Investigating the thermo-mechanical behaviour of cementitious materials using image processing techniques

Infrared thermography and Digital Image Correlation were used to analyse the mechanical behaviour of mortar, concrete, and high-performance concrete specimens under quasi-static loads. For specimens under compressive loads, Infrared thermography clearly showed the thermo-elastic coupling as well as thermal dissipations due to the microcracking state of freeze/thaw damaged concrete specimens. During an up to failure compressive test, localized thermal effects were observed at the macro-crack location before it appeared. Strain fields at the surface of steel-fibre high-performance concrete specimens under tensile and flexural loadings were determined using the Digital Image Correlation (DIC) technique. These experiments showed that the strain fields early became inhomogeneous. Strains concentrated in multiple localization zones which highlighted the role of the steel fibres in transmitting the internal forces.     

A novel automated image analysis method for maceral analysis

A new image analysis technique has been developed which allows maceral analysis of coal to be carried out. The technique is able to separate the liptinite component from the background resin by using two separate images of the surface captured with different camera exposure times. At normal exposure, the liptinite has a similar grey scale value to the surrounding resin, but at a higher exposure time, the resin remains black whilst the liptinite grey scale increases significantly enough to distinguish it from the resin. The method has been tested for repeatability and reproducibility and found to be within the ISO Standard requirements.     

Determination of particle shape distribution of clay using an automated AFM image analysis method

We have developed a direct imaging method for measuring particle shape distributions. It consists of a series of advanced automated algorithms that analyze 3D Atomic Force Microscopy (AFM) images of diluted pigment suspensions deposited onto glass cover slips. The method was applied to determine particle shape distributions of 10 different clay pigments from Brazil and Georgia, US. We found that the aspect ratio varies significantly and monotonically with particle diameter. The method gives generally lower average aspect ratios than those mentioned in previously published data, but still ranks pigments similarly. It was determined that Georgia clays generally have higher aspect ratios and broader shape distributions than Brazilian clays. This new direct automated AFM image analysis approach will be useful in pigment shape characterization and will provide important data for predicting coated paper performance.     

Digital image analysis of coating defects

A simple, low cost, easy to use computer-based Digital Image system has been developed for characterizing defects which occur in various types of organic films. The system uses an optical microscope, high resolution TV camera, frame grabber to display the image on Macintosh computer and software to analyze and characterize the image. All components are commercially available. Using this system, many different defects which are typically seen in organic coatings and the support on to which they are coated, such as spots, bubbles, reticulation streaks and pinholes can be rapidly characterized. Quantitative information about the defect, such as size and frequency can be rapidly obtained to assist in determining the cause. Images obtained of the defects can also be enhanced to obtain characterization information not easily seen in the defect. The system has applications in the R and D laboratory for understanding defect mechanisms, in trouble-shooting plant and end-use problems and in the control laboratory. It can also be used to provide routine quantitative testing information on defects that have been typically evaluated by subjective tests and comparison with go/no-go standards. The system is easier to use than viewing with a glass or conventional microscope and a permanent record of the defects can easily be stored and retrieved in a computer database to assist in troubleshooting.     

Automated air void analysis of hardened concrete — a Round Robin study

The RapidAir is an automatic system for analysing the air void content of hardened concrete. The analysis requires polishing of the concrete surface as described in ASTM C 457 as well as a contrast enhancement of the surface. The system can automatically analyse the air void system according to the ASTM C 457 and EN 480-11 standards.The sample preparation includes contrast enhancement steps ensuring white air voids in black concrete (aggregate and paste). For a well-lapped sample of good quality concrete the contrast enhancement procedure requires approximately 5-10 min to perform. The air content can be analysed in less than 15 min traversing 2413 mm (95 in.) — a significant improvement compared to several hours normally required to perform a manual linear traverse analysis.This paper describes the method and technique required for automatic analysis using the RapidAir system as well as data from a Round Robin study. Three samples were circulated to 7 different laboratories for automatic air void analysis. Prior to the automatic analysis the samples were analysed manually using linear traverse and point counting methods. The results of the Round Robin study showed very good repeatability and reproducibility of the RapidAir system but large variations when using manually performed analysis.     

