Sulphoaluminate Cement Mortar Research Articles

Multi-technique analysis of seawater impact on the performance of calcium sulphoaluminate cement mortar

The construction of offshore islands and reefs requires the development of new seawater sea-sand concrete materials. This study investigated the impact of seawater on the performance of calcium sulphoaluminate (CSA) cement mortar, with mechanism analyses by the acoustic emission (AE) and digital image correlation (DIC). For all uniaxial compression tests, cumulated AE, average AE frequency, rise angle, b-value, and βt coefficient were considered to perform the failure analysis. In addition, other techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were also employed to highlight the effects of seawater on the hydration products and microstructure of the CSA cement. The results show that seawater not only promotes the formation and growth of ettringite (AFt) but also interacts with cement hydration products to produce Friedel’s salt and various gel formations. Compared to freshwater mixing (0 %), using seawater mixing at normal concentrations (3.3 %) enhances the compactness of the CSA cement, thereby improving the strength and ductility of the CSA mortar. Specifically, the peak load increases from 77 kN to about 86 kN when mixed with seawater at normal concentration, whereas higher seawater concentrations (6.6 %, 9.9 %) resulted in a slight decrease in strength of the CSA mortar, with the peak load reaching approximately 80 kN, yet the ductility is enhanced, as evidenced by the softening post-peak branch of the loading curve. Additionally, AE bursts have a strong correlation with the fracture of the CSA mortar, which can also be forecast by the AE time-scaling coefficient βt. Therefore, when constructing oceanic island and reef foundations, this type of seawater sea-sand concrete is preferred due to its improved ductility and strength, which enhances the structural integrity of marine constructions and provides early warning for effective marine disaster prediction.

Mechanical properties of fiber‐reinforced calcium sulfoaluminate cement mortars

AbstractFiber contributes to the mechanical strength and toughness improvement of cementitious materials. In this study, effects of fibers types on the mechanical properties of sulphoaluminate (CSA) cement mortar were studied from aspects of mechanical strength and toughness. Polyvinyl alcohol fiber (PVAF) and steel fiber (SF) were chosen, with consecutive volumetric content from 0.4%, 0.8%, 1.2%, to 1.6%. Results show that the compressive strength of CSA cement mortar increases gradually with the increase of PVAF content within 1.2%. When the content exceeds 1.6%, the strength of PVAF reinforced CSA cement mortar decreases due to the agglomeration of fibers. The compressive strength of SF reinforced mortar increases with the increase of fiber content. Owing to the high bending stress and strength, SF shows better toughness in the bending test. PVAF exhibits better toughness in the tensile test, which is related to its better bonding with matrix.

Effect of nano admixtures on the engineering properties and microstructure of sulphoaluminate cement mortar at −10 °C

The traditional cement-based cementitious materials cannot hydrate at −10 °C, and the sulfoaluminate cement can hydrate, but the cement slurry has poor properties and low strength. Three kinds of nano admixtures (silica fume, nano-SiO2, nano-CaCO3) were selected as modified materials, and the effect of nano admixtures on the fluidity, strength, internal temperature, micro-morphology, mineral composition and pore structure of sulphoaluminate cement mortar were studied under the condition of mixing and curing of cooled materials at −10 °C. The results show that the fluidity, compressive strength and flexural strength of mortar increase first and then decrease with admixture content. When the content of silica fume, nano-SiO2 and nano-CaCO3 is 3 %, 0.5 % and 0.5 % respectively, the fluidity and strength of mortar are the maximum. With the optimum content of three kinds of nano admixtures, nano-SiO2 has the best improvement on the strength and internal temperature of mortar. The hydration of sulphoaluminate cement can continue at −10 °C. At the age of 1 d, ettringite is yielded in the mortar. After the addition of nano admixtures, the amount, characteristic diffraction peak and diffraction intensity of ettringite in mortar increase. The nano admixtures can optimize the pore structure of mortar with the age of 1 d. The fractal dimension of pore structure of mortar with 0.5% nano-SiO2 is the minimum.

