Calcium Sulphoaluminate Cement Research Articles

Sewer concrete subjected to biogenic acid corrosion: analysis of concrete deterioration phases using QEMSCAN

QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) was used to analyse the evolution of cementitious phases of sewer concrete after biogenic acid attack. Two concrete mixes; a blend of Sulphate Resisting Portland Cement and Fly Ash (SRPC+FA) and Calcium Sulpho-Aluminate (CSA) cement, with calcite and siliceous aggregates, were subjected to a field sewer environment, with a maximum H2S gas concentration of 100 ppm, for about two years. After exposure, both concretes experienced thickness losses, with CSA indicating mass gain and SRPC+FA mass loss. QEMSCAN analysis results indicated that SRPC+FA was rich in calcium silicate hydrates in the intact zone, Mg-silicate in the transition zone, and Al-silicate, gypsum, and quartz in the deterioration layer. CSA contained ettringite and portlandite in the intact zone, gypsum and aluminate phases in the deterioration zone, while the transition zone was challenging to observe due to the superimposition of ettringite before and after the attack. It was concluded that, despite CSA showing a lower corrosion rate than SRPC+FA, it exhibited severe deterioration under QEMSCAN. Therefore, QEMSCAN is a potential tool for preliminary analysing of concrete microstructural phases under biogenic acid attack. However, it should be incorporated with other microstructural analysis tools.

Polyvinyl-Alcohol-Modified Calcium Sulphoaluminate Cement Repair Mortar: Hydration and Properties

Polyvinyl alcohol (PVA) and calcium sulphoaluminate (CSA) cement were used to prepare repair mortar for the restoration of the walls of a building built with bricks. The preparation, hydration, and properties of the PVA-modified CSA cement repair mortar were studied. Besides this, the mechanism by which PVA improves the bonding strength is also discussed. The results demonstrate that PVA prolongs the setting time of CSA cement, which is ascribed to PVA inhibiting the dissolution of C4A3$ (4CaO·3Al2O3·SO3) and the precipitation of AFt (3CaO·Al2O3·3CaSO4·26H2O) within the hydration age of 0~60 min. PVA lowers the mechanical strength of CSA cement repair mortar at the hydration age of 6 h. After 6 h, the mechanical strength is improved. PVA could also improve the bonding strength between CSA repair mortar and bricks. This is mainly ascribed to the Al ions in both the hydration products of CSA cement and the clay bricks reacting with the hydroxyl group of PVA and forming the chemical bond C-O-Al. Therefore, a tighter combination between CSA cement repair mortar and the clay bricks forms, thereby improving the bonding strength.

Low-Temperature Calcination of Belite-Calcium Sulphoaluminate Cement Clinker and the Hydration Process

To reduce the calcination temperature of belite (β-C2S)-calcium sulphoaluminate (C4A3$) cement clinker, hydrothermal curing was applied to mixed raw materials before calcination. The influences of calcination temperature on the mineralogical composition of cement clinker were investigated, and the optimum β-C2S/C4A3$ ratio was deduced. The phase and microstructure evolution of the hydrated paste were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The compressive strength development was also tested. The results showed that after hydrothermal curing at 95°C, the belite-calcium sulphoaluminate cement clinker can be prepared with a low-temperature calcination of 1,200°C. When the β-C2S/C4A3$ ratio reached 50%/50%, the cement pastes had the highest 3- and 28-day compressive strengths of 37.34 and 62.94 MPa, respectively. The main hydration product formed in the cement paste was ettringite.

Thermal Properties of Calcium Sulphoaluminate Cement as an Alternative to Ordinary Portland Cement.

This paper presents the results of research into the heat of hydration and activation energy of calcium sulphoaluminate (CSA) cement in terms of the dependence on curing temperature and water/cement ratio. Cement pastes with water/cement ratios in the range of 0.3–0.6 were tested by isothermal calorimetry at 20 °C, 35 °C and 50 °C, with the evolved hydration heat and its rate monitored for 168 h from mixing water with cement. Reference pastes with ordinary Portland cement (OPC) were also tested in the same range. The apparent activation energy of CSA and OPC was determined based on the results of the measurements. CSA pastes exhibited complex thermal behaviour that differed significantly from the thermal behaviour of ordinary Portland cement. The results show that both the w/c ratio and elevated temperature have a meaningful effect on the heat emission and the hydration process of CSA cement pastes. The determined apparent activation energy of CSA revealed its substantial variability and dependence, both on the w/c ratio and the curing temperature.

