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Barbara Lothenbach - One of the best experts on this subject based on the ideXlab platform.
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effect of temperature curing on properties and hydration of wollastonite blended Magnesium Potassium Phosphate cements
Cement and Concrete Research, 2021Co-Authors: Frank Winnefeld, Barbara LothenbachAbstract:Abstract K-struvite, the main hydrate of Magnesium Potassium Phosphate (MKP) cements, dehydrates at ~50 °C, thus elevated temperatures at service conditions could affect cement properties and durability. In this study, properties and hydration of MKP cement without and with wollastonite were investigated at 20 and 50 °C. In hydrated pure MKP cement K-struvite decomposes progressively over time to MgKPO4·H2O at 50 °C, which leads to a strong reduction of solid volume and severe strength loss. The presence of wollastonite significantly slows down the decomposition rate of K-struvite, which is still observed after 393 days at 50 °C. K-struvite together with amorphous hydroxyapatite, M-(C)-S-H and CaK3H(PO4)2 from the wollastonite reaction result in a cement with good short and long-term strength at both 20 and 50 °C.
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Influence of wollastonite on hydration and properties of Magnesium Potassium Phosphate cements
Cement and Concrete Research, 2020Co-Authors: Barbara Lothenbach, Frank WinnefeldAbstract:Abstract This study investigates the effect of wollastonite on the hydration and properties of Magnesium Potassium Phosphate (MKP) cements. In MKP cements some efflorescence can occur; the presence of wollastonite suppresses efflorescence as the formation of Mg2KH(PO4)2·15H2O is prevented. The presence of wollastonite leads also to more heat (per g of MKP cement) due to the filler effect and due to the reaction of wollastonite, which increases strength, especially at low water-to-binder (w/b) ratio of 0.25 and at later ages, and lowers the pH values in the cement pore solution. The reaction of wollastonite does not lead to the formation of crystalline hydrates, both experimental and thermodynamic findings suggest the formation of amorphous hydroxyapatite and Magnesium silicate hydrates (M-S-H).
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influence of Magnesium to Phosphate ratio and water to cement ratio on hydration and properties of Magnesium Potassium Phosphate cements
Cement and Concrete Research, 2019Co-Authors: Frank Winnefeld, Barbara Lothenbach, Josef KaufmannAbstract:Abstract Magnesium-to-Phosphate (Mg/PO4) and water-to-cement (w/c) ratios are important factors controlling hydration and properties of Magnesium Potassium Phosphate (MKP) cements. This study investigated the influence of Mg/PO4 molar ratios (2.7, 4 and 8) and w/c (0.25 and 5) on cement hydration, compressive strength and volume stability. Low w/c ratio slowed down cement hydration at lower Mg/PO4 beyond 1 day, and prevented the precipitation of intermediate hydrates at higher Mg/PO4. At lower Mg/PO4 expansion and strength loss were observed with time due to the continuing hydration within the already hardened cement. Higher Mg/PO4 resulted in faster hydration, higher strength, and in the precipitation of traces of brucite, which had no significant influence on the long-term volume stability and strength. Therefore, moderate Mg/PO4 molar ratios between 4 and 8 depending on w/c ratio used are recommended for the production of MKP cements with robust performance.
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properties of fly ash blended Magnesium Potassium Phosphate mortars effect of the ratio between fly ash and magnesia
Cement & Concrete Composites, 2018Co-Authors: Barbara LothenbachAbstract:Abstract The ratio between fly ash (FA) and magnesia is an important factor for the optimum design of FA blended Magnesium Potassium Phosphate cements (MKPCs). In this study, a high CaO content FA (CaO = 12.5 wt%) was used to partially replace magnesia at 0 wt%, 30 wt%, 50 wt%, 70 wt%, and 90 wt%, respectively. The experimental results showed that a FA replacement of 50 wt% led to the highest compressive strengths. A FA replacement of 70 wt% is considered as upper limit, as the presence of more FA caused significantly lower strength. In the plain and the FA blended MKPCs, K-struvite (MgKPO4⋅6H2O) was the main hydrate. At very high FA contents, additional calcium Potassium hydrogen Phosphate (CaK3H(PO4)2) was observed as well as the destabilization of K-struvite to cattiite (Mg3(PO4)2⋅22H2O), which could be one of the main factors responsible for the lower strength of high FA blended MKPC mortars stored under water.
