The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Mirja Illikainen - One of the best experts on this subject based on the ideXlab platform.
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high strength fiber reinforced one part alkali activated slag fly ash binders with ceramic aggregates microscopic analysis mechanical properties Drying Shrinkage and freeze thaw resistance
Construction and Building Materials, 2020Co-Authors: Zahra Abdollahnejad, Mohammad Mastali, B Woof, Mirja IllikainenAbstract:Abstract One-part alkali-activated binders, also known as the “just-add-water” concept, have received great attention due to their advantages over two-part alkali-activated binders. By avoiding the use of dangerous alkali solutions, these binders are easier to both handle and transport. Ground granulated blast furnace slag is one of the side streams, which can be used in one-part alkali-activated binders to reach high compressive strength at an early age. However, using slag alone has some disadvantages, including a fast setting time and a large Drying Shrinkage, narrowing the application of these mix compositions and causing crack formation, respectively, thus shortening service life. Fly ash can be used in one-part alkali-activated materials to partially substitute for slag in order to both minimize Drying Shrinkage and prolong the setting time. Moreover, ceramic waste can be used as a replacement for normal sand, which is great achievement in terms of developing environmentally friendly alkali-activated materials exclusively from side steam. This paper presents new research on the effects on the fresh and hardened-state properties of one-part alkali-activated mortars of replacing up to 80% of slag with fly ash. These properties were characterized by the initial and final setting time, the strength development (compressive and flexural), and the Drying Shrinkage. Microstructural analyses (SEM/EDS, XRF, TGA/DTG) justified the results. Moreover, different fiber contents and combinations were used to reinforce the developed one-part alkali-activated slag/fly ash mortars to increase the strength, further reduce the Drying Shrinkage, and improve the freeze/thaw resistance. The results showed that fly ash and fibers can reduce the Drying Shrinkage and prolong the setting time. The weakened mechanical properties caused by decreasing the amount of slag are still adequate to let the composite slag/fly ash material be considered in construction applications.
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Drying Shrinkage in alkali activated binders a critical review
Construction and Building Materials, 2018Co-Authors: Mohammad Mastali, Paivo Kinnunen, A Dalvand, Mohammadi R Firouz, Mirja IllikainenAbstract:Abstract Alkali-activated binders have been proposed and have emerged as an alternative to ordinary Portland cement (OPC) binders with acceptable mechanical and durability performances in addition to positive environmental impacts. These alternative binders use a wide range of aluminosilicate precursors, with differing availabilities, reactivities, costs and CO2 emissions. Despite all the studies published on improving the characteristics of these materials in the last decades, some aspects of alkali-activated binders require further investigations. For instance, Shrinkage in alkali-activated binders due to the different chemical processes being involved is more complicated than OPC composites and it plays a key role in long-term performance. However, information on the Shrinkage behavior of these binder systems is scattered and fragmented. Therefore, this review critically surveys the Drying Shrinkage behavior of alkali-activated binders with slag, fly ash and metakaolin. The mechanisms of the Drying Shrinkage and the factors that affect Shrinkage are discussed. Different solutions to limit the Shrinkage are also presented. Then, an analysis is conducted based on the literature, and the main chemical elements affecting the Drying Shrinkage of alkali-activated materials are proposed. Finally, the feasibility of using the developed empirical models for predicting the Drying Shrinkage of OPC concretes is also investigated for alkali activated binders. This review shows that alkali-activated slag binders generally have the higher rate of the Drying Shrinkage compared to other alkali activated binders, albeit, reinforcing the plain compositions with fibers, using expanding admixtures, curing at elevated temperatures, using a combination of slag with fly ash or metakaolin reduces successfully the Drying Shrinkage. Moreover, utilizing ternary diagrams, it is revealed that the molar ratio of Ca/Si has the greatest impact on the rate of Drying Shrinkage in the alkali-activated binders.
Abir Altabbaa - One of the best experts on this subject based on the ideXlab platform.
