration depth of the chloride ions. The pore solution compositions of new types of binders differ from OPC‐based materials, which can affect the reaction of the indicator solution. To investigate the suitability of the RCM test, the chloride content in the depth of the color change was determined in mortars made from different types of novel binders. The results show that the test provides reliable results for the binder types with partial replacement of OPC by supplementary cementitious materials. For binder types without OPC, there is a deviation in the migration coefficient due to a differing chloride concentration that triggers the color change. [ABSTRACT FROM AUTHOR]

This research aims to comprehensively evaluate the performance of cold recycled mixtures treated with cement and plasticizer in laboratory and field settings. The study employed two recycled asphalt fractions, 0–40 mm and 0–20 mm, combined with varying proportions of portland cement (M500), water, and a plasticizer (ZHBI-S). Initial performance assessments were conducted using standard tests, followed by additional tests focusing on rutting resistance, beam fatigue, and elastic modulus of selected recycled asphalt pavement (RAP) compositions. Furthermore, field performance evaluation involved the collection of RAP mixture samples from the asphalt paver's bunker and core samples from the finished pavement. The investigation's outcomes suggest that the cold RAP mixture treated with cement and plasticizer can be applied as a binder or base course. [ABSTRACT FROM AUTHOR]

Given the long history of columns in the languages and lexicons of architecture, they are the ideal building elements with which to experiment in the pursuit of 3D‐printed concrete. Ana Anton and Benjamin Dillenburger of the Chair for Digital Building Technologies at ETH Zurich reveal how new technologies can produce sinuous filigree structures that are unachievable with conventional casting approaches, and also offer more advantages. [ABSTRACT FROM AUTHOR]

The performance of composite binders with high-volume steel slag (SS), granulated blast furnace slag (GBFS) and desulfurization gypsum (DG) were systematically investigated. The results show that the synergistic effects of high volume (40–60%) of SS with GBFS and less than 15% of DG could perform adequate setting time, higher strength, well volume stability and soundness as well as dense microstructure. The higher compressive strengths exceeding 70 MPa at 28 days and up to 80 MPa at 90 days could be obtained for composite pastes with high-volume SS, which exhibit tight relationships with [CaO]·[SO3]/[Al2O3]·[SiO2] and [CaO]·[Al2O3]/[SO3]2 molar ratios. More (15–19%) AFt and less (about 1%) portlandite produced during the hydration of composite binders. C–S–H gels and calcite crystals were formed. The composite binder possesses lower energy consumption, high carbon reduction and low cost compared with Portland cement in favor of the low-carbon cementitious material production and effective utilization of SS. [ABSTRACT FROM AUTHOR]

Amorphous silica (a-SiO2), found in rice husk ash, is a valuable material due to its high silica content, large surface area, excellent pozzolanic properties, and strong binding ability with cement. These characteristics make it ideal for use as a supplementary cementitious material and a sustainable alternative for the partial replacement of ordinary Portland cement. This study aims to optimize the recovery process of amorphous silica from rice husks cultivated under various soil conditions (normal, drought, saline, and acidic soils), which are experiencing significant fluctuations due to climate change in many rice-producing countries. Experiments were conducted on rice husks under different pyrolysis conditions at temperatures of 700 ℃, 800 ℃, and 900 ℃, with varying calcination durations. Through comprehensive analysis using Scanning electron microscopy (SEM) and X-ray diffraction (XRD), along with the evaluation of amorphous silica recovery efficiency, we identified the optimal conditions for producing amorphous silica from rice husks. The analysis revealed that the highest recovery efficiency was achieved at a pyrolysis temperature of 700 ℃ for 1 hour. Under these conditions, the recovery efficiencies were 87.9% for normal soil RHA, 96.5% for saline soil RHA, 94.8% for drought soil RHA, and 95.6% for acidic soil RHA. The phase structure, surface morphology, and particle size of the RHA-derived amorphous silica, ground to micrometer sizes, were found to be similar to commercial products such as ordinary Portland cement and silica fume. This study provides a foundation for scaling up the production of amorphous silica from rice husk ash on an industrial scale, considering the relationship between optimal recovery efficiency and the origin of the rice husk ash, thus contributing to the development of environmentally friendly construction materials. [ABSTRACT FROM AUTHOR]

Concrete production is associated with extensive energy consumption and significant CO2 emissions. In addition, tremendous amounts of freshwater are used as a mixing agent. Urgency is increasing to develop sustainable cementitious materials and promote freshwater-saving strategies. An environmentally friendly alternative binder, seawater mixed with one part alkali activated material, is studied. In this work, a cradle-to-gate life cycle assessment was applied to study the equivalent CO2 emission and cost properties of the clinker-free binder. The seawater mixed mortar possesses comparable mechanical properties to Portland cement, with 3 d flexural and compressive strengths of 5.3 MPa and 25.2 MPa. In addition, the mortar developed in this work is of similar cost as commercial cement, but reduces CO2 emissions by 44.8%. [ABSTRACT FROM AUTHOR]

Thermoactivated recycled cement (RC) is a growing area of research and development in the cement industry. The approach represents a reversible process of cement hydration in which dehydrated compounds with similar characteristics to cement are obtained by means of thermal activation. To avoid CO2 emissions during the production of such RC, this study assesses the possibility of replacing ordinary Portland cement (OPC) with hardened cement powder (HCP) prepared with different proportions of hydrated lime (HL), relying on a second pozzolanic reaction, and compares it with RC mortars. Due to the thermal activation of HCP, the compressive strength increases by 11.5%. The addition of 8% HL produced an important increase in strength from 28 days to 90 days by 12.8%, although without surpassing the strength values of mortar produced only with HCP or with RC. The compressive strength results suggest the existence of a secondary pozzolanic reaction when using HCP from a cement paste source, but such a pozzolanic reaction was fully perceived in XRD patterns when using concrete as parent material, unlike cement paste, possibly due to large crystalline sand peaks that could have hindered the effective identification of smaller crystalline peaks. [ABSTRACT FROM AUTHOR]

