Using Existing Pavement in Place and Achieving Long Life (2014)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

11 C h a p t e r 3 Introduction The major findings from the project were assembled into one application with several resource documents, which collectively serve as guidelines for roadway renewal using existing pavements. Implementation and use of the guide- lines will be largely dependent on the ease of use and prac- ticality of the products. To this end, an interactive software program was developed to package the major components of the guidelines. The software and associated resource doc- uments are described following an overview of the study development findings. Phase 2 activities built upon and refined the findings from Phase 1 to develop a comprehensive set of decision matrices, design tables, and resource documentation that, collectively, comprise the renewal guidelines. In developing these guide- lines, significant coordination took place with the agency partners as identified in Chapter 2. Long-Life Definitions Rigid Pavements Long-life concrete pavements exist in the United States, as evi- denced by the number of high-age pavements that remain in service. Fortunately, at this time, advances in design, construc- tion, and materials provide the knowledge and technology needed to consistently achieve a long life. Some distress development over a concrete pavement’s service life is expected. However, the rate of distress devel- opment is managed by incorporating sound designs, dura- ble paving materials, and quality construction practices. Generally recognized threshold values in the United States for distresses at the end of the pavement’s service life are listed in Table 3.1 for jointed plain concrete pavements (JPCPs) and continuously reinforced concrete pavements (CRCPs). Flexible Pavements The purpose of long-life flexible pavements is to significantly extend current pavement design life by restricting distress, such as cracking and rutting, to the pavement surface. Common dis- tress mechanisms such as bottom-up fatigue cracking and rut- ting in the unbound layers should, in principle, be eliminated for long life. However, surface-initiated (top-down) cracking will still be possible in hot-mix asphalt (HMA). This type of cracking is caused by a combination of pavement structure, load, and environmental and material characteristics. Although its causes are still not fully resolved, this deterioration mecha- nism involves a fatigue-like response in the upper layers of the pavement. In addition to fatigue cracking and rutting, in cold climates, low-temperature cracking and frost heave must be eliminated or significantly reduced. Another deterioration mechanism is aging. Aging mainly affects the top asphalt lay- ers and is manifested by increased stiffness and decreased flexibility over time. A common denominator of the distress mechanisms is that they are difficult to model using current mechanistic-empirical methods. Some of the distresses require advanced response and/or performance models. In the case of top-down cracking and permanent deformations in the asphalt-bound layers, new and improved design methods may address this in the future. For asphalt concrete pavements, achieving long life requires the combination of a rut- or wear-resistant surface layer with a rut-resistant intermediate layer and a fatigue-resistant base layer. As illustrated in Figure 3.1 (Newcomb, Buncher, and Huddleston 2001), this requires a high-quality HMA wearing surface or an open graded friction course, a thick stiff dense graded intermediate layer, and possibly a flexible (asphalt- rich) bottom layer. In addition, the pavement foundation must be strong enough to satisfy the limiting strain criteria. When using existing pavements in the renewal process, the inhibition of reflective cracking is crucial. Reflective cracking is caused by repetitive shearing—for example, when a new Findings and Applications

12 asphalt layer is laid upon an already cracked layer. With time, the crack will propagate through the new layer. This is true regardless of the existing pavement type [i.e., distressed HMA or portland cement concrete (PCC)], although experience shows that reflective cracking can be more predominant when the existing pavement is a rigid pavement. Background on Existing Renewal Approaches The project team sought information on highway renewal using existing pavements for both flexible and rigid pavement renewal types. In addition, questionnaires were distributed to state high- way agencies (SHAs) and international representatives to solicit input on experience with the various renewal approaches. The following sections provide an overview of both relevant litera- ture and practitioners’ experience. Details on the literature review can be found in Appendix A. Rigid Pavement Renewal Long-life rigid pavement renewal strategies involve concrete overlays. Smith, Yu, and Peshkin (2002) state that the success of long-life renewal alternatives using existing pavements hinges on two critical parameters: (1) the timing of the renewal and (2) the selection of the appropriate renewal strategy. The selec- tion and timing are dependent on factors such as the condition of the existing pavement, the rate of deterioration of the dis- tress, the desired performance, lane closures and traffic control considerations, and user costs. Recent concrete overlay terminology was described by Har- rington (2008). These definitions provide a straightforward description of concrete overlays as shown in Figure 3.2. Two categories are shown: (1) unbonded concrete overlays and (2) bonded concrete overlays. Subcategories are defined based on the underlying pavement, which can be (1) concrete, (2) asphalt, or (3) composite pavements. Detained performance observations of bonded concrete overlays were obtained from the Texas Department of Trans- portation (TxDOT), Washington State Department of Transportation (WSDOT), and Minnesota Department of Transportation (MnDOT). Observed performance of 4- to 8-in. bonded overlays by TxDOT personnel indicated that their thicker bonded CRCP overlays can be expected to per- form up to 25 years; however, TxDOT only recommends a Table 3.1. Threshold Values for Long-Life Concrete Pavement Distresses Distress Threshold Value Cracked slabs, % of total slabs (JPCP) 10–15 Faulting, mm (in.) (JPCP) 6–7 (0.25) Smoothness (IRI), m/km (in./mi) (JPCP and CRCP) 2.5–3.0 (150–180) Spalling (length and severity) (JPCP and CRCP) Minimal Materials-related distress (JPCP and CRCP) None Punchouts, no./km (no./mi) (CRCP) 10–12 (12–16) Source: Tayabji and Lim 2007. Source: Newcomb et al. 2001. Figure 3.1. Long-life flexible pavement design concept.

13 design life of 5 to 10 years for 4- to 7-in. bonded concrete overlays of asphalt pavements (TxDOT 2011). The literature and documented SHA experience with bonded concrete overlays is supported by the data within the Long-Term Pavement Performance (LTPP) database (dis- cussed in a subsequent section). These experience and perfor- mance data for slabs up to about 6 in. thick suggest that a 50-year life is unlikely for bonded concrete overlays. Harrington (2008) found that bonded overlays are used to “add structural capacity and/or eliminate surface distress when the existing pavement is in good structural condition. Bonding is essential, so thorough surface preparation is necessary before resurfacing.” Harrington also noted that unbonded overlays are used to “rehabilitate pavements with some structural dete- rioration. They are basically new pavements constructed on an existing, stable platform (the existing pavement).” This concept of unbonded concrete overlays being similar to new pavement construction is expanded below. A best practices document by Tayabji and Lim (2007) over- viewed a selection of design, materials, and construction fea- tures for new concrete pavements for four SHAs (Illinois, Minnesota, Texas, and Washington). These practices were updated based on recent information and are summarized in Table 3.2 and Table 3.3. Minnesota and Washington were grouped together in Table 3.2 since their practices are for JPCP. Illinois and Texas are summarized in Table 3.3 to reflect their CRCP practices. Although these practices were developed with new pavement construction in mind, they are applicable to long-life concrete overlay systems. This type of information illustrates the following: • For JPCP 44 Design lives range from 50 to 60 years. 44 Slab thicknesses range between 11.5 and 13.0 in. 44 Joint spacings are 15 ft long, doweled, and corrosion resistant. 44 Maximum water/cementitious ratios range between 0.40 and 0.44. • For CRCP 44 Design lives range from 30 to 40 years. 44 Slab thicknesses range between 13.0 and 15.0 in. A more specific example of a long-lasting concrete overlay over preexisting PCC comes from Washington State. WSDOT constructed an unbonded concrete overlay on I-90 over 35 years ago. Figure 3.3 is a photograph of this overlay taken in 2010. The overlay is still performing well as of 2011 with no observable distress. Belgium is the only country outside the United States iden- tified in this review as having reported appreciable experience with unbonded concrete overlays (Hall et al. 2007). Belgium constructed its first concrete overlay in 1960, over a concrete Source: Harrington 2008. Figure 3.2. Types of concrete overlays.

