| 1. |
- Hazarika, Amrita, 1993, et al.
(författare)
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Characterisation, activation, and reactivity of heterogenous natural clays
- 2024
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Ingår i: Materials and Structures. - 1871-6873 .- 1359-5997. ; 57
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Tidskriftsartikel (refereegranskat)abstract
- Although thermal and mechanochemical activations of natural clays are well-documented, there exists a dual research gap. Firstly, a thorough investigation into the interrelationship between these activation methods and the governing parameters of reactivity for various clays has been notably lacking. Secondly, there is a distinct scarcity of studies specifically focusing on heterogeneous clays compared to the extensive research dedicated to single-layer clays specially kaolinitic clays. This study investigates the correlation of activation methods, and changes in the clay mineralogy, particle size distributions, morphology, specific surface area, and the reactivity of heterogeneous clays. Traditional thermal and mechanochemical activation methods often fall short in achieving complete dehydroxylation of heterogeneous clay minerals and improving their reactivity beyond predefined low thresholds. The results in this paper emphasize that, despite these limitations, combining these activation methods brings about significant modifications in crucial parameters. Notably, integrating 20 min of mechanochemical activation at 500 rpm with prior thermal treatment leads to 158% increase in specific surface area compared to mechanochemical activation conducted on un-calcined clays. Simultaneously, these combined activations result in up to 127% improvement in reactivity levels of heterogenous clays compared to standalone mechanochemical activation. The results underscore that, even with the advancements brought about by combined activations, the presence of impurities like iron oxides and calcite remains a noteworthy factor influencing the reactivity of kaolinitic natural clays. The study concludes by highlighting the potential of combined treatments to enhance the pozzolanicity of low-reactive heterogeneous clays, unlocking avenues for future clinker supplementation with this abundant resource.
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| 2. |
- Huang, Liming, 1993, et al.
(författare)
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Distribution and dynamics of water in the blended pastes unraveled by thermoporometry and dielectric properties
- 2023
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Ingår i: Cement and Concrete Research. - 0008-8846. ; 174
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Tidskriftsartikel (refereegranskat)abstract
- Water distribution in hardened paste and its dynamics determine many properties related to durability. Moisture distribution was determined by thermoporometry combined with vacuum drying. Dynamics of confined water were measured by broadband dielectric spectroscopy. Water in pores <2.4 nm cannot form tetrahedral ice structure due to geometrical constraints. The volume of unfrozen water (in interlayer and gel pores) decreases after the drying at all relative humidity levels. An evident coarsening of gel pores occurs with drying between 75 % and 55 % RH. 35 % fly ash and slag have limited effects on relaxation processes of silanol hydroxyl groups and interlayer water. However, they slow down the dynamics of water in small gel pores, thereby enhancing interactions between water and the solid interface. This study clarifies the microstructural changes during the drying and reveals the sensitivity of water dynamics to the chemical environment in C-S-H of blended pastes.
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| 3. |
- Huang, Liming, 1993, et al.
(författare)
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Improving the performance of alkali-activated slag mortar with electro/chemically treated carbon fiber textile
- 2023
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Ingår i: Journal of Cleaner Production. - : Elsevier Ltd. - 0959-6526 .- 1879-1786. ; 418
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Tidskriftsartikel (refereegranskat)abstract
- Alkali-activated slag is a widely used low-carbon binder. Incorporation of textile can mitigate the brittle weakness of alkali-activated composites. The bonding between fibers and matrix is critical for the performance of textile reinforced mortar. This paper is focused on the effect of different treatment methods on the bonding properties of carbon fiber in alkali-activated slag. The interfacial shear strength of fiber bundles in matrix was determined by the pull-out test. The flexural strength of the reinforced mortar was evaluated by a repeated bending. A scanning electron microscopy test was performed to characterize the interfacial properties of the fiber bundles. The results show that the interfacial shear strength of carbon fibers in matrix is improved by the electroplating with calcium silica slurry (CSS), impregnation in different solutions, and plasma treatments. An electroplating in CSS has the best improvement in the bonding strength with an increase by 620%. The CSS treatment increases the maximum flexural strength of CFT reinforced mortar with 22.5% and 30% at 7 and 28 d respectively, and it significantly inhibits the crack growth under the cyclic loading. This effect becomes more significant after a longer curing age. The electroplating treatment eliminates the cracks in the interface of fiber yarns. Slag reacts with the plated portlandite to strengthen the bonding between mortar and fiber bundles, so it has a better inhibiting effect on the crack growth after a longer curing. © 2023 The Authors
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| 4. |
- Huang, Liming, 1993, et al.
