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In this study, we report a base‐catalyzed transesterification reaction of glycerol, a waste product of the biodiesel industry, with various dialkyl carbonates, which act both as reactants and solvents, to convert glycerol carbonate into an industrially useful molecular building block. The catalyst, being used for the first time, is also a waste product from industry, present in bauxite residues and in the Portland cement, simply known as tricalcium aluminate. Despite being well‐known and readily available, this solid is only extremely poorly researched catalyst, nevertheless, using dimethyl and diethyl carbonate, glycerol conversion rates >80% and glycerol carbonate yields >60% could be achieved in just 1 h (under air atmosphere and reflux). In a comparison of the performance with other catalysts commonly researched today, as well as with other components of red mud and cements, the results showed that tricalcium aluminate is excellent, cheap, and largely environmentally friendly material for this purpose. Reusability studies of the catalysts have also shown that they provide high conversion and product yields even after repeated use, although different material characterization techniques showed intense glycerol‐catalyst surface interaction and intermediate product formation, the deactivating side effects of which could be avoided by catalyst regeneration steps. [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]

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]

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]

The AFm phase found in hydrated Portland cements refers to a family of calcium aluminate phases. Their layer structure is derived from that of portlandite (calcium hydroxide (Ca(OH)2)), but with one third of the Ca2+ ions replaced by a trivalent ion, nominally Al3+ or Fe3+. The resulting charge imbalance gives the layers a positive charge, which is compensated by intercalated anions; the remaining interlayer space is filled with water (H2O). Hydrated cements will contain mixtures of AFm phases and their solid solutions. Portland cement is often modified by addition of soluble nitrate or nitrite salts to protect embedded steel or to shorten the setting time. These nitrate and nitrite ions are capable of entering and occupying AFm anion sites, hence impacting overall phase balances between cement hydrates. In this study AFm phases and solid solution formations were investigated between AFm phases containing SO42−, CO32−, OH−, Cl− and NO2− NO3− ions. Samples were synthesised and subsequently characterised using X-ray diffraction and through the measurement of aqueous solution compositions after 180 days of equilibration in water. [ABSTRACT FROM AUTHOR]

The experimental research focused on the influence of solutions containing chicken manure, pig slurry, and silage on the hydration processes of cements and clinker minerals such as C3S, β-C2S, C3A, and C4AF. The results showed that the hydration of C3S and β-C2S led to the formation of various phases, including Ca(OH)2, CaCO3, and various types of poorly crystalline C-S-H phases contaminated with Mg, S, P, Ti, K, and Cl elements. The C3A phase was the most susceptible to biological corrosion, while the C4AF phase was the most resistant. Studies on model cement demonstrated a significant influence of solution pH on bacterial presence, where pH ≥ 9 prevented their occurrence, while pH ≤ 4 and pH 6-7 favored their presence. The addition of γ-C2S and C12A7 phases to the model cement caused a modification of the sample's microstructure and revealed exceptional density, where all spaces were fully occupied by hydration products. Such a model of cement matrix construction prevents and limits the penetration of the corrosive agent into the sample interior. The obtained research results suggest the possibility of using such cement for bioreactor construction and employing additions of calcium aluminates and calcium ferrites to further enhance cement resistance to biological corrosion. [ABSTRACT FROM AUTHOR]

Alite(C3S)-Ye'elimite(C4A3$) cement is a high cementitious material that incorporates a precise proportion of ye'elimite into the ordinary Portland cement. The synthesis and hydration behavior of Alite-Ye'elimite clinker with different lime saturation factors were investigated. The clinkers were synthesized using a secondary thermal treatment process, and their compositions were characterized. The hydrated pastes were analyzed for their hydration products, pore structure, mechanical strength, and microstructure. The clinkers and hydration products were characterized using XRD, TG-DSC, SEM, and MIP analysis. The results showed that the Alite-Ye'elimite cement clinker with a lime saturation factor (KH) of 0.93, prepared through secondary heat treatment, contained 64.88% C3S and 2.06% C4A3$. At this composition, the Alite-Ye'elimite cement clinker demonstrated the highest 28-day strength. The addition of SO3 to the clinkers decreased the content of tricalcium aluminate (C3A) and the ratio of Alite/Belite (C3S/C2S), resulting in a preference for belite formation. The pore structure of the hydrated pastes was also investigated, revealing a distribution of pore sizes ranging from 0.01 to 10 μm, with two peaks on each differential distribution curve corresponding to micron and sub-micron pores. The pore volume decreased from 0.22 ± 0.03 to 0.15 ± 0.18 cm3 g−1, and the main peak of pore distribution shifted towards smaller sizes with increasing hydration time. [ABSTRACT FROM AUTHOR]

In order to increase the utilization rate of stainless steel slag, reduce storage needs, and mitigate environmental impacts, this study replaces a portion of limestone with varying amounts of stainless steel slag in the calcination of Portland cement clinker. The study primarily examines the influence of stainless steel slag on the phase composition, microstructure, compressive strength, and free calcium oxide (ƒ-CaO) content of Portland cement clinker. The results show the following: (1) Using stainless steel slag to calcine Portland cement clinker can lower the calcination temperature, reducing industrial production costs and energy consumption. (2) With an increase in the amount of stainless steel slag, the dicalcium silicate (C2S) and tricalcium silicate (C3S) phases in Portland cement clinker initially increase and then decrease; the C3S crystals gradually transform into continuous hexagonal plate-shaped distributions, while the tricalcium aluminate (C3A) and tetracalcium aluminoferrite (C4AF) crystal structures become denser. When the stainless steel slag content is 15%, the dicalcium silicate and tricalcium silicate phases are at their peak; the C3S crystals are continuously distributed with a relatively dense structure, and C3A and C4AF crystals melt and sinter together, becoming distributed around C3S. (3) As stainless steel slag content increases, the compressive strength of Portland cement clinker at 3 days, 7 days, and 28 days increases and then decreases, while ƒ-CaO content decreases and then increases. When the stainless steel slag content is 15%, the compressive strength at 28 days is at its highest, 64.4 MPa, with the lowest ƒ-CaO content, 0.78%. The test results provide a basis for the utilization of stainless steel slag in the calcination of Portland cement clinker. [ABSTRACT FROM AUTHOR]

