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The electrical resistivity is an important property for the structure concrete of metro track. In this work, the effect of dynamic flexural load on the electrical resistivity of concrete was investigated. Results show that the electrical resistivity of concrete first rapidly decreased and then slowly decreased with loading cycles; The higher the stress level and loading frequency, the greater the attenuation of concrete resistivity, the maximum value reached 33%. Acoustic emission test showed that the electrical resistivity is related to the damage of concrete. According to the theory of concrete fatigue damage, a new model was proposed to characterize the relationship between the dynamic damage of concrete and the electrical resistivity, R2 > 0.98. This work provides insight into development of the theory of electrical conductivity in concrete, and novel strategy for the dynamic damage monitoring of concrete. [ABSTRACT FROM AUTHOR]

Theoretically, there are two approaches to reducing the vibration induced by railway transit in cities: lowering structural stiffness, often used in subway design to isolate vibration, and absorbing the vibration by improving the damping ability of structural elements, which has rarely been studied. Based on the principle of energy absorption, a new vibration reduction measure—rubberized self-compacting concrete filling layer (RSCCFL)—was presented as a low-cost vibration reduction measure. In this study, the effects of rubber content on workability, compressive strength, and dynamic properties of rubberized self-compacting concrete (RSCC) were studied. The damping enhancement mechanism of RSCC is discussed. The vibration reduction performance of RSCCFL was evaluated by an environmental vibration prediction model. The results showed that incorporating rubber reduced the self-compacting concrete's workability, compressive strength, and dynamic modulus while increasing the damping ratio. The improvement in damping performance is related to the fact that rubber increased the energy dissipation of stress waves in the matrix. Compared with the self-compacting concrete (SCC) filling layer, RSCCFL had excellent vibration reduction performance, which gradually improved as the rubber content increased. The RSCCFL had a better vibration reduction effect on the environmental vibration above 40 Hz, and the low-frequency vibration (below 20 Hz) was also reduced by about 3–5 dB. In general, the vibration reduction effect of RSCCFL was equivalent to that of the subway primary vibration reduction measures, but it had a higher impact on low-frequency vibration. [ABSTRACT FROM AUTHOR]

CA mortar, as a filling layer, has been widely used in slab ballastless track. Since the creep deformation directly determines the track regularity and the train ride comfort, we investigated the effect of various stress levels on CA mortar creep. Results showed that the creep strain of CA mortar increased by 10 times when the stress level increased from 10% σ p to 40% σ p . Furthermore, it was first discovered that creep of CA mortar was attributed to the organic–inorganic interface slip and the propagation of microcracks. This work proposed a new CA mortar creep model based on the micro-meso structure characteristics, and its accuracy of prediction was much higher than previous models, R2 > 0.93. [ABSTRACT FROM AUTHOR]

In this work, ceramsite was utilized to fabricate the sound-absorbing boards, in which two types of structure were considered, specifically, single-layer board with homogenous structure and double-layer board with gradient structure. The physical, mechanical and acoustic properties of these prepared ceramsite sound absorbing boards were studied, including the bulk density, compressive strength, flexural strength, softening coefficient, sound absorption coefficient and sound reduction index. The results show that the double-layer board with appropriate mixture design exhibited almost identical bulk density and mechanical strength to the single-layer board. All ceramsite sound absorbing boards had compressive and flexural strengths of more than 3 MPa and 1 MPa, respectively, and also demonstrated good water resistance. In terms of sound absorption and sound insulation properties, the overall performance of the double-layer board with reasonable gradient structure was better than that of the single-layer board. In addition, the physical structure models of ceramsite sound absorbing boards were established to illustrate the variation of mechanical properties and disclose the mechanism of sound absorption and insulation in the material. [ABSTRACT FROM AUTHOR]

As one of the most innovative cement‐based materials, the properties of ultra‐high‐performance concrete (UHPC) have been widely investigated. This paper experimentally studies the effect of ceramsite sand on the properties and microstructure of UHPC to develop a new UHPC with low apparent density. The effects of the volume ratio of ceramsite sand and steel fiber content on the properties of UHPC were also studied. Various experiments, including apparent density, compressive and flexural strength, and microstructural properties were conducted on UHPC with different mixing parameters. The results showed that the addition of 18% ceramsite sand effectively improved the mechanical strength, specific strength, and pore structure as well as the interfacial transition zone of UHPC. Steel fiber and ceramsite sand worked together to make up for the lack of lightweight porous aggregate so that even when 100% ceramsite sand was used to prepare UHPC, the compressive strength of concrete could still exceed 100 MPa, and had a lower apparent density than normal UHPC. [ABSTRACT FROM AUTHOR]

