LIFE CYCLE COST ANALYSIS OF MITIGATING PAVEMENT REHABILITATION REFLECTION CRACKING

Transcription

1 LIFE CYCLE COST ANALYSIS OF MITIGATING PAVEMENT REHABILITATION REFLECTION CRACKING Susan Tighe, PhD, P.Eng Assistant Professor Department of Civil Engineering University of Waterloo Waterloo, ON N2L 3G1 Tel.: , Ext Fax: Ralph Haas, CM, PhD, P.Eng The Norman W. McLeod Engineering Professor and Distinguished Professor Emeritus Department of Civil Engineering University of Waterloo Waterloo, ON N2L 3G1 Tel.: , Ext Fax: Joseph Ponniah, PhD, P.Eng Senior Pavement Engineer Pavements and Foundation Section Ministry of Transportation of Ontario Downsview, ON M3M 1J8 Tel.: Paper offered for 82 nd Annual Meeting of the Transportation Research Board January 2003, Washington, D.C.

2 Tighe, Haas and Ponniah Page 2 of 18 ABSTRACT Reflective cracking is a major and costly problem in many countries. It occurs in the top (overlay layers above existing cracks in the lower (existing) pavement. This type of cracking can lead to premature deterioration of the pavement structure through the infiltration of moisture and debris. Although, extensive research has been directed toward mitigation of the problem it is evident that work needs to be done, as it still appears to be a major problem. In part, the problem is related to the fact that most of the work being done by highway agencies throughout North America involves rehabilitation. One of the most common types of rehabilitation of pavements is the use of an asphalt overlay. This paper focuses on the associated issue of economic benefits of reducing and treating reflection cracking prior to the placement of an asphalt overlay. In fact the Canadian Strategic Highway Research Program s (C-SHRP) Long Term Pavement Performance Study (LTPP) is entirely directed to overlays. The overall goal of the C-LTPP project is to increase pavement life and serviceability through the development of cost-effective rehabilitation strategies, based on a systematic observation of in-service pavement performance. A methodology for converting crack spacing to roughness is also presented. This information is used to examine how cracking is related to the measured IRI values. A model relating the amount of cracking to loss of serviceability and/or reduction in service life is presented. It illustrates, for example, that reducing transverse crack spacing from 5 m to 20 m should result in a 5 year extension of service life, with a cost saving of $25,000 per two-lane km. Measuring and treating cracking accordingly can also yield significant benefits. Benefit/cost ratios of measuring cracking can range from about 5 to 50, while proper and timely crack treatment (routing and sealing) can result in extending life by 2 years and cost savings in the order of $7,000 per lane-km. KEY WORDS: reflection cracking, pavement performance, life cycle cost analysis