Portland cement (PC) is ubiquitously used in construction for centuries, yet the elucidation of its early-age hydration remains a challenge. Understanding the initial hydration progress of tricalcium aluminate (C3A) at molecular scale is thus crucial for tackling this challenge as it exhibits a proclivity for early-stage hydration and plays a pivotal role in structural build-up of cement colloids. Herein, we implement a series of ab-initio calculations to probe the intricate molecular interactions of C3A during its initial hydration process. The C3A surface exhibits remarkable chemical activity in promoting water dissociation, which in turn facilitates the gradual desorption of Ca ions through a metal-proton exchange reaction. The dissolution pathways and free energies of these Ca ions follow the ligand-exchange mechanism with multiple sequential reactions to form the ultimate products where Ca ions adopt fivefold or sixfold coordination. Finally, these Ca complexes reprecipitate on the remaining Al-rich layer through the interface-coupled dissolution-reprecipitation mechanism, demonstrating dynamically stable inner-sphere adsorption states. The above results are helpful in unmasking the early-age hydration of PC and advancing the rational design of cement-based materials through the bottom-up approach. The hydration of tricalcium aluminate is an important initial step in the structural build-up of Portland cement. Here the authors use ab initio and accelerated dynamics to describe the reactions and dynamics of this process at the molecular level. [ABSTRACT FROM AUTHOR]

Supersulfated cement (SSC), a low-carbon, energy-efficient, eco-friendly cementitious material, is mainly made from industrial byproducts. However, SSC's slow early strength development leads to inadequate initial hardening and reduced durability, which restricts its practical application. This study investigated the potential enhancement of SSC by incorporating calcium aluminate (CA) and carbide slag (CS) alongside anhydrite as activators to address its slow early strength development. The effects of varying CA and CS proportions on the mechanical property and hydration mechanism of CA-CS-SSC were examined. Results indicate that employing 1% CA and 4% CS as alkaline activators effectively activates slag hydration in the 1CA-4CS-SSC, achieving a compressive strength of 9.7 MPa at 1 day. Despite the limited improvement in early compressive strength of other mixtures with higher CA and lower CS proportions in the CA-CS-SSC system, all mixtures exhibited enhanced compressive strength during long-term hydration. After 90 days, ettringite formation in the CA-CS-SSC system decelerated, whereas anhydrite remained. Concurrently, the formation of C-S-H continued to increase, promoting late compressive strength. The mechanism for enhancing the early compressive strength of the CA-CS-SSC system is attributed to the swift hydration of CA with anhydrite, dissolution of fine slag particles, and reaction with anhydrite under conditions with suitable alkali content to augment the ettringite production. This process also generates a C-S-H and OH-hydrotalcite to fill the void in the skeleton structure formed by ettringite, resulting in a dense microstructure that improves early compressive strength. [ABSTRACT FROM AUTHOR]

In some remote areas or islands, the availability of freshwater for infrastructures has encountered a huge shortage, which has prompted more researchers to explore the possibility of applying seawater to design green concrete or composites. This study investigated the mechanical and microstructural properties of cement-based pastes (CBPs) mixed with fly ash (FA) and limestone calcined clay (LC2) and seawater at different curing ages. The early-age hydration, exothermic evolution, hydration phase, unconfined compressive strength (UCS), pore distribution, microstructure and sustainability of CBPs were investigated. It was observed that seawater has an accelerating effect on OPC hydration and can significantly enhance the early UCS. Combining with seawater, the pozzolanic activity of LC2/FA can result in generating more C–S–H gels. Therefore, the combination of LC2 or FA with seawater can obtain better the mechanical properties of CBPs. Besides, the micro characteristics of CBPs are observed by X-ray diffraction, thermogravimetric analysis, mercury-pressure porosimetry and scanning electron microscopy technologies, and it is revealed that seawater and SCMs play significant role in the micro morphology of CBPs due to silicate, semicarbonate, calcium aluminate, C–S–H gels. This also leads to a denser and more complex microstructure, which lowers the total porosity, obviously leads to transferring macropores into gel pores and enhances the UCS. Additionally, CBPs with FA or LC2 or seawater show about 1/6–1/5 lower embodied energy (EE), 1/6–1/5 lower embodied carbon (EC) and 1/6–1/4 lower cost than the typical CBPs with freshwater, CBPs with SCMs and seawater are even more perfect in terms of EE, EC and cost per unit UCS. Overall, this work assesses the feasibility of adding LC2/FA and seawater to CBPs, and also can provide a better insight into the applications of seawater cementitious composites for marine infrastructures. [ABSTRACT FROM AUTHOR]

The phase composition, microstructure, and hydration process of C 3 A with different MgO content were compared to elucidate the mechanism of hydration resistance of CaO improved by MgO–C 3 A solid solution. The process of hydration heat release was detected by isothermal calorimetry and the hydration products were analyzed by X-ray diffraction and scanning electron microscope. The results showed that the addition of MgO resulted in lattice distortion of C 3 A. In the middle and late stages of the hydration process, Mg(OH) 2 and amorphous gel-like substances covered the surface of the unreacted C 3 A and reduced the hydration reaction rate. The addition of MgO effectively reduced the hydration activity of the MgO–C 3 A solid solution that indicated the addition of MgO can improve the hydration resistance of CaO materials. [ABSTRACT FROM AUTHOR]

