AGGREGATE BLENDING, ABSORPTION, & SPECIFIC GRAVITY. Aggregate Blending, Absorption & Specific Gravity 1

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1 AGGREGATE BLENDING, ABSORPTION, & SPECIFIC GRAVITY Aggregate Blending, Absorption & Specific Gravity 1

2 Topics to be Covered Aggregate Specific Gravities Gradations Blending Stockpiles Batching Combined Specific Gravities Aggregate Blending, Absorption & Specific Gravity 2

3 Specific Gravity Tests for Aggregates Two tests are needed Coarse aggregate (retained on the 4.75 mm sieve) Fine aggregate (passing the 4.75 mm sieve) Aggregate Blending, Absorption & Specific Gravity 3

4 Apparent Specific Gravity, G sa G sa = Mass of Aggregate, oven dry Volume of aggregate Aggregate Blending, Absorption & Specific Gravity 4

5 Bulk Specific Gravity, G sb Surface Voids G sb = Mass of aggregate, oven dry Vol of agg, + surface voids Vol. of water-perm. voids Aggregate Blending, Absorption & Specific Gravity 5

6 Effective Specific Gravity, G se Surface Voids G se = Mass, dry Effective Volume Solid Agg. Particle Vol. of water-perm. voids not filled with asphalt Absorbed asphalt Effective volume = volume of solid aggregate particle + volume of surface voids not filled with asphalt Aggregate Blending, Absorption & Specific Gravity 6

7 Water Absorption Surface Voids Solid Agg. Particle SSD weight - Oven dry weight Oven dry weight Aggregate Blending, Absorption & Specific Gravity 7

8 Coarse Aggregate Specific Gravity ASTM C127 Dry aggregate Soak in water for 24 hours Decant water Use pre-dampened towel to get SSD condition Determine mass of SSD aggregate in air Determine mass of SSD aggregate in water Dry to constant mass Determine oven dry mass Aggregate Blending, Absorption & Specific Gravity 8

9 Coarse Aggregate Specific Gravity Aggregate Blending, Absorption & Specific Gravity 9

10 Coarse Aggregate Specific Gravity Aggregate Blending, Absorption & Specific Gravity 10

11 Coarse Aggregate Specific Gravity Calculations G sb = A / (B - C) A = mass oven dry B = mass SSD C = mass under water G s,ssd = B / (B - C) G sa = A / (A - C) Water absorption capacity, % Absorption % = [(B - A) / A] * 100 Aggregate Blending, Absorption & Specific Gravity 11

12 Coarse Aggregate Specific Gravity Calculations - Example Problem Given: Mass oven dry (A) Mass SSD (B) Mass under Water (C) Aggregate Blending, Absorption & Specific Gravity 12

13 Coarse Aggregate Specific Gravity Calculations - Example Problem Apparent Specific Gravity - Gsa A / (A - C) Bulk Specific Gravity - Gsb A / (B - C) Absorption, % (B - A) / A Aggregate Blending, Absorption & Specific Gravity 13

14 Coarse Aggregate Specific Gravity Calculations - Example Problem Apparent Specific Gravity - Gsa / ( ) ) = Bulk Specific Gravity - Gsb / ( ) = Absorption, % ( ) / = 0.68 % Aggregate Blending, Absorption & Specific Gravity 14

15 Fine Aggregate Specific Gravity ASTM C128 Dry aggregate Soak in water for 24 hours Spread out and dry to SSD Add 500 g of SSD aggregate to pycnometer of known volume Pre-filled with some water Add more water and agitate until air bubbles have been removed Fill to calibration line and determine the mass of the pycnometer, aggregate and water Empty aggregate into pan and dry to constant mass Determine oven dry mass Aggregate Blending, Absorption & Specific Gravity 15

16 Fine Aggregate Specific Gravity Aggregate Blending, Absorption & Specific Gravity 16

17 Fine Aggregate Specific Gravity Aggregate Blending, Absorption & Specific Gravity 17

18 Fine Aggregate Specific Gravity Aggregate Blending, Absorption & Specific Gravity 18

19 Fine Aggregate Specific Gravity G sb = A / (B + S - C) Calculations A = mass oven dry B = mass of pycnometer filled with water C = mass pycnometer, SSD aggregate and water S = mass SSD aggregate G sb,ssd = S / (B + S - C) G sa = A / (B + A - C) Water absorption capacity, % Absorption % = [(S - A) / A] * 100 Aggregate Blending, Absorption & Specific Gravity 19

20 Fine Aggregate Specific Gravity Calculations - Example Problem Given A = mass oven dry =489.3 B = mass of pycnometer filled with water = C = mass pycnometer, SSD aggregate and water = S = mass SSD aggregate = Aggregate Blending, Absorption & Specific Gravity 20

21 Fine Aggregate Specific Gravity Calculations - Example Problem G sb = A / (B + S - C) = 498.9/( ) 982.3) = G sb,ssd = S / (B + S - C) = 500.1/( ) = G sa = A / (B + A - C) = 498.9/( ) 982.3) = Water absorption = [(S - A) / A] * 100 = ( )/498.9 = 0.24 % Aggregate Blending, Absorption & Specific Gravity 21

22 Aggregate Gradation Distribution of particle sizes expressed as percent of total weight Determined by sieve analysis Aggregate Blending, Absorption & Specific Gravity 22

23 Types Of Gradations * Open graded - Few points of contact - Stone on Stone contact - High permeability * Well graded - Good interlock - Low permeability * Gap graded - Lacks intermediate sizes - Good interlock - Low permeability Aggregate Blending, Absorption & Specific Gravity 23

