Practices for Bridge Approach Systems (2021)

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41   State of the Practice To develop a better understanding of the design, maintenance, and performance of bridge approach systems throughout the United States, a survey was sent to all of the 50 state DOTs and to the District DOT. The survey link was sent to the voting member of the AASHTO Committee on Bridges and Structures (COBS) for each state department of transportation via e-mail. The members were encouraged to fill out the survey or forward the link to the most appropriate individual within their agency to fill out the survey. The survey included 26 questions on four topics. A full list of the questions is shown in Appendix B, and the main four topics are as follows: 1. Design and construction of bridge approach systems, 2. Water and joint management, 3. Operation and maintenance, and 4. Performance issues and mitigation practices. A total of 44 agencies responded to the survey, an 86% response rate. Note that not all the agencies responded to all the questions and, therefore, there are less than 44 responses to some of the questions. A summary of the responses is presented and discussed in the following sections. Tabulated state DOT responses are provided in Appendix C. 3.1 Design and Construction of Bridge Approach Systems In the first section of the survey, agencies were asked to identify their standard and common designs, specifications, and construction practices for bridge approach systems. 3.1.1 Abutment Types Agencies were asked how often they use different types of abutments. The responses are shown in Figure 23. The results indicate that integral abutments are the most commonly used abutment type; approximately 61% of the responding state DOTs (27 out of 44) reported using integral abutments “always” or “often.” A total of three state DOTs (Alabama, Florida, and Mississippi) reported that they have never used integral abutments. Another two state DOTs (Alaska and Texas) reported that they had previously used integral abutments but are not currently. Full-height, spill-through abutments are the least commonly used abutment type; approx- imately 59% of the respondents (26 out of 44) stated they have never used full-height, spill- through abutments or that they had previously but are not currently. Mississippi was the only state DOT to report always using full-height, spill-through abutments. Missouri, Massachusetts, Connecticut, and South Carolina identified several alternative types of abutments. Their responses are summarized in Table 3. C H A P T E R   3

42 Practices for Bridge Approach Systems 3.1.2 Approach Pavement or Slab Agencies’ responses related to the type of approach slab or pavement used in bridge approach systems are presented in Figure 24. All of the state DOTs with the exception of Maryland reported using structural RC approach slabs. Maine and Massachusetts reported that they commonly use buried approach slabs, and Ohio reported sometimes using buried approach slabs. The most common structural slab thickness reported was 12 in., but thicknesses varied from 3 in. to 18 in. Maine, Massachusetts, South Dakota, and Alabama were the only DOTs to report thicknesses less than 12 in. A specified length of 20 ft was the most common and lengths for RC approach slabs varied from 10 ft to 50 ft. DOTs reported that thickness and/or length could vary based on • Type of route (major or minor), • ADT and/or average daily truck traffic, 4 1 3 1 1 23 12 12 3 8 3 7 17 18 17 11 6 5 7 7 9 16 7 3 6 1 15 4 15 2 1 2 3 11 1 1 1 0 5 10 15 20 25 30 35 40 45 Integral Semi-Integral Stub MSE Full-Height, Closed Full-Height, Spill-Through N o. o f Re sp on di ng D O Ts Type of Abutment No response Previously but not currently Never Rarely Occasionally Often Always Figure 23. Responses identifying how frequently the DOTs use each type of abutment. This question had a total of 44 responses. Other Abutment Types Frequency GRS-IBS Occasionally Freestanding Abutment Occasionally Geosynthetic Reinforced Rarely Semideep Previously but not currently NOTE: GRS-IBS is defined as geosynthetic reinforced soil-integrated bridge system. One DOT additionally noted using GRS-IBS abutments on an experimental basis in a later question. Table 3. Alternative abutment types identified by survey respondents.

State of the Practice 43   • Bridge skew, • Abutment depth, • Soil type, and • Distance to unexcavated embankment. Flexible pavement is the second-most-common roadway used for the bridge approach, with 25% of the responding state DOTs (11 of 44) reporting use of flexible pavement. Missouri, Pennsylvania, and West Virginia identified flexible pavement as an option for minor routes when the bridge experiences low traffic. Colorado commented that flexible pavement without an approach slab is used when settlement of the abutment embankment is not critical. Idaho, Montana, Pennsylvania, and Texas reported using conventional reinforced, rigid pavement for the bridge approach. Iowa was the only DOT to report using a conventional unreinforced-concrete slab approach as part of their typical system that includes a double- reinforced-concrete approach slab immediately after the bridge, followed by single reinforced slab, then an unreinforced concrete slab at the roadway. 3.1.3 Sleeper Slabs Of the responding state DOTs, approximately 57% (25 out of 44) reported using sleeper slabs. Nebraska additionally commented that their sleeper slabs are supported on piles. Several DOTs clarified that sleeper slabs are used when there is an expansion joint between the roadway and a concrete approach slab and relatively large thermal movements are anticipated, and one DOT (Texas) reported that sleeper slabs are used only when the adjacent roadway pavement is concrete. Iowa and Vermont reported that they do not routinely use sleeper slabs, but commented that sleeper slabs are applied in rare scenarios. 95% 2% 9% 25% 2% 80% 70% 61% 2% 18% 20% 14% 0 10 20 30 40 50 60 70 80 90 100 Reinforced Concrete Approach Slab Unreinforced Concrete Approach Slab Rigid Pavement Flexible Pavement Pe rc en ta ge o f R es po nd in g D O Ts (% ) Type of Roadway in Approach Did not respond Not used Included in Standard Specifications Figure 24. Responses identifying the types of roadways or slabs used in bridge approaches. This question had a total of 44 responses.