3 Tighe, Haas and Ponniah Page 3 of 18 INTRODUCTION Expenditures on pavements in many countries, including Canada, are now largely directed at corrective, preventive and rehabilitative maintenance rather than new construction. The largest portion of these expenditures is for rehabilitative maintenance, usually consisting of overlays. In fact the Canadian Strategic Highway Research Program s (C-SHRP) Long Term Pavement Performance Study (LTPP) is entirely directed to overlays [1]. The overall goal of the C-LTPP project is to increase pavement life and serviceability through the development of cost-effective rehabilitation strategies, based on a systematic observation of in-service pavement performance. Each of the 65 sections was designed and constructed with consideration of overlay thickness, traffic volume, overlay material, local climate and subgrade soil conditions [2]. One of the most prevalent problems with overlays is cracking, often occurring above a crack in the underlying, old pavement. While this is commonly termed reflection cracking it has been contended that the mechanism actually involves propagation of the crack downward from the top of the overlay [3]. The cause is thought to be due to construction induced micro cracks at the overlay surface, thereby creating a weakened zone over the old cracks. This, combined with higher thermally induced stresses at the surface, leads to a downward occurring propagation of the crack. At warmer temperatures, cracking may also occur due to excessive shear stresses in the overlay as heavy wheel loads pass over the old crack and its low or non existent load transfer capability. Whatever the causes of reflection cracking, it is a widespread problem and of the many mitigation treatments most have succeeded only in delaying the cracking. As a result, much time, effort and money has been expended in trying to solve the problem. That is the technical side; the other side of the problem is the economic implications of being able to reduce and treat cracking. It is this other side of the problem which is the subject of this paper. PROGRESSION OF REFLECTIVE CRACKING It is useful to review how reflective cracking through overlays progresses before examining the economic benefits of reduced cracking. In other words, does such cracking occur early in the life of the overlay, advance at a slow rate or occur later? This is an important question with regard to the magnitude of the economic benefits. It has generally been observed that thermally associated cracking in the original pavement as well as reflection cracking in overlays occurs early in the service life [4]. Of course a proper design in the first place would result in minimal cracking throughout the service life. The reality, however, is that if cracking exists in the old underlying pavement, reflection cracking will occur early. Suggested limits on cracking, based on cost implications, were first advanced in 1973 [4]. A summary of those limits is given in Table 1. It may be noted that the table incorporates cracking progression. A recent study for the Canadian Strategic Highway Research Program (C-SHRP) confirms that reflective cracking progresses rapidly in the early years of the overlay [5]. Of the 65 overlay test sites in C-SHRP s Long Term Pavement Performance (LTPP) Study, 21 overlays (32%) in fact had a greater total of cracking after 5 years than existed in the original old pavement. For example, Figure 1 illustrates this for centreline cracking on Site # in New Brunswick. Most variables at the site (asphalt concrete stiffness, annual precipitation, freezing index, etc.) are representative or approximately at the mid range of the 65 sections. Values of reflective cracking greater than 100% indicate additional cracking occurred in the overlay which can not be attributed to the underlying pavement. In essence, the economic impacts of reflection cracking need to recognize that if such cracking is going to occur at any given site, most of it will occur early in the service life; e.g., within 5 years. EFFECTS OF CRACKING ON REDUCING SERVICEABILITY AND SERVICE LIFE Cracking represents damage in any engineering structure (pavements, water lines, sewers, building components, foundations, etc.). As such, it might be expected that reduced life will occur to a greater or lesser degree [7]. In the case of pavements, very little comparative data is available which isolates the effect of cracking on performance. A major reason is that there are many other factors which can affect performance and thus confound any attempt to isolate individual factors. An example of these factors and their interactions are given in Figure 2. Road roughness is the primary measure of serviceability and one of the most important components in a pavement management system as it is often used as a trigger for pavement rehabilitation. The need for a universal standard for characterizing pavement roughness has existed for some years. Realization of this need was largely accomplished through studies initiated by The World

4 Tighe, Haas and Ponniah Page 4 of 18 Bank, such as described by Queiroz [8]. This was later updated by Sayers [9] to a new set of quarter car vehicle parameters and the QI measure was replaced by International Roughness Index (IRI). Pavement roughness is defined by the American Society of Testing and Materials (ASTM E807-82A) as The deviations of the surface from a true planar surface with characteristic dimensions that affect vehicle dynamics, ride quality, dynamic loads and drainage. It is an indicator of pavement performance, and it is associated with driving comfort, vehicle operating costs, and safety. One of the few quantitative studies carried out to relate cracking to a number of factors, and in turn to performance is described in Reference [6]. It involved 22 airport pavements across Canada. Since these consisted of runways, truck load effects were not a confounding factor. As well, the construction materials, etc. were no different than for roads. Average thicknesses were: Asphalt layers 140 mm Granular base 250 mm Granular subbase 200 mm These would be representative of most low to medium traffic volume roads. The Canadian study was able to correlate roughness in terms of Riding Comfort Index, RCI, with the amount of cracking (in terms of crack spacing, m) with an R 2 value of 0.72 as described in Equation 1. RCI = (crack spacing) (1) (crack spacing) 2 RCI is measured on a scale of 0 to 10, with 10 being perfectly smooth and 0 being impassable [6]. Since International Roughness Index, IRI, is a more universally recognized measure, conversion equations are available [6]. Equation (1) is shown in graphical terms in Figure 3. It clearly indicates increasing life with increased crack spacing (i.e., lower frequency of cracking). For example, 5 years longer life is obtained if the crack spacing increases from 5 m to 20 m, where the 5 m spacing would correspond to the normal initial design life of 15 years for these pavements. A further analysis using equation 1 involved examining the amount of cracking observed on the C-LTPP sections and how it relates to roughness in terms of RCI. Table 2 summarizes the observed cracking at 5 or 8 years and the calculated RCI using equation 1. The sections included in this summary are only those with less than 100 observed cracks. It is notable that only eleven of the C-LTPP sections described in Table 2 meet the cracking limits described in Table 1. The question raised based on this observation would be whether the numbers presented in Table 1 are consistent with in-service performance as clearly more cracks are being observed. The second question raised would be whether the use of Performance Graded Asphalt Cements (PGACs) would reduce cracking and thus result in observed cracking that is more consistent with the guidelines presented in Table 1. This requires long term performance data, which will hopefully assist designers in predicting and mitigating reflective cracking. Based on the observed cracking in Table 2, it is evident that cracking is still a problem on the overlays in the C-LTPP program. In order to assess how well the predicted RCI values using crack spacing, compared to the observed IRI values a conversion from RCI to IRI was necessary. The available conversion equations, 2 to 6, as follows, are provided in the Transportation Association of Canada s Pavement Design and Management Guide [7]. Equation (2) relates IRI which is correlated from actual profile measurements to Riding Comfort Index by a trained rating panel while Equation 3 relates IRI to RCI based on the British Columbia Roadway Pavement Management System (RPMA). Equation 4 is based on another similar study to the BC study while Equation 5 and 6 relate to Ontario studies. IRI = * RCI (2) RCI = 10 * e -0.18IRI (3) RCI = 10 * e -0.26IRI (4) RCR carusers = * IRI (5) RCR truckusers = * IRI (6) Where: IRI = International Roughness Index RCI = Riding Comfort Index RCR = Riding Comfort Rating

