Drying induced moisture losses from mortar to the environment. Part I: experimental research

Moisture conditions in the pore structure of hardening cementitious materials are known to have determinant influence on the onset and continuance of hydration reactions. Moisture loss from regions near exposed surfaces may jeopardize the quality of concrete cover in terms of both mechanical and durability issues. In addition, drying shrinkage, a phenomenon directly related to a moisture loss to the environment, is known to be responsible for several surface cracks that impair durability performance and pose aesthetical problems. Furthermore, evaporative cooling that occurs in concrete surfaces in the first minutes just after formwork removal may cause thermal cracking. For the above mentioned reasons, it is important to assess the mechanisms of moisture losses from cement-based materials to the environment, in order to rationally establish curing criteria. This paper describes an experimental campaign conducted with the purpose of better understanding the effect of various environmental conditions on the referred moisture interactions, accounting for influences such as the environmental temperature, the relative humidity (RH), the wind speed and direction, as well as the duration of curing. Numerical simulations with comparisons against test data, as well as some sensitivity analyses, are relegated to the companion paper that follows in this issue.     

A coupled numerical analysis of shield temperatures, heat losses and residual gas pressures in an evacuated super-insulation using thermal and fluid networks: Part I: Stationary conditions

This paper describes numerical simulations, using thermal networks, of shield temperatures and radiative and conductive heat losses of a super-insulated cryogenic storage tank operating at 77 K. Interactions between radiation and conductive heat transfer modes in the shields are investigated, by calculation of local shield temperatures. As a new method, fluid networks are introduced for calculation of stationary residual gas pressure distribution in the evacuated multilayer super-insulation. Output from the fluid network is coupled to the iterative thermal network calculations. Parameter tests concern thickness and emissivity of shields, degree of perforation, residual gas sources like desorption from radiation shields, spacers and container walls, and permeation from the inner container to the evacuated insulation space. Variations of either a conductive (thickness of Al-film on Mylar) or a radiative parameter (thermal emissivity) exert crosswise influences on the radiative or conductive heat losses of the tank, respectively.     

Further investigation on the dynamic compressive strength enhancement of concrete-like materials based on split Hopkinson pressure bar tests. Part II: Numerical simulations

Split Hopkinson pressure bar (SHPB) tests have been used widely to measure the dynamic compressive strength of concrete-like materials at high strain-rates between 10¹ and 10³ s⁻¹. It has been shown in companion paper (Zhang M, Wu HJ, Li QM, Huang FL. Further investigation on the dynamic compressive strength enhancement of concrete-like materials based on split Hopkinson pressure bar tests Part I: Experiments. Int J Impact Eng 2009;36(12):1327–1334) that the axial strain acceleration is normally unavoidable in an SHPB test on brittle materials. Axial strain acceleration introduces radial confinement in the SHPB specimens and consequently enhances the compressive strength of concrete-like specimens. This paper employs numerical simulation to further demonstrate that the unexpected radial confinement in an SHPB test is responsible for the increase of the dynamic compressive strength of concrete-like materials at strain-rates from 10¹ to 10³ s⁻¹. It confirms the observations in Zhang et al. (Zhang M, Wu HJ, Li QM, Huang FL. Further investigation on the dynamic compressive strength enhancement of concrete-like materials based on split Hopkinson pressure bar tests Part I: Experiments. Int J Impact Eng 2009;36(12):1327–1334) that the dynamic increase factor (DIF) measured in SHPB tests can be reduced either by using tubular SHPB specimens or by reducing the diameter of the SHPB specimen. A kinetic friction model is proposed based on kinetic friction tests and is implemented in the numerical model. It shows that it is necessary to use a kinetic friction model, rather than a constant friction model, for more accurate numerical simulation of SHPB tests.     

Mechanics of three-dimensional braided structures for composite materials – Part II: prediction of the elastic moduli

In the first part of this series of paper [Z.X. Zang, R. Postle, Mechanics of three-dimensional braided structures for composite materials – Part I: fabric structure and fibre volume fraction, Comp. Struct. 49 (2000) 451–459], it was demonstrated that the braiding angles and fibre volume fraction can be represented as functions of the normalized pitch length introduced as a key parameter of three-dimensional braided reinforced composite materials. In the present paper, the models for the prediction of the tensile and shear moduli of three-dimensional braided composites are established by numerical simulation and mathematical modelling. Three-dimensional braided preforms are produced from the material system comprising glass/polypropylene and their moduli are measured. The results predicted from the braided composite models are supported by the experimental data.     

