Microstructure Of Mixtures Research Articles

Analysis of cohesive and adhesive damage initiations of asphalt pavement using a microstructure-based finite element model

Cohesive and adhesive damages play essential roles in the asphalt pavements cracking behaviors; however, due to the microstructural complexity and heterogeneity of asphalt mixtures, it is difficult to effectively characterize these two damage initiations under the realistic service conditions. To address this issue, the presented study developed a multiscale finite element model to quantitatively investigate the distributions of cohesive and adhesive damages as well as their effects on the overall damage performance of asphalt pavement. The microstructure of the asphalt mixture and macrostructure of the asphalt pavement were simultaneously involved into a single finite element (FE) model, and the bilinear cohesive elements were inserted into the fine aggregate matrix (FAM) and the FAM-aggregates interfaces to respectively model the cohesive and adhesive damage initiations. The results showed that the great heterogeneity of the asphalt mixtures caused remarkable stress concentrations, which might be one of the main factors that contribute to the pavement cracking behaviors. In addition, it is illustrated that lower adhesive strengths tended to cause more damage initiations at the pavement surface, which suggested that the adhesive damage could be one of the major factors contributing to the “top-down” cracking initiations.

Texture Properties of a-2D Granular Mixture of an Angular Particle under Bi-axial Compression

Utilizing Discrete Element Modeling (DEM), we investigate the shear strength properties and microstructure of 2D granular mixture composed of various regular polygonal particles (from triangle to icosagon and disk) under biaxial compression. Three cases were considered: 1) increase of proportion and angularity started from disk (S1); 2) increase of proportion by decreasing the angularity started from triangle (S2); 3) increase of proportion by random angularity started from disk (S3) and polygons (S4). The results show that the shear strength changes with the mean angularity. On the other hand, the packing fraction slightly varies with the mean angularity. At the microscopic scale, the granular texture in term of the force, the contacts transmitted the force higher than the average force (strong force) are oriented in the direction of externally applied loading but they represent only 40% of the total number of contacts. Besides, the tangential contact forces direction tend to be consistent with the maximum shear strength direction.

Effects of Biochar on the Compression and Swelling Characteristics of Clayey Soils

In recent years, biochar has been widely used in environmental and geotechnical engineering applications, but minimal studies have been done on its influence on soil engineering properties. In this study, the effect of biochar on the compression and swelling characteristics of two clayey soils, namely PKE and XS, was studied by conducting standard consolidation tests and no-load swelling tests. The compression curves and swelling parameters of modified clays with different biochar content (0, 0.5, 1, 2%, w/w) and biochar particle sizes (< 0.15, 1–2 mm) were obtained. The microstructure of the biochar-clay mixture was analyzed by scanning electron microscopy (SEM) test. The results showed that: (1) the compressibility of clayey soils can be effectively reduced by adding biochar, and this effect is more significant with the increase biochar percentage; (2) the effect of reducing soil compressibility by fine biochar was better than coarse biochar; (3) under the same pressure, the settlement rate of soil increased with the increase of biochar content; (4) the incorporation of biochar had no obvious influence on the no-load swelling behaviour of PKE while it has significantly increased the swelling of XS (low expansive soil). Additionally, the fine-grained biochar has a significant effect than the coarse-grained biochar on clayey soils.

Study on microstructure influence mechanism to mechanical behavior of OGFC asphalt mixture

Microstructure characteristics of OGFC (open graded friction course) asphalt mixture are closely related to the mechanical behavior. To study the microstructure influence mechanism to mechanical behavior of OGFC asphalt mixture, the digital image processing technology is used to process the specimen’s fault images and obtain the microstructure parameters of the OGFC asphalt mixture with different gradation. At the same time, the microstructure influence on mechanical behavior of OGFC asphalt mixture is explored by using the Grey correlation theory based on the experimental results of mechanical performance and the microstructure parameters. The influence of four key sieve passing percentage (1.18, 2.36, 4.75, and 9.5 mm) on the microstructure was discussed by using the Grey correlation theory, and the influence mechanism to mechanical behavior of OGFC asphalt mixture was further revealed. The results show that with the increase of air void content, the total void area, the equivalent pore diameter, and the number of big voids (here, “big” means voids with an area greater than 10 mm2) increase, the length of void and corresponding void area increase synchronously, the drainage performance is enhanced, and the mechanical performance is decreased. With the increase of nominal maximum particle size, the average area of single void, the percentage of number of big voids, and the equivalent diameter increase, and the drainage performance, anti-skidding performance, and mechanical performance of pavement are enhanced. It is considered that the key sieve passing percentage affects the mechanical behavior by influencing the microstructure of asphalt mixtures. The influence degree of microstructure parameters on mechanical behavior and the influence degree of the key sieve passing percentage on microstructure parameters were obtained. The research results have a certain reference value for the optimization of mechanical behavior of OGFC asphalt mixture.

