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Akh Kwan - One of the best experts on this subject based on the ideXlab platform.
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effects of superplasticizer type on Packing Density water film thickness and flowability of cementitious paste
Construction and Building Materials, 2015Co-Authors: L G Li, Akh KwanAbstract:Superplasticizer (SP) is nowadays an indispensable ingredient for the production of concrete. With SP added, the cementitious materials would be dispersed to reduce agglomeration, and thus the Packing Density, water film thickness (WFT) and flowability of the cementitious paste could be improved. However, there have been few studies on the effects of SP type on the Packing Density and WFT. This study aims to evaluate the roles of SP type in the Packing Density, WFT and flowability of cementitious paste. In the study, cementitious paste samples with three cementitious material compositions, two SP types (namely, a naphthalene-based SP and a polycarboxylate-based SP) and increasing SP dosages were tested. The test results showed that the addition of either type of SP would significantly increase the Packing Density and WFT, but the polycarboxylate-based SP is more effective than the naphthalene-based SP. Besides, the combined effects of SP and WFT on the flowability of cementitious paste were analyzed.
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a 3 parameter Packing Density model for angular rock aggregate particles
Powder Technology, 2015Co-Authors: Akh Kwan, Vivian Taam Wong, W W S FungAbstract:Abstract The authors have in recent studies incorporated the wedging effect to develop a 3-parameter model for Packing Density prediction of binary and ternary mixes of spherical particles. This model has been restricted to only spherical particles because only the test results of spherical particles were used for derivation and validation. For more general applications to other types of particles, such as angular particles, the model needs to be further developed. In this study, an experimental program on the Packing Density of binary mixes of angular rock aggregate particles was carried out and the experimental results were used to derive the interaction functions of the three parameters (the loosening, wall and wedging effect parameters) for extending the 3-parameter model to binary mixes of angular particles. Apart from the experimental results obtained herein, the test results published by de Larrard and those obtained by the authors in an earlier study were also used to validate the extended 3-parameter model.
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adding fly ash microsphere to improve Packing Density flowability and strength of cement paste
Powder Technology, 2013Co-Authors: Akh Kwan, J.j. ChenAbstract:Abstract Fly ash microsphere (FAM) is a superfine fly ash. Being finer than cement, it can fill into the voids between cement grains. To study the effects of adding FAM, cement paste samples with FAM contents ranging from 0 to 60% and different water contents were made for Packing Density, flowability and strength measurements. The results showed that the addition of up to 40% FAM would significantly increase the Packing Density of the cementitious materials. With the voids partially filled by FAM and the same volume of water in the voids released, the addition of FAM could increase the water film thickness of the cement paste. Consequently, the addition of FAM could increase flowability at same strength, increase strength at same flowability, or increase both strength and flowability. Hence, FAM is an effective cementitious filler for improving the performance of cement paste and concrete.
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improving Packing Density of powder in cement paste for production of high performance concrete
Advanced Materials Research, 2010Co-Authors: Akh Kwan, J.j. Chen, W W S FungAbstract:The Packing Density of the powder in cement paste has great influence on the performance of the concrete. A higher Packing Density could at the same water/powder ratio increase the amount of excess water for lubricating the cement paste and thereby improve the flowability of the concrete. Alternatively, it would allow the water/powder ratio to be reduced to improve the strength of the concrete without compromising the flowability. Therefore, it is of great interest, especially for production of high-performance concrete, to maximize the Packing Density of the powder. This study aims to investigate the roles of superplasticizer and fillers in the Packing Density of the powder in cement paste. Packing Density tests were carried out to determine the Packing Density of cement with various dosages of superplasticizer and different fillers (limestone fine, superfine cement and condensed silica fume) added using a newly developed wet Packing method. The results showed that the addition of superplasticizer can significantly improve the Packing Density of cement while the addition of fillers can further improve the Packing Density of the powder.
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Packing Density of cementitious materials part 2 Packing and flow of opc pfa csf
Materials and Structures, 2008Co-Authors: Akh Kwan, H. H. C. WongAbstract:The wet Packing method developed in Part 1 [Wong HHC, Kwan AKH (2007) Packing Density of cementitious materials: part 1 measurement using a wet Packing method. Mater Struct (Paper No. MAAS3281)] has been successfully applied to measure the Packing densities of cementitious materials containing ordinary Portland cement (OPC), pulverised fuel ash (PFA) and condensed silica fume (CSF). The test results for non-blended materials revealed that whilst the addition of a superplasticiser would always increase the Packing densities of OPC and PFA, the addition of a polycarboxylate-based superplasticiser could decrease the Packing Density of CSF. On the other hand, the results for blended materials showed that the Packing Density could be improved by double blending OPC with either PFA or CSF, and further improved by triple blending OPC, PFA and CSF together in appropriate proportions. A maximum Packing Density of 0.752 has been achieved and a ternary Packing Density diagram for determining the mix proportions for maximum Packing Density has been produced. Furthermore, the positive influence of a higher Packing Density on cement paste rheology has been demonstrated using the mini-slump cone test. Based on these results, the concept of excess water ratio, which is the major factor governing the rheology of a paste, is introduced.
