ICAR Technical Reports

Permanent URI for this collectionhttps://hdl.handle.net/2152/32838

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Role of Aggregate Characteristics to Load in SMA
(2006-08) Gatchalian, Dennis; Masad, Eyad; Chowdhury, Arif; Little, Dallas N.
Stone matrix asphalt (SMA) mixtures rely on stone-on-stone contacts among particles to resist applied forces and permanent deformation. Aggregates in SMA should resist degradation (fracture and abrasion) under high stresses at the contact points. This study utilizes conventional techniques as well as advanced imaging techniques to evaluate aggregate characteristics and their resistance to degradation. Aggregates from different sources and types with various shape characteristics were used in this study. The Micro-Deval test was used to measure aggregate resistance to abrasion. The aggregate imaging system (AIMS) was then used to examine the changes in aggregate characteristics caused by abrasion forces in the Micro-Deval. The resistance of aggregates to degradation in SMA was evaluated through the analysis of aggregate gradation before and after compaction using conventional mechanical sieve analysis and nondestructive X-ray computed tomography (CT). The findings of this study led to the development of an approach for the evaluation of aggregate resistance to degradation in SMA. This approach measures aggregate degradation in terms of abrasion, breakage, and loss of texture.
Rapid Test to Establish Grading of Unbound Aggregate Products: Automation of Aggregate Characterization Using Laser Profiling and Digital Image Analysis
(2002-06) Haas, Carl T. (Carl Thomas); Rauch, Alan F.; Kim, Hyoungkwan; Browne, Craig
This final project report describes the development of a laser scanning device for measuring the gradation and other morphological characteristics of unbound construction aggregates. The device is called the LASS, for "Laser-based Aggregate Scanning System." The method of characterizing aggregate particles from three-dimensional (3D) laser profiling required the development of particle segmentation algorithms, particle measurement algorithms, and generalized particle descriptions. With the LASS, true 3D data of aggregate particles are obtained by laser profiling. This data is first transformed into digital images. Second, segmentation and particle measurement algorithms separate the particles and process each particle data individually with the aid of various digital image technologies. Finally, in order to provide a generalized, quantitative, and representative way to characterize aggregate particles, 3D particle descriptors were developed using the multi-resolution analysis feature of wavelet transforms. Verification tests show that this approach can characterize various aggregate properties in a fast, accurate, and reliable way. When implemented, this ability to automatically analyze multiple characteristics of an aggregate sample will lead to reduced labor costs in the laboratory, but more importantly, to better control of the quality of aggregate products. ICAT Project 503 was undertaken to study rapid, automated methods of determining the grain size distribution of unbound aggregate products. Automatic measurement of particle size and shape properties has the potential to overcome problems with manual measurements such as subjectivity, labor intensity, and slow speed. Testing machines that rely on 2D digital image analysis were evaluated as described earlier in Report ICAR 503-2.
Rapid Test to Establish Grading of Unbound Aggregate Products: An Evaluation of Automated Devices to Replace and Augment Manual Sieve Analyses in Determining Aggregation Gradation
(2002-02) Rauch, Alan F.; Haas, Carl T. (Carl Thomas); Browne, Craig; Kim, Hyoungkwan
Several automated devices are commercially available for measuring the gradation of unbound stone aggregates. These computerized machines, which provide a rapid alternative to manual sieving, capture and process two-dimensional digital images of aggregate particles to determine grain size distribution. Five of these automated gradation devices were evaluated for accuracy and performance. Fifteen aggregate test samples, with different size, shape, and mineral characteristics, were used in these tests. To quantify how well the machine results compare with data from standard sieve analyses, the CANWE statistic was developed and used. While the machine data did not match the sieve data exactly, the evaluated devices were found to provide good measures of particle gradation for most samples. These tests also indicate that some machines will give more repeatable results in multiple tests of a given material, while others yield better results when testing different materials. The methodology used in this study is suitable for objectively evaluating the accuracy of other rapid gradation machines for various applications. ICAR Project 503 was undertaken to study rapid, automated methods of determining the grain size distribution of unbound aggregate products. Two technologies were studied in detail: digital image analysis and laser profiling. This report summarizes the evaluation of digital imaging devices, while the second part of the final project report describes the development of a laser scanning device for grading aggregates.