Human posture simulation to assess cumulative spinal load due to manual lifting. Part II: accuracy and precision

For assessing a large number of variable manual lifting jobs, posture specification for using the University of Michigan Three Dimensional Static Strength Prediction Program and the revised National Institute for Occupational Safety and Health Lifting Equation may be time-consuming, tedious and subject to human errors. To expedite data analysis with desirable accuracy and precision for the two risk assessment tools, a new data analysis method based on human posture simulation was developed and evaluated. The accuracy and precision of the posture simulation method were evaluated by a repeated measures study design with six postures, three viewing angles and three trial repetitions as experimental factors. The effects of the experimental factors on the average accuracy and precision of the simulation method are reported and discussed. The study results also demonstrated pros and cons of human posture simulation as a means of posture specification for ergonomic risk assessments. The findings about the accuracy and precision of the human posture simulation method for quantifying the risk of musculoskeletal disorders due to manual materials handling may provide researchers with a new way of ergonomic assessments.     

Knowledge base for the systematic design of wet cooling towers. Part II: Fill and other design parameters

This paper describes the final part of the detailed methodology for the thermal design of wet, counterflow and crossflow types of mechanical and natural draught cooling towers. This part includes the following design steps: the fill or packing, total packed height and the number of decks, water and air loading, pressure drop across the packing, natural draught tower, fan design for a mechanical draught cooling tower, blowdown and make-up water rate, water distribution systems and drift eliminators. Different empirical relations and assumptions are used in this part of the design procedure.     

Correlation of microstructure, electrical properties and electrochemical phenomena in reinforced mortar. Breakdown to multi-phase interface structures. Part II: Pore network, electrical properties and electrochemical response

Since reinforced mortar is a multi-phase composite material at different levels of aggregation, a combination of techniques, namely electrochemical impedance spectroscopy (EIS) (for investigating the electrochemical phenomena on the steel reinforcement) and microstructure analysis (for qualifying and quantifying the composite bulk material), was used to provide insight into the macro- and micro-level interactions, involved in conditions of corrosion and cathodic protection for the here investigated reinforced mortar specimens.

After 120days of exposure to the relevant conditions of chloride-induced corrosion and impressed current cathodic protection (CP), it was found that the accumulation, volume expansion and propagation of corrosion products bring about significant structural alterations in the cement matrix. Further, the current flow involved in CP applications, along with the protection itself, contributes to additional changes in the bulk material. In this study, the elements of the equivalent electrical circuit from EIS measurements are discussed in correlation to the evolution of porosity, pore size distribution and pore interconnectivity of the bulk matrix, during corrosion and CP application. The results indicate that different parameters in the EIS modeling concept correspond well to specific interface microstructures.

The outcomes of this combination of techniques will possibly provide implications for computer simulation of the corrosion process and CP applications as well as modeling of concrete performance in aggressive environments.     

Effects of synthetic oil in a compression refrigeration system using R410A. Part II: quality of heat transfer and pressure losses within the heat exchangers

The consequences of the oil rejected by the compressor of a vapour-compression refrigeration system on the operation of the evaporator and condenser are analysed. The modelled prototype uses the mixture of HFC R410A and a synthetic polyolester (POE) oil. The rise of the amount of lubricant circulating in the system leads to a progressive change in the behaviour of the mixture of refrigerant and oil that, for the higher oil mass fraction, evolves like a zeotropic mixture. One also observes that the presence of lubricant is generally associated with a fall of the performances of the heat exchangers, except however in the evaporator where an optimum is observed when the quantity of oil is equal to 0.1% of the total mass of the mixture. Some conclusions are drawn about the choice of correlations for the calculation of the refrigerant side heat transfer coefficient in a plate evaporator.     

Scaling the response of circular plates subjected to large and close-range spherical explosions. Part II: Buried charges

This paper discusses scaling of the dynamic response of clamped circular plates subjected to close-range, large spherical blast loadings that are flush buried in dry sand. As a continuation of part I which dealt with air blasts, similarity is obtained by using replica scaling for all geometrical parameters, while the blast effect is scaled by using the Hopkinson scaling law.     