Influence of Martensite and Bainite Microstructure on Local Mechanical Properties of a Bainitic and Martensitic Multiphase Cast Steel

Here we utilized two cooling methods, forced air cooling and furnace cooling, to obtain two different triplex microstructures which were martensite-based and bainite-based, respectively. Compared with furnace cooled samples, the forced air cooled samples presented about 5% higher ultimate tensile strength, 10% higher hardness and 43% lower Charpy impact energy value. Nano-indentation test was conducted to reveal the local mechanical properties. The nano-hardness of martensite, bainite and the mixture microstructure is 5.633 GPa, 4.200 GPa and 5.082 GPa, respectively. Mn, S, C and Si segregation at the grain boundaries in martensite are severely detrimental to the toughness. High rotation angle grain boundaries and precipitates of rare earth element enhanced the toughness of bainite. Martensite with high density dislocations in fine laths exhibited higher nano-hardness than bainite with lower density dislocations in wider sized laths. The interaction of the two phases with martensite twinning sub structure between bainite laths showed intermediate nano-hardness. Differentiated multiphase microstructure dominated by martensite and bainite in a bainitic and martensitic multiphase wear-resistant cast steel were investigated. The variety of tensile strength, nano-hardness, grain boundary rotation angle and element precipitates were discussed. Martensite with high density dislocations in fine laths exhibited higher nano-hardness than bainite with lower density dislocations in wider sized laths. The interaction of the two phases with martensite twinning sub structure between bainite laths showed intermediate nano-hardness

Evaluation of the mechanical performance and durability of binary blended CAC-MK/natural fibe composites

The aim of this work was to develop strain hardening cementitious composites (SHCC) and durable composites based on calcium-aluminate cement (CAC) with variable metakaolin (MK) content (from 0 to 50 wt%) and flax nonwoven natural textile reinforcement. For this purpose, three experimental packages were performed in order to: a) evaluate the effect of MK content on the mechanical performance and cement mixture microstructure of the matrix, b) analyze the effect of the cement mixture on the performance of the natural fibers, and c) determine the bending behavior and durability of the composites. It was found that the strength and modulus of the 28 days cured cement paste under compression and bending modes decreased with MK content. Low degradation of the natural fibers on the CAC-MK matrix was found and this degradation was lower for higher MK content. The developed composites presented a ductile behavior and high tensile strength and maintained this performance after subjecting them to a 250 cycles of accelerated aging.

Effect of aggregate type on moisture susceptibility of modified cold recycled mix asphalt: evaluation by mechanical tests and Surface Free Energy method

There are deficiencies associated with cold mix asphalts, specifically, cold recycled mix asphalts in comparison with hot mix asphalt or hot recycled mix asphalt such as higher moisture susceptibility. Moisture damage of asphalt mixtures is inversely related to the bond quality between aggregates and binder. In this study, Portland cement (PC) and acryl polymer (AP) additives were employed to improve this bond. The effectiveness of used additives in improving the moisture susceptibility of cold recycled mix asphalt was examined using Surface Free Energy (SFE) method. Indirect Tensile Strength test and Dynamic Modulus test were performed to validate SFE method results. Moreover, scanning electron microscope (SEM) images were obtained for better understanding of mixture's microstructure. Also, effect of using granite, limestone and recycled asphalt pavement (RAP) aggregates was evaluated. The findings showed that cement and acryl polymer additives improved resistance of different studied mixtures, specifically, cold recycled mix asphalt against moisture damage by improving the adhesion between aggregate and asphalt. Considering effect of aggregates on moisture susceptibility, limestone-mixtures had the highest resistance while the RAP-mixtures performed the worst among the three. Finally, it was shown that results of SFE method were compatible with the mechanical tests in predicting moisture damage.