44 Practices for Bridge Approach Systems 3.1.4 Type of Connection Between Approach and Bridge Agencies were asked if the approach slab/pavement, as applicable, is typically rigidly connected to the abutment or bridge deck by steel ties or if the approach slab/pavement is permitted to move independently of the bridge structure. A summary of the results is presented in Figure 25. In general, rigid connections wherein the approach slab/pavement moves with the abutment are preferred; approximately 45% of the respondents (20 out of 44) reported that they always use rigid connections while only 11% (5 out of 44) reported that they always permit the approach slab/pavement to move independently of the abutment. Texas and South Carolina commented that they use systems that tie the abutment and the approach slab together, but permit rotation such that the connection behaves as a pin. For the remaining DOTs, the connection between the abutment and the approach slab or pavement varies depending on the abutment type. As shown in Figure 25, 45% of the responding DOTs (20 of 44) always rigidly connect the approach to the abutment, with 83% of the DOTs who use integral abutments (29 of 35) reporting rigid connections. 3.1.5 Backfill Materials The survey included questions regarding typical types of backfill materials used by DOTs and if their properties, including moisture content, density, and gradation, were specified. 3.1.5.1 Types of Backfill Materials Figure 26 presents a summary of the responses regarding the types of backfill materials used. The majority of the responding agencies (32 DOTs) specify a granular or porous granular material. Four DOTs specify other materials, which are summarized in Table 4. They are generally either flowable fill, which is similar to a controlled-density fill, or a structural backfill. Only one DOT (Arkansas) specifies manufactured sand. The majority of the responding DOTs only have one backfill material in their specifications. Approximately 28% of the respondents (12 of 44) have specifications for multiple backfill materials. A total of five of the DOTs stated that no backfill material is specified. 29 23 24 12 18 7 6 9 10 10 10 4 7 8 6 18 13 27 2 4 4 4 3 6 0 5 10 15 20 25 30 35 40 45 Integral Semi-Integral Stub MSE Full-Height, Closed Full-Height, Spill-Through N o. o f Re sp on di ng D O Ts Type of Abutment Did not respond Not applicable Move independently of each other Rigidly connected Figure 25. Responses identifying the type of connection between the approach and the bridge structure. This question had a total of 42 responses.

State of the Practice 45   3.1.5.2 Specified Properties of Backfill Figure 27 presents the number of responding agencies with specified requirements for compaction, gradation, percent fines (defined as percent passing a No. 200 sieve), and moisture content of the backfill material. As shown in Figure 27, compaction requirements were the most common type of require- ments specified by the DOTs. The most typical compaction requirement was a field density of 95% of the maximum dry density as measured by AASHTO T 180, Method of Test for Moisture- Density Relations of Soils Using a 4.54-kg (10-lb) Rammer and a 457-mm (18-in.) Drop, or a state-developed standard method, but required field densities varied from 90% to 100% of the maximum dry density. Some of the requirements were qualitative, such as requiring one pass with the compaction equipment or compaction to the satisfaction of the engineer. Both required gradations and limits on fines varied widely. Limits on fines, in percent by weight, varied from less than 2% by weight to less than 25% by weight and all of the responses were unique. Requirements for moisture content were typically either within 4% of the opti- mum moisture content, within 2% of the optimum moisture content, between 2% below the optimum moisture content and 4% above, or vice versa. Other types of requirements reported by the DOTs were related to specifying the maximum lift thickness during placement; plasticity index of the material; angle of internal friction; and chloride, sulfate, and organic contents. 73% 27% 18% 9% 2% 0 5 10 15 20 25 30 35 Granular or porous granular material Crushed gravel/rock Controlled-density fill material Other Manufactured sand N o. o f R es po nd in g D O Ts Type of Backfill Specified Figure 26. Number of responding DOTs that use the listed backfill materials behind abutments. This question had a total of 43 responses. The percentage of survey respondents (not question respondents) who selected each answer is shown; respondents could select multiple options. Structure backfill (Class 1) or structure granular backfill Cement stabilized and flowable fill Other Table 4. Other specified backfill materials.

46 Practices for Bridge Approach Systems 3.1.6 Additional Materials or Systems Behind Abutments State DOTs were asked if there were any additional materials behind the abutments, such as drainage systems, waterproofing systems, and elastic inclusions. Waterproofing and drainage systems are commonly composed of geosynthetics and these vertical systems are distinct from the horizontal geosynthetic reinforcement that may otherwise be found in the backfill. Figure 28 shows the percentage of agencies that use each type of material. “Other” materials 75% 57% 48% 34% 0 5 10 15 20 25 30 35 40 45 Compaction Gradation % Fines Moisture Content N o. o f R es po nd in g D O Ts Type of Requirement for Backfill Figure 27. Number of responding DOTs that specify the listed properties for backfill materials placed behind abutments. This question had a total of 39 respondents. The percentage of survey respondents (not question respondents) who selected each property is provided; respondents could select multiple options. 27% 17% 29% 7% 27% 29% 0 5 10 15 20 25 30 35 40 45 Waterproofing membrane system Geocomposite drain Geosynthetic Expanded polystyrene Other Material is not specified N o. o f R es po nd in g D O Ts Types of Materials Used Behind the Abutment Figure 28. Number of responding DOTs that use the listed materials behind bridge abutments. This question had a total of 41 respondents. The percentage of survey respondents (not question respondents) who selected each type of material is shown; respondents could select multiple options.