J.j. Chen - One of the best experts on this subject based on the ideXlab platform.
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Adding granite polishing waste as sand replacement to improve Packing Density, rheology, strength and impermeability of mortar
Powder Technology, 2020Co-Authors: J.j. Chen, Ann H. KwanAbstract:Abstract Reducing waste disposal from stoneware industry and reducing use of sand in construction industry are both important for sustainable development. One strategy to tackle both problems is to utilize the waste from stoneware factories to replace the sand in mortar/concrete production. To study the possible use of granite polishing waste (GPW) as sand replacement, a research programme was launched to test the flowability, cohesiveness, adhesiveness, strength and sorptivity of mortar mixes made with various GPW contents and water/cement ratios. To investigate the fundamental causes of the effects exerted by the GPW, the Packing Density, water film thickness and porosity of the mortar mixes were also measured. The results showed that adding a suitable amount of GPW as sand replacement would, apart from reducing waste disposal and sand consumption, also improve mortar performance by filling the voids between sand particles to decrease the voids ratio and porosity and increase the Packing Density and water film thickness. Overall, within the ranges of mix parameters covered in this study, the addition of GPW to replace 15% to 20% sand by volume would increase the strength by 31.2% to 70.9% and improve the rheology and impermeability.
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adding fly ash microsphere to improve Packing Density flowability and strength of cement paste
Powder Technology, 2013Co-Authors: Akh Kwan, J.j. ChenAbstract:Abstract Fly ash microsphere (FAM) is a superfine fly ash. Being finer than cement, it can fill into the voids between cement grains. To study the effects of adding FAM, cement paste samples with FAM contents ranging from 0 to 60% and different water contents were made for Packing Density, flowability and strength measurements. The results showed that the addition of up to 40% FAM would significantly increase the Packing Density of the cementitious materials. With the voids partially filled by FAM and the same volume of water in the voids released, the addition of FAM could increase the water film thickness of the cement paste. Consequently, the addition of FAM could increase flowability at same strength, increase strength at same flowability, or increase both strength and flowability. Hence, FAM is an effective cementitious filler for improving the performance of cement paste and concrete.
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superfine cement for improving Packing Density rheology and strength of cement paste
Cement & Concrete Composites, 2012Co-Authors: J.j. Chen, Ann H. KwanAbstract:Abstract Superfine cement is a cement ground to a much higher fineness than ordinary cement. The addition of a small quantity of superfine cement to fill into the voids of ordinary cement can improve the Packing Density of the cement and thereby reduce the amount of mixing water needed to fill the voids. In this study, the effects of superfine cement on the Packing Density of cement (directly measured by a wet Packing test), the water film thickness of cement paste (taken as the excess water to solid surface area ratio), and the flowability, rheology and strength of cement paste were investigated. The results showed that the addition of 10% to 20% superfine cement can significantly increase the Packing Density of the cement and the water film thickness of the cement paste. Such increases in Packing Density and water film thickness would then improve the flowability, rheology and strength of the cement paste. Hence, superfine cement is an effective cementitious filler for improving cement performance.
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improving Packing Density of powder in cement paste for production of high performance concrete
Advanced Materials Research, 2010Co-Authors: Akh Kwan, J.j. Chen, W W S FungAbstract:The Packing Density of the powder in cement paste has great influence on the performance of the concrete. A higher Packing Density could at the same water/powder ratio increase the amount of excess water for lubricating the cement paste and thereby improve the flowability of the concrete. Alternatively, it would allow the water/powder ratio to be reduced to improve the strength of the concrete without compromising the flowability. Therefore, it is of great interest, especially for production of high-performance concrete, to maximize the Packing Density of the powder. This study aims to investigate the roles of superplasticizer and fillers in the Packing Density of the powder in cement paste. Packing Density tests were carried out to determine the Packing Density of cement with various dosages of superplasticizer and different fillers (limestone fine, superfine cement and condensed silica fume) added using a newly developed wet Packing method. The results showed that the addition of superplasticizer can significantly improve the Packing Density of cement while the addition of fillers can further improve the Packing Density of the powder.
Ann H. Kwan - One of the best experts on this subject based on the ideXlab platform.
