Volumetric Properties of High RAP Mixtures Based on Calculated Bulk Specific Gravities
of RAP and Constituent Aggregates
Nassim SabahferMustaque Hossain, Ph.D.,P.E.
Department of Civil EngineeringKansas State University
Outline ● Background● Problem Statement ● Objective● Methodology● Laboratory Testing● Results● Conclusions & Recommendations● Acknowledgements
2
Background - Reclaimed Asphalt Pavement (RAP)
● Approx. 100 million tons of RAP produced each year and 80 million tons are reused
● Useful alternative to virgin aggregates in HMA:
Reduces cost 20% RAP with 5% binder 1% savings in new binder
Enables recycling Conserves energy RAP Stockpile at Shilling
Construction Co., Manhattan, KS
RAP Usage in the US
Problem Statement● Superpave mix design is predominantly used now and
permits use of RAP
● Superpave volumetric mix design is highly dependent on properties like VMA, VFA, and Dust-to-Binder Ratio
● These parameters need blend bulk aggregate specific gravity in the calculation process
● RAP aggregate specific gravity is tricky
Objectives● Compare RAP aggregate bulk specific gravity (Gsb)
obtained from various methods
● Investigate influence of this Gsb on the calculated VMA
● Investigate effect of asphalt absorption assumption
● Study RAP maximum theoretical specific gravity (Gmm) as RAP Gsb
Methodology● Choose RAP sources (5)
● Run maximum specific gravity tests (Gmm) on two replicates of each RAP
● Obtain RAP aggregates via (a) extraction and (b) ignition oven burn off
● Sieve into coarse (plus #4) and fine (minus #4) fractions
● Run bulk specific gravity tests and compare
● Compute VMA and compare
RAP Gradations (12.5 mm NMAS)
00
10
20
30
40
50
60
70
80
90
100
US 56
US 59
US 73
Konza
Shilling
0.075 0.15 0.3 0.6 1.18 2.36 4.75 9.5 12.5 19
Perc
ent P
assin
g
Measured RAP Properties
Source of RAP
Binder Content
(%)*Average Gmm
Asphalt Absorption (Initial Assumption)
(%)
US-56 5.18 2.424 1.5
US-59 6.86 2.470 1.5
US-73 5.77 2.342 1.5
Konza 4.20 2.477 1.5
Shilling 5.80 2.439 1.5
* Ignition oven
Gmm Test (KT-39)
Coarse and Fine Aggregates in RAP Materials
RAP Source Ignition Oven Solvent Extraction
% Coarse % Fine % Coarse % Fine
US-56 36 64 31 69
US-59 31 69 29 71
US-73 30 70 21 79
Konza 34 66 30 70
Shilling 28 72 25 75
RAP Aggregate Bulk Specific Gravity
● Method #1 ● Split extracted aggregates into coarse and fine
fractions● Determine bulk specific gravity of each fraction
● Method #2● Same as #1; use burned off aggregates
RAP Aggregate Bulk Specific Gravity
● Method #3 ● Determine RAP Gmm● Determine RAP binder content ● Calculate Gse of RAP:● Assume or know asphalt absorption, Pba● Calculate Gsb of RAP aggregate:
Aggregate Specific Gravity Test Results
US-56 US-59 US-73 Konza Shilling0
0.5
1
1.5
2
2.5
32.663 2.706
2.593 2.667 2.6912.557 2.471
2.319 2.3362.473
2.5672.436
2.244 2.3252.454
2.424 2.472.342
2.477 2.439
Gsb (Gse method)Gsb (Ignition oven)Gsb (Solvent extraction)RAP Gmm
Statistical Analysis
● Comparison of Gsb
Test method Compared to Reject H0
Gse Ignition oven Yes
Gse Solvent extraction Yes
Gse RAP Gmm Yes
Ignition oven Solvent extraction No
Ignition oven RAP Gmm No
Solvent extraction RAP Gmm No
Changes in Gsb as a function of asphalt absorption
1.2 1.5 1.82.5
2.55
2.6
2.65
2.7
2.75
2.671 2.663 2.655
2.713 2.706 2.697
2.6 2.593 2.585
2.675 2.667 2.659
2.699 2.691 2.683
US-56US-59US-73KonzaShilling
Asphalt Absorption (%)
Gsb
VMA Obtained Using Gsb from Different Methods (Konza RAP)
20% RAP 30% RAP 40% RAP 30% FRAP 40% FRAP0
2
4
6
8
10
12
14
16
14 14.1 14 14 14
11.710.6
9.210.4
9.2
12.4 12.211.4
1211.4
9 GseGsb (Ignition)Gsb (Extract)Gmm RAP
VMA (%)
KDOT Require-ment
VMA Obtained Using Gsb from Different Methods (Shilling RAP)
20% RAP 30% RAP 40% RAP 30% FRAP 40% FRAP0
2
4
6
8
10
12
14
16
14.1 14 14.2 14.1 14.312.6
11.811.3
11.9 11.412.511.5
1111.7
11.112.4
11.410.8
11.510.9
GseGsb (Ignition)Gsb (Extract)RAP Gmm
VMA (%)
KDOT Requirement
Statistical Analysis
VMA obtained from Compared to Reject H0
Gse Ignition oven Yes
Gse Solvent extraction Yes
Gse RAP Gmm Yes
Ignition oven Solvent extraction No
Ignition oven RAP Gmm No
Solvent extraction RAP Gmm No
Differences in calculated VMA as a function of RAP content
20 22 24 26 28 30 32 34 36 38 401
1.5
2
2.5
3
3.5
4
4.5
5
5.5
Gse and Ignition oven (Konza RAP)
Gse and Solvent extraction (Konza RAP)
Gse and Ignition oven (Shilling RAP)
Gse and Solvent extraction (Shilling RAP)
Percentage of RAP
Diff
eren
ce in
%V
MA
Conclusions● Gsbs obtained from the ignition oven and solvent
extraction methods are similar but both are different from that based on Gse
● Statistically RAP Gmm is not significantly different from Gsb obtained from the ignition oven or solvent extraction method
● VMA obtained from Gse-based Gsb is significantly different from the VMA’s obtained from other Gsbs
● Difference in VMA increases considerably as the RAP content increases
Recommendations
● RAP aggregate Gsb using either from the extraction or the ignition oven test method should be used in design of Superpave mixtures with RAP
Acknowledgements● This study has been sponsored by the Kansas
Department of Transportation (KDOT) ● Project Monitor: Brian Coree, Ph.D., P.E.
Thank You
