Laura Maria Goretti da Motta

Computed tomography in the fatigue test analysis of an asphaltic mixture

Abstract This work applies the computerized tomography technique to the study of an asphaltic mixture. It was required to detect and follow the evolution of a crack, when this mixture was submitted to fatigue tests. The fatigue tests to produce stresses were done in a diametral compression equipment of repeated loading. The trajectory of a crack is influenced by original voids in the specimen; it may be noted that troughs exist in all tomographic images at the same positions and, as these could be due to voids, with a sufficient sequence of applied loads they would be transformed into a small crack that would increase in size, causing the collapse of the specimen. It was possible to detect and follow the evolution of a crack as the 900 blows were applied to the phantom. It was also noted that the crack begins to appear in the central region of the specimen and is propagated in the direction of the applied load.

Applicability of Municipal Solid Waste Incineration Ash on Base Layers of Pavements

AbstractThis study presents the characteristics of municipal solid waste (MSW) incineration ash obtained from an electric energy generation plant and evaluates the MSW ash applicability in base road pavement layers through the mixture of ash with a nonlateritic regional clay soil. Chemical, physical, and mechanical tests and the mechanistic-empirical design for a typical pavement structure were carried out on the pure soil and also in the soil mixture with the addition of different ash content (20 and 40%). Fly ash reduced the expansion of the material, showing an increase in the California bearing ratio (CBR) and resilient modulus value. The results are satisfactory, depending on the content and type of ash used, highlighting the positive work of MSW fly ash for its use in base road pavement layers.

Research on fatigue cracking growth parameters in asphaltic mixtures using computed tomography

Abstract Distress of asphalt concrete pavement due to repeated bending from traffic loads has been a well-recognized problem in Brazil. If it is assumed that fatigue cracking growth is governed by the conditions at the crack tip, and that the crack tip conditions can be characterized by the stress intensity factor, then fatigue cracking growth as a function of stress intensity range ΔK can be determined. Computed tomography technique is used to detect crack evolution in asphaltic mixtures which were submitted to fatigue tests. Fatigue tests under conditions of controlled stress were carried out using diametral compression equipment and repeat loading. The aim of this work is imaging several specimens at different stages of the fatigue tests. In preliminary studies it was noted that the trajectory of a crack was influenced by the existence of voids in the originally unloaded specimens. Cracks would first be observed in the central region of a specimen, propagating in the direction of the extremities. Analyzing the graphics, that represent the fatigue cracking growth (dc/dN) as a function of stress intensity factor (ΔK), it is noticed that the curve has practically shown the same behavior for all specimens at the same level of the static tension rupture stress. The experimental values obtained for the constants A and n (of the Paris–Erdogan Law) present good agreement with the results obtained by Liang and Zhou.

Computed tomography: an evaluation of the effect of adding polymer SBS to asphaltic mixtures used in paving

This work applies the Computed Tomography (CT) technique to the study of asphaltic mixtures to which polymer has been added. An evaluation has been made of the effect of adding Brazilian produced polymer SBS (styrene-butadiene-styrene), to the asphaltic mixtures used in paving. Laboratory mechanical tests and non-destructive testing (NDT) of cylindrical specimens have been made. Three mixtures were prepared for the purpose of this study, all containing 5.4% of asphalt RASF (propane deashalting). One of the mixtures contained no polymer, while the other two were made with 7 and 5% of the SBS polymer. Investigations of Brazilian pavements have shown that cracking is the most important defect due to fatigue in the asphaltic contained overlay. Preliminary results of mechanical tests show that the polymer additive favorably enhances performance of the mixtures. It may be noted that adding polymer SBS to the asphaltic mixture used in paving increases the percentage void. Crack growth in specimens of asphaltic mixtures to which polymer has been added displays the same behaviors as that in specimens in which polymer has not been added.

Analysis of asphaltic binders modified with PPA by surface techniques.

Samples of unmodified and modified asphalt binders containing 1% polyphosphoric acid were studied. Fourier‐transform infrared spectroscopy was used to evaluate the structural indices of the functional groups present in the samples and the results indicated there was a strong interaction between the polyphosphoric acid and oxygenated species. Contact angle measurements indicated that adhesion of the binder to the aggregate depended on the polyphosphoric acid content. Atomic force microscopy was used to relate features observed on the surface of the asphalt binder 50/70, with their local mechanical properties such as stiffness and elasticity. It was observed that the surface of the sample containing 1% polyphosphoric acid provides stiffness values lower than the unmodified asphalt binder.