State of the Practice 47   listed include geotextiles, geofoams, subdrain systems, preformed cellular polystyrene, and honeycomb cardboard. There is no common practice that the majority of the responding DOTs follow. Approximately 25% of respondents (11 of 44) indicated that their agency does not specify any special material between the abutment and the backfill. The remaining DOTs indicated that a variety of materials are used across the DOTs, but in general, geosynthetic products intended to manage water are more common than elastic materials. 3.1.7 Experimental Bridge Approach Systems The use of experimental bridge-approach systems such as precast approach slabs was surveyed. Approximately 41% of the responding DOTs (18 out of 44) stated that they had used experimental approach systems. Except for Ohio, all of the DOTs who have used experi- mental systems indicated they had used precast approach slabs or panels at least once, and two more DOTs indicated they were planning to try precast approach slabs in the future. Nebraska reported having standards for precast approach slabs and Illinois reported that bridges longer than 260 ft routinely have precast approach slabs. Five DOTs stated that they had used precast slabs for accelerated bridge-construction applications. Colorado noted that contractors prefer to build CIP slabs. In addition to precast panels, Vermont stated that it had used GRS-IBS abutments, which Massachusetts and Connecticut identified as using “occasionally.” 3.1.8 Ground Improvement Methods A total of 17 responding DOTs indicated that they use ground improvement methods in bridge approach construction as shown in Table 5, of which 12 indicated ground improvement methods were used rarely or conditionally. Missouri and West Virginia both commented that ground improvement methods are most commonly used when MSE abutments are constructed while Idaho commented that ground improvement methods are used with stub abutments. Alternatively, ground improvement methods may only be used as recommended by the geo- technical investigation regardless of the abutment type. In addition to the three DOTs in Table 5, Texas has also used cement or lime treatments under approach slabs. However, the respondent commented that Texas discontinued the practice at least 15 years ago. Several unique methods of ground improvement not presented in Table 5 were listed by individual DOTs. Oklahoma uses a variety of measures to minimize postconstruction Method No. of Respondents Removal and replacement 5 Wick drains 5 Surcharge 4 Reinforced backfill 3 Lime/cement/fly ash treatment 3 Stone columns 3 Table 5. Summary of ground improvement methods used by the responding DOTs.

48 Practices for Bridge Approach Systems settlement including test rolling, monitoring settlement as a result of consolidation, and phasing construction. Both Oregon and South Carolina use ground improvement methods to mitigate seismic loads, including stone columns and wick drains as listed in Table 5, as well as jet or compaction grouting, precast concrete piles, earthquake drains, and soil mixing columns. Rammed aggregate piers were also listed as a ground improvement method. 3.1.9 Construction Acceptance Criteria Approximately 39% of the responding DOTs (17 out of 44) indicated that they specify construction acceptance or performance criteria for bridge approach systems. The type of criteria identified and the number of DOTs who use each are presented in Table 6. A localized roughness criterion based on a 10-ft straightedge was the most common. A total of eight DOTs identified that the surface roughness was to be characterized using a profiler or profilograph, but several did not identify which metric (IRI, MRI, or PI) was to be used. Oregon was the only DOT that stated that rideability was not analyzed and acceptance was based on the out-of-straightness of the joints. 3.2 Water and Joint Management The second section of the survey focused on design and construction practices related to water and joint management. Information about the types of drainage structures and expan- sion joints used and their locations and replacement needs was collected. 3.2.1 Water Management The management strategy for capturing and dealing with water runoff from the bridge and the approach was investigated. Figure 29 shows how many DOTs capture water from the bridge and/or the approach. Figure 30 summarizes where the water is released. The majority of the responding agencies (68%, or 30 of 44) stated that they capture water from both the bridge deck and the approach. Approximately 14% of DOTs (6 of 44) stated that they do not capture water from either the deck or the approach. Several DOTs commented that the water management system depends on flow volumes, the bridge location and type, and/or the traffic barrier and curb configurations. DOTs commonly have several options for release locations for water runoff. Concrete or rock flumes, ditches at the bottom of slopes, concrete chutes, and detention ponds are reportedly used in open systems. The least used option was releasing the water openly into the underlying Type of Criterion No. of Respondents Localized roughness/straightedge 10 International Roughness Index (IRI) 5 Unspecified profiler/profilograph measurements 2 Mean Ride Index (MRI) 2 Profile Index (PI) 1 Joint tolerance 1 Table 6. Types of criteria used for acceptance of bridge approaches.

State of the Practice 49   fill materials. Texas, Illinois, and Florida reported using this option. All three agencies indicated they use most reported types of open systems as well. Approximately 43% of the responding DOTs (19 of 44) indicated that they do not use closed systems. In comparison, Connecticut and New Jersey were the only agencies that stated that closed systems are typically preferred or did not report using any open drainage systems. Missouri noted that closed systems were more likely to be used in urban environments. 68% 7% 2% 14% 0 5 10 15 20 25 30 35 40 45 Bridge and Approach Bridge Only Approach Only Neither N o. o f R es po nd in g D O Ts Type of Run-off Collected Figure 29. Number of responding DOTs that collect water runoff from the locations listed. This question had a total of 40 respondents. The percentage of survey respondents (not question respondents) who selected each option is shown. 55% 36% 7% 23% 41% 5% 0 5 10 15 20 25 30 35 40 45 Openly onto the surface of a slope Openly at the bottom of a slope Openly into the underlying backfill or embankment fill An open drainage system is generally specified, but specifics are not provided Into a culvert, storm drain, or other closed system Other N o. o f R es po nd in g D O Ts Locations where Water Run-Off is Released Figure 30. Number of responding DOTs that permit release of water runoff from bridges and/or approaches in the locations or under the conditions listed. This question had a total of 41 respondents. The percentage of survey respondents (not question respondents) who selected each answer is shown; respondents could select multiple answers.