Rapid Test to Establish Grading of Unbound Aggregate Products: Evaluation of Potential Aggregate Grading Technologies
(2000-02) Rauch, Alan F.; Haas, Carl T. (Carl Thomas); Kim, Hyoungkwan; Browne, Craig
A research study is underway to develop automated methods for rapidly grading aggregates on the production line in a typical aggregate separation or mixing facility. This interim report serves to document preliminary work on this project and presents: (1) A discussion of typical plant layouts, to identify potential sampling locations. The best sampling locations appear to be just after final screening, where sorted material is sent to stockpiles, and just before mixing the final product, where aggregates are fed from either stockpiles or charge bins. (2) A thorough examination of six potential technologies that could be used to rapidly determine particle size. After a critical review and a formal decision analysis, both digital image analysis and laser profiling appear to be equally promising and worthy of additional study. (3) A discussion of our current thinking on how to configure scanning equipment of this kind. By considering innovative methods for presenting aggregate particles to the scanning sensor, the opportunity exists for advancing this technology. An outline of project work planned for the immediate future. Continuing our study of both digital image analysis and laser profiling, we plan to: 1. Conduct a limited, independent evaluation of three commercial particle-sizing machines, which all use digital image analysis. 2. Perform preliminary tests using a laser profiler. 3. Construct a laboratory test bed that can be used to test and evaluate various scanning sensors.
Characterization of Unbound Granular Layers in Flexible Pavements
(2001-12) Adu-Osei, Alex
The mathematical characterization of unbound granular materials should ideally be based on the behavior of the individual constituent elements and their interaction. Until particulate mechanics are developed to a level where it can easily be applied to characterize unbound granular materials, a nonlinear and cross-anisotropic model must be used to characterize the behavior of granular materials in pavements. Existing pavement design and analysis methods have generally taken a very conservative view of the relative strength properties of granular materials used as base and subbase layers in conventional flexible pavements. The mechanical properties of unbound granular layers in flexible pavements are important to the overall structural integrity of the pavement structure. Linear elastic analysis can be used with reasonable confidence for pavements with full depth asphalt layers, but it is inappropriate for unsurfaced or thinly surfaced flexible pavements unless the nonlinear behavior of unbound granular materials are properly taken into account. Work done by several researchers suggest that incorporating a cross-anisotropic elastic model significantly improves isotropic models and drastically reduces the tensile stresses computed within granular layers. This is due to the fact that the behavior of granular materials depends on particle arrangement. The laboratory determination of cross-anisotropic properties of granular materials has been a difficult task for researchers. In this study, a new laboratory testing protocol has been developed based on the theories of elasticity to determine cross-anisotropic properties of granular materials. The testing protocol is efficient and precise. The test is also an excellent tool for comparative analysis of compacted materials. The behavior of four unbound granular materials was studied. The resilient responses of the materials obey the Uzan type nonlinear model. It was observed that under low stress levels accumulation of permanent strain could stabilize in granular layers. However, at high stress levels, permanent strain will continuously accumulate. A finite element program was modified to incorporate the cross-anisotropic material model. Pavement sections were analyzed with the finite element program. It was observed that cross-anisotropic modeling eliminates the presence of tension zones predicted by isotropic resilient models. Deflection bowls predicted by nonlinear resilient models agree with field deflection bowls.
Field Validation of the Cross-Anisotropic Behavior of Unbound Aggregate Bases
(2001-03) Tutumluer, Erol; Adu-Osei, Alex; Little, Dallas N.; Lytton, Robert L.