5 Tighe, Haas and Ponniah Page 5 of 18 The measured IRI values for the C-LTPP test sections up to 8 years are provided and have been used in the comparison [2]. The IRI values are shown to be extremely smooth, despite observed cracking. Table 3, summarizes five Analysis of Variance (ANOVA s) that were performed to examine how the IRI calculated based on equations 2 through 6 relates to the observed IRI on the C-LTPP test sites. The intent of this evaluation was to confirm that roughness predicted using the crack spacing was related to measured IRI values. This ANOVA focused on the situation where less than 10 cracks were observed in 150m (eg. crack spacing of 15 m). Note these correspond with the cracking limits noted in Table 1. The measured IRI using a Dipstick was compared to the predicted IRI based on the crack spacing and conversion equations from RCI to IRI. Based on the results presented in Table 3, the IRI predicted using the RCI based on the Canadian Airport Model [6] was statistically not different from the observed IRI with the exception of equation (3) where the F CALCULATED was greater than the F CRITICAL and thus was shown to be statistically different. Based on these findings, it would be appropriate to use the Canadian Airport Model to predict roughness as an initial or starting point, with recognition that it is quite conservative. An update of this model and/or the development of a new model is highly desirable and should be a priority of future C- LTPP data analysis, particularly as the sections age and deteriorate. As well, there are undoubtedly factor interactions that should be captured in such an updated model (e.g., low temperature cracking frequency versus number of freeze-thaw cycles, or versus subgrade soil type, or versus amount of rainfall, etc.). ECONOMIC BENEFITS OF REDUCED CRACKING AND TIMELY MAINTENANCE INTERVENTIONS The economic benefits of reduced cracking should accrue from one or more of the following: (a) increased life of the original pavement and/or the overlay, (b) lower maintenance costs, (c) lower vehicle operating costs due to higher levels of serviceability, and (d) lower user delay costs because of later preventive and rehabilitative maintenance interventions. There is also an inherent benefit associated with measuring and treating cracking, as subsequently discussed in more detail. Regarding only (a), Figure 3 suggests that increasing crack spacing from 5m (occurring at the normal design life of 15 years) to 20 m would extend the life to 20 years. Assuming, for example, $100,000 per two-lane km for an overlay, this would result in a present worth of savings of approximately $25,000, using a 6% discount rate. In other words, delaying the spending of $100,000 by 5 years saves the agency $25,000. To carry this further, Deme has suggested that this saving would well justify the cost increase of using a high performance asphalt [10]. MEASURING AND TREATING CRACKING The argument could be made that there is no point in spending money on measuring existing cracking; just apply maintenance using inspection (based on the judgement of the engineer). In other words, the strategy would be to react to the cracking as it occurs. The counter argument is that periodic measurements of cracking, including the severity and density allow the most cost-effective treatment or intervention to be applied at the right time; moreover, that this will extend the life of the pavement and thus provide economic benefits. Based on the roughness study [2] on the CLTPP sections, there seems to be a steady progression of roughness over the approximately eight years of time. It appears to be essentially linear from a mean as-built IRI of about 1.2 m/km to a mean IRI of about 1.6 m/km in Even nine years later, a mean IRI of 1.6 m/km still represents quite smooth pavements, on average. A linear extrapolation of the data in Figure 4 would estimate that the average IRI will reach about 2.0 m/km in 2012, which is 22 years after construction. This would be roughly the same as the prior to overlay value of 2.0 m/km in [2]. An average overlay life of 22 years would certainly be encouraging. However, it should be clearly recognized that an overall national trend requires an aggregation over all the factors and provinces and inherently masks the individual differences. Moreover, this long term estimate of IRI is based only 8 years of data [2]. In other words, the extrapolation goes considerably beyond the inference space, which can be very risky if not erroneous. In practice, many pavements deteriorate faster in the second 10 years than they do in the first 10 years because of traffic growth and interaction effects with cracking, rutting, etc. However, if cracking is allowed to progress, this would diminish the life of the pavement.