14 Table 3.2. Examples of Long-Life JPCP Standards for MnDOT and WSDOT Item Minnesota DOT Washington DOT Design life • 60 years • 50 years Typical structure • Slab thicknesses = 11.5–13.5 in. • 3- to 8-in. dense-graded granular base • Subbase 12–48 in. select granular (frost resistant) • Slab thickness = 12–13 in. (typical) • 4-in. HMA base • 4-in. crushed stone subbase Joint design • Spacing = 15 ft with dowels • All transverse joints are doweled • Spacing = 15 ft with dowels • Joints saw cut with single pass • Hot poured sealant Dowel bars • Diameter = 1.5 in. (typical) • Length = 15 in. (typical) • Spacing = 12 in. • Bars must be corrosion resistant • Diameter = 1.5 in. • Length = 18 in. • Spacing = 12 in. • Bars must be corrosion resistant. Epoxy coatings not acceptable. Outside lane and shoulder • 14-ft lane with tied PCC or HMA • 12-ft lane with tied and dowel PCC Surface texture • Astroturf or broom drag • Longitudinal direction • Requires 1-mm average depth in sand patch test (ASTM E965) • Longitudinal texturing Alkali-silica reactivity (ASR) • Fine aggregate must meet ASTM C1260 (ASR Mortar-Bar Method) • Expansion ≤ 0.15% is OK. If ≥ 0.30%, reject. • Mitigation required by use of ground granulated blast furnace slag (GGBFS) or fly ash when expansion is between 0.15% and 0.30%. • Allow various combinations of Class F fly ash and GGBFS. Aggregate gradation • Use a combined gradation • Use a combined gradation. Concrete permeability • Use GGBFS or fly ash to lower permeability of concrete • Apply ASTM C1202 for rapid chloride ion permeability test. Air content • 7.0% ± 1.5% • 5.0% ± 2.0% Water/cementitious ratio • ≤ 0.40 • ≤ 0.44 • Minimum cementitious content = 564 lb/CY of PCC mix Curing • No construction or other traffic for 7 days or flexural strength ≥ 350 psi. • Traffic opening compressive strength ≥ 2,500 psi by cylinder tests or maturity method Construction quality • Monitor vibration during paving Sources: Tayabji and Lim 2007, MnDOT 2005, WSDOT 2010. pavement originally constructed in 1934. The jointed reinforced concrete pavement (JRCP) overlay is 7 in. thick. Figure 3.4 shows the overlay still in service nearly 45 years later. The study review found that design thicknesses of unbonded PCC overlays are typically greater than or equal to 9 in. for Interstate applications. This is supported by data from LTPP. In a study by Smith et al. (2002), a large number of unbonded overlay projects were identified and the highway agencies asked to rate their performance from good to poor. They found a strong correlation between thickness and perfor- mance, as shown in Figure 3.5. This figure was generated based on expert opinion from the study perform by Smith et al. (2002). It is evident that, for long-life pavements in high-traffic-volume applications, the unbonded overlay thick- ness should be 9 in. or greater. A recurring theme emerges in examining the literature and practices discussed above: (1) thick unbonded PCC slabs are used, (2) design lives are greater than or equal to 30 years ranging up to 60 years, and (3) PCC mix and materials require- ments are important. Thus, long-life PCC renewal options are not just about slab thickness but also about materials and construction, as expected. Key considerations include the following: • Foundation support (uniformity, volumetric stability— including stabilizing treatments); • Drainage design (moisture collection and removal and design for minimal maintenance); • Concrete mixture proportioning and components (selected, e.g., to minimize shrinkage and potential for chemical attack,

15 for low coefficient of thermal expansion, and to provide ade- quate strength); • Dowels and reinforcing (corrosion resistance, sized and located for good load transfer); • Construction parameters (including paving operations, surface texture, initial smoothness, etc.); and • Quality assurance/quality control (e.g., certification, pre- qualification, inspection). Flexible Pavement Renewal The review of flexible pavement renewal included the follow- ing seven approaches, each of which is briefly described below: • HMA over HMA renewal methods 44 HMA over existing HMA pavement and 44 HMA over reclaimed HMA (recycling). Table 3.3. Examples of Long-Life CRCP Standards for the Illinois and Texas DOTs Item Illinois DOT Texas DOT Design life • 30–40 years • 30 years Typical structure • Up to 14-in. CRCP slab • 4- to 6-in. HMA base • 12-in. aggregate subbase • Up to 13 in. CRCP slab with one layer of reinforcing steel • 14- to 15-in. CRCP slab with two layers of reinforcing steel • Uses stabilized base either 6-in. CTB with 1-in. HMA bond breaker on top or 4-in. HMA • Recommends tied PCC shoulders Tie bars • Use at centerline and lane-to-shoulder joints • Use 1-in. by 30-in. bars spaced at 24 in. CRCP reinforcement • Reinforcement ratio = 0.8% • Steel depth 4.5 in. for 14-in. slabs • All reinforcement in CRCP epoxy coated • Increased amount of longitudinal steel • Design details for staggering splices Aggregate requirements • Illinois DOT applies tests to assess aggregate freeze- thaw and alkali-silica reactivity (ASR) susceptibilities PCC mix • Limits the coefficient of thermal expansion of concrete to ≤ 6 microstrains per degree Fahrenheit. Construction requirements • Limits on concrete mix temperature = 50–90°F • Slipform pavers must be equipped with internal vibration and vibration monitoring • Curing compound must be applied within 10 min of concrete finishing and tining • Curing ≥ 7 days before opening to traffic • Revised construction joint details Sources: Tayabji and Lim 2007; TxDOT. Figure 3.3. Photo of 35-year-old unbonded PCC overlay on I-90 MP 74. Source: Hall et al. 2007. Figure 3.4. Belgium’s first concrete overlay after 45 years in service.

16 • HMA over PCC renewal methods 44 HMA over crack and seat JPCPs, 44 HMA over saw, crack, and seat JRCPs, 44 HMA over rubblized JPC pavements, 44 HMA over composite pavements, and 44 HMA over existing CRCPs. HMA Overlay and Existing HMA Pavement If there is no visible distress in the existing HMA pavement other than that in isolated areas, the existing pavement can be directly overlaid as long as it is determined to be structurally sound, level, clean, and capable of bonding to the overlay. How- ever, when visible surface distress is present and it is determined (through coring) to be near the surface, milling is required prior to the overlay. HMA Overlay and Reclaimed HMA In cases where the surface of the existing HMA layer is in poor condition, and the depth of the distress (cracking) is deeper in the pavement section, reclaiming the existing HMA pavement before the placement of new layers is required. To enable use of the existing pavement, this solution entails the pulverization of the existing HMA layer. However, by definition, once this solution is adopted, the reclaimed HMA material is considered a base layer and its thickness should not be included in the total HMA thickness that is used to calculate the limiting tensile strain at the bottom of that layer. The main limitation of this renewal solution is that the per- formance of partial- and full-depth reclamation with cement or asphalt emulsion has not been substantiated for long life. Records on performance are highly variable because there has not been a common definition applied to judge the com- parative performance levels. Causes commonly noted for poor performance using cold in-place recycling include (Hall et al. 2001) (1) use of an excessive amount of recycling agent; (2) premature application of a surface seal; (3) recy- cling only to the depth of an asphalt layer, resulting in delami- nation from the underlying layer; and/or (4) allowing a project to remain open for too long into the winter season. Also, excessive processing can result in higher fines content, leading to rutting because of low stability. HMA Overlay and Crack and Seat JPCP HMA over crack and seat JPCP is suitable for plain (unrein- forced) concrete pavements. The performance of this renewal option has been variable in the United States. This could be tied to the quality of the cracking operation. The rationale behind the crack and seat technique is to shorten the effective slab length between the transverse joints or cracks in the existing concrete pavement before placing the HMA overlay. This will distribute the horizontal strains resulting from thermal move- ments of the concrete more evenly over the existing pavement, thus reducing the risk of reflective transverse cracks in the HMA overlay. If construction guidelines ensure closely spaced, tight, full-depth vertical cracks, then potential for long life should be achievable. Experience in the United Kingdom has been excellent with crack and seat projects, but with a strict quality control pro- cess and a minimum HMA overlay thickness in excess of 6 in. (Jordan et al. 2008). Thinner overlays like those commonly used in the United States were not found to perform as well Source: Smith et al. 2002. Figure 3.5. Probability of poor performance for unbonded JPCP overlays.

