CVEEN3510_Homework 8 - Solutions

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University of Utah *

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3510

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Civil Engineering

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Apr 3, 2024

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pdf

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Page 1 of 4 CVEEN 3510-001 Civil Engineering Materials Homework 8- Grading Scheme Note: Only key points are mentioned in the grading scheme. Your answers have to be in full sentences 1) An asphalt concrete mixture includes 94% aggregate by weight. The specific gravities of aggregate and asphalt are 2.65 and 1.0, respectively. If the bulk density of the mix is 147 pcf, what is the percent voids in the total mix? Note: Use volumetric analysis (including the phase diagram) and ignore the absorption of asphalt by the aggregates. (10 points) Assume total volume V t = 1 ft 3 Determine mass of mix and components: Total mass = 1 x 147 pcf = 147 lb Mass of aggregate = 0.94 x 147 = 138.2 lb Mass of asphalt binder = 0.06 x 147 = 8.8 lb Determine volume of components: V s = 138.2/ (2.65 (62.4)) = 0.836 ft 3 Ignore absorption, therefore V be = V b V b = 8.8/ (1.0 (62.4)) = 0.141 ft 3 Determine volume of voids: V v = V t V s V b = 1-0.836-0.141 = 0.023 ft 3 Volumetric calculations: VTM = (V v / V t ) 100 = (0.023/1.00) 100 = 2.3% 2) An asphalt concrete specimen has the following properties: Asphalt content = 5.5% by total weight of mix, Bulk specific gravity of the mix = 2.475, Theoretical maximum specific gravity = 2.563, Bulk specific gravity of aggregate = 2.689. Ignoring absorption, calculate VTM, VMA, and VFA. (6 points) Eqn 9.8 of the textbook VTM = 100 {1- (2.475/2.563} = 3.4% Eqn 9.9 of the textbook VMA = 100 {1- 2.475( 94.5 /2.689)} = 13.0% Eqn 9.10 of the textbook VFA = 100 {0.130 0.034/0.130} = 73.8%
Page 2 of 4 3) Using the AASHTO T 283 test, three HMA specimens were freeze thaw conditioned and three were unconditioned. All the specimens had a diameter of 150 mm. Table below shows the thickness and load at failure of each specimen. (10 points) Determine: a) The tensile strength of each specimen in MPa. b) The average tensile strength of the conditioned and unconditioned specimens. c) The tensile strength ratio (TSR). d) Does the mix pass the Superpave criteria for moisture susceptibility? Thickness (mm) 64 63 63 63 64 62 Force (N) 11500 10500 10800 9000 9500 9200 Tensile strength (MPa) 0.76 0.71 0.73 0.61 0.63 0.63 Average tensile strength (MPa) 0.73 0.62 TSR = 0.62/0.73 = 85% . The mix passes the Superpave criteria for moisture susceptibility. 4) Name three methods of asphalt pavement recycling. Which one of them is the predominant method? Briefly summarize this method. (6 points) Section 9.12 of the textbook Recycling can be divided into three types: surface recycling, central plant recycling, and in-place recycling. Central plant recycling is the predominant type of recycling and offers the highest quality product. Central plant recycling is performed by milling the old pavement (Figure 9.41) and sending the reclaimed asphalt pavement (RAP) to a central asphalt concrete plant, where it is mixed with virgin aggregates and asphalt binder in the asphalt plant. The RAP material generally does not have the properties required for quality asphalt concrete so it is added to virgin aggregate and asphalt. The virgin materials are used to correct deficiencies in the RAP. The need to correct deficiencies in the RAP with virgin materials limits the percent RAP; generally the content of RAP ranges from 10 to 50%.
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