(författare)
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Influence of calcination temperature on the structure and hydration of MgO
- 2020
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Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618. ; 262
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Tidskriftsartikel (refereegranskat)abstract
- The performance of magnesium oxide-based cements and expansion agent closely relates to the reactivity of MgO. This paper systematically investigates the structure and hydration properties of MgO calcined from amorphous magnesite at a wide range of temperatures from 400 to 1150 ℃. XRD, SEM, BET and PSD tests were carried out to determine the structure and particle properties of MgO. The hydration reactivity of MgO was indexed with isothermal calorimeter, DTG, XRD and TEM test. Increasing temperature augments the crystallinity and size of MgO nanograins from about 23.85 nm to 86.37 nm, decreases the specific surface area but makes the particles agglomerate into smaller size. The increasing temperature prolongs the induction period and retards the hydration rate of main peak. The total cumulative heat from complete hydration of MgO is with a similar value of about 800 J/g. The hydration reactivity of MgO can be accurately indexed by its heat release. MgO calcined at 700 ℃ has high reactivity and it dissolves quickly leading to the precipitation of needle Mg(OH)2 initially. The needle brucite has poor crystallinity but it transforms into flake and clavate shape. MgO calcined at 1150 ℃ has very low dissolving rate. The dissolution starts from the (1 1 0) truncation at <1 0 0> edges, and then the cuts at (1 1 1) occur to create an octahedron shape. Some clavate brucite initially precipitates instead of needle brucite during the hydration of low reactive MgO.
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| 5. |
- Huang, Liming, 1993
(författare)
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Interaction of water with supplementary cementitious materials: Hydration mechanism, microstructure and moisture transport
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Supplementary cementitious materials (SCMs) offer a sustainable solution to reduce carbon emissions from the production of cement and concrete. This dissertation explores the impact of SCMs and the related additives on the hydration process of cementitious materials, which can affect their microstructure and transport properties. Water is involved in the whole life of the cementitious materials thereby determining the hydration, microstructure and durability. Advanced techniques were employed in this study to investigate the impact of additives on the hydration of C3S, examining microstructure refinement by SCMs and its relationship to transport processes, and assessing changes in water dynamics. A device was designed to continuously monitor the effect of SCMs on early hydration, and it was subsequently updated to monitor the hardening process of concrete containing SCMs. Results show that the dissolution theory fails to explain anomalous hydration of tricalcium silicate at high water to solid ratio. A new hypothesis in this study proposes that calcium silicate hydrate (C-S-H) primarily nucleates within the near-surface region, and this hypothesis bridges the gap between dissolution and protective layer theories. The designed device performs well in monitoring water interaction with SCMs. The evolution of electrical conductivity in hydrating pastes closely relates to chemical reaction processes and can be classified into four stages. The growth rate of the formation factor indicates the reactivity of different binders. Blending SCMs refines the pore structure, decreases pore connectivity and results in a higher formation factor. SCMs affect the pore structure of, the phase assemblage and water dynamics. The mesoscale pore structure in pastes with SCMs can be well indicated by water vapour desorption isotherms, but ion effects on water vapour equilibrium pressure must be considered when calculating pore size distribution. A novel approach works well in evaluating the hydration degree of SCMs by use of water vapour sorption and thermodynamic modelling. Thermoporometry and broadband dielectric spectroscopy effectively characterise moisture distribution and dynamics in hcps, respectively. SCMs have limited effects on the dynamics of structural water, primarily influencing water dynamic