Добірка наукової літератури з теми "Kneading compaction"

Based on influence of bridge structure caused by vibrating compaction and the properties of road roller, the combination of vibrating compaction and rubber-tyred kneading rolling can ensure the construction quality of cement concrete bridge deck asphalt mixture surfacing. It can guarantee the smoothness of asphalt mixture surfacing and avoid the shortage of compaction.

Although both mix variables and environmental variables are known to affect the fatigue response of asphalt-aggregate mixes, other factors—including specimen fabrication procedure and test equipment and procedures—are equally important. The development of a dynamic flexural beam fatigue test system is described, and the effects of specimen compaction method and equipment type on the precision of in situ fatigue lives of asphalt-aggregate mixes predicted by using laboratory strain-life relationships are discussed. Results indicate a coefficient of variation of 41 percent in fatigue life for the new fatigue equipment compared with one of 93 percent for an earlier electropneumatic version. The specimen compaction method was also found to influence significantly the precision of the predicted fatigue life. A 33 percent difference in coefficients of variation between the fatigue response of rolling wheel–compacted specimens and kneading-compacted specimens was observed. Consequently, twice as many specimens are required to achieve a given level of precision in in situ predicted fatigue life if kneading compaction is used instead of rolling wheel compaction. Similarly, if a pneumatic system and associated test procedure are used, approximately 12 times as many specimens are required to achieve similar precision in predicted fatigue life compared with the new servohydraulic fatigue test system.

Compaction is a critical step in asphalt pavement construction. The objective of this study is to analyze the mesoscale mechanical behaviors of coarse aggregates in asphalt mixtures during gyratory compaction through experiments and numerical simulation using the Discrete Element Method (DEM). A novel granular sensor (SmartRock) was embedded in an asphalt mixture specimen to collect compaction response data, including acceleration, stress, rotation angle and temperature. Moreover, the irregularly shaped coarse aggregates were regenerated in the DEM model, and numerical simulations were conducted to analyze the evolution of aggregate interaction characteristics. The findings are as follows: (1) the measured contact stress between particles changes periodically during gyratory compaction, and the amplitude of stress tends to be stable with the increase of compaction cycles; (2) the contact stress of particles is influenced by the shape of aggregates: flat-shaped particles are subjected to greater stress than angular, fractured or elongated particles; (3) the proportion of strong contacts among particles is high in the initial gyratory compaction stage, then decreases as the number of gyratory compactions grows, the contacts among particles tending to homogenize; (4) during initial gyratory compactions, the normal contact forces form a vertical distribution due to the aggregates’ gravity accumulation. The isotropic distribution of contact forces increases locally in the loading direction along the axis with a calibrated internal angle orientation (1.25°) in the earlier cyclic loading stage, then the local strong contacts decrease in the later stage, while the strength of the force chains in other directions increase. The anisotropy of aggregate contact force networks tends to weaken. In other words, kneading and shearing action during gyratory compaction have a positive impact on the homogenization and isotropy of asphalt mixture contact forces.

Numerous studies have been completed in recent years on the alteration of the hydraulic conductivity of clayey soils as a result of exposure to concentrated organic or inorganic permeants. These hydraulic conductivity changes have been attributed to either changes in microstructure, due to contraction of the diffuse double layer, or to the alteration of the macrostructure, as a result of volume changes leading to shrinkage fractures or fissures. In this paper, the change in hydraulic conductivity of a highly plastic natural clay during exposure to a concentrated sodium chloride (NaCl) solution is described. The performance of samples with three different initial soil structures, prepared by slurry, static compaction, and kneading compaction, were investigated under various levels of confining stress. Hydraulic conductivity tests were carried out before and after the samples were exposed to the NaCl solutions. Scanning electron microscope photography was used to compare the soil structures before and after brine permeation. The test results show that the alteration of hydraulic conductivity is strongly related to the initial soil structure and the level of confining stress. No significant change in the microfabric of the clay was observed; however, the size of the interaggregate pores appeared to increase as a result of the physicochemical volume change that occurred during brine permeation. The increase in hydraulic conductivity that occurred during brine permeation could be prevented by increasing the level of confining stress. The stress levels at which significant increases in hydraulic conductivity occurred appeared to be coincident with low levels of vertical stress which allowed the sample to undergo lateral shrinkage and a subsequent loss of confinement. Key words : hydraulic conductivity, clay soils, osmotic consolidation, sodium chloride brine, soil structure, scanning electron microscope.

