Calcium Aluminate Cement Research Articles

Impact of aluminate cements on the durability and mechanical performance of strain-hardening cementitious composites

Strain-hardening cementitious composites (SHCCs) are durable, ductile, fiber-reinforced cement-based materials. While fly ash (FA) is often used to partially replace Portland cement in SHCCs to enhance material performance, it can lead to long setting times and slow strength development. To address these limitations, this study investigates the use of aluminate cement as partial replacements for Portland cement in FA-based SHCCs. Furthermore, the study aims to fill a significant knowledge gap by thoroughly examining the influence of aluminate cement on the workability, durability, and strain-hardening behavior of SHCCs. Aluminate cements encompass both calcium sulfoaluminate (CSA) cement and calcium aluminate cement (CAC), distinguished by their composition rich in calcium aluminate phases. This study investigated the use of CSA and CAC cements as partial replacements for Portland cement in SHCCs. Both fresh and hardened properties of the CSA- and CAC-SHCCs were examined, while their microstructures and chemical phases were investigated using SEM and XRD analyses. Results showed that CSA and CAC cements reduced fluidity, setting time, and drying shrinkage but increased porosity and early strength development for SHCCs. CSA-SHCCs showed enhanced impermeability due to the refinement of interior pore space through the hydration products. While all modified SHCCs retained tensile strain hardening behavior, the tensile performance degraded due to the hydration effects of ye'elimite and calcium aluminates. The reduced tensile strain capacity was elucidated using the theory of steady-state crack opening.

Classical and new insights into the methodology for characterizing the hydration of calcium aluminate cements

Calcium aluminate cements [CACs] are typically used for cast-in-place structural work and high temperature applications due to their unique properties. The CaAl2O4 [CA] and Sm-doped CaAl2O4 [CA:Sm] cement clinkers obtained by the solid-state reaction were investigated using X-ray powder diffraction [XRD], scanning electron microscopy [SEM] and energy dispersive X-ray spectroscopy [EDS] and luminescence spectroscopy. The XRD result shows that the powders are pure CaAl2O4. As a next step, hydration behavior of as-synthesized cements was investigated by both classical methods including isothermal calorimetry and XRD, and the state-of-the-art techniques including time resolved electrochemical impedance spectroscopy [TR-EIS] and luminescence spectroscopy. The TR-EIS investigations were obtained by the Impedance Camera over the range of 100 Hz to 1 MHz frequencies. The evolution of obtained EIS and luminescence spectra easily manifested the beginning of the new solid formation and the hydration kinetics. The dynamics of hydration processes were also successfully traced by the changes of the luminescence intensity from the Sm3+ ions. This technique seems to be complementary, and consistent with other methods implemented in the cement chemistry, especially to investigate e.g. hydration of ordinary Portland cements [OPCs] and other binders.

Al2O3/SO3 molar ratio of PG-CAC-based binders on the macro-micro properties of cement-treated waste dredged clay

The binders promoting the generation of ettringite (AFt) are very suitable for stabilizing waste dredged clay (DC) with high water content, while the variability of components may lead to uncertain workability. In this study, a series of unconfined compression tests were conducted on the DC stabilized by the ternary hydration system consisting of ordinary Portland cement, recycled phosphogypsum and calcium aluminate cement, the effects of the Al2O3/SO3 molar ratio (m) on the mechanical properties were evaluated accordingly. Subsequently, a series of microstructure tests and mineralogical tests were performed to further reveal the influence of m on the mechanism of stabilized DC. The results demonstrate that at the same binder content, the unconfined compression strength (UCS, qu) shows a linear increase with m. The compactness of cement-treated DC was improved by the main generation of ettringite, while excessive ettringite may cause expansion and destroy the existing cementation. As m increases, the excessive Al2O3 promotes the generation of C-(A)-S-H and C-A-H after generating enough AFt, which not only cements the soil particles with the cementation effect, but also repairs cracks induced by the AFt expansion. The collaborative effects of the filling and cementation result in an improvement of qu from 11.2% to 129.5% when m increases from 0.133 to 1.414. It can be anticipated from the study that controlling m around 0.55 will play an important role in stabilizing the DC, thus further promoting the co-utilization of recycled DC and phosphogypsum.

