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Chi Sun Poon - One of the best experts on this subject based on the ideXlab platform.
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degree of hydRation and gel Space Ratio of high volume fly ash cement systems
Cement and Concrete Research, 2000Co-Authors: Y L Wong, Chi Sun PoonAbstract:Although fly ash has been widely used in concrete as a cement replacement, little work has been done on determining the degree of hydRation of high-volume fly ash/cement (FC) systems. In the present study, the degree of hydRation of the cement in Portland cement (PC) paste was obtained by determining the non-evaporable water (Wn) content. The degree of reaction of the fly ash in FC pastes was determined using a selective dissolution method. Based on the relation between the degree of cement hydRation and effective water-to-cement (w/c) Ratio, the degree of hydRation of the cement in FC pastes was also estimated. It was found that high-volume fly ash pastes underwent a lower degree of fly ash reaction, and in the pastes with 45% to 55% fly ash, more than 80% of the fly ash still remained unreacted after 90 days of curing while the hydRation of the cement in high-volume fly ash pastes was enhanced because of the higher effective w/c Ratio for the paste. This effect was more significant for the pastes with lower water-to-binder (w/b) Ratios. Thus, preparing high-volume fly ash concrete at lower w/b Ratios can result in less strength losses. This paper also introduces a model to describe the relationship between the w/c Ratio and the degree of cement hydRation and gel/Space Ratio. The gel/Space Ratios of the FC pastes, evaluated based on the proposed model, were found to be consistent with the gel/Space Ratio of PC pastes in terms of the relationship with compressive strength. The gel/Space Ratio data correlated (inversely) linearly with mercury intruded porosity, but the former correlated more with compressive strength than the latter.
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Degree of hydRation and gel/Space Ratio of high-volume fly ash/cement systems
Cement and Concrete Research, 2000Co-Authors: Linda Lam, Y L Wong, Chi Sun PoonAbstract:Although fly ash has been widely used in concrete as a cement replacement, little work has been done on determining the degree of hydRation of high-volume fly ash/cement (FC) systems. In the present study, the degree of hydRation of the cement in Portland cement (PC) paste was obtained by determining the non-evaporable water (Wn) content. The degree of reaction of the fly ash in FC pastes was determined using a selective dissolution method. Based on the relation between the degree of cement hydRation and effective water-to-cement (w/c) Ratio, the degree of hydRation of the cement in FC pastes was also estimated. It was found that high-volume fly ash pastes underwent a lower degree of fly ash reaction, and in the pastes with 45% to 55% fly ash, more than 80% of the fly ash still remained unreacted after 90 days of curing while the hydRation of the cement in high-volume fly ash pastes was enhanced because of the higher effective w/c Ratio for the paste. This effect was more significant for the pastes with lower water-to-binder (w/b) Ratios. Thus, preparing high-volume fly ash concrete at lower w/b Ratios can result in less strength losses. This paper also introduces a model to describe the relationship between the w/c Ratio and the degree of cement hydRation and gel/Space Ratio. The gel/Space Ratios of the FC pastes, evaluated based on the proposed model, were found to be consistent with the gel/Space Ratio of PC pastes in terms of the relationship with compressive strength. The gel/Space Ratio data correlated (inversely) linearly with mercury intruded porosity, but the former correlated more with compressive strength than the latter.
Y L Wong - One of the best experts on this subject based on the ideXlab platform.
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degree of hydRation and gel Space Ratio of high volume fly ash cement systems
Cement and Concrete Research, 2000Co-Authors: Y L Wong, Chi Sun PoonAbstract:Although fly ash has been widely used in concrete as a cement replacement, little work has been done on determining the degree of hydRation of high-volume fly ash/cement (FC) systems. In the present study, the degree of hydRation of the cement in Portland cement (PC) paste was obtained by determining the non-evaporable water (Wn) content. The degree of reaction of the fly ash in FC pastes was determined using a selective dissolution method. Based on the relation between the degree of cement hydRation and effective water-to-cement (w/c) Ratio, the degree of hydRation of the cement in FC pastes was also estimated. It was found that high-volume fly ash pastes underwent a lower degree of fly ash reaction, and in the pastes with 45% to 55% fly ash, more than 80% of the fly ash still remained unreacted after 90 days of curing while the hydRation of the cement in high-volume fly ash pastes was enhanced because of the higher effective w/c Ratio for the paste. This effect was more significant for the pastes with lower water-to-binder (w/b) Ratios. Thus, preparing high-volume fly ash concrete at lower w/b Ratios can result in less strength losses. This paper also introduces a model to describe the relationship between the w/c Ratio and the degree of cement hydRation and gel/Space Ratio. The gel/Space Ratios of the FC pastes, evaluated based on the proposed model, were found to be consistent with the gel/Space Ratio of PC pastes in terms of the relationship with compressive strength. The gel/Space Ratio data correlated (inversely) linearly with mercury intruded porosity, but the former correlated more with compressive strength than the latter.