Aerial additive manufacturing (AAM) represents a paradigm shift in using unmanned aerial vehicles (UAVs, often called 'drones') in the construction industry, using self-powered and untethered UAVs to extrude structural cementitious material. This requires miniaturisation of the deposition system. Rheological properties and known hydration times are important material parameters. Calcium aluminate cement (CAC) systems can be advantageous over purely ordinary Portland cement (OPC) binders as they promote hydration and increase early strength. A quaternary OPC/pulverised fuel ash (PFA)/CAC/calcium sulphate (CS) system was combined with polyvinyl alcohol (PVA) fibres and pseudoplastic hydrocolloids to develop a novel AAM material for miniaturised deposition. CAC hydration is affected by environmental temperature. Intending material to be extruded in situ, mixes were tested at multiple temperatures. OPC/PFA/CAC/CS mixes with PVA fibres were successfully extruded with densities of ≈1700 kg/m 3 , yield stresses of 1.1–1.3 kPa and a compressive strength of 25 MPa. Pseudoplastic OPC/PFA/CAC/CS quaternary cementitious systems are demonstrated to be viable for AAM, provided mixes are modified with retarders as temperature increases. This study can significantly impact industry by demonstrating structural material which can be extruded using UAVs in challenging or elevated in situ construction, reducing safety risks. [ABSTRACT FROM AUTHOR]

High Performance Aerogel Concretes (HPAC) are produced by embedding silica aerogels in high‐performance matrices, which were previously based on finely ground Portland cement CEM I 52.5 R and microsilica. On the one hand, this ensured a comparatively high compressive strength, but on the other hand it was associated with large shrinkage strains and a high global warming potential (GWP). In the following, approaches are presented on how these disadvantages can be counteracted by replacing Portland cement with alternative (ACM) or supplementary cementitious materials (SCM). In the experimental investigations, calcium aluminate cement, calcium sulfoaluminate cement, calcium sulfoaluminate belite cement and a CSH phase binder were used as ACMs; limestone powder, calcined clay, fly ash, glass powder, rice husk ash, brick dust and ground granulated blast‐furnace slag were used as SCMs. Based on extensive fresh and hardened concrete tests, it could be shown that with the (partial) replacement of Portland cement by ACMs or SCMs, High Performance Aerogel Concretes can be produced that have significantly reduced shrinkage deformations and a lower GWP with an unchanged good relationship between compressive strength and thermal conductivity. [ABSTRACT FROM AUTHOR]

The use of cementitious materials in deep sea environments, focusing on the durability challenges of low‐temperature seawater and hydraulic pressure, are presented in this paper. The authors conducted laboratory and deep‐sea field experiments, thermodynamic calculation, and evaluated the performance of different types of binders in deep sea conditions. Durability of rebar in cementitious materials was investigated. In situ construction methods using cementitious materials was demonstrated on the deep‐sea field. Testing results revealed that deep sea conditions, especially low‐temperature seawater, can accelerate the disintegration of cement hydrates, and the use of pozzolanic admixture and calcium aluminate cement can improve its resistance. Our study provides valuable insights and applicability of cementitious materials to deep sea infrastructure construction. [ABSTRACT FROM AUTHOR]

A titration method is used to analyse the acid neutralization/consumption capacity (ANC) of cement binders, which involves plotting the steady‐state pH against the amount of acid added to a diluted suspension of hardened cement samples. Despite ANC being employed for several decades, there is no reported application of ANC for metakaolin‐based geopolymers. This study compares the resistance of metakaolin geopolymers to acetic acid and hydrochloric acid with that of Calcium Aluminate Cement (CAC) and Portland Cement (PC). The proposed ANC test setup involves small acid dosage steps using an auto‐titrator, resulting in a high‐resolution titration curve. The effect of binder chemical composition on acid resistance is evaluated through cumulative and differential ANC analysis, providing a new rapid approach to evaluate the durability of geopolymers in low pH environments. [ABSTRACT FROM AUTHOR]

The Design of Experiment (DOE) is a widely recognized approach to designing and analyzing experiments. It is a statistical method utilized to simultaneously examine the impact of multiple factors on the results. In this study, two different DOE methods, including mixture and factorial design were employed to evaluate the influence of various factors on the performance of ternary binders. To assess the effect of each component such as Portland cement (PC), calcium aluminate cement (CAC) and sulphate (CŜHx) on the workability and strength of ternary binders, mixture design was utilized. A two‐stage factorial design was implemented to investigate the impact of various factors on the fresh and hard properties of ternary binders. In the first stage the influence of composition, supplementary cementitious material (SCM) and cement replacement ratio were examined. In the second stage the impact of composition, CAC and CŜHx type were analyzed. Principal Component Analysis was also employed to analyse the continuous data obtained from the XRD patterns. The study results indicated that increased CAC and CŜHx content in the mixture enhances the workability of the pastes. High compressive strengths were found to be a result of increased cement content in the mixture and low SCM substitution. [ABSTRACT FROM AUTHOR]

Cementitious materials employed in deep‐sea marine engineering must have excellent durability. In this study, the durability of a ternary binder‐based paste composed of Portland cement, calcium aluminate cement, and anhydrite was investigated after deep‐sea exposure at a depth of 3515 m for 438 days. The recovered paste specimen showed significant expansion. However, the hydrate phases in the ternary binder exhibited no changes with the exception of the formation of Friedel's and Kuzel's salts. One reason for this was the transformation from unstable monosulfate to stable ettringite under low‐temperature seawater conditions. However, the additional ettringite formation could lead to significant expansion of the paste specimen. [ABSTRACT FROM AUTHOR]

The subject of the research is features of synthesis of alumina cements on the basis of compositions of system CaO – CoO – Al2O3 – MoO3 with use of cobalt‐molybdenum‐containing waste for reception of refractory materials with a complex of the set properties. The processes of phase formation in raw mixtures have been investigated. X‐ray phase studies of clinkers fired at different temperatures and holding times proved that as a result of the interaction of the raw materials of the mixture in the material synthesizes a mixture of hydraulically active calcium mono‐ and di‐aluminate and refractory cobalt spinel, which provides the resulting complex high strength, accelerated curing time, fire resistance. The absence of phases corresponding to molybdenum compounds is explained by the fact that they are part of hydraulically active aluminates as limited solid solutions, deforming the crystal lattice and increasing hydraulic activity. Thus, it was found that the high strength of cement is due to the presence of calcium hydroaluminates such as C2AH8, aluminum hydroxide, as well as unhydrated grains of calcium aluminates, which will contribute to further long‐term strength. It is this coexistence of phases in both the crystalline and colloidal states provide high strength cement stone. [ABSTRACT FROM AUTHOR]

