Calcium Sulfoaluminate Cement Research Articles

Volume Deformation and Hydration Behavior of Ordinary Portland Cement/Calcium Sulfoaluminate Cement Blends.

Blends of ordinary Portland cement (OPC) and calcium sulfoaluminate (CSA) cement can be used to adjust the properties of cement for specific applications. In this study, CSA cement was used as a shrinkage-compensating admixture to improve the hydration behavior and performance (compressive strength and drying shrinkage) of OPC; the expansion behavior of the blended cement mortar was evaluate based on the saturation index of ettringite. The experimental results showed that incorporating CSA cement resulted in a delayed effect on the hydration of C3S, shortened the induction periods of the blended cement and decreased the setting time. The CSA cement also improved the early compressive strength and drying shrinkage of the OPC due to its compact microstructure. The drying shrinkage of the OPC mortar decreased by 27.8% when 6% CSA cement was used, but the formation of microcracks due to expansion could negatively impact its late compressive strength development and associated pore structures of the blends when the replacement content of CSA cement exceeded 6 wt.%. The results relevant to the expansion behavior of the CSA cements could induce crystallization stress, enhancing its resistance against shrinkage cracking.

Long-term performance of ferrite-rich calcium sulfoaluminate cement-based paste under seawater corrosion

Ferrite-rich calcium sulfoaluminate cement (FCSA) is widely used due to its characteristics of short setting time, high early strength, slight expansion and low CO2 emissions. In order to further study the long-term performance of FCSA under seawater environment, this study prepared a quaternary blend based on FCSA clinker, Ordinary Portland cement (OPC), anhydrite and limestone. Meanwhile, artificial seawater solutions were prepared by dissolving granular NaCl, MgSO4 and MgCl2 in deionized water. The long-term performance evolution of physical and mechanical characteristics such as mechanical properties, chloride content, hydration products and micro-structure property were investigated through uniaxial compression test, X-ray diffraction (XRD), thermogravimetric analysis (TG), mercury intrusion porosimeter (MIP) and other test methods by considering different salt concentrations of seawater and corrosion age. The results showed that the mass and expansion rate of corroded specimens increased logarithmically with the corrosion age. The quaternary blend could resist sulfate corrosion by absorbing it in seawater solution and promote the generation of ettringite. In addition, Friedel's salt was mainly generated by ion exchange between chloride and sulfate of monosulfoaluminate. The uniaxial compressive strength of all specimens showed a consistency of increasing first and then decreasing with corrosion age. Meanwhile, the corrosion resistance coefficient K of the specimens varied between 0.95 and 1.30 with the salt concentrations of seawater increasing. According to the mechanical behavior and micro-structure characteristics of the new quaternary blend, it’s indicated that the new cement-based material has adequate ability to resist seawater salt corrosion and has an excellent long-term stable performance.

Managing the Heat Release of Calcium Sulfoaluminate Cement by Modifying the Ye’elimite Content

Nowadays, calcium sulfoaluminate cement (CSA) is garnering a large amount of attention worldwide and is being promoted as a sustainable alternative to Portland cement for specific applications. This study aimed to control the heat release of CSA cement paste by choosing the appropriate composition. For this purpose, different calcium sulfoaluminate clinkers with up to 75 wt. % of ye'elimite were synthetized. Then, a reactivity study on the synthesized clinkers was conducted while varying the amount of gypsum added. The heat of hydration was measured by isothermal calorimetry. The influence of the ye'elimite content on the heat release and on the compressive strength was investigated. According to the findings, the amount of ye'elimite in the cement has a direct relationship with the heat release. The heat release as well as the mechanical performance increase with the increase in the ye'elimite content in the CSA cement. An equation allowing the prediction of the total heat release after 24 h is provided. Such data can be of particular interest to consultants aiming at the reduction of thermal cracking in massive concrete.

Effect of the fineness of limestone powder on the properties of calcium sulfoaluminate cement

Effect of the fineness of limestone powder on the properties of calcium sulfoaluminate cement

Development of high-early-strength low-carbon engineered cementitious composites with calcium sulfoaluminate cement incorporating high-volume fly ash

Engineered cementitious composites (ECC) is an ultra-durable construction material owing to its high tensile ductility and intrinsic crack width control. Here, a high-early-strength ECC (HE-ECC) was developed using calcium sulfoaluminate (CSA) cement with high-volume fly ash to facilitate rapid and sustainable repair application. Two water-to-binder ratios (0.25 and 0.35) and four fly ash dosages (50–80 wt% by binder mass) were investigated, and PVA fiber was added at 1.5 vol%. The composite mechanical properties were analyzed in association with the early hydration process. At 1 day, the HE-ECC was found to attain a tensile strain capacity of 3–4% while maintaining an ultimate tensile strength of 2–5 MPa. Most groups can maintain a tensile strain capacity over 3% at 28 days with an ultimate tensile strength of 3.1–5.4 MPa. The environmental impacts for producing HE-ECC can be reduced significantly, accounting for ∼38.7% less energy and ∼44.6% less carbon emission compared to conventional ECC. The satisfying early age mechanical performance makes it applicable for many constructions and the high sustainability of HE-ECC makes it promising to reduce environmental impacts substantially.

