International Journal of Pavement Engineering Vol. 11, No. 6, December 2010, 541–553
X-ray fluorescence detection of waste engine oil residue in asphalt and its effect on cracking in service Simon A.M. Hesp* and Herbert F. Shurvell Department of Chemistry, Queen’s University, Kingston, Ontario, K7L 3N6 Canada (Received 4 October 2009; final version received 20 April 2010) This paper documents the discovery of waste engine oil residues in pavements across Ontario, Canada. We have found that recovered asphalts from a large majority of poorly performing contracts test positive for zinc through X-ray fluorescence (XRF) analysis. In contrast, neither the aggregates nor any of the well-performing asphalts showed any signs of the metal. Since zinc dialkyldithiophosphates are universal additives in engine oils, we inferred that the use of waste oil residues in asphalt must be widespread. Further analysis of 2008 quality assurance samples taken for the Ontario Ministry of Transportation substantiated this, with most samples testing positive for zinc. XRF analysis of straight waste oil residues suggests that typical modification levels are in the 5 – 20% range. The damaging effect of this additive through increased physical and chemical hardening is briefly discussed with reference to previous studies on unexplained, premature and excessive thermal cracking. Keywords: asphalt cement; thermal cracking; fatigue cracking; waste engine oil residue; physical hardening; chemical ageing
1.
Introduction
Asphalt sellers are naturally motivated to use low-cost materials and production methods to meet a set of specifications set by the buyer. There is little reason for concern when the specifications ensure that the buyer gets a quality product that meets certain minimum performance criteria. However, when such a system is absent or incomplete, the consequences can be far reaching and often costly (Leclerc and Paradis 2002, Andriescu et al. 2004, Yee et al. 2006, Hesp et al. 2009a). Given the typical 25 –40-year life cycle of asphalt pavements, it often takes a long time and trained eyes for problems to be recognised, which means that significant damage can be done to an entire network before corrective action is taken. Hence, it is important to continue to develop improved specification test methods to better control real-world performance. In the meantime, to mitigate the potential damage, it is imperative that detrimental additives and processes be banned from the asphalt supply. This paper provides a discussion on the detection of waste engine oil residue in asphalt cements recovered from numerous Ontario pavements. This issue is not new in that similar findings have been reported in the Province of Quebec some 8 years ago (Leclerc and Paradis 2002). It includes a brief review of test results obtained on model systems, in which superior Cold Lake asphalt cement is blended with waste engine oil residue.
*Corresponding author. Email:
[email protected] ISSN 1029-8436 print/ISSN 1477-268X online q 2010 Taylor & Francis DOI: 10.1080/10298436.2010.488729 http://www.informaworld.com
2.
Background
The Strategic Highway Research Program (SHRP) of the early 1990s was intended to provide a specification system that is blind to asphalt cement source, production method, and modification type and level (Anderson and Kennedy 1993). In large part, the specification tests developed by the SHRP, now commonly known as Superpavew, were supposed to prepare for the increasing use of modifiers for asphalt cement. Ever-increasing traffic volumes required asphalt cement modification, and often this resulted in inconsistent performance depending on modification technology and the particular specification tests used. Low-temperature thermal stress cracking in asphalt pavements has long been recognised as a major form of pavement distress, with frequent studies aimed at finding a solution to this persistent problem. While the Superpavew specifications have been implemented in large parts of North America, the problem of thermal cracking seems unrelenting, with regular reports of premature and/or excessive failures (Andriescu et al. 2004, Yee et al. 2006, Hesp et al. 2009a). Since the introduction of Superpavew, many scientific papers and patents have described compositions of certain performance grades using low-cost diluents and chemical modifiers and processes (Kriech and Wissel 1989, Kamel and Miller 1991, Johnson and Juristovski 1995, Memom et al. 1995, Bonemazzi and Giavarini 1999, Hayner 1999, Collins and Jones 2000, Giavarini et al. 2000, Moore et al. 2000, Leclerc and Paradis 2002, Hagens et al. 2004, others).
S.A.M. Hesp and H.F. Shurvell
(a)
0
PI (original asphalt cement)
The patents all claim that significantly improved performance can be achieved, frequently through the gelation of inferior quality asphalt cements. The colloidal sol/gel nature of asphalt cements has been investigated for a very long time with important contributions published at regular intervals (Nellensteyn 1923, Pfeiffer and Van Doormaal 1936, Benson 1937, Pfeiffer and Saal 1939, Saal and Labout 1940, Traxler and Romberg 1952, Traxler 1961, Pechenyi 1977, Lesueur et al. 1996, 2009, and others). A sol material exhibits behaviour that is largely Newtonian while a gelled material behaves in a non-Newtonian manner with significant elasticity, delayed elasticity and non-linearity in viscoelastic properties (Saal and Labout 1940, Lesueur 2009). The general consensus in the literature is that overly gelled, blown or elastic materials should be avoided for paving applications (Traxler 1961, Pechenyi 1977, Van Gooswilligen et al. 1989, Van de Ven and Van Assen 1996, Isacsson and Zeng 1998, Such et al. 1999, and others). Thermal stresses are able to relax in sol-type asphalts but are retained in gel-type asphalts, often leading to premature and excessive cracking. However, few field observations regarding this problem have ever been published (McLeod 1972, Such et al. 1999, Hesp and Subramani 2009, Hesp et al. 2009a, 2009b, Soleimani et al. 2009). McLeod (1972) discussed a significant study on thermal cracking in three Ontario pavement trials. Each trial was constructed with asphalt cements from three local suppliers just west of Toronto, Ontario, for a total of nine test sections. Crack surveys in their 8th, 9th, 10th and 11th years of service were reported, and cracking distress was correlated with various asphalt cement properties. Yet, nearly 40 years after McLeod’s significant study, Ontario pavements are still riddled with thermal cracks largely attributable to the use of inappropriate materials. McLeod’s study was intended to show that the widely used penetration index (PI), as proposed some 36 years earlier by Pfeiffer and Van Doormaal (1936), failed to
– 0.2
Trial: 3 2
1
– 0.4 – 0.6 – 0.8 –1 Supplier 1 Supplier 2 Supplier 3
–1.2 –1.4 –1.6
(b)
0 – 0.2
Supplier 1 Supplier 2 Supplier 3
– 0.4 – 0.6 – 0.8 –1 –1.2 –1.4
Trial: 3 2
1
–1.6 0
Figure 1.