50 Practices for Bridge Approach Systems 3.2.2 Subdrains in Backfill The survey included questions regarding the use of subdrains in the backfill underneath the approach and to describe the subdrain configuration, if applicable. Approximately 55% of the responding agencies (24 of 44) reported that they use subdrains and 36% (16 of 44) reported that they do not use subdrains in the backfill. A total of three state DOTs (Arkansas, Delaware, and Montana) responded that subdrains are used conditionally depending on abutment type and site-specific conditions. Delaware typically uses subdrains with full-height abutments, but not with stub or MSE abutments, and Arkansas typically only specifies subdrains for integral abutments. When used, subdrains are typically located parallel to the abutment and at the bottom of the abutment, on top of the footing, and/or at the bottom of the backfill. Some DOTs commented that they specify that the drain be located a few feet away from the abutment. The subdrains typi- cally release the water near the base of the wingwalls or through weep drains in the abutment. The latter scenario is common for full-height abutments. Subdrains described in the responses to this question typically consisted of a perforated pipe embedded in a select aggregate and then wrapped in a geosynthetic filter fabric. Alternatively, the pipe may be wrapped prior to embedment in the aggregate, or the wrapped aggregate-pipe system may be embedded in a second type of aggregate. The pipes were sometimes at the top of the aggregate and at other times placed at the bottom of the aggregate. Pipes typically have a diameter of 4 or 6 in. and are sometimes corrugated. The section of pipe located behind the abutment is generally perforated. Outside of the width of the abutment, nonperforated pipes are commonly spliced to the perforated pipes to finish carrying the water outside the backfill. Pipes may be made of polyethylene or polyvinyl chloride (PVC), although one DOT stated that steel pipes are also acceptable. The select aggregates identified were typically coarse aggregates, such as crushed stone, but two DOTs responded that they use fine aggregates. Colorado and Louisiana noted that they consider the geotextiles or polyethylene sheeting located underneath the approach slab/pavement to be part of their subdrain systems. Colorado stated that the geotextile between the subbase course and the backfill is sloped and a geocomposite strip drain is used to carry water to the drainage system at the bottom of the backfill. Louisiana pointed out that the polyethylene sheeting the agency uses, typically placed to facilitate trans- lation of the approach slab in response to length changes of the bridge girders, is located on top of a bedding material. 3.2.3 Expansion Joint State DOTs were asked about their practices regarding the location of the expansion joint(s) with respect to the bridge abutment, the types of expansion joints used for bridge approaches, and how frequently the seals of the various joint types require replacement. 3.2.3.1 Expansion Joint Location Typical locations of the expansion joints varied by DOT and also by the type of abutment within each DOT as shown in Figure 31, which is sorted according to abutment type. Approxi- mately 39% of responding DOTs (17 of 44) indicated that expansion joint location does not vary with abutment type. Placing the expansion joint between the approach and the roadway or between the approach and the bridge are both common practices. Some DOTs indicated that there is no preference between these two locations for at least one of the abutment types.

State of the Practice 51   Four DOTs (Arkansas, Maine, North Carolina, and Wisconsin) reported using no expansion joint with integral, semi-integral, or MSE abutments, while three DOTs (Hawaii, Louisiana, and Texas) reported using two expansion joints for stub or MSE abutments. Massachusetts reported using no joints with GRS-IBS abutments and South Carolina reportedly places the expansion joint between the approach and the bridge for freestanding abutments. Kansas was unique in that it uses a multipanel approach slab and places the expansion joint between two of the panels, regardless of the abutment type. 3.2.3.2 Types of Expansion Joints Figure 32 summarizes the responses defining the types of joints used in bridge approaches. The most common “Other” types of expansion joints identified were asphaltic plug joints (five DOTs) and modular expansion joints (four respondents). Other joints that were identi- fied include • Precompressed membranes and sealant, • Foam joints, • Finger or tooth joints, • Full-depth filled joints, and • 4-ft asphaltic-concrete pressure relief joints. Delaware, West Virginia, and Utah commented that compression seals are commonly used for bridges with relatively small movements. Delaware and West Virginia stated that strip seals are used otherwise, while Utah indicated that compression seals are preferred over strip seals even at higher movements. Conversely, Illinois recently began using strip seals instead of compression seals and Louisiana noted that they no longer use compression seals. 20 18 11 10 7 3 7 8 20 6 18 9 2 3 4 2 2 4 2 2 2 2 11 13 7 22 17 32 0 5 10 15 20 25 30 35 40 45 Integral Semi-integral Stub MSE Full-height, closed Full-height, spill-through N o. o f R es po nd in g D O Ts Abutment Type Not applicable or did not respond Both ends of approach No expansion joint Either location (not specified) Between approach and bridge Between approach and roadway Figure 31. Locations of expansion joints for each abutment type. This question had a total of 41 responses.

52 Practices for Bridge Approach Systems 3.2.3.3 Expansion Joint Seal Replacement Frequency The replacement frequencies reported for strip seals, compression seals, and backer rods and sealants are presented in Table 7, and the replacement frequencies reported for less commonly used joints are reported in Table 8. In general, DOTs commented that joint repairs were reactive rather than proactive, and several agencies stated that joint seals were replaced upon failure or on an as-needed basis when asked about frequency. 3.2.4 Joints Between the Approach Slab/Pavement and Parallel Elements The DOTs’ practices related to the type of joint used between the approach slab/pavement and parallel members such as the wingwalls or the traffic barriers are presented in Figure 33. Materials used to fill and seal the joint included preformed fillers and hot-poured and cold-poured sealers. Colorado commented that if the joint was wide enough, asphalt pavement would be used. A total of four responding DOTs (Florida, Idaho, Nebraska, and Pennsylvania) extend the approach slabs over the top of the wingwall such that no joint is present. A bond breaker may be used to facilitate slab movement. Massachusetts also does not have a joint between the approach slab and the wingwall since the slab is buried. No joint may mean that they are built integrally. 73% 57% 48% 32% 0 5 10 15 20 25 30 35 40 45 Strip seal Compression seal Backer rod and sealant Other N o. o f R es po nd in g D O Ts Type of Expansion Joint Figure 32. Number of responding DOTs that use the types of expansion joints listed in bridge approaches. This question had a total of 41 respondents. The percentage of survey respondents (not question respondents) who selected each type of joint is shown; respondents could select multiple options. Expansion Joint Type Median Frequency (years) Minimum Frequency (years) Maximum Frequency (years) Strip seal 15 5 30 Compression seal 11 2 20 Backer rod and sealant 8 1 60 Table 7. Reported replacement frequencies for the seals of different types of expansion joints.

