| 1. |
- Wang, Shunfeng, 1991, et al.
(author)
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Co-utilization of quarry tailings and fly ash for non-sintered ultra-lightweight aggregates (ULWAs) by autoclave technology
- 2022
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In: Construction and Building Materials. - : Elsevier BV. - 0950-0618. ; 346
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Journal article (peer-reviewed)abstract
- Quarry tailings as solid waste with large output bring a heavy environmental and economic burden. The main objective of this study is to investigate the feasibility of co-utilizing quarry tailings and fly ash (FA) as the main sources in preparing the lightweight aggregates (LWAs). The expand perlite powder (characterized with low density and high surface area) and two chemical foaming agents (ammonium carbonate and Al powder) was added to reduce the density of LWAs furtherly and fabricate a type of ultra-lightweight aggregates (ULWAs) through autoclave curing. In spite of the basic properties (compressive strength, 1 h of water absorption, loose bulk density and apparent particle density), the evolution of pore structures in relation to the type of foaming agents were also determined by combining scanning electron microscope (SEM), mercury intrusion porosimetry (MIP) and Nuclear Magnetic Resonance (NMR). The results show that increasing the expand perlite content could increases the compressive strength and water absorption, decreases the loose bulk density, apparent density and the total porosity. The pores wall gradually reduces with the increase of chemical foaming agents. Isolated pores will transform into connected pores, which also increase the most probable pore diameter and total porosity. The loose bulk density of specimens with 3 wt% (NH4)2CO3 and Al powder are 873 kg/m3 and 798 kg/m3 compared to blank (1132 kg/m3). This work lays a solid foundation for the design and preparation of ULWAs from solid wastes.
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| 2. |
- Wang, Shunfeng, 1991, et al.
(author)
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Resourceful utilization of quarry tailings in the preparation of non-sintered high-strength lightweight aggregates
- 2022
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In: Construction and Building Materials. - : Elsevier BV. - 0950-0618. ; 334
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Journal article (peer-reviewed)abstract
- Quarry tailings are usually stockpiled due to stable crystalline structures below 100 °C and abundant sources, which lead to a serious environmental impacts and high ecological risks. This paper presents a study of transforming the fly ash and quarry tailings as the main raw materials into lightweight aggregates (LWAs) for using in civil engineering. A novel curing regime (autoclave technology) has been proposed to obtain higher compressive strength of LWAs. The effects of curing parameters (including temperature and steam pressure) on the properties (compressive strength, water absorption, loose bulk density, phase composition, pore structure and microstructure) of LWAs were systematically evaluated. On the other hand, this research also studies the effect of cement content on the basic properties of LWAs, which was decreased from 30 to 10 wt% for declining the CO2 emission. Results show that the strength sharply increases from 2.48 to 11.95 MPa and the water absorption decreases from 11.2 to 2.09% with increasing the elevated curing temperature from 25 to 190 °C. The LWA prepared with 70 wt% solid wastes (fly ash and quarry tailings) at 190 °C achieved the highest strength (11.95 MPa) and the lower loose bulk density (1160 kg/m3), which could meet the requirement of Chinese LWAs standard (GB/T 17431.1-2010). The water absorption of LWAs is below 5% except sample T25. The total porosity of LWAs decreases from 39.65% to 26.32% at 150 °C and from 42.54% to 27.24% at 190 °C while the cement content increases form 10 wt% to 30 wt%. At the same time, the percentage of pores (>50 nm) also gradually decreases. While the curing temperature, pressure and cement usage are above 150 °C, 1.00 MPa and 10 wt% respectively, will promote the formation of new phase composition (analcime). That also further increases the strength and percentage of harmless pores and few harmful pores. Therefore, this research offers a new curing method for producing LWAs from 70 to 90 wt% solid waste and is a rapid and sustainable solution for the large-scale recycling of quarry tailings.
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| 3. |
- Huang, Liming, 1993, et al.
(author)
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Distribution and dynamics of water in the blended pastes unraveled by thermoporometry and dielectric properties
- 2023
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In: Cement and Concrete Research. - 0008-8846. ; 174
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Journal article (peer-reviewed)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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| 4. |
- Huang, Liming, 1993, et al.
(author)
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Influence of calcination temperature on the structure and hydration of MgO
- 2020
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In: Construction and Building Materials. - : Elsevier BV. - 0950-0618. ; 262
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Journal article (peer-reviewed)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, et al.
(author)
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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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In: Cement and Concrete Research. - : Elsevier BV. - 0008-8846. ; 161:106949
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Journal article (peer-reviewed)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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| 6. |
- Huang, Liming, 1993, et al.
(author)
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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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In: Cement and Concrete Research. - : Elsevier BV. - 0008-8846. ; 152
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Journal article (peer-reviewed)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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| 7. |
- Huang, Liming, 1993, et al.
(author)
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Non-destructive test system to monitor hydration and strength development of low CO2 concrete
- 2023
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In: Construction and Building Materials. - 0950-0618. ; 408
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Journal article (peer-reviewed)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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| 8. |
- Huang, Liming, 1993, et al.
(author)
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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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In: Cement and Concrete Composites. - : Elsevier BV. - 0958-9465. ; 132
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Journal article (peer-reviewed)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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| 9. |
- Huang, Liming, 1993, et al.
(author)
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Recycling of the end-of-life lightweight aggregate concrete (LWAC) with a novel approach
- 2020
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In: Journal of Cleaner Production. - : Elsevier BV. - 0959-6526. ; 275
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Journal article (peer-reviewed)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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| 10. |
- Huang, Liming, 1993, et al.
(author)
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Using water vapour and N2 isotherms to unveil effects of SCMs on nanopores and evaluate hydration degree
- 2023
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In: Cement and Concrete Research. - : Elsevier BV. - 0008-8846. ; 164:February 2023
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Journal article (peer-reviewed)abstract
- Nanopores are critical for the durability of cement-based materials, but the refinement of these pores by SCMs is yet to have a clear understanding. This paper studied effects of the water–binder ratio, SCMs and the drying on the distribution of nanopores using water vapour and N2 sorption isotherms. Results show that data of water vapour sorption can be used for a practical evaluation of the hydration degree of SCMs with thermodynamic simulation. Fly ash increases the volume of large gel and capillary pores. It lowers the difference between the sorption of water vapour and N2. Slag evidently refines the nanopores by increasing the volume of ink-bottle gel pores with an interlayer-size neck. A higher w/b produces more large pores to reduce the effect of drying. Removal of water induces contraction of interlayer and reduces gel pores volume, which causes large difference between sorption of water vapour and N2.
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