Papers by Keyword: Hydration

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Authors: V. Manić, Lj. Miljković, B. Đurić-Stanojević
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Authors: Xiao Jun Wang, Xiao Yao Wang, Hong Fei Zhu, Chen Qian
Abstract: As the major structure of silica fume, the change of silica tetrahedron in the pozzolanic reaction during the hydration has not been revealed clearly in previous studies. In this study, 29Si solid-state MAS NMR was used to characterize the silica tetrahedron change of the silica fume in saturated alkali solution with 0.9, 1.2, 1.5 and 1.8 four different calcium/silica ratios. The amorphous Q4 silica tetrahedron structure in silica fume changed into Q1 silica tetrahedron at 1 day. Q2 silica tetrahedron formed from Q1 silica tetrahedron within 3 days. Q1 and Q2 silica tetrahedron reached a balance until silica fume completed pozzolanic reaction and the Q4 silica tetrahedron exhausted. The coexistence of Q1 and Q2 silica tetrahedron benefited the physical properties increase of cementitious system. 29Si solid-state MAS NMR results proved that the chain length of silica tetrahedron in C-S-H shortened in the silica fume hydration while the C/S ratio increased.
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Authors: Lenka Scheinherrová, Anton Trník, Eva Vejmelková, Pavel Reiterman, Igor Medveď, Robert Černý
Abstract: In this paper, the effect of elevated temperatures (up to 1000 °C) on thermal properties of two similar types of high-performance concrete containing fine ceramic waste and clay shale, respectively are used as a partial replacement of the cement binder is investigated. Samples were prepared in the same manner and both types of concrete contained from 0 to 60 mass% of either replacement. Both replacements were used in our study as a pozzolana active material which can partially replace cement binder and can improve the final properties of concrete. The aim of this paper is to compare the influence of two different pozzolana active materials on selected thermal properties of high-performance concrete at high temperatures up to 1000 °C. The investigation was performed using the differential scanning calorimetry and these results were supplemented by measurement on horizontal dilatometer.
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Authors: Marco Pepe, Eduardus Koenders, Romildo Dias Toledo Filho, Enzo Martinelli
Abstract: The construction sector is more and more committed to reduce its environmental impacts. One of the key actions undertaken in the last decade deals with the ability of turning construction and demolition waste into new raw materials. For instance, the use of recycled aggregates for producing new concrete was one of the most investigated. Thus, in the last decade, plenty of researches were involved in project on characterising the mechanical behaviour of concrete made with recycled aggregates. However, these projects were mainly experimental in nature and generally led to merely empirical formulations. Conversely, this paper is intended at providing a contribution for predicting the mechanical properties of Recycled Aggregates Concrete (RAC). Particularly, it aims at quantifying the effect of replacing ordinary aggregates with Recycled Concrete Aggregates (RCA) on the resulting compressive strength of RAC. To this end, a conceptual model considering both the relevant physical properties of regular and recycled aggregates, including the attached mortar content, and the hydration reactions of Portland cement paste is proposed. The actual predictive capacity of the proposed model is assessed through an experimental validation against experimental tests carried out on several concrete batches produced with various values for the different keys parameters, such as the nominal water-to-cement ratio, the aggregates replacement ratio and the initial moisture condition of aggregates. Both the experimental data and the theoretical formulations proposed in this paper stem out from the inter-university collaboration developed as part of the EU funded EnCoRe Project (www.encore-fp7.unisa.it).
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Authors: Hashem Al-Mattarneh, Abdullah Alwadie, Ahmad Malkawi, Muhd Fadhil Nuruddin
Abstract: A new measurement system is developed to monitor the early hydration of cementitious materials based on measured dielectric properties of the material in low electromagnetic frequency range. The objectives of this paper were to evaluate the changes in the electromagnetic properties for samples with different fly ash content and to establish the reliability of the measurement technique by comparing with results obtained by traditional method such as thermal method that is either time consuming or impractical. The method adopted in the present experimental work is a parallel plate electrode system (PPES). The suggested monitoring device for concrete hydration and strength development is based on the relationship between the electromagnetic properties such as dielectric constant, loss factor and the strength development during hydration process and curing time. In this research the electromagnetic properties of concrete is found to be dependent on the hydration and strength of concrete. Therefore the development of microstructure and concrete compressive strength can be determined by monitoring its electromagnetic properties in the frequency range of 1 to 100 kHz.