Rupture probability of coarse aggregate on fracture surface of concrete

In this work, the fracture surface of concrete was analyzed by the digital image analysis (DIA) technique, and the rupture probability of the coarse aggregate (RPCA) was used to represent the failure mode of the aggregate at the fracture surface. The relationships between the RPCA, the water-binder ratio (W/B), and the size and type of coarse aggregate were investigated. Preliminary results showed that: (1) RPCA increases with decreasing W/B of concrete. (2) RPCA of concrete with coarse aggregates having a maximum size of 16 mm is higher than that with other sizes of coarse aggregate. The influence of the size of coarse aggregate on the RPCA is more significant in high strength concrete than in normal strength concrete. (3) With reduction of W/B, the interfacial bond of concrete with crushed gravel improves more significantly than with round gravel according to their RPCA. (4) RPCA depends not only on the intrinsic strength, size, and shape but also on the reactivity of the coarse aggregate.     

Development of thermal energy storage concrete

In this paper, a two-step procedure to produce thermal energy storage concrete (TESC) is described. At the first step, thermal energy storage aggregates (TESAs) were made from porous aggregates absorbing phase changing materials (PCMs). At the second step, TESC was produced with a normal mixing method and using TESAs. An adequate amount of PCM can be incorporated into concrete by the two-step procedure. It can be seen experimentally that the energy storage capacity of the TESC was comparable with that of a commercially available PCM. The experimental results showed that the geometrical features of the porous structure of the aggregates had significant effect on their absorbing ability of the PCM. Aggregates with large pore connectivity factor and transport tunnel in boundary part can absorb more PCM. It was also found that the phase changing behavior was affected by the volume fraction of PCM in concrete.     

Shape and size effects on the compressive strength of high-strength concrete

In this paper we investigate the influence of the shape and of the size of the specimens on the compressive strength of high-strength concrete. We use cylinders and cubes of different sizes for performing stable stress-strain tests. The tests were performed at a single axial strain rate, 10^{− 6} s^{− 1}. This value was kept constant throughout the experimental program. Our results show that the post-peak behavior of the cubes is milder than that of the cylinders, which results in a strong energy consumption after the peak. This is consistent with the observation of the crack pattern: The extent of cracking throughout the specimen is denser in the cubes than in the cylinders. Indeed, a main inclined fracture surface is nucleated in cylinders, whereas in cubes we find that lateral sides get spalled leading to the so-called hour-glass failure mode. The remaining cube core gets fragmented due to crushing, in some cases exhibiting a dense columnar cracking in the bulk of the specimen. Finally, we investigate the relationship between the compressive strength given by both types of specimen for several specimen sizes.     

Identification and quantification of cracks in concrete by optical fluorescent microscopy

Cracks in concrete structures can indicate major structural problems and can damage the appearance of monolithic construction. Cracking of concrete is a major factor affecting for the material strength and durability. The development of a crack pattern can contribute to increasing the permeability and the diffusivity of concrete, which is generally connected with a substantial reduction of its durability. This paper describes a method for identification and quantification of crack patterns in concrete by means of optical fluorescent microscopy and image analysis. Results obtained for undamaged and deteriorated specimens are presented. The range of investigation included several concrete mixes made in the laboratory. In order to induce cracks, concrete mixes were exposed to freezing action 0, 1 and 2 h after mixing. The concrete cubes of 100-mm and 150-mm size were frozen for 0 (reference specimens) and 2 days. Investigation of compressive strength, water permeability, chloride migration and analysis of cracks was made after 28 days. The low-temperature deteriorated specimens showed a significant reduction of compressive strength and resistance to water and chloride penetration in concrete. Correlations between density of cracks and compressive strength, depth of water penetration and depth of chloride penetration have been proposed.     

Quantification and characterization of microporosity by image processing, geometric measurement and statistical methods: Application on SEM images of clay materials

A series of image processing technologies and geometric measurement methods is introduced to quantify multiple scale microporosity in images. All the operations are non-destructive so as to ensure the accuracy of the results. With the application of these methods, various basic geometric parameters of the pores can be computed automatically in the computer, such as area, perimeter, direction etc. On the basis of these geometric parameters, probability entropy, probability distribution index and fractal dimension were introduced to describe the distribution of the three major characteristics of pore system, direction, area and form factor, respectively. Computer software developed on the basis of these methods was used to quantify the SEM images of clay samples during shear test. According to the quantification result, total pore area and average pore form factor reduce during the test. The variation of pore area and form factor is related to probability distribution index and fractal dimension, which indicates the variation of microstructures between pores. Error analysis shows that the deviation using the image processing is within 5%, and the deviations of statistical parameters are smaller in comparison with those of basic geometric parameters. The statistical methods are adapted to the quantification of 2D multiple scale objects. This paper offers a reliable basis for the quantification and characterization of microporosity by image processing.     