AbstractThe environmental consequences of Portland cement (PC) manufacturing have prompted the exploration of alternative binders, such as the alkali activation of blast furnace slag (BFS), which is generated as a byproduct during the extraction of iron. While alkali-activated blast furnace slag (AAS) binders have some benefits over regular PC binders, they also suffer from disadvantages such as significant drying shrinkage. The study investigated the impact of Na dosage and curing conditions on alkali-activated blast furnace slag mortar (AASM). The consistency of the specimens was tested for fresh, hardened properties, and was conducted. The optimum Na dosage and curing conditions were selected. In the second stage, 0.1% and 0.2% glass and nylon fibers were added to the selected optimum mortar. Consistency, fresh, mechanical, and durability properties tests were conducted on the fiber mortars. The results showed that increasing the Na content increased the compressive and flexural strengths of AASM specimens. Thermal curing provided high compressive and flexural strengths, whereas fiber addition reduced water absorption and drying shrinkage. The drying shrinkage value was reduced by 26.82 % for AASM specimens with 0.2 % nylon fibers by volume compared to AASM without fibers. [ABSTRACT FROM AUTHOR]

The Behavior of Cement Portland Cooling Tower was evaluated numerically and experimentally. The three-dimensional simultaneous governing equations of the fluid flow, heat transfer and mass transfer were discretized and solved numerically, and the result of simulation were compared with measured data from the cement factory and with the available published result on the internet. Solid software was used as numerical software tool to predict the performance characteristics of cooling tower in Portland cement factory such as the velocity, temperature, stress and strain were simulated and compared with compute experiment. Experimentally the temperature, and pressure of gaseous and its emission across the cooling tower in White Portland cement factory were measured. The agreement seems acceptable between the numerical and experimental results. [ABSTRACT FROM AUTHOR]

t Based on desulfurized gypsum, the waterproof agent developed by modifying polyvinyl alcohol （PVA） catalyzed by liquid alkali activated Polymethyl hydrogen siloxane （PMHS） cooperated with portland cement to develop high-strength waterproof gypsum. The effects of modified PVA waterproofing agent and portland cement on the surface water absorption, mechanical properties and softening coefficient of desulfurization gypsum standard test block were investigated. The connection form of strong waterproof gypsum developed by modified hydrophobic agent and portland cement independently and cooperatively was determined by infrared spectrum. The influence of different additives on the thermal stability of gypsum was analyzed by thermogravimetry. The research shows that the best ratio of modified PVA waterproof agent and portland cement to produce high-strength waterproof gypsum is: waterproof agent 120 g and portland cement 150 g. At this time, the surface water absorption rate is 9. 35%, the absolute dry compressive strength is 22. 54 MPa, and the softening coefficient is 67. 57%. At the same time, the thermal stability of gypsum board is effectively improved. [ABSTRACT FROM AUTHOR]

Portland cements (PCs) and cement blends are multiphase materials of different fineness, and quantitatively analysing their hydration pathways is very challenging. The dissolution (hydration) of the initial crystalline and amorphous phases must be determined, as well as the formation of labile (such as ettringite), reactive (such as portlandite) and amorphous (such as calcium silicate hydrate gel) components. The microstructural changes with hydration time must also be mapped out. To address this robustly and accurately, an innovative approach is being developed based on in situ measurements of pastes without any sample conditioning. Data are sequentially acquired by Mo Kα1 laboratory X‐ray powder diffraction (LXRPD) and microtomography (µCT), where the same volume is scanned with time to reduce variability. Wide capillaries (2 mm in diameter) are key to avoid artefacts, e.g. self‐desiccation, and to have excellent particle averaging. This methodology is tested in three cement paste samples: (i) a commercial PC 52.5 R, (ii) a blend of 80 wt% of this PC and 20 wt% quartz, to simulate an addition of supplementary cementitious materials, and (iii) a blend of 80 wt% PC and 20 wt% limestone, to simulate a limestone Portland cement. LXRPD data are acquired at 3 h and 1, 3, 7 and 28 days, and µCT data are collected at 12 h and 1, 3, 7 and 28 days. Later age data can also be easily acquired. In this methodology, the amounts of the crystalline phases are directly obtained from Rietveld analysis and the amorphous phase contents are obtained from mass‐balance calculations. From the µCT study, and within the attained spatial resolution, three components (porosity, hydrated products and unhydrated cement particles) are determined. The analyses quantitatively demonstrate the filler effect of quartz and limestone in the hydration of alite and the calcium aluminate phases. Further hydration details are discussed. [ABSTRACT FROM AUTHOR]

This study introduces a novel mathematical approach rooted in X-ray spectroscopy principles to evaluate the oxidation state of sulfur, which is then applied in concrete and cementitious materials. Unlike previous studies that relied on an empirical quadratic relationship based on the ratios of characteristic X-ray lines (SKα, SKβ, and SKβ') for sulfur oxidation state determination, unique linear relationships between the intensities of the three X-ray lines for each oxidation state and total sulfur were utilized. Rational equations are then derived by combining these linear relationships for each species. Two independent rational calibration curves are constructed using the SKβ/SKα and SKβ'/SKβ ratios for samples containing sulfide-sulfate mixtures, irrespective of total sulfur concentration within the range of 0.3% to 2.0% by weight of concrete. These equations demonstrated interchangeability across three simulated matrices (Portland cement, concrete, and silica) and two sulfide species (pyrrhotite and pyrite). Absolute quantification of sulfide and sulfate species in concrete is achieved by independently measuring total sulfur. Compared to previous quadratic and linear equations, this approach is shown to minimize the difference between the experimental and calculated ratios of the calibration samples. Agreement was also observed between the sulfate ratio calculated through the rational approach and gravimetric analysis for concrete samples. [ABSTRACT FROM AUTHOR]

Sewage sludge ash (SSA), obtained by the incineration of sewage sludge, which is a byproduct of water treatment, could be used as a cement replacement material (CSR) to promote sustainability. SSA characteristics differ due to its different sources, compositions, and incineration methods. On the other hand, extensive investigations have highlighted the CSRs' ability to control alkali–silica reaction (ASR) as a destructive phenomenon, threatening durability. Hence, this study was conducted in order to study the ability of SSA with two finenesses, three replacement levels, and also its ternaries with trass or pumice, as natural pozzolans, to control ASR. The utilized SSA did not meet the requirements of a pozzolan at either finenesses. The results revealed that despite the fact that SSA generally reduced ASR expansion significantly, it only managed to control ASR at 50% replacement level. This was true for both finenesses. Furthermore, ternaries improved resistance against ASR expansion significantly, providing the ability to control ASR at lower replacement levels of SSA. The Si/Ca ratio was the key reason of SSA's ability to control ASR as it contained 1.5 and 2.5 times more SiO2 and Al2O3 than Portland cement respectively, and about one third of its CaO. Scanning electron microscopey (SEM), energy dispersive spectroscopy (EDS), and mapping confirmed that the relative amounts of Si, Al, and Ca in the SSA was crucial. [ABSTRACT FROM AUTHOR]