Effect of temperature field on damage initiation in asphalt pavement: A microstructure-based multiscale finite element method

The present study developed a microstructure-based multiscale finite element (FE) method to investigate the effect of temperature fields on the damage initiation within the asphalt pavement under traffic loading. Three heat transfer mechanisms that dominate the temperature distribution in the pavement structure, i.e., thermal radiation, convection, and conduction, were considered in the multiscale modeling. Both mechanical and thermal properties of asphalt concrete (AC) on two physical length scales, namely, global (pavement level) and the local (mixture level) scales, were included in the computation and connected via a homogenization process. A digital image processing (DIP) technology was adopted to establish the local-scale representative volume element (RVE) model that interpreted the realistic heterogeneity of the AC microstructure, and a bilinear cohesive zone model was employed to model the damage initiation in the RVEs. The results showed that the developed multiscale FE model provided an insight into the damage behavior of asphalt pavement subjected to temperature fields varying with time on both the global and local scales, indicating the importance of considering temperature fields in pavement structural analysis. By means of the presented method, the influence of temperature fields, pavement structures, mixture microstructures and component properties, and interface behavior between mortar matrix phase and coarse aggregates on the pavement damage initiation could be rationally taken into account in the analysis. In light of these benefits, the presented approach can be expected to be utilized as a mechanistic tool for improving the performance prediction and evaluation as well as mixture and structural design of asphalt pavements.

Assessment of post-heat behavior of cement mortar incorporating silica fume and granulated blast-furnace slag

Purpose With respect to the studies conducted so far and lack of researches on the post-heat behavior of cement mortars containing pozzolanic materials, the purpose of this paper is to investigate the post-heat mechanical characteristics (i.e. compressive, tensile and flexural strength) of cement mortars containing granulated blast-furnace slag (GBFS) and silica fume (SF). In doing so, selected temperatures include 25, 100, 250, 500, 700 and 9000c. Last, the X-ray diffraction test was conducted to study the microstructure of mixtures and subsequently, the results were presented as power-one mathematical relations. Design/methodology/approach Totally, 378 specimens were built to conduct flexural, compressive and tensile strength tests. Accordingly, these specimens include cubic and prismatic specimens with dimensions of 5 × 5 × 5 cm and 16 × 4 × 4 cm, respectively, to conduct compressive and flexural strength tests together with briquette specimen used for tensile strength test in which cement was replaced by 7, 14 and 21 per cent of SF and GBFS. To study the effect of temperature, the specimens were heated. In this respect, they were heated with a rate of 5°C/min and exposed to temperatures of 25 (ordinary temperature), 100, 250, 500, 700 and 900°C. Findings On the basis of the results, the most profound effect of using GBFS and SF, respectively, takes place in low (up to 250°C) and high (500°C and greater degrees) temperatures. Quantitatively, the compressive, tensile and flexural strengths were enhanced by 73 and 180 per cent, 45 and 100 per cent, 106 and 112 per cent, respectively, in low and high temperatures. In addition, as the temperature elevates, the particles of specimens containing SF and GBFS shrink less in size compared to the reference specimen. Originality/value The specimens were cured according to ASTMC192 after 28 days placement in the water basin. First, in compliance with what has been specified by the mix design, the mortar, including pozzolanic materials and superplasticizer, was prepared and then, the sampling procedure was conducted on cubic specimens with dimension of 5 × 5 × 5 mm for compressive strength test, prismatic specimens with dimensions of 16 × 4 × 4 mm for flexural strength test and last, briquette specimens were provided to conduct tensile strength tests (for each temperature and every test, three specimens were built).