Prediction of transport properties of wood below the fiber saturation point - A multiscale homogenization approach and its experimental validation. Part II: Steady state moisture diffusion coefficient

In this publication a multiscale homogenization model for moisture transport in wood is developed and validated. The model aims at prediction of macroscopic transport properties of clear wood samples from their microstructure and the physical properties of a few microscale constituents. In the first part of this two-part paper, the theoretical background and fundamentals of the model were presented, and its specification for the estimation of macroscopic thermal conductivities was shown. In this second part the model is applied to steady state moisture diffusion below the fiber saturation point. The model starts on a scale of about 50 μm, where the wood cells form a honeycomb-like structure. In a first homogenization step the effective moisture transport behavior of the cell structure is determined from moisture diffusion properties of the cell walls and the (moist) air in lumens, respectively. Further homogenization steps account for the larger vessels that exist in hardwood species, the annual rings which are a succession of layers with different densities, and finally wood rays, that form pathways in the radial direction throughout the stem. The model validation rests on experiments as in the case of heat conduction: The macroscopic diffusion coefficients predicted by the multiscale homogenization model for tissue-specific composition data (input data set II) are compared to corresponding experimentally determined tissue-specific diffusion coefficients under steady state conditions (experimental data set). As for thermal conductivity, the good agreement of model predictions and test data underlines the suitability of the presented multiscale model.     

Pseudophase information from the complex analytic signal of speckle fields and its applications. Part II: statistical properties of the analytic signal of a white-light speckle pattern applied to the microdisplacement measurement

To provide a theoretical background for the superiority of the signal-domain phase-only correlation (SDPOC) technique proposed here for microdisplacement measurement, we study the first- and the second-order statistical properties of the complex amplitude of an analytic signal of a white-light speckle pattern, under the assumption of a Gaussian random process, and give a formula for the autocorrelation function of the pseudophase associated with the complex analytic signal. Based on these results, we show mathematically that SDPOC has a performance advantage over conventional intensity-based correlation techniques.     

Cathodic electrodeposition of cerium based oxides on carbon steel from concentrated cerium nitrate. Part II: Influence of electrodeposition parameters and of the addition of PEG

The mechanisms of formation of cerium based oxides on carbon steel by cathodic electrodeposition from relatively concentrated cerium nitrate solutions were investigated in a previous work (Part I). It was shown that some corrosion products developed on the steel upon and soon after coating, thereby suggesting the films were not protective. This work (Part II) focuses on the influence of various elaboration parameters on the composition and morphology of the deposits likely to improve the corrosion resistance of carbon steel.     

New ‘ηpl'' and ‘γ'' functions to evaluate J–R curve from cracked pipes and elbows. Part II: experimental and numerical validation

Experimental evaluation of J–R curve in a crack growth situation requires ‘η_pl' and ‘γ' functions that are specific to a cracked geometry and loading condition. In Part I [Engng. Fract. Mech., in press] of this paper, new η_pl and γ functions, which are not available in the literature, for pipe and elbow geometry with various crack configurations under different loading conditions have been derived. In this paper, some of these newly proposed η_pl and γ functions have been validated experimentally through comparison of crack initiation load and J–R curve. In few cases, numerical validation has also been provided by comparing the J-integral values calculated through η factor approach and finite element method.     

Development of separation technology for the removal of radium-223 from targeted thorium conjugate formulations. Part II: purification of targeted thorium conjugates on cation exchange columns