Low-heat Portland cement and ground granulated blast furnace slag are widely used for the preparation of hydraulic concrete. Nevertheless, the effect and mechanism of corrosion on low-heat Portland cement paste mixed with ground granulated blast furnace slag need to be further explored. This paper investigated the impact of ground granulated blast furnace slag on the calcium leaching of low-heat Portland cement paste by evaluating its mass loss, porosity, leaching depth, compressive strength, and Vickers hardness, and comparing it with the leaching performance of ordinary Portland cement paste. Furthermore, the phase composition and morphology of low-heat Portland cement paste containing ground granulated blast furnace slag were analyzed by X-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy. The results indicate that, after 180 days of soaking in ammonium chloride solution, the mass loss rate, growth rate of porosity, leaching depth, and compressive strength loss rate of low-heat Portland cement paste were 8.0%, 43.6%, 9.1 mm, and 27.7%, respectively, while those of ordinary Portland cement paste were 7.4%, 37.8%, 8.4 mm, and 30.1%, indicating that low-heat Portland cement paste is slightly more damaging than ordinary Portland cement. The addition of ground granulated blast furnace slag could significantly improve the leaching resistance of low-heat Portland cement. For instance, after adding 20% ground granulated blast furnace slag, the above test values were 2.4%, 28.5%, 5.6 mm, and 20.8%, respectively. The reason for this is that ground granulated blast furnace slag has the potential to reduce the porosity of low-heat Portland cement paste, and it can also undergo the secondary hydration reaction with its hydration product Ca(OH)2 to enhance the paste structure. Considering the cost performance, the suitable dosage of low-heat Portland cement paste for satisfactory leaching resistance is about 20%. [ABSTRACT FROM AUTHOR]

In order to reduce the risk of early freezing damage to cement-based materials in winter construction, lime powder was used to improve the properties of the Portland cement–sulphoaluminate cement (PC–CSA) composite system at low temperatures. In this study, the effects of lime powder dosage on the properties of a PC–CSA blended system with two proportions (PC:CSA = 9:1 and 7:3) at −10 °C were investigated, and the mechanisms of improvement were revealed. The results showed that the compressive strength of the PC–CSA composite system was effectively improved, and the setting time was shortened by the addition of lime powder. Lime powder could effectively act as an early heating source in the PC–CSA composite system, as the maximum temperature of samples exposed to sub-zero temperatures was increased and the time before dropping to 0 °C was prolonged by the addition of lime powder. The extra CH generated by the hydration of lime powder provided an added hydration path for C4A3 S ¯ , which accelerated the formation of AFt at each stage. Frozen water as well as the early frost damage were effectively decreased by lime powder because of the faster consumption of free water at an early stage. The modification of the hydration products also contributed to the denseness of the microstructure. [ABSTRACT FROM AUTHOR]

Geopolymer concretes are considered to be a potential sustainable, low-embodied carbon alternative for Ordinary Portland Cement (OPC) concrete. Alkali leaching is considered to be a major esthetic concern for Na-silicate-based geopolymers as it can lead to the formation of efflorescence products on the surfaces of concrete members exposed to humidity. In this context, this research aims to investigate the effect of the alkali content and the FA/GGBS mass ratio on the alkali leaching and formation of the efflorescence products. Paste cylinders were fabricated and cured in ambient conditions. Samples were submerged in deionized water and the concentration of the leached-out ions was measured. Efflorescence potential was also investigated by partial immersion of the samples in deionized water. The results highlight the complexity of the interacting parameters governing the formation of efflorescence products in geopolymer materials. Establishing relationships between the concrete mix variables and the risk of efflorescence seems unfeasible particularly because of the wide range of possible precursors and activators available to design geopolymer concrete mixes. To overcome this barrier, a practical performance-based testing method is developed. For the first time, by testing a wide range of geopolymer materials, performance-based requirements associated with the risk of efflorescence for geopolymer concrete surfaces exposed to humidity are calibrated. Four categories of risk are proposed and typical suitable exposure conditions for geopolymer concrete surfaces are suggested for each risk category. [ABSTRACT FROM AUTHOR]

Grouting engineering is extensively employed in highway maintenance, tunnel excavation, mining, and other domains. As application scenarios become more complex, the demands for injectivity and toughness of grouting materials escalate. This research presents the fabrication of a dual-network cementitious material through acrylamide (AM) monomers in-situ polymerization and ultra-fine portland cement for grouting. The in-situ polymerization of AM increases the fluidity of cement paste, forms a hydrogel three-dimensional network structure, and significantly reduces the initial setting time from 345 to 35 min at a 5% AM content. The early-stage compressive strength (0–7 days) is inhibited by the in-situ polymerization, the flexural strength is notably increased, with an overall toughness improvement of 174.4% at a 7% AM content. The in-situ polymerization influences the early hydration behavior of ultra-fine portland cement by delaying the hydration induction period and affecting calcium hydroxide content and the bound water in calcium silicate hydrate. The complexation between metal ions (Ca2+, Al3+) in ultra-fine portland cement and carboxyl groups in the polymer enhances organic–inorganic interaction. The three-dimensional network structure of the cement hydration products and the polymer will form a dual-network structure, further enhancing the performance of the ultra-fine portland cement. In this research, the potential application of AM in-situ polymerization in the enhancement of ultra-fine portland cement grouting is proposed. [ABSTRACT FROM AUTHOR]

Sulfate plays a critical role in portland cement. The internal gypsum (CaSO4·2H2O) incorporating with clinker controls the hydration of cement, while the external gypsum can attack the hydration products. Magnesium sulfate is renowned for sulfate attack on concrete. This study aims to investigate the impact of the internal Mg2+ addition on the composition and microstructure of hardened portland cement paste. Notably, the test results demonstrate that internal Mg2+ does not show the same aggressive effect as external Mg2+ on the destabilization of portland cement. Instead, internal Mg2+ infiltrates into the calcium-silicate-hydrate (C-S-H) gels, displacing the Al-O tetrahedra on the Si chain, forming C-(A, M)-S-H gels by converting Ca octahedra to Mg octahedra or Al-O tetrahedra to Mg-O tetrahedra. This process contributes to a decrease in the Al/Si ratio and mean chain length of the C-S-H gels. Additionally, the displaced Al-O tetrahedra from the C-S-H gels react with AFt, resulting in the AFm formation. Consequently, these structural changes in the C-S-H gels, along with additional pore filling through AFm precipitation, play a significant role in refining the pore structure. [ABSTRACT FROM AUTHOR]