Improving local composition measurements of binary mixtures by image analysis

Composition quantification in granular mixtures through colorimetric imaging is addressed. Digital images of binary mixtures have been analysed with three different colour spaces: gray scale, L?a?b? and HSV. Experiments have been carried out on a small scale drum mixer. After blending, the mixtures have been impregnated with a binder, solidified and sliced. The colorimetric analysis has been carried out on the interior of the granular bed. Results obtained using the three colour-spaces have been performed and compared. The HSV colour space yields better results in terms of accuracy and computational effort. Effectiveness of HSV relies on its independence from shadows that are a distinctive feature of pictures of the three-dimensional granular surface. Very important, HSV does not require a calibration curve to convert colour information into composition, differently from the other colour spaces.     

Direct measurement of electrospray droplets in submicron diameter using a freezing method and a TEM image processing technique

The size distributions of electrospray droplets from the Taylor cone in cone-jet mode are directly measured by using a freezing method and a transmission electron microscope (TEM) image processing technique. These results are compared with the data obtained by an aerodynamic size spectrometer (TSI Aerosizer DSP). The use of glycerol seeded with NaI and a freezing method make it possible to sample droplets with their original sizes preserved. Since pictures of droplets are taken with TEM with very low vapor pressure of the solution, evaporation is suppressed by freezing. For liquid flow rates below 1 nl/s, the measured droplet diameters by the TEM image processing technique and the aerosizer are in the range of 0.25–0.32 and 0.30–0.40 μm, respectively. Both results are to some extent qualitatively in agreement with previous scaling law, however, they are two or three factors greater than those of the scaling law because of the much higher viscosity of the solution. Comparing the TEM data with the aerosizer measurements, it has been revealed that the TEM image processing technique can afford more accurate values of droplet size distributions in the submicron range of 0.1–0.4 μm.     

Estimation of the structure of air entrained concrete using a flatbed scanner

This paper describes the possibilities of estimating the structure of concrete with the help of automatic image analysis using a high-resolution flatbed scanner. Sample preparation techniques and components of the image analysis system are described. Concerning the structure of the entrained air voids system, it was found that the results obtained using a high-resolution flatbed scanner were comparable to those obtained by conventional methods, i.e. using a system equipped with stereomicroscope. The possibility of automatically measuring the paste content in hardened concrete by analysis of plane sections, taking into account information available in RGB histograms, is also presented. A new procedure is proposed for the identification of the distance from the cement paste to periphery of the nearest air void, which enables rapid evaluation of the quality of the air entrainment treatment The procedure also allows some characterization of the aggregate component.     

高纯氟化锂的制备与分析方法评述

论述了高纯氟化锂的主要制备方法,并将其归结为直接法、离子交换法与萃取法.同时对高纯氟化锂的一些常用分析方法,如石墨炉原子吸收法、火焰原子吸收法等进行了评述.     

Comparison of ASTM saturation techniques for measuring the permeable porosity of concrete

The aim of this study is to compare the efficacy of the ASTM saturation techniques for measuring the permeable porosity of concrete. The permeable porosity of two ordinary concretes has been determined by three ASTM saturation techniques, namely cold-water saturation (CWS), boiling-water saturation (BWS) and vacuum saturation (VAS). The concretes were prepared with the water-cement ratios of 0.50 and 0.60, and tested at ages of 7 and 28 days. Based on the test results of permeable porosity, the efficiency of the saturation techniques has been compared. In addition, the compressive strength of concretes was determined to justify the results of permeable porosity. The slump test was also performed to observe the workability. The overall experimental results reveal that vacuum saturation technique is more efficient than cold-water or boiling-water saturation and therefore this technique should be recommended for measuring the permeable porosity of concrete.     