in small gel pores and interfacial polarization. The first drying process decreases the volume of unfrozen water (< ~2.4 nm) under various levels of relative humidity. Gel pores coarsen significantly during the drying between 75 % and 50 %. Change of microstructure alters the transport of moisture and chloride in hcp. The decrease in both moisture transport coefficient and chloride migration coefficient induced by SCMs is notably more significant in hcp with a higher water to binder ratio. The modified moisture transport in blended systems is primarily due to pore structure refinement, specifically the reduction in pore connectivity. Both the formation factor and porosity of small pores determine the moisture transport properties of hcp, with the formation factor being more significant at high RH and the porosity of small pores being more significant at low RH. The effect of SCMs on chloride is also due to the decrease in pore. A simplified model based on the formation factor of hcp can be used to estimate the chloride migration coefficient for the blended pastes and mortars. The upgraded device provides a reliable non-destructive monitoring of concrete performance. Formation factor and ultrasonic pulse velocity are reliable indices for concrete strength; however, formation factor exhibits the optimal performance. This study provides insights into the mechanism of how water interacts with cementitious materials and a new non-destructive monitoring method to promote the application of SCMs in sustainable concretes.
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| 6. |
- Huang, Liming, 1993, et al.
(författare)
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Moisture and ion transport properties in blended pastes and their relation to the refined pore structure
- 2022
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Ingår i: Cement and Concrete Research. - : Elsevier BV. - 0008-8846. ; 161:106949
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study of the moisture transport properties in blended pastes measured by a new procedure and setup. The dependence of moisture transport coefficient on relative humidity (RH) is confirmed. The differences in the moisture dependency may be due to discrepancies in the critical RH for the percolation of liquid. Fly ash and slag increase the percentage of mesopores or “ink-bottle” pores with a mesoscale neck and they strongly reduce the pore connectivity in pastes. These effects cause the evident reduction in the moisture and chloride diffusivity. The additional replacement with limestone filler has little effect on the pore connectivity. The formation factor controls the moisture transport at the high RH interval, but the volume of small pores (middle capillary and mesopores) is the major determinant at a low RH interval. The relationship between water-binder ratio, pore structure and moisture transport or chloride migration coefficient is discussed.
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| 7. |
- Huang, Liming, 1993, et al.
(författare)
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New insights into the reaction of tricalcium silicate (C 3 S) with solutions to the end of the induction period
- 2022
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Ingår i: Cement and Concrete Research. - : Elsevier BV. - 0008-8846. ; 152
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Tidskriftsartikel (refereegranskat)abstract
- Although dissolution theory is widely used, in certain circumstance, it seems to be unable to explain the hydration of C3S. In this article, more attention is paid to the nucleation of hydration products. We find that the precipitation of C-S-H is a nonclassical nucleation process. It starts with nucleation of primary particles and then grows by particle attachment. A sharp increase in the reaction rate after induction period may come from the accelerating growth rate of C-S-H instead of dissolution of etch pits. The duration of induction period relates to the size of primary floc. Potassium salts influence the primary globule floc size and mitigate the effect from Al. The pH impacts ion species in solution to affect the dissolution and precipitation. A hypothesis regarding the dissolution of C3S and nucleation of C-S-H within the near-surface region may narrow the gap between dissolution theory and protective layer theory.
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| 8. |
- Huang, Liming, 1993, et al.