3D-printable construction and demolition waste-based geopolymer: Investigating the effects of additives on engineering properties

This paper focuses on the investigating the effects of various additives on the engineering properties of construction and demolition waste (CDW)-based geopolymer mortars. In this study, low-activity CDW-based precursors, specifically brick waste (BW) and concrete waste (CW), were employed. Additionally, industrial waste-based precursors such as slag (S) and silica fume (SF) were utilized to enhance the overall composition. To facilitate activation, a 5 M solution of NaOH was used. To address the efflorescence issue prevalent in geopolymer mixtures and to eliminate potential cracks that may arise due to the dimensional stability problem of 3D-printed CDW-based geopolymer, various kind of additives including calcite, polypropylene fiber, nano SiO2, Al2O3, and TiO2, carbon nano tubes (CNTs), graphene nanoplatelet (GNP), methyl cellulose (MC), Na2SiO3, calcium oxide (CaO), calcium aluminate cement (CAC), and Ca(OH)2 were incorporated into the matrix. The research utilized a comprehensive testing methodology, allowing for a detailed exploration of various properties and the performance of the geopolymer mixtures. The results indicated that nano SiO2 and Al2O3, Na2SiO3, BW, and CAC were recognized for their positive impact on improving the mechanical properties of the geopolymer. Notably, the geopolymer exhibited an impressive compressive strength of 29.8 MPa and a flexural strength of 5.4 MPa following a 28-day ambient curing (23 ± 2 °C and 50 ± 5% relative humidity). Furthermore, the inclusion of nano SiO2 and Al2O3, GNP, MC, Na2SiO3, CaO, CAC, and Ca(OH)2 proved effective in preventing efflorescence, while MC, Na2SiO3, CaO, CAC, and Ca(OH)2 successfully mitigated cracks formation. The results also demonstrated that the CDW-based geopolymer mixture is suitable for 3D printing, displaying satisfactory buildability, shape retention, and extrudability. A thorough testing approach highlighted the effectiveness of additives in shaping the properties of CDW-based geopolymer, positioning them as promising for improvement and addressing challenges.

Heat-resistant composites based on ternary binders with a low cement content: Characterization and performance

A reduction in cement consumption can be achieved through the use of supplementary cementitious materials (SCMs). In addition, the utilization of more than one SCM can show a beneficial synergic performance. In this paper, a combination of calcium aluminate cement, alumina admixtures and one other type of SCM was investigated. Namely: microsilica, ferrite powder, ceramic dust, calcined shale and sintered mullite were employed. The phase compositions of the designed binders were primarily characterized by XRD, XRF, DSC and SEM. Subsequently, the basic physical and mechanical properties as well as thermal expansion of the ternary binder-based composites up to 1400 °C were determined. The results revealed the synergic performance of used components. Calcined shale and ceramic powder were the most promising admixtures, exhibiting compressive strength of 80 MPa at room temperature and 117 and 128 MPa for ceramic powder and calcined shale, respectively, after exposure to 1400 °C.

Assessment of Cementitious Composites for High-Temperature Geothermal Wells.

High-temperature (HT) geothermal wells can provide green power 24 hours a day, 7 days a week. Under harsh environmental and operational conditions, the long-term durability requirements of such wells require special cementitious composites for well construction. This paper reports a comprehensive assessment of geothermal cement composites in cyclic pressure function laboratory tests and field exposures in an HT geothermal well (300-350 °C), as well as a numerical model to complement the experimental results. Performances of calcium-aluminate cement (CAC)-based composites and calcium-free cement were compared against the reference ordinary Portland cement (OPC)/silica blend. The stability and degradation of the tested materials were characterized by crystalline composition, thermo-gravimetric and elemental analyses, morphological studies, water-fillable porosity, and mechanical property measurements. All CAC-based formulations outperformed the reference blend both in the function and exposure tests. The reference OPC/silica lost its mechanical properties during the 9-month well exposure through extensive HT carbonation, while the properties of the CAC-based blends improved over that period. The Modified Cam-Clay (MCC) plasticity parameters of several HT cement formulations were extracted from triaxial and Brazilian tests and verified against the experimental results of function cyclic tests. These parameters can be used in well integrity models to predict the field-scale behavior of the cement sheath under geothermal well conditions.