6 Tighe, Haas and Ponniah Page 6 of 18 While not a justification of measuring cracking per se, it may be noted though that 45 of 48 U.S. states surveyed in a FHWA study of 1994 collect cracking data [11]. About two-thirds of the states collect the data annually and about one-third collect it biennially. Obviously, a vast majority of U.S. states place importance on cracking data collection. The U.S. approach is similar to that of provinces and municipalities in Canada, 90% of which collect cracking data with frequencies of 1 to 3 years depending on type of road [7]. There are four basic ways of measuring cracking: 1. Manual (using walking surveys or trained observers recording the cracking from video records) 2. Windshield survey (using trained observers to drive the road at speed and record the combined, approximate area and severity of cracking, such as 0 to 25%, 25% to 50% and greater than 50%, with severity levels of slight, moderate and severe) 3. Semi-automated (using trained observers in a slow-moving vehicle to enter type, severity and density of cracking on specially designed keyboards with digital recording this tries to replicate the manual method, but with a much higher level of productivity) 4. Automated (where special software analyzes video, CCD camera or 35 mm images to determine the type, severity and density of cracking this also tries to replicate the manual method, but with improved consistency and with a much higher level of productivity). The first method, because of productivity and cost reasons, often is carried out on a sampling basis. In the U.S. study [11], about half the states use the first method, with about half of these using samples of 500 ft. or less per mile and the other half using continuous recording. The semi-automated method has found widespread use in various states, provinces and municipalities cross North America because it allows for continuous recording at reasonable cost. Full automated methods are finding increasing use but in a relative sense they still account for a small percentage of crack surveys. From the point of determining maintenance treatment requirements it would obviously be desirable to have a continuous record of cracking. In this way the total length in metres, and/or areas involved, for various treatments could be established and the associated costs could be estimated more reliably. However, a well designed sampling survey of cracking should still be able to give reasonable estimates. The costs of measuring cracking depend on such factors as method used, frequency (annual, biennial, etc.), amount of km involved (economy of scale), traffic impediments (low traffic vs high traffic road), rural or urban, the amount of cracking to be measured (small to much of the area cracked), etc. As well, the processing costs vary with method used (manual, semi-automated, etc.). Table 4 lists some typical ranges of costs for cracking surveys. The assumptions behind these costs are: 1. At least 1,000 lane-km to be measured; rural; moderate traffic (for all methods) 2. Sample size of 150 m per km for method 1; some traffic control required 3. Continuous coverage for methods 2, 3 and 4 4. Data processing costs for method 3 includes only provision of diskette plus crack type, severity and density tabulations for short segment lengths (i.e., 20 m) 5. Data processing costs for method 4 includes only provision of image record (video, etc.) plus tabulations as in 3. The benefits of measuring cracking are incorporated in the savings realized by applying the right treatment at the right time. An example is described in the following section. It was demonstrated in the previous section that limited frequency of cracking (i.e., spacing of 20 m or more) could add up to 5 years of additional pavement life as compared to the normal frequency seen in many roads. However, if the cracks already exist the question now is one of the consequences of not sealing them. Sealing is generally acknowledged by most agencies and by SHRP [12] to be cost-effective, if carried out under the right conditions (crack preparation, time of season, type of crack sealant,