correlate with pavement cracking severity. The PI was largely considered to be a measure of temperature susceptibility, with higher (less negative) values for materials supposed to have rheological (flow) properties that change less with temperature. High PI materials are less temperature susceptible, while low PI materials change consistency more rapidly (Traxler 1961). What the PI failed to reflect is that the lower temperature susceptibility is often associated with higher elasticity and thus higher thermal stress during periods of the year when it matters most (e.g. spring thaw). McLeod (1972) proposed a penetration-viscosity number (PVN) which, instead of the softening point, includes a measure of viscosity at high temperatures. He observed that the PVN is often numerically similar and sometimes equivalent to the PI. Figure 1 provides the cracking distress in the three Ontario test roads as a function of the PI and PVN for the asphalt cements. The data clearly show that the most elastic asphalt cements (with high PI or low PVN values) were significantly more prone to thermal cracking in all three trials. Material from supplier 3 consistently ranked worst, while material from supplier 1 consistently ranked best. A handful of later publications have noted the desirability of having a loss tangent (tan d) at low temperatures that is high rather than low (i.e. viscous behaviour is preferred over elastic behaviour) (Pechenyi 1977, Van de Ven and Van Assen 1996, Isacsson and Zeng 1998, Such et al. 1999, and others). We have recently investigated a large number of regular paving contracts and trial sections in Ontario (Table 1) with the aim of validating improved asphalt cement specifications for thermal cracking (Hesp and Subramani 2009, Hesp et al. 2009a, 2009b, Soleimani et al. 2009). The current AASHTO M320 specification failed to accurately predict performance in a set of 20 regular contracts, of which nine had cracked prematurely and excessively and 11 had performed according to
PVN (original asphalt cement)
542
50 100 150 200 250 300 Number of cracks per lane mile
0
50 100 150 200 250 300 Number of cracks per lane mile
Cracking severity as a function of (a) PI and (b) PVN in three Ontario pavement trials (1969 surveys; McLeod 1972).
International Journal of Pavement Engineering Table 1. Site A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
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Pertinent contract information (location, age, traffic and cracking distress). Highway 6 11 11 17 28 28 33 35 41 41 41 41 41 60 60 62 62 138 138 416 60 65 144 401 417 417
Location Little Current Cochrane Smooth Rock Falls Petawawa Burleigh Falls Lakefield Conway Lindsay Dacre Denbigh Kaladar Northbrook Vennachar Bat Lake Wilno Bannockburn Bloomfield Cornwall Monkland Spencerville Barry’s Bay Elk Lake Timmins Lancaster Vankleek Hill Casselman
Year
AADT (% commercial)
2000 1999 1998 1996 1993 1997– 1998 1998 1997 2000 1996 1999 2000 1997– 1998 1998 1994 1997 1993 2000– 2001 1998 1999 2006 2005 2004 2005 2003 2006
3560 (11) 3227 (29) 2705 (24) 6565 (14) 3972 (13) 5740 (10) 1828 (4) 8062 (10) 1680 (20) 2950 (18) 3001 (12) 3330 (11) 1557 (18) 2550 (15) 2800 (10) 2500 (13) 3143 (4) 7750 (13) 4700 (15) 12,000 (13) 2250 (15) 242 (20) 1150 (28) 24,000 (44) 18,200 (16) 18,200 (18)
Cracking distress Excessive and premature Minor Minor Excessive and premature Minor Minor Minor Minor Minor Excessive and premature Severe and premature Severe and premature Moderate Severe and premature Excessive and premature Excessive and premature Minor Minor Excessive and premature Minor Significant and premature Significant and premature Significant and premature Significant and premature Excessive and premature Significant and premature
Notes: Additional information for contracts A – T can be found in Hesp et al. (2009a) and for contracts W and Y in Andriescu et al. (2004) and Yee et al. (2006). ‘Excessive’ represents large-scale transverse and longitudinal cracking throughout that is beyond further repair (Figure 3(b)). ‘Minor’ indicates occasional transverse, longitudinal and/or joint-related cracking after 5 – 10 years of service (Figure 3(a)). ‘Premature’ indicates significant cracking within the first 5 years of service. ‘Severe’ indicates regular transverse and longitudinal cracking which would still qualify for route and seal treatment. ‘Significant’ indicates regular transverse and longitudinal cracking within the first 2 – 3 years of service.
expectation. To address this widespread thermal cracking problem, the Ontario Ministry of Transportation has recently started to implement two improved standard test methods (MTO 2006a, 2006b) in several trial contracts:
However, it could relate to an error in the measurement or sample handling. Notwithstanding, the general trend agrees with the suggestion that colloidal instability, as reflected in the higher grade losses due to physical hardening, leads to
. LS-299 – Determining asphalt cement’s resistance
LS-299 captures the variations in strain tolerance (toughness) in the ductile state, while LS-308 captures the effect of physical hardening on the low-temperature grade of the asphalt cement. Since current specifications generally under-design the pavement for thermal cracking, LS-308 provides a beneficial way forward since it consistently penalises poor performers more than superior performers. Figure 2 provides the maximum grade loss after 3 days of conditioning at 2108C vs. the cracking severity in the 20 contracts (Hesp et al. 2009a). The graph shows that superior performers lost less than 38C from their low-temperature grade while poor performers lost more than 38C. Site M provides a single outlier for reasons that are not entirely clear.