To address the environmental problems caused by the storage of solid waste, such as red mud (RM), silica fume (SF), carbide slag (CS), and flue gas desulphurisation gypsum (FDG), and the poor corrosion resistance of Portland cement (PC), anti-erosion grouting materials (AGM) are synthesised from RM, SF, CS, and FDG. The synthesis, structural characterisation, and properties of AGM are reported and compared with those of typical PC. The results show that the AGM matrix is composed mainly of hydration phases: 68.3 wt.% β-dicalcium silicate (β-C2S), 21 wt.% tetracalcium ferroaluminate (C4AF), and 8.4 wt.% tricalcium aluminate (C3A). AGM prepared with 8 wt.% FDG exhibits the best compressive strength and rheological characteristics. Hydration of the AGM leads to the formation of ettringite, calcium alumino-ferrite hydrate (C3(A, F)H6), and aluminium gel, resulting in a compressive strength of 29.2 MPa at 210 days. The anti-erosion coefficients K of AGM after exposure to different erosion solutions for 28 days are > 0.99, indicating better corrosion resistance than PC. This anti-erosion property is due to a mineral composition characterised by low tricalcium silicate(C3S) content and high C4AF content. This study provides a feasible and promising method for the preparation of for coastal engineering materials. [ABSTRACT FROM AUTHOR]

The deterioration of the microscopic pore structure of concrete under external sulfate attack (ESA) is a primary cause of degradation. Nevertheless, little effort has been invested in exploring the temporal and spatial development of the porosity of concrete under ESA. This study proposes a mechanical-chemical model to simulate the spatiotemporal distribution of the porosity. A relationship between the corrosion damage and amount of ettringite is proposed based on the theory of volume expansion. In addition, the expansion strain at the macro-scale is obtained using a stress analysis model of composite concentric sphere elements and the micromechanical mean-field approach. Finally, considering the influence of corrosion damage and cement hydration on the diffusion of sulfate ions, the expansion deformation and porosity space-time distribution are obtained using the finite difference method. The results demonstrate that the expansion strains calculated using the suggested model agree well with previously reported experimental results. Moreover, the tricalcium aluminate concentration, initial elastic modulus of cement paste, corrosion damage, and continuous hydration of cement significantly affect concrete under ESA. The proposed model can forecast and assess the porosity of concrete covers and provide a credible approach for determining the residual life of concrete structures under ESA. [ABSTRACT FROM AUTHOR]

This article analyses the combined effect of a mixture of natural zeolite and ground soda lime silicate glass on the durability properties of concrete. The specimens were prepared by replacing 25% of the cement with a mixture of zeolite and glass at different proportions with zeolite particles of two different sizes and cured for 28 and 90 days. Chloride migration, the depth of water penetration under pressure, and freeze–thaw cycle tests were performed, and compressive strength was determined. The combined effect of the mixture on the composition and microstructure of the cement matrix was studied by analysing the results of XRD, TGA, SEM-BSE, and porosity tests. The test results showed that irrespective of the cement "dilution" effect, the mixture of additives had a beneficial combined effect: increased durability of concrete, a denser structure of the cement matrix, the formation of calcium aluminate hydrates, faster rate, and higher degree of hydration. [ABSTRACT FROM AUTHOR]

This study investigates the influence of various factors on the performance of ternary binders, utilizing statistical approaches. The research focuses on the influence of varying compositions of Portland Cement-Calcium Aluminate Cement-Calcium Sulphate (PC-CAC-CŜ), types and amounts of mineral powders, and chemical admixtures in ternary binders. Using the Taguchi design, the study required a limited number of experimental trials, utilizing a standard orthogonal array of seven factors across three levels. These factors encompassed binder composition (C1-C2-C3), mineral powder types (limestone, quartz, slag), replacement ratio (0%, 25%, 50%), retarder (0%, 0.1%, 0.2%), superplasticizer, viscosity modifying agent (stabilizer) and accelerator (0%, 0.05%, 0.1%). Measurements on hydration kinetics, dimensional stability, compressive strength, and microstructural analyses like X-ray diffraction were conducted. Principal Component Analysis (PCA) was employed to interpret the continuous data derived from heat of hydration curves, length change curves and X-ray diffraction (XRD) patterns. Results indicated that retarder quantity and binder type significantly impacted paste workability. Higher powder content led to reduced strength, whereas increased accelerator improved strength. A strong correlation was observed between accelerator content and the dimensional stability. The primary hydration product's formation was predominantly influenced by the PC-CAC-CŜ ratio, accelerator, and cement substitutions. [ABSTRACT FROM AUTHOR]

Calcium aluminate cement (CAC) is one of the alternative cements that is widely used for special applications. However, during the hydration process degradation of CAC microstructure, the so-called hydrate conversion process, hexagonal calcium aluminate hydrate (CAH10) transforms into a cubic (C3AH6) phase, resulting in increased porosity and reduced strengths. It is known that alternative means for stabilizing the CAC conversion are conducted by introducing fly ash (FA) in CAC, where its microstructure is attributed to aluminosilicates. However, no study has yet been conducted on different FA compositions influencing CAC performance. This study aims to evaluate the effects of different compositions of FA on CACs' fresh and hardened characteristics. Results revealed that the microstructure was denser when CAC was mixed with FA. Regarding reactivity, CAC with calcium-rich FA systems is 13% faster than the silica-rich one. The higher the density and the lower the porosity of calcium-rich FA mixtures were found compared with silica-rich FA in both micro- and macro-structures. As seen in the microscopic structure, this is due to the calcium-rich phase formation. [ABSTRACT FROM AUTHOR]

