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Cement production is responsible for 5%–7% of global CO2 emissions, highlighting the need for sustainable alternatives like geopolymer composite (GCOMP) to meet the growing demand for concrete. This study investigates the mechanical, microstructural, and thermal properties of GCOMP by incorporating nano‐alumina (n‐alumina) and MSF (MSF). The n‐alumina content was varied at 1%, 2%, and 3% by weight of the mix, while the MSF content remained fixed at 0.5% by weight. Thermal characterization was conducted up to 800°C. The performance of GCOMP blends with n‐alumina was compared to a control blend consisting of only 0.5% MSF. Various mechanical properties were evaluated for all GCOMP blends. Microstructural and mineralogical characteristics were analyzed using scanning electron microscopy (SEM), X‐ray diffraction (XRD), and Fourier‐transform infrared spectroscopy (FTIR). Thermogravimetric and differential thermal analysis were performed up to 800°C for the thermal analysis of the GCOMP mix. The results indicate that the optimal mechanical properties were achieved with 2% n‐alumina (compressive and flexural strength increased by 35.65% and 77.7%, respectively). Additionally, the incorporation of n‐alumina improves the interfacial zones and results in a denser structure. GCOMP mortars portrayed a mass loss between 25°C and 250°C, with a marginal mass loss occurring between 250°C and 715°C. No mass loss was observed between 715°C and 800°C. The MSF‐reinforced GCOMP mortars experienced an ultimate mass loss of approximately 12%, with the MSF showing negligible influence. The addition of n‐alumina particles to MSF‐reinforced GCOMP resulted in the development of stronger samples characterized by the presence of C–S–H, calcium aluminate oxide hydroxide, and quartz. [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]

We investigated the impact of CaCO3 addition on the density and compressive strength of calcium aluminate cement (CAC)-based cementitious materials in binder jetting additive manufacturing (BJAM). To confirm the formation of a uniform powder bed, we examined the powder flowability and powder bed density for CaCO3 contents ranging from 0 to 20 wt.%. Specifically, powders with avalanche angles between 40.1–45.6° formed a uniform powder bed density with a standard deviation within 1%. Thus, a 3D printing specimen (green body) fabricated via BJAM exhibited dimensional accuracy of less than 1% across the entire plane. Additionally, we measured the hydration characteristics of CAC and the changes in compressive strength over 30 days with the addition of CaCO3. The results indicate that the addition of CaCO3 to CAC-based cementitious materials forms multimodal powders that enhance the density of both the powder bed and the green body. Furthermore, CaCO3 promotes the formation of highly crystalline monocarbonate (C4AcH11) and stable hydrate (C3AH6), effectively inhibiting the conversion of CAC and showing compressive strengths of up to 5.2 MPa. These findings suggest a strong potential for expanding the use of BJAM across various applications, including complex casting molds, cores, catalyst supports, and functional architectural interiors. [ABSTRACT FROM AUTHOR]

Tricalcium aluminate (C3A) and tricalcium silicate (C3S) with gypsums play an important role in the hydration of oil well cement. This study aims to assess the influence of C3S and C3A with various gypsums on the hydration of oil well cement at 30, 50, and 80 °C through the analyses of hydration heat evolution by isothermal calorimetry analysis, setting and thickening times, strength, and hydration products by X-ray diffraction. The result reveals that C3A hydrates, in the presence of gypsums, rapidly at 80 °C to produce the C3AH6 phase leading to higher heat evolution. The conversion of AFt to AFm is observed in oil well cement paste at 50 °C. An increase in C3A leads to an increase in compressive strength and a decrease in permeability at 80 °C. An increase of C3S leads to the reduction of cumulative heat evolution and early compressive strength before 28 d. Gypsums shorten cement setting and thickening times opposite to the commonly known retardation effect due to the lower content of C3A and its acceleration on C3S hydration. Dihydrate and hemihydrate gypsums show a greater promotion effect on strength at 30 and 50 °C, while anhydrous gypsum presents a greater enhancing effect at 80 °C. Gypsum increases the permeability while the others show an unobvious effect at 80 °C. [ABSTRACT FROM AUTHOR]

Refractory materials containing calcium aluminate cement (CAC) are commonly used in the metallurgical and petrochemical industries due to their exceptional mechanical resistance, even at temperatures exceeding 1000 °C, and do not require additional reinforcement. This study seeks to advance this practice by developing ultra-high-performance structures that offer building protection against fire and explosions. Such structures require bar reinforcement to withstand accidental tension stresses, and the bond performance becomes crucial. However, the compressive strength of these materials may not correlate with their bond resistance under high-temperature conditions. This study investigates the bond behavior of ribbed stainless austenitic steel bars in refractory materials typical for structural projects. The analysis considers three chamotte-based compositions, i.e., a conventional castable (CC) with 25 wt% CAC, a medium-cement castable (MCC) with 12 wt% CAC, a low-cement castable (LCC), and a low-cement bauxite-based castable (LCB); the LCC and LCB castables contain 7 wt% CAC. The first three refractory compositions were designed to achieve a cold compressive strength (CCS) of 100 MPa, while the LCB mix proportions were set to reach a CCS of 150 MPa. Mechanical and pull-out tests were conducted after treatment at 400 °C, 600 °C, 800 °C, and 1000 °C; reference specimens were not subjected to additional temperature treatment. This study used X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM) methods to capture the material alterations. The test results indicated that the bonding resistance, expressed in terms of the pull-out deformation energy, did not directly correlate with the compressive strength, supporting the research hypothesis. [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]

