Author Description

"NCHRP Project 4-34, 'Application of LADAR in the Analysis of Aggregate Characteristics,' was conducted by Virginia Polytechnic Institute and State University, Blacksburg, Virginia, with participation by the University of Illinois at Urbana-Champaign. The objective of the project was to develop and evaluate a laser detection and ranging (LADAR) system capable of precise and accurate measurement of the aggregate characteristics of shape, volume, angularity, surface texture, specific surface area, and volumetric gradation. Ideally, the final system would be applicable to aggregate in three size categories--coarse (2 in. to #4), fine (#4 to #200), and microfine (P200)--and suitable for routine use in research, central, and field laboratories for Portland cement concrete and asphalt concrete mixture design and quality assurance. The project, which developed new equipment and computer algorithms, proved technically challenging. The project team developed a prototype Fourier transform interferometry (FTI) system with fully functional hardware and software. The system can characterize aggregate shape, angularity, texture, surface area, and volume of a wide range of aggregate sizes with high accuracy. Assembly and operation of the FTI system consisting of a chargecoupled device (CD) camera, a fringe source, a sample platform, and a software package are fully documented in the report. The accuracy and precision of the prototype FTI system are comparable to or better than those of other systems now available to automatically measure aggregate characteristics, but its current range of aggregate size--3/4 in. to #50--is narrower than desired. Extending this size range is possible in the future by using a CCD camera with a larger field of view and increasing the system resolution through appropriate selection of the equipment components."