State of the Practice 53   3.3 Operation and Maintenance The third section of the survey included questions about inspection frequency of bridge approaches and their elements; metrics used to assess approach performance, including ride quality; and repair techniques and criteria to initiate repair. 3.3.1 Periodic Inspection of Elements The current state of the practice includes periodic inspection of approach slabs and elements throughout their life. Distress related to differential settlement, joint seal failure, void formation or approach embankment erosion under slab, lateral spread of the approach embankment, and other distress type is routinely assessed by several DOTs as shown in Figure 34. The “Other” types of distress monitored were generally not elaborated upon, although several respon- dents identified approach slab distress or cracks at the connection between the approach and sleeper slabs. Expansion Joint Type Replacement Frequency (years) Foam joints 3 to 6 Asphaltic plug joints 7 to 15 Expansion joint seals 10 to 15 Modular expansion joints 20 to 25 Table 8. Reported replacement frequencies for seals in other expansion joints. 48% 18% 20% 0 5 10 15 20 25 30 35 40 45 Sealed joint Unsealed joint No joint N o. o f R es po nd in g D O Ts Type of Connection between Approach and Wingwalls/Traffic Barriers Figure 33. Number of responding DOTs that use the configurations listed for the joint between the approach slab/pavement and parallel elements. This question had a total of 38 respondents. The percentage of survey respondents (not question respondents) who selected each type of connection is shown.

54 Practices for Bridge Approach Systems The majority of responses indicated that these types of distress are monitored every 2 years during NBI inspections. The NBI inspection data is federally required to be collected and reported at least biennially, although longer inspection intervals can be approved. In recognition of the diverse bridge designs used by DOTs, elements that may not be present for every bridge, such as approach slabs and joints, are not required to be reported. However, it is expected that these elements will be reported if they are present. The MBEI published by AASHTO lists standard types of defects to be characterized for each element. Types of defects listed for joints include leakage; seal adhesion, damage, or cracking; debris impaction; metal deterioration or damage; and damage to the adjacent deck or header. No standardized defect types are identified for approach slabs, although the types of defects listed for concrete decks would apply. The MBEI considers general settlement of RC, prestressed concrete, timber, and masonry elements, but does not discuss differential settlement, void formation under approach slabs, or lateral spreading. For differential settlement, other inspection frequencies reported varied from biannually to 2 to 5 years. For the joint seal, alternative inspection frequencies were 2 years or more, 2 to 5 years, and 10 years. One respondent identified an inspection frequency of 4 years for lateral spreading. 3.3.2 Measurement of Differential Settlement DOTs were asked if they quantify differential settlement and what methods they use, if applicable. Figure 35 presents the responses. “Other” methods that were identified include a string line and a 1 to 5 scale rating. A total of five respondents reported using multiple types of measurements. As can be seen in Figure 35, 16 DOTs indicated that severity is not quantified while the majority of the respondents use qualitative description of ride quality to assess differential settlement. 57% 68% 48% 23% 30% 0 5 10 15 20 25 30 35 40 45 Differential Settlement Joint Sealant Failure Void Formation Lateral Spreading Other N o. o f R es po nd in g D O Ts Types of Distress Figure 34. Number of responding DOTs that regularly inspect the approaches and their components for the types of distress or degradation listed. This question had a total of 32 respondents. The percentage of survey respondents (not question respondents) who indicated inspection of each distress type is shown; respondents could select multiple options.

State of the Practice 55   3.3.3 Measurement of Ride Quality DOTs were asked if they measure ride quality of the approaches and what methods they use, if applicable. This question was divided into ride quality of the main roadway, of the approach slab/pavement, of the bridge deck, and of the joints. Figure 36 presents the number of agencies that measure the ride quality of these components. The methods used to measure ride quality or smoothness are summarized in Figure 37. In general, the methods listed are similar to those used as construction acceptance criteria, discussed in Section 3.1.9, except Rhode Island identified a unique ride quality criterion that the bridge deck must have a noise level of less than 100 decibels. 3.3.4 Repair Triggers The criteria used to trigger repair of poor ride quality (i.e., a “bump”) between the approach and the bridge or the approach and the roadway for the different respondents are presented in Figure 38. Approximately 57% of the responding DOTs (25 out of the 44) stated that they do have repair triggers, but none use a quantitative or explicit criterion. Maine, which responded “Other,” clarified that their criteria is based on impact damage to the joint. A total of nine DOTs stated that the decision to repair the bump is based on inspectors’ recommendations or inspection data. User complaints, safety concerns, poor ride quality, and inspector recommendations are generally used to trigger investigation and consideration for repair rather than directly instigating a repair project. The final decision is typically made by the maintenance personnel based on their assessment of repair need. Kansas stated that the bump would generally be fixed in conjunction with another repair but would not be an independent project. 46% 14% 9% 50% 9% 0 5 10 15 20 25 30 35 40 45 Severity is not quantified International Roughness Index (IRI) Rolling straight edge Qualitative description of ride quality Other N o. o f R es po nd in g D O Ts Measurement Methods Figure 35. Number of responding DOTs that use the methods listed to characterize severity of differential settlement in bridge approach systems. This question had a total of 35 respondents. The percentage of survey respondents (not question respondents) who selected each method is shown; respondents could select multiple methods.

56 Practices for Bridge Approach Systems 34% 32% 39% 18% 0 5 10 15 20 25 30 35 40 45 Roadway Approach slab/pavement Bridge deck Joints N o. o f R es po nd in g D O Ts Area Where Ride Quality Is Assessed Figure 36. Number of responding DOTs that assess ride quality of the bridge approach, bridge deck, main roadway, and joints. This question had a total of 34 respondents. The percentage of survey respondents (not question respondents) who selected each option is shown; respondents could select multiple options. 3 5 7 2 10 5 5 3 1 1 1 2 4 4 3 1 0 2 4 6 8 10 12 14 16 18 20 Roadway Approach slab/pavement Bridge deck Joints N o. o f R es po nd in g D O Ts Area Where Ride Quality Is Assessed Noise-based assessment Qualitative assessment General profilograph IRI, MRI, or PI Straightedge Figure 37. Number of responding DOTs that use the listed methods to assess ride quality or smoothness of the components of the bridge approach system. This question had a total of 34 respondents; respondents could select multiple options and list multiple methods of assessment.