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Adding granite polishing waste as sand replacement to improve Packing Density, rheology, strength and impermeability of mortar
Powder Technology, 2020Co-Authors: J.j. Chen, Ann H. KwanAbstract:Abstract Reducing waste disposal from stoneware industry and reducing use of sand in construction industry are both important for sustainable development. One strategy to tackle both problems is to utilize the waste from stoneware factories to replace the sand in mortar/concrete production. To study the possible use of granite polishing waste (GPW) as sand replacement, a research programme was launched to test the flowability, cohesiveness, adhesiveness, strength and sorptivity of mortar mixes made with various GPW contents and water/cement ratios. To investigate the fundamental causes of the effects exerted by the GPW, the Packing Density, water film thickness and porosity of the mortar mixes were also measured. The results showed that adding a suitable amount of GPW as sand replacement would, apart from reducing waste disposal and sand consumption, also improve mortar performance by filling the voids between sand particles to decrease the voids ratio and porosity and increase the Packing Density and water film thickness. Overall, within the ranges of mix parameters covered in this study, the addition of GPW to replace 15% to 20% sand by volume would increase the strength by 31.2% to 70.9% and improve the rheology and impermeability.
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Packing Density of mortar containing polypropylene carbon or basalt fibres under dry and wet conditions
Powder Technology, 2019Co-Authors: H X Zhuo, J Zhu, Ann H. KwanAbstract:Abstract The addition of fibres to concrete can significantly improve the hardened properties but may adversely affect the fresh properties. Apart from entangling with each other to hinder the flow of fresh concrete, the fibres might also interfere with the Packing of the solid particles in the concrete. However, the Packing Density of fibre reinforced concrete made with flexible fibres was rarely measured and thus the effects of flexible fibres on the Packing Density are still not well understood. Herein, the Packing densities of mortar containing polypropylene, carbon or basalt fibres under dry and wet and with and without superplasticizer added conditions were measured and compared to evaluate the effects of the flexible fibres on the Packing Density. It was found that the Packing Density of mortar containing these fibres is much higher under wet condition than under dry condition and that the fibre content, fibre length and superplasticizer all have certain influences on the Packing Density. Based on the test results, best-fit equations revealing the variations of the Packing Density with the fibre factor under different conditions are derived.
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superfine cement for improving Packing Density rheology and strength of cement paste
Cement & Concrete Composites, 2012Co-Authors: J.j. Chen, Ann H. KwanAbstract:Abstract Superfine cement is a cement ground to a much higher fineness than ordinary cement. The addition of a small quantity of superfine cement to fill into the voids of ordinary cement can improve the Packing Density of the cement and thereby reduce the amount of mixing water needed to fill the voids. In this study, the effects of superfine cement on the Packing Density of cement (directly measured by a wet Packing test), the water film thickness of cement paste (taken as the excess water to solid surface area ratio), and the flowability, rheology and strength of cement paste were investigated. The results showed that the addition of 10% to 20% superfine cement can significantly increase the Packing Density of the cement and the water film thickness of the cement paste. Such increases in Packing Density and water film thickness would then improve the flowability, rheology and strength of the cement paste. Hence, superfine cement is an effective cementitious filler for improving cement performance.
Stephen A. Burns - One of the best experts on this subject based on the ideXlab platform.
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Cone photoreceptor Packing Density and the outer nuclear layer thickness in healthy subjects.
Investigative Opthalmology & Visual Science, 2012Co-Authors: Toco Yuen Ping Chui, Hongxin Song, Christopher A. Clark, Joel A. Papay, Stephen A. Burns, Ann E. ElsnerAbstract:Purpose. We evaluated the relationship between cone photoreceptor Packing Density and outer nuclear layer (ONL) thickness within the central 15 degrees.