7 Tighe, Haas and Ponniah Page 7 of 18 application procedures, etc.) at the right time (when the severity and density of cracking is most appropriate). Ontario has been one of the leaders in this area [13, 14]. During the 1970 s and 1980 s they carried out several field studies to assess the influence of crack sealing on pavement performance. Their observations showed that if cracks were left untreated, the following occurred: Severe erosion at the bottom of the asphalt layers due to the pumping action of water caused by traffic loads, with only half the asphalt layer thickness remaining at the crack Upheaval of the pavement surface in the winter due to frost action on saturated base and subgrade layers, followed by depressions at the crack in the summer Accelerated loss in riding quality, with associated reduction of pavement life Frequent necessity of cutting a 1 m width out of the pavement and carrying out repairs, prior to rehabilitation, due to multiple cracking, depressions, etc. at the original crack location. The Ontario studies led to the development of routing and sealing procedures, also based on field studies, to determine the selection of materials, equipment, crack preparation and application techniques [13,14]. These field studies involved 37 test sites. Crack mapping was carried out every year. Performance curves were drawn for both the treated and control (untreated) portions of each test site. Figure 5 is typical. It shows an estimated increase in pavement life of 2 years for the treated section. The range of increased life was up to 5 years. Conservatively, the conclusion is that proper crack sealing should extend pavement life by at least 2 years. The Ontario work provides the following guidelines for carrying out routing and sealing of cracks: Crack opening between 3-12 mm; if mm evaluation by pavement experts to determine if appropriate; if greater than 19 mm, clean, dry and fill crack (not routing) Only consider transverse and longitudinal cracks (centre line, mid lane, wheel track single crack and meandering cracks) for rout and seal Rout size of 40x10 mm promotes good bonding Best time is in spring when temperatures are moderately cold Typical timing of crack rout and seal is 4 th and 8 th years after initial construction or rehabilitation; however, guidelines on crack width and condition should control. COST EFFECTIVENESS OF TREATING CRACKING A comprehensive life-cycle analysis of crack sealing was carried out by Ponniah and Kennepohl [15]. In an example of a two-lane, 21 km road in southwestern Ontario, with initial AADT of 750, annual growth rate of 4% and 18% trucks, and a design 115 mm asphalt concrete on a 350 mm of granular layers, they considered the following two alternative strategies over a 30-year analysis or life-cycle period: 50 mm overlay at years 11 and 21, with no crack sealing Crack routing and sealing at years 4 and 8, 50 mm overlay at year 13, crack routing and sealing at years 17 and 21, 50 mm overlay at year 25 and crack routing and sealing at year 29. Cost details of the routing and sealing future rehabilitations, user delay costs during reahbilitations, and residual value at the end of 30 years are provided in Ref. [12]. Using a discount rate of 5%, the total present worth of costs (PWC) of each alternative was as follows: PWC (no sealing) ~ $24,000 per lane-km PWC (with sealing) ~ $17,000 per lane-km The savings represented by alternative 2. are therefore $24,000-$17,000 ~ $7,000 per lane-km, or about 21 km x 2 lanes x $7,000 ~ $300,000 over the whole project. COST-EFFECTIVENESS OF MEASURING CRACKING The previous section showed life-cycle cost savings, typically, in the order of $7,000 per lane-km if proper crack routing and sealing is carried out. Measurement of cracks, including their severity and density, is the basis for determining the right timing for such crack treatment. It must be recognized, however, that it would be unreasonable to attribute all the savings to crack measurements because even if no measurements were carried out but crack sealing was done on some formula basis, there would likely be some benefits.