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Degree of hydRation and gel/Space Ratio of high-volume fly ash/cement systems
Cement and Concrete Research, 2000Co-Authors: Linda Lam, Y L Wong, Chi Sun PoonAbstract:Although fly ash has been widely used in concrete as a cement replacement, little work has been done on determining the degree of hydRation of high-volume fly ash/cement (FC) systems. In the present study, the degree of hydRation of the cement in Portland cement (PC) paste was obtained by determining the non-evaporable water (Wn) content. The degree of reaction of the fly ash in FC pastes was determined using a selective dissolution method. Based on the relation between the degree of cement hydRation and effective water-to-cement (w/c) Ratio, the degree of hydRation of the cement in FC pastes was also estimated. It was found that high-volume fly ash pastes underwent a lower degree of fly ash reaction, and in the pastes with 45% to 55% fly ash, more than 80% of the fly ash still remained unreacted after 90 days of curing while the hydRation of the cement in high-volume fly ash pastes was enhanced because of the higher effective w/c Ratio for the paste. This effect was more significant for the pastes with lower water-to-binder (w/b) Ratios. Thus, preparing high-volume fly ash concrete at lower w/b Ratios can result in less strength losses. This paper also introduces a model to describe the relationship between the w/c Ratio and the degree of cement hydRation and gel/Space Ratio. The gel/Space Ratios of the FC pastes, evaluated based on the proposed model, were found to be consistent with the gel/Space Ratio of PC pastes in terms of the relationship with compressive strength. The gel/Space Ratio data correlated (inversely) linearly with mercury intruded porosity, but the former correlated more with compressive strength than the latter.
Gilles Chanvillard - One of the best experts on this subject based on the ideXlab platform.
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dependence of compressive strength on phase assemblage in cement pastes beyond gel Space Ratio experimental evidence and micromechanical modeling
Cement and Concrete Research, 2014Co-Authors: Pipat Termkhajornkit, Remi Barbarulo, Quoc Huy Vu, Sophie Daronnat, Gilles ChanvillardAbstract:Abstract Cement paste is a complex material, with a porous microstructure spread over several orders of magnitude, filled with water and gas, and a solid matrix composed of many different minerals — unreacted anhydrous products and crystalline or amorphous hydRation products. The relationship between this complex phase assemblage and its mechanical properties is usually described through the ‘gel–Space Ratio’ descriptor, which links compressive strength to the Ratio between the volume of hydRation products to the sum of volumes of hydRation products and capillary porosity. Surprisingly, little has been done on how the nature of hydrates impacts on the mechanical properties of cement paste. This is partly due to the difficulty to quantify the different hydrates in the system, and partly due to the absence of morphology homogenization models enabling one to relate the mineral assemblage to its mechanical properties. In this work, we generated experimental results in order to explore the ‘mechanical efficiency’ of C–S–H compared to portlandite, by hydrating C3S or C2S. The experimental results show that C–S–H, in the domain explored, is the first-order parameter explaining compressive strength. On this basis, a micromechanical model was developed, in which the smallest scale consists in solid C–S–H and total porosity (self-consistent scheme). Residual anhydrous cement and portlandite are added in a second homogenization step, as inclusions (Mori–Tanaka scheme). Additional experiments were performed to assess the role of hydrated calcium sulfoaluminates by hydrating synthetic clinkers or blends made of C3S, C3A and calcium sulfate. Using the same model, we show that monosulfoaluminate (and all non C–S–H hydrates) can be considered, as for anhydrous cement and portlandite, as inclusions in the C–S–H + total porosity matrix.