Tumor targeting pharmaceuticals will play a crucial role in future pharma pipelines. The targeted thorium conjugate (TTC) therapeutic platform could provide real benefit to patients, whereby targeting moieties like monoclonal antibodies are radiolabelled with the alpha-emitting radionuclide thorium-227 (²²⁷Th, t_1/2?=?18.7?days). A potential problem could be the accumulation of the long-lived daughter nuclide radium-223 (²²³Ra, t_1/2?=?11.4?days) in the drug product during manufacturing and distribution. Therefore, the level of ²²³Ra must be standardized before administration to the patient. The focus in this study has been the removal of ²²³Ra, as the other progenies will have a very limited stay in the formulation. In this study, the purification of TTCs labeled with decayed ²²⁷Th has been explored. Columns packed with a strong cation exchange resin have been used to sequester ²²³Ra. The separation of TTC from ²²³Ra has been evaluated as influenced by both formulation and process parameters with a design of experiments (DOE) study; including citrate or acetate buffer, pH, buffer concentration, presence or absence of pABA?+?EDTA, resin amount and sodium chloride concentration. The aim was to achieve a separation with high sorption of ²²³Ra and accompanying low TTC sorption. The results were analyzed by multivariate analysis. Four regression models of TTC and ²²³Ra sorption from citrate and acetate buffered formulations were developed. The predictive accuracy of sorption in the four statistical models was given by standard deviations and confidence intervals. The TTC sorption in citrate and acetate buffered formulations was affected by the identical variables and the variation in TTC sorption was comparable for the two models. However, the DOE variables had a significantly stronger impact on the ²²³Ra sorption in citrate buffered formulations than the ²²³Ra sorption in acetate buffer. An optimal separation with a TTC sorption below 25% and ²²³Ra sorption above 90% can be achieved in both citrate and acetate buffered formulations. Stability studies of radiochemical purity (RCP) indicated that the measured ²²⁷Th values may be partly due to free ²²⁷Th and not TTC, but the results indicate that TTC stability may be controlled by optimizing formulation parameters. Hence, the sorption data and the regression models presented must be reviewed and further explored with regard to what is known about the stability of the TTC in the different buffered formulations.     

Transformation of BCC and B2 High Temperature Phases to HCP and Orthorhombic Structures in the Ti-Al-Nb System. Part II: Experimental TEM Study of Microstructures

Possible transformation paths that involve no long range diffusion and their corresponding microstructural details were predicted by Bendersky, Roytburd, and Boettinger [J. Res. Natl. Inst. Stand. Technol. 98, 561 (1993)] for Ti-Al-Nb alloys cooled from the high temperature BCC/B2 phase field into close-packed orthorhombic or hexagonal phase fields. These predictions were based on structural and symmetry relations between the known phases. In the present paper experimental TEM results show that two of the predicted transformation paths are indeed followed for different alloy compositions. For Ti-25Al-12.5Nb (at%), the path includes the formation of intermediate hexagonal phases, A3 and DO₁₉, and subsequent formation of a metastable domain structure of the low-temperature O phase. For alloys close to Ti-25Al-25Nb (at%), the path involves an intermediate B19 structure and subsequent formation of a translational domain structure of the O phase. The path selection depends on whether B2 order forms in the high temperature cubic phase prior to transformation to the close-packed structure. The paper also analyzes the formation of a two-phase modulated microstructure during long term annealing at 700 °C. The structure forms by congruent ordering of the DO₁₉ phase to the O phase, and then reprecipitation of the DO₁₉ phase, possibly by a spinodal mechanism. The thermodynamics underlying the path selection and the two-phase formation are also discussed.     

The Theory of Critical Distances to estimate the static strength of notched samples of Al6082 loaded in combined tension and torsion. Part II: Multiaxial static assessment

This paper is concerned with a novel reformulation of the Theory of Critical Distances (TCD) suitable for estimating static strength of notched ductile materials subjected to multiaxial loading. The main feature of the method proposed and validated here is that the static assessment is performed by directly post-processing the linear-elastic stress fields in the vicinity of crack initiation sites. In more detail, our theory is proposed to be applied in the form of both the Point Method (PM) and the Line Method (LM) and it is formalised so that it can be used in conjunction with any classical equivalent stress (i.e., Von Mises’ equivalent stress, Tresca’s equivalent stress, maximum principal stress criterion, etc.). The accuracy and reliability of such an approach was checked by using the experimental results we generated by testing cylindrical samples, containing notches of different sharpness, made of Al6082 and loaded in combined tension and torsion. Observations of the failure modes in these specimens (reported in Part 1 of this two-part series of papers) informed the development of the above approach. Our method proved to be capable of estimates characterised by the usual level of accuracy shown by the TCD when used in other ambits of the structural integrity discipline, that is, of predictions falling within an error interval of about ±20%. This result is very encouraging especially in light of the fact that our simple linear-elastic approach was used to estimate static strength even when the material in the vicinity of crack initiation sites experienced multiaxial plastic deformations and the observed cracking behaviour was rather complex. Thanks to its particular features, the approach formalised in the present paper can be considered as an interesting engineering tool suitable for performing the static assessment of notched ductile materials by directly post-processing the outputs from simple linear-elastic Finite Element (FE) models.