Insights into the positive effects of power ultrasound on the pore solution of Portland cement pastes

The influence of the direct application of power ultrasound (PUS) at several frequencies and power densities to Portland cement (PC) pastes is investigated in detail. Two PC pastes at water-to-cement ratios of 0.50 and 0.80 were studied. The composition of the pore solution and hydrates after introducing PUS irradiation for various periods were examined using ICP-OES, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) techniques. The results indicate for the first time that applied PUS used in this study, can disturb the early formation of ettringite whilst appreciably promoting the formation of amorphous aluminium hydroxide hydrate by considerably releasing the aluminium ions into the pore solution. Moreover, PUS can increase carbonates by intensifying the carbonation in the PC systems particularly the system with higher water content. The present research concludes that ultrasound could be a promising technique to enhance ternesite hydration in ternesite-rich belitic calcium sulphoaluminate cements.

Tartaric acid effects on hydration development and physico-mechanical properties of blended calcium sulphoaluminate cements

The fast setting of calcium sulphoaluminate (CSA) cement-based systems is typically controlled using set-retarding admixtures, despite the notable efficiency of tartaric acid (TA) in adjusting CSA-based mixtures setting times, its use has only been marginally investigated, with an almost exclusive focus on the early age properties of TA manufactured mortars. This paper aims at evaluating the effect of the addition of tartaric-acid retarder on the hydration mechanism and physical properties of CSA-based mixtures from 4 h to 84 days. Macro- and microstructural properties were investigated using X-ray diffraction and differential thermal-thermogravimetric analyses, mercury intrusion porosimetry measurements, mechanical tests and analyses at fresh and hardened state. The experimental results reveal that the use of TA delays the formation of ettringite, modifies the porosity of hardened mixtures and strongly reduces strength in the short term. Nevertheless, the addition of TA slightly influences the properties at longer periods.

Hydration, Microstructure and Compressive Strength Development of Seawater-mixed Calcium Sulphoaluminate Cement-based Systems

In-depth understanding of the calcium sulphoaluminate (CSA) cement, a type of environment-friendly cement, is essential for its wide application in engineering practice. Partial replacement of CSA by alternative alumina-rich powders has significant potential in the production of cost-effective CSA cement. In this work various supplementary cementitious materials (SCMs) including slag, metakaolin and silica fume with different replacement levels were added into CSA cement, and mixing with seawater, to prepare paste and concrete specimens. The development of hydration products in the paste specimens was characterized by X-ray diffraction and Thermogravimetric analysis. The pore structures of the seawater-mixed paste specimens obtained from mercury intrusion porosimetry tests, along with the pH value and free chloride content in the pore solution, were analyzed. Results show that various SCMs have significantly different effects on the pore solution chemistry, hydration and microstructural formation of the seawater-mixed CSA cement, resulting in different mechanical behavior and durability properties. The results of this work are helpful for the development of cost-effective CSA cement-based concrete used in marine constructions.

Intrinsic self-stressing and low carbon Engineered Cementitious Composites (ECC) for improved sustainability

Engineered Cementitious Composites (ECC) is an emerging cementitious composite material with ultra-high ductility. However, its higher cement dosage limits its material greenness and leads to concerns with drying shrinkage. In this research, an ECC utilizing limestone calcined clay cement (LC3) and calcium sulphoaluminate cement (CSA) is investigated, focusing on minimizing the material's embodied carbon while enhancing its durability with intrinsic self-stressing functionality. A self-stressing criterion is theoretically established and experimentally verified. X-ray diffraction patterns reveal an ettringite quantity that modulates the initial expansion and later expansion-reversal of LC3-CSA-ECC to support a persistent self-stressing mechanism. LC3-CSA-ECC has a lower (64%) carbon footprint and similar embodied energy compared to conventional concrete. When combined with the durability advantage (tiny crack, high ductility of 5.5%, and self-stressing function), this low carbon self-stressing ECC holds promise as a sustainable repair material that lowers the embodied and operational carbon in civil infrastructure.

