Q2. (a) Aggregate gradation determines almost every important physical property including stiffness, permeability, and workability. Briefly discuss the difference between open graded and gap graded. (6 marks) (b) The following Table Q2 (a), Table Q2 (b) and Figure Q2 (a) show the design requirements and test results of laboratory Marshall mix design for AC14 of a road project. Using the data given, answer the following questions: For which layer of road the Laboratory Marshall mix design was conducted? Density, Mg/cu.m 11. Determine the optimum bitumen content for the AC14 mixture. Please complete Table Q2(a) and plot the graphs in Figure Q2(a). Evaluate the results and compare with the standard requirements. TABLE Q2 (a): Results of Marshall Mix Design for AC14 (19 marks) (25 marks) (Bitumen Bulk Void filled Void in Stability Flow Content Specific bitumen total mix Stiffness (kg) (mm) (%) Gravity (%) (%) 4.0 2.282 54.4 8.4 1164 3.30 4.5 2.293 58.0 7.2 1321 3.50 5.0 2.335 65.0 5.5 1600 3.55 5.5 2.320 72.0 4.1 1550 3.65 6.0 2.300 79.5 3.8 1392 3.90 Stability, kg 1700 1600 1500 1400 1300 1200 1100 4.0 4.5 5.0 Bitumen Content, % 5.5 6.0 2.34 2.33 2.32 2.31 2.30 2.29 2.28 2.27 4.0 4.5 5.0 5.5 6.0 Bitumen Content, % VFB, % Stiffness, kg/mm VTM, % 4 9 00 8 7 10 3 4.0 4.5 500.0 450.0 400.0 350.0 300.0 4.0 4.5 5.0 Bitumen Content, % 5.0 Bitumen Content, % 5.5 6.0 5.5 6.0 85 80 75 70 65 60 55 50 4.0 4.5 5.0 5.5 in Bitumen Content, % 6.0 Flow, mm 5.00 4.50 4.00 3.50 3.00 4.0 4.5 5.0 5.5 6.0 Bitumen Content, % FIGURE Q2(a): Marshall Design Graphs TABLE Q2(b): Marshall Design Specification (JKR, 2008) Parameter Stability Flow Stiffness Voids in total mix Wearing course Binder course >800 kg >800 kg 2-4 mm 2-4 mm >200 kg/mm >200 kg/mm 3-5% 3-7% (VTM) Voids filled with 70-80% 65-75% bitumen (VFB)