Feasibility of using iron-rich phosphoaluminate cement to prepare anti-corrosive coatings for rebars

The anti-corrosive coating has been taken as an effective measure to keep rebars from corrosion. In this study, the iron-rich phosphoaluminate cement (IR-PAC) based anti-corrosive coating for rebar was prepared. The Cl- diffusion coefficient, strength against abrasion, and impact ductility of IR-PAC mortar were tested, with ordinary Portland cement (OPC) and sulphoaluminate cement (SAC) mortar as controls. The experimental results demonstrated that the chloride ion diffusion coefficient of IR-PAC was the lowest at any age. Compared with OPC and SAC, the strength against abrasion of IR-PAC at 90 d increased by 19.19 % and 14.32 %, respectively. The impact ductility of IR-PAC at 28 d increased by 28.21 % and 17.37 %, respectively. IR-PAC had good resistance to Cl- penetration, excellent strength against abrasion and impact ductility, which assisted the coating in blocking Cl- intrusion and resisting damage. The optimum SCMs based coating for rebar is as follows: 10.08 % Fly ash (FA), 0.1 % nano-silica (NS), and 0.65 % superplasticizer (SP). The coatings prepared with this formulation were used for electrochemical experiments. The rebars coated with IR- PAC had good corrosion resistance, which proved it is feasible to use IR-PAC to prepare anti-corrosive coatings for rebars.

A fast-setting and eco-friendly superhydrophobic high belite sulphoaluminate cement mortar

High belite sulphoaluminate cement (HBSC) has shown great potential as new lower CO2 footprint cementitious material. It makes sense to improve the hydrophobic property of HBSC to obtain high durability performance. In this paper, nontoxic short carbon chain lauric acid (LA) is used to match the early strength characteristic of HBSC to prepare fast-setting and eco-friendly LA-modified HBSC mortar (M-HBSCM). Sands modified with LA provide low surface energy for an integral hydrophobic effect. M-HBSCM exhibits superhydrophobicity even after hammering to expose the fractured internal structure, with a contact angle of 153.2°. And it shows outstanding self-cleaning property against contaminants such as sand and wet mud and a reduction in water absorption to around 23% of the ordinary HBSCM (O-HBSCM). The fabricated M-HBSCM has fast-setting property with an initial setting time of 29 min and a final setting time of 36 min. The abrasion test displays that the scratched area remains well superhydrophobic with high mechanical robustness when the droplets roll off on the inclined surface. Field-emission scanning electron microscope (FESEM) indicates that M-HBSCM contains more pores and coarser hydration products. The system of calcium alumina and pores exhibits a distinct hierarchical structure, providing the multilevel roughness required for the superhydrophobic surface. Fourier transform infrared (FTIR) spectrometer indicates that low surface energy functional groups have been successfully grafted onto M-HBSCM. The superhydrophobic concrete has good mechanical robustness, corrosion resistance, and fast-setting property, which can meet the demands of grouting reinforcement projects, the repair of various concrete structures, corrosion protection of marine structures and other projects.

The influence of different fine aggregate and cooling regimes on the engineering properties of sulphoaluminate cement mortar after heating

Previous experimental studies of sulphoaluminate cement after exposure to high temperatures have mainly concentrated on the resulting reduction of strength. Its behavior when heated continues to attract our attention because a systematic understanding of its heat-induced damage is needed to determine its reusability. The post-heating mechanical properties of sulphoaluminate cement mortar (SACM) made with three different types of fine aggregates after natural air cooling (NAC), water immersion cooling (WIC), and fire extinguisher cooling (FEC) are presented in this paper. Basalt and artificial sand have strong angularity, as indicated by their convexity and Wadell roundness values, which has an impact on improving their strength properties when heated. Convexity and Wadell roundness turn out to be independent, with convexity and circularity in good agreement. In addition, the loss of mechanical properties in river sand mortar was greater when either NAC or FEC was adopted than with WIC. The tests showed that independent of the type of sand, the SACM recovers its strength better when WIC or FEC is used in cooling rather than NAC.