Influence of cellulose ethers structure on mechanical strength of calcium sulphoaluminate cement mortar

This study investigates the influence of different types of cellulose ethers at selected dosage on mechanical strength of calcium sulphoaluminate cement mortar and discloses the correlation between the structural parameters of cellulose ethers and the mechanical strength. For the purpose, a few properties including the surface tension of cellulose ethers solution, the fresh mortar density, the compressive and flexural strength development of calcium sulphoaluminate cement mortar with curing time were measured, followed by linear fitting. It is demonstrated that hydroxyethyl cellulose ether has the least negative impact on these properties while the hydroxypropyl methyl cellulose ether with high hydroxypropyl molar substitution has the most. The development trends of mechanical strength with curing time are affected by both the choice of cellulose ethers and their dosage. It is shown that the 1 d flexural strength, 28 d flexural strength and 28 d compressive strength are highly correlated with the fresh mortar density which tends to decrease with the surface tension of cellulose ethers solution in a non-linear manner. Moreover, it is suggested that hydroxyalkyl molar substitution of cellulose ethers is the key parameter impacting most measured properties when methoxyl substitution exists. Methoxyl degree of substitution only correlates with certain properties when hydroxyalkyl molar substitution is low.

Preparation of eco-friendly lightweight gypsum: Use of beta-hemihydrate phosphogypsum and expanded polystyrene particles

Beta-hemihydrate phosphogypsum (β-HPG) as a cementitious material can be used for the preparation of lightweight gypsum to facilitate the utilization of phosphogypsum (PG) and reduce the energy consumption of buildings. In this work, expanded polystyrene (EPS) particles as lightweight aggregates were mixed with β-HPG during the preparation process. In order to improve the hydrophilicity of EPS particles, core–shell EPS particles were obtained by the modification of ethylene–vinyl acetate copolymers (EVA), triethanolamine (TEA) and the coatings of SAC paste. Effects of core–shell EPS particles and calcium sulphoaluminate cement (SAC) on the performance of lightweight gypsum were evaluated by compressive strength, bulk density, thermal conductivity and microstructure. The results show that lightweight gypsum with core–shell EPS particles has better interface and higher compressive strength compared to that produced with unmodified EPS particles. Moreover, SAC can further increase the compressive strength of lightweight gypsum. Ettringite, aluminate hydroxide and C-S-H gels are formed to optimize the microstructure and increase the compressive strength of lightweight gypsum through the addition of SAC. Eco-friendly lightweight gypsum with high compressive strength, adjustable bulk density and low thermal conductivity can be prepared. In general, this study provides a high value-added product for the utilization of PG and the improvement of building energy efficiency.

Influence of the Concentration of Seawater on the Early Hydration Properties of Calcium Sulphoaluminate (CSA) Cement: A Preliminary Study

This research investigates the effect of seawater of different concentrations on the hydration process and microstructure of calcium sulphoaluminate (CSA) cement. It studies the CSA cement pastes via experiments carried out to determine the initial and final setting times, mechanical strength and chemical shrinkage with X-ray diffraction (XRD), scanning electron microscopy (SEM) and simultaneous differential thermal-thermogravimetric (DTA-TG) analysis. The DTA-TG and XRD results showed that the main hydration products were ettringite (AFt) and aluminum hydroxide in the CSA cement paste mixed with both freshwater and seawater, while a small amount of ettringite (AFt) became monosulfate (AFm) in the freshwater-mixed CSA cement. The SEM results demonstrate that seawater can improve the microstructure of CSA cement paste in the early stage of hydration (1 d) but impairs the microstructure of the CSA cement matrix in the later stage of hydration (7 d). The experimental results also indicate that a high concentration of seawater can extend the setting time, increase the chemical shrinkage and decrease the mechanical strength of CSA cement.