Applicability of the Formation Factor for Different Alternative Binder Types Investigated on Mortars

The high energy demand and associated CO2 emissions to produce ordinary Portland cement (OPC) create the need for alternative types of binders that can be produced in a more environmentally friendly manner. These alternative binders either have a reduced OPC content or can be produced entirely without the use of OPC clinker. To allow their widespread use also in reinforced concrete components, these binders must meet the same durability requirements as types of cement that have already been standardized. This requires a thorough characterization of the materials and, in addition, a verification of the applicability of the evaluation criteria known from the traditional binders. One of the most important factors influencing the transport processes in the material and therefore the durability is the penetration resistance of the pore structure for aggressive species, such as chloride ions. One key parameter for describing the pore structure is the formation factor (FF), which is used for various applications to evaluate durability. It is determined based on the ratio of the electrical resistivity of the concrete and of the pore solution. A high resistivity also influences the corrosion process of depassivated steel reinforcement in concrete or mortar: by inhibiting ion transport, the corrosion rate may be limited. In this study, mortars produced with different alternative binders are characterized in terms of their FF and pore size distribution. In addition, chloride migration coefficients determined by the rapid chloride migration test are related to the FF. The test program includes nine different alternative binders and two reference cements. In addition to a CEM I and CEM III/B, two calcined clays and a modified steel mill slag were investigated as supplementary cementitious materials, as well as a calcium sulfoaluminate () cement and a calcium silicate hydrate (C-S-H) binder. Four materials belong to the group of alkali-activated mortars: Two geopolymers and two alkali-activated slags were investigated here. It is shown that the AC resistances and the conductivities of the pore solutions differ greatly among the mortars investigated. The FF is a suitable parameter for a simplified estimation of the chloride penetration resistance of the investigated alternative binders, provided that realistic values of the pore solution conductivities are determined and used for the calculations.

A critical review of the role of ettringite in binders composed of CAC–PC–C$ and CSA–PC–C$

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

Influence of polycarboxylate superplasticizer and calcium sulfoaluminate cement on the rheology, hydration kinetics, and porosity of Portland cement pastes

Binary systems composed of Portland cement (PC) and calcium sulfoaluminate (CSA) cement have stood out for applications requiring high early strengths. Nevertheless, the application of these systems may be limited due to their properties in the fresh state, which requires a better understanding of the rheological behavior of these materials. Thus, this study evaluated the incorporation of different polycarboxylate-based superplasticizer (SP) contents (0.15, 0.20, and 0.25 wt%) on PC and PC-CSA binary cement pastes. Rotational rheometry, isothermal calorimetry, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and nitrogen adsorption and desorption tests to assess the pore size distribution of cement pastes were conducted. While the SP incorporation reduced the dynamic yield stress of PC pastes, it progressively increased the yield stress of PC-CSA systems. The increase in SP content increased the main heat flow peak of PC-CSA pastes, although it did not significantly affect the cumulative heat after 160 h of hydration. FTIR and XRD confirm higher ettringite contents in the binary systems and indicate the presence of carboaluminates phases after 7 d of hydration in both PC and PC-CSA and hemicarboaluminate in PC-CSA pastes. The CSA incorporation reduced the cumulative pore volume by up to 32% compared to PC pastes, while the SP content evaluated did not significantly affect the porosity of PC-CSA pastes.

Synergistic Effect and Mechanism of Nano-C-S-H Seed and Calcium Sulfoaluminate Cement on the Early Mechanical Properties of Portland Cement.

