Effects of low- and high-calcium fly ash on magnesium oxysulfate cement

Zhang, Na; Yu, Hongfa; Wang, Nan; Gong, Wei; Tan, Yongshan; Wu, Chengyou

doi:10.1016/j.conbuildmat.2019.04.185

Cited by 61 publications

(16 citation statements)

References 30 publications

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“…After adding filler Q into the MOS cement system, no new hydration products forms, but filler Q can accelerate the hydration of periclase to form phase 3-1-8, which can further reduce the time of forming phase 5-1-7. This phenomenon is similar to the results of MOS cement with granite powder and Portland cement with some crystallin mineral additions; it is ascribed to the physicochemical performances of SiO 2 [29,30,[49][50][51][52]. The addition of filler Q increases the fluidity of MOS cement slurry due to its dilution and dispersion effects [29,30,50,51], which inhibits the aggregation of periclase particles in the MOS system, increasing the contact area of active MgO in the MgSO 4 solution.…”

Section: Discussionsupporting

confidence: 72%

“…Table2shows the pore size distribution of MOS paste containing different filler Q contents at 28-d. A 15 wt.%-30 wt.% addition of filler Q increased the contents of pores with a diameter of 10~100 nm (small capillary pores) and <10 nm (gel pores), while reducing the content of pores with diameter of >100 nm (large pore) for MOS cement. Furthermore, the 28-d total pore volume of MOS paste containing 15 wt.%~30 wt.% of filler Q was lower than that of MOS paste containing 50 wt.% of low-or high-calcium fly ash with D 50 of 5~10 µm[49]. The 28-d large pore of samples prepared using filler Q was much lower than that of the MOS samples which was prepared by using 20 wt.%~40 wt.% of filler granite with D 50 of approximately 10 µm[6].…”

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confidence: 87%

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Study of Using Quartz Powder as a Mineral Admixture to Produce Magnesium Oxysulfate Cement

Wang,

Pang,

Chen

et al. 2023

Minerals

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Magnesium oxysulfate (MOS) cement features potential advantages, including light weight, green and environmental protection, low thermal conductivity, and high frost- and fire-resistance, but its poor mechanical strength limits the extensive utilization in the architectural engineering. In this study, low-cost quartz (Q) was used as a mineral admixture to increase the mechanical strength of MOS pastes. The impact of the filler Q on the early and later mechanical strength of MOS cement was investigated, in which also had an impact on fluidity, setting times, volume stability, hydration processes, phase transformations, and microstructure. The results show that hydration of periclase to form 5Mg(OH)2·MgSO4·7H2O (phase 5-1-7) in this system was a multi-stage reaction process. 3Mg(OH)2·MgSO4·8H2O was the first sediment in this system and was converted into phase 5-1-7. The dilution and dispersion effects of the filler Q increased the early hydration rate, shortened the setting time, and increased the content and crystallite size of phase 5-1-7, increasing the early mechanical strength of MOS cement, while the volume-filling effect of the filler Q reduced the content of large pore and total pore volume, and improved the pore structure of the MOS cement, improving the later mechanical strength of MOS cement. MOS cement containing 15 wt.% of filler Q exhibited the highest early and later mechanical strength, and the lowest volume shrinkage, which is more suitable for application in architectural engineering. Based on these results, filler Q can be used as an enhancer in MOS cement, however its enhancement mechanisms are effective only when the content of filler Q is no more than 20 wt.%.

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Section: Discussionsupporting

confidence: 72%

mentioning

confidence: 87%

Study of Using Quartz Powder as a Mineral Admixture to Produce Magnesium Oxysulfate Cement

Wang,

Pang,

Chen

et al. 2023

Minerals

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“…In this work, the ultimate hydration stage corresponds to 80% hydration degree and is referred to as such stage in which the diffusion behavior is dominated in the paste. From these figures, it is expected that small MgO particles are totally hydrated due to the rapid reaction, while the The phase compositions of MOS pastes obtained from this work are compared with the ones from other literature [3,9,57], as shown in Table 10. Accordingly, when M = 8, the mass fractions of Phase 517 predicted in this work are 65.82 and 44.93 for H = 20 and H = 11, respectively, while the ones are 60.24 and 48.69 obtained from the previous experimental works.…”

Section: Initial and Ultimate Hydration Stagesmentioning

confidence: 90%

“…Therefore, in practical application of MOS cement, the appropriate value of H should be taken around 14 to 16 to form MOS cement paste with higher mechanical strength and better water resistance. The phase compositions of MOS pastes obtained from this work are compared with the ones from other literature [3,9,57], as shown in Table 10. Accordingly, when M = 8, the mass fractions of Phase 517 predicted in this work are 65.82 and 44.93 for H = 20 and H = 11, respectively, while the ones are 60.24 and 48.69 obtained from the previous experimental works.…”

