Calcium Sulfoaluminate Belite Research Articles

Durability Assessment of Expansive and Nonexpansive Calcium Sulfoaluminate Belite Cement Concrete in Chloride-Rich Environments

Durability Assessment of Expansive and Nonexpansive Calcium Sulfoaluminate Belite Cement Concrete in Chloride-Rich Environments

Bond of textile-reinforced belite calcium sulfoaluminate cement mortar to concrete substrate

The fast aging of existing building stock requires effective and sustainable strengthening solutions. Textile-reinforced mortars (TRM) have already proved to be very effective as well as versatile retrofitting solutions for reinforced concrete and masonry structures. TRMs can enhance the load bearing capacity of reinforced concrete structures; however, current TRM systems are based on standard Portland cement-based binders, which largely contribute to global human-induced CO2 emissions. This work, for the first time, explores the use of belite calcium sulfoaluminate (BCSA) binder for carbon textile reinforcement through a cross-disciplinary study combining structural engineering and materials science. An experimental study was carried out on concrete block members with externally bonded strips of carbon textile-reinforced mortars, similar to a typical TRM retrofitting system for concrete beams. The textiles were embedded in an ordinary Portland cement-based (OPC) binder or in a BCSA-based binder to compare the bond behaviour to the concrete substrate. The tests revealed a superior bond between the BCSA mortar and the concrete, as well as outstanding adhesion to the textiles achieved using the BCSA binder, with performance levels largely surpassing those measured in their counterparts that used the OPC-based binder. Scanning Electron Microscopy, X-ray diffraction, and thermogravimetric analyses were used to understand this behaviour difference and it was concluded that the ettringite phase is responsible for the enhanced performance in the studied system. The results of this study suggest that BCSA binders have the potential to be a more effective and “greener” alternative to the standard binders based on Portland cement in TRM strengthening applications.

Study on the Properties of Belite Calcium Sulfoaluminate Cement–Ordinary Portland Cement Composite Cementitious System

Due to low early strength and high shrinkage, ordinary Portland cement (OPC) has difficulty meeting the actual needs of modern construction projects, while belite calcium sulfoaluminate cement (BCSA–OPC) composite cement provides a new solution. The mechanical and the drying shrinkage properties of the BCSA–OPC mortar were determined, the hydration heat of the BCSA–OPC was studied, and the pore size distribution of the mortar was investigated. In addition, the hydration products of the BCSA–OPC were analyzed by X-ray diffraction (XRD) and simultaneous thermal analysis (TG-DSC), and the microscopic morphology of the BCSA–OPC mortar was observed by scanning electron microscopy (SEM). The results show that with the increase in BCSA dosage in the BCSA–OPC, compared with OPC, the flexural strengths of the mortar of 50% dosage of BCSA at the hydration age of 1 d, 3 d, 7 d, and 28 d are improved by 33.3%, 36.6%, 23.6%, and 26.8%, and the compressive strengths are improved by 50.8%, 35.7%, 13.4%, and 27.7%. The drying shrinkage and total porosity of the mortar at the hydration age of 28 d are reduced by 117.4% and 21.55%, respectively. It is attributed to the filling effect of a large amount of ettringite (AFt) and intertwined with the fibrous C-S-H gel to form a network. This study will provide a theoretical basis for the application of the BCSA–OPC engineering.

The performance of α′-belite calcium sulfoaluminate (C$A) cement preserved under SO2 atmosphere compared to commercial products

Increasing α′-belite/ye'elimite ratio is considered as a step towards reactive and sustainable C$A cements. The study compares a belite-C$A cement synthesized under SO2 containing atmosphere (TP5) against commercial products. The characterization of the clinkers by X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy in combination with electron backscatter diffraction (EBSD) in the scanning electron microscope (SEM) revealed the presence of α′-belite, variation in belite composition and crystallinity. Thereby the increase in concentration of minor elements in belite, reduced quality of EBSD pattern indicating lower crystallinity. The early hydration of clinkers was optimized by adding gypsum. After 28d of hydration, the hydration of belite was proven by the presence of strätlingite in samples with low gypsum content, in samples with higher gypsum content EDX analysis revealed the presence of Si in the hydrate matrix. Nevertheless, TP5 with highest belite content was the only one with significant strength gain from 7d to 28d, which is the result of increased belite reactivity at late stage.