Fly ash (FA) increases the performance of cement concrete through pozzolanic reaction and microstructure development at later ages. FA is usually associated with lower early age compressive strength especially at higher replacement levels. This study attempts at improving the early age strength of FA portland pozzolana cement with limestone calcined clay pozzolan (LC2). Different proportions of limestone and calcined clay (1∶1 , 1∶2 , and 2∶1) in tandem with FA at various replacements of cement clinker (30%, 40%, and 50%) were tested. The combined effect of using LC2 with FA has shown to enhance the early age hydration of cement along with improved compressive strength. Heat of hydration results showed increased heat release in FA mixes blended with LC2. Thermodynamic modeling analysis was used to study the change in phase assemblage of these mixtures. A higher solid volume observed in the thermodynamic simulations in the combined blends of FA and LC2 is hypothesized to be the cause of improved performance compared with only FA blended cement. Mercury intrusion porosimetry (MIP) results further confirmed an improvement in pore structure characteristics of FA cement blended with LC2. The possibility of reducing associated carbon emissions without compromising in strength are highlighted by using FA and LC2. [ABSTRACT FROM AUTHOR]

This manuscript presents an experimental investigation of fly ash-based geopolymer-reinforced concrete beams' dynamic characteristics and mechanical properties. The purpose of this study is to compare the performance of geopolymer and portland cement concrete in terms of the viscous damping ratio, resonance frequency, compressive strength, and modulus of elasticity. The scope of the effort includes fabricating 14 reinforced concrete beams, 12 of which were made with geopolymer concrete and 2 with portland cement concrete. In this study, the experimental modal analysis method was employed. Test beams were placed on polyurethane cube supports to achieve free-free mode or oscillation conditions. For data analysis, 44 equally spaced analysis points were determined on the beams. Some of these points were stimulated five times along the x-x axis using a modal hammer to obtain FRF and viscous damping ratio graphs. As a result, the resonance frequency of portland cement concrete was higher than that of geopolymer concretes, while the viscous damping rate was lower. Furthermore, it was determined that the modulus of elasticity changed inversely with the viscous damping ratio rather than the compressive strength when examining the relationship between modal parameters and mechanical properties. These findings have significant implications for using geopolymer concrete in construction, as it can help distribute loads homogeneously and increase the durability of structures. Overall, this study provides valuable insights into the relationship between dynamic characteristics and mechanical properties of geopolymer and portland cement concrete, informing the development of more sustainable and resilient construction materials. [ABSTRACT FROM AUTHOR]

This study examined the chloride binding properties of slag-blended cement at different replacement ratios with two water-to-binder (w/b) ratios and two curing temperatures. Hydrated samples were immersed in NaCl solutions, and bound chloride at equilibrium was determined, respectively. It is found that at each w/b and temperature, chemically and physically bound chloride increased with increasing slag ratio up to 50%, whereas a further increase of slag ratio to 70% tended to reduce chloride binding. Physically bound chloride accounted for a major portion in total binding. Moreover, Ca(OH)2 content and slag reaction degree were analyzed, indicating that slag reaction degree decreased with increasing slag ratio. According to the results, the influence of slag ratio on chloride binding is discussed. The relatively low chloride binding at 70% slag ratio is partially attributed to the low reaction degree of slag, resulting in a lower amount of C-S-H and AFm phase. It is also inferred that the decreased physical binding at 70% slag ratio is closely related to the changed surface electrical property of C-S-H. [ABSTRACT FROM AUTHOR]

Lately, dry stacking of filtered tailings has emerged as a safer alternative to traditional slurry disposal in ponds as it comprehends the compaction of the unsaturated cake to form piles. A cementing agent can be added to the mixture to improve the mechanical properties of the compacted tailings; however, it is essential to understand its response under different conditions. The present study examines the mechanical behavior of compacted iron ore tailings (IOT)-binder blends for dry stacking purposes, highlighting the effect of the cement type on the behavior of the tailings: two commercially available types of binders, portland pozzolan cement (PPC) and high early-strength portland cement type III (PC III); and one green alkali-activated cement (AAC). A full factorial design approach was used to study the influence of the following parameters on the strength and stiffness of the studied mixtures: dry unit weight (γd), cement content (C), type of cement (TC), and curing period (CP). To do so, a set of unconfined compression, ultrasonic pulse velocity, and consolidated drained triaxial tests were carried out. To compare the microstructural and compositional characteristics of the three different cement types, secondary scanning electron microscopy (SSEM) and backscattered scanning electron microscopy (BSEM)/energy dispersive spectrometry (EDS) analyses were performed. The stiffness and strength results have been successfully correlated to the porosity/cement index (η/Civ) and the statistical analysis has unveiled the great effects attributed to the cement content, type, and CP. Additionally, microstructural and macrostructural observations revealed that after seven days of curing, the IOT mixtures stabilized with PC III exhibited more robust microstructures and superior mechanical performance: around five times greater strength and stiffness than AAC-containing samples and two times higher considering the PPC-containing specimens. With extended CPs (90 days), the performances of PC III and PPC samples are equivalent, whereas the strength is around three times greater than that of the AAC samples. That is, there was a notable enhancement in the cementitious matrix for IOTs stabilized with PPC and AAC for a more extended CP. [ABSTRACT FROM AUTHOR]