In the presented study, ye'elimite-aluminate-calcium (YAC) cement was synthesized. Complete synthesis of crystalline phases was achieved at a temperature of 1300 °C, which is 150 °C lower than the temperature standardly used in the processes of obtaining calcium aluminate cements (CAC). The greatest amount of ye'elimite phase (Klein complex), roughly 87% by mass, was acquired utilizing a sulphur ion transporter derived from artificial dihydrate gypsum obtained in the flue gas desulphurization process (variation I). In the case of anhydrite, the amount of synthesized crystalline ye'elimite in the clinker was 67% by weight (variant II). Depending on the synthesis conditions in the clinkers, the quantity of obtained calcium aluminates (C12A7, CA, and CA2) ranged from 20 to 40% by weight. Studies on the hydration process of YAC cement samples showed that the main products are hydrated calcium aluminates and dodecahydrate calcium alumino-sulphate. In sinters of YAC and OPC, no crystalline ettringite was observed. Hydration analysis of Chinese cement revealed the presence of crystalline ettringite and dodecahydrate calcium alumino-sulphate, as well as hydrated calcium silicates of the CSH type accompanied with pseudo-crystalline Al(OH)3. The obtained clinkers from variants I and II constitute a special binder, which, due to its phase composition after hydration, can be used in the construction of reactors for biogas production in eco-energy applications. [ABSTRACT FROM AUTHOR]

In order to promote the resource utilization of steel slag, based on the stability evaluation of steel slag, using lime as alkali activator, the unconfined compressive strength test, X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to study the effects of different alkali-activated slag mix ratios and alkali-activated slag content on the compressive strength of slag-stabilized steel slag mixture. The hydration products and strength enhancement mechanism of slag-stabilized steel slag mixture was discussed. The research showed that the strength of the mixture increased first and then decreased with the increase of lime content, and the optimal mix ratio of lime and mineral powder was 1 ∶4. 2. Under this mix ratio, the 7 d strength of the mixture with 4. 5% alkali activated mineral powder content reached 6. 27 MPa, which met the technical requirements of high-grade pavement. With the increase of alkali-activated slag content, the compressive strength of the mixture increased, the elastic section of the load-deformation curve increased gradually, the plastic section and the descending section decreased, and the plastic deformation capacity decreased. Lime can better stimulate the potential activity of the slag-steel slag system. The hydration products included hydrated calcium silicate, hydrated calcium aluminate and Jennite. The internal honeycomb and fibrous cementitious structure made the internal structure of the mixture denser and improved the macroscopic strength and volume stability of the mixture. [ABSTRACT FROM AUTHOR]

The paper considers different aspects of natural and forced carbonization of binding agents and cement systems. It is shown that depending on the composition of binding agents, curing conditions, and transient factors, carbonization of hydrated cement can not only lead to corrosion and irreversible degradation, but also serve as a powerful productive endeavor for strengthening of concrete structures, self-healing of cracks in concrete, shrinkage reduction, and carbonization corrosion of constructional materials. Based on theoretical analysis of experimental data and the literature, a working hypothesis is developed concerning the observed processes of the structure formation based on the interaction of carbon dioxide and its derivatives with calcium aluminates and aluminate ferrites with the formation of hydrated calcium carboaluminates of various composition. Portlandite fixation is crucial for concrete structures capable of resisting to both carbon dioxide and sulfate corrosion and, sometimes, in introducing chemical additives, can lead to the structure strengthening. [ABSTRACT FROM AUTHOR]

Bauxite residue (BR) is a by-product from the aluminum industry, generated during the Bayer process to obtain alumina. It has valuable iron and alumina contents, with soluble ions that can interact with the cement compounds, which could make BR a new source of supplementary cementitious material. This work aims to determine the influence of different contents of BR in substitution to two types of Portland cement regarding the hydration reactions and chemical shrinkage during the first 48 h of hydration, as well as to monitor the crystalline phases with XRD and the amount of bound water and the hydrates formed with thermogravimetric analysis. The results show the interaction of BR and cement, with the formation of new products, such as N-A-S-H, C-A-S-H, aluminum silicate hydrate (AS), and calcium aluminate hydrate (CAH), that culminate in changes in the shrinkage as BR is added. It was also observed that BR accelerates and enhances the slag reactions due to its high alkalinity and soluble ions content and the fineness of the material added to the cement. [ABSTRACT FROM AUTHOR]

Alkali-activated cementitious materials (AAMs) are a kind of green building materials compared to Portland cement components. This review considers the related research on the AAMs to systematically summarize the results on its materials composition and performance influencing factors. The precursor material is mainly industrial solid waste containing Al2O3 and SiO2. The alkali activator is compound containing caustic alkali and basic elements, which can provide an alkaline environment. Meanwhile, some new green precursors and alkali activators are summarized in this review. The main mechanism of alkali-activated reaction is that the hydroxide ion from the alkali activator nucleophilically attacks the covalent bonds of Al–O and Si–O in the precursor material, which generates Si(OH)4 and Al(OH)4−. They generate three-dimensional network gel of tetrahedral structure of [SiO4] and [AlO4]− through polycondensation reaction, which forms cement stone-like block material after setting and hardening. Too high or too low concentration of alkali activator is detrimental to the workability and mechanical properties of AAMs. When the ratio of Na/K to Al is small, the mechanical properties of AAMs are reduced. When the Ca content in the AAM is high, calcium ions enter the polycondensation chain and reduce the degree of polymerization and mechanical properties of the aluminosilicate gel phase and increase the shrinkage deformation. The hydration products in the AAM are free of calcium hydroxide, calcium aluminate hydrate, ettringite, etc., and can resist the erosion of acid and sulfate media. The main aim is to provide an informed outlook on the advantages and drawbacks of AAMs and present a comprehensive review of the studies performed in this area. [ABSTRACT FROM AUTHOR]

Ettringite‐accelerated binders composed of CAC–PC–C$ (calcium aluminate cement–Portland cement–calcium sulfate) and CSA–PC–C$ (calcium sulfoaluminate cement–Portland cement–calcium sulfate) have been used widely for indoor applications, such as self‐leveling floor screeds, underlayment, and tile adhesives owing to their rapid setting, early strength gain, and shrinkage compensation properties. These properties also make these binders appealing candidates for outdoor rapid repair (e.g., highways, bridge decks, and airfield pavements). However, a central question remains: Does ettringite remain stable in outdoor exposure conditions? If so, which factors will contribute positively/negatively to the long‐term stability of ettringite in these systems? To address these questions, this critical review presents the current state of knowledge regarding the hydration of ternary binders composed of CAC–PC–C$ and CSA–PC–C$ with respect to ettringite formation and the factors affecting the stability of ettringite thereafter. The purpose of this review paper is to synthesize and analyze current research regarding conditions that promote or deter ettringite stability, establish what information is missing, unclear, or contradictory, and identify remaining research needs to address the identified knowledge gaps. [ABSTRACT FROM AUTHOR]