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]

As known, calcium oxide (CaO) is an alkaline material, which can be used widely to increase the clay-containing soils load carrying capacity, to produce aerated concrete and calcium aluminate cement. In the last few years, introducing CaO into alkali-activated materials (AAMs) became a hot topic and attained more attention than other times. Generally, CaO can be incorporated into AAMs as an additive/a part of the main precursor and a sole activator without/with an auxiliary activator. Incorporating CaO into the matrices may improve some properties and worsen others. This mainly depends on the ratio of CaO, curing conditions, activator type and activator concentration, precursor type and testing age. This review collected, summarized and analyzed the available studies focused on the effect of CaO on the fresh (reaction kinetic, workability, setting time) and hardened (mechanical strength, durability and length change) properties of AAMs. In addition, some recommendations for future works were included. The results showed that the inclusion of CaO in AAMs decreased workability and setting time. In spite of there are contradictory results about the effect of CaO on the compressive strength of AAMs, most of them reported higher compressive strength, especially at the early ages. The incorporation of CaO up to 5% in the matrix is more effective than the incorporation of higher ratios. The inclusion of CaO in the matrix decreased water absorption, decreased total porosity, increased wetting/drying as well as acid attack resistivity. The CaO (5–10%) can be used as a sole activator for precursors. Auxiliary activators such as Al2(SO4)3, Na2CO3, Na2SiO3, Na2SO4, CaSO4, NaOH, Ca(NO3)2, NaNO3, Mg(NO3)2, Mg(HCOO)2, Ca(HCOO)2, SO3, gypsum and MgO can be used to enhance the compressive strength of CaO-activated materials, especially at the early ages. [ABSTRACT FROM AUTHOR]

Premature decommissioning of a steel-teeming ladle lining due to critical localized damage, which significantly reduces lining functional properties, is one of the most acute problems in modern metallurgy. The main type of products used for steel-teeming ladle lining is periclase-carbon. In order to improve corrosion resistance and resistance to thermomechanical loads, additional additives, such as spinel, and high alumina CMA cement, are introduced into periclase-carbon products. In this article the effect of calcium aluminate-based additive on the properties of periclase carbon refractories is investigated. It is assumed that there is a potential for formation of magnesium aluminate spinel (MA) in periclase-carbon products with calcium-aluminate additives during heat treatment. Fused periclase is used as the raw material, the carbon component is represented by natural flaky graphite in an amount of 10 wt.%, and a combined binder. An additive based upon calcium aluminates is introduced, with a fractional size from 0 to 3 mm, while the amount of main fractions of fused periclase is reduced by the corresponding amount of the additive introduced. The compressive strength, apparent porosity, and bending strength values before and after coking firing are analyzed. The thermal coefficient of linear expansion, phase composition and microstructure of the products are also investigated. [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 present work focused on the evolution characteristics in the microstructure and properties of calcium aluminate composite ceramics after heat treatment for raw materials at different temperatures. The results showed that the apparent porosity of all the sintered samples firstly decreased to the minimum at a heat treatment temperature of 1200 °C and then increased with increasing heat treatment temperature. The compressive strength was greatly enhanced after the heat treatment for raw materials due to the significant decrease in porosity, presenting the opposite relationship with the change of porosity. The formation of the interlaced structure in the sintered samples was conducive to improving the densification of the calcium aluminate ceramics. This work provided new avenues of thought regarding the manufacturing of calcium aluminate ceramics and promoted its better application in metallurgy. [ABSTRACT FROM AUTHOR]

This paper studied the effect of elevated temperatures on the compressive strength of alkali-activated fly ash (so-called geopolymer) with the addition of calcium aluminate cement (CAC). In the elevated temperature tests (600 and 800 °C), the unstressed test method was adopted. Taguchi analysis was used to study the effect of three parameters (considered in mix design) on the hot strength. These parameters include the replacement ratio of fly ash by CAC, molarity of sodium hydroxide solution, and alkaline solution to fly ash ratio. The first parameter was found to be the most influential factor. XRD, TG/DSC and SEM techniques were then carried out to investigate the effects of the CAC content on the high-temperature performance of the geopolymer. The phase transformation taking place during the heat exposure was found to affect the compressive strength in the hot state directly. The retained strength of the optimal geopolymer mortar at 600 °C was around 2.5 times higher than that of ordinary Portland cement mortars with a similar original strength level. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society 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.)

