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Abstract View factor plays an important role in evaluation of radiative heat transfer. This paper gives a detailed account of setting up the Monte Carlo calculation models of view factors between some complex surfaces. Main purpose is to calculate view factor between cold-rolled strip and W-shaped radiant tube in continuous annealing furnace. Given advantages of Monte Carlo method, it has been used to calculate view factor between the strip and radiant tube. Firstly, the Monte Carlo calculation models for view factor between rectangular plane and parallel cylinder and for view factor between rectangular plane and torus are established and verified, respectively. Then, according to reciprocity and superposition rules of view factors, the Monte Carlo calculation model for view factor between the strip and radiant tube is established by the above models. By comparing with analytical expression, or checking reciprocity after performing the Monte Carlo analysis in each direction between surface pairs, the calculation errors of above Monte Carlo models are analyzed and the results show that the Monte Carlo method is effective and reliable in calculating view factors between some complex surfaces. [ABSTRACT FROM AUTHOR]

• A modified random hierarchical bundle model for predicting the permeability of cement-based materials was presented. • The intrinsic permeability of cement-based materials can be accurately simulated. • The apparent permeability and Klinkenberg constant of different gases can be predicted. Permeability is a fundamental property indicating the durability of cement-based materials, predicted according to the material's pore size distribution (PSD). The random hierarchical bundle model is a promising approach based on a random hierarchical assembly of capillary segments to estimate the permeability of porous media. However, the original model neglected the slippage effect during gas penetration—a common occurrence in cement-based materials and other low-permeability porous media. Thus, we considered this effect in a modified model proposed herein, and the permeability of cement-based materials can be directly predicted using the PSD obtained via mercury intrusion porosimetry. Compared with data from experiments and literatures for various mortars and concretes with permeabilities ranging over 3 orders of magnitude, the results revealed that this modified model can accurately predict the intrinsic permeability and Klinkenberg constant. Moreover, this model can predict the intrinsic permeability and apparent permeability of various gases and porous media. [ABSTRACT FROM AUTHOR]

Gas permeability is an important property associated with the durability of cement-based materials. In this study, an experimental method based on applying a quasi-stationary flow is adopted to evaluate the gas permeability of cement-based materials. The results indicate that the intrinsic permeability of dried cement-based materials is affected by the addition of limestone powder, fly ash, and aggregate. The Katz-Thompson equation could predict the intrinsic permeability by using the capillary porosity, average diameter, and pore tortuosity. The intrinsic permeability of partially saturated cement-based materials decreases when the water saturation increases. The Van Genuchten-Mualem model could describe the relative gas permeability of partially saturated cement-based materials, and the model parameters n value between 1 and 2 while m value ranging from 0.64 to 0.69 for cement and mortar. Moreover, the power function relationship between the intrinsic permeability and Klinkenberg constant of cement-based materials has also been corroborated. Finally, a prediction model of gas permeability of cement-based materials under arbitrary water saturation and pressure gradient is proposed. [ABSTRACT FROM AUTHOR]

An innovative apparatus guided by a proposed theoretical-model was developed for evaluating the radial gas-permeability of cement-based materials under steady-state flow. The testing condition is of higher inlet-gas pressure in an annular concrete cavity to monitor the pressure decrease over time. The gas-tightness for the cavity was effectively enhanced and quantitatively characterized by an ingenious silicone-rubber washer with embedded flexible sensors. The radial gas-permeabilities of the annular concrete with different water-to-cement (w/c) ratios of 0.35–0.55 were measured using various inlet-gas pressures (1.0 bar–30.0 bars) and compared to those obtained by the traditional axial-direction method. The results show that the concrete gas permeability in radial-direction reaches stable permeability zone (SPZ) with inlet-gas pressure exceeding 6.0 bars, which is faster than the SPZ with inlet-gas pressure exceeding 15.0 bars of the axial-direction gas permeability obtained by the traditional method. Under the same inlet-gas pressures of 6.0 bars–10.0 bars, the intrinsic permeability values in the radial and axial directions are near to each other with the standard deviations of 2.83%~9.90% while the apparent permeability values in the radial direction are lower than those in the axial direction by reductions of 3.69%~21.89%. The evolution of apparent gas permeability in radial-direction obeys well the typical model with the low coefficients of variation from 1.01% to 12.55%, indicating that the as-obtained apparatus combined with the proposed theoretical-model can quantitatively and accurately evaluate the radial-direction gas permeability of cement-based materials. • A device is initiatively designed for radial-direction gas permeability measurement. • Theoretical modeling is established for guiding the apparatus application. • By comparison, radial-direction inlet-gas mainly affects apparent gas permeability. • Apparent gas permeability evolution in radial-direction obeys well the typical model. [ABSTRACT FROM AUTHOR]