The portland cement (PC) industry is responsible for approximately 7% of all carbon dioxide (CO2) emissions in the world. Blast furnace slag (BFS) has been increasingly used as a substitute for PC, due to the efficient disposal of steel industry waste and reductions in CO2 emissions. The present work investigated the environmental benefits of cementitious materials with large volumes of BFS (up to 90% PC replacement for the S90 mixture) and the influence on porosity and compressive strength. By X-ray computed microtomography and mercury intrusion porosimetry, pore size distribution was assessed. Porosity was also evaluated by water absorption. The environmental impacts were investigated by analyzing the embodied CO2 emissions (ECO2) and embodied energy (EE) by using life cycle assessment methodology. Reductions of around 40% in the compressive strength of S90 were found, while reductions in EE and ECO2 were above 80%. The S90 showed higher porosity at the age of 28 days, but then promoted a more active pore closing effect over time, being nevertheless feasible for use in terms of porosity. The use of S90 is expected to increase durability due to its thinner porous matrix, and contribute to reducing environmental impact and advancing cleaner production. Practical Applications: Today, there is a global call to action to end poverty, protect the environment and climate, and ensure that people everywhere can enjoy peace and prosperity. Objectives set for the United Nations aim to help developing countries, like Brazil, achieve the 2030 Agenda for Sustainable Development. A highlight is given to "Sustainable Development Goal 9: Industry, Innovation and Infrastructure" (SDG 9), which aims to build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation. The portland cement (PC) industry is responsible for approximately 7% of all carbon dioxide (CO2) emissions in the world. The study carried out here points to the feasibility of using blast furnace slag (BFS) to replace up to 90% of PC clinker, and demonstrates the environmental advantages in terms of reducing CO2 emissions and energy consumption. In this context, the use of clinkers with higher concentrations of BFS, up to 90%, has emerged as a way to contribute to the sustainable development proposed by SDG 9. [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]

Cement production may involve excessive use of natural resources and have negative environmental impacts, as energy consumption and CO2 emissions can cause air pollution and climate change. Cement kiln dust (CKD), a by-product waste material, is also a primary issue associated with cement production. Utilizing CKD in mining applications is a pathway to eco-sustainable solutions. Cemented paste backfill (CPB) made with mine tailings is an efficient method for void backfilling in underground mines. Therefore, this study investigated the eco-sustainable utilization of CKD as a co-binder material that can partially replace cement in CPB prepared with copper tailings. At 7, 14, 28, 56, and 90-day curing times, the experimental campaign measured the physical and mechanical parameters of the cured CPB samples, including density, UCS, and elastic modulus (stiffness). Additionally, the CPB-cured mixes were analyzed using XRF, X-ray XRD, SEM, and EDX techniques to link the mineral phases and microstructure to mechanical performance. Four proportions (5, 10, 15, and 20%) of CKD represented in 75 samples were prepared to replace ordinary Portland cement (OPC) in the CPB mixtures, in addition to the reference mix (control) with 0% CKD. As all combinations exceed the compressive strength of CPB required for achieving stability in underground mines, the results showed that CKD could be utilized advantageously as a partial substitute for OPC with a proportion of up to 20% in the CPB mixture. When tested after 90 days, the combination modified with 5% CKD exhibited comparatively higher compressive strength than the control mixture. [ABSTRACT FROM AUTHOR]

Portland cement products are extensively used as parent materials in construction projects. However, the production and consumption of these products result in various environmental pollutants, including the emission of carbon dioxide gas and excessive water usage. Geopolymer products have emerged as a promising alternative to Portland cement and its products due to their diverse mechanical and chemical properties. Therefore, in this study, we aim to investigate the potential of geopolymer products as a replacement for Portland cement. To this end, the optimal mixing design was obtained by performing uniaxial compressive strength and flow table tests. Nailing is a commonly used method for stabilizing soil excavations and slopes, often involving the use of Portland cement as grout. Geopolymer is used as a potential replacement for cement grout in this system. Pullout tests were conducted to investigate the interaction between the soil and grout, considering the effect of curing conditions and environmental factors such as temperature, humidity, and overburden pressure for both the geopolymer and cement grouts. The results indicate that, in general, the pullout force of geopolymer samples is lower than that of cement samples. However, raising the temperature in geopolymer samples results in an increase in the pullout force, whereas an increase in temperature in cement samples leads to a decrease in pullout force. It can be concluded that geopolymer samples need to be modified by using an additive, such as sodium silicate, to achieve proper pullout force and suitable interlocking with soil grains. [ABSTRACT FROM AUTHOR]

Cement slurry is the medium of dispersion of coarse and fine aggregates when preparing concrete. The flow behavior of the cement slurries is governed by rheological parameters. The lower the value of these parameters is, the better the flowability and homogeneity of the cement slurry are. Static shear stress (τs), dynamic shear stress (τd), and the thixotropic index (β) are the basic rheological parameters. The effect of fly ash and silica fume on the rheology of Ordinary Portland Concrete (OPC) 43 and OPC 53 was studied by conducting tests on a coaxial rotating-type viscometer. Fly ash dosage was increased from 10% to 30% by the weight of cement in increment steps of 5% in binary and ternary mixes. Silica fume was kept constant at 5% in the ternary mixes. It was found that τs increases with fly ash in the OPC 43 but remains almost constant for the OPC 53 in both binary and ternary mixes. τd was almost constant for both the cement slurries in both binary and ternary mixes. β increases with an increase in fly ash for OPC 43 in binary and ternary slurries but decreases in OPC 53 slurries. The increment of fly ash increases the reversible built in the OPC 43 slurries, which can be broken on the application of shear. Thus, OPC 43 is a better cement from the rheological point of view in the development of various concrete mixes. [ABSTRACT FROM AUTHOR]

There are many environmental problems caused by factory waste. Sugar factory waste, in the form of bagasse ash, and PLTU factory waste, in the form of fly ash, are currently in the spotlight of science studies. This study used waste bagasse and fly ash to substitute Portland cement as the main ingredients for mortar. Baggash and fly ash waste were collected, processed, and then used to replace cement by up to 40% to determine to what extent they could be used in brick masonry work, wall plastering, and masonry paste. Experimental tests were carried out on mortar cube samples measuring 5×5×5 cm, comparing four types of samples consisting of Portland cement, bagasse ash, and fly ash. The compressive strength results were obtained after 28 days. Normal Mortar (MN=11.75 MPa) had higher compressive strength than the substitute mortar types MA (3.23 MPa), MB (3.09 MPa), and MC (2.98) MPa. According to SNI 6882- 2014, MA, MB, and MC mortars can be used as O-type mortar (2.4 MPa). Therefore, they can be applied to wall plastering or walls not bearing loads. [ABSTRACT FROM AUTHOR]