The ICAR Research Project 502 has focused on determining structural considerations of unbound aggregate pavement layers for a proper representation in the new AASHTO Pavement Design Guide 2002. The research team developed models for the resilient and permanent deformation behavior from the results of triaxial tests conducted at the Texas Transportation Institute (TTI) and at the University of Illinois. The studies have mainly indicated that the unbound aggregate base (UAB) material should be modeled as nonlinear and cross-anisotropic to account for stress sensitivity and the significant differences between vertical and horizontal moduli and Poisson's ratios. UABs were constructed at the TTI Riverside research facility and tested for response and performance using the one-third scale model of the Texas Mobile Loading Simulator. The resilient responses of the test sections were modeled. The nonlinear cross-anisotropic material models used in the base layer predicted vertical deflections that are close to field deflections in the analyzed TTI pavements. Field validation data were also collected from a full-scale pavement test study conducted at Georgia Tech. The test sections had extensive instrumentation and the pavement response variables, such as stresses, strains, and deformations, were measured in all pavement layers including the UABs. The validation of the anisotropic modeling approach was accomplished by analyzing these test sections using GT-PAVE finite element program, predicting UAB responses, and comparing them to the measured ones. Laboratory testing of the aggregate samples was conducted at the University of Illinois and the characterization models were developed for the stress sensitive, cross-anisotropic aggregate behavior. With nonlinear anisotropic modeling of the UAB, the resilient behavior of pavement test sections was successfully predicted at the same time for a number of response variables. In addition, the stress sensitive, cross-anisotropic representation of the base was shown to greatly reduce the horizontal tension computed in the granular base when compared to a linear isotropic representation.
Structural Characteristics of Unbound Aggregate Bases to Meet AASHTO 2002 Design Requirements: Interim Report
(2001-07) Adu-Osei, Alex; Little, Dallas N.; Lytton, Robert L.
This report gives the results of a study of the properties of unbound aggregate base materials using both laboratory testing data from full scale field tests in Illinois, Georgia, and Texas, and a model of cross-anisotropic elastic materials to characterize the behavior of the base materials under traffic loads. Using the cross-anisotropic model, the stress distribution in a base course is more realistic than that developed when the aggregate base is considered to be linear and isotropic. The stress distribution based on cross-anisotropic analysis is not only more correct, but it is also more favorable to the unbound aggregate in that significant tensile stresses are found not to occur. The analogy is presented in this report that the response of the aggregate base to the load is as if the stress distribution directly under the wheel load due to anisotropy acts as a moving column under the wheel in which the aggregate essentially produces its own confinement and does not enter into tension. Other findings in this report include the following: 1) The unbound aggregate base material should be modeled as non-linear and cross-anisotropic to account for stress-sensitivity and the significant differences between vertical and horizontal moduli and Poisson’s ratios. 2) The ICAR laboratory testing protocol is efficient and precise and should be considered as a candidate to model the unbound aggregate base. The protocol uses three stress regimes and ten stress levels within each regime to determine stress sensitivity and cross-anisotropy. A system identification method is used to select the five material properties based on the tests results necessary to properly characterize the aggregate base and to satisfy the requirements of elastic work potential theory. 3) The Fast Industrial Process Controls cell is efficient and should be used to characterize unbound aggregate bases. The ratio of the diameter to the specimen height is 1:1. While testing of such sample sizes is discouraged in the literature, improvements made to the IPC cell minimize frictional development between the sample and loading platens resulting in minimal constraint at the sample ends. This is verified in the report based on comparative triaxial testing and finite element analysis. 4) The ICAR testing protocol is an excellent tool for both unbound aggregate characterization and comparative analysis of materials. A compaction study on two very different aggregates (uncrushed river gravel and crushed limestone) was performed in which the aggregates were subjected to impact, kneading gyratory compaction. The difference in the tendency of the compaction techniques to produce varying levels of particle orientation (which affects anisotropy) was evident in the degree of anisotropy measured.
Increased Single-Lift Thicknesses for Unbound Aggregate Base Courses
(1998-10) Allen, John J.; Bueno, Jaime L.; Kalinski, Michael E.; Myers, Michael L.; Stokoe, Kenneth H.