17 in test sections in the United Kingdom (Coley and Carswell 2006). In addition, Caltrans (2004) has extensive experience with crack and seat processing of PCC slabs followed by an HMA overlay. The agency applies this treatment wherever the PCC pavement has an unacceptable ride and extensive slab cracking. The typical crack spacing is about 4 ft by 6 ft, fol- lowed by seating with five passes of a pneumatic-tired roller of at least 15 tons (Caltrans 2008). For several years, the over- lay thickness associated with the crack and seat process ranged from a minimum of 4 in. up to about 6 in. Service-life expectation was a minimum of 10 years with these thicknesses [or about 10 to 20 million equivalent single axle loads (ESALs)]. Starting in 2003 with the I-710 rehabilitation of existing 8-in.- thick PCC slabs near Long Beach (Monismith et al. 2009), the crack and seat process is followed by HMA overlays that are 9 in. thick. The design ESAL levels for these sections of I-710 have ranged between 200 and 300 million. This renewal strategy adopted by Caltrans implies a long life of at least 40 years. HMA Overlay and Saw, Crack, and Seat JRCP The crack and seat technique of fracturing reinforced concrete pavements (JRCPs) has generally not performed well because of its inability to shear the steel reinforcement or break the bond between the reinforcing steel and concrete. The bonded and unsheared reinforcing steel results in thermal contraction con- centrated at the existing transverse joints, thus leading to reflec- tive cracks through the HMA layer. An alternative solution used primarily in the United King- dom is the saw, crack, and seat approach, which involves sawing narrow transverse cuts into the concrete deep enough to cut through the longitudinal steel reinforcement, and then cracking the pavement at the locations of the sawed cuts, using the same crack and seat procedure described above (Merrill 2005). Verification coring should follow to ensure that fine, full-depth, vertical cracks are achieved. The U.K. Department of Transport Road Note 41 (Jordan et al. 2008) recommends a saw and crack spacing of 3 to 6 ft. Under these conditions, the critical features and limitations are the same as for the crack and seat approach. Similar to crack and seat process, thicker overlays were found to perform substantially better than thinner overlays in test sections in the United Kingdom (Coley and Carswell 2006). HMA Overlay and Rubblized JRCP and JPCP The rubblization approach effectively eliminates the problem of reflection cracking, because the technique is supposed to completely disintegrate the existing concrete slab and debond the concrete from the reinforcing steel. However, this also reduces the strength of the existing concrete pavement sub- stantially because it renders the concrete into broken frag- ments resembling an unbound base course, although with “aggregate” sizes much larger than a regular crushed aggregate base layer. Thus, it is the only approach that uses the existing concrete pavement and fully addresses slab movement respon- sible for reflective cracking, particularly for JRCP. Von Quintus et al. (2007) reviewed the performance of HMA overlays of PCC pavements from the 2005 LTPP data- base. Those findings suggest that sections without edge drains or those with rubblized pieces less than 2 in. in size exhibit higher levels of distress. SHA experience indicates construction difficulties with rub- blization if the foundation underneath the existing concrete is not sufficiently strong. The rubblization process can damage the base or subbase and/or the existing subgrade and produce an unstable condition. Sebesta and Scullion (2007) refined a risk assessment methodology for rubblization first developed in Illinois (Heckel 2002) based on dynamic cone penetrometer testing. This process is fully described in this project’s guide, Chapter 2 (Flexible Pavement Best Practices). HMA Overlay and Existing Composite Pavement HMA overlay of existing HMA-surfaced composite pavement is also a viable long-life HMA renewal solution. Sebesta and Scullion (2007) recommend milling the old HMA overlay completely off to expose the existing PCC pavement. The PCC pavement should be modified using either the crack and seat approach; the saw, crack, and seat approach; or the rubbliza- tion approach described above. HMA Overlay and Existing CRCP HMA over existing CRCP has significant potential to provide long life. This is because a CRCP eliminates moving joints within the concrete slab as it develops narrow transverse cracks at a regular spacing. If these cracks remain tight, then no reflection cracking should appear in the HMA overlay as long as the surface of the existing CRCP is in good condition and a good bond between the HMA overlay and the CRCP is achieved. This solution should lead to thinner HMA overlays compared to HMA over existing jointed concrete pavements. The main limitation of this renewal strategy is that any untreated or improperly treated defect in the existing CRCP can develop into a major repair. Studies have shown that the placement of HMA overlays can accelerate D-cracking, result- ing in poor performance of HMA overlays (Liu et al. 2003). Therefore, this approach would only apply to CRCP in good condition. Also, if bonding is not properly ensured, water caught between the HMA overlay and the existing CRCP can lead to stripping and HMA deterioration. Finally, the perfor- mance of HMA overlays on CRCPs has been variable in the United States. Therefore, the performance of HMA overlays using this solution has not been substantiated for a long life

18 (>50 years), and their use in the context of long-life pavements, while possible, is still unproven. Regardless of the flexible pavement renewal approaches reviewed, the following principles are required to achieve well- performing long-life pavements: • The quality of construction is essential in achieving long- life pavements. • Pavements are supposed to act as one layer; therefore, the bond between layers should never be compromised, and a few thick layers are better than multiple thin layers. • All joints are weaknesses; therefore, they need to be treated as such. • Good, continuous, and sustainable drainage is essential to long-life pavement; therefore, no matter how thick the renewal solution is, it can fail if drainage is not sufficient. • Foundation uniformity is essential to reduce or eliminate stress concentrations, which can cause future cracking. • A solid foundation allows good compaction; unsupported edges can never be properly compacted. • Thermal movements of the existing pavement are the under- lying cause for much reflective cracking; therefore, they must be eliminated (by fracturing the existing pavement). • Well-performing asphalt mixtures should have high binder content and low air voids (to have high durability) and smaller nominal size (to avoid segregation). Ltpp analyses The research team reviewed the LTPP database to provide insight into performance of various renewal approaches. A detailed analysis was made of the available, appropriate data. The analyses for both flexible and rigid pavement experiments are shown in Appendix B. In addition, selected projects from the LTPP database were examined by mechanistic-empirical design programs (MEPDG and PerRoad) to determine whether the basic roadway sections were likely to provide long- life pavements and to define critical features and limitations. The following is a summary of both the LTPP and related MEPDG analyses. Rigid Pavements The General Pavement Study 9 (GPS-9) (Unbonded PCC Overlay on PCC Pavement) and Specific Pavement Study 7 (SPS-7) (Bonded PCC Overlay on PCC Pavement) experi- ments were reviewed. The information for both experiments was extracted from the LTPP DataPave Online database (Release 21). The pavement performance criteria selected for the summary included transverse cracking, international roughness index (IRI), joint and crack faulting (JPCP), and punchouts (CRCP only). The original construction (preoverlay) date for the unbonded PCC overlay sections ranged from the early 1950s to the mid- 1970s. The actual overlays included both JPCP and CRCP. The average age of overlays until the test sections were taken out of service was about 17 years. The overlay thicknesses of the vari- ous test sections ranged from 5.8 to 10.5 in. with an average joint spacing of 16 ft. The load transfer mechanisms were either aggregate interlock or dowel bars. While a significant fraction of these unbonded PCC overlay GPS-9 test sections have potential for long-life performance, all were monitored for less than 20 years. Figure 3.6 provides a summary of transverse cracking as a function of overlay thickness for JPCP overlay sections. As can be seen, there is a clear difference in perfor- mance when overlay thicknesses are greater than 8 in. It should be noted that this finding is very similar to that from Smith et al. (2002) and shown in Figure 3.5. The LTPP SPS-7 experiment included bonded PCC over- lays on PCC pavement. Data from 18 CRCP, 9 JPCP, and Av er ag e N um be ro fT C Overlay Thickness Figure 3.6. JPCP overlay thickness versus average number of transverse cracks.

19 8 PCC (unreinforced PCC overlays of CRCP) test sections were analyzed. However, these 35 test sections only represent pavements in four locations since multiple SPS-7 test sections were constructed at each project. This is a limited data set given the grouping of test sections. The average age of overlays at the time the test sections were taken out of the LTPP study (and no longer monitored) was about 15 years. The overlay thicknesses of the various test sec- tions ranged from 3.1 to 6.5 in. The bonded overlays exhibited significant transverse cracking after 15 years of service and are unlikely candidates for long-life renewal. Because of the limited nature of this experiment, it is diffi- cult to assess the likelihood that bonded concrete overlays will provide a long-life service. This was confirmed with numerous discussions and project evaluations with TxDOT and other SHAs during Phase 2. Observed performance along with mechanistic-empirical analyses implies performance lives of up to 35 years, but 50-year service lives are unlikely. Flexible Pavements The following LTPP experiments were reviewed to determine the pavement life achieved for HMA-surfaced pavements where the existing pavement remained in place: • GPS-6A (Existing AC Overlay of AC Pavement); • GPS-6B (AC Overlay with Conventional Binder of AC Pavement); • GPS-7A (Existing AC Overlay of PCC Pavement); • GPS-7B (AC Overlay with Conventional Binder of PCC Pavement); • SPS-5 (Rehabilitation Strategies for AC Pavement); and • SPS-6 (Rehabilitation Strategies for PCC Pavement). Performance data including longitudinal cracking, fatigue cracking, transverse cracking, rut depth, and IRI were plot- ted against pavement age. Sections with the longest overlay ages were selected and traffic data (ESALs) corresponding to pavement age were extracted. The next step was to examine the better-performing sections to determine potential long- life pavement candidates. The majority of the test sections evaluated had overlays with ages of 16 years or less. Data from the GPS test sections with overlay ages of up to 34 years were available from the database. Although none of the test sections had overlays with 50 years of service, a selection of test sections exhibited perfor- mance that had the potential to meet the long-life criteria. These test sections were analyzed using the MEPDG and PerRoad software to model each of the test sections for performance. Limitations in the reflective cracking models, questionable predicted performance curves, and inability of the MEPDG to produce results using HMA over CRCP all limited findings that could be applied to the long-life renewal objectives of the project. Because of this, the sections were analyzed using the PerRoad software, which is based on the mechanistic-empirical approach of calculating pavement response mechanistically and estimating damage using empirical transfer functions and Miner’s rule. It uses the concept of limiting strain criteria. Per- Road estimates the time (i.e., pavement life) at which damage accumulation reaches 0.1 according to Miner’s rule. PerRoad results indicated that actual traffic loadings pro- duced horizontal and vertical strains well below reasonable thresholds. Although the field performance observations only captured about 16 years of actual performance, there is virtu- ally no fatigue damage observed for the sites. These findings support the notion that structural designs of flexible pavement renewal alternatives satisfying the limiting strain criteria for fatigue and subgrade rutting have the potential to achieve long- life service, assuming all other critical features are satisfied. Per- Road does not account for reflective cracking in its analysis, which must be considered when selecting the appropriate level of modification to the existing pavement structure. assessment of renewal approaches The results of the prior work were used to develop the features and describe the limits of each renewal alternative, which follow. Rigid Pavements Table 3.4 provides an overview of critical features and limita- tions of the rigid pavement renewal approaches. Flexible Pavements Table 3.5 provides a summary of critical features and limita- tions of each of the flexible pavement renewal approaches. Advantages and Disadvantages of Renewal Approaches In terms of advantages and disadvantages, Table 3.6 provides an overview of the rigid pavement renewal approaches, and Table 3.7 provides an overview of the flexible pavement renewal approaches. Rigid pavement renewal options require less modification to the existing pavement. As such, there are fewer approaches listed for the rigid pavement renewal as compared to the flexible pavement alternatives. Based on the preceding findings, decision matrices were developed with the intent of establishing a list of feasible alter- natives for a project based on existing conditions. These matri- ces were submitted in draft form for review and comment by