Acoustic emission behavior of polyvinyl alcohol (PVA) fiber reinforced calcium sulphoaluminate cement mortar under flexural load

The purpose of this study was to study the failure mechanism, fiber bridging and slip mechanism of PVA fiber reinforced calcium sulphoaluminate cement mortar (CSAM) under bending load. Firstly, the flexural toughness performance of PVA fiber reinforced CSAM was studied. Then, the change of acoustic emission (AE) behaviors was studied, including the change of AE parameters (counts and energy), the cracking mode reflected by the average frequency (AF) and RA values, the peak frequency and Ib value. The results showed that PVA fiber could significantly improve the flexural properties of CSAM. In contrast to PVA0, the AE count and energy of fiber reinforced CSAM remained at a high level after the peak load. The excellent bonding property between fibers and MPC paste didn't always lead to the strong local maximum of RA and the strong local minimum of AF at the time of main fracture. Compared with PVA fiber reinforced CSAM, the failure of specimen PVA0 was only controlled by tensile cracks. The peak frequency bands of 20–50 kHz, 90–110 kHz and 290–320 kHz, respectively corresponded to the friction and pull-out of the fiber, the matrix cracking of CSAM and the propagation and development of macro-cracks.

Bioreceptivity of Portland and calcium Sulphoaluminate cements in urban sewerage networks

This paper discusses the comparative biolcolonization of cementitious pastes made with two Portland Cements and two Calcium Sulphoaluminate Cements exposed for 18 months in an actual urban sewerage network at five different sites. After an incubation period of about 18 months all the cement pastes were found to be colonized by suphooxidizing bacteria in the 5 environments studied. The results obtained show that the cementitious nature is not a determining factor and that the conditions of the moment actually favour the accumulation of secondary phases on the surface due to the presence of sulphur that appears because of bacterial activity.

Characterization methods for sulfate ions diffusion coefficient in calcium sulphoaluminate mortar based on AC impedance spectroscopy

Calcium sulphoaluminate (CSA) cement has higher impermeability and resistance to sulfate attack than Portland cement. Determining the diffusion coefficient of sulfate ions can evaluate and predict the service life of the concrete. This paper proposes a new method to measure the diffusion coefficient of sulfate ions in CSA cement mortar by alternating current impedance (AC impedance). Results indicate that the immersion and electro-migration tests are not suitable for measuring the diffusion coefficient of sulfate ions in the CSA cement mortar, while the AC impedance method provides more accuracy. In addition, the critical pore diameter that influences the diffusion coefficient of SO42- is determined to be approximately 40 nm by low-field nuclear magnetic resonance. The diffusion coefficient is also linearly related to the cumulative porosity of diameter larger than 40 nm in the CSA mortars.

Influence of Water‐Cement Ratio and Type of Mixing Water on the Early Hydration Performance of Calcium Sulphoaluminate (CSA) Cement

The present work studies the influence of water‐cement ratio and types of mixing water on the hydration process and microstructure of calcium sulphoaluminate (CSA) cement. Experimental tests on the setting time, physical properties, compressive strength, chemical shrinkage, X‐ray diffraction (XRD), and scanning electron microscopy (SEM) of CSA cement paste were carried out. The XRD analysis confirmed that the main hydration product is ettringite in both freshwater and seawater mixed CSA cement with different w/c ratios. The SEM analysis and physical properties test show that both low w/c ratio and seawater can improve the microstructure of CSA cement. The test results also find out that the high w/c ratio can accelerate the hydration process, extend the setting time, lower the compressive strength, and increase the chemical shrinkage of CSA cement, and the seawater presents a similar influence except for the mechanical property. The seawater increases the compressive strength of CSA cement in the early stage of hydration but will increase the microcracks at the later hydration stage of CSA cement and reduce its mechanical properties.

Early Age Hydration Characteristics of Calcium Sulphoaluminate Cement Mortar Cured at a Temperature Range from −10 to 20°C

With the increasing number of infrastructures constructed in marine and cold regions, research on and applications of calcium sulphoaluminate (CSA) cement have been flourished, but the hydration process of CSA at low temperature has not been systematically investigated. To characterize the influence of low temperature on the hydration characteristics, freshly mixed CSA mortars were cured at −10, −5, 0, 5, and 20°C, respectively. The hydration process was investigated by electrical resistivity, compressive strength, and microstructure analyses. Results show that the hydration process (especially the induction period) is lengthened by low curing temperature. Both the electrical resistivity and compressive strength increase with an increase in the curing temperature. The compressive strength was reduced at a low curing temperature. Among these five curing temperatures, 5°C is the optimal curing temperature. Low temperatures do not change the kinds of hydrates, but reduce their amount. The scanning electron microscopy results illustrate that fewer hydrates fill the pores in specimens cured at low temperatures, while more hydrates form at higher temperatures. Moreover, low curing temperature contributes to the formation of coarse ettringite crystals. For the cement used at low temperature, the induction period should be reduced by adjusting the calcining process and composition proportion.