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Dependence of compressive strength on phase assemblage in cement pastes: Beyond gel–Space Ratio — Experimental evidence and micromechanical modeling
Cement and Concrete Research, 2014Co-Authors: Pipat Termkhajornkit, Remi Barbarulo, Sophie Daronnat, Gilles ChanvillardAbstract:Abstract Cement paste is a complex material, with a porous microstructure spread over several orders of magnitude, filled with water and gas, and a solid matrix composed of many different minerals — unreacted anhydrous products and crystalline or amorphous hydRation products. The relationship between this complex phase assemblage and its mechanical properties is usually described through the ‘gel–Space Ratio’ descriptor, which links compressive strength to the Ratio between the volume of hydRation products to the sum of volumes of hydRation products and capillary porosity. Surprisingly, little has been done on how the nature of hydrates impacts on the mechanical properties of cement paste. This is partly due to the difficulty to quantify the different hydrates in the system, and partly due to the absence of morphology homogenization models enabling one to relate the mineral assemblage to its mechanical properties. In this work, we generated experimental results in order to explore the ‘mechanical efficiency’ of C–S–H compared to portlandite, by hydrating C3S or C2S. The experimental results show that C–S–H, in the domain explored, is the first-order parameter explaining compressive strength. On this basis, a micromechanical model was developed, in which the smallest scale consists in solid C–S–H and total porosity (self-consistent scheme). Residual anhydrous cement and portlandite are added in a second homogenization step, as inclusions (Mori–Tanaka scheme). Additional experiments were performed to assess the role of hydrated calcium sulfoaluminates by hydrating synthetic clinkers or blends made of C3S, C3A and calcium sulfate. Using the same model, we show that monosulfoaluminate (and all non C–S–H hydrates) can be considered, as for anhydrous cement and portlandite, as inclusions in the C–S–H + total porosity matrix.
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effect of gel Space Ratio and microstructure on strength of hydrating cementitious materials an engineering micromechanics approach
Cement and Concrete Research, 2013Co-Authors: Bernhard Pichler, Christian Hellmich, Josef Eberhardsteiner, Jaromir Wasserbauer, Pipat Termkhajornkit, Remi Barbarulo, Gilles ChanvillardAbstract:Abstract Strengths of cement pastes with different mixture properties and maturities depend in a very similar overlinear fashion on the gel–Space Ratio, which is the Ratio of the volume of hydRation products over the volume of both hydRation products and capillary pores. We here investigate the underlying microstructural effects by the experimentally validated micromechanics model of Pichler and Hellmich [CemConRes 41(5), 2011]. This model shows that the macrostrength of cement pastes are not only triggered by the capillary porosity, but also by a strengthening effect of unhydrated clinker “reinforcements” which are embedded as inclusions in the hydrate foam. The analysis is continued with quantifying the strength of the hydrates, in terms of an extended model validation activity. Satisfactory model performance is the motivation to present model predictions for the biaxial compressive failure envelopes of cement pastes, again as a function of gel–Space Ratio.
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Effect of gel–Space Ratio and microstructure on strength of hydrating cementitious materials: An engineering micromechanics approach
Cement and Concrete Research, 2013Co-Authors: Bernhard Pichler, Christian Hellmich, Josef Eberhardsteiner, Jaromir Wasserbauer, Pipat Termkhajornkit, Remi Barbarulo, Gilles ChanvillardAbstract:Abstract Strengths of cement pastes with different mixture properties and maturities depend in a very similar overlinear fashion on the gel–Space Ratio, which is the Ratio of the volume of hydRation products over the volume of both hydRation products and capillary pores. We here investigate the underlying microstructural effects by the experimentally validated micromechanics model of Pichler and Hellmich [CemConRes 41(5), 2011]. This model shows that the macrostrength of cement pastes are not only triggered by the capillary porosity, but also by a strengthening effect of unhydrated clinker “reinforcements” which are embedded as inclusions in the hydrate foam. The analysis is continued with quantifying the strength of the hydrates, in terms of an extended model validation activity. Satisfactory model performance is the motivation to present model predictions for the biaxial compressive failure envelopes of cement pastes, again as a function of gel–Space Ratio.
Jiri Sonek - One of the best experts on this subject based on the ideXlab platform.
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Prefrontal Space Ratio in second- and third-trimester screening for trisomy 21
Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology, 2013Co-Authors: B. Yazdi, Jiri Sonek, C. Oettling, Markus Hoopmann, Harald Abele, M. Schaelike, Karl O. KaganAbstract:Objective To evaluate the prefrontal Space Ratio (PFSR) in second- and third-trimester euploid fetuses and fetuses with trisomy 21. Methods This was a retrospective study utilizing stored mid-sagittal two-dimensional images of second- and thirdtrimester fetal faces that were recorded during prenatal ultrasound examinations at the Department of Prenatal Medicine at the University of Tuebingen, Germany and at a private center for prenatal medicine in Nuremberg, Germany. For the normal range, 279 euploid pregnancies between 15 and 40 weeks’ gestation were included. The results were compared with 91 cases with trisomy 21 between 15 and 40 weeks. For the Ratio measurement, a line was drawn between the leading edge of the mandible and the maxilla (MM line) and extended in front of the forehead. The Ratio of the distance between the leading edge of the skull and the leading edge of the skin (d1) to the distance between the skin and the point where the MM line was intercepted (d2) was calculated. The PFSR was determined by dividing d2 by d1. Results In the euploid and trisomy 21 groups, the median gestational age at the time of ultrasound examination was 21.1 (range, 15.0–40.0) and 21.4 (range, 15.0–40.3) weeks, respectively. Multiple regression analysis showed that PFSR was independent of maternal and gestational age. In the euploid group, the mean PFSR was 0.97 ± 0.29. In fetuses with trisomy 21, the mean PFSR was 0.2 ± 0.38 (P < 0.0001). The PFSR was below the 5 th centile in 14 (5.0%) euploid fetuses and in 72 (79.1%) fetuses with trisomy 21. Conclusion The PFSR is a simple and effective marker in second- and third-trimester screening for trisomy 21. Copyright 2012 ISUOG. Published by John Wiley & Sons, Ltd.
