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The effect of resting time on the rheological properties of cement suspensions is generally explained by early formed structure and overconsumption of polycarboxylate superplasticizers (PCEs). In this paper, we propose that the influence of resting time on the rheological properties is closely related to size variation of non‐absorbed PCE. To identify this, glass bead suspensions were prepared with various amounts of PCE and ionic solution, and their rheological properties were evaluated at various times. We found that the yield stress increases with time at higher PCE concentrations and higher ionic strength solutions. Adsorbed PCE during resting tends to bridge the particles rather than disperse them. In addition, it was found that hydrodynamic radius of PCE increased with resting time, and depletion forces resulting from non‐absorbed PCE size changes correlate well with the increased yield stress. [ABSTRACT FROM AUTHOR]

Studies have shown that in an aqueous suspension of inert glass beads, the yield stress is increased as a function of resting time. This study investigates this unexpected phenomenon, focusing on solid surface potentials, PCE size in ionic solutions, and their possible relations to rheological behaviour with resting time. Results indicated that PCE in artificial pore solution will result in a higher yield stress with time. PCE with lower anionic charges and molecular weight can significantly increase the yield stress after 2 h of resting. The absolute value of the zeta potential grows to a certain degree after resting phase. Dynamic light scattering (DLS) results showed that the size of PCE molecules in ionic solutions increases over time, suggesting an enhanced depletion force or bridging force among glass bead particles, which could be the reasons for the increase in yield stress over time. Furthermore, the possible impacts of the depletion force or bridging force resulting from the PCE size change on the rheological properties of cement suspension are discussed. [ABSTRACT FROM AUTHOR]

Flue gas desulphurization (FGD) gypsum is a kind of industrial solid waste containing impurities (i.e., heavy metal ions Zn2+ and Ni2+), which may lead to threats to the ecological environment and public health. To safely use the FGD gypsum, this study investigated the mechanical strength, releasing property of SO42- and leachability of heavy metal ions of a series of FGD gypsum (40%) based mortar with various cement to slag ratios. The hydration process, pore structure, and morphology of the sample were then characterized and analyzed by isothermal calorimetry, H1 low-field nuclear magnetic resonance (NMR), and scanning electron microscope with energy dispersive X-Ray analysis (SEM-EDx). It was found that the highest mechanical strength could be obtained when the C/S ratio was 1:5, and the decrease of C/S ratios from 4:2 to 1:5 leads to less SO42- releasing from the mortar. The heavy metal leachability of the mortars is lower than that of the limitation of solid waste stipulated by the specification of GB5085.3-2007, and less of the heavy metal are leached from the sample as the C/S ratios decrease. The heat flow for the paste sample with 40% of FGD gypsum was delayed as the cement to slag ratio decreased from 5:1 to 2:4. In addition, the released amount of Zn2+ ions linearly decreases with the pore size of gel pores and capillary pores but increases with the pore size of macropores, and the ettringite in the paste exhibits the transformation from the needle to the clubbed shape when smaller cement to slag ratio was used. This work helps to understand how to reduce the heavy metals leachability of FGD gypsum from cementitious material and provides baseline for safely using the FGD gypsum for the preparation of building materials. [ABSTRACT FROM AUTHOR]

Water repellent (WR) has been widely used to improve the durability of cementitious materials (CMs) by reducing the absorption of water and aggressive ions. In this study, cement pastes were prepared with three types of WR, namely, waterborne pure nanosilicone emulsion (NS), isobutyltriethoxysilane (IS), and octyltriethoxysilane (OCT). The effects of WR on setting time, compressive strength, and water absorption were investigated. The influence of WR on the transverse relaxation time spectrum from 0 min to 28 days during the hydration process was monitored with a low-field nuclear magnetic resonance (LF-NMR). In addition, X-ray diffraction (XRD) and heat flow were employed to study the effect of WR on hydration characteristics. The results showed that the WR specimens exhibited a limited reduction of compressive strength compared with the control sample at 28 days. The use of WR reduced the water absorption of cement paste when compared to that of the control specimens. The results showed that the WR exhibited a retarding effect on hydration reactions, and the capillary and gel pores of the cement paste increased compared with that of the reference sample. XRD analysis showed that the formation of hydration products had been restricted with the addition of WR. The heat flow results showed that the retardation effect was enhanced as the WR dosages increased. [ABSTRACT FROM AUTHOR]