The synthesis of mayenite with differences in mineral composition and its influence on the properties of Ordinary Portland cement samples were examined. The synthesis of mayenite precursor was carried out in hydrothermal condition (CaO/Al 2 O 3 = 2.8, w/s = 10) within 1–72 h at 130 °C. It was observed that synthetic precursor which was formed after 4 h remained stable only till 275 °C, and, at a higher temperature (350 °C), it fully decomposed to mayenite. In addition, when the temperature increases, the diffraction peaks typical to mayenite increases and changes mineral composition. It was found that the highest amount of mayenite additive (7.5 wt%) with differences in mineral composition has a positive influence on OPC hydration. It was observed that the mineral composition of additives has influence on the OPC hydration mechanism: at the first stage of hydration, the calcination temperature exerts negative influence on the formation of ettringite; at the second hydration stage, the reaction of gypsum with the additive calcined at 900 °C is more accelerated. The mechanism of hydration (21–60 min) depends mostly on the calcination temperature of the additive. At this stage, ettringite in the systems OPC -mayenite (synthesized at 350 °C) and OPC - mayenite (synthesized at 900 °C) is partially decomposed into monosulfoaluminate and gypsum. Meanwhile, the new exothermic reaction between mayenite and ettringite in the OPC- mayenite (synthesized at 550 °C) system promoted the formation of monosulfoaluminate and hydrated calcium aluminate compounds. [ABSTRACT FROM AUTHOR]

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

Calcium aluminate cement (CAC) has been explored as a sustainable alternative to Portland cement, the most widely used type of cement. However, the hydration reaction and mechanical properties of CAC can be influenced by various factors such as water content, Li2CO3 content, and age. Due to the complex interactions between the precursors in CAC, traditional analytical models have struggled to predict CAC binders' compressive strength and porosity accurately. To overcome this limitation, this study utilizes machine learning (ML) to predict the properties of CAC. The study begins by using thermodynamic simulations to determine the phase assemblages of CAC at different ages. The XGBoost model is then used to predict the compressive strength, porosity, and hydration products of CAC based on the mixture design and age. The XGBoost model is also used to evaluate the influence of input parameters on the compressive strength and porosity of CAC. Based on the results of this analysis, a closed-form analytical model is developed to predict the compressive strength and porosity of CAC accurately. Overall, the study demonstrates that ML can be effectively used to predict the properties of CAC binders, providing a valuable tool for researchers and practitioners in the field of cement science. [ABSTRACT FROM AUTHOR]

Calcined clays, combined with limestone, exhibit significant potential as SCMs for achieving high clinker substitution levels. This is partly related to their high aluminum and silicon contents. Binary Portland cement – calcined clay (PC2) blends and ternary blends with limestone (LC3) have been examined using metakaolin (MK) as calcined clay for blends with low and high MK/clinker ratios. The hydration reactions (up to 420 days) and aluminum distribution within the C-(A)-S-H and calcium aluminate hydrate phases have been quantitatively assessed by 27Al and 29Si NMR spectroscopy. The presence of limestone induces higher amounts of ettringite in the LC3 blends, resulting in lower amounts of Al(4) in the C-(A)-S-H. For the high MK/clinker ratio blends, the increase of aluminum incorporated in the C-(A)-S-H phase after prolonged hydration coincides with a leveling off for the amount of AFm phases for the binary and ternary blends at 60 % and 40 % of MK reaction, respectively. [ABSTRACT FROM AUTHOR]

Calcium aluminate cement modified with sodium polyphosphate (CAP) contains precursors to hydroxyapatite (HAp) within its matrix. This study explored HAp crystallization in the CAP system by varying the concentrations of the sodium polyphosphate solution (ratios of sodium polyphosphate to water at 0.46, 0.80, and 1.14) and temperatures (60, 90, 120, and 150 °C). By curing for 7 days at 25 °C, the CAP system was able to solidify and avoid the conventional hydration reaction of calcium aluminate cement. When the ratio of sodium polyphosphate to water was 0.46, the hydrated minerals of calcium aluminate cement (hydrogarnet, gibbsite, and boehmite) and HAp crystallized together through thermal treatment. With a ratio of 0.80, monocalcium aluminate was entirely consumed by the thermal treatment, facilitating the formation of HAp and boehmite. However, with a ratio of 1.14, only a small amount of HAp crystallized, leaving many of the clinker phases unreacted. Furthermore, the FTIR results showed an increase in the peak corresponding to P-O-P or P-O-H (P-O-Na) as the sodium polyphosphate increased, suggesting that the formation of sodium calcium orthophosphate gel is less likely at higher levels of polyphosphate due to the presence of linear metaphosphate chains. These results indicate that the concentration of sodium polyphosphate in the mixing solution affects the types of amorphous gel in the CAP system. It was determined that the conditions where HAp crystals are most abundant suggest that the appropriate ratios of sodium polyphosphate to water and polyphosphate to cement are 0.80 and 0.40, respectively. • Calcium aluminate cement modified with sodium polyphosphate was synthesized. • CAP 23 system formed C-A-H gel due to low phosphate, not preventing hydrated phases. • CAP 40 system showed amorphous NaCaPO 4 -like gel, consuming unreacted CA. • CAP 57 system had excessive polyphosphate, with unreacted CA and undecomposed P-O-P. • Optimal phosphate for HAp is p/c ratio of 0.40; potential for environmental use. [ABSTRACT FROM AUTHOR]