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society 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.)

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]

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]

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]

The potential degradation of calcium aluminate cement (CAC) concrete due to the conversion of thermodynamically metastable compounds into stable phases is a well-known phenomenon. This research focuses on the effects of polymers on the hydration kinetics and strength development of calcium aluminate cement (CAC) mortars at two curing temperatures, i.e., 200 °C and 38 °C. The constant CAC content was used to prepare mortars. However, the sand was replaced by acrylic polymer (AP) (5%), vinyl acetate monomer/vinyl versetate polymer (VA/VV) (2%), and two different Poly (vinyl alcohol-co-vinyl acetate) (PVAc) (2%). Isothermal calorimetric investigations for 3 days, capillary absorption tests, flexural strength tests and compressive strength tests at 3, 7, 28, and 90 days were conducted. The hydration reactions of CAC mortars accelerated by replacing sand with polymer admixtures. The flexural strength of CAC mortar with the AP exhibited on-par compressive strength values at 20 °C. All the polymer-incorporated samples except VA/VV displayed an increase in their late-age mechanical properties than 28 days results, showing promising results for reduction in strength decline at a later stage. The PVAc-73 (i.e., 73% hydrolysis degree)-incorporated mortar was unaffected by increased curing temperature. The mortars exhibited early hydration behavior at increased temperatures. [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]

Bioceramic bone cements are increasingly studied, developed, and improved to become a viable alternative to polymethyl methacrylate (PMMA)-based cements. In this regard, we aimed to develop a new cement composed of calcium aluminate (C 12 A 7) and strontium aluminate (S 3 A) powders obtained via solution combustion synthesis (SCS) and chitosan/glycerin solution. The cement properties were optimized through a design of experiments. The approach used in the optimization process was the 2k factorial experimental design with insertion of 3 repetitions of the central point, which resulted in 11 compositions. All compositions were tested to determine the liquid/powder ratio (L/P), final setting time (ST), maximum hydration temperature (T max), compressive strength and radiopacity. The results were statistically evaluated by analyzing the effects, Pareto diagram, ANOVA analysis and response surface plot. The models obtained in this study could precisely predict three responses: T max , compressive strength, and radiopacity. An optimized composition for possible application as bone cement had an average T max of 40.34 °C, compressive strength of 7.75 MPa and radiopacity of 3.76 mm Al, all above the standard requirements. [ABSTRACT FROM AUTHOR]

In this work, the hydration of calcium aluminate cement (CAC, Al2O3 ≥ 70%) paste with nano admixtures (0, 0.05%, 0.1% and 0.2%) of nano-silica (NS) and carbon nano-cones (NC) when W/CAC = 0.35 was investigated. The methods of calorimetry, thermal analysis, X-ray diffraction (XRD), IR spectroscopy, and scanning electron microscopy (SEM) were used. In addition, the physical and mechanical properties of hardened cement pastes were determined after 3 days of hardening. NS was found to shorten the induction period of CAC hydration and accelerate the time of the secondary heat release effect, especially in the specimens with the highest NS content. The incorporation of NC (up to 0.2%) slows down the hydration process. After 3 days of hydration, the formation of hydration products, such as C2AH8, CAH10, C3AH6 and AH3 hydrates, was observed in CAC pastes, however, the quantitative compositions were different depending on the kind of nano admixture and its amount. SEM results obtained show differences in the effect of NS and NC on the formation of the structure of cement paste during its hardening. Significant changes in CAC paste microstructure were caused by the addition of NS and NC admixtures. Compressive strength was found to increase with the increase of NS and the optimal NS content was found to be 0.10 wt.%. The modification of the cement paste with an NS admixture results in a higher amount of hydrates, lower total porosity, and a higher amount of the smallest pores in the microstructure of the sample. NS and NC influence the hydration behaviour of CAC in different ways, which causes characteristic changes in the microstructure and properties of hardened samples. [ABSTRACT FROM AUTHOR]

The relatively low hydration rate of calcium aluminate cement (CAC) at 15–35 °C leads to retarded setting time and reduced production efficiency of CAC-bonded castables. To accelerate the hydration rate of CAC within this temperature range, the present work proposes the fabrication of nano-hydrates acting as seeds by pre-hydration of CAC in suspensions. CAC powders are dispersed in water with water-to-solid ratio of 4.5 and stirred for varying durations at 25 °C to achieve different pre-hydration degrees. Then the pre-hydrated CAC suspensions replace a small part of cement in the pastes. The influence of the CAC suspensions addition on the hydration heat release and strength development of fresh CAC pastes at 25 °C is investigated. The results indicate that nano-scale hydrates C 2 AH 8 and AH 3 form on the surface of pre-hydrated CAC particles in the suspensions and grow rapidly with the extension of stirring duration. The presence of nano-scale hydrates in the pre-hydrated CAC suspensions is found to shorten the induction period of CAC hydration and thus be beneficial to the accelerated hardening of CAC pastes. The pre-hydrated CAC suspension stirred for 3.5 h has the most significant effect on enhancing early strength of the CAC pastes. At this stage, the pre-hydrated CAC within the suspension is in the accelerated period, and has just begun to precipitate large amounts of nano-scale C 2 AH 8 and AH 3 acting as seeds to catalyze the hydration and refine the pore structure of CAC pastes. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society 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.)