As an inorganic–organic composite material, cement and emulsified asphalt (CA) mortar has been used widely in ballastless slab track structures, and its performance is influenced significantly by environmental conditions. In this study, we tested the long-term creep of CA mortar at different temperatures using a self-designed loading device, and explored the mechanisms by which high temperatures influence CA mortar creep based on several microscopic testing methods. The results indicated that high temperatures cause the creep degree and rate of CA mortar to increase significantly. Subsequent to creep at high temperatures, the mechanical properties and microstructure of CA mortar changed remarkably, and asphalt migration may be an important cause of changes in CA mortar at high temperatures. This will be useful for future studies of the evolution of CA mortar performance under long-term service conditions. [ABSTRACT FROM AUTHOR]

To clarify the volume deformation characteristics and residual expansion deformation formation mechanism of steam-cured concrete, the content of free water and air of fresh concrete before heating, and the hydration kinetics and mechanical characteristics evolution of concrete during the steam curing process were obtained by experiment and fitting. The residual expansion strain calculation model of steam-cured concrete was proposed and its accuracy was verified by a non-contact test. Results showed that: (i) the volume deformation characteristics of steam-cured concrete could be divided into two stages: rapid expansion in heating stage, then rapid shrinkage in constant temperature treating period and gentle shrinkage in cooling period; besides, an irrecoverable residual deformation was gained at the end of cooling period; (ii) the tested peak value of residual expansion strain of steam-cured concrete appeared at 0.5–1 h later than the fitting value, and the final tested residual expansion strain is lower than the fitting value; (iii) the higher the initial free water content and the lower the initial structural strength, the greater the final residual expansion deformation of steam-cured concrete. This paper aims to reveal the mechanism of residual expansion deformation and propose a method of restraining the deformation of high-speed railway steam-cured concrete. This paper could provide technical support for the production of steam-cured concrete prefabricated components and predict the residual expansion deformation. [ABSTRACT FROM AUTHOR]

Steam‐cured concrete products have been widely employed in building slab ballastless track for China High‐Speed Railway lines, such as track sleeper and track slab. These components are usually subjected to long‐term fatigue load due to the wheel‐rail interactions by high‐speed trains. Especially in Northeast China where the winter temperature keeps subzero for months, the concrete elements are exposed to the coupling effects of fatigue load and minus temperature environment. Therefore, this paper investigated the mechanical damage evolutionary behavior of steam‐cured concrete under coupling effects of flexural fatigue loading and minus temperature. Additionally, the mechanism behind it was discussed. The results showed that the mechanical damage of steam‐cured concrete subjected to fatigue loading under minus temperature was more significant than that under room temperature. The influences of ice content on the degradation in mechanical properties of steam‐cured concrete are illustrated by the phenomenological model. A two‐stage statistical damage variable can well reveal the impact of fatigue cycles and temperature on fatigue damage and total damage concrete. Steam‐cured concrete based on PC‐FA‐GGBS binder system exhibits better resistance to the flexural fatigue loading and minus temperature coupling effects due to its better pore structure and less ice content. [ABSTRACT FROM AUTHOR]

This letter, published in the journal Clinical Rheumatology, discusses a study on primary Sjögren's syndrome (pSS) complicated with interstitial lung disease (ILD) and the risk factors for respiratory infections in these patients. The study found that higher levels of certain markers, such as ESSDAI, CRP, ESR, and C3, may be correlated with an increased risk of infection. Pulmonary arterial hypertension (PAH) and reduction of diffusing capacity of the lung for carbon monoxide (DLCO) were identified as independent risk factors. However, the letter also points out a statistical error in the study, suggesting that more infection cases need to be included for a reliable analysis. [Extracted from the article]