Novel material to enhance the integrity of CCUS cement sheath: Exploration and application of calcium aluminate cement

Carbon dioxide (CO2) emissions are being reduced using the technique known as CCUS (Carbon Capture, Utilization, and Storage). At present, cementing cement paste based on ordinary silicate cement (OPC) and compounded with CO2 corrosion-resistant materials are often used in CCUS wells. CAC cement is characterised by low alkaline hydration content and its study in CCUS wells has rarely been reported. Therefore, CAC cement will be a new cement material for CCUS wells. In this study, we have developed an experimental device to simulate the working conditions of CCUS based on the actual well conditions of CCUS and investigated the effects of stress-coupled CO2 corrosion environment on the performance of CAC cement. According to the experimental findings, CAC cement's compressive strength degraded at a rate of 30.6% after 60 days of CO2 corrosion, which was lower than that of OPC cement (38.3%). When compared to OPC cement, the peak strain and stress of CAC cement increased by 57.2% and 7.85%, respectively. Furthermore, compared to OPC cement sheath, the CAC cement sheath's bearing capacity increased by 8 MPa after stress corrosion, and the crack area of the CAC cement sheath after failure was considerably smaller at 275 mm3 than at 735 mm3. Additionally, after being subjected to stress-coupled CO2 corrosion, the integrity of the CAC cement sheath was much superior to that of the OPC cement sheath, offering a fresh viewpoint for building CCUS cement slurry systems.

Effects of thermal shocks on integrity of existing and newly-designed sealants for CCS applications

Sealants that can guarantee long-term wellbore sealing integrity are of great significance to the safe and sustainable storage of CO2 in carbon capture and storage (CCS). In this study, we investigate how abrupt cyclic thermal shocks affect the integrity of four sealants of different compositions. These sealants include two reference OPC-based blends (S1 and S2), one newly-designed OPC-based blend that contains CO2-sequestering additives (S3), and one calcium aluminate cement (CAC)-based blend designed for CCS applications (S4). We have measured the thermal properties of these samples, followed by quenching and flow-through experiments to apply strong cyclic thermal shocks on samples of the four sealants, where we heated the samples to 120 °C, and quenched them in, or flowed through water of 20 °C. Using X-ray tomography (32 µm/voxel) before and after the experiment showed that both S1, S2 (reference OPC-based) and S4 (CAC-based) broke after thermal-shocking experiments. Cracks and new voids developed in the samples. Post-treatment strength testing shows that thermal shocks reduce the unconfined compressive strength of these three sealants. This implies that these compositions may not be optimal materials for long-term wellbore sealing during CO2 injection and storage afterward. For all these three sealant compositions, quenching resulted in a greater reduction in strength (by 53 % on average) than flow-through experiments (by 29 % on average). On the contrary, we have not observed any cracks after either quenching or flow-through experiments in S3 sealant (OPC with CO2-sequestering additives). We attribute the intactness of this sealant after thermal shocks to its higher thermal diffusivity than the other three sealants. Heat transfers more rapidly in this sealant and the associated thermal stresses are mild and insufficient to cause any damage to its integrity, which makes this sealant a good candidate for wellbore sealing material that can effectively withstand strong thermal shocks encountered during CCS, though further studies are required.

Carbonation study of new calcium aluminate cement-based CO2 injection well sealants

In injection-well carbon storage projects, the degradation of Portland cement under harsh CO2 conditions is a primary concern. This study introduces novel CO2-resistant calcium aluminate cement (CAC) systems with addition of rubber latex and hollow glass microspheres which are added to the system to enhance the set cement resistance to CO2 corrosion and in the same time to optimize it for the application in a wide variety of well conditions. After exposure to near supercritical CO2 conditions (100 °C, 7 MPa) these systems exhibited enhanced compressive strength and reduced porosity compared with conventional Portland cement (PC) system, especially the one without latex. By subjecting degradation depth-resolved samples to thermogravimetry (TG) and X-ray diffraction (XRD) techniques, coupled with scanning electron microscopy (SEM), the study scrutinized alterations in microstructural properties. This methodological approach unveiled a profound grasp of carbonation mechanisms. Confirmed through TG and XRD analyses, the considerable reduction in carbonation establishes CAC as a compelling choice for CO2-resistant sealing within injection-well CO2 storage endeavors.