20 Table 3.4. Summary of Rigid Pavement Renewal Features and Limitations Approach Critical Features Limitations Unbonded PCC overlay over existing PCC • Overlay thickness is critical to performance • Repair locally failed areas • Stable subbase • 1.5-in. diameter rust-resistant dowels • 15-ft maximum joint spacing • Interlayer should not trap water • Thicker HMA interlayer performed better • Adequate drainage • Significant surface elevation increase • Consistent foundation support when widening • Consistent drainage when widening Unbonded PCC overlay over existing HMA • Overlay thickness is critical to performance • Locally failed areas must be repaired • Stable subbase • 1.5-in. diameter rust resistant dowels • 15-ft maximum joint spacing • Adequate drainage • Significant surface elevation increase • Consistent foundation support when widening • Consistent drainage when widening Bonded PCC overlay over existing PCC • Adequate surface preparation • Bonding is a critical feature • Locally failed areas must be repaired • Match joint location, width, type of existing PCC • Adequate drainage • Existing pavements with materials-related distress are not good candidates • Existing pavements with voids are not good candidates • Working cracks can cause debonding of overlay • Service life up to 35 years Table 3.5. Summary of Flexible Pavement Renewal Features and Limitations Approach Critical Features Limitations HMA over existing HMA • Absence or removal of full-depth cracking • Good foundation support • No stripping • Adequate drainage • Reconstruction required if base or subgrade is poor • Milling required to remove surface cracking HMA over reclaimed HMA • Good foundation support • Adequate drainage • Proper surface prep and tack coat • Cement and/or emulsion have not yet been proven in field for long life • Reclaimed layer considered as base material HMA over existing CRCP • Good foundation support • Adequate drainage • No evidence of pumping • Existing pavement is structurally adequate • Absence or repair of major defects • Good bond of CRCP and HMA • CRCP has to be in good condition with few major defects (which must be repaired) • Inadequate bonding can lead to poor performance • Unproven for 50-year life HMA over crack and seat JPCP • Good foundation support • Adequate drainage • No evidence of pumping • Inability to break and seat JRCP has been documented • Crack and seat is not viable for reinforced PCC HMA over saw, crack, and seat JRCP • Good foundation support • Adequate drainage • No evidence of pumping • Saw cuts must extend below reinforcement HMA over rubblized • Good foundation support • Adequate drainage • No evidence of pumping • Pavement needs to be adequately drained before rubblization • Performance tied to quality of rubblization process • When subgrade conditions are inadequate, significant damage to base or subgrade has created construction problems

21 Table 3.6. Advantages and Disadvantages of Rigid Pavement Renewal Approaches Rigid Pavement Renewal Approach Advantages Disadvantages Unbonded concrete overlay over PCC • Very good long-term performance with minimal maintenance or rehabilitation • Insensitive to existing pavement condition • Best documented record of projects in place that have achieved long life • Significant surface elevation gain • Placement or cure time may make work-zone management difficult Bonded concrete overlay • Smallest vertical elevation gain • Unlikely to be viable for service lives longer than 35 years Unbonded concrete overlay over HMA • Requires little preparation for existing pavement • Easily accommodates lane addition • Significant surface elevation gain • Placement or cure time may make work-zone management difficult Table 3.7. Advantages and Disadvantages of Flexible Pavement Renewal Strategies Flexible Pavement Renewal Approach Advantages Disadvantages HMA over reclaimed/milled HMA pavement • Elimination of all existing deterioration that could lead to reflective cracking • Existing pavement is considered base material in renewal structural design • Significant thickness of new HMA required over modified existing structure HMA over CRCP • Utilizes CRCP in place as part of renewal • HMA wearing surface will need to be removed or replaced at 10- to 20-year cycles HMA over crack and seat • Does not diminish the structural competency as much as rubblization • Reflection cracking risk • Performance dependent on quality of crack and seat • HMA wearing surface will need to be removed/ replaced at 10- to 20-year cycles HMA over saw, crack, and seat • Does not diminish the structural compe- tency as much as rubblization • Reflection cracking risk • Performance dependent on quality of crack and seat • HMA wearing surface will need to be removed or replaced at 10- to 20-year cycles • Costs associated with sawing HMA over rubblized • Elimination of features in existing pavement that cause reflective cracking • Stiffness of rubblized material greater than granular base • Total HMA thickness is less than that over granular base • Construction risk with weak or wet subgrade • Performance dependent on quality of rubbliza- tion process • Poorly rubblized material cannot be improved through additional rubblization • Raises surface elevations • HMA wearing surface will need to be removed or replaced at 10- to 20-year cycles the study review panel. Details are discussed in the following section. Design Guides The development of design guides started with development of a draft decision process based on the initial study results. The following strategies were included: • HMA over existing HMA; • HMA over reclaimed or milled existing HMA pavement; • HMA over existing CRCP; • HMA over crack and seat existing JPCP; • HMA over saw, crack, and seat existing JRCP; • HMA over rubblized existing JPCP or JRCP; • Unbonded concrete overlay over existing JPCP, JRCP, or CRCP; and • Unbonded concrete overlay over existing HMA. Development of Decision Matrices A set of decision matrices, organized as tables, were devel- oped to aid in the scoping of renewal strategies. Separate matrices, with associated decision paths, were developed for selecting renewal options for the various, existing pavement types. The existing pavement types include flexible, rigid

22 (JPCP, JRCP, and CRCP), and composite pavements. Specific decision tables, regardless of existing pavement type, use three levels of decision making, as illustrated in Table 3.8. The sur- face condition of the existing pavement is the primary infor- mation required for starting the renewal decision-making process. The guidelines were developed to help designers in select- ing either a rigid or flexible reconstruction approach that can reasonably be expected to provide long-life pavement perfor- mance. For this project, long-life performance was defined as providing 50 years of service without major structural dete- rioration. It is anticipated that any approach selected will require some form of rehabilitation or resurfacing during the service life of the pavement. The final selection of the most appropriate design should be based on a life-cycle cost analy- sis of the various approaches, including all rehabilitation or resurfacing costs over the life of the pavements. The development of the decision matrices followed a pro- cess where team members laid out an outline of the decision process. The outline had the basic form seen on the tables with pavement type, distress present, and potential renewal approaches for those conditions. The outline was circulated to the full team and modified as additional considerations were added. The outline was presented at the kickoff meet- ings and then circulated among the participating agencies for comment, and again adjustments were made. To make the process clearer the decision matrix was put in a set of tables. The tables were then circulated again to the full R23 team and the participating agencies, who provided more comments (most likely because the tables were easier to follow than the outlines). The tables were then used to build an interactive Flash-based program that would simplify using the decision matrix. In building the logic for the interactive program, a few more decision points were added based on the more rig- orous nature of that process. After the program was devel- oped, it was evaluated through a series of trials that included a wide range of potential applications. The decision tables were adjusted again based on errors or omissions found in that process. The interactive program and the decision tables were again presented to the participating agencies for review and comment and final adjustments were made to the pro- gram and the tables presented in this report. The decision matrices account for deterioration and surface distress types present in existing pavement, as well as structural response (i.e., deflections) and subgrade conditions. They pro- vide a feasible set of alternatives based on in situ conditions of the existing pavement. For example, if full-depth cracking is present and the quantity is large enough to make full-depth patching cost prohibitive, the decision matrix eliminates the alternative to mill existing HMA and overlay with new HMA. Table 3.8. Organization and Decision Levels for Renewal Selection Decision Levels First Level Second Level Third Level Basis for Decision Identify Distress Category Identify Specific Distress Type within a Distress Category Select Renewal Pavement Type Renewal Action Design Resources Details associated with each decision. Decision tables a function of the existing pavement type. Existing flexible • Environmental cracking • Materials caused distress • Full-depth fatigue cracking • Top-down cracking • Transverse or block cracking • Stripping • Longitudinal or alli- gator cracking Either a flexible or rigid option can be selected for each specific distress or category. Describes what is to be done to the existing pavement and the type of renewal strategy. Describes the design resources to be used to complete the scoping process. Existing JPCP or JRCP • Materials caused distress • Pavement cracking • Joint faulting and movement • Pumping • D-cracking • Alkali-silica reactivity (ASR) • Fault depth • Joint deflection Existing CRCP • Punchouts — Existing composite • Surface course condition —

