Effect of Asphalt Rejuvenating Agent used in Hotin-Place Recycling on Reclaimed Asphalt Pavement Presented By Masoumeh Tavakol Department of Civil Engineering Kansas State University By Nassim Sabahfar, Mustaque Hossain, and Greg Schieber 2015 Mid-Continent Transportation Research Symposium, Ames, Iowa, August 2015 1
Overview Introduction Objective
Asphalt binder price increase Greener alternative Cost- effective & sustainable replacements for virgin paving materials In-place recycling Improve skid resistance Improve ride quality Minimize traffic disruption Minimize construction time Roadway replaced at its original level
Cold In-Place Recycling (CIR) Mill the first few inches of the existing pavement Mix with asphalt emulsion or a different additive Lay back in place/put wearing coarse on top In-Place Recycling Full-Depth Reclamation (FDR) Hot In-Place Recycling (HIR) Rip off the full thickness of HMA * + base/subbase layers Mix with an additive to make a uniform blend Lay back in place/put final HMA layer on top * hot-mix asphalt Heat the existing HMA layer Scrape off the first few inches Mix with ARA/virgin binder and virgin aggregates Lay back in place and open to traffic Applicable In-Place method depends on the severity of distresses and thickness of the existing HMA pavement
The most effective way of recycling HMA is to re-use material in its original format Higher proportions of RAP in construction of new pavements HIR recycles 70% to 100% of the existing, aged asphalt pavement and is being increasingly used in Kansas: Is the current practice effective in maintaining the performance requirements for another service life, which can be up to 10 years.
Investigate the effectiveness of current practice (addition of ARA) by conducting different performance tests Investigate oxidation with aging and rejuvenation with ARA Study the miscibility as it occurs; Between aged binder and ARA Between aged and virgin binders in presence of ARA Test the uniformity of different blends in the laboratory
HIR Sample Collection Mixture Studies Extract RAP Binder Low Temp Moisture Susceptibility Cracking & Rutting Propensity Micro structure & Miscibility Studies Rheology Studies TSRST KT - 56 OT @ 21 o C OT @ 4 o C Flow No. HWTD Dynamic Modulus SEM EDT DSR BBR Mechanical Evaluation Rheological & Miscibility Evaluation
HIR Train
Sample Collection In front of the Paver (No ARA) Behind the Paver (with ARA)
Sampling Locations in this Study K14 US 56 US 59
Modified Lottman Test (KT 56) Moisture Susceptibility Determines the performance reduction after one freeze/thaw cycle Hot water bath Saturation Freezing Prep - Average tensile strength of the samples that are undergone one freeze/thaw cycle is compared to average tensile strength of dry samples - The mixture is acceptable if Tensile Strength Ratio (TSR) is more than 80%
Texas Overlay Test (OT) Cracking Propensity Determines the resistance to cracking (reflection cracking) of HMA mixture - Higher number of cycles before failure shows better cracking performance - Failure is defined as 7% reduction in initial load carrying capacity (test was ceased after reaching 1,000 cycles)
Flow Number Test Rutting Propensity Evaluates rutting resistance of HMA mixture - Primary Zone: Deformation rate decreases with loading cycle - Secondary Zone: Deformation rate is constant with loading cycles - Tertiary Zone: Deformation rate increases with loading cycles - Flow number is the number of load pulses when the minimum rate of change in permanent strain has reached - Higher number of load cycles before failure indicates better rutting resistance
Rutting Propensity Hamburg Wheel Tracking Device Test Evaluates rutting and stripping resistance of HMA mixture - Higher number of wheel passes before reaching a certain rut depth indicates better rutting performance - The test was ceased when -20mm rut depth or 40,000 wheel passes was reached
Dynamic Modulus Test Cracking & Rutting Propensity Evaluates rutting and fatigue resistance of HMA mixture Applied Stress Measured Strain - E* is defined as pick-to-pick stress divided by pick-to-pick strain - Test is conducted at six frequencies and three temperatures - Higher E* resembles stiffer HMA mixture
