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1 1.1 Project Background Aggregates are an important component in asphalt con- crete, cement concrete, granular base, and treated base. Their characteristics, including shape, angularity, surface texture, and surface area, significantly affect the properties of mix- tures. Historically, tremendous efforts have been made to quantify these characteristics both directly and indirectly and correlate them to performance at both a state level and national level. Some national efforts in the past few years focused on evaluation of the direct measurement methods using two-dimensional (2-D) image analysis. There are some limitations for the 2-D and semi-3-D methods (i.e., the 2.5-D). The intent of NCHRP Project 4-34 was to develop and evaluate a 3-D aggregate characterization system and analy- sis method using laser detection and ranging (LADAR) for aggregate shape, angularity, texture, and surface area. Com- pared to X-ray computerized tomography (XCT), the aggre- gate imaging system developed in this project costs less and can be made portable for field testing more conveniently. Morphological characteristics of both coarse and fine aggre- gates have a significant influence on the performance of paving materials and pavements. Shape, angularity, and texture influ- ence aggregate mutual interactions and strengths of bonds between aggregates and asphalt binders, cement paste, and lime (Al-Rousan et al., 2006). The interactions and bond strengths are vital to the rheological properties related to workability and friction resistance of mixtures. Therefore, characterization of aggregate morphological characteristics is important for better quality control of aggregates and performance of pavements. There are two fundamental ways to measure the shape, angularity, and texture of aggregates: direct methods and indirect methods. Direct methods are conducted by measur- ing aggregates with either visual inspection or digital image analysis, or by measuring the three dimensions of aggre- gates using calipers (AASHTO T 304, AASHTO TP 56, and ASTM D3398). A concern with current direct methods is that some are time consuming and laborious (Rao et al., 2000; Fletcher et al., 2003). On the other hand, indirect methods may measure the shear strength of specimens composed of graded aggregates or the air void contents of uncompacted specimens (ASTM D4791, ASTM D5821). This is usually based on the assumption that uncompacted void content and shear strength are related to the shape, angularity, and texture of aggregates. The indirect methods usually cannot separate the contributions to strength by shape, angularity, texture, and gradation, which affect the strength and deformation via differ- ent mechanisms. The indirect methods, however, can directly measure the angularity and texture of aggregates (Al-Rousan et al., 2006). Motivated by the advancements in digital imaging and availability of low-cost and fast image processing software, various image techniques have recently been developed to provide a cost-effective means for rapid quantification of aggregate morphological characteristics. Some image tech- niques analyze aggregates by using 2-D shape analysis, which is not accurate enough to represent 3-D morphological char- acteristics of aggregates. Besides, the current imaging tech- niques use different image acquisition methods and different definitions of shape, angularity, and texture. The results are sometimes not directly comparable. This research has developed an aggregate imaging system named the Fourier Transform Interferometry (FTI) system that acquires 3-D surface coordinates and analyzes the mor- phological characteristics using Fourier transform through a user-friendly matrix laboratory (MATLAB) program devel- oped for this project. This chapter presents the description of the various chapters and appendices in a logically inte- grated flow. These chapters and appendices present the fun- damentals of FTI, the components and integration of the FTI system, the morphological characterization methodology that the FTI system has adopted, the FTI analysis results of both coarse and fine aggregates, a statistical analysis of the results, an assessment of the accuracy of the FTI results by comparison to C h a p t e r 1 Introduction
2manual measurements, and a comparison of the FTI results with those of peer systems including the Aggregate Imaging Measurement System (AIMS) II and University of Illinois Aggregate Image Analyzer (UIAIA). Chapter 7 presents con- clusions and recommendations for future research. 