Study on Carbonation Resistance of Polymer-Modified Sulphoaluminate Cement-Based Materials

The use of tricyclic copolymer latex (AMPS) can effectively improve the carbonation resistance of sulphoaluminate cement. This paper investigated polymer AMPS and polycarboxylic acid to modify sulphoaluminate cement materials by exploring the carbonation level of sulphoaluminate cement paste and mortar and the strength before and after carbonation. Then, the optimal dosage of polymer and polycarboxylic acid was obtained so that the carbonation resistance of sulphoaluminate cement reached the best state. The compressive strength was significantly improved by adding AMPS for sulphoaluminate cement paste and mortar. After carbonation, the strength decreased and combined with the carbonation level; it was concluded that the carbonation resistance of sulphoaluminate cement materials was the best when the optimal dosage of AMPS and polycarboxylic acid was 5% and 1.8%, respectively. Due to the addition of AMPS, the hydrated calcium aluminosilicate (C-A-S-H) and hydrated calcium silicate (C-S-H) gels, generated by the hydration of sulphoaluminate cement and the surface of unreacted cement particles, are wrapped by AMPS particles. The water is discharged through cement hydration. The polymer particles on the surface of the hydration product merge into a continuous film, which binds the cement hydration product together to form an overall network structure, penetrating the entire cement hydration phase and forming a polymer cement mortar with excellent structural sealing performance. To prevent the entry of CO2 and achieve the effect of anti-carbonation, adding polycarboxylic acid mainly improves the sample's internal density to achieve the anti-carbonation purpose.

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.

Effect of curing method on compressive strength of rapid hardening sulphoaluminate cement mortar at -10 °C

Rapid hardening sulphoaluminate cement has been widely studied and applied under low temperature, normal temperature and high temperature conditions, but the research under negative temperature conditions has just started. Through three curing methods: constant negative temperature curing, negative temperature changing positive temperature curing, and pre-curing, the influence of different curing methods on the compressive strength of rapid hardening sulphoaluminate cement mortar at -10 °C is discussed. The results show that pre-curing measures can significantly improve the early compressive strength of rapid hardening sulphoaluminate cement mortar. The longer the pre-curing time, the greater the compressive strength. Under the condition of -10 °C, the rapid hardening sulphoaluminate cement can still be continuously hydrated, and the hydration products remain unchanged.

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.

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.

Thermophysical Properties Characterization of Sulphoaluminate Cement Mortars Incorporating Phase Change Material for Thermal Energy Storage

Efficient use of solar energy by thermal energy storage composites and utilizing environmentally friendly cementitious materials are important trends for sustainable building composite materials. In this study, a paraffin/low density polyethylene (LDPE) composite shape-stabilized phase change material (SSPCM) was prepared and incorporated into a sulphoaluminate cement (SAC) mortar to prepare thermal energy storage mortar. The thermal and mechanical properties of SSPCM and a SAC-based thermal energy storage material (SCTESM) were investigated. The result of differential scanning calorimeter (DSC) analysis indicates that the latent heat of SCTESM is as high as 99.99 J/g. Thermogravimetric analysis demonstrates that the SCTESM does not show significant decomposition below 145 °C. The volume stability test shows the volume shrinkage percentage of the SCTESM is less than that of pure SAC mortar and far less than that of ordinary Portland cement mortar. The SCTESM has high early strength so that the compressive strength at 1-, 3-, and 7-day curing age is up to that at 28-day curing age of 67.5%, 78.3%, and 86.7%, respectively. Furthermore, a mathematical prediction model of the SCTESM compressive strength was proposed. The investigation of latent heat storage characteristics and the thermoregulating performance reveals that SCTESMs have the excellent capacity of heat storage and thermoregulating.

Enhancing ultra-early strength of sulphoaluminate cement-based materials by incorporating graphene oxide

Abstract In order to meet the increasing engineering requirements, the ultra-early strength of sulphoaluminate cement (SAC)-based materials need to be improved to achieve road repair, engineering rescue and other objectives. Graphene oxide (GO) of 0.04 wt% was incorporated into SAC mortar to prepare GO enhanced SAC mortar (GO-SAC). It was found that the compressive strength of GO-SAC was increased by 46.9% at the age of 6 hours, and the flexural strength of GO-SAC was increased by 121.4% at the age of 100 minutes, compared with the control SAC mortar. The mechanism analysis based on the characterization results derived from XRD, BET, in situ ATR-FTIR, hydration heat measurement, TG–DSC and SEM showed that, the addition of minute quantities of GO led to the formation and growth of ribbon-like AFt,which further resulted in the improvement of the ultra-early strength of GO-SAC. This work indicates that GO has great potential for practical application in the preparation of high-performance SAC-based materials with ultra-early strength.