Supplementary cementitious materials (SCMs) are commonly introduced into the concrete mix to increase their properties, addressing the current need for durable and robust pavements. With every ton of Ordinary Portland Cement (OPC) produced through processes such as fossil fuel combustion and limestone fermentation, carbon dioxide is released into the atmosphere. Conversely, Ground Granulated Blast-furnace Slag (GGBS), being abundantly available, presents a viable more environmentally friendly alternative to cement for various concrete applications. This work studies the influence of GGBS, in combination with chemical admixtures, on M40 grade binary blended concrete mixtures. The aim of the study was to improve the strength characteristics at various stages of concrete curing. The results indicated that the GGBS-incorporated concretes (replacing 60%, 65%, and 70% of the cement) exhibited an increase in compressive strength after prolonged curing. The average density of fresh concrete mixes containing GGBS did not exhibited a noticeable increase. A marginal disparity in air content was observed in the replacement mix. Minimal length changes were observed in the drying shrinkage test after a curing duration of 360 days compared to conventional concrete mixtures. [ABSTRACT FROM AUTHOR]

Accurately predicting the 28-day compressive strength of Portland cement clinkers is challenging due to their complex multiphase nature, especially when production processes and environmental conditions vary. To address this issue, the TransXRD model was introduced, which is a novel deep learning approach that combines the Transformer architecture with CNN design. 214 clinker samples were collected from 6 cement plants. The diffraction peak sequence of samples ranging from 10° to 55° was used as required input for the model. A combination of one-dimensional convolution is incorporated to extract local features, and self-attention mechanisms are leveraged to perform global feature integration. XRD data were directly utilized, bypassing additional processing to minimize signal loss. Compared to other DNN (deep neural network) models, the TransXRD model demonstrates promising performance, achieving a root mean square error (RMSE) of 1.15, a mean squared error (MSE) of 1.33, a mean absolute error (MAE) of 0.93, and a mean absolute percentage error (MAPE) of 1.76 on the test set. Notably, in the training set, 100% of the data exhibit prediction errors within 2 MPa, while within the test set, 90% of the prediction errors are within 2 MPa. The application potential of XRD data in predicting the compressive strength of cement clinker also offers novel insights into predicting the performance of other materials. [ABSTRACT FROM AUTHOR]

The building sector is figuring out how to lower its embodied CO2 in a sustainable way. The technology, known as Carbon Capture, Utilization, and Storage (CCUS), offers a possible remedy for this issue. Accelerated carbonation is one method of sequestering CO2 in concrete. In this study, an M25 grade of concrete is made using Ordinary Portland Cement with 0–30% replacements of Class F fly ash. The specimens were exposed to accelerated carbonation curing for 6 h, 24 h, and 72 h, and then the specimens were tested for their compressive strength, carbonation depth, and pH. The CO2 uptake was measured by Thermogravimetric analysis (TGA), and the occurrence of carbonation was confirmed using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The results of the study indicate a significant improvement in the compressive strength with a percentage increase of 70.46%, 111.28%, 30.36%, and 36.69%, respectively, for 0%, 10%, 20%, and 30% fly ash contents in concrete samples subjected to 72 h of accelerated carbonation curing without affecting its alkalinity. The study reiterated that accelerated carbon curing is an advisable method for countries like India that are undergoing rapid economic developments. [ABSTRACT FROM AUTHOR]

The construction industry is a significant contributor to global CO2 emissions, primarily due to the extensive use of ordinary portland cement (OPC). In response to the urgent need for sustainable construction materials, calcium sulphoaluminate (CSA) cement has emerged as a promising alternative. CSA cement is renowned for its low carbon footprint, high early-age strength, and superior durability, making it an attractive option for reducing the environmental impact of construction activities. While CSA cement offers benefits in carbon emissions reduction, its susceptibility to carbonation presents challenges. Although the body of literature on CSA cement is rapidly expanding, its adoption rate remains low. This disparity may be attributed to several factors including the level of scientific contribution in terms of research focus and lack of comprehensive standards for various applications. As a result, the present study sets out to track the research trajectory within the CSA cement research landscape through a systematic literature review. The study employed the Prefer Reporting Item for Systematic Review and Meta-Analysis (PRISMA) framework to conduct a literature search on three prominent databases, and a thematic analysis was conducted to identify the knowledge gap for future exploration. The study revealed that while CSA concrete demonstrates superior early-age strength and environmental resistance, its susceptibility to carbonation can compromise structural integrity over time. Key mitigation strategies identified include the incorporation of supplementary cementitious materials (SCMs), use of corrosion inhibitors, and optimization of mix designs. The review also highlights the global distribution of research, with notable contributions from the USA, China, and Europe, emphasizing the collaborative effort in advancing CSA concrete technology. The findings are crucial for enhancing sustainability and durability in the construction sector and advancing CSA binders as a sustainable alternative to traditional cement. [ABSTRACT FROM AUTHOR]

Sand mining tailing (ST) is a byproduct of the sand extraction of submerged pits, a process which is carried out to obtain aggregates for civil construction. This tailing consists of fine particles from the pulp washing process, usually disposed of in decantation ponds. The present study proposes ST as a supplementary cementitious material (SCM) for Portland cement concrete, thereby reintegrating this tailing into the production chain. In this sense, ST was characterized, and concretes containing 2% to 14% of cement replacement (%vol) by ST were produced and evaluated. STs showed natural fineness, particles with angular morphology, a significant amount of kaolinite, and 36% amorphous content. ST concretes exhibited a compressive strength of up to 57.9 MPa at 28 days under 7.0% of cement replacement, 38.8% higher than the reference. Consequently, only 5.6 kg/m3 of Portland cement was required to attain 1.0 MPa, representing a 33.6% reduction compared to the reference. The ultrasonic pulse velocities measured in ST concrete with 2.0%, 4.0%, 7.0%, and 14.0% cement replacement were 3.0%, 6.1%, 9.3%, and 6.6% higher than the reference, respectively. These results indicate enhanced mechanical properties, improved matrix uniformity, and superior environmental performance across all SCM levels compared to the reference, with optimal efficiency observed at 7.0% ST content. [ABSTRACT FROM AUTHOR]