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Authors: Koen Van Den Abeele, W. Desadeleer, Geert de Schutter, Martine Wevers
Abstract: An integrated system of dynamic nondestructive experiments for material process monitoring is proposed, consisting of a combination of the AE technique with Nonlinear Elastic Wave Spectroscopy (NEWS). Using this system, we evaluate the microstructural properties of freshly poured concrete during hydration, with the ultimate goal to correlate these properties to its long-term behavior. The integrated system allows online monitoring of the condition parameters, of the internal microstructural activity by continuously triggering AE events and of the linear and nonlinear elastic properties of the microstructure through ultrasonic pulsed and continuous wave transmission measurements at regular time intervals. The internal temperature readings, the evolution in the acoustic emission events and the behavior of the linear and nonlinear elastic properties can be related to the different stages in the hydration process of concrete. The data are analyzed as a function of the degree of hydration for various concrete compositions during the first three days of the hydration process.
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Authors: Yu Qing Zhao, Chun Zhen Qiao, Wei Jiao Chen
Abstract: The carbonation characteristics of Ca-based CO2 absorbent hydrated by water were investigated as part of a multi-cycle performance study, and the change of the microstructure, pore radius and specific surface area of the absorbent with the number of cycles was researched. The results show that, conversion of sorbent hydrated by water is enhanced to 85% after 10 cycle, significantly higher than the 20% achieved by dry limestone cycle. Because the specific surface area is greatly enhanced, as well as the distributions of pore radius is improved in the hydration process, which develop an effective way to retain the fine qualities of Ca-based CO2 sorbents in a repetitive calcination-carbonation process.
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Authors: Peng Xue, Qi Xing Yang, Gui Qun Liu, Feng Lan Han, Liang Jiang, Fredrik Engström, Bo Björkman
Abstract: A steel slag has been treated by air granulation, in order to enhance cementitious properties of the slag. Two samples with sizes ranged 1.68-2.38mm and 212-297μm and coded as Slag A and Slag B, respectively, were chosen from the granulated slag for investigations. A sample of the original steel slag was also studied. XRD analyses indicated the formations of α-C2S, β-C2S, C2F, C2MS2, f-MgO and α-C2S, C2F, f-MgO in Slag A and Slag B, respectively. The phases in the two slag samples were quite different from the phases found in steel slag. The SEM results show a reduction of C2S sizes from 10-20μm for the steel slag to nano-scales by air quenching for Slag B. This treatment of air quenching has increased the cumulative heat of hydration to 105.35J/g measured for Slag B, almost two times greater than that of the steel slag. The study results demonstrate a high potential for utilizations of the steel slag in cement and concrete applications after the slag treatment by air quenching. The treatment may thus lead to an environmental friendly and cost-effective recycling for the steel slag. This can also contribute to the sustainable developments in the steel and cement/concrete industries.
488
Authors: Zhong Zi Xu, Qing Lin, Yan Bao Li, Xiang Hui Lan, Chun Hua Lu
Abstract: The aim of this study was to evaluate the suitability of CaF2 doping tricalcium silicate (Ca3SiO5, C3S) as dental restorative materials. The solid state reaction method was used to prepare CaF2 doping C3S (F-C3S) using CaCO3, SiO2 and CaF2 as the starting materials. The in vitro bioactivity, the rate of heat evolution and the compressive strength were investigated. The in vitro bioactivity was examined by soaking the pastes in simulated body fluid (SBF). The FTIR and SEM results indicated the hydroxycarbonate apatite (HCA) layers of F-C3S pastes and pure C3S pastes occurred after soaking for 1 day and 3 days, respectively. The difference in bioactivity was attributed to the formation of F-substituted apatite, which has a Ksp lower than HCA. As compared with the pure C3S, the rate of heat evolution during the hydration of F-C3S was slower. This was avail to the dimensional stability of dental restorative materials. The pastes of F-C3S had a lower early compressive strength in the early stage, but a higher compressive strength in the later stage. Our results indicated that F-C3S would be bonded better to the teeth because of the earlier formation of HCA and the higher later compressive strength. F-C3S may be a progressive candidate for dental restorative materials.
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Authors: Dong Yu Xu, Lei Qin, Shi Feng Huang, Xin Cheng
Abstract: 1-3 type cement/epoxy resin based piezoelectric composite was designed and fabricated aiming at providing a new method for cement hydration monitoring. Combining with piezoelectric impedance technology, the cement hydration reaction process was monitored by using the composite. The research results show that in the initial cement hydration period, the resistance-frequency curves of the sensor drift toward low frequency direction, while the anti-resonance resistance value decreases gradually. With increasing cement hydration time, the resistance-frequency curves of the sensor drift toward high frequency direction and the anti-resonance resistance value shows fluctuation changes. The cement hydration reaction process can be divided into different periods according to changes of anti-resonance frequency and anti-resonance resistance value of the sensor.
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