• An innovation apparatus is developed based on the analyzation of a theoretical model. • The GIP method has been developed based on the proposed apparatus. • The porosity of cementitious materials tested by gas is comparable with that by water (WIP). • Compared to GIP, mercury intrusion porosimetry (MIP) has underestimated the porosity. • Gas is a more proper medium for intrusion porosimetry compared to water and mercury. Pore-structure in cementitious materials determines their chemical and physical properties. However, the quantitative characterization of pore-parameters has yet been investigated in depth. In this work, gas intrusion porosimetry (GIP) is accomplished by a proposed apparatus based on the theoretical model. The porosities of cementitious materials measured by GIP are compared to those obtained by conventional methods including water intrusion porosimetry (WIP) and mercury intrusion porosimetry (MIP). The three methods are assessed by an established empirical-model for the porosity-strength relationship of cementitious materials. The results show that the porosities obtained by GIP are near to those obtained by WIP and the difference is below 2.88%. The porosities determined by the MIP technique were 7.15%~16.71% smaller than those determined by GIP. The results deduced from the empirical model agree well with the measured data obtained by GIP (R2 > 0.95). Both the WIP and MIP decreased the empirical-model effectiveness to predict a trend. [ABSTRACT FROM AUTHOR]

• Gas permeability of concrete was measured considering on coarse aggregate settlement. • Concrete permeability was tested using various gas pressures and confining pressures. • Permeability curve can be observed with four zones following gas-pressure increasing. • Steady zone with 15.0–30.0 bar gas pressures was recommended for permeability test. • Confining pressure of 50 bar was suggested for concrete gas-permeability measurement. Permeability is an important characteristic associated with the durability of cementitious materials. Gas permeability testing could overcome some shortcomings of traditional methods but its key parameters have so far not been identified for long periods, reducing comparability of test results. In this study, coarse-aggregate settlement in concrete was taken into consideration by dividing concrete cores into smaller segments and the gas-permeability of concrete specimens was measured by the modified CemBureau method. Apparent gas-permeability (K a) values of the segments were determined under multiple inlet-gas pressures (1.0 bar–40.0 bar) and various confining-pressures (30 bar–90 bar), which then were applied to calculate the intrinsic permeability (K int) values and Klinkenberg coefficient (β k) to obtain optimal parameters of inlet-gas pressure and confining-pressure. Meanwhile, X-ray computed tomography (X-ray CT), mercury intrusion porosimetry method (MIP) and specific gravity method (SG) were used for auxiliary calibration of test parameters. The results showed that four zones with different inlet-gas pressures were observed for apparent gas-permeability: unstable zone, metastable zone, stable zone, and anamorphic zone. Combined with gas-permeability, pore characteristics were employed for auxiliary calibration of parameter optimization. In sum, 15.0 bar–30.0 bar inlet-gas pressure and 50 bar confining-pressure were determined as the best parameters for concrete gas-permeability testing. [ABSTRACT FROM AUTHOR]

We have designed a new jointless tendon-driven exoskeleton plan for the human hand that provides a correct and stable motion sequence while keeping the structure lightweight, compact and portable. Before the development, anatomy analysis and a kinematics study of the human finger were performed, and bending angle relationships among the metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints were analyzed. Detailed implementation is discussed, including the basic theory of the joint motion coupling method, related formula derivations and mechanical design of an experimental device. An experimental setup was built, and series of experiments was conducted to examine and evaluate the developed joint motion coupling plan.The results indicated that the new plan worked correctly as desired, that an incorrect finger motion sequence did not occur and that the new coupled tendon driven plan can drive finger bending as naturally as a human. The compactness and light weight of the entire structure of the device means that its parts can be arranged for a hand glove or fingerstall more easily than most bar-linkage exoskeleton structures. [ABSTRACT FROM AUTHOR]