A recent study published in Clinical Rheumatology titled "Digital gangrene in systemic sclerosis patients: not only due to the microvascular disease" investigated the causes of digital gangrene in 43 systemic sclerosis (SSc) patients. The study found that smoking history, anti-centromere antibody (ACL) positivity, anti-neutrophil cytoplasmic antibody (ANCA) positivity, and anti-phospholipid antibody (APL) positivity, as well as elevated erythrocyte sedimentation rate (ESR), were independent risk factors for gangrene. However, the authors of a letter to the editor raised concerns about the study, stating that using ten variables to analyze 43 outcomes may have resulted in overfitting of the regression model. The authors suggested reducing the number of variables or including more SSc patients with gangrene in future studies. The letter was written by Youjun Xie and Hongying Zhao. [Extracted from the article]

Steam-cured concrete with high early strength has been widely applied in high-speed railway. However, heat damage caused by the steam curing process brings adverse effects on the pore structure and durability of steam-cured concrete. It has been found that phase change materials (PCMs) help improve the durability of cement-based materials. Therefore, the influences of two PCMs on the strength, water absorption, and microstructure of steam-cured mortar are discussed in this study. Two PCMs used include pure paraffin and a composite phase change material composed of porous diatomite and paraffin (D/P). The results show that the addition of appropriate PCMs does not significantly reduce the strength of steam-cured mortar. The addition of a small amount of PCMs shows little influence on the pore structure of steam-cured mortar but effective in improving the water-penetration resistance. This is partially attributed to the improvement of hydrophobic characteristics in the pores, resulting from the adhesion of hydrophobic PCMs on the pores during the steam curing. Compared with specimens containing pure paraffin, the pore structure of specimens containing D/P is refined, resulting in higher compressive strength. This may be due to the uniform distribution of small particles D/P in the specimen and the pozzolanic reaction of diatomite in D/P. The use of suitable phase change materials will be helpful to improve the durability of steam-cured concrete. [ABSTRACT FROM AUTHOR]

The steam curing technology is worldwide applied in the production of concrete prefabricated components, including the production of track slab and girder used for the high‐speed railway in China. However, the steam curing process at elevated temperature will often generate the heat damage on concrete and thus degrade the long‐term performance of the steam‐cured concrete prefabricated components. It is very important to deeply understand the mechanism of heat damage and thus to find effective method reducing or avoiding the damage of steam curing on concrete. The main purpose of this paper is to systematically classify the types of thermal damages on concrete during the steam curing and its mechanism. The influences of main factors on three thermal damages such as the unrecoverable expansion deformation, the surface layer defect, and the embrittlement of the steam‐cured concrete are discussed in detail. The controlling methods of thermal damages including optimization of the steam curing regime and mixing proportions, the addition of supplementary additives, the self‐healing technology, and other curing technology are compared and summarized based on the literatures. Finally, suggestions for future research are proposed in order to effectively reduce or even avoid the thermal damage of the steam‐cured concrete. And also, some new technology for developing the green and high performance early strength concrete with low CO2 emission are presented. [ABSTRACT FROM AUTHOR]

Filling layer self-compacting concrete (FLSCC) is a key material in newly-built China Rail Track System (CRTS), which is commonly subjected to cyclic dynamic load from high-speed train and various ambient temperature during service. In this paper, a series of indoor simulating experiments was conducted to investigate the impact resistance of FLSCC suffering from cyclic flexural load and different temperature conditions with a Φ75 mm split Hopkinson pressure bar (SHPB). The dynamic increase factors were introduced to evaluate the strain rate effect on various mechanical properties of FLSCC and the corresponding mechanisms were explained. Results show that the dynamic increase factor of compressive strength (DIFc) and peak strain (DIFε) of FLSCC increase linearly with logarithm of strain rate, while specific energy absorption increases exponentially with strain rate. The impact resistance of FLSCC is greatly influenced by cyclic flexural load and low temperature. The strain rate sensitivity of compressive strength of FLSCC at minus temperature (−20°C) is weaker than that at normal temperature (20°C) and after freeze-cyclic load coupling action the sensitivity decreases further. Similar tendencies were also observed in peak strain and specific energy absorption. [ABSTRACT FROM AUTHOR]

