The Experts below are selected from a list of 13212 Experts worldwide ranked by ideXlab platform
Jun Zhang - One of the best experts on this subject based on the ideXlab platform.
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zeolite to improve strength Shrinkage performance of high strength engineered cementitious composite
Construction and Building Materials, 2020Co-Authors: Jun ZhangAbstract:Abstract Engineered cementitious composite (ECC) is a class of high-performance material because it displays strain hardening by multiple crack formation under tension. This unique property makes ECC an ideal constructional binding mortar or repairing material particularly for concrete cracks in existing structures. However, a major issue of ECC is the high Shrinkage, which creates differential Shrinkage and extra tensile stress that adversely affects its durability. To mitigate Shrinkage, a novel way of using zeolite as an internal curing agent without sacrificing the strength of ECC is herein advocated. Zeolite is structurally porous that can trap water and act as a water reservoir to increase internal relative humidity (IRH). In this paper, the Shrinkage, IRH and compressive strength of ECC containing 15% (18%), 20% (24%), and 30% (36%) of zeolite replacing quartz sand by weight (and by volume) is studied experimentally. Test results indicate that the 28-day total Shrinkage of ECC decreases with the zeolite replacement ratio. From the Shrinkage-to-strength ratio, it shows that ECC with 30% zeolite yields the lowest Shrinkage per compressive strength, and hence the optimal ratio for quartz sand replacement in this study. With the beneficial effect observed, zeolite replacement ratio greater than 30% (36%) is recommended for future study on Shrinkage Reduction of ECC.
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Experimental study on Shrinkage Reduction of calcium sulphoaluminate cement concrete with addition of pre-wetted lightweight aggregate
Construction and Building Materials, 2020Co-Authors: Jun Zhang, Yuzhang LiuAbstract:Abstract In the present paper, Shrinkage Reduction with pre-wetted LWA of calcium sulphoaluminate cement (CSA) concrete is experimentally investigated. In the test programs, Shrinkage of low, medium and high strength CSA concrete with and without internal curing with pre-wetted LWA is measured. Water movement between a single pre-wetted ceramsite particle and the surrounding cement paste during cement hydration is directly measured through a glass tube connected with the ceramsite. The test results show that the main component of Shrinkage of CSA concrete, no matter low or high strength concrete, is autogenous Shrinkage other than drying Shrinkage. Autogenous Shrinkage of high strength CSA concrete is much higher than that of low strength CSA concrete. The addition of pre-wetted LWA can greatly reduce the autogenous Shrinkage of CSA concrete even the internal curing water to cement ratio used in the concrete is as low as 0.04. The efficiency of Shrinkage Reduction is influenced by concrete strength or water to binder ratio. The higher the strength, the greater the Shrinkage Reduction. Water contained in LWA starts to release at about 15–25 min after mixing depending on water to binder ratio of the cement paste. Water movement between LWA and surrounding cement matrix during cement hydration obeys a two-stage mode, a fast releasing stage followed with a slow releasing stage. Amount of releasing water from LWA is obviously influenced by the initial air content in the LWA and the water to binder ratio of the paste. As air content is varied between 0 and 50% in volume, the more the air content, the more the water moved out of LWA. For given initial air content, the lower the water to binder ratio, the more the water removed from the LWA.
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High-strength concrete mixture with calcined zeolite particles for Shrinkage Reduction
Magazine of Concrete Research, 2019Co-Authors: Jun Zhang, Xiaoping Ding, Qing Wang, Xuan ZhengAbstract:In this study, calcined zeolite particles with average size of 0·18 mm were used as an internal curing agent for high-strength concrete. The purpose of the study was to explore the mixture design o...
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Effective solution for low Shrinkage and low permeability of normal strength concrete using calcined zeolite particles
Construction and Building Materials, 2018Co-Authors: Jun Zhang, Xiaoping Ding, Qing Wang, Xuan ZhengAbstract:Abstract The purpose of this paper is to explore the mixture design of normal strength concrete towards low Shrinkage and low permeability using calcined zeolite as internal curing agent. Shrinkage, strength and permeability tests were conducted on the concretes. Through above tests, efficiency of Shrinkage Reduction using pre-wetted calcined zeolite particles in normal concrete, and impacts of porous zeolite particles in concrete on the movement of ions in concrete, are evaluated. Based on the present study, the following conclusions can be drawn: 1) the use of pre-wetted zeolite particles in normal strength concrete can reduce Shrinkage of the concrete, especially the drying Shrinkage; 2) the addition of the porous zeolite may negatively influence the permeability of concrete at early-ages. However, the long-term permeability of concrete (such as 90 days) is better than that of the control concrete; 3) designed four mixtures with addition of pre-wetted zeolite particles have a comparable cement amount normally used in practice for normal strength concrete based on the present study.
Khandaker M A Hossain - One of the best experts on this subject based on the ideXlab platform.