Effect of SCMs on the freeze-thaw performance of iron-rich phosphoaluminate cement

Due to the low durability of ordinary Portland cement (OPC), the deterioration of OPC-based materials is very severe in marine structures exposed to cold weather. In contrast, iron-rich phosphoaluminate cement (iron-rich PAC) has good durability and is promising for applications in marine construction. In this context, in the present study, the freeze-thaw (F-T) performance of iron-rich PAC mortar was evaluated and compared with those of OPC and sulphoaluminate cement (SAC) mortars. In addition, the influences of supplementary cementitious materials (SCMs), such as fly ash (FA), limestone powder (LP) and gypsum (GP), on the F-T behaviour of the blended iron-rich PAC mortar were carefully investigated by testing the compressive and flexural strengths, analysing the pore structure using mercury intrusion porosimeter (MIP), and examining the microstructure using XRD and SEM-EDS analysis. The experimental results elucidated that the F-T performance of the iron-rich PAC mortar was far better than those of the OPC mortar and the SAC mortar. In the SCM blended iron-rich PAC systems, the most favourable modification results were obtained with replacement by LP at the optimum dosage of 3–9% (wt%). In this replacement range, the F-T resistances of the LP blended iron-rich PAC systems were better than that of the reference PAC (without SCMs). Further, the F-T performances of the FA and LP blended iron-rich PAC systems were superior to those of the OPC and SAC systems.

A Feasibility Study on HPMC-Improved Sulphoaluminate Cement for 3D Printing.

A novel 3D printing material based on hydroxypropyl methylcellulose (HPMC)—improved sulphoaluminate cement (SAC) for rapid 3D construction printing application is reported. The hydration heat, setting time, fluidity of paste and mortar, shape retainability, and compressive strength of extruded SAC mortar were investigated. HPMC dosage, water-to-cement (W/C) ratio, and sand-to-cement (S/C) ratio were studied as the experimental parameters. Hydration heat results reveal HPMC could delay the hydration of SAC. The initial and final setting time measured using Vicat needle would be shortened in the case of W/C ratio of 0.3 and 0.35 with HPMC dosage from 0.5% to 1.5%, W/C ratio of 0.40 with HPMC dosage of 0.5%, 0.75%, and 1.5%, and W/C ratio of 0.45 with HPMC dosage of 0.45, or be extended in the case of W/C ratio of 0.4 with HPMC dosage of 1.0% and W/C ratio of 0.45 with HPMC dosage from 0.75% to 1.5%. Fluidity measurement shows HPMC significantly improves the shape retainability. Furthermore, the addition of HPMC remarkably increased the compressive strength of extruded mortar. The results showed that HPMC could be used to prepare 3D printing SAC having satisfactory shape retainability, setting time and compressive strength.

Development of a novel sulphoalumitate cement-based composite combing fine steel fibers and phase change materials for thermal energy storage

To increase the mechanical strength and thermal energy storage/release efficiency, fine steel fibers and graphite-modified shape stabilized phase change materials (GM-SSPCM) were added into sulphoaluminate cement mortar. Paraffin, low density polyethylene and flake graphite were heating mixed to produce GM-SSPCM. Fine steel fibers were used to reinforce sulphoaluminate cement-based thermal energy storage composite (STESC) for improving mechanical strength and thermal conductivity. The thermophysical and microstructure of GM-SSPCM, and the thermal and mechanical properties of steel fiber reinforced sulphoaluminate cement-based thermal energy storage composite (SF-STESC) were investigated. The results indicated that about 50% paraffin could be effectively encapsulated in GM-SSPCM with multi-level space network structure. And, the steel fiber can increase the mechanical and thermal properties of SF-STESC. When a 3.5 vol% steel fiber was added, the 28-day compressive strength and flexural strength of the SF-STESC were increased by 7.3% and 40.6%, also the compressive/flexural strength ratio was decreased by 21.6%. The three-dimensional reinforcement of steel fibers reduced the volume shrinkage of the composites. In addition, the thermal conductivity of SF-STESC increases with the increase in volume fraction of the steel fibers. When the steel fiber volume fraction increases from 0 to 3.5%, the thermal conductivity of SF-STESC is increased by 51.3% while the inner paraffin is in solid state and 84.5% while the inner paraffin is in liquid state. The results of thermal energy storage/release performance tested using a self-designed setup showed that the steel fiber reinforced STESC leads to a high thermal energy storage/release rate.