1.2 Objectives and Scope The objective of NCHRP Project 4-34 was to develop and evaluate a prototype FTI system capable of precise and accurate measurement of aggregate characteristics, includ- ing shape, volume, angularity, surface texture, specific sur- face area, and volumetric gradation. The FTI system needed to be applicable to aggregate in each of three size categories: coarse (2 in. to #4), fine (#4 to #200), and microfine (P200), and be suitable for routine use in research, central, and field laboratories for Portland cement concrete (PCC) and hot- mix asphalt (HMA) mixture design, and quality control and acceptance (QC/QA). To develop a system that is capable of imaging such a wide range of particle sizes without using dif- ferent hardware settings is a paramount challenge. A promis- ing technique is FTI, which can achieve very high resolution with a large view field. Nevertheless, to image particles passing #200 is not a realistic operation. Based on the overall objective of the project, the FTI system provides 3-D images with the highest possible resolution for a wide range of particle sizes (please note that size range and resolution are two conflicting requirements) and quantifies the aggregate morphological characteristics based on the 3-D high-resolution images. The system needs to be able to collect images of a particle from mul- tiple views and then reconstruct a 3-D surface of the object for the characterization of shape, angularity, surface texture, sur- face area, and volume of the particle. Therefore, the research work focused on the following aspects: (1) Development of an imaging system to generate 3-D coordinates of the aggregate surfaces. (2) Development of a computational program for analyzing 3-D coordinates and abstracting morphological charac- teristics that are consistent with qualitative evaluation with the unaided human eye. (2) Morphological characterization results that are consis- tent with manual measurement, and characterization results that are consistent with other available aggregate imaging techniques. 1.3 Report Outline Figure 1-1 presents the flowchart of the final report. There are seven chapters and ten appendices. Chapter 1 presents the project background, supported with a comprehensive lit- erature review on imaging techniques for aggregate morpho- logical characterization presented in Appendix A (available, with Appendices E through J, at http://apps.trb.org/cmsfeed/ TRBNetProjectDisplay.asp?ProjectID=867). The scope and objectives of the project are also outlined in Chapter 1. Chapter 1 Introduction Chapter 2 Fourier Transform Interferometry (FTI) Aggregate Image System Appendix A Literature Review Appendix B The FTI System Components Appendix D Test Protocol in AASHTO Format Chapter 3 Aggregate Shape, Angularity, and Texture Analysis Methods Chapter 4 FTI Results Chapter 5 Statistical Analysis Appendix F FTI Analysis Results Appendix I AIMS II Analysis Results Appendix J UIAIA Analysis Results Chapter 6 Discussion Chapter 7 Conclusions Appendix H Manual Measurements Appendix E Photographs of Aggregate Samples Appendix C Initial Efforts for the Particle Mounting System Appendix G Histogram and Quantile Plot Figure 1-1. Flowchart of the final report.
3 Chapter 2 introduces the final version of the FTI system, which consists of a charged-coupled device (CCD) camera, a fringe source, an angled mirror, an adjustable-height particle tray, and a MATLAB software package. Some of the various intermediate versions of the systems (or components) are presented in the appendices. The efforts for these intermediate versions were sig- nificant and could not be avoided due to the innovative nature of the project. The MATLAB software package is composed of three modules: (1) a main program to process images into 3-D coordinates, (2) an error correction program to remove errors from the data file generated by the main program, and (3) a morphology analysis program to analyze the corrected data for computing shape, angularity, and texture. The specifics of the components of the FTI system are listed in Appendix B. The initial efforts for developing the particle mounting system are presented and discussed in Appendix C. Chapter 3 presents the analysis method developed for the morphology analysis program. The program uses the 2-D Fourier transform method to analyze the 3-D coordinates and computes morphological characteristics such as angu- larity and texture. The program can also calculate shape fac- tors such as sphericity, the flatness ratio, and the elongation ratio. A draft test protocol in AASHTO format is presented in Appendix D. Chapter 4 presents the morphological characterization results by the FTI method for both coarse and fine aggregates, with raw data presented in Appendix F. Images of the coarse aggregate samples in Set 1 are presented in Appendix E. The manual measurements of the coarse aggregate dimensions for Set 1 are presented in Appendix H. Chapter 5 presents the statistical analysis of FTI results of coarse aggregates. Both analysis of variance (ANOVA) and t-tests were performed to compare the mean values of the FTI results and the corresponding parameters of man- ual measurements and those of the AIMS II and UIAIA systems. The histograms and quantile plots are presented in Appendix G. Chapter 6 compares the FTI results to those of manual measurement and the AIMS II and UIAIA systems. The pol- ishing and crushing effects due to Micro-Deval testing on the changes of morphological characteristics of aggregates are also discussed in this chapter. The results of AIMS II and UIAIA for aggregates in Set 1 are presented in Appendix I and Appendix J, respectively. Chapter 7 presents general conclusions, possibilities for future research, and a list of potential applications. Imple- mentation plans and cost assessments are presented at the end of this chapter.
