AASHTO PP 41-02 pdf free download
AASHTO PP 41-02 pdf free download.Designing Stone Matrix Asphalt (SMA).
4. SUMMARY OF THE PRACTICE
4.1. Materials Selection- Asphalt binder, aggregate, mineral illers, and stabilizing additives that meet the applicable specification are selected.
4.2. . Selecting Optimum Gradation- -The three recommended trial aggregate gradations from the selected aggregates are blended. The dry-rodded unit weight for the coarse aggregate for each trial gradation is determined in accordance with T 19/T 19M. For each trial gradation, an initial trial asphalt binder content is selected and at least two specimens are compacted in accordance with T 312. Where no previous history is available, an initial trial asphalt binder content between 6.0 and 6.5 percent is recommended. The gradation is selected to ensure that minimum VMA requirements and stone-on-stone contact are achieved.
4.3. Selecting Design Binder Content- -Replicate specimens are compacted in accordance with T 312 at three binder contents. The design binder content is selected on the basis of satisfactory conformance with the requirements of Section 10 (Note 2). Note 2- _When an SMA mix cannot be designed within the minimum binder content requirements, the guidelines given in Table X1.11 can be used to establish minimum binder content requirements based on the combined-aggregate bulk specific gravity.
5.4.3. Into separate pans for each test specimen, weigh sufficient material to produce compacted samples of the desired volume, approximately 4700 g. Mix the aggregate in each pan. Place the aggregate in an oven and heat to a temperature not exceeding the mixing temperature established in Section 5.3 by more than approximately 28°C (50°F). Heat the asphalt binder to the established mixing temperature. The stabilizing additive is added to the heated aggregate prior to the introduction of the asphalt binder. Note 4 -It is recommended that the stabilizing additive be manually mixed with the heated aggregate. This procedure is needed to ensure an even distribution of the stabilizing additive during the laboratory mixing process. The use of stabilizing additives generally requires slightly longer mixing times.
5.4.4. Form a crater in the dry blended aggregate and stabilizing additive, and weigh the preheated required amount of asphalt binder into the crater. Care must be exercised to prevent loss of the mix during mixing and subsequent handling. At this point, the temperature of the aggregate and asphalt binder shall be within the limits of the mixing temperature established in Section 5.3. Mix the aggregate and asphalt binder rapidly until the aggregate is thoroughly coated.
5.5. Compaction of Specimens- The compaction temperature is determined in accordance with Section 5.3. Laboratory samples of SMA are short-term conditioned in accordance with R 30 and then compacted for 100 gyrations. Note 5- When aggregates have a Los Angeles Abrasion loss value greater than 30 percent, the desirable number of SGC design gyrations is 75.
6. SELECTION OF TRIAL GRADATIONS
6.1. The trial gradations must be selected to be within the desired specification range as defined in MP 8. To design an SMA mixture, it is recommended that at least three trial gradations be initially evaluated. It is suggested that one of the trial blends fall along the coarse limits, one along the fine limits, and one in the middle of the gradation bands as defined in MP 8. When the bulk specific gravities of the different aggregates to be used in the mixture vary by more than 0.2, the trial blend gradations should be based upon volumetric percentage. An example problem illustrating how to blend aggregates based on volume is given in Appendix X1.1.AASHTO PP 41-02 pdf download.
