Increasing the chloride binding capacity of hydration products is an effective countermeasure to improve the chloride resistance of cement-based materials. The alumina content of binder is usually ...adopted to evaluate the chloride binding capacity, in terms of Friedel’s salt. However, the influences of aluminum on the characteristics of C–S–H and finally on physically bound chloride are not taken into account. In the present study, the characteristics of hydration products were widened by introducing silica fume and metakaolin into Portland cement pastes, respectively; then, the consequent chloride binding capacity was followed using Freundlich binding isotherms; chemically and physically bound chlorides were further distinguished. The results show that the chloride binding capacity of cement pastes reduced with the increase of SF addition, but proportionally increased with the increasing MK addition. The amount of chemically bound chloride was doubled by adding 16% MK (15.07 mg/g), which was about 6 times as high as that of cement paste with 16% SF. The chemically bound chloride through formation of Friedel’s salt by ion-exchange mainly related to the monocarboaluminate content, whereas the physically bound chloride was largely depended on the specific surface area of cement pastes. Moreover, MK promoted the substitution of Al
3+
for Si
4+
in C–S–H, resulting in more sites for chloride binding and then a higher amount of physically bound chloride. In contrast, SF increased the protonation degree of C–S–H, leading to a lower positive charge density on the surface of C–S–H and finally a lower amount of physically bound chloride due to poor electrostatic adsorption.
This study investigates the structural characteristics and hydration kinetics of modified basic oxygen furnace steel slag. The basic oxygen furnace steel slag (BOFS) was mixed with electric arc ...furnace steel slag (EAFS) in appropriate ratios and heated again at high temperature in the laboratory. The mineralogical and structural characteristics of both BOFS and modified steel slag (MSS) were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy, Raman and Fourier transform infrared spectroscopies. The results show that modification increases alite content in MSS and decreases alite crystal size with the formation of C
6AF
2. One more obvious heat evolution peak appears in MSS's heat-flow rate curves in comparison to BOFS, becoming similar to that of typical Portland cement paste. As a result, its cementitious activity is much improved.
Abstract-Visible light communication (VLC) is an important complementary technology to traditional radio frequency (RF) communication due to the abundance of available frequency resources and the ...high data rates. VLC systems are, however, constrained by the low −3 dB bandwidth of light-emitting diodes (LED) and high bit error rates (BER). Herein, we propose a vertical-structure microLED array with an Si-doped first quantum barrier (FQB) that suppresses the quantum confinement Stark effect (QCSE), increasing the radiative recombination rate. The micro-LED array exhibits an −3 dB bandwidth of 578 MHz at 2000 A / cm2 when the Si doping content of the FQB is <inline-formula> <tex-math notation="LaTeX">8 \times 10^{18} \mathrm{~cm}^{-3} </tex-math></inline-formula>. A data rate of <inline-formula> <tex-math notation="LaTeX">1.61 \mathrm{~Gb} / \mathrm{s} </tex-math></inline-formula> with a BER of <inline-formula> <tex-math notation="LaTeX">3.51 \times 10^{-3} </tex-math></inline-formula> over the distance of 1 m free space was demonstrated using the on-off keying (OOK) modulation scheme. This work shows great potential for high-speed VLC systems by proposing a simple way to improve communication performance.
The digital image correlation (DIC) technique was applied to the analysis of displacement fields along the surface cracks of ultra-high-performance fiber-reinforced concrete (UHPFRC) under a bending ...load. Analysis was performed on the fiber bridging forces acting on a unit area of cracked sections belonging to different regions (perfect bonding region, partial debonding region, and full debonding region), according to the fiber distribution characterization and DIC data. By using the DIC technique, the visualization and quantification of the UHPFRC fracture properties could be determined. The length of the uniform zone increased, whereas the fracture process decreased under the external load of the limit of proportionality (LOP). With the appearance of macro-cracks under the external load of the modulus of rupture (MOR), the length of the uniform and fracture process zones increased as the fiber content increased. However, the localization zone decreased. The steel fiber volume fractions had limited influence on the tensile strain at cracking and the complete debonding of fibers.
To elucidate the effect of aggregate size and volume on the non-uniform strain distribution in concrete, drying shrinkage of mortar and concretes were determined with 3D digital image correlation ...(3D-DIC). The distribution of shrinkage displacements and strains in mortar and concrete were analyzed. The results show that 3D-DIC makes it possible to measure non-uniform displacement distributions initiated by shrinkage in mortar and concrete. The non-uniformity became more remarkable with drying time. The presence of aggregates larger than 5 mm in concrete have locally changed the displacement and strain fields. Aggregates within 5–25 mm make non-uniform strain of concrete more fluctuant, especially when the aggregate size is larger than 10 mm. The maximum and minimum principal strain distributions became more heterogeneous with decreasing volume of aggregates.