Carbonation of calcium sulfoaluminate belite binder: mechanism and its implication on properties

Calcium sulfoaluminate belite (CSAB) binder is an alternative low CO2 binder. CSAB cement has ye’elimite as the primary clinker phase which hydrates to form monosulfate or ettringite as the main hydration product. The hydration and mechanical characteristics of CSAB cement and PC-CSAB blended cement have been reported in several studies; however, studies on the durability characteristics such as carbonation are limited. This study focuses on evaluating the microstructural and mechanical alterations due to carbonation in a CSAB binder system and understanding the underlying mechanism of development of the carbonation front. CSAB binder was found to carbonate rapidly compared to PC binder, accompanied by a reduction in compressive strength. This was attributed to the increase in the pore volume due to the carbonation of the ettringite-rich microstructure, facilitating further ingress of CO2 into the microstructure. The rate of carbonation in CSAB binders diverged significantly from the square root of time model used for PC binders.

Utilization of air granulated basic oxygen furnace slag as a binder in belite calcium sulfoaluminate cement: A sustainable alternative

Basic oxygen furnace (BOF) slag negatively impacts ordinary Portland cement performance when replacement levels exceed 5%. This necessitates the exploration of alternative applications for the slag. Simultaneously, a high-volume slag utilization is desired to benefit slag recycling as supplementary cementitious materials. Therefore, this study aims to optimize the air granulated BOF slag substitution potential in belite calcium sulfoaluminate cement by investigating the hydration products in standard mortar. The reactivity of the novel binder is correlated with workability, and mechanical performance by thermal, mineralogical, and microstructure analysis. Consequently, the 10–30% replacement delays the final setting time by inhibiting the ettringite formation leading to a decrease in mechanical performance till 28 days. At later ages (28–180 days), the 30–50% substitution exhibited the synergy in mechanical performance, which is attributed to the hydrogarnet, calcium silicate hydrate, and strätlingite formation. Moreover, all the mortar samples exhibited heavy metals’ leaching and drying shrinkage below the permissible limit.

Effect of additive compounding on early properties of belite sulfoaluminate cement

Belite sulfoaluminate cement is attracting increasing attention and being considered as a potential alternative to ordinary Portland cement owing to lower preparation temperature and carbon dioxide (CO2) emission. However, it still has disadvantages of poor workability and low early strength. This study investigated the effects of compound polycarboxylate superplasticiser (PCE) and early strength agent, calcium nitrite (Ca(NO2)2), on flowability and early strength of belite calcium sulfoaluminate (BCSA) cement. Variation patterns of setting time, fluidity, strength and polycarboxylate superplasticiser (PCE) adsorption of the paste were measured; the hydration products and microscopic morphology were also analysed by the heat of hydration, X-ray diffraction and scanning electron microscopy. Results showed that calcium nitrite effectively enhanced adsorption of PCE onto the surface of BCSA cement particles, leading to notable improvement in the fluidity of the paste (reaching up to 275 mm). In the initial hydration stage, 0.7% PCE compounded with 1.2% calcium nitrite inhibited the formation of ettringite (AFt), resulting in prolonged setting time. However, it deepened the degree of hydration of BCSA for 3 days and refined the hydration product, AFt crystals. Consequently, the compressive strength was increased to 95.75 MPa and 107.13 MPa for BCSA cement at 3 days and 28 days, respectively.

Investigations on the Suitability of Alternative and Supplementary Cementitious Materials to produce High Performance Aerogel Concrete

AbstractHigh 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.