4000
Cracking severity (m/km)
to ductile failure using double-edge-notched tension (DENT) test and . LS-308 – Determination of performance grade of physically aged asphalt cement using extended bending beam rheometer (BBR) method.
O
D
3000
N
K S 2000
J
L
A P
1000
R C H Q E T B I GF
M
0 0
3 6 Three-day grade loss at –10˚C (˚C)
9
Figure 2. Cracking distress vs. LS-308 grade loss in extended BBR test after 3 days of conditioning at 2 108C (Hesp et al. 2009a). (Note that a 38C limit on the grade loss in LS-308 would provide a specification criterion with 95% overall accuracy and 100% success in predicting failures for this data set.)
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Figure 3. Representative photographs for two contracts on Highway 138. (a) Superior performing contract south of County Road 43 (Site R, AADT ¼ 7750, new construction in 2000/2001, wide angle and close-up of centreline joint). (b) Inferior contract north of County Road 43 (Site S, AADT ¼ 4700, new construction in 1998 and 66 km of cracks sealed in 2004).
a reduced ability to relax thermal stress, and this in turn leads to higher thermal cracking distress. Figure 3 provides representative photographs for stretches of adjacent contracts on Highway 138 north of Cornwall, Ontario. These images show enormous differences in cracking distress for asphalt cements of supposedly the same grade. Note that both contracts are of identical design, sub-grade and climate, but the superior performer carried almost twice the number of cars and trucks. With further dynamic shear rheometer and BBR testing of the same materials from these 20 contracts, it was demonstrated that the loss tangent, tan d, the viscous creep compliance, Jv(t), and the elastic recovery (ER) in the BBR could all provide better accuracy compared to the regular BBR test (AASHTO M320) and equal or better accuracy to the extended BBR test (LS-308; Hesp and Subramani 2009, Soleimani et al. 2009). The limiting loss tangent of ,0.55, which we found, corresponds to a phase angle of ,298, which agrees remarkably well with the work of Such et al. (1999) who settled on a limit of 278 to explain thermal cracking distress in French pavements. Both Jv(t) and ER in the
BBR at low temperatures did much better than the current S(t) and m-value specification at predicting failure, which is likely due to the confounding effects of viscous and elastic deformation in the latter. Viscous deformation is desirable, but a high degree of elasticity is likely undesirable since it could reflect a significant degree of thermal stress retention. The fact that some asphalt cements graded similar but cracked to very different degrees can be explained through the study limitations. Asphalt cements were extracted from the top 5 cm of the pavement, while chemical and physical ageing occurs most significantly in the top 1 –2 cm (Coons and Wright 1968). Weather data were obtained for the nearest weather stations available in the LTPPBindw (1999) software, which was not always as close to the contract site as hoped. Finally, the contracts ranged in age from approximately 8 to 15 years. While the results presented in Figures 2 and 3 are consistent and in agreement with those obtained for carefully controlled pavement trial sections (Iliuta et al. 2004, Zhao and Hesp 2006, Bodley et al. 2007, Hesp et al. 2009b), it has proven rather difficult to convince those with an
International Journal of Pavement Engineering interest in the current state of affairs of the benefits offered by the new specifications. Hence, our focus has switched to the chemical analysis of asphalt cements used in Ontario. While the physical properties of the asphalt cement determine the low-temperature performance, it is of course the chemical composition that affects these physical properties in positive or negative ways. Paraffins play an important role in thermal cracking since this class of compounds is known to promote asphaltene precipitation, in addition to having a tendency to crystallise at low temperatures (Traxler 1961, Pechenyi and Kuznetsov 1990, Claudy et al. 1991). Hence, they can contribute to physical hardening and thermal cracking distress. 3.