Section: Influence Of Molar Ratios On Hydrated Productsmentioning

confidence: 99%

Fractal Analysis on Pore Structure and Hydration of Magnesium Oxysulfate Cements by First Principle, Thermodynamic and Microstructure-Based Methods

Huang

et al. 2021

Fractal Fract

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Magnesium oxysulfate (MOS) cement is a typical eco-friendly cementitious material, which presents excellent performances. In this work, a novel multiscale modeling strategy is proposed to simulate the hydration and pore structure of MOS cement system. This work collected and evaluated the Gibbs free energy of formation for main hydrates and equilibrium constant of main reactions in MOS cement system based on a first principle calculation using Material Studio. Followingly, the equilibrium phase compositions of MOS cement system were simulated through PHREEQC to investigate the molar ratio dependence of equilibrium phase compositions. Results showed that large M (MgO/MgSO4) was beneficial for the formation of 5Mg(OH)2·MgSO4·7H2O (Phase 517) and large H (H2O/MgSO4) tended to decompose MOS cement paste and cause leaching. The microstructure-based method visualized the hydration status of MOS cement systems at initial and ultimate stages via MATLAB and the results showed that large M was significant to reduce porosity, and similar results for the case of small H. Fractal analysis confirms that fractal dimension of pore structure (Df) was significantly decreased after the hydration of MOS and was positively correlated to the porosity of the paste. In addition, it can be referred that large M and small H were beneficial for modifying the microstructure of MOS paste by decreasing the value of Df.

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“…Adding FA to OPC concrete members subjected to impact and dynamic loads is also recommended to enhance the microcrack resistance [21]. The complete replacement of OPC concrete with FA has been widely assessed [22][23][24][25][26][27][28][29][30][31]. However, most of the previous studies on AA concrete have focused mainly on the mix design and microscale investigation [22][23][24], which supports the potential of FA as a promising building material [24][25][26][27][28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%

Tension Stiffening and Cracking Behavior of Axially Loaded Alkali-Activated Concrete

Abdulrahman,

Muhamad,

Shukri

et al. 2023

Materials

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Alkali-activated concrete is an eco-friendly construction material that is used to preserve natural resources and promote sustainability in the construction industry. This emerging concrete consists of fine and coarse aggregates and fly ash that constitute the binder when mixed with alkaline activators, such as sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). However, understanding its tension stiffening and crack spacing and width is of critical importance in fulfilling serviceability requirements. Therefore, this research aims to evaluate the tension stiffening and cracking performance of alkali-activated (AA) concrete. The variables considered in this study were compressive strength (fc) and concrete cover-to-bar diameter (Cc/db) ratios. After casting the specimen, they were cured before testing at ambient curing conditions for 180 days to reduce the effects of concrete shrinkage and obtain more realistic cracking results. The results showed that both AA and OPC concrete prisms develop slightly similar axial cracking force and corresponding cracking strain, but OPC concrete prisms exhibited a brittle behavior, resulting in a sudden drop in the load–strain curves at the crack location. In contrast, AA concrete prisms developed more than one crack simultaneously, suggesting a more uniform tensile strength compared to OPC specimens. The tension-stiffening factor (β) of AA concrete exhibited better ductile behavior than OPC concrete due to the strain compatibility between concrete and steel even after crack ignition. It was also observed that increasing the confinement (Cc/db ratio) around the steel bar delays internal crack formation and enhances tension stiffening in AAC. Comparing the experimental crack spacing and width with the values predicted using OPC codes of practice, such as EC2 and ACI 224R, revealed that EC2 tends to underestimate the maximum crack width, while ACI 224R provided better predictions. Thus, models to predict crack spacing and width have been proposed accordingly.

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Effects of low- and high-calcium fly ash on magnesium oxysulfate cement

Cited by 61 publications

References 30 publications

Study of Using Quartz Powder as a Mineral Admixture to Produce Magnesium Oxysulfate Cement

Study of Using Quartz Powder as a Mineral Admixture to Produce Magnesium Oxysulfate Cement

Fractal Analysis on Pore Structure and Hydration of Magnesium Oxysulfate Cements by First Principle, Thermodynamic and Microstructure-Based Methods

Tension Stiffening and Cracking Behavior of Axially Loaded Alkali-Activated Concrete

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