Microstructure and its effect on mechanical and thermal properties of Al-based Gd2O3 MMCs used as shielding materials in spent fuel storage

In this study, novel Al-based Gd2O3 metal matrix composites were designed and synthesized using powder metallurgy to overcome the shortcomings of common neutron absorbers used as shielding materials in spent fuel storage. With an increase in the ball-milling time, the size of powder particles was gradually refined to nanometer scale. Meanwhile, monoclinic Gd2O3 was induced by collision pressure and, according to dynamic analysis, the solid solution was inconspicuous. Al3Gd and Gd3Al5O12 were formed during ball-milling, which was further accelerated during sintering because thermodynamics analysis indicated that the reaction was endothermic. The microstructures of powder mixtures and sintered bulks were seen. Particles of various shapes were found to be dispersed in the bulk matrix; their shapes and sizes varied with milling time, sintering time and temperature, and concentration of Gd2O3. With the increase in sintering temperature and time, the number of porosities and nanoparticles were found to decrease, whereas the sizes of the particles increased. The microhardness of the samples prepared under various conditions was measured, and its relationship with the microstructure was analyzed. It was found that microhardness was positively correlated with the areas of the particles, whereas it was negatively correlated with their sizes. Further, the thermal parameters of the sintered bulks were also measured and the effect of their microstructure and components was analyzed.

Design of Multifunctional Titania-Based Photocatalysts by Controlled Redox Reactions.

This work aims at the preparation of multifunctional titania-based photocatalysts with inherent capabilities for thermal co-activation and stabilisation of anatase polymorph, by designing the phase composition and microstructure of rutile-silicon carbide mixture. The processing involved a conventional solid state route, including partial pre-reduction of rutile by SiC in inert Ar atmosphere, followed by post-oxidation in air. The impacts of processing conditions on the phase composition and photocatalytic activity were evaluated using Taguchi planning. The XRD studies confirmed the presence of rutile/anatase mixtures in the post-oxidised samples. The results emphasise that pre-reduction and post-oxidation temperatures are critical in defining the phase composition, while post-oxidation time is relevant for the photocatalytic performance. Microstructural studies revealed the formation of core-shell particles, which can suppress the photocatalytic activity. The highest apparent reaction rate of the photodegradation of methylene blue was observed for the sample pre-reduced in Ar at 1300 °C for 5 h and then calcined in air at 400 °C for 25 h. Though its performance was ~1.6-times lower than that for the same amount of nanostructured industrial P25 photocatalyst, it was achieved in the material possessing 2–3 times lower surface area and containing ~50 mol% of SiO2 and SiC, thus demonstrating excellent prospects for further improvements.

Characterization of fatigue damage mechanism of asphalt mixtures with acoustic emission

Understanding the fatigue damage mechanism of asphalt mixtures is essential to prolong the service life of asphalt pavements. Acoustic emission (AE) technique can effectively detect minor damage and evaluate material mechanical properties. The objective of this paper was to investigate the temporal-spatial variation of AE parameters associated with fatigue damage behavior of asphalt mixtures and characterize the irreversibility of damage evolution utilizing the Kaiser effect. Firstly, the semi-circular bending (SCB) tests with different rest time and AE tests were carried out simultaneously to discuss the AE characteristics of fatigue damage behavior of asphalt mixtures. Secondly, the spatial evolution of AE events was analyzed to correlate with the crack propagation path of asphalt mixtures. Finally, the Felicity ratio (RF) and wavelet scalogram were utilized to reveal the irreversible characteristics of the AE process of asphalt mixtures. The results show that the “blank area” in AE energy temporal, representing the intensity of AE activities in asphalt mixtures during the process of microcracks concentration, gradually disappears with the increase of rest time. The inflection point of the decline of AE amplitude b-value could be considered as a precursor to the rupture of asphalt mixtures. The spatial distribution of AE events from disorder to order reflects the influence of the microstructures of asphalt mixtures and loading mode on crack propagation. The change of RF could be divided into the three stages, corresponding to the deformation and compaction stage where 1 ≤ RF, microcracks initiation and concentration stage where 0.4 ≤ RF < 1, and macrocracks extension stage where RF < 0.4. The Kaiser effect mainly exists at the stage of deformation and compaction of asphalt mixtures. After the occurrence of macrocracks, the AE process would lose irreversible characteristics. The damage mechanisms related to the Kaiser effect and the Felicity effect could be identified by the energy distribution of AE waveforms.