Early Age Performance of OPC-GGBFS-Concretes Containing Belite-CSA Cement Cured at Sub-Zero Temperatures

This study determined how replacing sodium nitrate-based antifreeze admixture (AF) with belite-calcium sulfoaluminate (belite-CSA) cement affects the early age properties of ecological concretes based on ordinary Portland cement (OPC) and ground granulated blast-furnace slag (GGBFS). Concrete specimens were cured at −15 °C and treated in various ways before testing, i.e., no treatment, stored at 20 °C for 12 and 24 h. Generally, the addition of belite-CSA cement shortened the setting time due to the rapid formation of ettringite. The incorporation of 25 wt% of antifreeze admixture (AF) to the OPC-GGBFS concrete cured at −15 °C partially inhibited ice formation and enabled the continuation of hydration processes. This trend was observed for all samples, independent of the applied AF after freezing curing. On the contrary, the addition of 20 wt% of CSA failed to inhibit the ice formation and increased the risk of frost damage for concretes despite the treatment after freezing. These concrete specimens had lower hydration, lower strength, and a more porous binder matrix. The microstructure of the binder matrix was significantly affected by the amount of CSA and extreme negative curing, followed by no notable recovery post-curing at room temperature. Therefore, pre-curing at room temperature for at least 6 h has the potential to avoid frost damage. Concrete containing 25 wt% AF combined with 12 h and 24 h of curing at 20 °C after removal from freezing and prior to testing could enhance the compressive strengths of all concretes. The renewed hydration was indicated as the main influencing factor.

Influence of iron content on processing conditions and early age hydration of ye’elimite

Ye’elimite is the primary reactive component in calcium sulfoaluminate-belite (CSAB) cement, and it has relatively lower raw material carbon footprint compared to Portland clinker phases. Ye’elimite produces ettringite when hydrated in the presence of calcium sulfate, and monosulfate in the absence of a sulfate source. The early age hydration properties in CSAB based binders are mainly controlled by the amount and reactivity of ye’elimite in the system. The reactivity of the ye’elimite can be affected by the presence of minor elements in raw mix during clinkering and distribution of other phases in the binder. This paper aims to study the formation and hydration o f ye’elimite incorporated with iron, which is commonly found in industrial by-products suitable for CSAB cement production. The influence of iron on the clinkering conditions and its incorporation in the ye’elimite phase are investigated using characterization techniques such as X-ray diffraction and thermogravimetric analysis. The iron-incorporated ye’elimite, synthesized using laboratory-grade chemicals, is examined for early-age hydration using isothermal calorimetry to study the effect of iron content on the hydration reactivity of ye’elimite. The iron content in the raw mix was found to affect clinkering reactions by accelerating the decomposition of calcite and calcium sulfate. The iron incorporation also resulted in changes in the crystal structure and early age hydration of ye’elimite.

Effect of strontium slag on early hydration and mechanical properties of belite-C4A3$ cement

Belite-calcium sulfoaluminate (Belite-C4A3$) cement is one type of low-calcium clinker with good long-term compressive strength and durability. Yet, its early mechanical property is lower than P·І 42.5. In this paper, the effect of strontium slag on the preparation and performance of belite-C4A3$ cement was investigated. Moreover, the effect of SrO on crystal form and hydration characteristic of silicate minerals was studied. It was found that SrO could improve the early hydration activity of silicate minerals by stabilizing the β-type C2S and M-type C3S. The experiment results showed that the addition of strontium slag improved the burnability of cement, stabilized the high temperature active crystalline form of silicate minerals and promoted its formation, which were benefited to the rapid generation of hydration products and increase of early compressive strength of belite-C4A3$ cement. It was found that the compressive strength of belite-C4A3$ cement at different ages was increased to various degrees under the content of 1∼8% strontium slag. The optimal content of strontium slag was 5%, and its compressive strength of 1, 3, 7 and 28 days was 8.43, 35.83, 71.25 and 103.73 MPa, respectively. Compared with the blank group without strontium slag, the compressive strength was increased by 270%, 210%, 320% and 13%, respectively. This indicated that strontium slag had a significant effect on improving the early mechanical properties of belite-C4A3$ cement.

