Discussions and Closures Closure to “Degradation-Related Changes in Ballast Gradation and Aggregate Particle Morphology” by Yu Qian, Huseyin Boler, Maziar Moaveni, Erol Tutumluer, Youssef M. A. Hashash, and Jamshid Ghaboussi Yu Qian, Ph.D., A.M.ASCE Assistant Professor, Dept. of Civil and Environmental Engineering, Univ. of South Carolina, 300 Main St., Columbia, SC 29208 (corresponding author). ORCID: https://orcid.org/0000-0001-8543-2774. E-mail: yuqian@ sc.edu Huseyin Boler, S.M.ASCE Ph.D. Student, Graduate Research Assistant, Dept. of Civil and Environ- mental Engineering, Univ. of Illinois at Urbana-Champaign, 205 North Mathews, Urbana, IL 61801. E-mail: boler2@illinois.edu Maziar Moaveni, Ph.D., A.M.ASCE Postdoctoral Research Associate, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, 205 North Mathews, Urbana, IL 61801. E-mail: moaveni1@illinois.edu Erol Tutumluer, Ph.D., M.ASCE Professor, Paul F. Kent Endowed Faculty Scholar, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, 205 North Mathews, Urbana, IL 61801. E-mail: tutumlue@illinois.edu Youssef M. A. Hashash, Ph.D., P.E., F.ASCE Professor, William J. and Elaine F. Hall Endowed Professor, John Burkitt Webb Endowed Faculty Scholar, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, 205 North Mathews, Urbana, IL 61801. E-mail: hashash@illinois.edu Jamshid Ghaboussi, Ph.D., M.ASCE Professor Emeritus, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, 205 North Mathews, Urbana, IL 61801. E-mail: jghabous@illinois.edu DOI: 10.1061/(ASCE)GT.1943-5606.0001706 The authors greatly appreciate the valuable comments as well as what this discussion article provides as an opportunity to discuss further the study findings and exchange opinions. The authors are well aware of and greatly appreciate the work conducted by Raymond and Diyaljee (1979) and the importance of conducting both Los Angeles abrasion (LAA) and mill abrasion (MA) tests. Although in this study only LAA testing was con- ducted, in previous publications (e.g., Boler et al. 2012), the writers spoke appropriately about the importance of Raymond and Diyaljee’ s(1979) study findings. Boler et al. (2012) state the following: Accordingly, both toughness and hardness are important properties of aggregates. While former one is a measure of resistance to breakage, latter is more related to durability of surface wearing. Commonly LAA tests are believed to measure aggregate toughness but not as much the hardness property. Using only the LAA value may not be sufficient to predict ballast aggregate degradation characteristics in the field. According to Raymond and Diyaljee (1979), additional tests should also be conducted to measure hardness of aggregates such as the mill abrasion (MA) test. Unlike the LAA test, MA tests tended to create finer material passing 0.075 mm sieve size since degradation was mostly caused by wearing aggre- gates (Selig and Boucher 1990). Klassen et al. (1987) intro- duced the abrasion number (AN) as the sum of LAA and five times MA values. Raymond and Bathurst (1994) stated that AN had good correlations with ballast permanent deformation characteristics from cyclic triaxial testing. The limestone and granite aggregates studied in the LAA tests by the writers already included information on the LAA number, which is determined at 1,000 revolutions of the LAA drum. It is common knowledge to an educated reader that limestone, being a sedimentary rock, is much weaker and more prone to degradation than are igneous granite aggregates. In fact, this is why the AREMA (2016) manual and most railroads typically recommend the use of granite ballast aggregates. The degraded aggregate gradations after the same number of LAA turns was never an assumption adopted/used by the writers. The writers merely plotted degraded gradations after each of 125 or 250 turns and plotted the gradation curves. This process was con- tinued until all gradation curves obtained reached a final fouling index (FI) value of 40, corresponding to a heavily fouled ballast condition as reported by Selig and Waters (1994). The writers agree with the possibility that the field samples may have been contaminated in track. This is a valid comment, and the writers greatly appreciate the insight that the field samples reported in previous studies in the literature may have been contaminated in track by fouling from other materials such as coal fines, windblown dust particles, clay fines, and in-service weathering of the ballast material because of climatic variations during their in-service period before the field samples were taken. Finally, the writers greatly appreciate pointing out the mistake found in the text description of Fig. 15 in the original paper: “ Accordingly, the distribution curves tend to get closer to each other as they shift towards left, representing a higher number of drum turns. ” Undoubtedly, this sentence should have been: “ Accordingly, the distribution curves tend to get closer to each other as they shift towards right, representing a higher number of drum turns. ” References AREMA (American Railway Engineering and Maintenance-of-Way Asso- ciation). (2016). Manual for railway engineering, Lancaster, MD. Boler, H., Wnek, M., and Tutumluer, E. (2012). “Establishing linkages be- tween ballast degradation and imaging based aggregate particle shape, texture and angularity indices. ” Proc., 2nd Int. Conf. on Transportation Geotechnics, Hokkaido Univ., Sapporo, Japan. © ASCE 07018012-1 J. Geotech. Geoenviron. Eng. J. Geotech. Geoenviron. Eng., 2018, 144(5): 07018012 Downloaded from ascelibrary.org by 104.129.36.186 on 10/29/19. Copyright ASCE. For personal use only; all rights reserved.