Dual-energy computerized tomography in compacted soil

This paper describes an alternative nondestructive technique for bulk density and water content determination in soils using dual-energy computerized tomography. A first generation tomographic system (STAC-1) was used in the analysis of the specimens. The system used 137Cs (∼662 keV), 192Ir (∼316 keV) and 241Am (∼60 keV) as radiation sources and a Sodium Iodine crystal (NaI(Tl)) with photomultiplier tube as the detector. The specimens of soil tested were from different regions, one from São Paulo, and the other from Rio de Janeiro. The bulk density and the water content were determined point by point, in a transverse section of the soil specimens, using a computational algorithm that generated images of bulk density and water content. By utilizing the average pixel values of linear attenuation coefficient in these images, for each specimen, a characteristic curve could be built for each soil. The linear attenuation coefficient values agreed with the expected data. The compaction curves presented good agreement between the tomographic technique and the standard geotechnical method.

Numerical-Experimental Approach to Characterize Fracture Properties of Asphalt Mixtures at Low Temperatures

Fracture damage mechanisms are some of the most significant causes of structural failure in asphalt mixtures. Ye t much research is still needed to understand properly the fracture process in such complex materials. The study reported in this paper investigated several experimental testing protocols available in the literature to characterize fracture properties of asphalt mixtures. Two bending tests (i.e., semicircular bending, single-edge notched beam) and one tension test (disk-shaped compact tension) were performed. An integrated approach that combined experimental tests and numerical simulations was applied to characterize fracture properties of a fine aggregate mixture. The experimental tests were simulated with a computational model on the basis of the finite element method, which was incorporated with material viscoelasticity and cohesive zone fracture. Two cohesive zone fracture parameters (i.e., cohesive strength, fracture energy) were determined through a calibration process until a good match between experimental and numerical results was observed. To illustrate the efficiency of the integrated numerical–experimental approach, fracture properties also were determined through a traditional methodology that used globally averaged material displacements far from the actual fracture process zone. The results indicated that different fracture properties at low temperatures might be obtained from simulations of a single test, regardless of the sample geometry or loading configuration. Through further testing and analysis, it is expected that the modeling approach employed in this work can provide meaningful insights into the effects of constituents on an overall mixtures performance, with significant savings in experimental cost and time.

Chemical, Microstructural, and Rheological Characterizations of Binders to Evaluate Aging and Rejuvenation

This study evaluated the effects of the commercial product, AR 5, and two alternative products, waste cooking oil and castor oil, in the rejuvenation process of two asphalt binders. The analyses were carried out on microscopic and macroscopic scales on virgin, aged, and rejuvenated binders. Tests in a dynamic shear rheometer were performed to characterize rheological properties of the binders. Then, an atomic force microscope was used to identify microstructural changes in the materials. A digital image analysis technique enabled the quantification of key variables such as area fraction and spatial and size distributions of the binder constituents. Finally, the following chemical tests were performed to identify changes in the chemical composition of the binders resulting from the aging and rejuvenation processes: SARA (which measures saturates, asphaltenes, resins, and aromatics), gel permeation chromatography, and nuclear magnetic resonance. The results obtained from the tests were further compared to identify correlations between the properties evaluated in different scales. The results demonstrated the efficiency and potential of the rejuvenators evaluated in this study. The results also highlighted the importance of the use of advanced techniques to characterize and understand the material aging and rejuvenation processes.

Permanent deformation parameters of fine – grained tropical soils

In this work, the permanent deformation response of fine-grained soils of different classifications was studied through repeated load triaxial tests under different stress states for a number of load cycles greater than 150.000. Soils were moulded at optimum water content compressed with an amount of energy equivalent to intermediate or normal Proctor. Seven fine-grained soils were selected with the following MCT (Miniature, Compacted, Tropical) classifications: four lateritic clayey, one lateritic sandy, one non lateritic sand and one non lateritic silt. The values of total permanent deformation are presented. The parameters of deformability Ψi were estimated. The permanent deformation calculations were simulated for three different stress levels: low, medium and high.

INSTRUMENTATION OF THE DNER CIRCULAR TRACK

ABSTRACT This paper presents the instrumentation used on the Experimental Circular Track of Brazils National Highway Department (DNER—Departamento Nacional de Estradas de Rodagem), with the purpose of studying the use of concrete (whitetopping) to resurface flexible pavements. This instrumentation was made up of six strain gauges which were imbedded in the pavement layers. The results obtained from the sensor measurements were then compared against values calculated using the computer programs: ELSYM5, DIPLOMAT, ILSL2 and KENSLABS. These comparisons yielded similar results, especially against those of programs ELSYM5 and DIPLOMAT (with full friction).ABSTRACT This paper presents the instrumentation used on the Experimental Circular Track of Brazils National Highway Department (DNER—Departamento Nacional de Estradas de Rodagem), with the purpose of studying the use of concrete (whitetopping) to resurface flexible pavements. This instrumentation was made up of six strain gauges which were imbedded in the pavement layers. The results obtained from the sensor measurements were then compared against values calculated using the computer programs: ELSYM5, DIPLOMAT, ILSL2 and KENSLABS. These comparisons yielded similar results, especially against those of programs ELSYM5 and DIPLOMAT (with full friction).