TxDOT
Forensic Investigation for Micorsurfacing on US69 Jenny Li, PhD, P.E. Feng Hong, PhD, P.E.
2017 Southeast Pavement Preservation Partnership Annual Meeting
Background The new microsurfacing placed on US69 in May 2015 started showing premature pavement distress. Flushing in the wheel paths Pushing in several locations
2
Objective To determine the cause of the flushing and instability observed in the micro-surfacing
3
Forensic Study Procedure Field study Distress survey Coring Skid
Laboratory test
Binder content Gradation Binder stiffness X-Ray Florescence (XRF) fingerprinting
4
Coring Locations Site 1: RM 436-0.05, Southbound, Moderate Flushing Site 2: RM 436+0.9, Southbound, Slight Flushing, No seal coat underneath Site 3: RM 442+0.0, Southbound, Different Microsurfacing Project with no performance issues Site 4: RM 440+0.63, Northbound, Pushing/Instability, Flushing Site 5: RM 440+0.61, Northbound, Good performance
5
Site 1 SB (pushing, flushing)
6
Seal from the North End (Typical Condition before Micro)
7
Site 2 Northbound, Slight Flushing
8
Site 3 – SB Microsurfacing from Different Contractor
9
Site 4 NB, bad area, pushing, some milling already done
10
Site 5 Beginning of a Long Stretch of Good Performance
11
Skid Test
Northbound
Southbound Skid Number
Skid Number
Distance (miles)
Distance (miles)
12
What’s Next? Laboratory testing and evaluation on the cores
13
Bonding Six-inch diameter cores were taken in both the left and right wheel path. Intact cores were obtained at all locations revealing a very good bond of both the microsurfacing to the seal coat and of the seal coat to the asphalt surface.
14
Microsurfacing layer The microsurfacing on the cores was trimmed away from the surface. The asphalt was extracted and recovered using solvent extraction methods from the microsurfacing to determine the following: • Asphalt content, % • Stiffness of the asphalt (by determining the higher end of the PG grade) • XRF fingerprinting to identify individual components in the binder.
15
Asphalt Content and Performance Grade
Location
AC Content, %
PG Grade
Site 1 LWP
7.9
88+
Site 1 RWP
7.1
79
Site 2 LWP (3/4in thick)
9.3
88+
Site 2 RWP
6.2
78
Site 3 (other project)
5.9
81
Site 4 LWP
8.3
88+
Site 5 RWP
6.3
76
Target from Design
8.3
-
16
Intensity
XRF Results on Recovered Binders
17
Gradation From Mix Design Provided by District
From Recovered Mix in the Cores and Stockpiles
Sieve
Ext Agg from Site 1 RWP
Avg of 4 TxDOT stockpile samples
3/8
0.8
0.8
#4
13.8
6.5
#8
57.6
45.3
#16
79.4
67.1
#30
87.3
77.1
#50
90.6
82.3
#100
92.8
86.0
#200
95.1
88.9
18
Summary of Findings Is the binder from the seal coat bleeding through the microsurfacing • Nothing particularly points to the seal coat bleeding through based on XRF observations. • Asphalt contents not above target. • More conclusive proof should be gained through XRF testing of seal coat binder.
What is causing the pushing/flushing • No evidence of debonding problems in the 60+ cores taken in November. • Based on DSR values, asphalt was not “soft” • AC Content was quite variable throughout the project. In general, the areas with lower AC looked better. • Field gradation seems much coarser than the mix design which would typically result in a lower target asphalt content.
19
Summary of Findings Does the project fail the warranty spec • Skid numbers fail the warranty spec in over 1/3 of the southbound direction which is probably due to the flushing.
What differences do we see between the North (poor) and South (good) micro jobs? • Based on Google Earth, pre-existing conditions looked very similar for both jobs. • The other project had a lower AC content.
20
Acknowledgements
TxDOT Lufkin District Cindy Estakhri, Research Engineer, TTI Tom Scullion, Senior Research Engineer, TTI
21
Thank You Questions?