23 Instead, for the flexible alternative, full-depth pulverization or reclamation is recommended along with HMA overlay. The decision process would also recommend an unbonded concrete overlay as a rigid renewal alternative. The intent of the decision matrices is to provide a set of feasible long-life alternatives. Both flexible and rigid renewal options are included as outputs. The decision matrices are shown in Table 3.9 (renewal of existing flexible pavement), Table 3.10 (renewal of existing JPCP and JRCP), Table 3.11 (renewal of existing CRCP), and Table 3.12 (renewal of composite pavements). Three rules are commonly refer- enced in Tables 3.9 through 3.12 under the Design Resources column. Rule 1 Rubblization of existing PCC and then application of AC overlay are detailed in this project’s guide. Rubblization guidelines include the following: • If the subgrade MR < 6,000 psi or CBR < 4%, do not rub- blize, thus defaulting to crack and seat only. • If the subgrade MR ≥ 6,000 psi but MR < 10,000 psi, consult the TTI rubblization guidelines as to whether rubblization is viable (Sebesta and Scullion 2007). • If the subgrade MR ≥ 10,000 psi, then rubblization is a viable option. The selection of the AC thickness is based on a drop-down menu of subgrade moduli of 5,000 psi, 10,000 psi, or 20,000 psi. The existing pavement shall be characterized by one of four pos- sible moduli: 30,000 psi, 50,000 psi, 75,000 psi, or 100,000 psi. It is recommended that an existing pavement modulus equal to 50,000 psi be used to reflect rubblized PCC. Rule 2 Regarding crack and seat existing PCC followed by applica- tion of AC overlay, see Tables 3.13 through 3.15. The selection of the AC thickness is based on a drop-down menu of sub- grade moduli of 5,000 psi, 10,000 psi, or 20,000 psi. The exist- ing pavement shall be characterized by one of four possible moduli: 30,000 psi, 50,000 psi, 75,000 psi, or 100,000 psi. It is recommended that an existing pavement modulus of 75,000 psi be used for crack and seat PCC to produce thickness in line with those recommended in TRL Road Note 41 (Jordan et al. 2008). Rule 3 Use Table 3.16 for thickness determination of an unbonded PCC overlay and place on a 2-in.-thick AC bond breaker. The unbonded PCC overlay thickness is independent of subgrade support conditions. Development of Renewal Thickness Designs In part of its study, the project developed the thickness design tables that the decision matrices reference. These thicknesses provide approximate ranges for scoping purposes. They can also be used as a starting point for project-level design, but the agency-specific design methodologies should be used to develop the final thickness design. The flexible pavement renewal thickness design tables were developed using the limiting strain approach via the PerRoad, Version 3.5 software. Numerous scenarios were analyzed using PerRoad, including combinations to account for the following factors: • Traffic levels; • Subgrade stiffness; • Base stiffness; • Base thickness; • Seasonal temperatures (from climatic data) for five locations; • Standard PG binder specifications for five locations; • Tensile strains at the bottom of the HMA layer; and • Damage ratio scenarios (0.1 at 10 years and 0.1 at 50 years). For each combination of factors, PerRoad was run itera- tively to find the HMA thickness that would provide a dam- age ratio less than or equal to 0.1 at 10 years and 50 years of service life. Details about the analyses can be found in this project’s guide. The final design thicknesses used in the guidelines are shown in Tables 3.13 through 3.15. These thicknesses are representative of analyses from five U.S. locations. It is expected that any agency using the guidelines will refine the design thickness using their standard design procedure. The rigid pavement renewal thickness design tables were developed in a similar fashion as the flexible pavement renewal alternatives. AASHTO 93 and MEPDG Version 1.1 were used in the development of the rigid pavement thick- ness design tables. AASHTO 93 was used during a prelimi- nary investigation on thickness requirements. Numerous iterations were conducted using MEPDG to account for the following factors: • Traffic levels; • Performance criteria thresholds; • Mixture properties; • Shoulder support; and • Geographic location. (continued on page 30)

24Table 3.9. Feasible Renewal Alternatives for Existing Flexible Pavements Distress Category Specific Distress Description Distress Present? Renewal Pavement Type Option Action Design Resources Environmental cracking Transverse or block cracking Yes Flexible Pulverize pavement structure full depth followed by a thick AC overlay. Pulverize and use residual material as untreated base (50 ksi). Apply AC thickness from Tables 3.13–3.15. Pulverize and treat residual material with emulsion or foamed asphalt resulting in a treated base (100 ksi). Apply AC thickness from Tables 3.13–3.15. Rigid No mitigation required; place an unbonded PCC overlay. Use Table 3.16 for thickness determination of an unbonded PCC overlay. No — Continue to “materials-caused distress.” — Materials-caused distress Stripping Yes Flexible If stripping is found through all layers, pulverize pave- ment structure full-depth followed by a thick AC overlay. Pulverize and use residual material as untreated base (50 ksi). Apply AC thickness from Tables 3.13–3.15. Pulverize and treat residual material with emulsion or foamed asphalt resulting in a treated base (100 ksi). Apply AC thickness from Tables 3.13–3.15. If stripping is found in specific layers, remove AC to maximum depth of stripping followed by a thick AC overlay. Use Tables 3.13–3.15 with 30-ksi base and the sub- grade mR to determine total depth of AC thickness, then subtract remaining AC thickness to determine overlay thickness. Rigid Place unbonded PCC overlay. If grade limits require, mill existing pavement. AC overlay over stripped pavement may be required to stabilize HMA. Use Table 3.16 for thickness determination of an unbonded PCC overlay. No — Continue to “full-depth fatigue cracking.” — (continued on next page)

25 Full-depth fatigue cracking Longitudinal or alli- gator cracking in wheelpaths Yes Flexible <15% fatigue cracking: patch and repair, moderate thickness AC overlay. Use Tables 3.13–3.15 with 30-ksi base for AC overlay thickness, then subtract existing AC thickness to determine overlay thickness. >15% fatigue cracking: pulverize pavement structure full-depth followed by a thick AC overlay. Pulverize and use residual material as untreated base. Apply AC thickness from Tables 3.13–3.15 with 50-ksi base. Pulverize and treat residual material with emulsion or foamed asphalt resulting in a treated base. Apply AC thickness from Tables 3.13–3.15 with 100-ksi base. Rigid Patch severely cracked areas, place an unbonded PCC overlay. Profile elevation may require milling existing AC pavement. Use Table 3.16 for thickness determination of an unbonded PCC overlay. No — Continue to “top-down cracking.” — Top-down cracking Longitudinal or alli- gator cracking in wheelpaths Yes Flexible <15% patch and overlay. Use Tables 3.13–3.15 with 30-ksi base and the subgrade mR to determine total depth of AC thickness, then subtract the thickness milled out to eliminate the top-down cracking (unless indicated the assumed depth is 2 in.). Where patching only, subtract existing depth to calculate overlay. >15% mill down to bottom of cracking followed by a moderate thickness AC overlay. Rigid Place an unbonded PCC overlay. Use Table 3.16 for thickness determination of an unbonded PCC overlay. Table 3.9. Feasible Renewal Alternatives for Existing Flexible Pavements (continued) Distress Category Specific Distress Description Distress Present? Renewal Pavement Type Option Action Design Resources