8 Tighe, Haas and Ponniah Page 8 of 18 Even if, very conservatively, only 25% of the saving were attributed to crack measurements, and conservatively rounding off the savings at $5,000 per lane-km, then the benefit-cost ratios of the methods listed in Table 2 would be as follows: 1. Manual, $5,000 x 25% / $100 to $200 B/C = 13 to 6 2. Windshield not applicable 3. Semi-Automated, $5,000 x25% / $25 to $50 B/C = 50 to Automated, $5,000 x 25% / $30 to $80 B/C = 40 to 15 CONCLUSIONS With increased emphasis on rehabilitation of pavements premature cracking of overlays needs to be addressed. This paper has attempted to address this cracking by quantifying reductions in serviceability. It involves examining the C-SHRP LTPP database and indicates that reflective cracking in Canada is still a major problem. It has also been demonstrated that cracking related to reflection can result in a reduced service life of a pavement and significant costs. Thus, it is imperative that cracks be measured and treated appropriately prior to the construction of the overlay to yield significant cost savings. REFERENCES [1] Canadian Strategic Highway Research Program (C-SHRP), Pavement Research Technical Guidelines, Transportation Association of Canada, 1989 [2] Tighe, Susan, Ralph Haas and Ningyuan Li, Overlay Performance in the Canadian Strategic Highway Research Program s LTPP Study, 21 pp., Accepted for Publication In Transportation Research Record, National Academy of Sciences, Washington, D.C., [3]Abdelhalim, A.O., Phang, W.A. and Haas, Realizing Structural Design Objectives Through Minimization of Construction Induced Cracking, Proceedings of the Sixth International Conference on Structural Design of Asphalt Pavements, University of Michigan, 1987 [4] Haas, R.C.G., A Method For Designing Asphalt Pavements to Minimize Low-Temperature Shrinkage Cracking, Res. Report 73-1, The Asphalt Institute, College Park, Maryland, USA, Jan., 1973 [5] Frechette, Luc and Shalaby, Ahmed, Reflective Cracking Trends in C-SHRP LTPP Sites, Trans. Assoc. of Canada Report, 1997 [6] Haas, Ralph, Low Temperature Cracking of Airport Pavements, Proc., 5 th Annual Int. Airport Pavement Maintenance and Management Symposium, Bloomington, Minnesota, April, 1991 [7] Transportation Association of Canada, Pavement Design and Management Guide, Ottawa, 1997 [8] Queiroz, C.A.V., "A Procedure for Obtaining a Stable Roughness Scale From Rod and Level Profiles", Working Document 22, Brazil-UNDP Road Cost Study, September [9] Sayers, M.W., T.D. Gillespie and W.D. Paterson, "Guidelines for the Conduct and Calibration of Road Roughness Measurements", World Bank Technical Paper 46, Washington, D.C., [10] Deme, Imants, Prevention of Pavement Cracking and Rutting With Multigrade Type Bitumens, Paper presented to 31 st Annual Congress of the Association Québécoise du Transport et des Routes, Québec, Québec, March 24-27, 1996 [11] TRDF, A Summary of Pavement Performance Data Collection and Processing Methods Used by State DOT s, Report submitted to Federal Highway Administration, Oct., 1994 [12] FHWA, Pavement Maintenance Effectiveness, Publ. No. FHWA-SA , Oct., 1995 [13] Chong, G.J., Rout and Seal Cracks in Flexible Pavement: A Cost-Effective Maintenance Procedure, Report PAV-89-04, Ontario Ministry of Transportation, Aug [14] Joseph, P., Field Evaluation of Rout and Seal Treatment in Flexible Pavements, Report PAV-90-03, Ontario Ministry of Transportation, 1990 [15] Ponniah, Joseph and Gerhard Kennepohl, Crack Sealing in Flexible Pavements: A Life-Cycle Cost Analysis, Paper presented to TRB, Wash., Jan., 1995

9 Tighe, Haas and Ponniah Page 9 of 18 LIST OF FIGURES FIGURE 1 Reflective cracking at 5 years in C-SHRP LTPP Site in New Brunswick. 11 FIGURE 2 Factors, and interactions, which can affect pavement performance 13 FIGURE 3 Influence of cracking on pavement life. 14 FIGURE 4 Boxplot of overall national IRI s for all C-LTPP sections. 17 FIGURE 5 Example of extended pavement life due to crack treatment (rout and seal). 19 LIST OF TABLES TABLE 1 Suggested Limits for Cracking 12 TABLE 2 C-LTPP Crack Progression and Roughness Prediction 15 TABLE 3 ANOVA for IRI Prediction and Observed IRI With 15m Crack Spacing 16 TABLE 4 Typical Range of Costs for Cracking Surveys 18