The combined utilization of mineral accelerators and nano-seeding materials is a novel method to promote the early strength of cement-based materials. In this paper, the effects of nano-C-S-H seed (NCS) on the early compressive strength of the Portland cement (PC)- calcium sulfoaluminate cement (CSA) binder were investigated. The results showed that NCS and CSA synergistically contributed to the early strength of PC. In detail, a 326.3% increase in the 10 h compressive strength of PC paste was obtained through the addition of NCS (2 wt%) and CSA (5%) in common. This was higher than the sum of the increases observed with the single additions of CSA (157.9%) or NCS (87.6%), with the same above dosage, in PC. Meanwhile, the early strength enhancement effects of NCS and CSA, when used together in PC, lasted longer than the effects of either used alone. Moreover, the synergetic effect mechanism was analyzed by isothermal calorimeter, QXRD, TGA, MIP, and SEM techniques. The calorimetry, XRD, and TGA results demonstrated that the synergistic mechanism was associated with the synergistic promotion effects of CSA and NCS on the hydrates. The fast hydration of CSA produced large amounts of ettringite and also consumed partial free water to promote the performance of the seeding effect of NCS which, simultaneously, further accelerated the precipitation of C-S-H gel and CH. The high alkie environment was also beneficial for the continuous generation of ettringite. In addition, the results of MIP and SEM measurements showed that the micro-filling effect of NCS significantly optimized the pore structure of a PC-CSA blend-hardened paste. Thus, the synergistic strength enhancement effects of CSA and NCS on PC were attributed to the matching of the promotion of hydration generation and the optimization of pore structures in hardening cement paste. The results of this article provide a new approach to achieving the rapid development of the early strength of cementitious materials, with potential applications in precast concrete and low-temperature construction.

Portland/Sulfoaluminate Cement Blends for the Control of Early Age Hydration and Yield Stress

Early age hydration and the rheological behavior of cement pastes are related to their reactivity. The reactivity of Ordinary Portland Cement (OPC) and calcium sulfoaluminate cement (CSA) blends, with a CSA percentage of less than 10%, are investigated in this paper. Different percentages of CSA replacement are studied. First, an isothermal calorimetry study of the different cement pastes is performed to understand the effect of CSA on the evolution of the heat of hydration. Then, in order to understand the reactional mechanism of these cement pastes, X-ray diffraction (XRD) and thermogravimetric analysis (TGA/DTG) studies were conducted on one blended mix made out of 7% CSA and compared to the pure cement pastes of OPC and CSA. Later, the evolution of the yield stress as a function of the CSA percentage was studied. A synergy is shown between both OPC and CSA once mixed together, leading to a 57% and 45% higher ettringite formation for the blend compared to 100% OPC and 100% CSA cement pastes, respectively. This implies that the CSA amount affects the reactivity of OPC/CSA blends. This was confirmed by the variation in both the heat of hydration and yield stress evolution as a function of the percentage of CSA.

Effects of thermal treatment on the mechanical properties, microstructure and phase composition of an Ettringite rich cement

Recently calcium sulfoaluminate cements gain increasing attention due to their significant potential to reduce the carbon footprint of cement production compared to Portland cement. However, the conditions applied during its processing play a crucial role for the stability and longevity of the material. Thereby, the temperature has a decisive influence, as it is already known from numerous studies that ettringite structurally changes significantly upon thermal induced dehydration. Within this background, the present study subjects a holistic view of the mechanical, morphological, phase and structural changes of a commercial calcium sulfoaluminate cement related to the dehydration of the contained ettringite upon treatment at drying temperatures from 23 °C to 100 °C for 7 and 28 days. By complementary methods it is shown that with increasing curing temperature, the mechanical stability decreases, the total pore area and porosity increase, while the permeability of the microstructure is lower for samples stored at 100 °C. Removal of water increases the intercolumnar distance within the ettringite lattice, thereby inducing strain which is released upon rehydration. Although during storing at a temperature of 100 °C ettringite is transformed into an X-ray amorphous product, the initial morphology of the crystals embedded in the cementitious matrix is retained.

Influence of Silanes on Carbonation of Calcium Sulfoaluminate Cement Produced from Solid Industrial Wastes

Production of calcium sulfoaluminate (CSA) cement from solid industrial wastes consumes enormous amounts of wastes and provides an environmentally friendly binder for the construction sector. However, carbonation of CSA cement is much faster than that of portland cement. Silane was used to reduce water absorption of portland cement concrete and thus promote its carbonation resistance. To clarify the effect of silane on carbonation resistance of CSA cement prepared from solid industrial wastes, three silanes, including glycidoxypropyltrimethoxysilane (GOPTS), vinyltrimethoxysilane (VTMS), and dodecyltrimethoxysilane (DTMS), were employed in this research. Their influence on early-age hydration and water absorption of CSA cement mortar was investigated. Accelerated carbonation was performed. The results show that GOPTS and VTMS retarded early-age hydration of CSA cement and slightly decreased 28-day compressive strength, whereas DTMS had less influence. All three silanes decreased water absorption of mortar. However, they bring about more pores larger than 200 nm, which would facilitate the spread of CO2 in mortar. Nevertheless, other than silane’s effect on water absorption and the pore structure of mortar, carbon chain length of silane determines the carbonation resistance of CSA cement mortar. DTMS accelerates carbonation due to its long chain, but, GOPTS and VTMS, with shorter chains, promote resistance of mortar.