2017 Southeast Pavement Preservation Partnership Conference
22
2017 Southeast Pavement Preservation Partnership Annual Meeting
Background The new microsurfacing placed on US69 in May 2015 started showing premature pavement distress. Flushing in the wheel paths Pushing in several locations
2
Objective To determine the cause of the flushing and instability observed in the micro-surfacing
3
Forensic Study Procedure Field study Distress survey Coring Skid
Laboratory test
Binder content Gradation Binder stiffness X-Ray Florescence (XRF) fingerprinting
4
Coring Locations Site 1: RM 436-0.05, Southbound, Moderate Flushing Site 2: RM 436+0.9, Southbound, Slight Flushing, No seal coat underneath Site 3: RM 442+0.0, Southbound, Different Microsurfacing Project with no performance issues Site 4: RM 440+0.63, Northbound, Pushing/Instability, Flushing Site 5: RM 440+0.61, Northbound, Good performance
5
Site 1 SB (pushing, flushing)
6
Seal from the North End (Typical Condition before Micro)
7
Site 2 Northbound, Slight Flushing
8
Site 3 – SB Microsurfacing from Different Contractor
9
Site 4 NB, bad area, pushing, some milling already done
10
Site 5 Beginning of a Long Stretch of Good Performance
11
Skid Test
Northbound
Southbound Skid Number
Skid Number
Distance (miles)
Distance (miles)
12
What’s Next? Laboratory testing and evaluation on the cores
13
Bonding Six-inch diameter cores were taken in both the left and right wheel path. Intact cores were obtained at all locations revealing a very good bond of both the microsurfacing to the seal coat and of the seal coat to the asphalt surface.
14
Microsurfacing layer The microsurfacing on the cores was trimmed away from the surface. The asphalt was extracted and recovered using solvent extraction methods from the microsurfacing to determine the following: • Asphalt content, % • Stiffness of the asphalt (by determining the higher end of the PG grade) • XRF fingerprinting to identify individual components in the binder.
15
Asphalt Content and Performance Grade
Location
AC Content, %
PG Grade
Site 1 LWP
7.9
88+
Site 1 RWP
7.1
79
Site 2 LWP (3/4in thick)
9.3
88+
Site 2 RWP
6.2
78
Site 3 (other project)
5.9
81
Site 4 LWP
8.3
88+
Site 5 RWP
6.3
76
Target from Design
8.3
-
16
Intensity
XRF Results on Recovered Binders
17
Gradation From Mix Design Provided by District
From Recovered Mix in the Cores and Stockpiles
Sieve
Ext Agg from Site 1 RWP
Avg of 4 TxDOT stockpile samples
3/8
0.8
0.8
#4
13.8
6.5
#8
57.6
45.3
#16
79.4
67.1
#30
87.3
77.1
#50
90.6
82.3
#100
92.8
86.0
#200
95.1
88.9
18
Summary of Findings Is the binder from the seal coat bleeding through the microsurfacing • Nothing particularly points to the seal coat bleeding through based on XRF observations. • Asphalt contents not above target. • More conclusive proof should be gained through XRF testing of seal coat binder.
What is causing the pushing/flushing • No evidence of debonding problems in the 60+ cores taken in November. • Based on DSR values, asphalt was not “soft” • AC Content was quite variable throughout the project. In general, the areas with lower AC looked better. • Field gradation seems much coarser than the mix design which would typically result in a lower target asphalt content.
19
Summary of Findings Does the project fail the warranty spec • Skid numbers fail the warranty spec in over 1/3 of the southbound direction which is probably due to the flushing.
What differences do we see between the North (poor) and South (good) micro jobs? • Based on Google Earth, pre-existing conditions looked very similar for both jobs. • The other project had a lower AC content.
20
Acknowledgements
TxDOT Lufkin District Cindy Estakhri, Research Engineer, TTI Tom Scullion, Senior Research Engineer, TTI
21
Thank You Questions?
2017 Southeast Pavement Preservation Partnership Conference
22