Redispersible Polymer Powder-Modified Sulphoaluminate Cement Mortar

The super-softening property of redispersible polymer powder can improve the flexibility of cement-based materials while guarantees other work performances. In this study, the influences of different mixing amounts of redispersible polymer powders on the compressive strength, flexural strength, flexural compression ratio and bonding strength of sulphoaluminate cement mortar were investigated. The microscopic morphological structure of redispersible polymer powder-modified sulphoaluminate cement mortar was also observed through SEM to analyse the influence mechanism. Results show that, with the mixing amount of 2.0%, the compressive strength of cement mortar was improved. This mixing amount also increased the 28d flexural strength to 8.21 MPa (5.0% improvement) and 14d bonding strength to 5.6 MPa (27.3% improvement). Addition of more redispersible polymer powder resulted in the increase in flexural compression ratio because the powder particles formed water-insoluble continuous polymer colloidal film in hardened paste. This film generated a network with cement dydration products throughout the paste, consequently promoting the flexibility of cement.

Influence of Cement Type and Water-to-Cement Ratio on the Formation of Thaumasite

Cement mortar prisms were prepared with three different cement types and different water-to-cement ratios plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, these samples were submerged in 2% magnesium sulfate solution at 5°C and the visual appearance and strength development for every mortar were measured at intervals up to 1 year. Samples selected from the surface of prisms after 1-year immersion were examined by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The results show that mortars with sulfate resisting Portland cement (SRC) or sulphoaluminate cement (SAC) underwent weaker degradation due to the thaumasite form of sulfate attack than mortars with ordinary Portland cement (OPC). A lower water-to-cement ratio leads to better resistance to the thaumasite form of sulfate attack of the cement mortar. A great deal of thaumasite or thaumasite-containing materials formed in the OPC mortar, and a trace of thaumasite can also be detected in SRC and SAC mortars. Therefore, the thaumasite form of sulfate attack can be alleviated but cannot be avoided by the use of SAC or SRC.

Study on the Performance on Some Admixture of Sulphoaluminate Cement Waterproof Mortar

The influence of the naphthalene superplasticizer, aliphatic superplasticizer and water repellent on the properties of sulphoaluminate cement mortar such as strength and anti permeability was studied by orthogonal test method, and the microstructure of hydration products of hardened mortar was observed by X-Ray and SEM. The results showed that, adding amount of additive in sulphoaluminate cement, can improve mechanical properties of sulphoaluminate cement, and effectively improve waterproof performance and impermeability of mortar. When the water repellent admixture is 0.2%, the naphthalene superplasticizer 0.7%, aliphatic superplasticizer 1%, mortar impermeability is at its best, reaching 1.6MPa.

Influence of Polymer on Properties of Sulphoaluminate Cement Waterproof Mortar

This paper studies on the effects of different contents of redispersible emulsion powder and cellulose ether on mechanical properties of sulphoaluminate cement waterproof mortar, water absorption rate and impermeability, observes the microstructure of cement mortar by SEM and discusses the mechanism of polymer effects on properties of cement mortar. The results show that: as to the influence on strength, the two kinds of polymers may cause the decrease of early strength, but have no influence on the later strength; about water absorption rate, two polymers can significantly reduce the water absorption rate of sulphoaluminate cement mortar, and cellulose ether is slightly more effective than that of redispersible emulsion powder; as to the influence on impermeability, cellulose ether works far better than redispersible emulsion powder, especially when cellulose ether content reaches 1.5‰ and more, the impermeability pressure of sulphoaluminate cement mortar can reach above 2.2MPa.