26Table 3.10. Feasible Renewal Alternatives for Existing JPCP and JRCP Pavements Distress Category Specific Distress Description Distress Present? Renewal Pavement Type Option Action Design Resources Materials-caused distress D-cracking with light severity Yes Flexible option for JPCP Rubblization or crack and seat JPCP followed by a thick AC overlay. For rubblization, apply TTI guide- lines (Sebesta and Scullion 2007). Apply Rule 1. Apply Rule 2. Flexible option for JRCP Rubblization or saw, crack and seat JRCP with a thick overlay. For rubblization, apply TTI guidelines (Sebesta and Scullion 2007). Apply Rule 1. Saw, crack, and seat existing PCC followed by application of AC overlay from Tables 3.13–3.15; otherwise, Rule 2 applies. Rigid option Apply 2-in. AC overlay bond breaker followed by an unbonded PCC overlay. Apply Rule 3. No — Continue to next level of “D-cracking.” — D-cracking with moderate to high severity Yes Flexible option with rubblization if subgrade meets TTI guidelines Rubblize followed by a thick AC overlay. For rubblization, apply TTI guidelines. Apply Rule 1. Flexible option if does not meet TTI guidelines for rubblization Do not use the existing pavement; requires all new pavement. — Rigid option Full-depth patch and apply 2-in. AC overlay bond breaker followed by an unbonded overlay. Apply Rule 3. No — Continue to “ASR.” — Alkali-silica reactiv- ity (ASR) Yes Flexible option Rubblize followed by thick AC overlay. For rubblization, apply TTI guidelines. Apply Rule 1. Rigid option Patch plus 2-in. AC bond breaker followed by unbonded PCC overlay. Apply Rule 3. No — Continue to “pavement cracking.” — Pavement cracking % multiple cracked panels Yes Flexible option for low to moder- ate multiple cracked panels (1 to 10% of panels) Rubblization or crack and seat JPCP with a thick AC overlay. For rubblization, apply TTI guidelines (Sebesta and Scullion 2007). Apply Rule 1. Rigid option for low to moderate multiple cracked panels (1% to 10% of panels) Place a 2-in. AC bond breaker followed by an unbonded PCC overlay. Apple Rule 3. Flexible option for moderate to high multiple cracked panels (>10% of panels) If subgrade meets or exceeds TTI criteria, apply rubblization followed by a thick AC overlay. Apply Rule 1. If subgrade does not meet TTI criteria, options include crack and seat or do not use existing pavement. Apply Rule 2. Rigid option for moderate to high multiple cracked panels (>10% of panels) Replace rocking or shattered slabs followed by a 2-in. AC overlay bond breaker followed by an unbonded PCC overlay. Apply Rule 3. No — Continue to “joint faulting.” — (continued on next page)

27 Joint faulting — Yes Flexible option for low faulting (<0.25 in.) Rubblization or crack and seat JPCP with a thick AC overlay. For rubblization, apply TTI guidelines (Sebesta and Scullion 2007). Apply Rule 1. Rubblization or saw, break and seat JRCP with a thick AC overlay. For rubblization, apply TTI guide- lines (Sebesta and Scullion 2007). Apply Rule 2. Apply Rule 1. Saw, crack, and seat existing PCC followed by application of AC overlay from Tables 3.13–3.15; otherwise, Rule 2 applies. Rigid option for low faulting (<0.25 in.) Place a 2 in. AC overly followed by an unbonded PCC overlay. Apply Rule 3. Yes Flexible option for high faulting (>0.25 in.) Rubblization or crack and seat JPCP with a thick AC overlay. For rubblization, apply TTI guidelines (Sebesta and Scullion 2007). Apply Rule 1. Apply Rule 2. Rubblization or saw, break, and seat JRCP with a thick AC overlay. For rubblization, apply TTI guide- lines (Sebesta and Scullion 2007). Apply Rule 1. Saw, crack, and seat existing PCC followed by application of AC overlay from Tables 3.13–3.15; otherwise, Rule 2 applies. Rigid option for high faulting (>0.25 in.) Place a 2-in. AC overlay followed by an unbonded PCC overlay. If joint deflections >40 mils (0.040 in.), then consider crack and seat JPCP or saw, break, and seat JRCP to stabilize slabs. Apply Rule 3. No — Continue to “pumping.” — Pumping — Yes Flexible Crack and seat JPCP with a thick AC overlay if the drainage can be improved. Apply Rule 2. Saw, crack, and seat JRCP with a thick AC overlay if the drainage can be improved. Saw, crack, and seat existing PCC followed by application of AC overlay from Tables 3.13–3.15; otherwise, Rule 2 applies. If drainage cannot be improved, then AC based renewal should not be used. — Rigid If joint deflections >40 mils (0.040 in.), consider crack and seat followed by a 2-in. AC bond breaker fol- lowed by an unbonded PCC overlay. Drainage must be improved. Apply Rule 3. No — — — Table 3.10. Feasible Renewal Alternatives for Existing JPCP and JRCP Pavements (continued) Distress Category Specific Distress Description Distress Present? Renewal Pavement Type Option Action Design Resources

28 Table 3.11. Feasible Renewal Alternatives for Existing CRCP Pavements Distress Category Specific Distress Description Distress Present? Renewal Pavement Type Option Action Design Resources Punchouts — Yes Flexible option with ≤5 punchouts per mile Repair all punchouts; place thick AC overlay to achieve a longer service life. Apply AC overlay from Tables 3.13–3.15. The selec- tion of the AC thickness is based on a drop-down menu of subgrade moduli = 5,000 psi, 10,000 psi, or 20,000 psi. The existing pavement shall be characterized by one of four possible moduli to select from: 30,000 psi, 50,000 psi, 75,000 psi, or 100,000 psi. Rigid option with ≤5 punchouts per mile Repair major punchouts if slab load sup- port in question. Follow repairs with a 2-in. AC bond breaker followed by an unbonded PCC overlay. Apply Rule 3. Flexible option with >5 punchouts per mile Rubblization of CRCP with a thick AC overlay. For rubblization, apply TTI guidelines (Sebesta and Scullion 2007). Apply Rule 1. Rigid option with >5 punchouts per mile Repair major punchouts if slab load sup- port in question. Follow repairs with a 2-in. AC bond breaker followed by an unbonded PCC overlay. Apply Rule 3. No — — —

29 Table 3.12. Feasible Renewal Alternatives for Existing Composite Pavements Distress Category Specific Distress Description Distress Present? Renewal Pavement Type Option Action Design Resources Surface course in fair to poor condition Can be a range of distress types. For the underlying PCC, these are mostly crack- ing related. Yes Flexible option Remove existing AC surface(s). Apply rubbliza- tion if meets TTI criteria. Apply Rule 1. Remove existing AC surface(s). Use crack and seat or saw, crack, and seat. Following crack and seat or saw, crack, and seat of existing PCC pavement. Apply Rule 2. Rigid option Place unbonded PCC overlay. If grade limits require, mill existing AC pavement. Apply Rule 3. Surface course in very poor condition Can be a range of distress types. For the underlying PCC, these can include severe D-cracking and ASR. Yes Flexible option Remove and replace existing pavement structure. — Rigid option Place unbonded PCC overlay. If grade limits require, mill existing AC pavement. Apply Rule 3.