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reaction mechanism of Magnesium Potassium Phosphate cement with high Magnesium to Phosphate ratio
Cement and Concrete Research, 2018Co-Authors: Barbara Lothenbach, Andreas Leemann, Frank WinnefeldAbstract:Abstract Understanding reaction mechanisms of Magnesium Potassium Phosphate (MKP) cement is of significant importance, as it is closely related to the optimum design of MKP cement-based materials. In this study, reaction mechanisms of MKP cements with a high Magnesium-to-Phosphate (Mg/PO4) molar ratio of 8 were investigated at two different water-to-solid (w/s) ratios of 0.5 and 5. The experimental findings show that the use of this high Mg/PO4 molar ratio suppresses the formation of Potassium-free Magnesium Phosphate hydrates. K-struvite is mainly formed with probably more Phosphate than the theoretical value. Moreover, the w/s ratio plays a crucial role on governing the reaction path of MKP cements. The lower w/s ratio (w/s = 0.5) leads to higher Potassium concentration and pH value, thus suppressing the formation of intermediate product, Mg2KH(PO4)2·15H2O, which is formed at the higher w/s = 5. However, it causes the formation of minor amount of brucite at 28 d, which coexists with K-struvite in the paste.
Jianming Yang - One of the best experts on this subject based on the ideXlab platform.
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study on water instability of Magnesium Potassium Phosphate cement mortar based on low field 1h nuclear magnetic resonance
Measurement, 2021Co-Authors: Yong Wang, Zhining Liu, Weidong Zhuo, Qiang Yuan, Changping Chen, Jianming YangAbstract:Abstract Low-field 1H nuclear magnetic resonance (LF-NMR) is applied to investigate water instability of Magnesium Potassium Phosphate cement (MKPC) mortar immersed in neutral and alkaline solutions, aiming to introduce a in-situ monitoring of microstructure to demonstrate the deterioration process of MKPC mortar. By tracking the evolution of water bearing pore, the deterioration is well characterized, and mainly attributed to the coarsening of micro-pores in the K-struvite network. Compared with tap water, 2.5 wt% NaCl and MgSO4 solutions, dramatical deterioration of strength and microstructure are detected in the MKPC mortar exposed in 2.5 wt% NaOH solution. In addition, the millimeter sized water cavity is formed due to the opening of the spherical closed pores in the later exposure stage in both neutral and alkaline solutions.
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influence of nickel slag powders on properties of Magnesium Potassium Phosphate cement paste
Construction and Building Materials, 2019Co-Authors: Qi Wang, Changjuan Yu, Xuancheng Xu, Linlin Chong, Jianming Yang, Qisheng WuAbstract:Abstract This paper aims to study the effect of nickel slag powders on the properties of Potassium Magnesium Phosphate cement (MKPC) paste. MKPC pastes containing different contents of nickel slag powders were prepared. We then tested their fluidity, setting time, compressive strength, the residual ratio of compressive strength under water curing condition, shrinkage deformation and hydration temperature. The micro morphology and the phase compositions of hardened MKPC pastes were also analyzed. The results indicate that adding some nickel slag powders in MKPC can improve the particle gradation of alkali components in MKPC and further improve the fluidity of fresh MKPC paste. The water stability of MKPC paste can be improved obviously by adding 30–40% nickel slag powders. The 60-day compressive strength of MKPC paste with 30–40% nickel slag powers exceeds 70 MPa and the residual ratio of compressive strength under water curing condition is higher than 100%. This should be attributed to the decrease in the proportion of harmful pores in hardened MKPC paste with some nickel slag powers. In addition, adding some nickel slag powders can obviously reduce the shrinkage deformation of MKPC paste. The 60-day drying shrinkage rate of hardened MKPC paste with 30% nickel slag powders is only 48.2% of that of the reference sample without nickel slag powders. This is attributed to the improvement of particle size distribution of alkali components, the micro-aggregate effect of nickel slag powders and less water use. These factors result in the decrease in the total porosity of the hardened MKPC paste with nickel slag powders and finally smaller shrinkage deformation.
