Evaluation of Lime Kiln Dust as a Mineral Filler in Stone Matrix Asphalt

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$influence of filler fractional voids on mastic and mixture performance$

West and James 3 including soil conditioning and stabilization, industrial waste stabilization, Portland cement production, and agricultural uses. Unused LKD is usually stockpiled near the lime plant but can be disposed of in approved landfills. Case Studies of the Use of Lime Kiln Dust as a Mineral Filler in SMA Alabama Lime kiln dust was used in several SMA projects in Alabama between 2001 and 2002. According to the Alabama Department of Transportation, a number of these SMA projects exhibited discolored surfaces soon after construction. The discoloration was generally observed as a blotchy grey color. One Alabama project with lime kiln dust did result in more significant pavement problems. This SMA project was constructed on Highway 80 in Selma, Alabama in the summer of 2002. This project was intended to correct significant rutting on this heavy trafficked section of roadway. The existing rutted pavement was milled five inches and two layers of SMA were placed to complete the reconstruction. The first layer was a 1-½ inch Maximum Aggregate Size (MAS) SMA which was placed 3 to 3.5 inches thick. The surface layer was a ½ inch MAS SMA that was placed 1.5 to 2 inches. The 1-½ inch SMA mix contained nine percent lime kiln dust and the ½ inch SMA mix contained six percent lime kiln dust. In less than one year after construction, several areas of distress were observed. Flushing of the surface was observed, followed by rutting, shoving, cracking, and potholes. A light tan powder was evident along the edge of pavement in the distressed areas. Cores taken from the pavement in the distressed areas found that the underlying SMA layer was severely stripped. It was suspected that the lime kiln dust in the first layer of SMA contained excessive amount of available calcium oxide. The Alabama Department of Transportation subsequently disapproved LKD as a mineral filler for SMA mixtures. Texas In August 2003, an SMA project was started on SH-105 in Sour Lake, Texas. Paving of the SMA began with a test section on the project located. The construction of the SMA test section was cut short due to extended heavy rains in the area. A few days after the rain, the entire surface of the SMA pavement had turned a grayish white color. The surface of the SMA was friable and the test section had to be removed and replaced. The investigation of the failure led to the mineral filler which was determined to be a lime kiln dust. Subsequent tests on samples of the LKD from the contractor’s mineral filler silo indicated the LKD contained 54 percent available calcium oxide content, an unusually high amount. The SMA mix design and TSR tests, which had been conducted several months before, did not indicate any problems. However, lab tests with the QC samples of the SMA did reveal that the mix was reactive in water. It was apparent that the characteristics of the LKD mineral filler had changed from the time the mix designs were performed and when the mineral filler was delivered to the contractor’s plant. Kentucky In September 2004, a project using lime kiln dust in SMA was completed on AA highway near Bracken, Kentucky. The mix design contained six percent lime kiln dust and the available lime TRB 2006 Annual Meeting CD-ROM Original paper submittal – not revised by author. 3
West and James 4 content for this mineral filler was between 20 and 22 percent. No problems were encountered with the use of lime kiln dust at any point in the project. Mix production went well and target roadway densities were met despite a 45 mile haul. Production volumetric properties were very consistent and on target. The pavement has performed very well to date. No pavement discoloration has been observed. LABORATORY EVALUATION Physical Characteristics of LKD and Marble Dust Key physical characteristics of the mineral fillers including gradation, specific gravity, and Rigden voids were determined. The gradations of the mineral fillers were determined using a Coulter Model LS-200 particle size analyzer. Specific gravities of the mineral fillers were determined using the method described in section 21 of ASTM C 110-00. The Rigden voids test was performed on both mineral fillers in accordance with the procedure described in NAPA publication IS 101 (8). SMA Mix Designs The SMA component materials selected for this study included a standard set of materials used by NCAT in several other SMA research studies. Information on the materials is provided in Table 1. The asphalt binder used in the study was a PG 67-22. Most agencies would normally specify a higher PG grade, such as a PG 76-22 instead of the PG 67-22 for highway construction projects. However, the PG 67-22 was intentionally selected because it was believed that the softer asphalt grade would accentuate the effects the mineral fillers in the subsequent moisture susceptibility tests. Mix designs were completed in accordance with AASHTO PP 41 Designing Stone Matrix Asphalt (6). Samples were compacted in a Superpave Gyratory Compactor to 75 gyrations. Moisture Damage Susceptibility A series of tests were performed to assess the potential for moisture damage and/or reactions of available lime with water for the SMA mixtures. The first series of tests utilized the industry’s most commonly specified moisture damage test, AASHTO T283. This test is also referred to as the modified Lottman test or the TSR (tensile strength ratio) test. Additional moisture damage susceptibility tests were performed with harsher conditioning procedures. Conditioning and testing of these specimens followed the procedure in AASHTO T 283 except that one set of specimens was subjected to two freeze-thaw cycles and another set was subjected five freezethaw cycles before the conditioned tensile strengths were determined. Another series of TSR specimens were subjected to one freeze-thaw cycle, but the hot water soak period was extended for 48 and 96 hours. Samples of the SMA mixtures with the LKD and rock dust were also prepared and tested to evaluate the potential for expansion due to reaction of free lime in the mineral filler with water. Samples were compacted in the Superpave Gyratory Compactor in the same manner as for T283. This yielded 150 mm diameter specimens with approximately 6% air voids and 95 TRB 2006 Annual Meeting CD-ROM Original paper submittal – not revised by author. 4
Page 1 and 2: EVALUATION OF A LIME KILN DUST AS A
Page 3: West and James 2 EVALUATION OF A LI
Page 7 and 8: West and James 6 The results of the
Page 9 and 10: West and James 8 The performance of
Page 11 and 12: West and James 10 TABLE 1. Material
Page 13 and 14: West and James 12 TABLE 3. Mix Desi
Page 15 and 16: West and James 14 TABLE 5. Results
Page 17 and 18: West and James 16 TABLE 7 Effect of
Page 19 and 20: West and James 18 LIST OF FIGURES F
Page 21 and 22: West and James 20 FIGURE 2. Photogr
Page 23: West and James 22 Rut Depth (mm) 40

Evaluation of Lime Kiln Dust as a Mineral Filler in Stone Matrix Asphalt

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