•BOFS and SF had influence on formation of hibschite, α-C2SH and tobermorite.•Pore structure was coarsened at high lime content or by BOFS, but refined by SF.•Compressive strength and thermal ...properties wereclosely related to pore structure.•A random model was developed to simulate pore structure and thermal conductivity.•Temperature profile and heat flow based on the simulation model were discussed.
Lime-pozzolana pastes with high volumes of fly ash (FA) are widely used as masonry cement and autoclaved building materials. In this work, four sets of pastes with varying lime content from 12% to 25% were prepared and autoclaved at 180 °C for 8 h, and basic oxygen furnace steel slag (BOFS) and silica fume (SF) were added as replacements of FA in each set. The properties assessed were compressive strength, thermal properties by transient plane source method, porosity and pore size distribution by mercury intrusion porosimetry (MIP). The microstructure was investigated by means of XRD and SEM-EDS. Results show that both pore structure and microstructure of the pastes were significantly altered by variations in compositions. High lime content resulted in an increase of porosity and more capillary pores were formed, replacement of FA with BOFS coarsened the pore structure but the opposite was observed for SF. The compressive strength was closely related to pore structure and microstructure as expected. The thermal conductivity and thermal diffusivity decreased with increasing lime content and were further decreased by incorporating BOFS and SF. Only SF could effectively increase the specific heat due to the interfaces between SF particles and matrix as a thermal barrier. A random model was developed to simulate pore structure and thermal conductivity of the pastes based on the assumption of two phases (gas and solid). These achievements contribute to better understanding of the lime-pozzolana pastes and are desirable for their proper modeling and design.
•Clarifying the volatilization behavior of heavy metals in sewage sludge combusted in cement kilns.•The volatilization of Cu, Ni and Pb increased with increasing Cl to sludge ratio.•High temperatures ...typically caused a high removal of heavy metals.
To clarify the volatilization of heavy metals (Cu, Ni, Pb, and Zn) in sewage sludge during co-combustion in cement kiln, effects of addition and types of four chlorides and temperature on the volatilization of heavy metals in raw meal with 25wt.% sewage sludge were investigated. The results showed that the volatilization of Cu, Ni, and Pb increased significantly with increase of chlorides addition, while no obvious change in the volatilization of Zn was observed. The effectiveness of chlorides on the volatilization of heavy metals depended on their release capacity of chlorine radicals and the chlorine combined capacity of heavy metals. Higher calcination temperature resulted in dramatically increase in the volatilization of heavy metals due to easier formation of volatile heavy metal chlorides. The results will provide a guideline for co-combusting heavy metals contained solid wastes in cement kiln on the basis of security.
Basic oxygen furnace steel slag (BOFS) has not yet been widely used as a cementitious material due to low cementitious activity and poor soundness. Through the approach proposed, BOFS was separated ...into iron concentrate (about 60% Fe
2O
3) and residual slag product (consisting mainly of hydraulically active silicates). Blended cements with 30–60% slag product have comparable properties with Portland cement. The approach is very helpful to conserve natural resources and energy, achieve cost saving and reduce CO
2 emissions.
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► Silicates and ferrites are inclined to exist in fine and coarse BOFS fractions, respectively. ► Fine BOFS fractions present high cementitious activity and qualified autoclave soundness. ► Iron concentrate (about 60% Fe
2O
3) accounted for about 25% by mass of raw BOFS can be reclaimed. ► Blended cements with 30–60% residual slag product have comparable properties with Portland cement. ► The approach is helpful to conserve resources and energy, achieve cost saving and reduce CO
2 emissions.
Basic oxygen furnace steel slag (BOFS) is a by-product of steel-making process that has rarely been utilized in the past and is usually deposited as waste. BOFS fractions with different size were characterized in terms of chemical and mineral compositions, cementitious activity, autoclave soundness and activity index in the present study. The results show that silicates and iron concentrate are inclined to exist in fine and coarse BOFS fractions, respectively. Fine BOFS fractions also present qualified autoclave soundness, high cementitious activity and strength contribution. Iron concentrate, containing about 60% Fe
2O
3, can be reclaimed from BOFS through a new approach proposed. Blended cements with 30–60% residual slag product have comparable properties with Portland cement. The approach is very helpful to conserve natural resources and energy, achieve cost saving and reduce CO
2 emissions.
Concrete generally deforms and cracks in a non-uniform manner under drying-induced stress. This study used the lattice fracture model to simulate the drying-induced non-uniform deformations, ...stresses, and micro-crack propagation in concrete. Experiments were designed to validate the lattice fracture model, wherein the drying-induced non-uniform deformations and micro-crack patterns in concrete were measured using a digital image correlation technique and a fluorescent epoxy impregnation method, respectively. It was found that the simulated non-uniform deformations and micro-crack patterns were close to the experimental observations. The interaction mechanism between drying-induced non-uniform stresses and micro-cracks was analysed based on the validated lattice fracture model. The micro-cracks were found to cause stress concentration both in coarse aggregate and the mortar that covered coarse aggregate, which could lead to high micro-cracking risk as drying continues.
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