Browsing by Subject "Angularity"
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Item Effect of soil type and compaction methods on the confined stiffness of soil-geogrid composites(2023-12) Alam, Mahfooz, M.S. in Engineering; Zornberg, Jorge G.When subjected to vehicular loading, pavements undergo relatively small deflections consisting of elastic and plastic components. Under repeated loading, the plastic components of these deflections accumulate and result in permanent deflections that typically cause pavement distress such as surface rutting and asphalt cracking. To improve pavement performance and extend service life, geosynthetics have been used as stiffening elements in the unbound aggregate layers, such as base layers, providing lateral restraint against particle displacement. The lateral restraint and the resulting improvement in layer stiffness rely on the tensile properties of the geosynthetic and the shear behavior of the soil–geosynthetic interface. These concepts are encapsulated in the soil– geosynthetic composite (SGC) model and the resulting parameter, the stiffness of the soil-geosynthetic composite (K_{SGC}), reflects the composite behavior under small strains. In this study, soil geosynthetic interaction (SGI) tests were conducted to investigate the effect of aggregate type, density, and compaction method on the K_{SGC} of geogrids. Accordingly, specimens were tested in the SGI setup at multiple density levels using aggregates of different angularity and grain sizes. In addition, the effect of the compaction method on the results was investigated with specimens prepared using the existing impact-based compaction procedure and the vibratory compaction procedure, which was developed as part of this study to eliminate particle crushing during specimen preparation. Evaluations with different aggregate types show that particle size highly influences the K_{SGC} parameter of soil-geogrid composites, as both angular and rounded aggregates of the same particle size distribution yield comparable results . However, the K_{SGC} parameters obtained with angular aggregates are consistently higher than those obtained with rounded aggregates. In addition, the results show a positive correlation between aggregate density and K_{SGC}, which can be attributed to the increased interaction (interlocking and friction) at the interface. Lastly, the results obtained from specimens prepared using impact-based and vibratory compaction methods were found to be in good agreement, provided that the same soil density is achieved. This validates the use of vibratory compaction developed in this study, which is recommended as the preferred method of specimen preparation, particularly for aggregates that are prone to particle crushing.Item Effects of Aggregate Gradation and Angularity on VMA and Rutting Resistance(2001-06) Park, Dae-Wook; Chowdhury, Arif; Button, Joe W.The Superpave system adopted the voids in mineral aggregate (VMA) criteria developed by McLeod using the 75-blow Marshall compactor for conventional dense-graded hot mix asphalt (HMA) mixtures. This VMA criteria is a function of only the nominal size of aggregate regardless of shape, texture, or gradation. The Superpave volumetric mixture design process contains a required minimum value for fine aggregate angularity (FAA) as a function of traffic level and position of the layer within the pavement structure. This parameter is reported as the percentage of uncompacted air voids, with larger values generally indicating increased aggregate angularity and, thus, higher VMA and better resistance to permanent deformation. The purpose of this study was to evaluate the effects of FAA and gradation on the resulting VMA of certain HMA mixtures. The effect of FAA was evaluated using mixtures containing coarse limestone combined with six different fine aggregates. Mixtures with three gradations which pass through, above, and below the restricted zone; three different mineral filler contents; and four different values of FAA were analyzed to evaluate the effects of these parameters on VMA of Superpave mixtures. Based on analyses of these tests, mixtures containing fine granite or limestone showed less permanent deformation than mixtures containing fine river gravel or natural rounded sand. FAA values and permanent deformation did not correlate well. Gradations that pass through the restricted zone did not significantly affect mixture VMA. Mineral filler contents and FAA value did affect mixture VMA significantly. Higher FAA values yielded higher VMA.Item Evaluation of Superpave Fine Aggregate Angularity Specification(2001-05) Chowdhury, Arif; Button, Joe W.; Kohale, Vipin; Jahn, David W.The validity of the Superpave fine aggregate angularity (FAA) requirement is questioned by both the owner agencies and the paving and aggregate industries. The FAA test is based on the assumption that more fractured faces will result in higher void content in the loosely compacted sample; however, this assumption is not always true. Some agencies have found that cubical shaped particles, even with 100 percent fractured faces, may not meet the FAA requirement for high-volume traffic. State agencies are concerned that local materials, previously considered acceptable and which have provided good field performance, cannot meet the Superpave requirements. Researchers evaluated angularity of 23 fine aggregates representing most types of paving aggregates used in the USA using seven different procedures: FAA test, direct shear test, compacted aggregate resistance (CAR) test, three different image analyses, and visual inspection. The three image analyses techniques included Hough Transform at University of Arkansas at Little Rock (UALR), unified image analysis at Washington State University (WSU), and VDG-40 videograder at Virginia Transportation Research Council (VTRC). A small study was performed to evaluate relative rutting resistance of HMA containing fines with different particle shape parameters using the Asphalt Pavement Analyzer (APA). The FAA test method does not consistently identify angular, cubical aggregates as high quality materials. There is a fair correlation between the CAR stability value and angle of internal friction (AIF) from the direct shear test. No correlation was found between FAA and CAR stability or between FAA and AIF. Fairly good correlations were found between FAA and all three image analysis methods. Some cubical crushed aggregates with FAA values less than 45 gave very high values of CAR stability, AIF, and ‘angularity’ from imaging techniques. Moreover, the three image analysis methods exhibited good correlation among themselves. A statistical analysis of the SHRP-LTPP (Strategic Highway Research Program-Long-Term Pavement Performance) database revealed no significant evidence relationship between FAA and rutting. This lack of relationship is not surprising since many uncontrolled factors contribute to pavement rutting. The APA study revealed that FAA is not sensitive to rut resistance of HMA mixtures. Image analysis methods appear promising for measuring fine aggregate angularity. Until a suitable replacement method(s) for FAA can be identified, the authors recommend that the FAA criteria be lowered from 45 to 43 for 100 percent crushed aggregate. Analysis of the FAA versus rutting data should be examined later as the amount of data in the SHRP-LTTP database is expanded.Item Quantifying the characteristics of fine aggregate using direct and indirect test methods(2013-12) Alqarni, Ali Saeed; Fowler, David W.The characteristics of fine aggregates, such as shape, angularity, and surface texture, have been shown to influence the performance of concrete and asphalt mixtures and to play an important role in obtaining valuable properties of early age concrete such as workability, and compatibility. However, the measurement of fine aggregate characteristics is not easy. In the present study, 26 fine aggregates, covering a wide spectrum of mineralogy, were examined using direct and indirect test methods in order to evaluate the shape, angularity, and surface texture, as well as to analyze the gradation. The direct test methods, such as AIMS and Camsizer, which provide a digital image of the aggregates proved to be the best. However, the cost of such systems can limit the use of digital imagining systems in practice. The indirect test methods which provide an estimate of aggregate surface characteristics, such as uncompacted void test, mortar flow test, compressive strength test, and flakiness test gave variable results. The uncompacted void test (Method A) was shown to be the most accurate indirect test method. The Camsizer and the sieve analysis test produced identical gradation analysis results when an adequate sample was used. General correlations were developed between the direct and indirect test methods. The non-approved fine aggregates on the TxDOT’s list were analyzed and compared to those of the approved fine aggregates to see whether they could be successfully used. It was found that both LS-5 and LS-8 had good results—even better than the results of some of the approved fine aggregates. Thus, they could be successfully used.