598 CIVL Asphalt Paving Materials
AGGREGATE BLENDING, ABSORPTION, & SPECIFIC GRAVITY
Aggregates
Topics to be Covered
Specific Gravity Tests for Aggregates
Aggregate specific gravities Gradations Blending stockpiles
Two tests are needed
Coarse aggregate (retained on the 4.75 mm sieve) Fine aggregate (passing the 4.75 mm sieve)
Apparent Specific Gravity, Gsa
Bulk Specific Gravity, Gsb
Surface Voids
Gsb =
Mass of aggregate, oven dry Vol of agg, + surface voids
Mass of Aggregate, oven dry Gsa = Volume of aggregate
Vol. of water-perm. voids
1
Effective Specific Gravity, Gse
Surface Voids
Water Absorption
Surface Voids
SSD weight - Oven dry weight
Gse =
Mass, dry
Effective Volume
Solid Agg. Particle
Vol. of water-perm. voids not filled with asphalt Absorbed asphalt
Solid Agg. Particle
Oven dry weight
Effective volume = volume of solid aggregate particle + volume of surface voids not filled with asphalt
Coarse Aggregate Specific Gravity
ASTM C127
Coarse Aggregate Specific Gravity
Dry aggregate Soak in water for 24 hours Decant water Use pre-dampened towel to get SSD precondition Determine mass of SSD aggregate in air Determine mass of SSD aggregate in water Dry to constant mass Determine oven dry mass
Coarse Aggregate Specific Gravity
Coarse Aggregate Specific Gravity
Calculations
Gsb = A / (B - C)
A = mass oven dry B = mass SSD C = mass under water
Gs,SSD = B / (B - C) Gsa = A / (A - C) Water absorption capacity, %
Absorption % = [(B - A) / A] * 100
2
Coarse Aggregate Specific Gravity
Calculations - Example Problem
Coarse Aggregate Specific Gravity
Calculations - Example Problem
Given:
Apparent Specific Gravity - Gsa
A / (A - C)
Mass oven dry - 3625.5 (A) Mass SSD - 3650.3 (B) Mass under Water - 2293.0 (C)
Bulk Specific Gravity - Gsb
A / (B - C)
Absorption, %
(B - A) / A
Coarse Aggregate Specific Gravity
Calculations - Example Problem
Fine Aggregate Specific Gravity
ASTM C128
Apparent Specific Gravity - Gsa
3625.5/ (3625.5-2293.0) = 2.721 (3625.5-
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
Bulk Specific Gravity - Gsb
3625.5 / (3650.3 - 2293.0) = 2.671
Pre-filled with some water PreAdd more water and agitate until air bubbles have been removed Fill to calibration line and determine the mass of the pycnometer, aggregate and water pycnometer, Empty aggregate into pan and dry to constant mass Determine oven dry mass
Absorption, %
(3650.3 - 3625.5) / 2293.0 = 0.68 %
Fine Aggregate Specific Gravity
Fine Aggregate Specific Gravity
3
Fine Aggregate Specific Gravity
Calculations
Gsb = A / (B + S - C)
Fine Aggregate Specific Gravity
A = mass oven dry B = mass of pycnometer filled with water C = mass pycnometer, SSD aggregate and pycnometer, water S = mass SSD aggregate
Gsb,SSD = S / (B + S - C) Gsa = A / (B + A - C) Water absorption capacity, %
Absorption % = [(S - A) / A] * 100
Fine Aggregate Specific Gravity
Calculations - Example Problem
Fine Aggregate Specific Gravity
Calculations - Example Problem
Given
A = mass oven dry =498.9
B = mass of pycnometer filled with water = 666.5 C = mass pycnometer, SSD aggregate and pycnometer, water = 982.3 S = mass SSD aggregate = 500.1
Gsb = A / (B + S - C) = 498.9/(666.5+500.1-982.3) 498.9/(666.5+500.1= 2.707 Gsb,SSD = S / (B + S - C) = 500.1/(666.5+500.1-982.3) 500.1/(666.5+500.1= 2.714 Gsa = A / (B + A - C) = 498.9/(666.5+498.9-982.3) 498.9/(666.5+498.9= 2.725 absorption Water = [(S - A) / A] * 100 = (500.1-498.9)/498.9 = 0.24 % (500.1-
Aggregate Gradation
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
Distribution of particle sizes expressed as percent of total weight Determined by sieve analysis
4
Superpave Aggregate Gradation
Percent Passing
100 max density line
Design Aggregate Structure
restricted zone
nom max size max size
control points
0 .075 .3 2.36 4.75 9.5 12.5 19.0
100 100 90 72 65 48 36 22 15 9 4
Definitions
100 99 89 Nominal Maximum Aggregate Size 72 one size larger than the first sieve to65 48 retain more than 10% 36 Maximum Aggregate Size 22 one size larger than nominal 15 maximum size 9 4
Sieve Size (mm) Raised to 0.45 Power
Superpave Mix Size Designations
9.5 mm
Superpave Designation 19.0 mm 12.5 mm 9.5 mm
Nom Max Size (mm) 19 12.5 9.5
Max Size (mm) 25 19 12.5
12.5 mm
19.0 mm
Blending of Aggregates
Reasons for blending
Blending of Aggregates
Numerical method
Obtain desirable gradation Single natural or quarried material not enough Economical to combine natural and process materials
Trial and error Basic formula
5
Blending of Aggregates
P = Aa + Bb + Cc + ....
Where:
Blending of Aggregates
P = Aa + Bb + ...
Material % Used % Used Sieve Sieve 3/8 3/8 No. 4 No. 4 No. 8 No. 8 No. 16 No. 16 No. 30 No. 30 No. 50 No. 100 No. 50 No. 200 No. 100 No. 200
P3/8 = (0.50 * 100) + (0.50 * 100) = 100.0
Blend Target
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 Aggregate No. 1 No. 2 a 50.0% b 50.0% % Passing % Batch % Passing % Batch % Passing % Batch % Passing % Batch 50.0% 50.0% B 100 A 100 100 100 45.0% 50.0% B 100 A 90 90 100 30 100 15.0% 50.0% 30 100 44.0% 7 88 3.5% 7 88 3 47 1.5% 23.5% 3 47 1 32 0.5% 16.0% 1 32 0.0% ...