Copper slag (CS), an industrial by‐product, can be used as supplementary cementitious materials in the mortar to achieve sustainable development of the copper and the cement industries. However, available evaluation and prediction models for CS cementitious material considering the comprehensive effect of multiple factors are very scarce. In this study, a reliable experimental database with 141 sets of data was developed via compressive strength tests and reviews of the literature at first. Subsequently, the gray correlation analysis was performed to evaluate the correlation between the influencing factors and the compressive strength of mortar with CS addition. The results demonstrated that the strength was most sensitive to the water to binder ratio and CS chemical composition, which could not be ignored to compare and evaluate the strength acquired from different works. Besides, for the same batch CS used in this study, the compressive strength at 3 d depended on the curing program; while it was more easily affected by the CS fineness after 28 d. Finally, a reliable prediction model for the compressive strength of the mortar with CS addition was implemented by the back‐propagation neural network. The established network with four neurons in the hidden layer had a high accuracy as well as a good generalization ability, which can be used as an effective tool for detecting trends of the compressive strength and designing CS‐added mortar with a user‐defined compressive strength. [ABSTRACT FROM AUTHOR]

This document is a correction notice for an article titled "Resting time effect on the rheological behaviour of glass beads and cement suspension: The role of PCE size and ionic strength." The correction addresses errors in the names of three authors: Alexander Mezhov, Regine von Klitzing, and Schmidt Wolfram. The correct names should appear as Alexander Mezhov, Regine von Klitzing, and SchmidtWolfram. The article has been corrected online. The reference for the original article is provided for further reading. [Extracted from the article]

Previous studies focused on the determination and simulation of the bleeding extent of fresh cement paste and provided objective conclusions. However, few studies exist on the influence of bleeding on the final structure of cement paste. This study focused on the microstructure development during the hydration of cement paste with various bleeding caused by the water-cement ratio, the slag replacement, and the superplasticizer. To obtain information on the porosity profile and pore size distribution, the sample was measured using a low-field nuclear magnetic resonance (NMR) with Hahn spin sequence and Carr-Purcell-Meiboom-Gill (CPMG) sequence from top to bottom. The results showed that increasing bleeding thickness leads to a heterogeneous structure from top to bottom in terms of porosity profile and pore size distribution. Moreover, hydration can reduce the difference in the pore structure, especially when the bleeding depth is small. It was also found that the influence of bleeding depth on the pore size distribution of gels pores during hydration is minor compared with that of the capillary pores. Furthermore, detailed discussions on the connections between the bleeding and the final structure are presented in this paper. [ABSTRACT FROM AUTHOR]

In this study, a novel method for calculation of surface fractal dimensions ( D f ) of pore structure based on 1 H low-field NMR was proposed. Influencing parameters including water cement ratio and specific areas of cements on the fractal dimensions were investigated. In addition, the relationship between pore structure and fluidity value as well as bleeding velocity was also discussed in this paper. Results confirm that the pore structure of fresh cement paste has a significant fractal feature, and fractal regions, region i (2.0 < D f < 2.2) and ii (2.6 < D f < 3.0), are found for the pore structure in the distribution of the transverse relaxation time ( T 2 ). It is found that the D f for region ii is sensitive to both water cement ratio and specific surface of cements. Moreover, the initial fluidity of fresh cement paste increase with the T 2 position, and with identical T 2 position, fresh cement paste with high D f can generate a low fluidity. Results also suggest that high D f of pore structure lead to a low velocity of bleeding, and D f can be a main factor for migration of the bleeding water when the T 2 positions are close. [ABSTRACT FROM AUTHOR]

In this paper, a brief overview of the current literature on the dispersion mechanism of polycarboxylate-type superplasticisers (PCEs) is first presented. Then, the available free water amount and fluidity of cement paste with various water-to-cement ratios ( w/ c) and PCE dosages are measured. The phase and particle size distribution of early cement hydrates are analysed by X-ray diffraction and laser particle size analysis, respectively. As a result, a surprising tendency is observed: the increase rate of fluidity increases with decreasing w/ c ratio when the dosage of PCE gradually increases. This phenomenon cannot be explained by the steric effect. The authors also conclude that not less than 2·0% of solids volume of 'AFt-PCE' structures (early hydrates of ettringite (AFt) coated with PCE, < 200 nm) are dispersed well in the interstitial pore space along with non-adsorbed PCE. Based on these results, the authors present a possible dispersion mechanism in the PCE-cement system studied here based on the repulsion originating from the exclusion of free polymers (non-adsorbed PCE, 'AFt-PCE' structure and some other fine matters coated with PCE) from the gap between cement particles. [ABSTRACT FROM AUTHOR]

A new solidification process called non-interfacial-gap permanent-mold casting (NIGPMC) is proposed to improve the cooling rate by eliminating the metal-mold interfacial gap. High-Cr steel ingots were prepared by this process and conventional permanent-mold casing (CPMC) separately. Comparing with CPMC, the primary dendrite arm spacing obtained by NIGPMC is greatly refined. It is demonstrated that the NIGPMC is a promising pathway to refine the microstructure of the large ingot. [ABSTRACT FROM AUTHOR]