The cement industry is known for being highly energy-intensive and a significant contributor to global CO2 emissions. To address this environmental challenge, this study explores the potential of using the waste materials of steel slag (SS) and eggshell powder (ESP) as partial replacements for cement in alkali-activated mortars (AAMs) production, activated by NaOH and Na2SiO3. Mortar samples are prepared with 50% of ordinary Portland cement (OPC) as part of the total binder, and the remaining 50% is composed of ESP, incrementally replaced by SS at levels of 10%, 20%, 40%, and 50%. The activation process was performed with an 8% NaOH concentration and a silica modulus of 2. Key findings include that the workability of AAMs decreased with increasing SS content, requiring admixtures like superplasticizers or additional water to maintain workability. At 50% SS replacement, the water consistency and slump flow values were 32.56% and 105.73 mm, respectively, with a setting time reduction of approximately 36%, losing plasticity within 2 h. Both absorption capacity and porosity decreased as SS content increased from 10% to 50% of ESP. Additionally, the bulk density, compressive strength, and uniformity of the hardened mortar samples were enhanced with higher SS content, achieving maximum compressive strength (28.53 MPa) at 50% SS replacement after 56 days of curing. Furthermore, OPC-based AAMs incorporating SS and ESP demonstrate good resistance to sulfate attack and thermal heating. Microstructural analysis reveals the presence of C–S–H, C–A–S–H, and N–A–S–H phases, along with minor amounts of unreacted particles, and the microstructure shows a dense, highly compacted, and homogeneous morphology. These findings suggest that replacing eggshell powder with up to 50% steel slag enhances the hardened properties of AAMs. Further research is recommended to explore cement-free alkali-activated granular ground blast furnace slag (GGBFS) with ESP for more sustainable construction solutions. [ABSTRACT FROM AUTHOR]

Basalt powder (BP) is the residue of a plant that crushes basalt stones. This work deals with the effect of waste BP on the properties of cement mortars and the physical properties of hardened mortars. Modified concrete was prepared by partial replacement of BP in amount of 5, 10, 20% by weight of cement. Physico-mechanical properties and corrosion resistance were investigated. Electrochemical impedance spectroscopy (EIS) was used to examine the corrosion behavior of cement pastes with a partial addition of basalt powder in aggressive solutions of 5% NaCl and 5% MgCl2 for up to 270 days. Infrared spectroscopy (IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were also performed to investigate the hydration process and microstructure formation of the basalt blended paste. Results indicate that the addition of basalt powder as a partial replacement of cement influences the microstructure of the interfacial transition zone (ITZ), which is denser and stronger than in cement paste without basalt powder. The filler effect of the basalt powder improves the compressive strength of cement paste. Also, comparing BP0 and BP20 in 5% NaCl after 270 days, the partial substitution of cement with BP resulted in a higher compressive strength of 671 and 895 kg/cm2, respectively. The EIS results also showed the highest values of Rp 953 ohms cm2 after 270 days. This high corrosion resistance might indicate the binding by high Al2O3 that reduced the free aggressive chloride ions in the solution. Article Highlights: The addition of basalt powder as a partial replacement of cement, improved the compressive strength of the concrete. The physicochemical and mechanical investigations showed that the basalt addition led to physical densification and more ITZ robust of cement matrix. EIS measurements showed that BP20 sample in 5% NaCl had a high Rp, 953 ohms cm2 after 270 days indicated higher corrosion resistance. [ABSTRACT FROM AUTHOR]

Due to the large increase in human population, the need for more buildings and other amenities is widening. Concrete is considered one of the most abundant and popular materials used in the structure and construction fields. It is known as a composite mix composed of cement and aggregates including fine and coarse and water. Despite its good properties, its capability to be formed in different shapes and its ability to resist severe conditions, concrete will struggle with the presence of extremely high temperatures. So, different types of concrete must be found to resist those challenging conditions. Refractory concrete can be considered a good choice to be used in places exposed to elevated temperatures and severe conditions. Mainly, refractory concrete is made up of ordinary Portland cement replacement well known as refractory cement, specific types of fine and coarse aggregates and are known as refractory or temperature-bearing aggregates and water. To the best authors' knowledge, review papers about refractory concrete are rare. For this reason, more than 65 papers were consulted including many recently published. This review describes the different types of materials used in refractory concrete. Furthermore, the different fresh, hardened, structural, durability and thermal properties of refractory concrete are also included such as slump, density, compressive strength, flexural strength, tensile strength, modulus of elasticity, ultrasonic pulse velocity, shrinkage, mass loss, porosity, water absorption, damage level and thermal conductivity. [ABSTRACT FROM AUTHOR]

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This paper investigates the effects of pozzolanic substitutions for ordinary Portland cement (OPC) with silica fume (SF) and metakaolin (MK) on the mechanical and toughness performances of steel fiber reinforced concrete (SFRC). Initially, a reference concrete mix with a water‐to‐binder ratio of 0.4 is blended with different volume fractions of steel fibers with varying geometry: crimped steel (CS) and straight steel (SS), both individually and in combination, to examine their mechanical properties. In the subsequent phase, the study investigates the impact of combining macro‐ and microsteel fibers on flexural toughness, to determine potential synergy for suitable combinations. Also, the possible influence of pozzolans in the variation of flexural toughness of hybrid steel fiber reinforced concrete (Hy‐SFRC) was evaluated. Hybridization of steel fibers was found effective in improving the workability of the concrete mix up to 11%. SFRC mixes containing pozzolans exhibited a significant enhancement in compressive strength, modulus of rupture, and modulus of elasticity compared to non‐pozzolanic SFRC. The hybrid combination of CS 1.5% and SS 0.5% was considered the best in terms of mechanical properties. Additionally, the results of synergy assessment showed that hybridization of steel fibers in the pozzolanic concrete mix was particularly effective in the post‐cracking stages with a positive 14% compared to a negative 8% in the pre‐cracking stage. The pozzolanic addition improved the flexural toughness of Hy‐SFRC to about 10%–20%. Blending of SF and MK in Hy‐SFRC was found effective in enhancing the toughness mechanism of concrete compared to Hy‐SFRC mixes containing binary SF and MK, indicating a stronger bond between the fibers and the matrix resulting from the pore refinement and hydration products developed at the interface. Hy‐SFRC containing a ternary pozzolanic mix of SF 10% and MK 10% gave the best results in flexural toughness, and the corresponding synergy values were found to be the maximum. The results were consistent with the morphology analysis, which revealed an increase in hydration products at the interface between the aggregate and concrete matrix, as well as between the steel fiber and concrete matrix, due to the ternary blending of SF and MK. [ABSTRACT FROM AUTHOR]