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OC20.01: The prefrontal Space Ratio in second and third trimester screening for chromosomal abnormalities
Ultrasound in Obstetrics & Gynecology, 2012Co-Authors: Karl O. Kagan, Jiri Sonek, B. Yazdi, Harald Abele, M. Schaelike, Markus HoopmannAbstract:Results: In all women with atrophy and normal endometrium EI for endometrium was 0–2 points (72 women). In patients who had polyps, hypertrophy and cancer in the pathological result (34 women), EI was 3–4 points. The difference was significant (χ2 Pearson test; P < 0.0001). Conclusions: Elastography combined with conventional transvaginal ultrasonography is a helpful tool in differentiation of uterine bleeding in perimenopausal women and may decrease the number of unnecessary invasive procedures.
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prefrontal Space Ratio comparison between trisomy 21 and euploid fetuses in the second trimester
Ultrasound in Obstetrics & Gynecology, 2012Co-Authors: Jiri Sonek, Francisca S Molina, A K Hiett, Melanie M Glover, David S Mckenna, K H NicolaidesAbstract:Objective To evaluate a novel ultrasound measurement, the prefrontal Space Ratio (PFSR), in second-trimester trisomy 21 and euploid fetuses. Methods Stored three-dimensional volumes of fetal profiles from 26 trisomy 21 fetuses and 90 euploid fetuses at 15–25 weeks’ gestation were examined. A line was drawn between the leading edge of the mandible and the maxilla (MM line) and extended in front of the forehead. The Ratio of the distance between the leading edge of the skull and that of the skin (d1) to the distance between the skin and the point where the MM line was intercepted (d2) was calculated (d2/d1). The distributions of PFSR in trisomy 21 and euploid fetuses were compared, and the relationship with gestational age in each group was evaluated by Spearman’s rank correlation coefficient (rs). Results The PFSR in trisomy 21 fetuses (mean, 0.36; range, 0–0.81) was significantly lower than in euploid fetuses (mean, 1.48; range, 0.85–2.95; P < 0.001 (Mann–Whitney U-test)). There was no significant association between PFSR and gestational age in either trisomy 21 (rs = 0.25; 95% CI, −0.15 to 0.58) or euploid (rs = 0.06; 95% CI, −0.15 to 0.27) fetuses. Conclusion The PFSR appears to be a highly sensitive and specific marker of trisomy 21 in the second trimester of pregnancy. Copyright 2012 ISUOG. Published by John Wiley & Sons, Ltd.
Kypros H. Nicolaides - One of the best experts on this subject based on the ideXlab platform.
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Second-Trimester Screening for Trisomy-21 Using Prefrontal Space Ratio
Fetal diagnosis and therapy, 2013Co-Authors: Petya Chaveeva, Maria Agathokleous, Leona Poon, Desislava Markova, Kypros H. NicolaidesAbstract:Objective: To investigate the potential value of prefrontal Space Ratio (PFSR) in second-trimester screening for trisomy-21. Methods: A retrospective study utilizing stored midsagittal two-dimensional images of fetal profiles in 240 euploid and 45 trisomy-21 pregnancies at 16+0-23+6 weeks' gestation. The vertical distance between the leading edge of the skull and that of the skin (D1) and the distance between the skull and the mandibulo-maxillary line (D2) were measured and the D1:D2 Ratio (PFSR) was calculated. In euploid pregnancies, regression analysis was used to determine the association between D1, D2 and PFSR with gestational age (GA). D1 and D2 were expressed as delta (Δ) values with gestational age. ΔD1, ΔD2 and PFSR in cases and controls were compared. Results: In trisomy-21, compared to controls, ΔD1 was increased (1.417 vs. 0.000 mm, p Conclusion: The PFSR is an effective marker in second-trimester screening for trisomy-21.