Prediction of the coefficient of permeability of asphalt mixtures using the lattice Boltzmann method

The Lattice Boltzmann method (LBM) is widely accepted to simulate fluid flow in porous materials. The objective of this study is to predict the coefficient of permeability of asphalt mixtures using the LBM. The numerical method was verified by simulating fluid flow in Poiseuille flow, parallel tubes, and sandstone samples. The three-dimensional microstructures of asphalt mixtures were reconstructed with X-ray computed tomography techniques and used as inputs for LBM simulations. The factors that affect the stability and accuracy of the simulations were also discussed. These factors include time steps, applied pressure gradient, and image resolution. The results of LBM simulations were compared with the experimental results. It was revealed that the LBM simulations successfully predicted the coefficient of permeability of asphalt mixtures.

Phase behavior, thermodynamic and microstructure of concentrated pea protein isolate-pectin mixture: Effect of pH, biopolymer ratio and pectin charge density

The impact of pH, pea protein isolate (PPI)–pectin mixing ratio and pectin charge density on phase behavior (co-solubility, soluble complex and complex coacervates) of concentrated biopolymer mixture was investigated using state diagram and ζ–potential measurement. The microstructure, thermodynamic behavior, and non-covalent bonding of PPI to pectin were further explored by confocal laser scanning microscopy (CLSM), isothermal titration calorimetry (ITC), and Fourier transform infrared spectroscopy (FTIR). In general, the pH of soluble complex, complex coacervate formation shifted towards higher pH as PPI–pectin mixing ratio increased. Low methoxyl pectin (LMP) is favorable for complex coacervate over a wider pH range compared with high methoxyl pectin (HMP) due to its higher overall charge density. The CLSM images revealed that larger aggregates were formed in PPI-LMP coacervates. Both ITC and FTIR analyses indicated that soluble complex and complex coacervates were formed through the electrostatic interaction and hydrogen bonding between PPI and pectin.

Evaluation of optimum mixing conditions for rubberized asphalt mixture containing reclaimed asphalt pavement

The use of reclaimed asphalt pavement (RAP) represents an environmentally positive method of recycling besides saving cost. Experience has shown that properly designed hot-mix asphalt (HMA) containing RAP performs as well as HMA produced with virgin materials. Crumb rubber asphalt represents, on the other hand, a promising paving material that recycles waste tires. The combination of the two techniques has promising environmental significance, i.e. recycling asphalt concrete pavement using rubberized asphalt, which remains a virgin research topic. In this paper, microstructure of rubberized asphalt mixture containing RAP was studied to obtain its optimum mixing conditions. Specimens were prepared in the laboratory and scanned by X-ray Computed Tomography (CT) system to identify distribution of the components. An improved Otsu’s algorithm was used to segment the mixture images. The results indicate that the algorithm could effectively solve the uneven brightness problem of scanned images. Statistical indicators were used to analyze uniformity of component distribution. Three mixing time and three mixing temperatures were used in the blending process to evaluate effects of mixing time and mixing temperature on the distribution of mixture component. It was found that distribution of air voids and virgin aggregates are relatively more sensitive to mixing time and mixing temperature. Optimum mixing time is 150 s and it should not be less than 90 s to achieve well distribution of components. Optimum mixing temperature is at least 150 °C.

Phase diagrams of mixtures of n-hentriacontane and saturated monoacid triacylglycerols

Gelation of vegetable oils with candelilla wax (CW) and saturated triacylglycerols (TAGs) is a promising strategy for engineering fat-based foods, cosmetics, and drug delivery systems. n-hentriacontane (C31) defines, to a large extent, the thermal properties of CW. Therefore, the phase behavior and microstructure of binary mixtures of C31 and trimyristin (MMM), tripalmitin (PPP), or tristearin (SSS) were studied to provide a better understanding of complex mixtures of CW and saturated fats. Phase diagrams were developed by differential scanning calorimetry and X-ray diffraction measurements. The mixtures showed a eutectic phase behavior, in which the C31-TAG mixtures below the solidus line were solid dispersions of crystals rich in C31 and crystals rich in the corresponding TAG. This segregation in the solid phase was attributed to the incompatible subcell-packing of the pure components in the stable polymorphic form, which was orthorhombic for C31, and monoclinic for TAGs in the β-polymorphic form. C31 had a major effect on TAGs microstructure. Morphological changes at the microstructural level were caused by the heterogeneous nucleation of MMM on C31 crystals. Conversely, microstructural changes for TAGs crystals in C31-PPP and C31-SSS mixtures were induced by the inhibition of crystal growth due to the transient adsorption of C31 molecules at the growing crystal surface.