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Effect of Municipal Solid Waste Incineration Fly Ash on Properties of Magnesium Potassium Phosphate Paste
Journal of Materials in Civil Engineering, 2019Co-Authors: Jianming Yang, Shucong ZhenAbstract:AbstractThis paper studied the effect of municipal solid waste incineration fly ash (MSWI FA) on properties of Magnesium Potassium Phosphate cement (MKPC) paste. MKPC pastes containing different co...
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effect of curing regime on water resistance of Magnesium Potassium Phosphate cement
Construction and Building Materials, 2017Co-Authors: Linlin Chong, Jianming Yang, Caijun ShiAbstract:Abstract In this paper, the effects of curing conditions (dry air, moist air and water), state of water (static water and flowing water) and initial air curing time (5 h, 3 d and 28 d) on the corrosion behavior of Magnesium–Potassium Phosphate cement (MKPC) paste subjected to water attack were investigated. The strength residual ratio and mass loss rate were used as deterioration indexes of MKPC paste in water. The pH value and leaching amounts of soaking liquid were also employed to evaluate the water corrosion behavior. X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-gravimetry analysis (TG) and mercury intrusion porosimetry (MIP) were used to investigate the microstructure of MKPC paste before and after water corrosion. The experimental results showed that the water environment lead to a lower compressive strength of MKPC pastes, but the strength loss of MKPC paste under the flowing water curing was higher. Furthermore, prolonged initial air curing time could improve the water resistance of MKPC pastes, the specimens cured in air for the first 3 days then in water showed the best water resistance among all specimens immersed in water for 60 days. The deterioration mechanism of MKPC paste derived from the strength and mass loss test results was also clarified based on microstructural observation.
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the effect of seawater curing on properties of Magnesium Potassium Phosphate cement
Construction and Building Materials, 2017Co-Authors: Jianming Yang, Qingqing Tang, Zhixiang SunAbstract:Abstract This paper investigated the effect of early seawater curing on properties of Magnesium Potassium Phosphate cement (MKPC) paste. First, the MKPC paste was prepared by mixing overburning MgO powders, KH 2 PO 4 , the composite retarder (CR) and water in a certain proportion. Then, we measured the compressive strength, drying shrinkage deformation, and mass change of it under different curing conditions. The results were as follows. For MKPC paste specimens under seawater curing condition, the hydration ages before they were soaked in seawater had a significant effect on their compressive strength, drying shrinkage and mass increase. For MKPC paste specimens cured in seawater after 3-day natural curing, their 28-day and 60-day compressive strengths were 112.8% and 105.4% of those of MKPC paste specimens with same hydration ages under natural curing condition, respectively. In addition, the 60-day shrinkage strain of them (0.82 × 10 −4 ) was significantly less than that of MKPC paste specimens with the same hydration age under natural curing condition (5.14 × 10 −4 ). Moreover, they had higher mass increase ratio (1.23%). These were due to higher production, higher degree of crystallinity and less defects of MKP crystals, and more perfect pore size distribution in MKPC specimens soaked in seawater after 3-day natural curing.
Neil C Hyatt - One of the best experts on this subject based on the ideXlab platform.
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response to the discussion by hongyan ma and ying li of the paper characterization of Magnesium Potassium Phosphate cement blended with fly ash and ground granulated blast furnace slag
Cement and Concrete Research, 2018Co-Authors: Laura J Gardner, Susan A Bernal, Sam A Walling, Claire L Corkhill, John L Provis, Neil C HyattAbstract:We recently reported the first comprehensive investigation of Magnesium Potassium Phosphate cements (MKPCs) blended with supplementary cementitious materials (pulverized fuel ash and granulated blast furnace slag) for the encapsulation of radioactive wastes [Gardner et al., Cem. Concr. Res. 74 (2015) 78–87]. Using a combination of characterization techniques, we demonstrated the important role of the reaction of the supplementary cementitious materials in contributing to the development of the microstructure and strength of MKPC composites. Here, we clarify aspects of our experimental design, and elaborate on the interpretation of our data, following discussion by Ma and Li.