Filling layer self-compacting concrete (FLSCC) is a key construction material in China Rail Track System (CRTS) III slab ballastless track and its resistance to impact loading is of great importance to the service security of high-speed train. In this paper, the dynamic mechanical characteristics of FLSCC under impact loading were investigated with a split Hopkinson pressure bar (SHPB) at strain rates ranging from 101 s−1 to 102 s−1. Results show that the compressive strength, peak strain, elastic modulus and toughness ratio of FLSCC all increase with strain rate. The increase factors of compressive strength (DIF c) and strain (DIF ɛ) of FLSCC increase linearly with decimal logarithm of strain rate. The elastic modulus (E d) and toughness ratio (TR) increase linearly with strain rate. Self-compacting concrete (SCC) shows greater strain rate effect than normal concrete (NC). However, FLSCC presents lower strain rate effect but better toughness performance than normal SCC. The incorporation of large content of SP and VMA provides FLSCC with higher porosity, which makes it possess excellent dynamic mechanical performance. [ABSTRACT FROM AUTHOR]

This paper develops an algorithm for generating the three-dimensional (3D) heterogeneous microstructure of asphalt concrete based on random modeling. The asphalt concrete was modeled as heterogeneous material with fine aggregate matrix (FAM), coarse aggregates, and air voids. We generated 3D aggregate shapes with three two-dimensional (2D) projections randomly selected from the aggregate image database. We generated the 3D models of asphalt concrete by randomly placing 3D aggregates and air voids into the virtual specimen with compact packing. We predicted the dynamic modulus of asphalt concrete specimens with different microstructures through finite element (FE) analysis and validated with experimental data. The relative differences between the average dynamic modulus and the experimental data ranged from 0.32 to 6.01% for different frequencies, which indicates that the 3D heterogeneous microstructure model is acceptably accurate. The volume of aggregate in each sieve is the major factor controlling bulk material properties like dynamic modulus. We also generated 2D heterogeneous models of asphalt concrete by cutting the 3D model from different cross sections. The variation of dynamic modulus with the 2D models was much greater than the variation with the 3D models. The ratio of coarse aggregate content in the 2D and 3D models can range from 0.86 to 1.35. Although, in general, the predicted dynamic modulus increases as coarse aggregate content increases in 2D models, we observed variations due to differences in microstructure. [ABSTRACT FROM AUTHOR]

Due to the lack of study on basalt fiber (BF)-reinforced asphalt mucilage based on silane coupling agent (SCA) modification, researchers used SCA to modify BF and then prepared fiber-reinforced asphalt mucilage (FRAM) specimens. FRAM's high- and low-temperature rheological performances were evaluated by BBR and DSR and the reinforcement mechanism of modified BF (MBF) was analyzed by ESEM and FTIR. Tests showed that the number of MBF's Si–O–Si bonds increased. MBF was rough, which was responsible for fiber's mechanical property and multi-direction-bridging reinforcement. When the powder–binder ratio was between 0.8 and 1.0 and the MBF content was between 0.3% and 0.6%, FRAM's anti-shearing and anti-cracking performances enhanced efficiently. [ABSTRACT FROM PUBLISHER]

The influences of four nanoparticles of nanosilica (SiO2), nano-calcium carbonate (CaCO3), nano-aluminium oxide (Al2O3) and nano-iron oxide (Fe2O3) on workability, hydration, pore structure and mechanical strength of reactive powder concrete (RPC) are investigated by macro/microscopic methods. The aim of this study is to provide an essential basis for exploiting new-generation cementitious materials with ultra-high strength and super-long service life by employing modern nano-modification technology. The results indicate that addition of low-dosage nanoparticles to RPC shows a remarkable influence on the mechanical strength, hydration and pore structure compared to the ordinary cement system with a relatively high water/cement ratio. The compactness and mechanical strength of RPC can be greatly improved by incorporating nanoparticles. The promotive ratio of flexural and compressive strength of RPC is up to 30%. The elevated temperature further promotes the effect of nanoparticles on the strength of RPC. The seeding effect of nanoparticles on hydration of cement and the nano-size filling role are strengthened in the RPC system. [ABSTRACT FROM AUTHOR]