A study was conducted to evaluate the feasibility of compacting unbound aggregate base courses in thicker lifts than currently permitted by state departments of transportation (DOTs). At present, the majority of states allow a maximum lift thickness of 8 inches or less. This project constructed and tested full-scale test sections using a variety of material types. Two test pads were constructed in an aggregate quarry in Texas utilizing crushed limestone. Three crushed granite test sections were built as part of a road widening project in Georgia, and two test pads were constructed of uncrushed and partially crushed gravel with loess fines at a gravel production facility near Memphis, Tennessee. Single-lift thicknesses varied from 6 inches to 21 inches. Moisture contents and densities were evaluated using the Nuclear Density Gauge (NDG). Nondestructive seismic testing, using the Spectral-Analysis-of-Surface-Waves (SASW) technique, was used to evaluate stiffness profiles within the compacted lifts. Cyclic plate load tests were accomplished by means of the Rolling Dynamic Deflectometer (RDD), modified for this static application. Results showed that compaction targets could be attained for lifts up to 21 inches thick. Density and stiffness results for 13-inch thick lifts in the Georgia tests were equal to, or better than, the results for the base placed in two lifts, a 7-inch lift followed by a 6-inch lift. Higher moisture contents during compaction yielded lower shear wave velocity and Young’s modulus values. Seismic results show that the upper 3 inches of the final test pads had lower stiffness values, presumably from lower effective stresses near the surface and possibly from some disturbance caused by the compaction equipment. This zone of lower stiffness and slightly less compaction is less evident in the density measurements.
Prediction of Working Load Displacements Under Plate Loading Tests from Seismic Stiffness Measurements
(1998-10) Myers, Michael L.; Stokoe, Kenneth H.; Allen, John J.
A study was conducted to evaluate the feasibility of compacting unbound base courses in thicker lifts than currently permitted by state departments of transportation (DOTs). At present, the majority of states allow a maximum lift thickness of 8 inches or less. This project constructed and tested full-scale test section using a variety of material types. Two test pads were constructed in an aggregate quarry in Texas utilizing crushed limestone. Three crushed granite test sections were built as part of a road widening project in Georgia, and two test pads were constructed of uncrushed and partially crushed gravel with loess fines at a gravel production facility near Memphis, Tennessee. Single-lift thicknesses varied from 6 inches to 21 inches. Moisture contents and densities were evaluated using the Nuclear Density Gauge (NDG). Nondestructive seismic testing, using the Spectral-Analysis-of Surface-Waves (SASW) technique, was used to evaluate stiffness profiles within the compacted lifts. Plate load tests were conducted on the surface of the crushed limestone test pads by means of the Rolling Dynamic Deflectometer specially modified for this fixed site application. Low frequency cyclic loads were applied to determine axial stiffness under transient working loads of varying magnitude. The base courses were tested at to moisture contents. The results were evaluated and compared with small strain seismic tests result. Strain amplitudes in the plate load tests led to a 5% to 25% reduction in measured stiffness as compared to the seismic results.
A Study on the Feasibility of Compacting Unbound Graded Aggregate Base Courses in Thicker Lifts Than Presently Allowed by State Departments of Transportation
(1998-10) Bueno, Jaime Luis; Stokoe, Kenneth H.; Allen, John J.
A study was conducted to evaluate the feasibility of compacting unbound aggregates base courses in thicker lifts than currently permitted by state departments of transportation (DOTs). At present, the majority of states allow a maximum lift thickness of 8 inches or less. This project constructed and tested full-scale test sections using a variety of materials types. Two test pads were constructed in an aggregate quarry in Texas utilizing crushed limestone, and three crushed granite test sections were built as part of a road widening project in Georgia. Single-lift thickness varied from 6 inches to 21 inches. Moisture contents and densities were evaluated using the Nuclear Density Gauge (NDG). Nondestructive seismic testing, using the Spectral-Analysis-of Surface-Waves (SASW) techniques, was used to evaluate stiffness profiles within the compacted lifts. Results showed that compaction targets could be attained for lifts up to 21 inches thick. Density and stiffness results for 13-inch thick lifts in the Georgia tests were equal to, or better than, the results for the base placed in two lifts, a 7-inch lift followed by a 6-inch lift. Higher moisture contents during compaction yielded lower shear wave velocity and Young’s modulus values. Seismic results show that the upper 3 inches of the final test pads had lower stiffness values, presumably from lower effective stresses near the surface and possibly from some disturbance caused by the compaction equipment. This zone of lower stiffness and slightly less compaction is less evident in the density measurements.
Alkali-Silica Reaction in Portland Cement Concrete: Testing Methods and Mitigation Alternatives
(2001-07) Touma, Wissam; Fowler, David W.; Carrasquillo, Ramón L.