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evolution of phase assemblage of blended Magnesium Potassium Phosphate cement binders at 200 and 1000 c
Advances in Applied Ceramics, 2015Co-Authors: Laura J Gardner, Susan A Bernal, Claire L Corkhill, John L Provis, V Lejeune, Martin C Stennett, Neil C HyattAbstract:The fire performance of Magnesium Potassium Phosphate cement (MKPC) binders blended with fly ash (FA) and ground granulated blast furnace slag (GBFS) was investigated up to 1000°C using X-ray diffraction, thermogravimetric analysis and SEM techniques. The FA/MKPC and GBFS/MKPC binders dehydrate above 200°C to form amorphous KMgPO4, concurrent with volumetric and mass changes. Above 1000°C, additional crystalline phases were formed and microstructural changes occurred, although no cracking or spalling of the samples was observed. These results indicate that FA/MKPC and GBFS/MKPC binders are expected to have satisfactory fire performance under the fire scenario conditions relevant to the operation of a UK or other geological disposal facility
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evolution of phase assemblage of blended Magnesium Potassium Phosphate cement binders at 200 degrees and 1000 degrees c
2015Co-Authors: Laura J Gardner, Susan A Bernal, Claire L Corkhill, John L Provis, V Lejeune, Martin C Stennett, Neil C HyattAbstract:The fire performance of Magnesium Potassium Phosphate cement (MKPC) binders blended with fly ash (FA) and ground granulated blast furnace slag (GBFS) was investigated up to 1000°C using X-ray diffraction, thermogravimetric analysis and SEM techniques. The FA/MKPC and GBFS/MKPC binders dehydrate above 200°C to form amorphous KMgPO4, concurrent with volumetric and mass changes. Above 1000°C, additional crystalline phases were formed and microstructural changes occurred, although no cracking or spalling of the samples was observed. These results indicate that FA/MKPC and GBFS/MKPC binders are expected to have satisfactory fire performance under the fire scenario conditions relevant to the operation of a UK or other geological disposal facility.
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characterisation of Magnesium Potassium Phosphate cements blended with fly ash and ground granulated blast furnace slag
Cement and Concrete Research, 2015Co-Authors: Laura J Gardner, Susan A Bernal, Sam A Walling, Claire L Corkhill, John L Provis, Neil C HyattAbstract:Abstract Magnesium Potassium Phosphate cements (MKPCs), blended with 50 wt.% fly ash (FA) or ground granulated blast furnace slag (GBFS) to reduce heat evolution, water demand and cost, were assessed using compressive strength, X-ray diffraction (XRD), scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) spectroscopy on 25 Mg, 27 Al, 29 Si, 31 P and 39 K nuclei. We present the first definitive evidence that dissolution of the glassy aluminosilicate phases of both FA and GBFS occurred under the pH conditions of MKPC. In addition to the main binder phase, struvite-K, an amorphous orthoPhosphate phase was detected in FA/MKPC and GBFS/MKPC systems. It was postulated that an aluminium Phosphate phase was formed, however, no significant Al–O–P interactions were identified. High-field NMR analysis of the GBFS/MKPC system indicated the potential formation of a Potassium-aluminosilicate phase. This study demonstrates the need for further research on these binders, as both FA and GBFS are generally regarded as inert fillers within MKPC.
Laura J Gardner - One of the best experts on this subject based on the ideXlab platform.
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response to the discussion by hongyan ma and ying li of the paper characterization of Magnesium Potassium Phosphate cement blended with fly ash and ground granulated blast furnace slag
Cement and Concrete Research, 2018Co-Authors: Laura J Gardner, Susan A Bernal, Sam A Walling, Claire L Corkhill, John L Provis, Neil C HyattAbstract:We recently reported the first comprehensive investigation of Magnesium Potassium Phosphate cements (MKPCs) blended with supplementary cementitious materials (pulverized fuel ash and granulated blast furnace slag) for the encapsulation of radioactive wastes [Gardner et al., Cem. Concr. Res. 74 (2015) 78–87]. Using a combination of characterization techniques, we demonstrated the important role of the reaction of the supplementary cementitious materials in contributing to the development of the microstructure and strength of MKPC composites. Here, we clarify aspects of our experimental design, and elaborate on the interpretation of our data, following discussion by Ma and Li.