The dynamic mechanical property of concrete is one of the key parameters, which greatly influences durability of infrastructures subjected to continuous heavy loading, such as girder and track slab of high-speed railway foundation structure. This paper reports serials of experiments designed to investigate the deterioration of dynamic mechanical properties of different concretes under fatigue loading condition. Four parameters including relative dynamic elastic modulus ( RDEM), relative dynamic shear modulus ( RDSM), relative compressive strength ( RCS) and water absorption ( WA) of concrete were evaluated to assess the dynamic properties and microstructures of concretes. Results show that the fatigue stress levels and fatigue cycle durations significantly influence the dynamic mechanical properties of concrete including dynamic elastic modulus and dynamic shear modulus. Addition of proper mineral admixture can improve the dynamic mechanical characteristics of concrete and increase its resistance against the fatigue loading effect. Keeping the amount of mineral admixture in concrete constant, its dynamic mechanical property with fly ash is lower than that with fly ash and silica fume. The water absorption in concrete, which is an indirect parameter reflecting capillary porosity, increases evidently after bearing fatigue-loading. There is a close correlation between the deterioration of dynamic mechanical property and the increasing of water absorption of concrete. This indicates that the damage of microstructure of concrete subjected to fatigue loading is the indispensable reason for the decay of its dynamic mechanical performance. [ABSTRACT FROM AUTHOR]

Steam-cured concrete is widely used to manufacture prefabricated units of high-speed railway foundation structure such as girder and track slab. The dynamic mechanical property of steam-cured concrete is one of the key properties affecting service performance of high-speed railway foundation structure. In the present paper, serial macro/micro-experiments were carried out to investigate the dynamic elastic modulus, shear modulus, damping ratio, and microstructure of steam-cured concrete. The relationships between compositions, curing regime, microstructure, and dynamic properties of steam-cured concrete as well as the corresponding mechanisms were discussed. The results indicate that steam-cured concrete in early age has a larger dynamic elastic modulus and shear modulus as well as a smaller damping ratio compared with standard-cured concrete. On the contrary, at a later age a slightly smaller dynamic elastic modulus and a larger damping ratio of steam-cured concrete are observed. Addition of mineral admixture results in a bit lower dynamic elastic modulus and damping ratio of concrete than that of the control specimen without mineral admixtures. The achievements can provide some fundamental suggestions for materials parameters selection during structural design of steam-cured concrete precast element. [ABSTRACT FROM AUTHOR]

Cement and emulsified asphalt (CA) mortar is a compound of cement, emulsified asphalt, sand, water and admixtures that is widely used in high-speed railway applications in China, Germany and Japan. Mixing to disperse the components and entrain air is very important in the production of CA mortar. In the study reported in this paper, the power consumption method was used to study the mixing kinetics of CA mortar. The theory of air entrainment was used to interpret the effects of mixing speed, fluidity and mixing time on the air content of the mortar. Based on the changes in power consumption, the results showed that the evolution of the paste during mixing can be divided into seven periods and, based on fluctuations of the power consumption, the evolution can be divided into three homogenisation zones. Exponential formulae are proposed to describe the effect of mixing time on air content. The experimental results agreed well with the formulae. [ABSTRACT FROM AUTHOR]

To investigate the durability, especially the long-term stability of cement-based materials with very low w/b, the air permeability test, carbonation test, capillary absorption rate test and dilation potential test were adopted under long-term heat treatment condition. Microstructure of these materials is also analyzed by scanning electronic microscopy (SEM) and mercury intrusion porosimeter (MIP) in order to further unveil its mechanism and interrelation between microstructure and its properties. The results indicate that in the area investigated, cement-based material with w/b 0.17, like RPC, possesses low porosity and excellent durability. Moreover, its porosity will further decrease under long-term heat treatment compared with normal heat treatment. Its long-term durability is much superior to that of other cement-based materials with w/b 0.25 or 0.35 as high strength concrete(HSC). [ABSTRACT FROM AUTHOR]