Cobalt immobilization performance and mechanism analysis of low carbon belite calcium sulfoaluminate cement

Cementitious materials are well acknowledged as one of the most adaptable materials for immobilizing heavy metals. Belite calcium sulfoaluminate cement (BCSA), one of the low-carbon alternative binders to cement with superior properties regarding chemical resistance and mechanical properties, is found with a desirable capability for waste immobilization. In this study, BCSA was used for Co(II) immobilization with a dosage of up to 2.5% by weight of BCSA. The results showed that Co(II) could promote the hydration of BCSA pastes, specifically accelerated the hydration of ye’elimite. More hydration products could be generated in the Co(II)-doped BCSA pastes, leading to the construction of a denser microstructure. The compressive strength of BCSA pastes would be slightly improved when BCSA was used for Co(II) immobilization, and the electrical resistivity would decrease. In terms of Co(II) immobilization, BCSA cement exhibited a desirable capacity for Co(II) immobilization. The majority of the Co(II) could be immobilized within the first 100 min of mixing BCSA with Co(II) solutions. The immobilization degrees of Co(II) in hardened BCSA pastes could approach about 99.99% after 7d. The acquired results indicated that BCSA cement is effective for Co(II) immobilization. Therefore, BCSA has a low-carbon advantage with superior strength development over time and prospective capacity of heavy metals immobilization.

Comment On Energy-Efficient Alternative for Different Types of Traditional Soil Binders

Abstract Due to urban sprawl, the demand for land has increased for the purpose of construction. It is unlikely that soil available at different construction sites will be suitable for designed structures. For improving the load-bearing capacity of the soil, different soil binders are used, which are present in distinct states. In this review, the authors have collected details about various binders, which are generally used in the soil stabilization, and their effect as a binding agent on the soil. In this article, the authors tried to review different traditional binders. After studying various research articles, the authors found that lime, ground-granulated blast slag (GGBS) polypropylene, polyurethane grouting, and asphalt mix are frequently used binders. However, the authors also gathered information about the negative environmental impact of these traditional soil binders, which led to the need for alternatives to these commonly used soil binders. To diminish this issue, different alternate hydraulic and non-hydraulic binders are discussed. The authors found alternatives to cement and lime with the alkali-activated material consisting of Na2O and silica modulus and belite-calcium sulfoaluminate ferrite, which is also known as “Aether™.” According to the research, both alternatives emit 20–30% less CO2 into the environment and also improve the compressive strength of the soil. The various studies promotes bitumen modification. Incorporating 20-mesh crumb rubber and bio-oil into the bitumen reduces its viscosity and improves its fatigue value. When waste oil is mixed with asphalt, it revitalizes the bitumen, improves fatigue resistance, and increases compressive strength. The soil particles treated by Eko soil are held together by enzymes, which give them the same strength as cement. Apart from that, low-carbon binders such as basic oxygen furnace slag, bamboo fiber, enzyme-based soil treatment, zebu manure for stabilization, and lignin-contained biofuels and coproducts are discussed. Replacing these traditional binders helps with energy savings. All waste products are recycled, and energy is saved by not manufacturing traditional binders. Additionally, energy is saved, which is required to avoid the detrimental effects of these conventional binders, making them energy-efficient alternate binders. The authors also summarize the methods used, impacts, and changes that occur in soil properties after using substitutes in place of traditional binders. From the review, the authors determined that different binders have various properties in terms of chemical and physical compositions, and they show different variations in terms of strength when added to soil with low bearing capacity or poor stability.