Evolution of porosity in suspension thermal sprayed YSZ thermal barrier coatings through neutron scattering and image analysis techniques

Porosity is a key parameter on thermal barrier coatings, directly influencing thermal conductivity and strain tolerance. Suspension high velocity oxy-fuel (SHVOF) thermal spraying enables the use of sub-micron particles, increasing control over porosity and introducing nano-sized pores. Neutron scattering is capable of studying porosity with radii between 1 nm and 10 μm, thanks to the combination of small-angle and ultra-small-angle neutron scattering. Image analysis allows for the study of porosity with radii above ～100 nm. For the first time in SHVOF 8YSZ, pore size distribution, total porosity and pore morphology were studied to determine the effects of heat treatment. X-ray diffraction and micro-hardness measurements were performed to study the phase transformation, and its effects on the mechanical properties. The results show an abundant presence of nano-pores in the as-sprayed coatings, which are eliminated after heat treatment at 1100 °C; a transition from inter-splat lamellar to globular pores and the appearance of micro-cracks along with the accumulation of micro-strains associated with the phase transformation at 1200 °C.     

Image processing and analysis for determination of concentrations of powder mixtures

The quality of the pharmaceutical powder mixing strongly influences the potency and properties of the tablets. Furthermore, in order to optimize powder mixing processes, fast and accurate methods are sought for determining the concentration of powder mixtures. This work describes an optical method based on an image processing system to determine concentration of powders in a mixture that can be sensed by its gray-level values.The methodology was developed utilizing univariate and multivariate gray image analysis. The effect of difference in mean gray value (DMGV) on the precision and accuracy of the vision system was determined. The results that were obtained from the vision system were compared to those obtained with near-infrared spectroscopy.The multivariate gray image analysis methodology using frequency of each gray-level value (Φ) of gray scale as the independent variables obtained the best predictions. The vision system produced high precision with a standard deviation of about 1.7% w/w and a 2.6% relative standard deviation. The accuracy indicated by the root mean standard error of prediction (RMSEP) was around 1.7% w/w. The mixtures analyzed with the vision system and the near-infrared spectrometer yielded similar results. Analysis of all results confirms that the vision system is an adequate technology for determination of powder mixture concentrations.     

Determination of the energy consumption during the production of various concrete recipes

This article presents a report of the mixing of concrete on the laboratory scale in a single-shaft and twin-shaft mixer. For both mixers we selected five concrete recipes that cover a broad spectrum of concrete mixing techniques. The concrete recipes differ from each other amongst other things by virtue of the aggregate-sized distribution curves, water-cement ratio, flow properties, compressive strength and mixing times. The specifically volume-related application of energy - which is necessary for the homogenization of the particular recipe in the mixer - is an essential influencing variable.The comparison of the specifically volume-related application of energy is possible only if the concrete recipes possess the same homogeneity. The time curve of the homogeneity plotted against the necessary mixing time indicates the mixing efficiency, which in turn is determined by an imaging measurement process. Comprehensive mixing experiments show that the resulting application of energy, measured via the current composition, does not provide sufficient information in order to define the actual homogeneity in the mixture. A method was developed for the purpose of comparing concrete mixtures based on various recipes with the same homogeneity in relation to the specifically volume-related application of energy. The particular application of energy can be determined via the required mixing time and the power output process in terms of time.     

A multiscale model for effective moduli of concrete incorporating ITZ water-cement ratio gradients, aggregate size distributions, and entrapped voids

This paper develops a model for the effective elastic properties of concrete, which is a function of the volume fractions, size distributions, and elastic properties of fine aggregate (FA) and coarse aggregate (FA) and entrapped voids. Furthermore, the model is a function of the overall water-cement ratio and specific gravity of cement. Explicitly modeled are the water-cement ratio gradients through the interfacial transition zone (ITZ), which, in turn, affect the variation of the cement paste elastic properties through the ITZ, while maintaining the total fractions of cement and water consistent with the overall water-cement ratio. The ITZ volume is also conserved.     

微混合技术--颗粒材料制备的关键之一

分散混合是化工生产过程中的一个重要单元,特别是在液相法制备固体颗粒材料方面.针对混合技术的最新发展--微混合技术进行讨论,描述了微通道和膜分散两种微混合方式的基本原理,结合已有工作对微混合技术在固体颗粒材料制备方面的优势进行了分析,并指出了微混合技术的研究方向及其发展前景.