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The shear bond of interface between concrete and basalt fiber reinforced polymer (BFRP) bars during freeze-thaw (F-T) cycles is crucial for the application of BFRP bar-reinforced concrete structures in cold regions. In this study, 48 groups of pull-out specimens were designed to test the shear bond of the BFRP-concrete interface subjected to F-T cycles. The effects of concrete strength, diameter, and embedment length of BFRP rebar were investigated under numerous F-T cycles. Test results showed that a larger diameter or longer embedment length of BFRP rebar resulted in lower interfacial shear bond behavior, such as interfacial bond strength, initial stiffness, and energy absorption, after the interface goes through F-T cycles. However, higher concrete strength and fewer F-T cycles were beneficial for enhancing the interfacial bond behavior. Subsequently, a three-dimensional (3D) interfacial model based on the finite element method was developed, and the interfacial bond behavior of the specimens was analyzed in-depth. Finally, a degradation bond strength subjected to F-T cycles was predicted by a proposed mechanical model. The predictions were fully consistent with the tested results. The model demonstrated accuracy in describing the shear bond behavior of the interface under numerous F-T cycles. [ABSTRACT FROM AUTHOR]

To enhance the toughness of the geopolymer, silane (amino, epoxy, and methacrylate-based)-grafted sodium polyacrylate (PAA-Na) was used as additives. The interfacial features of the polymer slag paste, including the microstructure, physicochemical interaction or bonding, and mechanical properties, are the main determinants of the ductile qualities of the final concrete. This study examined how the polymer affected the evolution of the strain field, fracture characteristics, and micromechanical properties of slag geopolymer. The flexural strength and the fracture toughness of incorporating 5% 3-methacryloxypropyl trimethoxysilane (KH570) + 2% PAA-Na increased by 296.10% and 81.20%, compared with the reference. Additionally, the addition of 5% KH570 + 2% PAA-Na expanded the distribution of the strain field of geopolymer with 2615.89 με, 2300.57 με, and 1821.54 με under the maximum load of 2833 N. The formation of hydration product C–A–S–H/(5% KH570 + 2% PAA-Na) with a high degree of polymerization had a relatively low elastic modulus of 26.17 GPa. The carboxyl and silane groups of methacrylate-based PAA-Na and KH570 were polycondensed with the hydroxyl group on the surface of C–A–S–H resulting in 12.17% Ca (COO)2 and 65.36% O–Si–O with a higher degree of polymerization. The slag-based geopolymer became more ductile as a result of the generation of the C–A–S–H/polymers, which had an organic–inorganic cross-linked network structure composed of Opolymer–Ca–OC–A–S–H and Opolymer–Si–OC–A–S–H bonds. [ABSTRACT FROM AUTHOR]

In water resource allocation engineering, the flow velocity is the most important factor influencing corrosion damage in the elbow sections of steel pipes. This study reports the effect of flow velocity on the corrosion performance of carbon steel at different pipe elbow section locations though which freshwater flows. The corrosion damage of carbon steel was accelerated in flowing freshwater; however, this accelerating effect was weakened with high flow velocity. Furthermore, the corrosion rate at the outer wall was higher than that of the inner wall of the pipe elbow section with low flow velocity; when high flow velocity was used, more uniform corrosion damage was found at the pipe elbow section. The influence of flow velocity on the corrosion performance of the carbon steel was closely related to the hydrodynamic parameter distribution and the nonuniform accumulation of corrosion products at different locations of the pipe elbow section in flowing freshwater. [ABSTRACT FROM AUTHOR]