Solidification/Stabilization of Waste Incineration Fly Ash by Modified Calcium Aluminate Cement

Solidification/Stabilization of Waste Incineration Fly Ash by Modified Calcium Aluminate Cement

Geopolymers: A viable binder option for ultra-low-cement and cement-free refractory castables?

Alternative binders offer an avenue for advancing ultra-low-cement and cement-free castables while reducing carbon emissions and energy consumption. In this study, geopolymer binders partially or fully replaced calcium aluminate cement (CAC) in high-alumina castables. The formulations underwent diverse testing, including flowability, physico-thermo-mechanical measurements, and XRD, ATR-FTIR, and SEM analyses. The findings highlighted the feasibility of utilizing geopolymers to craft innovative refractories. The formulation comprising 2.7 wt% CAC and 1.3 wt% geopolymer (AT-3 C-1 G*) exhibited the most successful performance. At 1400 °C, these samples displayed shrinkage of 1.18%, elastic modulus of 135 GPa, flexural strength of 39.1 MPa, and high thermal shock resistance (∆T∼1000 °C). The interaction between CAC and geopolymer inhibited cement hydration while enhancing the geopolymerization process. Moreover, firing the samples at 800–1400 °C led to liquid phase and nepheline formation from the geopolymeric gel, resulting in viscous sintering and improved ceramic densification. These developments produced refractories with remarkable overall performance, surpassing the reference material.

Industrial by-products-derived binders for in-situ remediation of high Pb content pyrite ash: Synergistic use of ground granulated blast furnace slag and steel slag to achieve efficient Pb retention and CO2 mitigation

Ordinary Portland cement (OPC) is a cost-effective and conventional binder that is widely adopted in brownfield site remediation and redevelopment. However, the substantial carbon dioxide emission during OPC production and the concerns about its undesirable retention capacity for potentially toxic elements strain this strategy. To tackle this objective, we herein tailored four alternative binders (calcium aluminate cement, OPC-activated ground-granulated blast-furnace slag (GGBFS), white-steel-slag activated GGBFS, and alkaline-activated GGBFS) for facilitating immobilization of high Pb content pyrite ash, with the perspectives of enhancing Pb retention and mitigating anthropogenic carbon dioxide emissions. The characterizations revealed that the incorporation of white steel slag efficiently benefits the activity of GGBFS, herein facilitating the hydration products (mainly ettringite and calcium silicate hydrates) precipitation and Pb immobilization. Further, we quantified the cradle-to-gate carbon footprint and cost analysis attributed to each binder-Pb contaminants system, finding that the application of these alternative binders could be pivotal in the envisaged carbon-neutral world if the growth of the OPC-free roadmap continues. The findings suggest that the synergistic use of recycled white steel slag and GGBFS can be proposed as a profitable and sustainable OPC-free candidate to facilitate the management of lead-contaminated brownfield sites. The overall results underscore the potential immobilization mechanisms of Pb in multiple OPC-free/substitution binder systems and highlight the urgent need to bridge the zero-emission insights to sustainable in-situ solidification/stabilization technologies.

Effect of cement type and water-to-cement (w/c) ratio on characteristics of lightweight mortars produced with pumice: a comparative study on calcium aluminate (rapid hardening) and ordinary Portland cements

Effect of cement type and water-to-cement (w/c) ratio on characteristics of lightweight mortars produced with pumice: a comparative study on calcium aluminate (rapid hardening) and ordinary Portland cements

Investigation of Compressive Strength and Modulus of Elasticity of Calcium Aluminate Cement Concretes with Different Water/Cement Ratios at High Temperature