Influence of tartaric acid dosage on the early-age and long-term properties of calcium sulfoaluminate belite cement composites

Increasing the use of low carbon footprint calcium sulfoaluminate belite (CSAB) cement is a potential way to reduce carbon dioxide emissions related to the cement and concrete industry. However, rapid setting is one of the barriers limiting the large-scale applications of CSAB cement. To address this issue, experimental studies were carried out to investigate a sustainable retarder—tartaric acid—and its dosage on the hydration reaction, early-age properties, and long-term properties of CSAB cement composites from their fresh state to 2 years. The results confirmed that tartaric acid is a powerful retarder for CSAB cement; it showed a stronger retarding effect than citric acid, sodium gluconate, borax, and molasses. A proper tartaric acid dosage (≤ 0.75 %) extended the initial setting time of CSAB cement from 5 min to up to 154 min without compromising long-term strength. When the tartaric acid dosage was no more than 0.5 %, it hardly affected the strength from 2 h to 2 years. However, over dosage (≥ 1%) should be avoided since it significantly affected the strength development from 2 h to 2 years. Overall, this study provided a knowledge base for the mixture design of CSAB cement composites, which can benefit the popularization of low carbon footprint CSAB cement.

Performance of photocatalytic, carbonated calcium sulfoaluminate-belite cement

Carbonated and non-carbonated paste samples containing white Ordinary Portland Cement (OPC) or Calcium Sulfoaluminate-Belite (CSAB) cement with TiO2 were evaluated for NOx removal, optical properties, and CaCO3 polymorphs using chemiluminescence NOx analyzer, UV-Vis-NIR spectrophotometer, and X-Ray Diffraction, respectively. NOx removal of photocatalytic CSAB cement was 43% and 28% lower than white photocatalytic cement for non-carbonated and carbonated samples, respectively. Partially replacing the cements with fly ash decreased NOx removal in the non-carbonated state but reduced the negative impact of carbonation on photocatalytic efficiency. The decrease in NOx removal of carbonated samples were a combination of decrease in surface porosity, coverage of TiO2 sites by carbonation products, and decrease in activated TiO2 sites caused by a lower average diffuse reflectance in UV-A region despite an increase in photoconductance. All the TiO2-doped paste had a lower band edge energy than pure nano TiO2, and Urbach absorption tail, indicating presence of localized defects.

Ternesite-calcium sulfoaluminate cement: Preparation and hydration

Ternesite-calcium sulfoaluminate (TCSA) cement exhibits excellent properties. However, it is hard for sulfoaluminate (C4A3$) and ternesite (C5S2$) to coexist in the clinker. In this study, phosphogypsum (PG) was used for producing TCSA cement clinker. The joint effects of P2O5 and F in PG as well as the CaSO4 content in raw meals on the coexistence of C4A3$ and C5S2$ were investigated. The grindability and morphology of TCSA cement clinker were characterized. By the comparison with belite-calcium sulfoaluminate (BCSA) cement, the hydration and properties of TCSA cement were investigated. Results shows that the coexistence of C4A3$ and C5S2$ is achieved under the joint effects of P2O5, F and a sufficient amount of CaSO4. TCSA cement clinker could be prepared at 1125–1200 °C for 15–30 min and the clinker exhibits a good grindability. Ternesite in TCSA cement clinker presents a rodlike or granular shape Compared with BCSA cement, due to higher hydration rate of C4A3$, the setting time of TCSA cement is shorter and early compressive strength is higher. Due to the hydration of C5S2$, TCSA cement exhibits a higher late age compressive strength.

Nondestructive Monitoring Hydration of Belite Calcium Sulfoaluminate Cement by EIS Measurement.

In this study, the impact of water-to-cement (w/c) ratios of belite calcium sulfoaluminate cement (BCSA) on the hydration kinetics and the electrochemical impedance spectroscopy (EIS) parameters is studied. According to the analysis of classic hydration measurements, such as calorimetry tests, chemical shrinkage content, and chemically bound water content, it can be concluded that a higher w/c ratio clearly accelerates the hydration of BCSA cement paste. The electrical resistivity of BCSA0.35 cement paste is more than 4.5 times that of BCSA0.45 and BCSA0.5, due to the gradually densified micropore structure blocking the electrical signal transmission rather than the free charged-ion content. The porosity of BCSA0.5 is 27.5% higher than that of BCSA0.35 and 7.8% higher than that of BCSA0.45, which proves the resistivity is clearly related to the variation in microstructure, especially for the porosity and pore size distribution. The novelty of this study is the linear regression with logarithm terms of electrical resistivity and classic hydration parameters such as chemical shrinkage, cumulative hydration heat, and chemically bound water is established to extend the classical expression of cement hydration degree. It indicates that the electrochemical impedance spectroscopy can be taken as a nondestructive testing measurement to real-time monitor the cement hydration process of cement-based materials.