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self healing of Drying Shrinkage cracks in cement based materials incorporating reactive mgo
Smart Materials and Structures, 2016Co-Authors: Tanvir Qureshi, Abir AltabbaaAbstract:Excessive Drying Shrinkage is one of the major issues of concern for longevity and reduced strength performance of concrete structures. It can cause the formation of cracks in the concrete. This research aims to improve the autogenous self-healing capacity of traditional Portland cement (PC) systems, adding expansive minerals such as reactive magnesium oxide (MgO) in terms of Drying Shrinkage crack healing. Two different reactive grades (high 'N50'and moderately high '92–200') of MgO were added with PC. Cracks were induced in the samples with restraining end prisms through natural Drying Shrinkage over 28 days after casting. Samples were then cured under water for 28 and 56 days, and self-healing capacity was investigated in terms of mechanical strength recovery, crack sealing efficiency and improvement in durability. Finally, microstructures of the healing materials were investigated using FT-IR, XRD, and SEM-EDX. Overall N50 mixes show higher expansion and Drying Shrinkage compared to 92–200 mixes. Autogenous self-healing performance of the MgO containing samples were much higher compared to control (only PC) mixes. Cracks up to 500 μm were sealed in most MgO containing samples after 28 days. In the microstructural investigations, highly expansive Mg-rich hydro-carbonate bridges were found along with traditional calcium-based, self-healing compounds (calcite, portlandite, calcium silicate hydrates and ettringite).
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strength and Drying Shrinkage of slag paste activated by sodium carbonate and reactive mgo
Construction and Building Materials, 2015Co-Authors: Abir AltabbaaAbstract:This paper investigates the potential of combining Na2CO3 and reactive MgO as a sustainable activator for ground granulated blastfurnace slag. Two very different reactivity MgOs were added at 5–10 % and the Na2CO3 content varied from 4% to 8% by the weight of slag. The strength and Drying Shrinkage of the activated slag pastes were tested up to 90 d. It was found that the optimum reactive MgO addition was 5% regardless of the MgO type and Na2CO3 content. MgO with the higher reactivity significantly increased the early strength of the paste but had almost no effect on the strength at 90 d. On the other hand, the effect of the lower reactivity MgO on the strength was more profound at later ages and low Na2CO3 dosage. In terms of Drying Shrinkage, increasing the Na2CO3 content from 4% to 6% caused a remarkable decrease of Drying Shrinkage while increasing it from 6% to 8% had negligible effect. X-ray diffraction and thermogravimetric analysis revealed that the major hydration products were calcium silicate hydrate gel and hydrotalcite-like phases, similar to those in conventional alkali-activated slag cements. There was also a large quantity of calcite formed especially in the 8% Na2CO3 pastes due to causticisation. It was concluded that the combination of reactive MgO and Na2CO3 could serve as a potential sustainable activator for slags.
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strength and Drying Shrinkage of reactive mgo modified alkali activated slag paste
Construction and Building Materials, 2014Co-Authors: Fei Jin, Abir AltabbaaAbstract:Conventional alkali-activated slag (AAS) cements suffer from significant Drying Shrinkage which hinders their widespread application. This paper investigates the potential of using commercial reactive MgO to reduce the Drying Shrinkage of AAS. Two different reactive MgOs were added at a content of 2.5–7.5 wt% of the slag, which was activated by sodium hydroxide and water–glass. The strength and the Drying Shrinkage of those reactive MgO modified AAS (MAAS) pastes were measured up to 90 days. It is found that MgO with high reactivity accelerated the early hydration of AAS, while MgO with medium reactivity had little effect. The Drying Shrinkage was significantly reduced by highly reactive MgO but it also generated severe cracking under the dry condition. On the other hand, medium-reactive MgO only showed observable Shrinkage-reducing effect after one month, but the cement soundness was improved. The hydration products, analysed by X-ray diffraction, thermogravimetric analysis and scanning electron microscopy techniques, showed that Mg was mainly incorporated in the hydrotalcite-like phases. It is concluded that the curing conditions and the time of hydrotalcite-like phases formation and their quantity are crucial to the developed strength and Shrinkage reduction properties of MAAS, which are highly dependent on the reactivity and content of reactive MgO.
Caijun Shi - One of the best experts on this subject based on the ideXlab platform.