Identifying the susceptibility of an aggregate to alkali-silica reaction (ASR) before using it in concrete is one of the most efficient practices for preventing damage and failure. Several tests have been developed for identifying aggregates subject to ASR, but each has its limitations. A three-year research study was initiated on January 1, 1998 at The University of Texas at Austin for investigating ASR in portland cement concrete. The scope of the study was essentially three fold: (1) investigate the predictive ability of ASTM C 1260 and C 1293, (2) develop more accurate and more efficient modifications of these procedures, and (3) investigate ASR mitigation alternatives. Aggregate samples from 14 sources from around the United States were acquired for the investigation. Aggregates were used in an extensive testing program during which guidelines for predicting the potential ASR of aggregates were developed and recommendations for minimizing concrete damage due to ASR were formulated. This report includes a review of the state-of-the-art of ASR, an evaluation of testing protocols and recommendations for dramatically shortening test time, test results, and mitigation options.
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.
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.
Use of High Fines Concrete (HFC) in Insulated Concrete Form (ICF) Construction
(2001-09) Zollinger, Dan G. , 1952-
This project work consisted of developing technical data to justify, from the standpoint of material properties (of aggregate fines and HFC), construction efficiency, cost competitiveness, and energy performance, a basis for the use of high-fines concrete (HFC) inside ICF wall systems. Although several aspects of the study are listed above, the report primarily concentrates on the material aspects of a limited number of aggregate fines sources and their use in HFC relative to strength development and placeability. Originally, emphasis was planned to be placed upon the use of a controlled low strength material (CLSM) but due to strength requirements currently in force for ICF construction, it was determined that greater benefit would be derived from highlighting the advantages of using aggregate fines in ICF concrete. A framework for developing suitable HFC mixture designs for different ICF wall systems relative to placement and strength characteristics is discussed. These guidelines were based upon results from the construction to two residential structures using HFC and the placement of 4 trial wall systems. One of the structures consisted of a “test model” that was used to investigate methods of construction and the energy efficiency of an ICF wall system.
An Experimental Study on the Guidelines for Using Higher Contents of Aggregate Microfines in Portland Cement Concrete
(2001-12) Fowler, David W.; Ahn, Nam-Shik
The use of manufactured fine aggregate (MFA) in portland cement concrete becomes more common as sources of natural sands are depleted. There is a great need to utilize MFA better, particularly the minus 75µm sizes. The development of specifications that aid aggregates producers, engineers, and specifying agencies in the utilization of MFA is of interest to many parties. Better utilization of crushed aggregates has both economic and environmental benefits for the construction and materials industry. This report presents some of the effects of high-fines on the properties of cement mortar and concrete. A total of 50 sands were used in this mortar study, 10 of which were included in the concrete research. A summary of aggregate characteristics that affect the properties of mortar and concrete are presented along with the correlations evaluated between these properties.
Framework for Development of a Classification Procedure for Use of Aggregate Fines in Concrete
(2001-10) Zollinger, Dan G. , 1952-; Sarkar, Shondeep L.
Although data on use of aggregate fines in portland cement concrete are largely very encouraging, there is a lack of proper definition, and knowledge regarding nature, and characteristics of different aggregate fines, their properties, and effects on portland cement concrete. The focus of this project was to examine the methods and test procedures used in the past to characterize the properties of fines, and develop, on a preliminary basis, a framework to characterize and catalogue the properties of aggregate fines, propose new ones that would eventually complement a set of guidelines for the use of aggregate fines in portland cement concrete. A test run of this classification process is provided as a demonstration of its utility to distinguish aggregate fines possessing different properties and characteristics. Possible applications of aggregate fines, such as in high-performance concrete, controlled low strength materials, and insulated concrete forms are discussed as future directions of research.