Experimental
3.1 Paving contract details A detailed discussion on the observed distress for the 20 contracts investigated earlier is presented in a previous publication (Hesp et al. 2009a). The cracking distress information provided in Figure 3 reveals the enormous differences in performance for asphalt cements of nearly the same AASHTO M320 grade. A summary of pertinent contract information is provided in Table 1. In addition to the investigation of these 20 contracts (Sites A to T), this study also considered a number of more recent premature failures (Sites U to Z). These six contracts were not included in the previous study because of their young age. (Rheological properties used for performance grading change rapidly in the first few years of service, so it is only meaningful to compare materials of similar and sufficient age.) All pavements were constructed to standard end result specifications (ERS), and contractors were either rewarded or penalised for their workmanship. The asphalt cement contents as determined through the ERS process varied from 5.0 to 5.7%. Air voids and voids in the mineral aggregate (VMA) were also kept within a narrow range, as accepted through the ERS system. The range for voids was 3.5 –4.4% and for VMA was 14 – 18%. All asphalt cements were of a grade (Superpavew or penetration grade) that should have provided a driving surface free of cracks for the expected design life of the pavement (Hesp et al. 2009a). Recovered asphalt cements were tested according to the current AASHTO M320 specification, and all of them passed the required continuous grade for the nearest weather station within a 38C margin of error. 3.2
Materials
Materials investigated were extracted from core samples using tetrahydrofuran (THF). A detailed discussion on the sampling and recovery process is provided in our earlier publication (Hesp et al. 2009a). In brief, the top 5 cm slices of pavement cores were soaked in THF overnight to
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remove most of the asphalt cement. Aggregate so obtained was rinsed an additional four to six times, using a total of approximately 4 –6 litres of THF. The fine aggregate was left to sediment, after which most of the THF was distilled using a rotary evaporator at low pressure (, 500 mbar) and moderate temperatures (50 – 708C). The remaining THF was removed at low pressure (30 – 40 mbar) and 1508C over a period of 1 h. Infrared spectra of the asphalt cement were taken before and after THF evaporation, confirming that no changes had occurred in chemical composition (oxidation) due to the recovery process and that no THF was left after recovery. This study also investigated the presence of waste engine oil residues in all of the 2008 quality assurance (QA) samples from the Ministry of Transportation contracts in the northeastern and eastern regions of Ontario. These samples were obtained from the QA testing laboratories in early 2009. Finally, additional experiments were done to show how waste engine oil residue affects a superior quality Cold Lake asphalt cement obtained from the Imperial Oil refinery in Edmonton, Alberta. Waste engine oil residues for these experiments were obtained from two local suppliers. 3.3 Procedures 3.3.1 Distress surveys All investigated contract locations were visited during autumn and summer of 2007 to take core samples and measure cracking distress at the beginning, middle and end of each contract site. The locations of transverse and longitudinal cracks were recorded and classified by their length across a quarter lane, half lane, full lane or full width of the pavement. Cracks spanning less than a quarter of a lane wide were ignored in the severely cracked pavements but were documented in the long-life pavements. The average of the three counts was used to calculate the approximate cracking distress expressed as total metres of cracks per kilometre. Further details are provided in our earlier publication (Hesp et al. 2009a). 3.3.2
XRF analysis
XRF spectra for recovered and virgin asphalt cements and aggregates were collected using a handheld Innovative X-Ray Technologies (Innov-X) model XT-440L analyser. The XRF instrument irradiates the surface of the material with high-energy X-rays, causing the ejection of inner K-shell electrons from heavy elements. The vacancies so produced are reoccupied by electrons from the outer L- and M-shells. The descent of electrons from these outer shells is accompanied by the emission of a lower energy X-ray with a characteristic energy for the element being irradiated. The XRF analyser detects the emitted radiation, and a plot of intensity vs. the X-ray energy provides
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Table 2. Elements detected by XRF and their respective fluorescence energies. Element P S K Ca Ti V Cr Mn Fe Co Ni Cu Zn Pb* Mo
Atomic number
Ka (keV)
Kb (keV)
15 16 19 20 22 23 24 25 26 27 28 29 30 82 42
2.01 2.31 3.31 3.69 4.51 4.95 5.41 5.90 6.40 6.93 7.48 8.05 8.64 10.55 17.48
2.14 2.46 3.59 4.01 4.93 5.43 5.95 6.49 7.06 7.65 8.26 8.91 9.57 12.61 19.61
Notes: Only those elements relevant for this study are given. The Ka line is generally much more intense than the Kb line. Silicon and carbon are not detected by XRF. *The energies indicated for Pb (lead) are in fact for La and Lb, respectively.
qualitative as well as quantitative information on the presence of a range of heavy elements. Peak heights in the spectrum provide a quantitative measure of the presence of the metal, but calibrations for each metal are required to provide absolute comparisons between metals (fluorescence yields vary between different elements). Table 2 provides a list of common elements that can be detected and the associated peak energies. Note that the Ka line originates from the transition of an electron from the L-shell (second highest energy level) to the K-shell (highest energy level), while the Kb originates from the transition from the M-shell (third highest energy level) to the K-shell (highest energy level).
strain tolerance in the ductile state and has shown a strong correlation with thermal and fatigue cracking distress (Andriescu 2006, Hesp et al. 2009a). 3.3.4 Regular BBR testing of model systems (AASHTO M320) The regular BBR test was conducted to determine the AASHTO M320 low-temperature grade for the straight and modified Cold Lake asphalt cements (AASHTO M320 2002). Samples were cooled for 1 h at test temperatures of 2 10, 2 20 and 2 308C prior to creep testing. The continuous low-temperature grade was determined from the warmest temperature where the creep stiffness, S(t), reached 300 MPa or the slope of the creep stiffness master curve, m(t), reached 0.3 after 60 s of loading. 3.3.5
The extended BBR method as embodied in LS-308 – determination of performance grade of physically aged asphalt cement using the extended BBR method is a simple elaboration on the regular BBR protocol (MTO 2006b). Specimens were conditioned at 2 10 and 2 208C for 1, 24 and 72 h prior to testing. The continuous lowtemperature grade was determined from the warmest temperature where the creep stiffness, S(t), reached 300 MPa or the slope of the creep stiffness master curve, m(t), reached 0.3 after 60 s of loading. Both pass and fail tests were conducted to determine continuous grades by interpolation. Besides the absolute grade, LS-308 also determines the grade loss after 24 and 72 h compared to AASHTO M320, which uses only 1 h of conditioning. 4.