Mixing polyethylene glycol (PEG) solution and ordinary Portland cement (OPC) to prepare cement-based phase change composite (CPCC) is an emerging paradigm that has attracted much attention. However, the non-setting problem of CPCC at high PEG content limits the improvement of its heat storage capacity. In this study, the setting process of CPCC was promoted by the modification of calcium aluminate cement (CAC), furthermore, its phase evolution, microstructure and thermo-mechanical properties were investigated by Rietveld quantization, SEM, DSC and conductometer. The results show that monocalcium aluminate from CAC reacts with gypsum from OPC to accelerate the formation of ettringite, thus shortening the setting time of CPCC. Alternatively, the excess aluminum ions inhibit the hydration of alite, thereby reducing the compactness of CPCC. A looser microstructure means a larger pore diameter and porosity, the former reducing the confining effect of pores on PEG, resulting in an increase in latent heat, but the latter increases the thermal conduction path, resulting in a decrease in thermal conductivity. Nevertheless, the mechanical strength of CPCC increases with the increase of CAC content, which is inferred to be due to the increased content of high-strength AFm and strätlingite. When the CAC content is increased from 0 wt% to 40 wt%, the setting time of CPCC is shortened by 86.0 %, the latent heat and 28d compressive strength are increased by 71.3 % and 50.2 %, respectively. This study provides a methodological and theoretical reference for improving the paradigm of CPCC. • Mixing PEG solution and OPC prepare cement-based phase change composite (CPCC). • The hydration process and microstructure of CPCC doped with CAC are studied. • The setting progress of CPCC is analyzed based on its phase evolution. • The thermo-mechanical properties of CPCC are discussed based on its microstructure. [ABSTRACT FROM AUTHOR]

Understanding the kinetics and mechanisms involved in early-age hydration of tricalcium aluminate (C 3 A) in chloride solutions holds promise for implementing seawater-mixed concrete in the marine environment, as C 3 A remains the most reactive component of Portland cement (PC), affecting both PC and concrete's early-age hardening and long-term durability. Herein, we conducted a series of meticulously designed ex-situ and in-situ experiments to elucidate the intricate hydration behaviors of C 3 A in various chloride solutions. The results reveal that C 3 A exhibits distinct hydration kinetics and structural evolution processes in different solutions. The rapid precipitation of alumino-ferrite-mono (AFm) and C 3 AH 6 phases contributes to the swift development of hydration heat and storage modulus in water and NaCl solutions, with a slight acceleration observed in the later one. Conversely, the formation of C 3 AH 6 is delayed in CaCl 2 and MgCl 2 solutions before 20 min, with the subsequent precipitation of Cl-AFm enhancing its later production, particularly in CaCl 2 solutions. Ab-initio calculations further elucidate that the acceleration effect of Cl ions originates from the ionization and structurization of hydrated surface Ca ions. However, this positive effect is significantly offset by Cl pairing with counterions, resulting in a dramatic adverse effect of solution Ca ions originated from the negative entropy effect of structuralized water molecules and electrostatic repulsion with like-charged surface Ca ions and solvent dipoles. Our findings provide valuable insights for sustainable and durable designs on cement-based materials mixed with seawater. [ABSTRACT FROM AUTHOR]

Phosphate modified calcium aluminate cement (CAPC) has been demonstrated to be superior to Portland cement under harsh conditions including high temperature and severe corrosiveness. A systematic and quantitative investigation into phase evolution of hardened CAPC pastes cured under 60 °C is conducted to lay a technical basis for cementing CO 2 storage wells. It is found that increasing phosphate dosage results in decreasing contents of C 3 AH 6 and AH 3 , the typical hydration products of calcium aluminate cement (CAC), and increasing content of C-A-P-H gel in hardened CAPC pastes. The critical phosphate dosage for complete depletion of C 3 AH 6 lies in 20%–30% by weight of CAC. Furthermore, C-A-P-H gel, known as the characteristic reaction product of CAPC, is proposed to be constituted of Na-substituted nano-hydroxyapatite and pseudo boehmite clusters. Hardened CAPC pastes exhibit remarkably smaller pore sizes due to C-A-P-H gel, explaining their higher compressive strength compared with hardened CAC pastes. [ABSTRACT FROM AUTHOR]

The hygrothermal stability of ettringite in cementitious systems composed of calcium aluminate cement (CAC) blended with ordinary portland cement (OPC) and calcium sulfate (CŠ) has been investigated for five simulated environmental conditions- i) 23 °C-100% RH (Relative Humidity), ii) 23 °C-50% RH, iii) 38 °C-50% RH, iv) 50 °C-50% RH, and v) 60 °C-50% RH. Two types of ternary systems were used, one rich in CAC (with a higher mass ratio of CAC compared to OPC) and the other rich in OPC (with a higher mass ratio of OPC compared to CAC), both with a water-to-cement (w/c) ratio of 0.35. The volume change and mechanical properties were evaluated by dimensional change, mass change, compressive strength, and flexural strength measurements. Hydration and microstructural properties were evaluated by isothermal calorimetry, thermogravimetric analysis (TGA), and Quantitative X-Ray Diffraction (QXRD) via the G-factor method. QXRD results showed that the studied CAC-rich binder formed 26.0 ± 1 wt% and the OPC-rich binder 28.9 ± 1 wt% ettringite after 24 h of hydration. However, with the increase in temperature, decrease in relative humidity, and time of exposure, the OPC-rich binder showed higher shrinkage, higher mass loss, and a significant decrease in ettringite content compared to the CAC-rich binder. [ABSTRACT FROM AUTHOR]

In this study, pumice based geopolymer (PGP) mortars were produced by replacing 10, 20, and 30 wt.% of the pumice with fly ash and/or calcium aluminate cement. After curing at ambient temperature and 60 °C, the mortars were placed in a 5% sulfuric acid (H2SO4) solution on the 28th day and kept for 120 days. The change in appearance, weight loss and residual compressive strength of the PGP samples due to the effect of sulfuric acid were determined on the 60th and 120th days and compared with the Portland Cement based reference mortar. The study showed that the reference samples underwent a weight loss of 25.6% at the end of 60 days by dissolving of hardened cement paste in the sulfuric acid medium. However, it was observed that the PGP mortars did not undergo any visual change in sulfuric acid solution, except for the samples containing 20 and 30% calcium aluminate cement (for ambient curing). In addition, it was determined that the PGP samples cured at ambient temperature and 60 °C had a maximum weight loss of 6.5% and 4.1, respectively, at the end of 120 days. PGP mortars underwent compressive strength losses of up to 70% in the 120-day sulfuric acid solution. However, with sufficient fly ash and calcium aluminate cement substitution, the compressive strength of PGP mortars increased significantly as well as the sulfuric acid resistance. [ABSTRACT FROM AUTHOR]