Role of pore structure on resistance to physical crystallization damage of calcium sulfoaluminate belite (CSAB) cement blends

The resistance to physical sulfate damage was tested for a variety of cementitious mixtures including ordinary portland cement, calcium sulfoaluminate belite (CSAB) cement, a CSAB-fly ash blend and an air-entrained CSAB. Mortar bars were exposed to DI water or 5 % sodium sulfate solutions under cyclical wet-dry conditions. The expansions of the specimens were measured after each wetting cycle. A water sorptivity test, thermogravimetric analysis, x-ray diffraction analysis, mercury intrusion porosimetry method, and micro-computed tomography were applied to study differences in expansion and cracking in the mixtures. The results showed that the incorporation of fly ash into the CSAB matrix reduced cumulative pore volumes and slightly increased micropore sizes – both of which contributed to failure of the CSAB-fly ash systems. Use of the air-entraining agent in CSAB produced more, smaller, and more uniform pores, but did not influence the performance of CSAB. Both the CSAB and air entrained CSAB mixtures showed good resistance to physical sulfate damage. Samples with average pore diameters <15 nm prevented infiltration of sulfate ions and slowed the onset of salt crystalization damage.

Preparation and Performance of Ternesite-Ye'elimite Cement.

Ternesite–ye’elimite (TCSA) cement is a new type of environmentally advantageous binder prepared by introducing ternesite, a reactive phase, into belite calcium sulfoaluminate cement clinker. This paper reports the laboratory production of TCSA cement by the addition of minor elements to achieve the coexistence of ternesite and ye’elimite. The influence of dopants on the mineralogical composition of clinkers and the clinkering conditions for the preparation of TCSA cement clinkers were investigated by X-ray powder diffraction and scanning electron microscopy. The mechanical properties and hydration products of the cement pastes were also studied. The results indicated that the addition of CaF2, P2O5 and Na2O can promote the coexistence of ternesite and ye’elimite, and that Na2O is the most effective candidate. TCSA cement clinkers could be successfully prepared at 1150 °C for 30 min by doping 0.3% Na2O. The TCSA cement clinkers exhibited shorter setting times than the BCSA cement clinkers. The later strength of TCSA cement showed a significant increase compared with BCSA cement. The effect of Na2O was different on the strength development for TCSA and BCSA cement. The dissolution of ternesite could promote the formation of ettringite. The reactivity of belite was higher in TCSA cement due to the formation of strätlingite.

Mitigating early age cracking in 3D printed concrete using fibres, superabsorbent polymers, shrinkage reducing admixtures, B-CSA cement and curing measures

3D printed concrete is vulnerable to severe early age shrinkage-related cracking due to the absence of formwork and coarse aggregates. To address this, several potential mitigation measures are compared based on their ability to reduce free shrinkage and cracking severity at dosages which do not adversely affect the printability or buildability of a well-developed 3DPC mixture. The results show that a low dosage of short polypropylene microfibres eliminates early age cracking. The external application of a curing agent and multiple applications of misting water are less effective. Calcium sulfoaluminate–belite cement is used to accelerate structuration and proves beneficial in crack mitigation while enhancing buildability. Internal curing, with superabsorbent polymers, is less effective in mitigating plastic cracks but reduces autogenous shrinkage and increases the rate of stiffening. At the dosage used in this study, the shrinkage reducing admixture is relatively ineffective in crack mitigation, with higher dosages adversely affecting the buildability.