Microstructure & Miscibility Scanning Electron Microscope (SEM) Analysis surface morphology and miscibility on microstructure level 5 5 mm Silicon wafer - A focused beam of electron, shot from the electron gun, scans the sample - Secondary electrons, emitted from surface due to excitation caused by primary electron, are detected - Detectable signals contain information of sample s surface topography and composition - Nanometer scale resolutions are achievable using SEM
Exudation Droplet Test (EDT) Microstructure & Miscibility Evaluates the exudation tendency of the asphalt binder - Droplets of asphalt binder on marble plates are kept under Nitrogen flow for 96 hours - Using a microscope, droplets are checked under UV light - Rings thicker than 1.5 mm show high exudation tendency of asphalt binder, indicating a non homogenous mixture
Moisture Susceptibility Test Results (KT-56) Avg. Strength (kpa) 2,000 1,800 1,600 1,400 1,200 1,000 800 600 400 %TSR=92 %TSR=74 %TSR=86 %TSR=80 %TSR=53 %TSR=55 Avg. Dry Strength Avg. Wet Strength 200 0 US-56 With ARA US-56 W/O ARA US-59 With ARA US-59 W/O ARA K-14 With ARA K-14 W/O ARA ARA made significant improvements on the moisture susceptibility of HIR mixtures (p- value = 0.041)
Texas Overlay Test Results (OT) 1,200 Number of Cycles Before Failure 1,000 800 600 400 200 Avg. no of cycles before failure at 21C Avg. no of cycles before failure at 4C 0 US-56 With ARA US-56 W/O ARA US-59 With ARA US-59 W/O ARA K-14 With ARA K-14 W/O ARA High standard deviation and unpredictable performance at both temperatures No significant changes in performance at these temperatures or in mixtures with or without ARA
Flow Number Test Results 8,000 Flow Number Cycles 7,000 6,000 5,000 4,000 3,000 2,000 1,000 0 Mixture with ARA Mixture W/o ARA US - 56 US- 59 K-14 Two tailed t-test results P-value = 0.086 P-value = 0.055 P-value = 0.26 No significant changes in performance of the HIR mixtures with or without ARA
Hamburg Wheel Track Device (HWTD) Test Results 40,000 No. of wheel passes 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 Rut depth at 40,000 cycles = -9.3 mm Rut depth at 40,000 cycles = -2.6 mm Rut depth at 40,000 cycles = -2.5 mm Rut depth at 40,000 cycles = -13.5 mm US-56 US-59 K-14 With ARA W/O ARA Mixtures with ARA had fewer number of reps before reaching 20 mm rut depth KDOT min. requirement was met by all mixtures
Dynamic Modulus Test 10,000 1,000 E* (ksi) 100 US 56 With ARA US 56 W/O ARA 10 US 59 With ARA US 59 W/O ARA K 14 With ARA K 14 W/O ARA 1 1.E-06 1.E-04 1.E-02 1.E+00 1.E+02 1.E+04 1.E+06 Reduced Frequency (Hz) Addition of ARA made HIR mixes softer
Exudation Droplet Test (EDT) Results Ring Diameter Blend with ARA Blend w/o ARA K-14 1.53 mm 1.23 mm US-56 1.42 mm 1.29 mm US-59 1.76 mm 1.66 mm ARA does not stay embedded in the binder matrix and migrates to the aggregates The mixture of aged binder and ARA, made at field, is not uniform Based on the temperature and time of mixing, a balanced mixture can be achieved
Introduction US-59 with ARA US-59 W/O ARA+50% VB US-59 W/O ARA US-59 W/O ARA+20% ARA US-59 W/O ARA Scanning Electron Microscope (SEM) Imaging
Energy Dispersive X-ray Spectroscopy (EDXS) Expected combination: C: 82.8% H: 10.2% N: 0.7% S: 3.8% O: 0.7% C: 67.3% O: 24.9% Pb: 6.5% Ni: 0.8% Fe: 0.4% Na: 0.2% C: 85.9% O: 6.3% Al: 4.2% S: 2.6% Si: 1.0% C: 88.5% O: 8.6% S: 1.1% Si: 0.8% Na: 0.6% Al: 0.4% C: 78.4% O: 14.7% Pb: 4.1% Si: 1.5% Br: 0.8% Na: 0.5%
US-59 with ARA +50% VB + 15ARA C: 93% O: 5.6% Si: 0.7% S: 0.7% C: 62.3% O: 29.2% Al: 1.9% Si: 5.8% S: 0.8% C: 59.9% O: 5.1% Si: 1.3% Fe: 33.7%
Results & Discussions Summary 1. Mechanical Properties: HIR mixtures with and without ARA could easily pass KDOT minimum rut depth requirements in HWTD test Dynamic modulus test results confirmed ARA addition would result in softer asphalt mixture OT test results were not sensitive to the addition of ARA Flow number test results did not show any significant improvement when ARA was added KT-56 test results showed higher TSRs for mixtures with ARA with significant improvements
Results & Discussion Summary 1. Miscibility/Rheology : EDT results showed that the addition of ARA tends to constitute a nonhomogenous binder SEM images showed great diversity in aged HIR binder microstructure as well as physical dispersion of different particles Variable nature of aged HIR binder, as displayed by SEM images and EDXS, can be a reason for the varying mechanical test results of HIR
Acknowledgements This study has been sponsored by