Effects of factors such as water to cement ratio, fly ash and silica fume on the resistance of concrete to sulfate attack were investigated by dry-wet cycles and immersion method. The index of the resistance to sulfate attack was used to evaluate the deterioration degree of concrete damaged by sulfate. The relationship between the resistance of concrete to sulfate attack and its permeability/porosity were analyzed as well as its responding mechanism. Results show that the depth of sulfate crystal attack from surface to inner of concrete can be reduced by decreasing w/ c and addition of combining fly ash with silica fume. The variation of relative elastic modulus ratio and relative flexural strength ratio of various specimens before and after being subjected to sulfate attack was compared. [ABSTRACT FROM AUTHOR]

Direct electric curing (EC) is a new green curing method for cement-based materials that improves the early mechanical properties via the uniform high temperature produced by Joule heating. To understand the effects of EC and steam curing (SC) on the mechanical properties and microstructure of cement-based materials, the mortar was cured at different temperature-controlled curing regimes (40 °C, 60 °C, and 80 °C). Meanwhile, the mechanical properties, hydrates and pore structures of the specimens were investigated. The energy consumption of the curing methods was compared. The results showed that the EC specimens had higher and more stable growth of mechanical strength. The hydration degree and products of EC samples were similar to that of SC samples. However, the pore structure of EC specimens was finer than that of SC specimens at different curing ages. Moreover, the energy consumption of EC was much lower than that of SC. This study provides an important technical support for the EC in the production of energy-saving and high early-strength concrete precast components. [ABSTRACT FROM AUTHOR]

In order to improve the stability of air bubbles in fresh concrete, it is of great significance to have a better understanding of the mechanisms and main influencing factors of bubble stability. In the present review, the formation and collapse process of air bubbles in fresh concrete are essentially detailed; and the advances of major influencing factors of bubble stability are summarized. The results show that the surface tension of air–liquid interface exerts a huge impact on bubble stability by reducing surface free energy and Plateau drainage, as well as increasing the Gibbs surface elasticity. However, surface tension may not be the only determinant of bubble stability. Both the strength of bubble film and the diffusion rate of air through the membrane may also dominate bubble stability. The application of nano-silica is a current trend and plays a key role in ameliorating bubble stability. The foam stability could be increased by 6 times when the mass fraction of nano-particle reached 1.5%. [ABSTRACT FROM AUTHOR]

In order to solve the problems of the sudden loss of fluidity and low expansion rate of CAM I (cement asphalt mortar type I) in a construction site with high environmental temperature, this paper studies the effect of temperature on the fluidity, expansion ratio and pH value of CAM I. The mechanism of action was analyzed by IR (infrared spectrometry), SEM (scanning electron microscopy) and other test methods. The results showed that a high temperature accelerates aluminate formation in cement paste. Aluminate adsorbs emulsifiers leading to demulsification of emulsified asphalt, and wrapped on the surface of cement particles, this causes CAM I to lose its fluidity rapidly. The aluminum powder gasification reaction is inhibited, resulting in an abnormal change in the expansion ratio. Based on findings, the application of an appropriate amount of superplasticizers can effectively improve the workability and expansion characteristics of CAM I at a high temperature. [ABSTRACT FROM AUTHOR]

Rheological curves of cement–fly ash (C–FA) paste incorporating nanomaterials including nano-SiO2 (NS), nano-CaCO3 (NC) and nano-Al2O3 (NA) at different resting times (hydration time of 5 min, 60 min, and 120 min) were tested with a rheometer. The rheological behaviors were described by the Herschel–Bulkley (H–B) model, and the influences of these nanomaterials on rheological properties of C–FA paste were compared. Results show that the types, content of nanomaterials and resting time have great influences on the rheological properties of C–FA paste. Incorporating NS and NA increases yield stress and plastic viscosity, and decreases the rheological index of C–FA paste. When the content of NS and NA were 2 wt%, the rheological index of C–FA paste was less than 1, indicating rheological behavior changes from shear thickening to shear thinning. Meanwhile, with rising resting time, yield stress and plastic viscosity increased significantly, but the rheological index decreased evidently, showing paste takes on shear thinning due to the rise of resting time. However, incorporating 3 wt% NC and the rising of resting time did not change the rheological properties of C–FA paste. These differences are mainly that the specific surface area (SSA) of NS (150 m2/g) and NA (120 m2/g) are much larger than that of NC (40 m2/g). The huge SSA of NS and NA consume lots of free water and these tiny particles accelerate the hydration process during resting time. [ABSTRACT FROM AUTHOR]