Development of a calcium sulfoaluminate-Portland cement binary system for twin-pipe 3D concrete printing

Recently, the twin-pipe pumping (TPP) system has been developed for 3D concrete printing which involves pumping two mixtures, typically a Portland cement-based mixture and a pure limestone powder-based mixture that contains an accelerator. Following this, the two mixtures are allowed to be intermixed in a static mixer placed just prior to the nozzle which causes immediate stiffening and a very high buildability for the printed concrete post-extrusion. However, the flow division pattern produced by the mixing baffles of the static mixer results in striations consisting of unmixed limestone powder resulting in weak zones that lower the mechanical strength of the printed element. In this study, we present a TPP system consisting of Portland cement-based mixtures and a borated calcium sulfoaluminate (CSA) cement-based mixture. The mixtures are capable of reacting independently with water as compared to the pure limestone powder-based mixture. After getting blended in the static mixer right before extrusion, the retardation in the borated CSA cement is destroyed by the alkaline component contained in the other stream, leading to the rapid hardening and a high construction rate post extrusion from the nozzle. The hydration characteristics were studied using a Vicat penetrometer, isothermal calorimetry, and ultrasonic pulse velocimetry, while the early age mechanical behavior was characterized by using uniaxial unconfined compression and slow penetration tests. Results indicate that Portland cement alone cannot produce enough alkalinity to destroy the ulexite phase and reinitiate the hydration of CSA cement, while adding a nominal dosage of calcium hydroxide can provide enough increase in pH to design a system suitable for the stiffening control. However, abundant calcium hydroxide would reduce the hydration rate at later ages due to the dilution effect, as indicated by the P-wave velocity evolution and yield stress evolution. In addition, the hardened behavior of printed elements was studied by performing compression and flexural tests. Results show that the CSA-Portland cement binary binder system avoids the formation of weak zones and hence improves the mechanical behavior.

Effect of Class C and Class F Fly Ash on Early-Age and Mature-Age Properties of Calcium Sulfoaluminate Cement Paste

To promote the sustainable development of eco-efficient calcium sulfoaluminate (CSA) cements through the partial replacement of the CSA clinker with supplementary cementitious waste products, the effects of coal fly ashes on the early-age and mature-age properties of a calcium sulfoaluminate (CSA)-based cement paste were investigated. The impacts of both Class C and Class F fly ashes on the rheological properties, hydration kinetics, and compressive strength development of CSA cement paste were studied. Rheology-based workability parameters, representing the rate of loss of flowability, the rate of hardening, and the placement limit, were characterized for the pastes prepared with fixed water-to-cement (w/c) and fixed water-to-binder (w/b) ratios. The results indicate a slight improvement in the workability of the CSA paste by fly ash addition at a fixed w/b ratio. The isothermal calorimetry studies show a higher heat of hydration for the Class C fly ash-modified systems compared to the Class F-modified systems. The results show that fly ash accelerates the hydration of the calcium sulfoaluminate cement pastes, chiefly due to the filler effects, rather than the pozzolanic effects. In general, ettringite is stabilized more by the addition of Class F fly ash than Class C fly ash. Both fly ashes reduced the 1-day compressive strength, but increased the 28-day strength of the CSA cement paste; meanwhile, the Class C modified pastes show a higher strength than Class F, which is attributed to the higher degree of reaction and potentially more cohesive binding C-S-H-based gels formed in the Class C fly ash modified systems. The results provide insights that support that fly ash can be employed to improve the performance of calcium sulfoaluminate cement pastes, while also enhancing cost effectiveness and sustainability.

Nondestructive Evaluation for Hydration and Setting Time of Gypsum Modified Calcium Sulfoaluminate Cement Paste.