Molecular insights into the impacts of iron(III) ions on membrane fouling by alginate.

Molecular mechanisms responsible for the filtration behaviors of sodium alginate (SA) in presence of different iron(III) ion concentration were explored in this study. It was found that specific filtration resistance (SFR) of alginate mixtures (1.0 gSA/L) firstly increased and then decreased to a trough with iron(III) concentration increase from 0 to 2.5 mM. Alginate mixture interacting with 0.1 mM iron(III) possessed an SFR as high as 1.65 × 1014 m kg-1, which could be explained by Flory-Huggins lattice theory related with gel filtration. Optical observation showed significant morphology transition (from gel to granular solids) of foulant layers with iron(III) concentration increase. A series of characterizations indicated the change of microstructure, pH and surface charge of alginate mixture with iron(III) concentration. Density functional theory (DFT) simulation suggested that iron(III) ion preferentially forms coordination bonds with three terminal carboxyl groups of alginate chains, facilitating elongation and cross-linking of alginate chains. Such a coordination mode induces formation of a slime and homogeneous gel, corresponding to high SFR. Continuous increase in iron(III) concentration leads to non-terminal coordination, which makes alginate chains more clustered and coiled. This effect, together with effects of the reduced surface charge and electric double layer compression, significantly decrease SFR of alginate mixtures. This study provided deep molecular insights into effects of iron(III) ions on alginate fouling.

Finite Element Modeling of Asphalt Mixture Based on Image Recognition

This study describes a method for establishing a mechanical model of heterogeneous finite element method. With the combination of digital image recognition technology and the theory of automatic mesh generation, it is possible to establish an inhomogeneous finite element model for mechanical calculation. Firstly, the micro-structure of the two-dimensional mixture is identified. Then all the boundary points are imported into ANSYS. Finally, the finite element mesh model of the micro-structure of the asphalt mixture is obtained by using the automatic finite element mesh generation technology. Taking Marshall specimen as an example, meshing the model proves that the method is feasible.

The corrosion rate and microstructure of Portland cement and calcium aluminate cement-based concrete mixtures in outfall sewers: A comparative study

This paper presents a comparative study on the corrosion rate and microstructural characteristics of Portland cement (PC) and calcium aluminate cement (CAC) -based concrete mixtures subjected to microbially-induced sulphuric acid (biogenic H2SO4) attack for 120 months in an outfall sewer. The higher amount of the amorphous AHx within the CAC-based concrete matrix provides a higher neutralisation capacity to the attacking acid, thus giving it better performance than PC-based concrete mixtures during biogenic H2SO4 attack. In addition the results show that the biogenic corrosion rate of PC-based concrete mixtures increases with the cement content while that of CAC-based concrete mixtures decreases with the cement content.

Acoustic and Microstructural Properties of Partially Molten Samples in the Ice–Ammonia System

We measured the ultrasonic properties and microstructure of two-phase binary mixtures of the ice–ammonia partial melt system, which was selected based on its importance for numerous planetary bodies. The equilibrium microstructure of ice–ammonia melt was examined using a light microscope within a cold room. The measured median dihedral angle between the solid and melt at 256 K is approximately 63°, with a broad distribution of observed angles between 10° and 130°. P-wave velocities in the partially molten samples were measured as a function of temperature (177 &lt; T(K) &lt; 268) and composition (1–6.4 wt % NH3). Vp decreases approximately linearly with increasing temperature and melt fraction. We compare the results of this study to those of other potential binary systems by normalizing the datasets using a vertical lever (TL–TE) and articulating the potential effects on the mechanical behavior and transport capabilities of partially molten ice in icy satellites.