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evolution of phase assemblage of blended Magnesium Potassium Phosphate cement binders at 200 and 1000 c
Advances in Applied Ceramics, 2015Co-Authors: Laura J Gardner, Susan A Bernal, Claire L Corkhill, John L Provis, V Lejeune, Martin C Stennett, Neil C HyattAbstract:The fire performance of Magnesium Potassium Phosphate cement (MKPC) binders blended with fly ash (FA) and ground granulated blast furnace slag (GBFS) was investigated up to 1000°C using X-ray diffraction, thermogravimetric analysis and SEM techniques. The FA/MKPC and GBFS/MKPC binders dehydrate above 200°C to form amorphous KMgPO4, concurrent with volumetric and mass changes. Above 1000°C, additional crystalline phases were formed and microstructural changes occurred, although no cracking or spalling of the samples was observed. These results indicate that FA/MKPC and GBFS/MKPC binders are expected to have satisfactory fire performance under the fire scenario conditions relevant to the operation of a UK or other geological disposal facility
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evolution of phase assemblage of blended Magnesium Potassium Phosphate cement binders at 200 degrees and 1000 degrees c
2015Co-Authors: Laura J Gardner, Susan A Bernal, Claire L Corkhill, John L Provis, V Lejeune, Martin C Stennett, Neil C HyattAbstract:The fire performance of Magnesium Potassium Phosphate cement (MKPC) binders blended with fly ash (FA) and ground granulated blast furnace slag (GBFS) was investigated up to 1000°C using X-ray diffraction, thermogravimetric analysis and SEM techniques. The FA/MKPC and GBFS/MKPC binders dehydrate above 200°C to form amorphous KMgPO4, concurrent with volumetric and mass changes. Above 1000°C, additional crystalline phases were formed and microstructural changes occurred, although no cracking or spalling of the samples was observed. These results indicate that FA/MKPC and GBFS/MKPC binders are expected to have satisfactory fire performance under the fire scenario conditions relevant to the operation of a UK or other geological disposal facility.
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characterisation of Magnesium Potassium Phosphate cements blended with fly ash and ground granulated blast furnace slag
Cement and Concrete Research, 2015Co-Authors: Laura J Gardner, Susan A Bernal, Sam A Walling, Claire L Corkhill, John L Provis, Neil C HyattAbstract:Abstract Magnesium Potassium Phosphate cements (MKPCs), blended with 50 wt.% fly ash (FA) or ground granulated blast furnace slag (GBFS) to reduce heat evolution, water demand and cost, were assessed using compressive strength, X-ray diffraction (XRD), scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) spectroscopy on 25 Mg, 27 Al, 29 Si, 31 P and 39 K nuclei. We present the first definitive evidence that dissolution of the glassy aluminosilicate phases of both FA and GBFS occurred under the pH conditions of MKPC. In addition to the main binder phase, struvite-K, an amorphous orthoPhosphate phase was detected in FA/MKPC and GBFS/MKPC systems. It was postulated that an aluminium Phosphate phase was formed, however, no significant Al–O–P interactions were identified. High-field NMR analysis of the GBFS/MKPC system indicated the potential formation of a Potassium-aluminosilicate phase. This study demonstrates the need for further research on these binders, as both FA and GBFS are generally regarded as inert fillers within MKPC.
Ying Li - One of the best experts on this subject based on the ideXlab platform.
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discussion of the paper characterisation of Magnesium Potassium Phosphate cement blended with fly ash and ground granulated blast furnace slag by l j gardner et al
Cement and Concrete Research, 2018Co-Authors: Ying LiAbstract:Abstract A recently published paper authored by Gardner et al. [Characterisation of Magnesium Potassium Phosphate cement blended with fly ash and ground granulated blast furnace slag, Cem. Concr. Res. 74 (2015) 78–87] is discussed. This work is of great significance in understanding the reaction mechanism of Magnesium Potassium Phosphate cement blended with supplementary cementitious materials. However, several points in this work need to be further discussed, as shown in this discussion, including the mix proportion, paste morphology, mechanism of the synergy between MKPC and fly ash/ground granulated blast furnace slag.