User’s Manual for Finite Element Pavement Response Analysis Software TTI-PAVE
(2009-10-30) International Center for Aggregates Research
A finite element program was developed to calculate the responses of the pavement under traffic load. The finite element procedure and the code was originally derived by Owen and Hinton (1980) using elasto-plastic formulation. This software is developed to analyze an axisymmetric problem with material nonlinearity. Liu modified the program by developing a mesh generation algorithm, implementation of several constitutive models and non-symmetric solutions... Later in 2000 Park made another set of modification to the software to incorporate stress dependent Poisson ratio nonlinear analysis using load increments. Adu-Osie later modified the program to incorporate cross-anisotropy in the formulations. Adu-Osie implemented Uzan’s model presented in equation 1 instead of the nonlinear elasto-plastic model for pavement analysis.
Methodology for designing aggregate mixtures for base courses
(2009-08-31) Ashtiani, Reza S.; Little, Dallas N.
The aggregate base layer is a vital part of the flexible pavement system. Unlike rigid pavements, the base layer provides a substantial contribution to the load bearing capacity in flexible pavements, and this contribution is complex: stress dependent, moisture dependent, particle size dependent, and is anisotropic in nature. Furthermore, the response of the aggregate layer in the pavement structure is defined not only by resilient properties of the base layer but also by permanent deformation properties of the aggregate layer. Before the benefits of revolutionary changes in the typical pavement structures, such as deep unbound aggregate base (UAB) layers under thin hot mix asphalt surfaces and inverted pavement systems can be justified, an accurate assessment of the UAB is required... In the realm of geotechnical engineering, the ratio of the horizontal modulus to vertical modulus is commonly referred to as the level of anisotropy. When the vertical and horizontal moduli are equal, the system is isotropic, but when they differ, the system is anisotropic. This research showed that the level of anisotropy can vary considerably depending on aggregate mix properties such as gradation, saturation level, and the geometry of the aggregate particles. Cross anisotropic material properties for several unbound and stabilized aggregate systems were determined. A comprehensive aggregate database was developed to identify the contribution level of aggregate features to the directional dependency of material properties. Finally a new mechanistic performance protocol based on plasticity theory was developed to ensure the stability of the pavement foundations under traffic loads.
The Prediction of Coarse Aggregate Performance by Micro-Deval and Soundness Related Aggregate Tests
(2006-07) Fowler, David W.; Allen, John J.; Lange, Alexander; Range, Peter H.
This research project concentrated on determining whether or not a correlation existed between laboratory aggregate tests and observed aggregate field performance. For this purpose, aggregate samples were collected from the majority of the U.S. states as well as several Canadian provinces and subjected to a variety of strength, soundness, and intrinsic particle property tests. Additionally, performance data on the aggregates was obtained by contacting multiple DOTs where aggregates were in use in several categories – hot-mix asphalt, portland cement concrete, base course, and open-graded friction course. Numerical and qualitative analyses were performed to evaluate the success of separating good performers from fair and poor performers using the micro-Deval test alone as well as the micro-Deval test combined with another test. Special attention was paid to aggregate mineralogical composition. Furthermore, attempts were made to determine if a correlation exists between any two tests.
Acceptability criteria for high fines content aggregate pavement layers
(2007-12-31) Ashtiani, Reza S.; Little, Dallas N.
The objective of this study was to evaluate the impact of increasing fines content on the performance of unbound (unstabilized) and lightly stabilized aggregate systems. The aggregate systems analyzed varied in the amount of mineral fines, the moisture state during curing and at the time of testing, and the amount of Portland cement used to stabilize the blend. The evaluation was based on measurements of anisotropic resilient properties, permanent deformation, and unconfined compressive strengths of aggregate systems. In addition, the nonlinear anisotropic resilient properties of the aggregate blends were used in a finite element program to determine critical pavement responses. Aggregate systems with higher fines contents were, as expected, more sensitive to moisture than control systems with standard fines contents. The increase in the fines content in the unbound systems when molding moisture was greater than optimum dramatically diminished the quality of performance. However, the aggregate systems with higher fines benefited considerably from low percentages of cement stabilizer. Researchers found that with the proper design of fines content, cement content, and moisture, the performance of the stabilized systems with high fines content can perform equivalent to or even better than systems with standard fines content. This was clearly demonstrated that by enhancing the resilient properties (an increase in stiffness and a decrease in the level of anisotropy), permanent deformation of the aggregate systems were significantly reduced. This finding was in conformity with unconfined compressive strength of lightly stabilized high fine systems.

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