This study investigates the effect of loading rate on Asphalt Concrete (AC) in the laboratory using Three-Point Bending test. As a first step, beam samples were prepared using kneading compactor and final shape of the sample was obtained by laboratory saw. The samples were then subjected to bending loading at different deformation rates at room temperature of 20 °C. The initial stiffness, failure stress (tensile strength) and failure strain were monitored. Results show that the stiffness and the failure stress-strain increase with the increase in loading rate. The findings of the study are expected to be useful to understand the performance of AC due to slow loading such as slow cooling.

This study focuses on the analysis of structural elements of the Marfa kurgan in the Stavropol Territory. We list and examine terms referring to such elements, and suggest our own. A description of the kurgan, its natural environment, excavation techniques, sampling, and analytical methods is provided. The material of which the kurgan was made is assessed, and its advantages over other materials are demonstrated. We studied mud blocks (or “bricks”), their clay coatings, and a striped adobe element from the kurgan. Results of chemical and granulometric analyses are outlined, along with those of the micromorphological analysis of soils underlying the kurgan, of the material of which the “bricks” and the coatings were made. The blocks were molded by thoroughly kneading and compacting a moistened material consisting of loess with the addition of river silt, without plant admixture. Clay coatings were much denser, as it consisted of a coherent finely dispersed clay-carbonate material. Clay mortar, similar to coatings in composition and properties, was used to connect the blocks and the stones of the crepidoma. The same mortar was used for foundations of clay “bricks” buildings. The adobe element with thinnest variously colored stripes resulted from a destruction of an earlier structure.

The microstructure of low plastic highly dispersive sandy silty clay (CL) deposit obtained from the terraces of the River Nile in Northern Sudan was studied using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) in relation to its dispersive characteristics. The study showed that the silt size of the CL is mostly aggregates of clay particlescemented by organic matter and iron oxide bonds. Kneading experiments have shown that these aggregates are unstable and could be broken by kneading and compaction. Pinhole tests on specimens prepared at wide ranges of density and water content and kept for different curing times (hours to one year) have shown that neither water content, density andcuring times have pronounced effect on the dispersivity and erosion characteristics of the tested soil.

Compaction is one of the most critical steps in asphalt pavement construction. Traditional compaction relies heavily on engineering experience and post-construction quality control and can lead to under/over compaction problems. The emerging intelligent compaction technology has improved compaction quality but is still not successful in obtaining mixture properties of a single pavement layer. Besides, very few studies have discussed the internal material responses during field and laboratory compaction to explain the meso-scale (i.e., particle scale) compaction mechanism. Knowledge in those areas may greatly promote the development of smart compaction. Therefore, this study aims to investigate the kinematic behavior of the asphalt mixture particles (translation and rotation) under six types of field and laboratory compaction methods and establish the relationship between the field and the laboratory compaction by using a real-time particle motion sensor, SmartRock. It was found that particle movement pattern was mainly affected by the compaction mode. At the meso-scale where particle behavior is the focus, the kneading effects of a pneumatic-tire roller can be simulated by laboratory gyratory and rolling wheel compaction, and the vibrating effects of a vibratory roller can be simulated by Marshall compaction. However, none of those laboratory compaction methods can completely simulate the field compaction. Under vibratory rolling, particle acceleration decreased fast in the breakdown rolling stage. Under pneumatic-tire rolling, particle angular position change was related to aggregate skeleton, and particle relative rotation showed a decreasing trend that was consistent with the laboratory gyratory compaction results. Those kinematic responses can potentially be used to monitor density change in field compaction.