The ultra-early age strength of shotcrete with Portland cement-based materials in various supporting constructions is crucial for safety and engineering efficiency. However, concerns exist about the low strength and uncertain mechanism when using aluminum sulfate, the main component of most-used alkali-free accelerators. This study addresses these concerns by introducing ettringite seeds into the Portland cement system with aluminum sulfate. Significant improvement in ultra-early age compressive strength of mortar, i.e., 242 % at 6 h and 201 % at 8 h, was achieved by mere 1 % seed addition. Analyses of hydration heat, composition and microstructure demonstrate that the ettringite seeds mainly affect the mechanical performance by forming a more prolonged and coarser ettringite skeleton, rather than directly accelerating cement hydration. Such an enhanced skeleton was proved to establish stronger interactions between particles in the Monte Carlo simulations. Additionally, the synergistic effect of the ettringite skeleton and C–S–H gel on ultra-early age strength was also explored. These proposed strengthening mechanisms were verified by the C 3 S and equivalent CaCO 3 systems. [Display omitted] [ABSTRACT FROM AUTHOR]

• A logarithmic model with three parameters is developed based on the analytical solution of kinetics function of capillary absorption. • The inlet height of capillary bundle increases with the decrease in the maximum pore size, and the capacity of capillary absorption increases with time of absorption. • An interesting phenomenon, capillary oscillations, is found during the test of the capillary water absorption in mortar with different saturation. Capillary water can transmit in capillary tube induced by hydrostatic pressure, which has an important impact on the durability and shrinkage of concrete. In this study, the ultimate height of capillary rise under various conditions was analyzed based on thermodynamic equilibrium of capillary water where capillary water is subjected to six types of force. Subsequently, a logarithmic model of capillary rising with three parameters (Jurins's height h c , permeability coefficient k , characteristic time τ) was proposed according to the analytical solution of kinetics function of capillary absorption. To better understand capillary behavior in capillary bundle with different radius, the spatio-temporal distribution of saturation, and the variation of water content with time and saturation are predicted according to the kinetics of capillary rise in single capillary. Additionally, the kinetics of capillary absorption in porous materials was discussed. Finally, the developed model was verified by testing the true rising height of water in a mortar specimen using X ray computed tomography. The equivalent height of adsorbed water in mortar with varied saturation under different time was obtained by gravimetric method. The results show that the logarithmic model gives a good description of the kinetics data of water absorption in mortar. [ABSTRACT FROM AUTHOR]

Natural sand resources are becoming increasingly scarce with the rapid development of infrastructure. Therefore, manufactured sand usage is inevitable. However, the significant differences in granite powder content between manufactured- and natural sand have a remarkable impact on the pore structure and permeability of cement-based materials, which are crucial for material durability. In this work, several granite powder dosages (0–32 %) of granite-manufactured sand were considered for preparing manufactured sand concrete, and a suitable physical filling model was chosen to quantify the material particle filling for characterizing the overall pore-filling effect. Mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) were used to examine the pore structure of the specimens. The quasi-stationary flow method was used to test the gas permeability of concrete. Finally, a random hierarchical bundle model using the NMR-MIP method is proposed to predict the gas permeability of cementitious materials based on their pore size distribution. The results show that granite-manufactured sand and an appropriate amount (i.e., 8 %) of granite powder can improve the filling effect and anti-permeability performance of concrete. There is a good correlation between the pore structure parameters and gas permeability, where the physico-mathematical relationships can be modeled. The maximum relative difference between the predicted and experimental values of the random tube bundle model was reduced to 30.93 % using the NMR-MIP method compared to 70.87 % with the traditional MIP method. • Physical filling modeling to quantify different fine aggregate particle morphologies and stacking states between powders. • Selection of the main developed "quasi-static flow method" to test the air permeability of concrete. • The NMR-MIP method is proposed to construct a random hierarchical bundle model to predict gas permeability. [ABSTRACT FROM AUTHOR]