3.3.3
Ductile failure testing of model systems (LS-299)
The ductile failure properties for a number of Cold Lake asphalt cements modified with various amounts of waste engine oil residue were determined according to standard procedures embodied in LS-299 – determining asphalt cement’s resistance to ductile failure using the DENT test (MTO 2006a). In brief, samples were poured into brass DENT moulds and were kept overnight at the test temperature of 158C. The specimens were tested at a constant rate of 50 mm/min, and the total failure energy was determined by integration of the force– displacement curve. The total specific failure energy, wf, was plotted vs. the ligament length (distance between the notches), L, and the specific essential work of fracture, we, was determined from the intercept of the curve (Andriescu 2006, MTO 2006a). The specific essential work of fracture was divided by the net section stress, sn, 5 mm, in the smallest ligament sample to obtain an approximate critical crack-tip opening displacement (CTOD). The CTOD provides a measure of
Extended BBR testing of model systems (LS-308)
4.1
Results and discussion Distress surveys
The main observation for Sites A to T is that nine showed excessive amounts of transverse cracking and 11 showed minimal amounts (Figures 2 and 3). Detailed discussions on the cracking distress for Sites A to T are provided in our earlier publication (Hesp et al. 2009a). For Sites U to Z, the cracking distress varied and included significant longitudinal as well as transverse cracking. However, these six contracts all cracked in their first or second winter and hence are expected to show identical performance to the other sites within a few years. (U) Highway 60 near Barry’s Bay. This 7.1 km stretch of Highway 60 was reconstructed in 2006. The pavement design consisted of two layers. A regular 50 mm-thick binder course was placed directly on the pulverised base, and a 40 mm-thick Superpavew 12.5 mm course was placed as the surface. The traffic volume on this road is approximately 2250 vehicles per day with 15% trucks. The PG 58-34 asphalt cement was optimised at 5.0%
International Journal of Pavement Engineering by weight of the aggregate. An amine-type anti-stripping agent was added to prevent moisture damage. Hairline cracking was observed throughout the contract in early 2007 (Isaac 2007). Intermittent wheelpath cracking was observed in all lanes. In several areas, the longitudinal joint showed reflection cracking. In addition, the entire contract also showed intermittent loss of fine aggregate. In 2009, the longitudinal hairline cracking had increased in severity throughout the contract and started to sprout early transverse cracks. The PAV residue was graded as a PG-36 and lost 3.58C after 3 days of conditioning in the extended BBR protocol, bringing it closer to a PG-33, which should still be sufficient for this area. Hence, low strain tolerance in the ductile state is likely to blame for this early distress. (V) Highway 65 west of Elk Lake. This 18 km stretch of Highway 65 was reconstructed in 2005. The pavement design consisted of a 50 mm Superpavew 12.5 mm course directly on top of a 50 mm levelling course of granular material placed on a further 100– 200 mm of full-depth reclaimed base. The traffic volume on this road is approximately 242 vehicles per day with 20% trucks. The PG 52-34 asphalt cement was optimised at 5.0% by weight of the aggregate. An amine-type anti-stripping agent was added at 0.75% by weight of the asphalt cement to prevent moisture damage. Extensive thermal cracking was observed in 2007. The distress was found throughout the contract with a full-width transverse crack approximately every 30 –35 m and occasional longitudinal wheelpath and centreline joint cracking. Neither BBR nor DENT tests were conducted on material from this contract. (W) Highway 144 south of Timmins. This 20 km contract was constructed in 2004 on a stretch of Highway 144 south of Timmins. The pavement design consisted of a 50 mm Superpavew 12.5 mm lift on a reclaimed asphalt base. The reclaimed asphalt base was constructed through processing of the existing pavement to a depth of 100 mm using an expanded (foamed) asphalt process. The traffic volume on this road is approximately 1150 vehicles per day with 28% trucks. The PG 52-34 asphalt cement was optimised at 5% by weight of the aggregate. The cracking observed in 2005 was considered extensive throughout (Yee et al. 2006). In total, 56 fullwidth transverse cracks and 34 shorter transverse cracks were counted in this contract. In the northbound lane, left wheelpath cracking was observed in about 30 locations, while in the southbound lane this type of cracking was sporadic. The contract was cored during summer 2005 to obtain insight into the nature of the transverse cracking. Four out of eight cores clearly showed that cracking had started on top and that the underlying expanded asphalt was undamaged. For the other four cores, the situation was less clear, but the damage to the expanded asphalt had
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likely occurred due to coring or due to water intrusion during spring. The PG-34 PAV residue lost a considerable amount of 8.58C in the extended BBR protocol, bringing it closer to a PG-26, which is obviously insufficient for this area (Yee et al. 2006). (X) Highway 401 near Lancaster. This 15 km stretch of Highway 401 was resurfaced in 2005 with a two-lift asphalt concrete overlay on a Portland cement concrete surface. The traffic volume on this road is approximately 24,000 vehicles per day with 44% trucks. The PG 64-34 asphalt cement was optimised at 5.0% by weight of the aggregate. Transverse cracks started to become visible prior to the first winter in 2006. In spring 2006, nearly all concrete joints had reflection cracks showing and many of the crack edges were already spalling (Isaac 2006). In addition to the transverse cracking distress, there were areas of longitudinal cracking and surface ravelling. Neither BBR nor DENT tests were conducted on material from this contract. (Y) Highway 417 near Vankleek Hill. This 9 km stretch of Highway 417 near Vankleek Hill was overlaid in 2003 with a single lift of Superpavew 12.5 mm asphalt concrete. The existing pavement structure was 265 mm deep, consisting of various layers of asphalt. The AADT for this stretch of highway is 18,200 with approximately 16% trucks. The PG 64-34 asphalt cement was optimised at 5.0% by weight of the aggregate. Cracking observed in 2004 was extensive, and cracks had opened up by as much as 25 mm in many locations. The average crack spacing was approximately 8 m throughout the length of the contract, with the edges of many cracks already starting to deteriorate. The site also showed approximately 800 m of longitudinal cracking in driving and passing lanes (Andriescu et al. 2004, Yee et al. 2006). The recovered asphalt cement graded as a PG-38 and lost 48C in the extended BBR protocol, bringing it closer to a PG-34, which still compared well to the minimum 2 248C pavement surface temperature determined from local weather data (Andriescu et al. 2004). While moderate reflection cracking is to be expected after a single mild winter, the amount and type of thermal distress in this contract was considered excessive and premature. (Z) Highway 417 west of Casselman. This stretch of Highway 417 was overlaid with two lifts of asphalt concrete in 2006. The existing asphalt pavement consisted of several layers of asphalt concrete with extensive thermal cracking throughout. Due to the severity of the existing distress, it was decided to do full-depth repairs on all cracks prior to construction of the new surface. Approximately 2000 thermal cracks were repaired in this manner. The AADT for this stretch of Highway 417 is 18,200 with approximately 18% commercial vehicles. The PG 64-34 asphalt cement was optimised at 5% by weight of the aggregate. Fresh thermal cracks occurred in the first winter with an approximate spacing of 10 m over 5 –6 km in this contract.