L'étude du comportement des sols traités à la chaux est axée sur l'analyse de l'influence des conditions de mise en œuvre en laboratoire et in situ avec une attention particulière sur l'évolution de la microstructure. Les échantillons de sol prélevés dans un remblai constitué d’un sol traité à la chaux, soumis à l'exposition atmosphérique pendant 7 ans, montrent une évolution significative des performances du matériau, notamment sa résistance à la compression. Ces résultats mettent en évidence l'influence du traitement à la chaux sur le long terme. Le remblai étudié a été mis en oeuvre par "compactage par pétrissage", dont le mécanisme est moins étudié dans la littérature. Le pétrissage semble améliorer la dispersion de la chaux dans le sol,ainsi que sa structuration. Cette propriété est favorable à l'hydratation de composés cimentaires, particulièrement, en cas de présence d'eau disponible. L'effet du fluide interstitiel sur la performance hydraulique des sols traités à la chaux, et le mécanisme de lixiviation associé sont étudiés en fonction du volume des pores traversés par le fluide. Le nombre de volume de pore traversé s’avère être un paramètre clé pour l’étude de la durabilité des performances des sols traités. L'eau déminéralisée s'avère être plus agressive qu'une solution à faible force ionique. Cela démontre l'importance de prendre en compte le type de solution perméante. La performance à long terme du sol traité à la chaux soumis au cycle d’humidification séchage, sous différentes conditions d'essai et différents fluides, est évaluée. L'étude a révélé la contribution de la nature du fluide d'imbibition et des effets de la température sur l'évolution des propriétés physico-chimiques et microstructurales du sol traité à la chaux. Ainsi, la condition de compactage mise en œuvre, la nature du fluide d'essai et les conditions d'essai à l'échelle du laboratoire doivent se rapprocher de la situation sur le terrain
Investigation of the behavior of limetreated soil with emphasis on laboratory and field implementation technics and microstructural observations is made. Field investigation of a 7-year atmospherically cured embankment, thanks to measurement of sampled materials performances, shows a significant evolution in compressive strength, evidencing the long term benefits of lime treatment. This embankment was subjected to ‘kneading compaction’, which mechanism is less investigated. At laboratory scale, ‘kneading compaction’ is found to improve lime-dispersion and soil fabric. Such features, if accompanied by available water, favors the development of cementitious compounds. The effect of pore fluid on the hydraulic conductivity, k evolution, and leaching mechanism of kneaded lime-treated soil is studied. Using demineralized water as pore fluid is found to be comparatively aggressive than a low-ionic strength solution. Thus, demonstrating the importance of consideration of the type of permeant solution. Long-term performance of lime-treated soil by subjecting them to wetting-drying cycle using different testing conditions and different wetting fluids is evaluated. The evaluation revealed the importance of consideration of the nature of wetting fluid and temperature effects on the physicochemical and microstructure evolution of lime-treated soil. Thus, the reproduced compaction procedure, nature of the permeant solution, and testing conditions in the laboratory scale must be closer to the field situation

Asphalt mixture compaction is an important procedure of asphalt mixture construction and can significantly affect the performance of asphalt pavement. Many laboratory compaction methods (or devices), have been developed to study the asphalt mixture compaction. Nevertheless, the whole process from the selection of aggregate to laboratory compaction is still time-consuming and requires significant human and material resources. In order to better understand asphalt mixture compaction, some researchers began to use finite element method (FEM) to study and analyze mixture compaction. However, FEM is a continuum approach and lacks the ability to take into account the slippage and interlocking of aggregates during compaction. Discrete Element Method (DEM) is a discontinuum analysis method, which can simulate the deformation process of joint systems or discrete particle assembly under quasi-static and dynamic condition. Therefore, it can overcome the shortcomings of FEM and is a more effective tool than FEM to simulate asphalt mixture compaction. In this study, an open source 3D DEM code implemented with the C++ programming language was modified and applied to simulate the compaction of hot-mix asphalt (HMA). A viscoelastic contact model was developed in the DEM code and was verified through comparison with well established analytical solutions. The input parameters of the newly developed contact model were obtained through nonlinear regression analysis of dynamic modulus test results. Two commonly used compaction methods (Superpave gyratory compaction and asphalt vibratory compaction) and one linear kneading compaction based on APA machine were simulated using the DEM code, and the DEM compaction models were verified through the comparison between the DEM predicted results and the laboratory measured test results. The air voids distribution within the asphalt specimens was also analyzed by post processing virtual DEM compaction digital specimens and the level of heterogeneity of the air void distribution within the specimens in the vertical and lateral directions was studied. The DEM simulation results in this study were in a relatively good agreement with the experimental data and previous research results, which demonstrates that the DEM is a feasible method to simulate asphalt mixture compaction under different loading conditions and, with further research, it could be a potentially helpful tool for asphalt mix design by reducing the number of physical compactions in the laboratory.

Comparisons of the dynamic properties of intact and remolded offshore clay specimens has been carried out. The clay specimens were obtained from Campeche Bay, offshore Mexico. Combined resonant column and torsional shear (RCTS) equipment at the University of Texas at Austin was used to determine the dynamic soil properties. Each soil specimen was tested twice, first in the intact condition and second as remolded material. Remolding was done by kneading the intact material and then reforming the specimen by compacting in a mold. The effects on the dynamic properties, expressed by shear modulus and material damping ratio, between intact and remolded conditions are discussed. As expected, shear modulus and material damping at small and large strains are affected by remolding. Interestingly, the normalized modulus degradation curves were changed very little by remolding up to strains between 0.06 and 0.1%. The results offer insight into the effects of sampling disturbance on linear and nonlinear dynamic soil properties.