Rheological behaviors and structure build-up of 3D printed polypropylene and polyvinyl alcohol fiber-reinforced calcium sulphoaluminate cement composites

The uncontrollable printed structure and poor toughness of three dimensional (3D) printed cement composites hamper their application in buildings. In this study, the polypropylene (PP) and polyvinyl alcohol (PVA) fibers were introduced into the 3D printed calcium sulphoaluminate cement composites (CSACCs) to achieve the stable shape retention and high mechanical strength by controlling the rheological parameters. Experimental results show that the PP and PVA fibers enlarge the linear viscoelastic region (LVR) and increase the elastic modulus of CSACCs. Moreover, these two fibers clearly increase the yield stress and improve the thixotropy of CSACCs in the fiber content of 0.50–1.25%. The relationship between the rheological parameters and structure deformation is revealed by the radar map, and it indicates that the printed structure deformation is improved by controlling the coupling rheological parameters. Furthermore, both PP and PVA fibers are beneficial to the improvement of toughness in the 3D printed CSACCs, and the optimal contents are 0.75 and 1.00%, respectively. In conclusion, developing the 3D printed fiber-reinforced CSACCs with the controllable rheological parameters is significant for improving the printed structures and toughness, which shows a considerable potential in buildings.

Improvement Mechanism of Calcium Sulphoaluminate Cement on the Early Mechanical Properties of Shotcrete at Low Temperature

Improvement Mechanism of Calcium Sulphoaluminate Cement on the Early Mechanical Properties of Shotcrete at Low Temperature

Determination of sulfate content in OPC and CSA cement by sodium carbonate extraction method

The penetration of sulfate ions into the concrete often causes durability problems such as spalling, cracking, and strength loss. Traditional methods for sulfates content test in cement-based materials, a large number of toxic and high-risk chemical reagents such as hydrochloric acid, barium chloride, barium chromate are used. In this research, the sodium carbonate extraction (SCE) method was used to determine the sulfates content in Ordinary Portland cement (OPC) and Calcium sulphoaluminate (CSA) cement while the gravimetric method was used as standard method to evaluate the accuracy of SCE method. The optimum SCE method operation conditions were determined as 0.30 mol/L sodium carbonate solution, liquid–solid ratio at 100:1 and particle size smaller than 500 μm. The results indicated that the replacement of gravimetric method with SCE method for sulfates content test is acceptable in CSA cement but improper for Portland cement system. Through the FTIR, XRD, and TG-DSC analysis, it was found that the absorption of sulfate ions by C-S-H gels was responsible for the failure of SCE method in Portland cement system.

Application potential of Bacillus megaterium encapsulated by low alkaline sulphoaluminate cement in self-healing concrete

With the help of microbial mineralization to accelerate carbonate deposition, microbial self-healing concrete has developed into a promising technology because it is environmentally friendly. At the same time, how to assemble properly microorganisms and nutrients to reduce the negative impact on the performance of concrete itself has become a bottleneck of this technology. In this research, microbial spores of Bacillus megaterium, nutrients and low-alkaline carriers were assembled as a whole by extrusion. Low alkali calcium sulphoaluminate (CSA) cement was used as the carrier to protect spores from the high alkalinity environment caused by cement hydration. After studying the protective effect of this assembly method on spores, this integrated self-healing agent was applied in concrete, and then repairing efficiency of cracks was evaluated by area repairing ratio, recovery of water resistance, recovery of resistance to chloride ions and healing depth. Meanwhile, the repairing products were analyzed by XRD and SEM equipped with an EDS. Moreover, two different nutrients were used as precursors for microbial mineralization, and their negative effects have also been studied. The results showed that Bacillus megaterium could use glucose and calcium lactate as the precursors, and this new repairing system significantly improves the efficiency of self-healing. Compared to glucose, calcium lactate has a better repair effect when used as a precursor, and the average healing depth reached 4000 µm. At the same time, CSA cement was an excellent carrier for spores and could reduce the negative impact of nutrients on concrete when microorganisms and nutrients were assembled with CSA cement.