Self-levelling underlayments (SLUs) based on Portland cement (PC) are susceptible to cracking due to drying shrinkage. The present study evaluated the influence of binder contents on systems consisting of calcium aluminate cement (CAC), PC, and a source of calcium sulfate (C$), derived from the flue gas desulfurization process (FGD), on the mechanical (flexural and compressive) properties and drying shrinkage of SLUs. The main objective was to analyze the influence of replacing limestone filler (LF) by bottom ash (BA) and red mud (RM) wastes on the properties of SLUs based on the CAC/FGD/PC (56/24/20) binder system. For this purpose, mini-slump flow, setting times, water absorption, mechanical (flexural and compressive) strength, linear shrinkage, and X-ray diffraction essays were performed. The replacement at a level of 0.2 filler with wastes reduced linear shrinkage while replacing 0.3 filler level provided greater initial (1 day) compressive strength. [ABSTRACT FROM AUTHOR]

Replacement of Portland cement (PC) by fly ash (FA) is currently limited to 15–30% by mass, mainly due to low early age strength development of concrete. This research uses calcium formate (Ca(HCO2)2; CF) as an admixture to high-volume FA (HVFA) composites to improve its strength properties. HVFA represents 60–70% of cement replaced by FA and dosage of CF varies from 0.5% up to high dosage of 9% of cement content. Compressive strength, isothermal calorimetry, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy were conducted to investigate the effects of CF on hydration and microstructural aspects. The results show that both HVFA pastes with 60% and 70% FA achieved the highest strength at the CF dosage of 3%. At the age of 28 days, adding 3% CF to HVFA mixes led to higher consumption of FA as well as higher formation of calcium hydroxide (Ca(OH)2), calcium silicate hydrates, calcium carbonate (CaCO3) and ettringite, which contribute to the increase of strength. The addition of very high dosages of CF at 9% increased the hydration of tricalcium aluminate but could hinder the hydration of tricalcium silicate in both PC and HVFA pastes with 60% and 70% FA. [ABSTRACT FROM AUTHOR]

This study examined the effect of elevated temperatures on the properties of refractory concrete made with recycled aggregates from wastes of alumina-silicate bricks and calcium aluminate cement as a binder. Mixture proportions were determined according to the Dreux-Gorisse design method for micro-concretes. The evolution of the concrete rheological behavior from quasi-brittle, between room and 900 °C, to viscous at higher temperatures was shown by compression tests performed from room temperature to 1200 °C on cubic (40 x 40 x 40 mm³) specimens. Physical characteristics and compressive strength of hardened samples are also investigated at the room temperature after being fired at various temperatures. Investigated physical properties included bulk density and porosity. The results indicate that the density as well as the compressive strength decrease in the temperature range of 25 °C. to 1200 °C. By contrast, porosity is inversely proportional to temperature and density. [ABSTRACT FROM AUTHOR]

This work aims to investigate the coexistence of the poly(phospho-siloxo) networks and calcium phosphates on the compressive strengths of the acid-based geopolymers obtained at room temperature. Waste fired brick and phosphoric acid were used as an aluminosilicate and chemical reagent, respectively. Calcium aluminate hydrate was prepared by mixing calcium hydroxide from the calcined eggshell and calcined bauxite. Calcium silicate hydrate was obtained by the mixture of rice husk ash and calcium hydroxide. The molar ratios CaO/Al2O3 and CaO/SiO2 in the calcium aluminate and calcium silicate hydrates are equals to 1.0. The X-ray patterns of the acid-based geopolymers indicate the broad hump structure between 18 and 38°(2θ). In addition to this broad band, those from the mixture of calcium sources show the reflection peaks of monetite and brushite. The compressive strength of the reference is 56.43 MPa. Those obtained with the addition of 10, 20, 40 and 50 g of calcined eggshell are 30.15, 22.85, 21.16 and 13.47 MPa, respectively. The ones from calcium aluminate hydrate are 32.62, 31.58, 17.83 and 16.33 MPa, respectively. Whereas those containing calcium silicate hydrate are 44.02, 42.71, 40.19 and 18.59 MPa, respectively. This work demonstrates that the formation of calcium phosphates in the structure of the acid-based geopolymers decreases the poly(phospho-siloxo) chains and therefore reduces their compressive strengths. The moderate addition of calcium silicate hydrate reduces slightly the compressive strengths of the acid-based geopolymers which can be comparable to the one of CEM II 42.5R. [ABSTRACT FROM AUTHOR]