(författare)
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Non-destructive test system to monitor hydration and strength development of low CO2 concrete
- 2023
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Ingår i: Construction and Building Materials. - 0950-0618. ; 408
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Tidskriftsartikel (refereegranskat)abstract
- Application of supplementary cementitious materials for production of low CO2 concrete affects the reaction kinetics, which alters the setting time and strength development. The different early-age behavior is of concern for quality control of concrete. Non-destructive test is very useful for monitoring the quality of low CO2 binder systems. This paper presents a new technique to monitor the electrical conductivity and temperature at different depths of hydrating concrete. Indices from monitoring system (conductivity, maturity and formation factor) are compared with data from widely-used methods (ultrasonic pulse velocity, penetration resistance and isothermal calorimetry). Results show that indices from the system can replicate the hydration evolution, setting time and compressive strength of low CO2 concrete. Electrical conductivity of concrete is very sensitive to mineral reactions and it reflects the hydration kinetic consistent with evolution of heat release. Linear correlations are found for penetration resistance in relation to ultrasonic pulse velocity, formation factor and maturity, respectively. The effects of binder type and water-to-binder ratio on hardening are strongly dependent on temperature. The proposed approach enables to include all these factors in characterizing the hardening process of concrete onsite. It is shown that formation factor performs better than ultrasonic pulse velocity on indicating the setting process. Formation factor is also a good parameter for quantitative description of compressive strength development, which is independent of the binder types, mixture proportions and curing ages.
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| 9. |
- Huang, Liming, 1993, et al.
(författare)
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Real-time monitoring the electrical properties of pastes to map the hydration induced microstructure change in cement-based materials
- 2022
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Ingår i: Cement and Concrete Composites. - : Elsevier BV. - 0958-9465. ; 132
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the supplementary materials (SCMs) on the moisture content and ion diffusivity at different hydration time is important for the service life modelling of modern concrete. This study designed a simple but valid method to monitor the microstructure change in pastes during hydration. A procedure easy to implement was proposed to detect the water content in pastes. The electrical conductivity of pore solution was evaluated by the evaporable water content in pastes and chemical composition in the binders. Results show that the electrical properties of pastes (conductivity, formation factor and its growth rate) can effectively indicate the hydration reactivity of binder, pore connectivity and volume of pore solution in the hardened pastes. The effect of waterbinder ratio and SCMs on the structure of pastes are effectively indexed by the formation factor which is the conductivity of pore solution divided by that of paste. The inflection point of average growth rate of formation factor is a good index for the final setting of pastes. The relation between volume of evaporable water and formation factor is well demonstrated by the extended percolation theory. The real-time monitored electrical conductivity and formation factor of pastes can be used to calculate the chloride migration coefficient in hardened cement pastes.
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| 10. |
- Huang, Liming, 1993, et al.
(författare)
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Recycling of the end-of-life lightweight aggregate concrete (LWAC) with a novel approach
- 2020
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Ingår i: Journal of Cleaner Production. - : Elsevier BV. - 0959-6526. ; 275
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Tidskriftsartikel (refereegranskat)abstract
- This work proposed an environmental-friendly approach for high-grade recycling of the end-of-life LWAC. The mechanical performance of mortar with recycled powder (RP), mortar with recycled fine aggregate (RFA) and recycled lightweight aggregate concrete (RLWAC) were investigated. Microstructure of mortar and RLWAC was detected to identify the properties of interfacial transition zone (ITZ). RP can prolong the setting of reference cement and the 10% dosage is better than 2% in not only retarding effect but also strength development. An appropriate content of RFA is beneficial for compressive strength. Replacing standard sand with 10% RFA increases the compressive strength of mortar by approximately 10%. However, a high replacement content (40%) of RFA brings about a reduction of compressive strength. The amount of RFA below 20% will not increase the dry shrinkage of mortar. The compressive strength of RLWAC is reduced by 10% RLWA but it has a significant increase when the replacement content reaches 30%. In mortar with RFA, cracks initiate from the ITZ of new sand and new paste and few cracks generate from old paste and old sand. Four types of ITZ that have distinct features are observed between cement paste and LWA in RLWAC.
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