30 Table 3.13. Flexible Pavement Renewal Designs ESALs (millions) Existing Pavement or Base Modulus 30,000 psi 50,000 psi 75,000 psi 100,000 psi ≤10 10.0 9.0 8.0 6.0 10–25 11.0 10.0 8.5 6.5 25–50 12.0 11.0 9.0 7.0 50–100 13.0 11.5 9.5 7.5 100–200 14.0 12.0 10.0 7.5 Note: Subgrade mR = 5,000 psi. Table 3.14. Flexible Pavement Renewal Designs ESALs (millions) Existing Pavement or Base Modulus 30,000 psi 50,000 psi 75,000 psi 100,000 psi ≤10 10.0 8.0 7.0 6.0 10–25 11.0 9.0 8.0 6.5 25–50 12.0 9.5 8.5 7.0 50–100 12.0 10.0 8.5 7.0 100–200 13.0 11.0 9.0 7.0 Note: Subgrade mR = 10,000 psi. Table 3.15. Flexible Pavement Renewal Designs ESALs (millions) Existing Pavement or Base Modulus 30,000 psi 50,000 psi 75,000 psi 100,000 psi ≤10 9.5 7.5 6.5 5.5 10–25 10.0 8.5 7.0 6.0 25–50 11.0 9.0 7.5 6.5 50–100 11.5 9.5 8.0 6.5 100–200 12.0 10.0 8.5 7.0 Note: Subgrade mR = 20,000 psi. Table 3.16. Rigid Pavement Renewal Designs (AASHTO 93, MEPDG, and WSDOT Results) ESALs (millions) AASHTO 93 for k 5 500 pci Design Thicknesses from WSDOT Pavement Policy Thickness Range for MEPDG for MR 5 5–10 ksi PCC Slab Thickness for R23 Study (in.) ≤10 10.0 9.0 7.75–8.25 8.5 10–25 11.5 10.0 8.75–9.0 9.5 25–50 12.5 11.0 9.25 10.5 50–100 14.0 12.0 11.5–12.25 11.5 100–200 15.5 13.0 11.25–15.5 13.0 Initial evaluations indicated that for purposes of thickness tables for the guidelines, Baltimore, Maryland, would provide results that were representative of the range of climates found in the United States. The default calibration coefficients in MEPDG were used in the analysis and yielded results that were similar to those of other geographic locations. The results were also compared to the thickness catalog recently developed by WSDOT for long-life concrete pavement projects based on MEPDG runs calibrated to actual pavement performance in Washington State. The final design thicknesses selected for use in the guidelines are provided in Table 3.16. Results from the assessment of the LTPP test sections along with findings from prior studies suggest that unbonded concrete overlay thicknesses greater than 8.5 in. exhibit long-life potential. Complete details on the analy sis conducted in developing the rigid pavement design thickness table can be found in Appendix D. Validation Throughout this project, the team made several visits to the participating agencies to solicit feedback on the guidelines. During the first set of visits, the findings from Phase 1 along with objectives of the project were discussed. Additionally, field visits were made to multiple renewal projects throughout each agency. A second round of visits with the agencies focused on soliciting feedback on the decision matrices and thickness design tables, as well as the resource documentation. The interactive software was in beta version for many of these meetings. The team provided access to the beta version along with presentations explaining the development and use of the software. Through this process, valuable comments were received from the agencies. The team also worked with each agency to identify one proj- ect to be used as a test case—as noted in Chapter 2. This test case would be used to compare the agency’s standard design (continued from page 23)

31 approach for pavement renewal with the recommendations provided by the new guidelines. During the visit, the team acquired detailed design information on the project from each agency to be used as a test case. This included design traffic lev- els, existing pavement structure, subgrade conditions, falling weight deflectometer (FWD) data (if available), materials test results, and any project constraints (e.g., maintenance of traffic, vertical clearances). In many cases, the team made a field visit to the project to conduct a visual assessment of the site and cap- ture photographs of the pavement and drainage features. The following projects were used as test cases for this study: • Michigan: I-75 in Cheboygan County; • Minnesota: I-35 in Chisago County; • Missouri: I-55 in Perry County; • Texas: US-75 Loy Lake Road to Exit 64; • Virginia: I-95 in Caroline County; and • Washington: I-5 in Skagit County at Bow Hill. The data collected from each agency were used to develop a design report using the guidelines and interactive software. For each test case, feasible flexible and rigid renewal strategies were developed and documented. The results were compared to the agencies’ standard design approach for each project. As an example, the test case for the Virginia DOT was on I-95, a major traffic corridor for that state. Maintenance of traffic was a major concern and a primary limiting constraint of the renewal strategy selected. For this particular test case, the analysis was expanded to include construction productiv- ity, lane closure alternatives, and traffic impacts. Each of the scenarios was analyzed using CA4PRS and the results were summarized in a report. In most cases, the recommendations differed between the guidelines and agency standard practice. This was mostly due to differences in thickness design methodologies and design life. The guidelines provide recommendations for 50-year service life, whereas many of the agencies were designing for 20 to 30 years. In other cases, the agency adopted the recommendations that came out of the guidelines. Table 3.17 provides a summary of the renewal strategies for each test case. For the Washington test case, WSDOT estimated that using the existing pavement in the renewal process reduced the costs by over 25% compared to removing and replacing the existing pavement. There was also a comparable reduction in the time required for construction. The team organized and facilitated one pilot workshop in Washington and two regional workshops in Virginia and Missouri. Near the end of each workshop, every participant was asked to complete a questionnaire. Overall, the participants viewed the guidelines as valuable and useful. In particular, the resource documentation (see next section) was viewed by attendees as excellent content for pavement designers. All comments received were reviewed and addressed in the final guidelines. resource Knowledge Base The knowledge base assembled as part of the guidelines includes six documents developed specifically for this project, all of which are provided in this project’s guide: • Guide, Chapter 1—Project Assessment Manual; • Guide, Chapter 2—Flexible Pavement Best Practices; • Guide, Chapter 3—Rigid Pavement Best Practices; • Guide, Chapter 4—Guide Specifications; • Guide, Chapter 5—Life-Cycle Cost Analysis; and • Guide, Chapter 6—Emerging Pavement Technology. A synopsis of each document developed as part of this study is provided below. In addition, several other resources developed under separate research efforts have been referenced in the knowledge base. Table 3.17. Comparison of Study and Agency Renewal Approaches Agency R23 Recommendation (Flexible) R23 Recommendation (Rigid) Agency Renewal Approach MDOT 9-in. HMA over rubblized or 8-in. HMA over saw, crack, and seat 9.5-in. unbonded concrete overlay (UBCOL) with 2-in. HMA bond breaker 8.5-in. HMA over rubblized PCC pavement MnDOT 9-in. HMA over pulverized AC pavement 10.5-in. UBCOL 6-in. bonded PCC OL (20-year design) MoDOT 9.5-in. HMA over rubblized or 8.5-in. HMA over saw, crack, and seat 10.5-in. UBCOL with 2-in. HMA bond breaker 8-in. UBCOL with 1-in. HMA bond breaker or 12-in. HMA over rubblized PCC TxDOT 9.5-in. HMA over crack and seated PCC pavement 11.5-in. UBCOL with 2-in. HMA bond breaker 6-in. bonded PCC OL (special test case) VDOT Mill 6-in. stripped HMA then place 9-in. new HMA 13-in. UBCOL Mill all 10-in. HMA and replace with 12-in. HMA WSDOT Remove existing HMA over PCC, crack and seat PCC, and place 7.5-in. HMA 10.5-in. UBCOL Remove existing HMA over PCC, crack and seat PCC, and place 8.5-in. HMA

32 Project Assessment Manual The Project Assessment Manual was prepared to offer agencies a systematic collection of relevant pavement-related data. Fur- thermore, such data need to be organized to maximize the use- fulness in the pavement decision-making process. To that end, this manual provides an overall assessment scheme (Figure 3.7). The types of data collection in the manual range from basic information such as a distress survey to insights on construction-related traffic impacts. The last section in the Project Assessment Manual provides information on life-cycle assessments (environmental accounting). This type of assess- ment is receiving increasing use and is likely to be more widely applied in the future. The complete manual can be found in this project’s guide, Chapter 1. The use of the manual is to complement the design tools developed by the study. The types of data critical for making pavement-related decisions are described along with meth- ods (analysis tools) for organizing the information for deci- sion making. It is not assumed that all data categories will be collected or assessed for a specific renewal project. The following 10 data types are contained in the Project Assessment Manual: • Pavement distress surveys; • Pavement rut depths and roughness; • Nondestructive testing—FWD; • Ground-penetrating radar; • Pavement cores; • Dynamic cone penetrometer; • Subgrade soil sampling and tests; • Traffic loads for design; • Construction productivity and traffic impacts; and • Life-cycle assessment (environmental accounting). Flexible Pavement Best Practices The Flexible Pavement Best Practices document can be found in this project’s guide, Chapter 2. This document pro- vides a collection of best practices for the design and con- struction of long-life flexible pavement alternatives using existing pavements. The intent is to restrict distress such as cracking and rutting to the pavement surface. The docu- ment provides an overview of the renewal strategies and the reasoning behind their selection, as well as the critical fea- tures associated with each strategy, including construction issues. The document also provides a discussion of HMA con- struction quality control and ties that discussion to the Guide Specifications also provided in the guidelines. Design issues associated with transitions beneath structures are included as illustrated in Figure 3.8. Rigid Pavement Best Practices The Rigid Pavement Best Practices document can be found in this project’s guide, Chapter 3. This document provides rec- ommendations for the design and construction of long-life rigid pavement alternatives using existing pavements. The goal of achieving long-life concrete pavements requires an understanding of design and construction factors that affect both short-term and long-term concrete pavement performance. This requires an understanding of how con- crete pavements deteriorate and fail, as well as what is required to provide long life both from the structural design and from construction details. The rigid pavement approaches using existing pavements, as well as the supporting information for their selection, are described. Material considerations common to all approaches Figure 3.7. Outline of Project Assessment Manual scheme.