• Coir fibers at the adopted dosage have a negligible influence on cement hydration kinetics. • Internal curing effect of saturated coir fibers. • Water competition introduced by dry coir fibers. • Saturated coir fibers decrease autogenous shrinkage and drying shrinkage of cement materials. • NMR can be used to track water transportation and shrinkage in cement materials. Nuclear Magnetic Resonance (NMR) is used to study the early-age hydration as well as autogenous shrinkage and drying shrinkage of cement paste with the addition of coir fibers. The dosage and water content of coir fibers are evaluated. The results show that added coir fibers have a negligible influence on cement hydration kinetics. However, the internal curing effect of saturated coir fibers and water competition induced by dry fibers are visualized. As the saturated fiber content increases, autogenous shrinkage and drying shrinkage decrease due to the internal curing and reinforcing effects of fibers. Dry fibers generate more autogenous shrinkage but less drying shrinkage than saturated fibers of the same dosage due to the introduced water competition. NMR is proven able to track water transportation and shrinkage in cement composites. [ABSTRACT FROM AUTHOR]

The flow around a body of revolution with an appendage controlled by electromagnetic force is calculated by a finite volume method in order to assess the influence of the appendage on the flow and the control effect of the electromagnetic force. The Reynolds number (Re) base on the hull length is 1.0 × 107. An electromagnetic actuator is flush-mounted on the surface of the appendage to generate streamwise eletromagnetic force (Lorentz force) for flow control. The flow around the body at straight course and 6° yaw controlled by Lorentz force is simulated and discussed. The results indicate that the elliptical appendage introduces a complex wake structure and force fluctuation. The wake of the appendage has less influence on the boundary layer of the body at 6° yaw than at straight course. When the Reynolds number is as high as 1.0 × 107, the flow field and dynamic characteristic of the body approximate to the Euler solution. The Lorentz force may suppress the near-wall separation from the appendage effectively and reduce the drag and vibration, especially in the straight course case. [ABSTRACT FROM AUTHOR]

1H spin-lattice relaxometry (T1, longitudinal) of cement pastes with 0 to 0.18 wt % polycarboxylate superplasticizers (PCEs) at intervals of 0.06 wt % from 10 min to 1210 min was investigated. Results showed that the main peak in T1 relaxometry of cement pastes was shorter and lower along with the hydration times. PCEs delayed and lowered this main peak in T1 relaxometry of cement pastes at 10 min, 605 min and 1210 min, which was highly correlated to its dosages. In contrast, PCEs increased the total signal intensity of T1 of cement pastes at these three times, which still correlated to its dosages. Both changes of the main peak in T1 relaxometry and the total signal intensity of T1 revealed interferences on evaporable water during cement hydration by dispersion mechanisms of PCEs. The time-dependent evolution of weighted average T1 of cement pastes with different PCEs between 10 min and 1210 min was found regular to the four-stage hydration mechanism of tricalcium silicate. [ABSTRACT FROM AUTHOR]

In this study, the setting property and mechanical strength of cement pastes containing accelerators (CPCA) with or without superabsorbent polymers (SAPs) were first studied. The early microstructure evolution and water distribution at 7 and 28 days were probed by 1D (T2) and 2D (T1-T2 maps) H1 nuclear magnetic resonance (NMR) relaxometry, and the microstructure was systematically investigated by using mercury intrusion porosimetry (MIP), back-scattered electron (BSE) image and energy-dispersive X-ray spectroscopy (EDX) analysis. Results showed that the SAPs in the cement paste containing accelerators had various influences on setting time and compressive strength depending on the type of accelerators. The presence of SAPs in the cement paste containing alkaline free accelerators could alleviate the decrease of internal relative humidity, promote hydration and help to modify the pore structure. Moreover, it was observed that the SAP cavities could be nicely filled with calcium hydroxide (CH) in the cement paste with alkaline free accelerators. [ABSTRACT FROM AUTHOR]

In this study, the setting property and mechanical strength of cement pastes containing accelerators (CPCA) with or without superabsorbent polymers (SAPs) were first studied. The early microstructure evolution and water distribution at 7 and 28 days were probed by 1D ( T ₂) and 2D ( T ₁- T ₂ maps) H¹ nuclear magnetic resonance (NMR) relaxometry, and the microstructure was systematically investigated by using mercury intrusion porosimetry (MIP), back-scattered electron (BSE) image and energy-dispersive X-ray spectroscopy (EDX) analysis. Results showed that the SAPs in the cement paste containing accelerators had various influences on setting time and compressive strength depending on the type of accelerators. The presence of SAPs in the cement paste containing alkaline free accelerators could alleviate the decrease of internal relative humidity, promote hydration and help to modify the pore structure. Moreover, it was observed that the SAP cavities could be nicely filled with calcium hydroxide (CH) in the cement paste with alkaline free accelerators.