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Internally cured high performance concrete with magnesium based expansive agent using coal bottom ash particles as water reservoirs
Construction and Building Materials, 2020Co-Authors: Roberto Rodríguez-Álvaro, Belén González-fonteboa, Sindy Seara-paz, Khandaker M A HossainAbstract:Abstract Shrinkage is one of the main concerns related to high performance concrete (HPC) durability. Its high density paste, consequence of a low water to binder ratio, can be unprofitable if cracks appear due to excessive tension when volume changes are restrained. Therefore, volume stability is a priority. In this work, three different strategies have been studied with that purpose: integration of fly ash as a low reactive supplementary cementitious material, internal curing via coal bottom ash particles as water reservoirs and the use of an expansive agent based on magnesium oxide (MEA). Many research works address the three Shrinkage Reduction strategies individually. However, studies regarding their simultaneous use are not prevalent so this work proposes its combined application. Results indicate that internal curing and MEA have a synergistic effect in HPC. Internal curing enhances MEA expansion due to the lack of water in this kind of concrete, contributing to autogenous Shrinkage compensation. When concrete is affected by air-drying conditions, the use of MEA, internal curing, or both together make Shrinkage to increase. MEA effectively expands in wet cured HPC although internal curing is not effective in this condition due to the absence of self-desiccation and limited porous aggregate water desorption. Taking into account the effects of each Shrinkage Reduction strategy and curing condition, it has been concluded that the use of fly ash as supplementary cementitious material, internal curing and MEA is recommended together with prevention of water evaporation from HPC surface.
Xuan Zheng - One of the best experts on this subject based on the ideXlab platform.
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High-strength concrete mixture with calcined zeolite particles for Shrinkage Reduction
Magazine of Concrete Research, 2019Co-Authors: Jun Zhang, Xiaoping Ding, Qing Wang, Xuan ZhengAbstract:In this study, calcined zeolite particles with average size of 0·18 mm were used as an internal curing agent for high-strength concrete. The purpose of the study was to explore the mixture design o...
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Effective solution for low Shrinkage and low permeability of normal strength concrete using calcined zeolite particles
Construction and Building Materials, 2018Co-Authors: Jun Zhang, Xiaoping Ding, Qing Wang, Xuan ZhengAbstract:Abstract The purpose of this paper is to explore the mixture design of normal strength concrete towards low Shrinkage and low permeability using calcined zeolite as internal curing agent. Shrinkage, strength and permeability tests were conducted on the concretes. Through above tests, efficiency of Shrinkage Reduction using pre-wetted calcined zeolite particles in normal concrete, and impacts of porous zeolite particles in concrete on the movement of ions in concrete, are evaluated. Based on the present study, the following conclusions can be drawn: 1) the use of pre-wetted zeolite particles in normal strength concrete can reduce Shrinkage of the concrete, especially the drying Shrinkage; 2) the addition of the porous zeolite may negatively influence the permeability of concrete at early-ages. However, the long-term permeability of concrete (such as 90 days) is better than that of the control concrete; 3) designed four mixtures with addition of pre-wetted zeolite particles have a comparable cement amount normally used in practice for normal strength concrete based on the present study.
Abir Altabbaa - One of the best experts on this subject based on the ideXlab platform.
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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.
F Puertas - One of the best experts on this subject based on the ideXlab platform.
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effect of Shrinkage reducing admixtures on the properties of alkali activated slag mortars and pastes
Cement and Concrete Research, 2007Co-Authors: Marta Palacios, F PuertasAbstract:Abstract The effect of a Shrinkage-reducing admixture (SRA) based on polypropylenglycol on the dimensional stability of waterglass-activated slag mortars was studied. The analysis also showed the effect of the admixture on pore structure of the mortars as well as on the mineralogical composition and microstructure of the alkali-activated slag pastes. The SRA reduced the Shrinkage by up to 85 and 50% when the alkali-activated slag mortar specimens were cured at relative humidities of 99 and 50%, respectively. The mechanism primarily involved in Shrinkage Reduction is the decrease in the surface tension of pore water prompted by the admixture. The SRA also modified the pore structure – under both curing conditions – increasing the percentage of pores with diameters ranging from 1.0 to 0.1 μm. Capillary stress is much lower in these pores than in the smaller capillaries prevailing in mortars prepared without admixtures. Microstructurally, the SRA occasioned a slight increase in the proportion of Si units Q 2 in the CSH gel and a decrease in the percentage of Al replacing the Si in the gel structure. The admixture did not, however, modify the mineralogical composition of the pastes. Finally, the SRA admixture retarded the alkaline activation of the slag, more intensely at higher admixture dosages. While the admixture did not significantly alter the degree of reaction in pastes cured for 7 days at RH = 99%, the value of this parameter dropped by 7% in the presence of the admixture in pastes cured at 50% relative humidity.