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In addition, severe ravelling occurred on bridge structures, and longitudinal cracking was observed in several other locations.
X-ray fluorescence intensity
4.2 XRF analysis of waste engine oil residues, asphalt cements and aggregates Two different waste engine oil residues from local suppliers were scanned and analysed in order to compare the XRF results from straight and recovered asphalt cements with samples of known composition. One of the residues was mixed at various proportions with straight Cold Lake asphalt cement to obtain a calibration curve for the zinc signal at 8.6 keV. Figure 4 shows XRF spectra for the two waste engine oil residues, while Table 3 lists all the elements found in this analysis together with peak intensities. Both residues produced similarly strong zinc signals, so the element was selected to gauge the amount of waste engine oil residue in recovered asphalt cements. Zinc dialkyldithiophosphate (ZDDTP) is a universal and deliberate antioxidant and anti-wear additive in engine oils, and zinc is therefore expected to be present in these residues in relatively
Supplier A
Supplier B
constant amounts. However, this is only an assumption since this study merely obtained XRF spectra for two single samples obtained from two Canadian sources. Furthermore, zinc carbonate or zinc sulphate is sometimes added during the production of polymer-modified asphalt cements to scavenge hydrogen sulphide (H2S) produced during the sulphur grafting reaction. However, most producers of polymer-modified asphalt use scrubbers to remove H2S and do not rely on scavengers. Iron originates from engine wear but can also be found in straight asphalt cement and aggregate and is therefore a less reliable indicator for the presence of waste engine oil residues. In spite of this, it should be noted that iron, copper and manganese have a much more detrimental effect than zinc on long-term chemical oxidation, since they are effective catalysts in the decomposition of hydroperoxides, while zinc is inert (Petersen 2009). Figure 5 shows the calibration curve for various amounts of waste oil residues blended with Cold Lake asphalt cement. It is apparent that the zinc signal at 8.6 keV is directly proportional to the amount of the residue in the blend and there is a reasonably high degree of accuracy. Recovered materials from contracts listed in Table 1 were investigated since no QA samples could be located. To ascertain that the zinc signals originated from the asphalt cements and not the aggregates, the latter were washed with copious amounts of THF and scanned for comparison. Typical XRF spectra for asphalt cements and aggregates from Sites P (positive for zinc) and Q (negative for zinc) are provided in Figures 6 and 7, while Table 4 provides the qualitative results for all elements of interest for all sites investigated. Table 4 shows that the presence of zinc is strongly associated with the occurrence of premature and excessive
0 3 6 9 12 X-ray fluorescence energy (keV)
15
Figure 4. XRF spectra of waste engine oil residues obtained from two local suppliers. Table 3. Elements detected by XRF in two commercial waste engine oil residues. Element P Ca Fe Mn Cu Zn Pb
Supplier A, counts
Supplier B, counts
1.5 3.4 5.0 0.0 3.0 148.0 3.0
1.0 3.0 10.0 0.5 4.5 125.0 2.0
Notes: The counts represent the fluorescence intensity as measured from the Ka line corrected for baseline differences. The only other notable element detected in the waste engine oil residues was molybdenum (Mo) at 17.48 keV.
120 XRF peak intensity at 8.64 keV
0
100 80 60 40 20 0 0
20 40 60 80 Used engine oil residue (wt %)
100
Figure 5. Calibration curve for zinc signal at 8.6 keV as a function of waste engine oil residue content in Cold Lake asphalt cement (r 2 ¼ 0.998).
X-ray fluorescence intensity
International Journal of Pavement Engineering
regarding the amounts of waste engine oil residue likely added to the asphalt supply. Table 5 provides the relevant findings for a total of 22 samples from paving contracts in the northeastern and eastern regions of Ontario. There is obvious cause for concern when all samples from the northeastern region test positive for approximately 11 –15% waste engine oil residue and when 70% of the samples from the eastern region test positive for approximately 4 – 12%. If the excessive cracking in the poorly performing contracts provides an indication of what is to come, then there is serious concern for the future health of the road network in Ontario’s northern regions.
Asphalt cement
Aggregate 0 0
3 6 9 12 X-ray fluorescence energy (keV)
15
X-ray fluorescence intensity
Figure 6. Typical XRF spectra for recovered asphalt cement and washed aggregate for Site P. (Note that y-axis scales are normalised for asphalt cement and aggregate spectra.)