Son yıllarda yüksek performanslı beton tasarımında bağlayıcı olarak kalsiyum alüminat çimentosu kullanılabilmektedir. Kalsiyum alüminat çimentosu yüksek sıcaklıklara ve asidik ortamlara karşı üstün performans gösteren bir çimento türüdür. Aynı zamanda çok hızlı sertleşme kabiliyeti sayesinde tamir harcı olarak da kullanılabilmektedir. Ancak Portland çimentosunun aksine hidratasyon mekanizması sıcaklık ve nemden büyük ölçüde etkilenir. Hidratasyon ürünleri belli dönüşümlere uğramak suretiyle kararlı hale geçme eğilimindedirler. Bu dönüşümler kalsiyum alüminat çimentolu betonun mekanik özelliklerini negatif anlamda etkiler. Bu nedenle kalsiyum alüminat çimentosunun hidratasyon mekanizmasına etki eden faktörlerin araştırılması gerekir. Özellikle kalsiyum alüminat çimentolu betonda optimum su/çimento oranın tespiti bu açıdan oldukça önemlidir. Bu çalışmada farklı su/çimento oranlarına sahip (0.35, 0.40, 0.45) kalsiyum alüminat çimentolu betonların normal sıcaklıkta ve yüksek sıcaklıkta (600 ºC) basınç dayanımları ve elastisite modülleri araştırılmıştır. Çalışma sonucunda yüksek sıcaklık altında kalsiyum alüminat çimentolu betonda su/çimento oranı arttıkça basınç dayanımı ve elastisite modülü değerlerindeki azalma oranının arttığı tespit edilmiştir. İşlenebilirlik ve dayanım parametreleri birlikte değerlendirildiğinde kalsiyum alüminat çimentolu betonun tasarımında 0,35-0,40 aralığındaki su/çimento oranının makul bir değer olabileceği değerlendirilmiştir.

Effect of sulfidic mine tailings used as mineral admixtures on the hydration of common and alternative cements

In this work, we investigate the use of pyrite-rich tailings from an operational mine as mineral admixture in different cement matrices [Portland cement, calcium aluminate cement (CAC), and calcium sulfoaluminate cement (CSA)]. Hydration and microstructure changes were studied on cement pastes produced with a 30 wt% replacement of cement with tailings, up to 200 days. Based on our results, the effect of the tailings on the hydration of Portland cement is limited to a physical effect, and no sulfide-induced degradation is observed. In the CAC and CSA pastes, minor mineral phases present in the tailings chemically react, leading to changes in the mineral phase composition of CAC and CSA hydrated pastes. In addition, in all cement pastes studied, and more effectively in the CSA pastes, most of the metal(loid)s contained in the tailings were safely immobilized. Cement chemistry notation: C: CaO; A: Al2O3; F: Fe2O3; S: SiO2; S̅: SO3; c: CO2; H: H2O.

Enhancing semi‐insulating refractory performance with polymeric microspheres and distinct calcium aluminate cements

AbstractEnergy‐related expenses represent a significant concern for industries engaged in high‐temperature processes. In this context, macroporous refractories have garnered notable attention for their potential use as thermal insulators, offering the prospect of energy‐savings and decreased production costs across various industrial sectors. This study investigated the physico–thermo–mechanical performance of semi‐insulating refractory compositions containing pre‐expanded polymeric microspheres as pore‐forming additives and different types of calcium aluminate cements (CACs) as binders. Various experimental tests were employed to characterize the prepared samples, including flowability, modulus of rupture, apparent porosity and density, thermal shock resistance, and thermal conductivity measurements, among others. The incorporation of .6 wt.% of polymeric microspheres into the silica‐based refractory resulted in specimens with relatively moderate porosity values (34.70%), decreased density (1.51 g/cm3) and limited modulus of rupture (3.04 MPa) after firing at 815°C. The alumina‐rich CAC (Secar 71) emerged as the most advantageous binder choice, as the resultant specimens presented mechanical strengths of 9.21 and 4.3 MPa after drying (110°C) and firing (815°C), respectively, enhanced thermal shock resistance and reduced thermal conductivity (.66 W/m K at 800°C). Hence, the designed formulations resulted in semi‐insulating ceramic samples with a porous microstructure and favorable attributes for the fabrication of pre‐molded components.