Nanomaterials are widely used in cement to improve the various properties of cement-based materials. Nano-CSH is considered as an effective accelerator for the hydration of cement. This paper studied the effects of nano-CSH on the hydration behavior and compressive strength of cementitious materials with various mineral admixtures. Isothermal calorimetry test was used to study the early hydration of cement paste. Thermogravimetric and X-ray diffraction tests were used to study the evolution of hydration product and unhydrated mineral phases in the hydrated cement paste. The presentation of compressive strength can evaluate the influence of nano-CSH on the property of cement-based material at the macro level. The obtained results show that the used nano-CSH can promote the hydration of tricalcium silicate (C3S), and is more active on the hydration of tricalcium aluminate (C3A) in the samples with GGBFS. The presence of nano-CSH can definitely accelerate the secondary hydration reaction of mineral admixtures. [ABSTRACT FROM AUTHOR]

The objective of this study was to explore the influence of an alkali liquid accelerator based on sodium aluminate (ASa) on the early hydration behaviour of cement paste, tricalcium aluminate (C3A) and tricalcium silicate (C3S) and identify its accelerating mechanism. The setting times and mechanical properties of cement paste and mortar mixed with different amounts of ASa were determined. Isothermal calorimetry showed that the addition of ASa increased the first exothermic peak of cement hydration and advanced the second exothermic peak. The morphology of hydration products was analysed by scanning electron microscopy (SEM) and a model for the early hydration of cement paste was established. X-ray diffraction and SEM were also used to analyse the phase composition and morphology changes of C3A and C3S with or without ASa and early hydration models were established. Analysis of the experimental results revealed that the sodium hydroxide produced by ASa hydrolysis had the function of consuming gypsum, breaking calcium silicate hydrate gel film and increasing the calcium hydroxide concentration in the cement paste. The ettringite in the hydration products interweaved together to form a skeleton structure, which was conducive to cement paste hardening. [ABSTRACT FROM AUTHOR]

To further explore the effects of limestone powder (LP) on the hydration of Portland cement as well as the formation and transformation mechanism of calcium carboaluminate phases, the hydration reaction between LP and tricalcium aluminate (C3A) is thoroughly studied in this paper. Due to the crucial influence of gypsum on the hydration of C3A, two systems are well studied, viz. the C3A–LP–H2O and the C3A–LP–CaSO4·2H2O–H2O system. The replacement levels of LP are 0, 5 mass%, 15 mass% and 25 mass% by mass of total binder. The hydration behavior of these two systems are studied using isothermal calorimetry, XRD and quantitative XRD, and chemical shrinkage. The obtained results show that more LP delays the formation of hemicarboaluminate. In the C3A–LP–CaSO4·2H2O–H2O system, the formation of calcium carboaluminate phases only begins after gypsum is consumed. Moreover, LP can reduce the chemical shrinkage resulting from the volume increase of the formation of calcium carboaluminate phases. [ABSTRACT FROM AUTHOR]

In hydrating Portland cements, more than one of the AFm family of calcium aluminates may exist. Depending on the amount of carbonate and sulfate present in the cement, the most common phase to precipitate is monosulfate, monocarbonate and/or hemicarbonate. It has been reported in the literature that hemicarbonate often appears in measurements such as XRD but not predicted to form/equilibrate in thermodynamic models. With the ongoing use of commercial cements such as CEM I and CEM II containing more and more limestone, it is important to understand which hydrate solids physically precipitate and numerically predict over time. Using 27 cement samples with three w/c ratios analysed at 1, 3 and 28 days, this paper shows that although hemicarbonate was observed in a hydrating commercial Portland cement, as well as being predicted based on its carbonate (CO2/Al2O3) and sulfate (SO3/Al2O3) ratios, thermodynamic analysis did not predict it to equilibrate and form as a solid hydrate. Regardless of the w/c ratio, thermodynamic analysis did predict hemicarbonate to form for calcite contents < 2 wt.%. It appears that the dominant stability of monocarbonate in thermodynamic models leads to it precipitating and remaining as a persistent phase. [ABSTRACT FROM AUTHOR]

Improved chloride binding stability for calcium aluminate cements is proposed by the doping of phosphorus. Phosphorus‐modified aluminates clinker has an improved chloride binding stability compared to pristine aluminates, ordinary Portland cement and sulfur‐modified calcium aluminates, as verified by experimental observation. The existence of the newly found phosphorus‐modified Friedel's salt (PFS) accounts for the excellent chloride binding stability, which was understood by density functional theory calculations. Local density of states of the valence band minimum is predominantly localized around P atoms in the PFS, but evenly distributed in the Friedel's salt (FS). The frontier band energy of the partial density of states on Cl and O elements in the PFS is lower than that in the FS by 0.21 and 0.05 eV, respectively. This makes the PFS more stable than the FS salt to ionic attack. [ABSTRACT FROM AUTHOR]

Cement references were reviewed and whole pattern methods were developed for the quantitative phase analysis (QPA) of Type I Portland Cements. A set of control references were established for phase identification and quantitative analysis using laboratory diffractometers. Both RIR and Rietveld whole pattern fitting methods were used in the analyses. A block refined, parameter restricted, Rietveld method produced the best QPA results by comparison with known mixtures. Similar to prior literature findings, care has to be taken because of the severe peak overlap of the major calcium silicate and calcium aluminate phases in Portland cement and the complexity of the chemistry and structures involved. Two of the four major phases identified are doped supercells and the major C3S phase is also disordered. [ABSTRACT FROM AUTHOR]