Hollow structured material (HSM) consisting of monodisperse hollow silica nanospheres (HSN) shows a promising potential for construction insulation due to its affordable cost and simple process. Yet the studies of high-yield and low-energy for the synthetic of HSN are still insufficient. This research reported the comparison of morphology and performance of synthesize HSN utilizing TEOS and Na2SiO3 as silica source. The average yield of Na2SiO3-based samples can reach 93.75%, which is about 10 times higher that of TEOS-based samples. Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM) results revealed that the shell morphology of TEOS-based samples was raspberry-like or smooth structure, while the shell of the Na2SiO3-based samples was round honeycomb-like structure. Hot Disk thermal constant analyzer results demonstrated that the thermal conductivity of the Na2SiO3-based samples was lower than that of the TEOS-based samples with similar inner-diameter and shell thickness. Thereafter, the influence mechanism of the morphology on thermal insulation performance was also investigated. The prepared HSN as filler significantly enhanced the thermal insulation of acrylic coating. This research confirms that the synthesis route with Na2SiO3 was a greener method which can solve the low yield and high energy consumption caused using TEOS as a silica source. Excellent thermal insulation properties indicate HSN will have a broad application prospect in heat-insulating and energy-saving construction. [ABSTRACT FROM AUTHOR]

Among the troika of clinicopathologic features of asthma, airway remodelling has gained sufficient attention for its contribution to progressive airway narrowing. Much effort has been directed at the management of airway smooth muscle cells (ASMCs), but few attempts have proven to prevent the progression of remodelling. Recently, accumulating data have shown the anti-inflammatory/anti-proliferative potency of melatonin (a crucial neurohormone involved in many physiological and pathological processes) in diverse cells. However, no evidence has confirmed its effect on ASMCs. The present study investigates the benefits of melatonin in asthma, with an emphasis on airway remodelling. The results indicated that melatonin significantly attenuated airway hyperresponsiveness (AHR), inflammation and remodelling in a house dust mite (HDM) model. Melatonin markedly alleviated goblet cell hyperplasia/metaplasia, collagen deposition and airway smooth muscle hyperplasia/hypertrophy, implying the achievement of remodelling remission. The data obtained in vitro further revealed that melatonin notably inhibited ASMCs proliferation, VEGF synthesis and cell migration induced by PDGF, which might depend on STAT3 signalling. Moreover, melatonin remarkably relieved ASMCs contraction and reversed ASMCs phenotype switching induced by TGF-β, probably via the Akt/GSK-3β pathway. Altogether, our findings illustrated for the first time that melatonin improves asthmatic airway remodelling by balancing the phenotypic proportions of ASMCs, thus highlighting a novel purpose for melatonin as a potent option for the management of asthma. [ABSTRACT FROM AUTHOR]

During the construction of islands and reefs far from the mainland, local marine materials are expected to be used in concrete from the viewpoint of economy, rapid and convenient construction. As abundant chloride with local marine materials is involved into concrete, ordinary Portland cements are not recommended due to their low chloride binding capacity and poor corrosion resistance of steel bar. In the present study, geopolymer, gap-graded blended cement as well as Portland cement and inter-ground blended cement as references were mixed directly with NaCl to simulate the chloride in local marine materials, their hydration process, mechanical properties, corrosion resistance of steel bar and microstructure were compared. The results showed that the hydration processes of blended cements were accelerated after introducing NaCl, resulting in a dramatic increase in early strengths. In contrast, the compressive strengths of Portland cement and geopolymer kept constant, whereas the late flexural strengths reduced gradually. Geopolymer had slightly better corrosion resistance of steel bar than Portland cement due to low porosity and pore size refinement, and gap-graded blended cement presented a superior corrosion resistance of steel bar even in chloride-rich environment, as the chloride binding capacity of gap-graded blended cement paste was about 4 times higher than that of geopolymer. [ABSTRACT FROM AUTHOR]

Fly ash was used as catalytic support for carbon nanotubes (CNTs) growth by chemical vapor deposition (CVD) due to having ideal compositions (SiO2,Al2O3, and Fe2O3). In this paper, CNTs were synthesized on Ni catalyst/fly ash substrate using CVD method. The influence of parameters (e.g., reaction temperature and gas flow rate) on the carbon yield and structure of the resulting CNTs was on the carbon yield and structure of the resulting CNTs was investigated by thermo-gravimetric analyses, Scanning electron microscopy, and Raman spectroscopy analysis. The results indicated that the growth temperature controlling had a significant effect on the diameter of CNTs. And the proper acetylene and hydrogen flow rate would decrease in defect density and increase in yield of as-grown CNTs on fly ash. Finally, the amorphous carbon on the surface of as-grown CNTs were removed by heating in air. Experimental results showed that the hydrophobic of the annealed CNTs was weak due to introducing functional groups to the surface of CNTs. [ABSTRACT FROM AUTHOR]