Asphalt cement
Aggregate 0 0
3 6 9 12 X-ray fluorescence energy (keV)
549
15
Figure 7. Typical XRF spectra for recovered asphalt cement and washed aggregate for Site Q.
thermal cracking distress. Twelve of the 15 poorly performing contracts tested positive for the presence of significant quantities of zinc and hence were likely contaminated with waste engine oil residues. An additional 2 of the 15 poorly performing contracts showed traces of zinc and manganese in the asphalt cement, which could have caused premature oxidation and gel formation (note that XRF is significantly less sensitive to the presence of manganese). The presence of manganese indicates these could have been trials of Chemcretee, a mixture of manganese naphthanates. Marketed to stiffen asphalt cements in the 1980s, it has been shown to cause excessive cracking similar to that in Figure 8 (Mellot 1986, Adams and Button 1987, Paul 1989, and others). In contrast, none of the 11 superior performing contracts showed any sign of zinc. All 2008 QA samples were tested for the presence of zinc in order to obtain more quantitative information
4.3 Ductile failure properties of straight and modified Cold Lake asphalt cements (LS-299) The same materials used to produce the calibration curve for Figure 5 were RTFO/PAV aged, tested according to LS-308 and reused for evaluation according to LS-299. The findings are provided in Figure 9, which shows the approximate CTOD vs. the low-temperature AASHTO M320 grade of the material. It is seen from this graph that unadulterated Cold Lake asphalt cement has improved strain tolerance (as reflected in high approximate CTODs) for soft grades. When a hard Cold Lake asphalt is diluted with waste engine oil residue to obtain similar low-temperature AASHTO M320 grades, this improved strain tolerance is absent. The experimental results for these model systems show that LS-299 is able to distinguish the Cold Lake asphalt cements that were modified with waste engine oil residue from the unmodified materials of similar low-temperature grades. Waste engine oil residues are largely comprised of saturates, and hence they have a tendency to gel the asphaltenes (Hesp et al. 2007, Lesueur 2009, Petersen 2009). The elastic gel structure prevents the dissipation of strain energy and thus lowers the strain tolerance in the ductile state (Kodrat et al. 2007). Gel formation is also known to make the asphalt cement more prone to physical and oxidative hardening (Hesp et al. 2007, Lesueur 2009, Petersen 2009), leading to a further deterioration in fracture performance. Our previous study on the recovered asphalt cements from Sites A –T found that phosphorous could be detected in most of the poorly performing contracts (Hesp et al. 2009a). This could be a sign for the presence of phosphoric acid (H3PO4) or polyphosphoric acid (PPA), deliberately added by the asphalt supplier, or it could have been a remnant of ZDDTP (i.e. ZDDTP from the waste engine oil residue). What, if any, role the possible presence of phosphoric acid has had in the premature cracking is therefore difficult to unravel. However, previous DENT testing on PPA-modified asphalt cements has shown that
550 Table 4.
S.A.M. Hesp and H.F. Shurvell Detection of P, Ca, Cr, Fe, Mn, Cu and Zn in recovered asphalt cements and aggregates. Elements detected by XRF
Site A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Highway
Asphalt cement
Aggregate
Cracking distress
6 11 11 17 28 28 33 35 41 41 41 41 41 60 60 62 62 138 138 416 60 65 144 401 417 417
P, Ca, Mn, Fe, Cu, Zn Ca, Fe Fe Ca, Mn, Fe Ca, Fe Ca, Fe Ca, Fe Ca, Fe Ca, Mn, Fe Ca, Mn, Fe, Zn Ca, Mn, Fe, Cu, Zn Ca, Fe, Zn Ca, Fe Ca, Fe Ca, Mn, Fe Ca, Mn, Fe, Zn Ca, Fe P, Ca, Mn, Fe Ca, Mn, Fe, Cu, Zn Ca, Fe Mn, Zn P, Ca, Mn, Fe, Cu, Zn Ca, Cr, Mn, Fe, Cu, Zn Ca, Cr, Fe, Zn Ca, Fe, Zn Ca, Cr, Fe, Zn
P, Fe P, Ca, Fe Ca, Fe P, Mn, Fe P, Ca, Fe Ca, Mn, Fe P, Ca, Fe Ca P, Ca, Fe Ca, Fe Ca, Fe Ca, Fe Ca, Fe Ca, Fe Ca, Mn, Fe P, Ca, Mn, Fe Ca Ca, Fe P, Ca, Fe P, Ca, Mn, Fe – Ca, Fe – – Ca, Fe Ca, Fe
Excessive and premature Minor Minor Excessive and premature Minor Minor Minor Minor Minor Excessive and premature Severe and premature Severe and premature Moderate Severe and premature Excessive and premature Excessive and premature Minor Minor Excessive and premature Minor Significant and premature Significant and premature Significant and premature Significant and premature Excessive and premature Significant and premature
Notes: Other elements detected included sulphur, potassium, titanium, vanadium, cobalt, nickel, lead and molybdenum. Only qualitative information is given since the extraction process may not have removed all the material of interest. Aggregates for Sites U, W and X were no longer available and hence could not be tested.
these can reduce the strain tolerance in the ductile state due to excessive gelling (Kodrat et al. 2007). 4.4 Grade losses due to isothermal conditioning for modified Cold Lake asphalt cements (LS-308) The modified Cold Lake samples were tested after conditioning times of 1, 24 and 72 h at both 2 10 and 2 208C in order to further validate LS-308 (Figure 2).