State of the Practice 57   3.3.5 Repair Methods for Restoring Ride Quality DOTs were asked which methods they use to restore ride quality and how frequently they are applied. The responses are summarized in Figure 39. Slab replacement is most commonly done followed by polyurethane foam or cementitious grout injection. “Other” repair options identified include mudjacking, asphalt wedging, application or replacement of an asphalt overlay, and milling. 25% 43% 32% 14% 23% 0 5 10 15 20 25 30 35 40 45 No criteria User-complaint Safety Ride quality Other N o. o f R es po nd in g D O Ts Type of Criteria Figure 38. Number of responding DOTs that use the listed types of criteria to determine when to repair a “bump” on either side of the approach. This question had a total of 36 respondents. The percentage of survey respondents (not question respondents) who selected each type of criteria is shown; respondents could select multiple options. 45% 50% 57% 32% 0 5 10 15 20 25 30 35 40 45 Portland Cement Grout Injection Expanded Polyurethane Injection Replacement Other N o. o f R es po nd in g D O Ts Repair Figure 39. Number of responding DOTs that use the listed repairs to restore ride quality of bridge approaches. This question had a total of 36 respondents. The percentage of survey respondents (not question respondents) who selected each repair is shown; respondents could select multiple options.

58 Practices for Bridge Approach Systems In general, these repair actions are conducted rarely or on an as-needed basis. Nebraska and Wyoming were the only respondents to report using portland cement grout injection, expanded polyurethane (EPU) injection, and/or replacement frequently. Oregon DOT estimated that each type of injection is done about 1 or 2 times per year, which was considered infrequent, and Delaware and South Dakota indicated injections are done “occasionally.” North Dakota noted that EPU injection is only completed if other work is required. 3.4 Performance Issues and Mitigation Practices The fourth and last section of the survey included questions related to the expected life of bridge approach systems, performance issues they experience, and repairs employed to address these issues. The last question focused on any significant changes that were made in the last 15 years to address issues with the bridge approach system. 3.4.1 General Bridge Approach System Performance DOTs were asked to identify their most common bridge approach systems in regard to abutment type, approach pavement type, and joint location. Agencies were additionally asked to provide estimates of the typical service life expected for the different systems. 3.4.1.1 Common Bridge Approach Systems The most common systems reported are presented in Table 9, the second-most-common systems in Table 10, and the third-most-common systems in Table 11. Almost all DOTs that responded to this question stated that their common bridge approach systems use RC approach slabs. The exceptions were Massachusetts, Texas, Hawaii, Missouri, and West Virginia, as noted in Table 9 through Table 11. Massachusetts uses a buried approach slab and, therefore, reported using a flexible approach pavement for all three of the DOT’s most common systems. Texas reported using a rigid approach pavement as the DOT’s third-most-common system, and Hawaii, Missouri, and West Virginia reported using a flexible approach pavement in their second- or third-most-common systems. The most common systems reportedly have integral or semi-integral abutments and an expansion joint located between the approach and the roadway. In the third-most-common systems, the most popular abutment type is a stub abutment and the most commonly reported joint location is between the approach and the bridge. Joint Location/Abutment Type Integral Semi- Integral Full-Height, Closed Full-Height, Spill-Through Stub MSE Totals Between approach and roadway 121 3 0 0 0 0 15 Between approach and bridge 2 1 42 0 2 0 9 Both sides of approach 1 0 0 0 1 0 2 No joint 3 1 0 0 0 0 4 Totals 18 5 4 0 3 0 30 1One respondent (Kansas) stated that the joint is located between several panels within their approach slab. Between the approach and the roadway was deemed the most fitting category. 2One respondent (Massachusetts) stated the system uses a flexible pavement instead of an RC approach slab. Table 9. Most common bridge approach systems.

State of the Practice 59   Placing the expansion joint between the approach and the roadway or between the approach and the bridge were both common joint configurations. Only six DOTs (Hawaii, Maine, Missouri, North Carolina, South Carolina, and Washington) reported using no joint in at least one of their common systems, and only three DOTs (Colorado, Louisiana, and Nebraska) reported using a joint at both ends of the approach in at least one of their common systems. 3.4.1.2 Service Life DOTs were asked what service life is expected for each bridge approach system, where service life was defined as the time until rehabilitation or replacement of the approach was required, excluding rehabilitation or replacement of the joints. The reported range included estimates from 2 years to 75 years and the median life reported was 25 years. This large variation is likely a result of the variety of different repairs that could be required, and several respondents provided clarification regarding which repairs or rehabilitation actions they considered. These responses are summarized in Table 12. In general, DOTs provided the same estimate regardless of which system was considered. Only four agencies (Alaska, Missouri, Nebraska, and West Virginia) reported different service life estimates for their most common systems. Texas DOT commented that service life depends on construction quality and weather events. Joint Location/Abutment Type Integral1 Semi- Integral Full-Height, Closed Full-Height, Spill-Through Stub MSE Totals Between approach and roadway 0 8 1 0 2 1 12 Between approach and bridge 1 1 3 0 3 2 102 Both sides of approach 0 1 0 0 0 0 1 No joint 1 0 0 0 0 0 1 Totals 33 10 4 0 5 3 25 1All respondents in this column (Hawaii, Massachusetts, and Missouri) stated the system uses a flexible pavement approach instead of an RC approach slab. 2One respondent (South Carolina) identified their second-most-common bridge approach system as using an “other abutment type” and a joint located between the approach and the bridge. 3One respondent (Hawaii) did not identify the location of the joint but did identify integral abutments as part of their second-most-common system. Table 10. Second-most-common bridge approach systems. Joint Location/Abutment Type Integral Semi- Integral Full-Height, Closed Full-Height, Spill-Through Stub MSE Totals Between approach and roadway 0 1 0 0 21 0 3 Between approach and bridge 2 2 2 2 42 1 13 Both sides of approach 0 0 0 0 2 0 2 No joint 0 0 0 0 1 0 1 Totals 2 3 2 2 103 1 20 1One of these respondents (Texas) stated the system uses a rigid pavement approach instead of an RC approach slab. 2Two of these respondents (Massachusetts and West Virginia) stated the system uses a flexible pavement instead of an RC approach slab. 3One respondent (Hawaii) did not identify the location of the joint but did identify stub abutments as part of their third- most-common system. Table 11. Third-most-common bridge approach systems.