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autogenous Shrinkage and Drying Shrinkage of recycled aggregate concrete a review
Journal of Cleaner Production, 2021Co-Authors: Yuguang Mao, Caijun Shi, Jianhui LiuAbstract:Abstract This paper comprehensively reviews the factors influencing the autogenous Shrinkage and Drying Shrinkage of recycled aggregate concrete (RAC). Compared with natural aggregate concrete (NAC), RAC has a lower autogenous Shrinkage because of the internal curing effect of recycled concrete aggregate (RCA). However, the internal curing efficiency of RCA is less than that of the lightweight aggregate because of its lower porosity and different pore structure. The Drying Shrinkage of RAC is larger than that of NAC, which is mainly caused by the mortar attached to the original virgin aggregate (OVA). Therefore, the methods of strengthening adhered or removing adhered mortar can reduce the Drying Shrinkage of RCA effectively. Some methods of strengthening adhered mortar are more environmentally friendly than removing adhered mortar. Finally, the existing autogenous Shrinkage and Drying Shrinkage prediction models of RAC are discussed. The models obtained by seeing RCA as the two-phase composite has a higher degree of accuracy. This paper can support a better and more comprehensive understanding of the autogenous and Drying Shrinkages of RAC and how to reduce the cracking risk of RAC, which provides a theoretical base for future research and applications of RAC in the construction industry.
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autogenous and Drying Shrinkage of alkali activated slag mortars
Journal of the American Ceramic Society, 2019Co-Authors: Caijun Shi, Zuhua ZhangAbstract:Shrinkage of alkali‐activated slag (AAS) cement is a critical issue for its industrial application. This study investigated the mechanisms and effectiveness of Shrinkage‐reducing agent (SRA) and magnesia expansive agent on reducing autogenous and Drying Shrinkage of AAS mortars that were activated by liquid sodium silicate (LSS) solution with modulus (SiO2/Na2O molar ratio) of 0‐1.5. The results showed that the autogenous Shrinkage of AAS mortars increased with the increase of LSS modulus from 0 to 0.5, then decreased as modulus increased up to 1.5. The Drying Shrinkage consistently increased with the increase in the modulus of LSS. The oxyalkylene alcohol‐based SRA could significantly reduce the autogenous and Drying Shrinkage of AAS mortars while the magnesia expensive agent was comparatively less effective. The autogenous Shrinkage of AAS mortars was inversely proportional to the internal relative humidity, while the Drying Shrinkage was more related to the mass loss of samples. Mathematical models were established to describe the autogenous and Drying Shrinkage behavior of AAS mortars.
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Drying Shrinkage and cracking resistance of concrete made with ternary cementitious components
Construction and Building Materials, 2017Co-Authors: Caijun Shi, Zhenguo Shi, Baihui Tong, Geert De SchutterAbstract:Abstract The compressive strength, free and restrained Drying Shrinkage and cracking resistance of concrete under Drying condition were investigated for ternary cementitious systems containing Portland cement, slag and fly ash. The restrained Shrinkage test (ring test) was carried out following ASTM C1581 . The results showed that the increased replacement level of slag or fly ash from 0 to 50% led to a gradual decrease in 28d compressive strength of concrete. The free Drying Shrinkage increased with the increase of slag content, but reduced with the fly ash content. The cracking resistance was well related to the free Drying Shrinkage of concrete, other factors such as strength also showed certain effects on cracking resistance of concrete. The cracking resistance of concrete was enhanced with the addition of fly ash while weakened with the slag replacement level up to 50%.
Zuhua Zhang - One of the best experts on this subject based on the ideXlab platform.
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autogenous and Drying Shrinkage of alkali activated slag mortars
Journal of the American Ceramic Society, 2019Co-Authors: Caijun Shi, Zuhua ZhangAbstract:Shrinkage of alkali‐activated slag (AAS) cement is a critical issue for its industrial application. This study investigated the mechanisms and effectiveness of Shrinkage‐reducing agent (SRA) and magnesia expansive agent on reducing autogenous and Drying Shrinkage of AAS mortars that were activated by liquid sodium silicate (LSS) solution with modulus (SiO2/Na2O molar ratio) of 0‐1.5. The results showed that the autogenous Shrinkage of AAS mortars increased with the increase of LSS modulus from 0 to 0.5, then decreased as modulus increased up to 1.5. The Drying Shrinkage consistently increased with the increase in the modulus of LSS. The oxyalkylene alcohol‐based SRA could significantly reduce the autogenous and Drying Shrinkage of AAS mortars while the magnesia expensive agent was comparatively less effective. The autogenous Shrinkage of AAS mortars was inversely proportional to the internal relative humidity, while the Drying Shrinkage was more related to the mass loss of samples. Mathematical models were established to describe the autogenous and Drying Shrinkage behavior of AAS mortars.