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variation of cone photoreceptor Packing Density with retinal eccentricity and age
Investigative Ophthalmology & Visual Science, 2011Co-Authors: Hongxin Song, Toco Yuen Ping Chui, Ann E. Elsner, Zhangyi Zhong, Stephen A. BurnsAbstract:As the first stage of vision, the photoreceptors provide the spatial information to higher stages of visual processing. Packing Density and arrangement of photoreceptors are related to the development, function, and evolution of the visual system.1–4 The human cone photoreceptors distribution has the following features2,5,6: (1) a high peak cone Packing Density at the foveal center; (2) a rapid decrease in Packing Density within the central 2 mm of retina and then a more gradual decrease farther away; and (3) isoDensity contours of cone photoreceptor distribution that are elongated along the horizontal axis, sometimes referred to as a cone streak.2 Previous studies of the effect of aging on the retina suggest that normal aging is accompanied by photoreceptor changes. Both rod7 and cone8 outer segments have been reported to become disorganized with aging, especially when they are close to the fovea. Cone photopigment is also reduced with age4,9 and Swanson et al.10 reported that the decreased photopigment is largest in the central 1° of the retina, suggesting a change in foveal architecture with age, which is supported by findings of changes in both photopigment and macular pigment distributions.11 However, the question of whether there is loss of cone photoreceptors with aging in the human retina is still controversial. Pandajonas et al.12 found a loss of 37% of rods and 18% of cones extrapolated to a lifespan of 100 years. Gao et al.13 and Curcio et al.14 found that loss of rods occurs with age but did not find a decrease in cone Density, although variability among individuals was high.2 A limitation of these histologic approaches is that these measurements have been possible only ex vivo, which requires experimental manipulation of tissue before the measurements. The best data can only be collected in very fresh tissue, which is hard to obtain, and thus the total sample of data is relatively small and the age distribution sampling is variable. In recent years, adaptive optics has enabled high-resolution retinal imaging, sufficient for measuring the cone Packing Density in vivo.5,6,15–20 In the present study, we used state-of-the-art adaptive optics scanning laser ophthalmoscopes (AOSLO),21,22 to measure the variation in cone photoreceptors in two normal populations that differed in age. We used the rapid acquisition capability to systematically collect data along four retinal meridians from near the fovea to approximately 12° retinal eccentricity. The cone Packing Density was compared as a function of retinal eccentricity, meridian, and age.
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individual variations in human cone photoreceptor Packing Density variations with refractive error
Investigative Ophthalmology & Visual Science, 2008Co-Authors: Toco Yuen Ping Chui, Hongxin Song, Stephen A. BurnsAbstract:PURPOSE To measure the variation in human cone photoreceptor Packing Density across the retina both within an individual and between individuals with different refractive errors.
A K H Kwa - One of the best experts on this subject based on the ideXlab platform.
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roles of Packing Density and water film thickness in strength and durability of limestone fines concrete
Magazine of Concrete Research, 2017Co-Authors: J J Che, A K H KwaAbstract:Recent studies have revealed that the use of limestone fines (LF) to replace an equal volume of cementitious paste in concrete could improve the strength and durability of the concrete and reduce the carbon dioxide footprint of concrete production. However, there are different views on how and why the use of LF as a cementitious paste replacement without changing the mix composition of the paste could increase the performance of hardened concrete, bearing in mind that LF are not inherently cementitious. In this work, the effects of the addition of LF on the Packing Density and water film thickness (WFT) of concrete mixes were investigated, and the roles of Packing Density and WFT were studied by correlating the strength and durability to the voids ratio (determined from the Packing Density) and WFT. Based on the results of this study, it is suggested that the use of LF as a cementitious paste replacement improves strength and durability mainly through increasing the Packing Density (the same as decreasing...
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effects of fines content on Packing Density of fine aggregate in concrete
Construction and Building Materials, 2014Co-Authors: A K H Kwa, K Y HueAbstract:Abstract The fines content (particles finer than 75 μm) in aggregate has substantial effects on the performance of concrete. Since the fines content has large surface area that would increase the water demand, maximum limits are often imposed. However, the fines content would also fill into the voids between larger particles to increase the Packing Density and thus reduce the volume of voids to be filled with cement paste. Hence, the fines content is not entirely undesirable and it has been suggested to raise the limits on the fines content. Somehow, due to measurement difficulties, the effects of fines content on the Packing Density are still not well understood. Herein, the Packing Density of fine aggregate with varying fines content was measured using both the dry and wet Packing methods. It was found that under wet condition, the highest Packing Density generally occurs at a fines content of about 15%.
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Packing Density of concrete mix under dry and wet conditions
Powder Technology, 2014Co-Authors: A K H KwaAbstract:Abstract It is well known that the Packing of particles in concrete has great effects on the performance of concrete, but existing codified methods for Packing Density measurement are all carried out under dry condition and do not account for the effect of water in the concrete mix. In recent studies by the authors, a wet Packing method has been developed and the Packing densities of cementitious materials, fine aggregate and blended fine plus coarse aggregate were found to be higher under wet condition than dry condition. In this study, both the dry and wet Packing methods were applied to concrete mixes containing cementitious materials, fine aggregate and coarse aggregate. It was found that for the entire particle system in a concrete mix, the Packing Density is higher, the voids ratio is smaller and the filling effects of ultrafine supplementary cementitious materials are better revealed under wet condition than dry condition. Therefore, when measuring the Packing Density of a concrete mix, the wet Packing method should always be used.