33 are discussed. The design and construction for the different long-life approaches are presented in some detail along with quality control and assurance needs. Standard practices for added lanes and transitions to adjacent structures are also discussed as illustrated in Figure 3.9. Guide Specifications The project team used AASHTO Guide Specifications (2008) as a starting point in specification development. This was done, in part, because there are a wide variety of pavement- oriented specifications developed and maintained by AASHTO committees. Furthermore, the AASHTO specifications pro- vide a common set of terms and structure on which to add components from state specifications. The approach was to review existing state agency and AASHTO guide specifica- tions, select sensible components (or elements), and place those in lists. The guide specifications are organized into three sections: (1) guide specifications for pavement components that are not contained within the AASHTO Guide Specifications, (2) elements that can be added to or can otherwise modify existing AASHTO Guide Specifications, and (3) summaries for relevant state SHA and AASHTO specifications that were used to produce the elements in item 2. An illustration of specifica- tion elements is shown in Table 3.18 for tack coats—a basic paving process spanning several renewal options. The complete specification documentation can be found in this project’s guide, Chapter 4. Four guide specifications are not contained in the AASHTO Guide Specifications, but the R23 team felt them necessary for this study: Stone Matrix Asphalt (SMA); Open Graded Friction Course (OGFC); Rubblization of PCC; and Saw, Crack, and Seat. Life-Cycle Cost Analysis These guidelines provide a range of approaches for the design of long-life pavements using existing pavements. The deter- mination as to which approach should be selected will depend on how well they meet the engineering requirements of the project and which is the most cost effective. Determining the cost effectiveness of the various approaches requires a life-cycle cost analysis. Most public agencies have specific procedures in place and it is expected that those agencies will follow those procedures. Where an agency does not have a specific procedure in place, a general discussion of life-cycle cost analysis is included. Figure 3.8. Illustration of flexible pavement transitions to overcrossings. Figure 3.9. Illustration of rigid pavement transitions to overcrossings.

34 The complete Life-Cycle Cost Analysis manual can be found in this project’s guide, Chapter 5. Emerging Pavement Technologies Some PCC and flexible pavement technologies are not yet con- sidered to be long-life renewal options but may become so in the future. One technology that was reviewed, precast concrete pavement, is likely a long-lasting renewal option at this time. The limitation is that there are too few projects under traffic to make that type of assessment. Thus, the term “emerging pavement technologies” does not necessarily imply that the concept is “new.” Several of these promising technologies were selected for a brief overview and include the following: • Rigid pavements 44 Ultrathin CRCP overlays and 44 Precast concrete pavement. • Flexible or composite pavements 44 Resin-modified pavement (illustrated in Figure 3.10). Without doubt, there are other technologies that could be featured; however, featuring them is not the primary purpose Table 3.18. Specification Elements Developed from Multiple Sources for Tack Coats AASHTO Paragraph R23 Recommendations Source 404.02 Materials Binder Use either an asphalt cement (AASHTO M320) or emulsified asphalt (AASHTO M140 or M208) in accordance with local practice. AASHTO 404 Texas 340 Virginia 310 404.03 Construction Weather limitations Apply tack coat during dry weather only. AASHTO 404 Michigan 501 Surface preparation Patch, clean, and remove irregularities from all surfaces to receive tack coat. Remove loose materials. AASHTO 404 Minnesota 2357 Missouri 407 Application surfaces 1. Apply the bond coat to each layer of HMA and to the vertical edge of the adjacent pavement before placing subsequent layers. 2. Apply a thin, uniform tack coat to all contact surfaces of curbs, structures, and all joints. Michigan 501 Texas 340 Application rate 1. Apply undiluted tack at a rate ranging from 0.05 to 0.10 gal/SY. 2. Many SHAs allow dilution with water up to 50%. Range generally falls within most state limits Application temperatures Use manufacturer recommendations. Study team Sources: AASHTO 2008; MDOT 2003; MnDOT 2005; MoDOT 2004; TxDOT 2004; VDOT 2007. (a) (b) Courtesy of Joe Mahoney. Figure 3.10. Resin-modified pavement in South Africa. (a) Resin-modified pavement at a truck weigh station on the N-3 near Johannesburg, South Africa. (b) A close-up of the resin-modified cement that was placed in open-graded HMA.

35 of this study. This short treatment simply suggests that tech- nologies exist which should be monitored as they continue to evolve and which may be or become viable components for long-lasting pavement renewal. The complete Emerging Pavement Technology document can be found in this project’s guide, Chapter 6. Interactive application The project resulted in the development of several docu- ments and reference tools that provide guidance on scoping and estimating long-life renewal strategies for pavements. The following goals and objectives were identified during the study in order to foster broad implementation of the research results: • Provide a user-friendly means of navigating the large amount of design and best practice information contained within the work product. • Provide guidance and a method for selecting an appropri- ate rehabilitation strategy based on information specific to a given project. • Provide a transparent view of the decision-making process as users are selecting the appropriate rehabilitation strat- egy, design, and best practices given their local practices. To meet these objectives and facilitate accelerated adoption of the research results, a computer-based application to guide users to the applicable research findings—in essence a “scoping tool” for users—was developed to aid implementation. The following sections outline the requirements, approach, and results of the application development portion of the study. User Requirements To best serve the intended audience of the application (scop- ing tool), the project team determined that the following end-user requirements must be met: • The application must run on any computer (PC/Mac) with commonly installed libraries. • The application must be distributable on CD-ROM, with option for web distribution in the future. • No third-party licenses or controls to be required by end users to install or distribute. • Provide capabilities to periodically update renewal strate- gies and guidance. • Provide printable report available to users. • Minimize application support and maintenance needs. These requirements were then assessed against several dif- ferent implementation technologies to determine the best approach to the application design. Application Design To meet the preceding user requirements, the project team performed an initial assessment of available technologies regarding whether they best meet the preceding goals. Several technologies were considered, although, ultimately, the Adobe Flash platform and Flex Builder toolkit were selected. Adobe’s Flash Player is currently the world’s most pervasive software, reaching 99% of Internet-enabled desktops in mar- kets such as the United States and Western Europe, and provid- ing a medium for both connected (web) and nonconnected (CD-ROM) distribution. The platform also provides users the option of running applications directly via the web, or directly from CD-ROM without need for installation files or impact on the user’s computer. Other technologies considered for implementation included Java, .NET, HTML 5, and Microsoft Office (Excel). Although each of these technologies could perform the required function of the scoping tool application, each was unable to meet the user requirements at the same level as Adobe Flash. Data Structure The scoping tool was designed to allow subject-matter experts the ability to modify the renewal strategy language and recom- mendations that result from ongoing feedback without having to recompile the application. To do so, an Extensible Markup Language (XML) data structure was devised to store all of the application logic and workflow information. Screen shots of the major pages in the application follow in Figure 3.11. Interactive Software Steps The interactive software developed for this project guides users through the following five steps: 1. Specify existing and proposed section information. 2. Specify existing pavement condition. 3. Confirm section design parameters. 4. Select renewal strategy. 5. Receive recommended section design. These five steps allow the user to input the parameters needed to obtain feasible renewal options from the decision matrices and thickness design tables discussed previously. In Step 1, the user inputs the existing pavement structure and the design information for the proposed renewal project (i.e., traffic levels, subgrade conditions, geometric constraints). The software uses this information to determine the type of existing pavement being evaluated and selects the appropri- ate decision matrix from Tables 3.9 through 3.12. Design information for the proposed renewal is stored for later use

36 (e) Section summary (f) Proposed renewal strategy (c) Pavement condition (d) Selection of renewal strategy (a) Opening screen (b) Section information Figure 3.11. Screen shots from the interactive software.

37 in determining the renewal-layer design thickness (described in Step 5). In Step 2, users input the condition of the existing pavement in terms of key distress types. These distress types are used in the decision matrices to determine feasible renewal alter- natives. The presence of certain types of distress (or distress in high quantities and/or severities) precludes some of the renewal strategies from achieving long life. These alternatives are eliminated by the program during Step 2. Step 3 provides the user with an overall summary of the existing pavement type and layering, existing condition, and proposed design parameters. With the existing pavement and proposed design elements confirmed, the user can select the type of renewal (i.e., flexible or rigid) in Step 4. The program utilizes the selection, along with the existing conditions stored in Step 2, to determine a list of feasible renewal options, recommended actions and considerations, and a description of the approach. This infor- mation is pulled from the decision matrices listed in Tables 3.9 through 3.12. The user can choose from the list of feasible options and select the existing pavement or base modulus. (This information will be used in Step 5.) In Step 5, the software uses the thickness design tables listed previously in Tables 3.15 and 3.16. The software uses the pro- posed design parameters entered in Step 1 along with the renewal strategy and modulus selected in Step 4 to determine a proposed renewal thickness. In addition, the software provides an overview of the existing pavement, the recommended design, and all of the pertinent design parameters. Links to the specific resource documentation for the renewal strategy are also listed.