10 Tighe, Haas and Ponniah Page 10 of 18 % Reflective Cracking After 5 Yrs Sec.1: 107mm HMAC & RAP Sec.2: 90mm Virgin HMAC Sec.3: 30mm Virgin HMAC Sec.4: 35mm Virgin HMAC (change in aggregate gradation) Wheelpath Centerline Edge Transverse FIGURE 1 Reflective cracking at 5 years in C-SHRP LTPP Site in New Brunswick [5].

11 Tighe, Haas and Ponniah Page 11 of 18 TABLE 1 Suggested Limits for Cracking[3] Max. No. of Full Transverse Cracks per 150 m Year Secondary Roads (< 2,000 AADT) Primary and Secondary Roads (> 2,000 AADT)

12 Tighe, Haas and Ponniah Page 12 of 18 ENVIRONMENT Moisture Temperature (Min., Max, Radiation 0 Days, etc.) Freeze-thaw Cycles STRUCTURE Layer Variations Thicknesses in Thickness Layer Types & Properties & Properties Subgrade Type & Properties Measure(s) of Serviceability or Deterioration CONSTRUCTION Timing Variance Methods As-Built Quality TRAFFIC Axle Group Loads Tire Types Axle Spacing, & Pressures Speed, Repetitions Age MAINTENANCE Treatments Quality Timing Methods FIGUR E 2 Factors, and interactions, which can affect pavement performance

13 Tighe, Haas and Ponniah Page 13 of 18 RIDING COMFORT INDEX Average spacing 9 between trans. cracks: 8 2 m 7 5 m 10 m 6 20 m 5 Minimum acceptable level = 5 RCI AGE (Years) Design Life 15 Years FIGURE 3 Influence of cracking on pavement life [5].

14 Tighe, Haas and Ponniah Page 14 of 18 TABLE 2 C-LTPP Crack Progression and Roughness Prediction Test Site Section Actual Cracks (/150m) Airport 1)- Model RCI Pavement Age (Years) Observed IRI ) ) ) ) ) ) ) ) ) ) ) ) ) RCI= CRACKINGAPACING-11.62/(CRACKINGSPACING)2[6] 2) Refers to those sections that meet the maximum number of cracks as per Table 1 [3]

15 Tighe, Haas and Ponniah Page 15 of 18 TABLE 3 ANOVA for IRI Prediction and Observed IRI With 15m Crack Spacing Comparison 1) - Test F CALCULATED Equation (2) IRI AND Table 2 Observed IRI Equation (3) IRI AND Table 2 Observed IRI Equation (4) IRI AND Table 2 Observed IRI Equation (5) IRI AND Table 2 Observed IRI Equation (6) IRI AND Table 2 Observed IRI Between 2) - Observed & Predicted Between 2) - Observed & Predicted Between 2) - Observed & Predicted Between 2) - Observed & Predicted Between 2) - Observed & Predicted F CRITICAL P-value Degrees of Freedom ) Uses C-SHRP test sections to predict IRI with different equations and compares to observed IRI. 2) Represents the differences in the predicted IRI and the observed cracking where the null hypothesis states regardless of how IRI is determined (observed or predicted), the values will be equal.

16 Tighe, Haas and Ponniah Page 16 of IRI (m/km) st Quartile Mean Median 3rd Quartile Prior Overlay FIGURE 4 Boxplot of overall national IRI s for all C-LTPP sections [2].

17 Tighe, Haas and Ponniah Page 17 of 18 TABLE 4 Typical Range of Costs for Cracking Surveys Method Manual Windshield survey Semi-automated Automated Cost Per Lane-km $100 to $200 $ 25 to $ 50 $ 25 to $ 50 $ 30 to $ 80

18 Tighe, Haas and Ponniah Page 18 of 18 Pavement Condition Index minimum acceptable level of service predicted control treated Years of Service FIGURE 5 Example of extended pavement life due to crack treatment (rout and seal) [15].