The present study investigated the microstructural properties of ordinary Portland cement (OPC)-modified with minimum dosage of nano TiO2 on fresh and hardened cement mortar surfaces and intermixed samples. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) were used to analyze the morphology and hydration products of the OPC specimens doped with nanotitanium (NT).Additionally, XRD coupled with Rietveld refinement was employed to quantify the crystal phases and refine the crystal structure model through the comparison of the calculated diffraction pattern to the measured pattern. Subsequently, crystallographic analysis was conducted to evaluate the crystallographic structure and to confirm the existence of specific atoms and bonds within the crystal structure altered with NT. The findings revealed that the addition of minimal NT resulted in a more compact and denser microstructure, characterized by increased formation of calcium silicate hydrate (CSH) gel and a reduction in calcium hydroxide (CH) crystals.This led to a reduction in the porosity of the hardened coating surface, with similar improvements observed for the fresh coating and intermixed samples compared to those of the control mortar. A decrease in the lattice parameters, accompanied by an increase in the number of atoms, bonds and polyhedra in the crystal structure, led to alterations in the interatomic spacing and contributed to the densification of the cementitious matrix.The findings also showed that NT integration led to a more compact structure with shorter bond distances and smaller polyhedral volumes for the Ti samples than for the control sample. Moreover, compared with the freshly cast and hardened coating samples, the NT-intermixed samples exhibited the shortest Ti–O bond distances and the smallest polyhedral volume. Overall, the analysis presented in this study significantly contributes to the development of novel and environmentally friendly photocatalytic cementitious materials at minimal dosages. [ABSTRACT FROM AUTHOR]

Although alkali-activated materials (AAMs) are considered potential substitutes for Portland cement, they still come with elevated costs and significant carbon dioxide emissions. The development of alternative activators, such as sodium silicate based on the dissolution of rice husk ash (RHA), could partially overcome these disadvantages. However, to maximise the mechanical performance of AAMs, the production of RHA-based sodium silicate (RHA-SS) needs to be fully understood. The production process of an alternative RHA-SS activator was thus investigated through experimental evaluations of RHA grinding time, RHA dissolution time and thermal curing temperature and time. Mechanical performance was evaluated through compressive strength tests carried out on alkali-activated pastes made up of metakaolin, as a precursor, and two different activators (RHA-SS and a commercial sodium silicate). Microstructural features were evaluated through X-ray diffraction, scanning electron microscopy and thermogravimetry analyses. Optimal production was obtained for a grinding time of 30 min, a thermal curing temperature of 40°C, dissolution time of 6 h and a thermal curing time of 8 h. The results show the efficiency of the alternative alkaline activator, which may represent a technically viable solution for larger scale application to AAMs. [ABSTRACT FROM AUTHOR]

Steel slag (SS) is a by-product of the steel industry, and its recycling is of great significance. In this study, the influence of SS fineness and curing regimes on the hydration properties of cement and the effects of SS content on the compressive strength of pastes were investigated. The hydration products and microstructure of pastes were further explored through X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the compressive strength decreases gradually with the increase of SS, and increases with the increase of the specific surface area of SS. The compressive strength of paste after steam curing is improved, and the compressive strength of the paste mixed with 30% SS can reach more than 50 MPa after 90 days of steam curing. The hydration products of paste mixed with SS are not significantly different from those of cement, which mainly comprise calcium hydroxide (Ca(OH)2) and calcium silicate hydrate (C–S–H) gel, accompanied by a small amount of calcium carbonate (CaCO3). SS has secondary hydration after long-term ageing and can fill and refine the pore structure, according to SEM. Using SS as a supplementary material is beneficial in terms of reducing cement cost and lowering carbon dioxide (CO2) emission. [ABSTRACT FROM AUTHOR]

The problem of loss of strength caused by the conversion reaction with calcium aluminate cements (CAC) is well known. It has been shown that the addition of ground granulated blast furnace slag (GGBS) to CAC inhibits the conversion process. Different slags can have a different chemical and mineralogical composition depending on their origin and production process, which can significantly influence their reactivity. This work investigated the extent to which the R3 test, developed for Portland cement and based on isothermal calorimetry and/or bound water, was used to predict the reactivity of ground granulated blast furnace slag in a CAC. Mortars and cement pastes with a 30% replacement of slag were tested to evaluate their compressive strength and microstructure. The results show that slags with higher reactivity due to their hydraulic properties lead to a lower compressive strength loss within the first 6 h, a higher strength loss after 24 h due to stratlingite formation and a lower strength loss after 28 days due to pozzolanic reaction and stratlingite formation. The results also confirm that the R3 test was used as a rapid method to predict the effects of slag on the compressive strength of CAC. [ABSTRACT FROM AUTHOR]

Fly ash–slag-based alkali-activated materials have excellent mechanical performance and a low carbon footprint, and they have emerged as a promising alternative to Portland cement. Therefore, replacing traditional Portland cement with slag–desulfurization gypsum-based alkali-activated materials will help to make better use of the waste, protect the environment, and improve the materials' performance. In order to better understand it and thus better use it in engineering, it needs to be characterized for performance and compositional design. This study developed a novel framework for performance characterization and composition design by combining Categorical Gradient Boosting (CatBoost), simplicial homology global optimization (SHGO), and laboratory tests. The CatBoost characterization model was evaluated and discussed based on SHapley Additive exPlanations (SHAPs) and a partial dependence plot (PDP). Through the proposed framework, the optimal composition of the slag–desulfurization gypsum-based alkali-activated materials with the maximum flexural strength and compressive strength at 1, 3, and 7 days is Ca(OH)2: 3.1%, fly ash: 2.6%, DG: 0.53%, alkali: 4.3%, modulus: 1.18, and W/G: 0.49. Compared with the material composition obtained from the traditional experiment, the actual flexural strength and compressive strength at 1, 3, and 7 days increased by 26.67%, 6.45%, 9.64%, 41.89%, 9.77%, and 7.18%, respectively. In addition, the results of the optimal composition obtained by laboratory tests are very close to the predictions of the developed framework, which shows that CatBoost characterizes the performance well based on test data. The developed framework provides a reasonable, scientific, and helpful way to characterize the performance and determine the optimal composition for civil materials. [ABSTRACT FROM AUTHOR]