Calcium sulfoaluminate (CSA) cement is a promising solution for reducing CO2 emissions. While previous studies have attempted to investigate the usefulness of CSA cement via various approaches, early age nondestructive evaluations for the setting and hydration of CSA cement mixtures have not been reported. In this study, we measured the ultrasonic pulse velocity and electrical resistivity of early age CSA cement paste. Six types of samples were prepared according to different water-to-solid ratios and different amounts of gypsum. In addition, various microstructural analyses were performed to understand CSA cement hydration with the obtained nondestructive parameters. Consequently, the effect of added gypsum in CSA cement paste was discussed in terms of ye'elimite dissolution and the precipitation of ettringite, and different pore distributions produced by added gypsum were discussed in terms of compressive strength. The 5% addition of gypsum in CSA cement paste enhanced the hydration evolution, such as ettringite, and it can induce the faster setting time up to 6 h and strength development during 24 h.

Effect of CaO Sourced from CaCO3 or CaSO4 on Phase Formation and Mineral Composition of Iron-Rich Calcium Sulfoaluminate Clinker.

The performance of iron-rich calcium sulfoaluminate (IR-CSA) cement is greatly affected by mineral composition and mineral activity in the clinker. This study aims to identify the effect of CaO sources, either CaCO3 or CaSO4, on the phase formation and mineral composition of the IR-CSA clinker. Targeted samples were prepared with different proportions of CaCO3 and CaSO4 as CaO sources at 1300 °C for 45 min. Multiple methods were used to identify the mineralogical conditions. The results indicate that the mineral composition and performance of the IR-CSA clinker could be optimized by adjusting the CaO source. Both Al2O3 and Fe2O3 tend to incorporate into C4A3-xFxS¯ with an increase in CaSO4 as a CaO source, which leads to an increased content of C4A3-xFxS¯ but a decreased ferrite phase. In addition, clinkers prepared with CaSO4 as a CaO source showed much higher x value in C4A3-xFxS¯ and higher compressive strength than clinker prepared with CaCO3 as the sole CaO source. The crystal types of both C4A3-xFxS¯ and C2S were also affected, but showed different trends with the transition of the CaO source. The findings provide a possible method to produce IR-CSA cement at a low cost through cooperative utilization of waste gypsum and iron-bearing industrial solid wastes.

New insights into determining the “time zero” of autogenous shrinkage in low water/binder cement-based composites (LW/B-CC) system based on relaxation theory

This study proposes a novel insight to accurately determine the time zero of autogenous shrinkage in low water/binder cement-based composites (LW/B-CC) based on relaxation theory. Firstly, low-field nuclear magnetic resonance (NMR) technology is used to study the process of water consumption inside the LW/B-CC and clarify the evolution of capillary tension to determine the time zero of autogenous shrinkage. Then, the Laplace equation is used to establish the relationship between water consumption, capillary tension, and autogenous shrinkage in LW/B-CC. The results show that the time corresponding to the development of capillary tension and water consumption in pores is considered as “time zero” of autogenous shrinkage. Furthermore, the capillary tension generated by internal water consumption, about 100 KPa ∼200 KPa, can cause enormous autogenous shrinkage, which easily leads to cracking. In addition, expansion products produced by calcium sulfoaluminate cement (CSA) hydration facilitate the formation of the matrix skeleton and reduce autogenous shrinkage in LW/B-CC. In general, low-field NMR technology is an effective tool to determine the time zero of autogenous shrinkage.

Novelty in bacteria source production and concrete binders in self-healing cementitious samples

One of the challenges associated with creating bacterial-concrete systems capable of biomineralizing CaCO3 to fill cracks is the high pH environment of the hydrated cement paste. In this study two approaches to address this challenge were investigated: (i) the use of calcium sulfoaluminate (CSA) cement, which develops a naturally lower pH, and (ii) the use of non-axenic bacterial cultures, which may facilitate growth of bacterial strains more resilient to harsh alkaline conditions. Axenic B. subtilis and a non-axenic bacterial system from soil were produced and utilized in ordinary portland cement (OPC) and CSA samples. The mechanical properties, water absorption, calcium carbonate precipitation capability, and survivability of bacteria were investigated. The highest B. subtilis and soil bacteria viability was obtained through use of CSA cement and may enable greater later age crack healing potential than mixtures using OPC. Incorporation of axenic bacteria resulted in increased bacteria survivability in the mortar samples when compared to non-axenic bacteria mixes. However, in both cementitious systems, use of B. subtilis and soil bacteria led to similar improvements, suggesting that non-axenic cultures may be used in concrete effectively.

Shear Capacity of Reinforced Concrete Made with Belitic Calcium Sulfoaluminate Cement

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Calcium Sulfoaluminate Cement Manufacturing in India— Prospects and Prognosis of Environmental Impacts

Calcium Sulfoaluminate Cement Manufacturing in India— Prospects and Prognosis of Environmental Impacts