Currently, the utilization rate of red mud is very low, and the problems of occupying land and polluting the environment are becoming increasingly prominent. This study utilized CaO to prepare Red Mud-based cementitious material (RMC) to achieve clean and efficient utilization of red mud. The mechanism of Ca2+ enhancing the strength of RM and the carbonation reaction in RMC were studied using X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), Thermogravimetric Analysis (TGA), Scanning electron microscopy (SEM) and other analysis methods. The results showed that the carbonization of CaO in RMC bonded the red mud particles and provided early strength. CaO activated the components of gibbsite, diaspore, and silica in RM, and hydration reaction generated gel-like Al-substituted tobermorite (Ca 5 Si 5 Al(OH)O 17 ·5 H 2 O), ensuring the increase of later strength. At the age of 28 days, the RMC with a CaO content of 25% had the highest unconfined compressive strength, reaching 2.19 MPa. When the CaO content exceeded 25%, the compressive strength of RMC gradually decreased. This is due to the reaction of calcium carbonate and aluminate to form a large number of sheets of calcium aluminate monocarbonate (Ca 4 Al 2 O 6 CO 3 ·11 H 2 O), which weakened the carbonation binding effect and competitively consumed aluminate, resulting in an increase in structural cracks and pores, and a decrease in the compressive strength of RMC. • CaO strengthens red mud by carbonization and hydration. • The hydration reaction in the sample mainly comes from the residual aluminum ore in the red mud. • Ca2+ can be partially substituted with desiliconized products in red mud. • The formation of calcium aluminate monocarbonate affects the strength of the sample. [ABSTRACT FROM AUTHOR]

Residual hydrated cement powder (HCP) produced from recovering recycled concrete is usually restricted from being directly reused in concrete due to its high water absorption and porous structure. This study aims to enhance the properties of HCP via CO2 treatment. The simultaneous impacts of CO2 treatment and water-to-cement (w/c) ratio on physical properties and microstructure of HCP were studied. The findings showed that carbonation can effectively reduce the porosity of HCP owing to the formation of calcite, and the calcite content increases with increasing w/c ratio. Furthermore, there was a reduction in the 28-day compressive strength of paste specimens containing uncarbonated HCP, while paste containing 5%–20% of carbonated HCP (CHCP) achieved higher strength than the control paste. It is believed that the presence of calcite in CHCP leads to the formation of more stable calcium aluminate monocarbonate. The mass ratio of highly crystalline to poorly crystalline CaCO3 increased with an increase in the replacement level of CHCP, and the w/c ratio exhibited no significant influence at a given replacement ratio. [ABSTRACT FROM AUTHOR]

The influence of sodium chloride (NaCl) on the hydration evolution of calcium aluminate cement (CAC) cured at 5°C, 20°C and 40°C was investigated by calorimetry, X-ray diffraction, differential scanning calorimetry–thermogravimetry, scanning electron microscopy and mercury intrusion porosimetry. The chloride binding capacity and compressive strength of the CAC were also determined. The results showed that the chloride binding capacities of all the CAC samples increased with an increasing sodium chloride content, but the trend of growth gradually slowed. The influence of sodium chloride on the hydration of CAC was found to be highly dependent on its dosage and the curing temperature. At 5°C and 20°C, the early hydration of CAC was accelerated by a small amount of sodium chloride, leading to greater amounts of CAH10. Additionally, the pore structure of hardened cement paste was optimised for a higher compressive strength. However, excessive sodium chloride was found to delay the early hydration to some extent. When the curing temperature was increased to 40°C, sodium chloride accelerated the phase conversion, accompanied with an increase of harmful pores and a sharp decrease in compressive strength. The findings indicate a potential application of CAC-based constructions made with sea sand, especially at temperatures below 20°C. [ABSTRACT FROM AUTHOR]

Application of calcium aluminate cement in construction faces the challenges of high manufacturing cost and volumetric instability associated with hydrates conversion. This work introduces a newly developed high‐performance Ca20Al26Mg3Si3O68 (Q phase)‐metakaolin (MK) composite binder. The influence of MK on the conversion and strength development of Q phase paste cured at 40°C was investigated. The mechanism of MK on the stability of synthetic hydrate was studied by solution chemistry, XRD, and NMR. The pure Q phase paste experiences a significant strength reduction due to hydrates conversion, whereas the Q phase paste containing 15% MK exhibits a continuous increase in strength. MK promotes the formation of CAH10, contributing to the refinement of pore structure and enhanced mechanical property. The AlV and AlIV dissolved from MK increase the Al(OH)4‐ concentration in the pore solution, and then the solubility of CAH10 decreases due to the common‐ion effect, thus inhibiting the subsequent precipitation of C3AH6. In addition, the release of dissolved alumina from MK considerably impedes silica dissolution, and consequently, the formation of C2ASH8 is hindered at a higher content of MK. [ABSTRACT FROM AUTHOR]