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 Al3+ for Si4+ 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. [ABSTRACT FROM AUTHOR]

The compounds of MgO-silica fume (SF) pastes constitute magnesium silicate hydrate (M-S-H) in a new generation of basic castables. However, Mg(OH) is a common reaction product with the formation of M-S-H. This study aims to reduce the formation of Mg(OH) in MgO-SF pastes. In this study, MgO powders were prepared by calcining magnesite at different temperatures and then mixed with SF and water to prepare MgO-SF pastes. The properties of MgO powders were characterized, and the pH values in the pore solutions of MgO-SF pastes were measured. The MgO-SF pastes cured for 90 days were calcined at 500, 700, 900 and 1200 °C, and the microstructure was characterized afterward. The results showed that both the reactivity of MgO powders and the pH value of the pore solution of MgO-SF pastes were diverse, which essentially depended on the grain sizes and the crystalline degree of MgO. Increasing the calcination temperature of MgO was beneficial to reduce the formation of Mg(OH) or even stop it when using MgO calcined at 1450 °C. Enstatite and forsterite formed for all MgO-SF pastes after calcination. However, the microstructure of MgO-SF paste with MgO calcined at 1450 °C was denser than others. MgO-SF pastes were suitable for the new-generation refractory castables. Notably, using MgO calcined at 1450 °C is more appropriate. [ABSTRACT FROM AUTHOR]

Requirements of self-compacting concrete (SCC) applied in pre-stressed mass concrete structures include high fluidity, high elastic modulus, low adiabatic temperature rise and low drying shrinkage, which cannot be satisfied by ordinary SCC. In this study, in order to solve the problem, a few principles of SCC design were proposed and the effects of binder amount, fly ash (FA) substitution, aggregate content and gradation on the workability, temperature rise, drying shrinkage and elastic modulus of SCC were investigated. The results and analysis indicate that the primary factor influencing the fluidity was paste content, and the main methods improving the elastic modulusof SCC were a lower sand ratio and an optimized coarse aggregate gradation. Lower adiabatic temperature rise and drying shrinkage were beneficial for decreasing the cement content. Further, based on the optimization of mixture, a C50 grade SCC (with binder amount of only 480 kg/ m3, fly ash substitution of 40%, sand ratio of 51% and proper coarse aggregate gradation ( V : V : V = 30%: 30%:40%)) with superior workability was successfully prepared. The temperature rise and drying shrinkage of the prepared SCC were significantly reduced, and the elastic modulus reached 37.6 GPa at 28 d. [ABSTRACT FROM AUTHOR]

The thermo-dynamics of reactions between carbonatite and sodium silicate solution at ordinary temperature (25 °) were investigated. The calculated results indicate that at ordinary temperature, the reactions between dolomite, calcite, Ca and Mg in carbonatite and HSiO, HSiO and HSiO in sodium silicate solution to form the cementitious products of hydrated calcium silicate or hydrated magnesium silicate all possibly happen; among these reactions, the reactions to form gyrolite (2CaO·3SiO·2.5HO) and serpentine (3MgO·2SiO·2HO) are the most possible to occur. Further, the dissociation degree of dolomite and calcite and the activity of HSiO, HSiO and HSiO ions are the key factors to influence the reactions. [ABSTRACT FROM AUTHOR]

To improve the properties of steel slag blended cements, a chemical activator was added into blended cements, the mechanical properties and durability of steel slag blended cements were investigated. The results show that steel slag in blended cement pastes presents low hydraulic activity and makes practically no contribution to strength development. After the addition of chemical activator, the mechanical properties and durability of ternary blended cements are increased significantly. The hydration process and micro-structural development of blended cement was investigated by isothermal calorimeter and scanning electric microscope, respectively. Steel slag started hydration in the first 3 days in the presence of chemical activator, steel slag and granulate blast furnace slag reacted with Ca(OH) to form a dense microstructure as curing proceeded. Therefore, both early and late compressive strengths of steel slag blended cement with 35% cement clinker and 30% steel slag can be comparable with those of Portland cement. [ABSTRACT FROM AUTHOR]