24 Superpave Aggregate Gradation Percent Passing 100 Design Aggregate Structure max density line 0 control points nom max size max size Sieve Size (mm) Raised to 0.45 Power Aggregate Blending, Absorption & Specific Gravity 24

25 Definitions Nominal Maximum Aggregate Size one size larger than the first sieve to retain more than 10% Maximum Aggregate Size one size larger than nominal maximum size Aggregate Blending, Absorption & Specific Gravity 25

26 Superpave Mix Size Designations Superpave Nom Max Size Max Size Designation (mm) (mm) 19.0 mm mm mm Aggregate Blending, Absorption & Specific Gravity 26

27 9.5 mm 12.5 mm 19.0 mm Aggregate Blending, Absorption & Specific Gravity 27

28 Blending of Aggregates Reasons for blending Obtain desirable gradation Single natural or quarried material not enough Economical to combine natural and process materials Aggregate Blending, Absorption & Specific Gravity 28

29 Blending of Aggregates Numerical method Trial and error Basic formula Aggregate Blending, Absorption & Specific Gravity 29

30 Blending of Aggregates P = Aa + Bb + Cc +. Where: P = % of material passing a given sieve for the blended aggregates A, B, C, = % material passing a given sieve for each aggregate a, b, c,.. = Proportions (decimal fractions) of aggregates to be used in blend Aggregate Blending, Absorption & Specific Gravity 30

31 Blending of Aggregates P = Aa + Bb + P 3/8 = (0.30 * 100) + (0.70 * 100) = Material Aggregate Aggregate No. 1 No. 2 Blend Target % Used a 30.0% b 70.0% Sieve % Passing % Batch % Passing % Batch 3/8 A % B % 100.0% P 100 No % % 97.0% 90 to 100 No % % 79.0% 36 to 76 No % % 63.7% No % % 33.8% No % % 22.7% No % % 16.8% No % % 7.0% 2 to 10 Aggregate Blending, Absorption & Specific Gravity 31

32 Blending of Aggregates P = Aa + Bb + P 3/8 = (0.30 * 100) + (0.70 * 100) = Material Aggregate Aggregate No. 1 No. 2 Blend Target % Used a 50.0% b 50.0% Sieve % Passing % Batch % Passing % Batch 3/8 A % B % 100.0% P 100 No % % 95.0% 90 to 100 No % % 65.0% 36 to 76 No % % 47.5% No % % 25.0% No % % 16.5% No % % 12.0% No % % 5.0% 2 to 10 Aggregate Blending, Absorption & Specific Gravity 32

33 Classroom Problem Aggregate Blending, Absorption & Specific Gravity 33

34 Blending of Aggregates Aggregate 1 Aggregate 2 Aggregate 3 % Agg Used: 70.0% 25.0% 5.0% Sieve Size % Pass % Batch % Pass % Batch % Pass % Batch Blend Specification 3/ % % % 100.0% No % % % 90.9% 90 to 100 No % % % 74.1% 36 to 76 No % % % 41.6% No % % % 32.6% No % % % 22.3% No % % % 16.0% No % % 2 to % 4.4% 34

35 Batching of Aggregate Blends Why Batch? We Want To Reproduce the Desired Gradation for Mix Design Aggregate Blending, Absorption & Specific Gravity 35

36 Batching Things We Need To Know To Batch % of Each Stockpile in Blend % Retained For Each Sieve of Each Stockpile Aggregate Blending, Absorption & Specific Gravity 36

37 Batching M per sieve = %Ret * %Agg * M batch M per sieve = Mass of one aggregate in the blend for one sieve size %Ret = Percent retained on the sieve expressed in decimal form %Agg = The percent of the stock pile to being used in the blend in decimal form EXAMPLE: How much 1.18 mm material do I need from Aggregate #1 for a 4,000 gram batch given the following: % Retained on 1.18 mm sieve = 23.0 % % Agg. #1 Used in Blend = 30.0 % Total Batch wt. = 4000 grams Mass of 1.18 mm material = * * 4000 = grams Aggregate Blending, Absorption & Specific Gravity 37

38 Example Problem Aggregate Blending, Absorption & Specific Gravity 38

39 Batching of Aggregates Total Batch Size: grams Material Aggregate Aggregate Mass of Mass of No. 1 No. 2 Agg Agg % Used 50.0% 50.0% # 1 # 2 Sieve % % % % Passing Retained Passing Retained 3/ No No No No No No No Passing Total Mass Aggregate Blending, Absorption & Specific Gravity 39

40 Classroom Problem Aggregate Blending, Absorption & Specific Gravity 40

41 Batching of Aggregates Total Batch Size: grams Material Aggregate Aggregate Mass of Mass of No. 1 No. 2 Agg Agg % Used 30.0% 70.0% # 1 # 2 Sieve % % % % Passing Retained Passing Retained 3/ No No No No No No No Passing Total Mass Aggregate Blending, Absorption & Specific Gravity 41

42 Combined Specific Gravity G sb = ( P A + P B + P C ) P A P B P C + + G A G B G C Where: P A, P B & P C = percent by mass of each aggregate in blend G A, G B & G C = Bulk Specific Gravity of each aggregate Aggregate Blending, Absorption & Specific Gravity 42

43 - Example Problem - G sb = ( P A + P B + P C ) Where: P A, P B & P C = percent by mass of P A + P B + P C each aggregate in blend G G A G B G A, G B & G C = Bulk Specific Gravity C of each aggregate Based on the information given: P A = 50% P B = 25% P C = 25% G A = G B = G C = G sb = ( ) = Aggregate Blending, Absorption & Specific Gravity 43

44 Questions does it all make sense? Aggregate Blending, Absorption & Specific Gravity 44