Monocalcium aluminate (CaAl2O4, CA) and quaternary (Q) phase (Ca20Al26Mg3Si3O68) are the two principal hydraulic phases in calcium aluminate cement. Their strength development has been reported. However, little information about the difference of their hydration and hydrates composition is available. For this reason, the hydration process of CA and Q phase was investigated and compared. Results of conductometry indicate that the rate of Q phase hydrates precipitation is much slower than that CA latter. Hydrates identification demonstrates that the most prominent difference between the hydrates for these two compounds is the amorphous AH3 content. The quantity of amorphous AH3 (A=Al2O3, H=H2O) in Q phase hydrates is evidently less than that of CA, as confirmed by FTIR, TG and BSE. Even-distributed amorphous AH3 fills in the crystalline skeleton of calcium aluminate hydrates (C–A–H) enhancing the compactness of CA paste. Hence, CA exhibits a higher 72-day compressive strength than Q phase. [ABSTRACT FROM AUTHOR]

Aluminate containing phases such as tricalcium aluminate (C3A) and dodecacalcium heptaaluminate (C12A7) play a key role in the reaction between Portland cement and cellulose ether. In order to simplify such impact from calcium aluminate, calcium aluminate cement (CAC) was applied as a carrier. Effects of hydroxyethyl methyl cellulose ether (HEMC) on the hydration of CAC were characterized by means of isothermal calorimetry, X-ray diffraction analysis, thermal analysis and scanning electron microscopy, respectively. Meanwhile, the setting times, water retention, air content and compressive strengths of HEMC modified CAC pastes or mortars were also determined. Results indicate that HEMC prominently delays the hydration of CAC within 1 day, and the higher dosage of HEMC, the longer setting times. HEMC exerts no obvious impact on the formation amount of CAH10, only leads to a smaller crystal size. From aspect of physical and mechanical properties, the addition of HEMC improves the water retention of fresh CAC mortars, and only with addition of 0.1% HEMC, the water retention of fresh CAC mortars almost approaches 100%. Additionally, the addition of HEMC also significantly promotes the air content of fresh CAC mortars, leading to an obvious decrease in the compressive strengths. [ABSTRACT FROM AUTHOR]

Calcium aluminate cement (CAC) is an alternative to Portland cement, valued for its superior early strength and thermal resistance. Partially replacing CAC with Fly ash (FA) can reduce carbon footprint and production costs of CAC, producing sustainable cementitious binders. This research investigates on various properties (i.e., hydration kinetics; phase assemblage evolution; compressive strength) of [CAC + FA] binders. Using 13 distinct FAs, up to 50% of CAC was substituted. The study measures hydration kinetics, compressive strength, and employs the number of constraints to estimate FA reactivity. Advanced quantitative analysis draws links between hydration kinetics and compressive strength and elucidate the role of FA (including composition and reactivity) on binder performance. Techniques such as X-ray diffraction and thermodynamic modeling illuminate phase compositions in [CAC + FA]. This study also develops a novel method that evaluates the degree of reaction of FA in non-Portland cement binders. Then the correlation between degree of reaction of FAs at 3 days number of constraints is revealed. • A systematic study of fly ashes' influence on performance of calcium aluminate binders is conducted. • 13 fly ashes with distinct chemical compositions and molecular structures are used. • Correlations between fly ash reactivity and properties of calcium aluminate binders are revealed. • A novel method to estimate the degree of reaction of fly ash in non-Portland cement binders is proposed. [ABSTRACT FROM AUTHOR]

• CaSO 4 had influenced on hydration and conversion of calcium aluminate cement (CAC). • The reduction of strength of CAC specimens was inhibited. • The incorporating of CaSO 4 inhibited the formation of unstable CAH 10 by direct precipitation of ettringite. Conversion from metastable phase to stable phase in calcium aluminate cement (CAC) causes volumetric instability, resulting in loss of compressive strength. This study investigated the effect of CaSO 4 on the phase conversion of calcium aluminate cement. The specimens with different dosage of CaSO 4 were exposed to 60 °C to trigger the phase conversion of CAC after curing at 20 °C for 7 days. Analysis with X-ray diffraction, thermogravimetry, mercury intrusion porosimetry, and scanning electron microscopy were conducted. The incorporation of CaSO 4 inhibited the formation of unstable CAH 10 by direct precipitation of ettringite. As a result, the reduction of strength of CAC specimens due to the increased pore volume by conversion was inhibited by ettringite and monosulfate formation. [ABSTRACT FROM AUTHOR]