60 Practices for Bridge Approach Systems 3.4.2 Performance Issues DOTs were asked to identify how often they experience different types of performance issues pertaining to ride quality, joint integrity, concrete cracking, drainage, and erosion. The responses of 38 agencies are shown in Figure 40; six agencies did not respond to the question. Failure of the sealant within the expansion joint was reported as the most common issue, followed by poor ride quality at joints between the approach and the bridge or the roadway and erosion of backfill. Failure of the paving corbel was reportedly the least common issue encountered. 3.4.3 Prevention, Mitigation, and Repair of Bridge Approach Systems Agencies were asked what strategies are used to address the performance issues discussed in Section 3.4.2, Performance Issues. They are presented in order of frequency, from issues that occur most frequently to issues that occur least frequently. Element Requiring Repair or Replacement Service Life Estimate Wearing surface 10 to 15 years 15 years Deck slab 50 to 60 years Joint 10 years 10 to 15 years 10 to 20 years (asphaltic plug joints) 30 years (strip seals) Table 12. Estimated service life for elements related to bridge approaches. 10 3 11 19 7 1 1 8 2 7 18 17 20 14 16 16 13 5 21 9 15 10 15 6 3 11 18 21 29 8 21 11 3 1 2 4 3 3 4 1 6 5 0 5 10 15 20 25 30 35 40 N o. o f R es po nd in g D O Ts Performance Issue Did not respond Rarely Occasionally Often Figure 40. Frequency with which each of the performance issues listed is encountered. This question had a total of 38 responses.

State of the Practice 61   3.4.3.1 Expansion Joint Sealant Failure The responses describing strategies to prevent or repair sealant failures in expansion joints are summarized in Table 13. The majority of responding DOTs reported that the sealant or joint would be replaced. Three agencies stated that they replace the sealant with a different material; Kansas uses an “easily maintained” material while Iowa and Utah both replace failed expansion joint seals specifically with compression seals. Indiana stated that updated, precompressed foam-expansion joints are used whenever possible. Two DOTs provided unique strategies. North Carolina stated that the agency uses routine joint replacement and Alaska stated that the agency sometimes protects strip seals with steel cover plates to prevent joint failures. 3.4.3.2 Bump Between Approach and Roadway or Bridge The responses describing strategies to prevent, mitigate, or repair poor ride quality between the approach and the main roadway and between the approach and the bridge are summarized in Table 14. Strategies were categorized based on whether they are implemented during the design phase, during the construction phase, or during operation of the bridge approach. The majority of the responding DOTs described repairs to be conducted retroactively, including overlays, joint repair, wedge paving, injection or jacking, grinding, patching, or a combination of these strategies. There were two agencies—North Carolina and South Dakota— that stated that their agencies rely on construction inspections to prevent these issues. For ride quality issues, five DOTs stated that they have built-in preventive strategies in their designs. The reported strategies include the use of • A buried approach slab and extension of the main, bituminous pavement to the bridge; • A load transfer dowel between the approach and the roadway; • Reinforcing ties between the approach slab and the abutment; • An RC sleeper slab at the end of the approach slab; • A large sleeper slab at the roadway end of the approach; • A layered geotextile-fabric system intended to create a block of soil interaction to spread the sleeper slab loads into the embankment; • Piling to support the sleeper slab; • Reinforced-soil mass backfill with geotextile layers; or • Updated subgrade and subbases. Action No. of Respondents General replacement/repair of sealant/joint 16 Replacement with or use of alternative materials 4 Miscellaneous 2 Table 13. Strategies to address expansion joint sealant failure. Type of Strategy Approach/Roadway Approach/Bridge Design based 5 5 Quality based 2 2 Repair based 14 15 Table 14. Strategies to address poor ride quality across joints.

62 Practices for Bridge Approach Systems 3.4.3.3 Erosion of Backfill The responses describing strategies to prevent, mitigate, or repair erosion of backfill are categorized in Table 15. These categories are not mutually exclusive, as some DOTs listed multiple options to choose from or indicated they conduct a combination of activities from the different categories. Additionally, two agencies stated that action is only taken if the situation warrants it or if the problem is severe. The majority of respondents to this question stated that they fill the void. Materials identified include flowable fill, grout, concrete, foam, and shotcrete. Flowable fill was the most frequently mentioned material. A total of four respondents stated that the approach slab and possibly the backfill would be removed and replaced. Of the DOTs that discussed strategies to address erosion of backfill, South Dakota, Kansas, and Minnesota stated that drainage would be improved retroactively. Nebraska stated that the agency uses good drainage details, implying a proactive strategy. West Virginia and North Carolina have unique strategies to address erosion. West Virginia restated that its use of reinforced backfill with geotextile layers helps prevent this issue, while North Carolina stated that construction inspection of the backfill and continued, biennial inspection prevent erosion issues. 3.4.3.4 Sealant Failure in Other Joints The responses describing strategies to prevent or repair sealant failures in joints other than the expansion joint are summarized in Table 16. Specific materials that were called out included an “easily maintained” material (Kansas), a silicone or asphalt material (Missouri), and concrete patching (Pennsylvania). 3.4.3.5 Differential Settlement The responses describing strategies to prevent, mitigate, or repair differential settlement are summarized in Table 17. Retroactive, repair-based strategies are most common and include replacement of the approach slab and backfill, slab jacking by foam injection or compaction grouting, overlay installation or repaving, and patching. The three DOTs who identified design-based strategies are West Virginia, Louisiana, and Alaska. As discussed, West Virginia uses a reinforced-soil mass backfill with geotextile layers and Louisiana has begun using larger Strategy No. of Respondents Removal and replacement 4 Void injection or filling 14 Drainage improvements 4 Miscellaneous 2 Table 15. Strategies to address erosion of backfill. Action No. of Respondents Replace/repair sealant/joint 13 Replace with a specific material 3 “Not applicable” or “none” 5 Table 16. Strategies for sealant failure in joints other than expansion joints.