Owing to poor bonding between coarse fly ash particles and hydration products, gap-graded blended cements with fly ash usually show lower compressive strengths than Portland cement. Surface cementitious properties of coarse fly ash were improved by dehydration and rehydration processes in the present study. The results show that during the calcination at 750 °C, C-S-H gel is mainly transformed into a new nesosilicate, which is similar to a less crystalline CS. The formation of melilite from hydration products is also noticed at 900 °C, however, this will not contribute to rehydration of calcined fly ash. Rehydration of new generated nesosilicate on the surface of coarse fly ash leads to a better bonding between coarse fly ash particles and hydration products. As a result, both early and late mechanical properties of gap-graded blended cements containing 25% cement clinker and 39% calcined coarse fly ash are higher than those of 100% Portland cements. [ABSTRACT FROM AUTHOR]

To optimize the hydration process of blended cement, cement clinker and supplementary cementitious materials (SCMs) were ground and classified into several fractions. Early hydration process of each cementitious materials fraction was investigated by isothermal calorimeter. The results show fine cement clinker fractions show very high hydration rate, which leads to high water requirement, while fine SCMs fractions present relatively high hydration (or pozzolanic reaction) rate. Cement clinker fractions in the range of 8-24 μm show proper hydration rate in early ages and continue to hydrate rapidly afterward. Coarse cement clinker fractions largely play 'filling effect' and make little contribution to the properties of blended cement regardless of their hydration activity (or pozzolanic activity). The hydration process of blended cement can be optimized by arranging high activity SCMs, cement clinker, and low activity SCMs in fine, middle, and coarse fractions, respectively, which not only results in reduced water requirement, high packing density, and homogeneous, dense microstructure, but also in high early and late mechanical properties. [ABSTRACT FROM AUTHOR]

The paste was prepared by mixing MgO, microsilica and HO in the presence of water reducer at different reaction ratios and temperatures, and characterized by XRD, DTA, TGA, IR, and solid-state 29Si NMR. The experimental results showed that, besides Mg(OH), magnesium silicate hydrate (M-S-H) was formed at a low temperature such as 25 and 50 °C. At a high temperature of 100 °C, Mg(OH) can be further transformed into M-S-H completely, for instance, within ca. 1 month in an excess of microsilica. The average composition and structure of M-S-H was mainly related to the reaction mixture and curing temperature and was discussed in detail. [ABSTRACT FROM AUTHOR]

This research focused on using the waste rubber powder as a kind of regenerate resources to improve the mechanical properties of cement mortar. The two kinds of hybrid modified rubber powder TRP and ATRP were prepared by sol-gel method and then used in cement mortar. The structures and properties of them were studied. It is shown that the nano Si-O-Si network is generated in TRP and ATRP networks and the hydrophilic group is grafted on the surface of ATRP. The mechanical properties of rubber-treated mortar (RTM) were tested and the microstructures of them were also studied. Compared to the mortars with unmodified rubber powders (RP), NaOH treated rubber powder (SRP) and coupling agent treated rubber powder (CRP), the RTM with ATRP has the highest compressive strength and flexural strength. The stress-strain curves shown that the peak of stress of RTM with ATRP is increased and indicated the higher compression deformation and toughness. It is found that the interfacial adhesion between the ATRP and cement mortar is increased distinctly by SEM, which results in enhanced ductility and mechanical properties of RTM with ATRP. [ABSTRACT FROM AUTHOR]

The half cell potential (HCP) and corrosion current of reinforced concrete specimens doped with sodium chloride were determined after electrochemical chloride extraction (ECE). The experimental results show that when ECE treatment is removed, HCP becomes more negative and corrosion current becomes larger in comparison to those before ECE treatment, then HCP shifts positively and corrosion current decreases with time. After 30 days ECE treatment, the HCP of cored specimens turn to about −100 mV due to the existence of sufficient oxygen around the exposed steel bars, but for un-cored specimens, longer time, about two months, is to be taken. The non-homogeneous HCP distribution at different layers of the same specimen after ECE treatment might induce secondary corrosion of steels. [ABSTRACT FROM AUTHOR]