In this work, two PC pastes were used to carry out accelerated carbonation experiments, and phase assemblages of paste samples collected at different sampling depths were analyzed. The source of CaCO 3 originating from the carbonation reaction of hydrates in cement was quantitatively determined by a novel method based on the transformation of hydrates. Experimental results indicated that the phase assemblages in the carbonated zone of two PC pastes showed minor differences. C(A)SH, ettringite, AFm-CO 3 , and unhydrated cement particles in the complete carbonation zone of two cement pastes were carbonated and transformed into other phases. For the surface of two PC pastes (0–3 mm), calculations showed that the CaCO 3 originating from the carbonation of calcium hydroxide and C(A)SH accounted for 75.3% and 72.6% of the total CaCO 3 , respectively. A concentration of 20% CO 2 was not beneficial for the diffusion of CO 2 and the subsequent precipitation of CaCO 3 at the later period of carbonation. • The change in phase assemblages of two carbonated PC pastes collected at different depths was analyzed. • A calculation method was proposed to analyze the source of CaCO 3 originating from the carbonation of hydrates in PC. • For the surface, the CaCO 3 originating from the carbonation of portlandite and C(A)SH accounted for 75.3% of the total CaCO 3. [ABSTRACT FROM AUTHOR]

It is found that in order to ensure the polishing slurry involved in polishing process is sufficient, the supply of polishing slurry has to be excessive in conventional polishing process. However, actually only a limited amount of polishing slurry is involved in polishing process compared with the supplied polishing slurry, and the overwhelming majority is directly discharged which increases waste emissions. On the other hand, the issue of industrial waste is increasingly attracting scientific and public attention due to the magnitude of the problem in China, and various types of polishing slurries will cause serious pollution to rivers and soils. This paper focuses on a novel and successful polishing slurry waste reduction method which realizes waste reduction on the premise of ensuring the polishing performance. The proposed method is based on ultrasonic atomization, which can make the polishing slurry with low supply rate form a soft and low velocity fine mist spray and realize the even distribution of abrasive particles in slurry, and is called ultrasonic atomization polishing. In order to prove the feasibility of this waste reduction method, this paper has proved that (i) the introduction of ultrasonic atomization contributes the improvement of surface quality and polishing efficiency and (ii) ultrasonic atomization polishing can greatly realize polishing slurry waste reduction, moreover, multi-objective optimization scheme of polishing parameters for ultrasonic atomization polishing is obtained, which are all of great significance to guide the waste reduction in actual production. [ABSTRACT FROM AUTHOR]

• The saline soil does not change the internal degradation mechanism of mortar, and the degradation products are still mainly composed of gypsum and ettringite. • The degradation rate of saline soil containing sodium sulfate to mortar is faster than that of sodium sulfate solution. It is contrary for saline soil containing magnesium sulfate. • When the mortar is degraded by sulfate, an obvious movable corrosion interface is observed in mortar along corrosion direction. The sulfate attack of salt solution and saline soil on concrete structures is an essential factor threatening their durability. The degradation of saline soil to concrete structures has attracted more attention than the salt solution in recent years. Thus, the degradation of mortar buried in saline soil containing sulfate ions was investigated in this study. Combined with the macro and micro degradation results, the saline soil does not change the internal degradation mechanism of mortar because the degradation products are also mainly composed of gypsum and ettringite. The degradation rate of soil containing sodium sulfate to mortar is more vital than that of the corresponding salt solution. However, the results are contrary for soil containing magnesium sulfate and the corresponding salt solution. An evident and movable degradation interface in the eroded mortar is observed based on a color difference along the direction of degradation; The fly ash with a high replacement (60 wt%) is unfavorable to the resistance of the mortar under sulfate attack, because it contains a high aluminum phase to form ettringite. The slag can increase the resistance of the mortar under sulfate attack due to its smaller content of aluminum phase and higher activity. [ABSTRACT FROM AUTHOR]

• The self-designed conductometric titrator can test the conductivity of solution and can test the concentration of sulfate. • The conductivity of Na 2 SO 4 and BaCl 2 solution increases linearly in the temperature range of 25–70 °C. • When titrating sulfate in cement-based materials, 0.02 mol/L BaCl 2 , 0.828 mL/s titrating rate of, and 10 mL volume titrated are recommended. The concentration of sulfate ion in cement-based materials is the basic data for the design and evaluation of concrete structures exposed to sulfate lakes and saline soil areas. In this study, a conductivity titrator was developed and used to test the sulfate concentration in concrete corroded by sulfate attack based on the Internet of Things. The theories of conductivity measurement and conductivity titration were described; The main hardware composition and software design of conductometric titrator were introduced; Then, the effects of temperature, concentration, hydroxyl ion and hydrogen ion on the conductivity of solution of sodium sulfate and barium chloride were explored by the titrator; The titration parameters, the influence of hydroxyl and hydrogen ion on sodium sulfate titration were determined by test of sulfate ion titrated by barium chloride with known concentration; Finally, the titrator was used to test the sulfate concentration in cement-based materials after sulfate attack. The results show that the titrator can measure the conductivity of solution with 0.4% accuracy and the concentration of sulfate ion with 0.8% accuracy; During the titration of sulfate ion, the concentration of barium chloride should be twice that of sulfate ion, the titration rate should be less than 0.828 mL/s, and the titration volume should be at least 10 mL; It is found that the influence of hydroxyl ion can be effectively eliminated by adding nitric acid or hydrochloric acid, and the influence of hydrogen ion can be effectively eliminated by adding sodium carbonate. This conductivity meter can accurately test the sulfate concentration in the concrete after corrosion. [ABSTRACT FROM AUTHOR]