Mohammad Mastali - One of the best experts on this subject based on the ideXlab platform.
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high strength fiber reinforced one part alkali activated slag fly ash binders with ceramic aggregates microscopic analysis mechanical properties Drying Shrinkage and freeze thaw resistance
Construction and Building Materials, 2020Co-Authors: Zahra Abdollahnejad, Mohammad Mastali, B Woof, Mirja IllikainenAbstract:Abstract One-part alkali-activated binders, also known as the “just-add-water” concept, have received great attention due to their advantages over two-part alkali-activated binders. By avoiding the use of dangerous alkali solutions, these binders are easier to both handle and transport. Ground granulated blast furnace slag is one of the side streams, which can be used in one-part alkali-activated binders to reach high compressive strength at an early age. However, using slag alone has some disadvantages, including a fast setting time and a large Drying Shrinkage, narrowing the application of these mix compositions and causing crack formation, respectively, thus shortening service life. Fly ash can be used in one-part alkali-activated materials to partially substitute for slag in order to both minimize Drying Shrinkage and prolong the setting time. Moreover, ceramic waste can be used as a replacement for normal sand, which is great achievement in terms of developing environmentally friendly alkali-activated materials exclusively from side steam. This paper presents new research on the effects on the fresh and hardened-state properties of one-part alkali-activated mortars of replacing up to 80% of slag with fly ash. These properties were characterized by the initial and final setting time, the strength development (compressive and flexural), and the Drying Shrinkage. Microstructural analyses (SEM/EDS, XRF, TGA/DTG) justified the results. Moreover, different fiber contents and combinations were used to reinforce the developed one-part alkali-activated slag/fly ash mortars to increase the strength, further reduce the Drying Shrinkage, and improve the freeze/thaw resistance. The results showed that fly ash and fibers can reduce the Drying Shrinkage and prolong the setting time. The weakened mechanical properties caused by decreasing the amount of slag are still adequate to let the composite slag/fly ash material be considered in construction applications.
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Drying Shrinkage in alkali activated binders a critical review
Construction and Building Materials, 2018Co-Authors: Mohammad Mastali, Paivo Kinnunen, A Dalvand, Mohammadi R Firouz, Mirja IllikainenAbstract:Abstract Alkali-activated binders have been proposed and have emerged as an alternative to ordinary Portland cement (OPC) binders with acceptable mechanical and durability performances in addition to positive environmental impacts. These alternative binders use a wide range of aluminosilicate precursors, with differing availabilities, reactivities, costs and CO2 emissions. Despite all the studies published on improving the characteristics of these materials in the last decades, some aspects of alkali-activated binders require further investigations. For instance, Shrinkage in alkali-activated binders due to the different chemical processes being involved is more complicated than OPC composites and it plays a key role in long-term performance. However, information on the Shrinkage behavior of these binder systems is scattered and fragmented. Therefore, this review critically surveys the Drying Shrinkage behavior of alkali-activated binders with slag, fly ash and metakaolin. The mechanisms of the Drying Shrinkage and the factors that affect Shrinkage are discussed. Different solutions to limit the Shrinkage are also presented. Then, an analysis is conducted based on the literature, and the main chemical elements affecting the Drying Shrinkage of alkali-activated materials are proposed. Finally, the feasibility of using the developed empirical models for predicting the Drying Shrinkage of OPC concretes is also investigated for alkali activated binders. This review shows that alkali-activated slag binders generally have the higher rate of the Drying Shrinkage compared to other alkali activated binders, albeit, reinforcing the plain compositions with fibers, using expanding admixtures, curing at elevated temperatures, using a combination of slag with fly ash or metakaolin reduces successfully the Drying Shrinkage. Moreover, utilizing ternary diagrams, it is revealed that the molar ratio of Ca/Si has the greatest impact on the rate of Drying Shrinkage in the alkali-activated binders.
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comparative study on the effects of recycled glass fiber on Drying Shrinkage rate and mechanical properties of the self compacting mortar and fly ash slag geopolymer mortar
Journal of Materials in Civil Engineering, 2017Co-Authors: Z Abdollahnejad, Mohammad Mastali, A DalvandAbstract:AbstractIn this comprehensive experimental study, the effects of recycled glass fiber on the Drying Shrinkage and mechanical properties of the self-compacting mortar and fly ash–slag geopolymer mor...