State of the Practice 63   sleeper slabs with a geotextile system underneath. Alaska uses a special structural fill placed for 50 ft from the abutments and compacted to 98% of the maximum dry density. South Dakota and North Carolina rely on good-quality construction and proper compaction of the backfill. 3.4.3.6 Poor Ride Quality Along the Approach The responses describing strategies to prevent, mitigate, or repair poor ride quality of the approach slab or pavement are summarized in Table 18. The responses are similar to those for other ride quality issues. Retroactive repair-based strategies identified include replacement, overlays, milling and/or filling, and injection or jacking. The number of DOTs that use each strategy is summarized in Table 19. Design-based strategies consist of using buried or stronger approach slabs. Nebraska uses a second mat of steel in the paving section and Louisiana has begun using a thicker approach slab designed as a simply-supported span servicing heavier truck loads to reflect modern traffic. As for other performance issues, North Carolina and South Dakota rely on good construc- tion inspection. Pennsylvania stated that all repairs required for smooth ride quality are to be conducted after construction. 3.4.3.7 Transverse and Longitudinal Cracking The responses describing strategies to prevent, mitigate, or repair transverse and longitudinal cracking in the approach slab or pavement are summarized in Table 20. A general crack sealer was the most used strategy for traverse cracking as well as for longitudinal cracking. North Carolina noted that biennial inspections play an important role in addressing cracking and Type of Strategy No. of Respondents Design based 3 Quality based 2 Repair based 11 Table 17. Strategies to address differential settlement. Type of Strategy No. of Respondents Design based 4 Quality based 3 Repair based 11 Table 18. Strategies to address poor ride quality of the approach slab or pavement. Action No. of Respondents Replacement of slab or panel 3 Asphalt overlay or repaving 6 Local repairs, milling, and/or filling 4 Injection or jacking 4 Table 19. Repair-based strategies to address poor ride quality of the approach.

64 Practices for Bridge Approach Systems Strategy Blocked Subdrain Drainage Infiltration Replacement/repair 3 4 Maintenance 3 0 Design and quality 2 3 Table 21. Strategies to address blocked subdrains and drainage infiltration. Strategy Transverse Cracking (No. of Respondents) Longitudinal Cracking (No. of Respondents) Replace or repave 3 3 Overlay 2 1 General crack sealer 8 6 Flood coat sealer 2 2 Crack chasing 2 2 Inspection 1 1 Robust design 4 2 Table 20. Strategies to address transverse and longitudinal cracking. noted that the approach slab design plays a role as well. South Dakota and Indiana stated that they use increased reinforcement or two mats of rebar to prevent cracking, and Louisiana noted that a more robust sleeper slab is used to prevent transverse cracking. 3.4.3.8 Blocked Subdrains and Drainage Infiltration The responses describing strategies to prevent, mitigate, or repair blocked subdrains and drainage infiltration are summarized in Table  21. Repairs varied in significance, from full replacement of the abutment drainage system to replacement of the pipe or filter or repair of a drainage curb or joint. Design- and quality-based strategies reported consist of inspection of the backfill after construction and use of strong drainage pipes and filter fabric. One DOT (Iowa) commented that the agency builds redundancy into the drainage system to help mitigate the effects of drainage infiltration. The subdrain in this system is embedded in granular draining fill behind the abutment and has two outlets. 3.4.3.9 Failure of Paving Corbel The majority of the respondents to this issue stated that failure of the paving corbel is a major repair or rehabilitation project, typically consisting of replacement of the corbel and possibly the abutment backwall as well. Only one DOT (Rhode Island) reported using a less invasive repair method of placing additional asphalt. North Carolina responded that their preventive strategy addressing failure of the paving corbel is incorporated in the abutment design. 3.4.4 Recent Revisions to Standards Agencies were asked if they had made any significant changes to the standard design or maintenance practices of their bridge approach systems since 2005 to address performance issues. The responses are summarized in Figure 41. Approximately 68% of the respondents (30 of 44) stated that they have made major revisions within the last 15 years.

State of the Practice 65   In general, there is a shift toward using integral and/or semi-integral abutments and moving the expansion joint from the bridge side of the approach to the roadway side. Several DOTs commented that they added sleeper slabs to their designs when they moved the expansion joint to the roadway side. Changes to approach slab design and use varied. Alaska began using approach slabs for most bridges and North Dakota began supporting some approach slabs on piles, while Missouri and Montana began using less robust and fewer rigid approach slabs, respectively. The respondent from Missouri commented that the DOT investigated the use of cost-effective approach slabs that have less reinforcing steel, no sleeper slab, and a shorter length for application on minor routes. Contractors are currently permitted to use this reduced approach slab or a thick asphalt pavement for minor routes. Regarding joints, New Jersey began using 2-½ in. strip seal joints and Colorado is investigat- ing using a flexible joint instead of a strip seal joint. Colorado also reported decreasing joint construction time by using polyester concrete at the end dams of modular joints. Minnesota reported that the DOT has observed improved drainage and reduced performance issues since the DOT began mounting the traffic barriers directly on the slab instead of the wingwalls. 39% 30% 25% 16% 16% 9% 7% 5% 0 5 10 15 20 25 30 35 40 45 N o. o f R es po nd in g D O Ts Type of Revision Figure 41. Types of major revisions made to bridge approach system standards between 2005 and 2020. This question had a total of 32 responses. The percentage of survey respondents who selected each type of revision is shown; respondents could select multiple options.