• The use of supersonic steam jet technology to smash steel slag can not only achieve ultrafine steel slag, but also optimize the composition characteristics of steel slag. • The replacement of cement by USS converted the fly ash–cement binary system block into fly ash–cement–USS ternary system block, high strength and good wear resistance inorganic gelling material may be prepared. We studied the properties and activity index on ultrafine steel slag (USS) ground with a supersonic steam-jet smasher. We show that the use of supersonic steam-jet technology to smash steel slag not only significantly increases its specific surface areas (768 m2/kg), but also optimizes its composition characteristics and improves its activity. We prepared a fly ash–cement gelation block and a fly ash–cement block in which the cement was partially replaced by USS. We then analyzed its compressive strength, water absorption, frost resistance, and wear resistance. The results showed that the replacement of cement with USS converted the fly ash–cement binary system block into a fly ash–cement–USS ternary system block, increasing the compressive strength and wear resistance of the block. In this paper, the enhancement mechanism of USS on a gelation block was studied based on X-ray diffraction and thermogravimetric analysis. The results reveal the effectiveness of USS at producing a certain amount of hydrated iron calcium aluminate, improving the late compressive strength of a fly ash–cement–USS block. [ABSTRACT FROM AUTHOR]

The main goal of the investigation reported in this paper was the preparation of a novel aromatic admixture and its use for improving the physicochemical and rheological properties of fresh and hardened ordinary Portland cement (OPC) pastes. The effects of the addition of 0·25, 0·50, 0·75 and 1·00% (by mass of OPC) of the novel aromatic organic admixture (sodium 5,5′-diformyl-2,2′-dioxido-1,1′-binaphthyl-4,4′-disulfonate (SDD)) on the hydration characteristics, rheological and mechanical properties of OPC pastes were studied. The admixture was characterised using elemental analysis, infrared spectra and hydrogen magnetic resonance spectra techniques. The results revealed that the addition of SDD to OPC pastes caused a notable improvement in both rheological and mechanical properties of various hardened cement pastes at almost all ages of hydration. The results of X-ray diffraction analysis, differential scanning calorimetry and thermogravimetric analysis obtained for the neat and admixed OPC hardened pastes indicated that the main hydration products formed were nearly amorphous and microcrystalline calcium silicate hydrates, gehlenite-like calcium alumino-silicate hydrate and/or calcium aluminate hydrate and portlandite. [ABSTRACT FROM AUTHOR]

Cementitious fire-retardant coatings are widely used for fire protection of structures. Recently, blended pastes of ordinary Portland cement (OPC) and calcium aluminate cement (CAC) have started to be used as binders in cementitious fire-retardant coatings, but the fire resistance and chemical composition of various OPC/CAC pastes are still not clear. The residual compressive strengths of binary cement pastes with various OPC/CAC ratios after fire exposure were studied in this work. The mineral composition and microstructure of the pastes were characterised by X-ray diffraction and environmental scanning electron microscopy/energy dispersive spectrometry, respectively. It was found that the paste with an OPC/CAC ratio of 60/40 was the most fire-resistant. [ABSTRACT FROM AUTHOR]

Phosphoaluminate cement (PAC) clinker had good mechanical properties at early and long-term period. In comparison, the compressive strength of PAC clinker modified by BaO was more prominent. As primary mineral phase for PAC clinker, CA's mineralogical structure and hydration characteristics were intimately related to the compressive strength of hardened cement paste. In this study, the effects of BaO content on the calcination, mineralogical structure and hydration characteristics of CA were investigated. Experimental results showed that the appropriate calcination temperature of CA was 1400 °C. No more than 11% (the substitution ratio of BaO for CaO) addition of BaO can promote the conversion of C12A7 to CA and increase the formation ratio of CA. Appropriate content of 7 mol% BaO could endow the hardened paste with excellent compressive strength. In CA mineral phase the high limit addition of BaO was 15 mol%. The addition of BaO decreased and even restrained the formation of C2AH8 and C3AH6 of CA hydration products and also improved the content of CAH10. The addition of BaO dramatically decreased the hydration velocity and cumulative heat of CA mineral. [ABSTRACT FROM AUTHOR]