Histopathological pulp response of teeth capped with calcium aluminate cement and biodentine: Experimental study on rodents

Histopathological pulp response of teeth capped with calcium aluminate cement and biodentine: Experimental study on rodents

Mechanical, freeze-thaw, and sorptivity properties of mortars prepared with different cement types and waste marble powder

The cement production process contributes significantly to CO2 gas emissions and environ- mental pollution. To reduce this adverse effect, the substitution of waste marble powder as a cement additive was investigated. In this study, the properties of mortar specimens were analyzed by using waste marble powder as a partial substitute for three different cement types: CEM I 42.5R Ordinary Portland Cement (OPC), CEM II/B-L 42.5R White Cement (WC) and CA-40 Calcium Aluminate Cement (CAC). Waste marble powder has been replaced with ce- ment at 5%, 10%, and 15%. The compressive and flexural strength, capillary water absorption, and sorptivity values of the prepared mixtures were determined before and after freezing and thawing. It was carried out after 28 days of water curing on 50 x 50 x 50 mm specimens for compressive strength and 160 x 40 x 40 mm specimens for flexural strength test. Freeze-thaw testing of the mixture samples was conducted according to ASTM C666 Procedure A. Test re- sults showed that the highest compressive strength before freeze-thaw was obtained in calcium aluminate cement-based mortars containing 10% by weight waste marble powder replacement for cement. The appropriate waste marble powder ratio was determined as 10% in all cement types used in the study. Before freeze-thaw, the mechanical properties of CAC-based mixtures were higher than those of other cement types. However, as the number of freeze-thaw cycles increased, the strength losses were more significant compared to OPC and WC.

Influence of micro‐sized CaCO3 on hydrates formation of residual calcium aluminate cement in castables during drying

AbstractThe addition of CaCO3 powder in calcium aluminate cement (CAC) is reported to accelerate the hydration of CAC and generate mono‐carbonate C4AC̅H11, which is conducive to shortening the curing time of CAC‐bonded castables at ambient temperatures. Although the hydration of CAC is relatively fast, there is still residual un‐hydrated CAC in castables after curing. The residual CAC would continue to hydrate to produce C3AH6 and AH3 during the subsequent drying procedures in the absence of CaCO3. But it is worth pondering which type of hydrate would be generated in the presence of CaCO3 during the drying at around 110°C. In this study, the effect of micro‐sized CaCO3 addition on the hydrate formation of CAC‐bonded castables during drying at 110°C was investigated. The results indicate that the C4AC̅H11 formed at the curing temperature of 30°C is not decomposed or converted during drying. The CaCO3 remained after curing does not participate in the hydration of residual CAC during drying at 110°C, and thus the residual CAC continues to hydrate to generate C3AH6 rather than C4AC̅H11.

Influence of MgO-Al2O3 hollow sphere content on the microstructure and mechanical properties of calcium hexaluminate porous ceramics

ABSTRACT Calcium hexaluminate (CA6) porous ceramics were prepared by foaming and pore-forming agent methods, with Al2O3 and calcium aluminate cement (CAC) as raw materials and magnesium aluminum spinel hollow spheres (MASHSs) as pore-forming agent. The effects of the amount of magnesium aluminum spinel hollow sphere on the phase composition, bulk density, apparent porosity, flexural strength, microstructure, and thermal conductivity of CA6-based porous ceramics were systematically studied. The pores of such porous ceramics are mainly formed by the enhanced amount of MASHSs and the generation of CA6 phase. The results demonstrate that with the elevation of MASHSs content, the microstructure of the samples transforms from a uniform distribution of closed pores to an interconnected micro-pore arrangement. Notably, the fracture paths transition from cohesive to interfacial interactions between MASHSs. This intricate interplay culminates in a remarkable outcome – our ceramics exhibit thermal conductivities ranging from 0.210 to 0.451 W/(m/k), an augmented gas permeability of 25.96 × 10−11m2, and exceptional compressive strengths reaching up to 22.3 MPa. Overall, this study provides insights into the influence of MASHSs content on the microstructure and thermal-mechanical properties of porous materials, which may contribute to the development of advanced ceramic materials with tailored properties.