• Developing a novel high ductility hybrid fibre sheet for strengthening timber beams. • Obtaining the macroscopic and microscopic failure mechanisms of specimens. • Evaluating the enhancement law of different layers, types, angles and hybrid modes. • Contributing to state of art on round timber beams reinforced with hybrid fibre sheets. Timbers with defects are often used in historical buildings. However, the existing fibre sheet reinforcing technology for the timber beams is difficult to balance the strength, ductility and cost. This paper aims to develop novel high ductility hybrid fibre sheets for strengthening timber beams at a lower cost than available methods. First, four types of unidirectional and two types of bidirectional fibre reinforced polymer (FRP) sheets were designed and evaluated using scanning electron microscopy (SEM) and tensile tests. Then, the FRP sheets were used to make 68 timber beams with square and round cross sections for bending tests. Finally, parameter analysis was conducted to evaluate the enhancement law of specimens with different sheet layers, fibre types, reinforcement angles and interlaminar hybrid modes. The results show that the reinforcement angle of a round timber beam has a great influence on its ultimate bearing capacity, for which the recommended value range is 45°∼60°. Unidirectional fibre sheets with a fibre ratio of carbon fibre:aramid fibre:glass fibre = 2:1:1 have a positive hybrid effect on bearing capacity and can improve the ultimate deflection of timber beams by 69.2–115.4% with one layer. These research results can contribute to state-of-the-art knowledge about round and square section timber beams strengthened with hybrid fibre sheets and the conservation of timber structures. [ABSTRACT FROM AUTHOR]

• A structural kinetics model was developed by combining a kinetic equation of the structural parameter λ and the relationships between yield stress τ y. • Yield stress is more suitable to characterize the structural build-up of fresh cement paste than viscosity and rheological index. The test of the yield stress needs to consider the structure of the rheometer. • When the specific area of limestone exceeds 600 m2·kg−1, it can accelerate the establishment rate of the dynamic structure. When the specific area is 400 m2·kg−1, the content of limestone corresponding to the maximum structuration rate is reduced. The structural build-up of fresh cement-based materials is of great significance to the early forming and later performance. A structural kinetics model (SKM) used to indicate the structural build-up was developed by combining a kinetic equation described by structural parameter (λ) and a relationship between yield stress (τ y) and λ in the paper. SKM transforms the structuration rate (A thix ) in linear Roussel model and the characteristic time (t c) in non-linear Perrot model into more specific indicators such as initial solid volume fraction (ϕ 0) , rate of hydration during induction period (α ̇ ind) , and shear rate (γ.). The yield stress (τ y) obtained by RHEOLAB QC rotary viscometer was explored the dynamic and static structural build-up of fresh cement paste. The yield stress of fresh cement paste (W/C = 0.4) exhibits a quasilinear pattern with rate of 0.42 Pa/s for 210 min of mixing, with rate of 0.88 Pa/s for 100 min of resting after 4 min of mixing. The static yield stress of fresh cement paste evolves from linear to non-linear patterns within 100 min of resting after beyond 30 min of mixing. The fitting results show that SKM can well fit the evolution of yield stress including linear and nonlinear phases. Comparing with the dynamic structural build-up, the effect of limestone powder on the static structural build-up of cement paste is more obvious. When the mixing process is longer than 60 min, the content of limestone powder less than 20 wt% is beneficial to the structural build-up of fresh paste. Additionally, a declined rate of cement hydration in the induction period with increasing mixing time indicates that the rising yield stress, in this case, cannot be attributed entirely to the contribution of hydration to structural build-up. [ABSTRACT FROM AUTHOR]