Highlights • Mortar was made from fresh and aged CAC and its mixtures with additives. • Mortar flowability worsens with cement ageing. • Ageing influences hydration in mortar during its hardening. • Ageing decrease density and compression strength of hardened mortar. • Additives influence the hydration processes and values of technical characteristics of mortar. Abstract This paper presents an on-going study of the influence of the ageing of calcium aluminate cement (CAC) and its mixtures with additives on the properties of fresh and hardened mortar without any deflocculants. DTA, TG, XRD, and SEM methods for hardening products and structure analysis and as well methods for evaluation technical characteristics of mortar, such as the flowability, compressive strength, density, and ultrasonic wave propagation velocity, were used in the work. The results revealed that the ageing of the raw materials in a climatic chamber at 95% relative humidity (RH) and 20 ± 1 °C for 7 days caused a decrease in the flowability of fresh mortar. This characteristic was also influenced by the properties of the additives. The mortar prepared from 14-days-aged raw materials was not flowable. The overall weight loss upon heating and the XRD data indicated a significant increase in the hydration products formed during mortar hardening when the ageing time of the raw materials was extended from 7 to 14 days compared to the amount of hydration products in the hardened mortar prepared from 7-days-aged raw materials. This increase is probably due to the peeling of the carbonated hydration products of cement particles, formed during ageing for 7 days, from the surface when the ageing time is prolonged beyond 7 days, leading to an increased hydration of the cement particles. The ageing of the raw materials has a negative effect on the compressive strength and density of hardened mortar. The formation of hydration products during mortar hardening and the compressive strength and density are affected by the properties of the additives. [ABSTRACT FROM AUTHOR]

Abstract The effect of elevated temperatures on a calcium aluminate mortar with clinker aggregates is the subject of this paper. After an exposure period of 3 h at temperatures ranging from 25 to 1000 °C, specimens were tested in residual conditions in order to evaluate changes on the mechanical and microstructural properties. A simplified hydration model based on the chemical reactions of the principal minerals is proposed to predict the evolution of matrix composition from the early-age hydration. The improvement of the mechanical properties occurring due to the conversion reactions between 25 °C and 200 °C, is attributed to an increased hydration reaction of both cement and clinker aggregate. Furthermore, when compared to the metastable reactions, an improved interlocking effect at the reactive aggregate interface, and a more dense nature of the stable hydration products, were observed. These phenomena balance the adverse effects promoted by conversion reactions on porosity and mechanical properties. [ABSTRACT FROM AUTHOR]

In the present study, the development of strength in different calcium aluminate cement (CAC) mixture mortars with granulated ground blast-furnace slag (GGBS) was investigated. The substitution of GGBS levels was 0, 20, 40, and 60% weight of binder, of which the CAC used in this study naturally contained C2AS clinker as a secondary phase. To activate a hydraulic nature of the phase, in addition to the mineral additive, all specimens were cured at 35 ± 2°C for the first 24 hours and then stored in a 95% humidity chamber at 25 ± 2°C. The penetration resistance of fresh mortar was measured immediately after pouring, and the mortar compressive strength was monitored for 365 days. Simultaneously, to evaluate the hydration kinetics at early ages, in terms of heat evolution, the calorimetric analysis was performed at the isothermal condition (35°C) for 24 hours. The hydration behavior in the long term was characterized by X-ray diffraction, which was supported by microscopic observation using scanning electron microscopy with energy dispersive spectroscopy. Furthermore, an examination of the pore structure was accompanied to quantify the porosity. As a result, it was found that an increase in the GGBS content in the mixture resulted in an increased setting time, as well as total heat evolved for 24 hours in normalized calorimetry curves. In addition, the strength development of mortar showed a continuous increased value up to 365 days, accounting 43.8–57.5 MPa for the mixtures, due to a formation of stratlingite, which was identified at the pastes cured for 365 days using chemical and microscopic analysis. However, GGBS replacement did not affect on the pore size distribution in the cement matrix, except for total intrusion volume. [ABSTRACT FROM AUTHOR]

Ettringite-based binders are used in niche applications that require a high compressive strength in a very short period of time to minimize construction times and disruption to the traveling public or user. High early strength is achieved due to the formation of ettringite within the first few hours of hydration, which results in a non-expansive system capable of reaching strengths of approximately 20 MPa (2900 psi) in the first 3 hours of hydration. Ettringitebased binders also carbonate at a faster rate than ordinary portland cement (PC)-based systems as a result of the limited amount or absence of portlandite (CH). Carbonation results in the conversion of ettringite into products that occupy less space, resulting in a loss of strength and increased porosity. The formation of ettringite is achieved through the use of systems composed of calcium aluminate cement (CAC, main phase CA) and calcium sulfate (CS), or calcium sulfoaluminate cement (CSA, main phase C4A3S) interground with calcium sulfate. In many cases, ettringite-based binders are used to accelerate ordinary PC-based systems to achieve a relatively high compressive strength and a suitable working time while still maintaining the hydration characteristics of PC. This study compared the performance of carbonated and noncarbonated concrete in terms of the resistance of the near-surface concrete to deicer-salt scaling and chloride ion penetration. Chloride binding tests were also conducted on the carbonated and noncarbonated cement paste samples and mechanical properties conducted on mortar specimens. The results show that CSA-based binders carbonate at a much faster rate than both CAC and PC based systems as a result of the increased ettringite content within the system. A decrease in the mechanical properties of carbonated ettringite-based binders is also observed as a result of the conversion of ettringite. [ABSTRACT FROM AUTHOR]