Grade temperatures according to AASHTO M320 criteria were determined from pass and fail tests. AASHTO M320 and LS-308 results of this analysis are given in Figure 10. It is striking that the AASHTO M320 grade goes down with increasing amounts of waste engine oil residue, whereas the LS-308 grade appears to first remain constant and go up at high levels of modification. Since suppliers are currently paid based on the AASHTO M320 grade, the data show why waste engine oil residues find their way into the
Figure 8. Representative photographs for Highway 60 (Site O) contract for which the recovered asphalt cement tested positive for traces of zinc and manganese.
International Journal of Pavement Engineering Table 5.
551
Foreign elements and waste engine oil residues contents in QA samples.
Sample
Elements detected
Zinc count
Waste engine oil residue (%)
NER-1 NER-2 NER-3 NER-4 NER-5 NER-6 NER-7 NER-8 NER-9 NER-10 NER-11 NER-12 ER-1 ER-2 ER-3 ER-4 ER-5 ER-6 ER-7 ER-8 ER-9 ER-10
P, S, Ca, V, Fe, Ni, Cu, Zn, Pb, Mo P, S, V, Mn, Fe, Ni, Cu, Zn, Pb, Mo P, S, Ca, V, Fe, Ni, Cu, Zn, Pb, Mo P, S, Ca, Fe, Ni, Cu, Zn, Pb, Mo P, S, Ca, V, Fe, Ni, Cu, Zn, Pb, Mo P, S, V, Fe, Ni, Cu, Zn, Pb, Mo P, S, V, Fe, Ni, Cu, Zn, Pb, Mo P, S, Ca, Fe, Ni, Cu, Zn, Pb, Mo P, S, Ca, Fe, Ni, Cu, Zn, Pb, Mo P, S, Ca, Fe, Ni, Cu, Zn, Pb, Mo P, S, Ca, V, Fe, Ni, Cu, Zn, Pb, Mo P, S, Ca, V, Fe, Ni, Cu, Zn, Pb, Mo P, S, V, Fe, Ni, Zn, Pb, Mo Fe P, S, Fe, Ni, Cu, Zn, Pb, Mo P, S, Fe, Zn P, S, Fe, Zn Fe P, S, V, Fe, Ni, Cu, Zn, Pb, Mo P, S, V, Cr, Fe, Ni, Cu, Zn, Pb, Mo V, Fe, Ni P, S, V, Fe, Ni, Zn, Pb, Mo
21 15 15 20 18 18 19 21 20 20 20 15 7 0 12 2 5 0 16 8 0 6
17 12 12 16 14 14 16 17 16 16 16 12 8 0 10 1.6 4 0 13 6 0 5
Notes: NER, northeastern Ontario; ER, eastern Ontario. Quantitative information is given based on the calibration curve provided in Figure 10. Note that any of the three asphalt suppliers may have used waste engine oil residue from another source, with more or less zinc; hence, the listed waste oil contents provide only a rough estimate.
asphalt cement supply. However, if we make the reasonable assumption that LS-308 provides a more critical grade, which assures the prevention of thermal cracking, then the grade loss between AAHSHTO M320 (1 h conditioning) and LS-308 (72 h conditioning) increases in direct proportion to the amount of waste engine oil residue in the asphalt cement. Figures 9 and 10 clearly reveal the detrimental effect of waste engine oil residue destabilising the asphaltene structure, with the negative consequence of physical and chemical hardening, and premature/excessive
thermal cracking, should this material be used in practice (Hesp et al. 2007, Lesueur 2009, Petersen 2009). 5.
Conclusions and summary
Given the review of the literature and the findings presented in this paper, the following conclusions and summary are provided: . XRF spectroscopy is able to detect zinc and other
heavy elements in asphalt cements sampled during construction and recovered from the field. –22
Low-temperature grade (˚C)
Approximate CTOD (mm)
15
10
5
0
–28
–34
–40 –37
–34
–31
–28
Low-temperature AASHTO M320 grade (°C)
Figure 9. Ductile strain tolerance as expressed by approximate CTOD for straight (W) and waste engine oil residue modified (A) Cold Lake asphalt cements (rate ¼ 50 mm/min, T ¼ 158C).
0
4 8 12 16 20 Waste engine oil residue (%)
24
Figure 10. Comparison of AASHTO M320 (W) and LS-308 (A) limiting temperatures for straight and waste engine oil residuemodified Cold Lake asphalt cements.
552
S.A.M. Hesp and H.F. Shurvell . The presence of zinc and a host of other heavy
elements indicates that the use of waste engine oil residues for asphalt cement modification is widespread in Ontario. . Physical hardening and losses in strain tolerance due to the presence of waste engine oil residues are largely to blame for the observed premature and excessive failures in the Ontario road network. It is up to the government to exercise its role as guardian of the public interest. Given the findings of this research, an early ban on waste engine oil residues and other detrimental additives in asphalt cement appears justified. In the long term, these problems can only be avoided through the implementation of improved specification test methods and acceptance protocols. Both LS-299 and LS-308 provide real improvements to specification grading and deserve to be implemented at an early opportunity. Acknowledgements The authors wish to thank Imperial Oil of Canada, EI du Pont Canada, the Ontario Ministry of Transportation, and the Natural Sciences and Engineering Research Council of Canada for their continuing financial support. Undergraduate students Eric Moult and Irsan Kodrat are thanked for the collection of samples and experimental data, and Ryan Marchildon is thanked for checking the proof. The Art Conservation program at Queen’s University is thanked for allowing us to use their XRF analyser for this study. Appreciation is expressed to Maureen Garvie for the proofreading of the manuscript and to staff of the Ontario Ministry of Transportation for their assistance with the collection of contract information and experimental data. None of the sponsoring agencies necessarily concur with, endorse or agree to adopt the findings, conclusions or recommendations either inferred or expressly stated in subject data developed in this study.
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