highway 400 precast concrete inlay panel project ... · 137 precast panel pavements have been used...

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Highway 400 Precast Concrete Inlay Panel Project:

Instrumentation Plan, Installation, and Preliminary Results

Journal: Canadian Journal of Civil Engineering

Manuscript ID cjce-2018-0044.R1

Manuscript Type: Article

Date Submitted by the Author: 26-Mar-2018

Complete List of Authors: Pickel, Daniel; University of Waterloo, Civil and Environmental Engineering Tighe, Susan; University of Waterloo, Department of Civil Engineering Lee, warren; Government of Ontario Ministry of Transportation Downsview, Pavements and Foundations Section Fung, Rico; Cement Association of Canada

Keyword: Precast Concrete, Pavement Rehabilitation, Precast Concrete Inlay Panel,

High-Volume Highway Repair

Is the invited manuscript for consideration in a Special

Issue? : Not applicable (regular submission)

https://mc06.manuscriptcentral.com/cjce-pubs

Canadian Journal of Civil Engineering

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Title: Highway 400 Precast Concrete Inlay Panel Project: Instrumentation Plan, 1 Installation, and Preliminary Results 2

Authors: Daniel Pickel MASc, BEd (corresponding author) 3

PhD Candidate 4

University of Waterloo 5

200 University Ave. W., Waterloo, ON, CAN 6

N2L 3G1 7

(519) 888 4567 x 30187 8

[email protected] 9

Susan Tighe, PhD, P.Eng, MCSCE 10

Norman W. McLeod Professor in Sustainable Pavement Engineering 11

Director Centre for Pavement and Transportation Technology 12

University of Waterloo 13

200 University Ave. W., Waterloo, ON, CAN 14

N2L 3G1 15

(519) 888 4567 x 33152 16

[email protected] 17

Warren Lee, M.A.Sc., P.Eng 18

Ministry of Transportation of Ontario 19

145 Sir William Hearst Avenue, Room 232, Downsview, ON, CAN 20

M3M 0B6 21

(416) 235-6643 22

[email protected] 23

24

Rico Fung, P.Eng 25

Former Director, Markets & Technical Affairs-Ontario Region 26

Cement Association of Canada 27

709-44 Victoria Street, Toronto, ON, 28

29

30

31

32

Word Count: 5398 33

Figure Count: 10 34

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2 Pickel, D., Tighe, S., Lee, W., & Fung, R.

ABSTRACT 35

The Ministry of Transportation of Ontario (MTO) was interested in a rehabilitation 36 strategy that could be used to address deep-seated rutting issues encountered on its 400-series 37 highways. A precast concrete inlay panel (PCIP) rehabilitation design was developed and 38 constructed involving the installation of precast panels into partially-milled asphalt pavement. 39

Sub-surface instrumentation was installed at the PCIP-asphalt interface including earth 40 pressure cells (EPCs) and moisture sensors installed in six instrumentation clusters. This 41 instrumentation has been monitored to gather information regarding the PCIP trial installation. 42

Readings from the moisture sensors indicate that water penetrates beneath the PCIPs in 43 precipitation events, though these moisture levels recede under dry conditions, indicating that the 44 water can exit the sub-slab area. 45

Static load testing using a fully-load gravel truck was used to determine the different 46 support reactions caused by different loading configurations. Higher loads were generally found 47 beneath the joints in the two loading situations studied. 48

49

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INTRODUCTION 50

Precast concrete panels (PCPs) have been used as a paving material since as early as 1931 51 in the Soviet Union (Rollings & Chou 1981); however, their use has only started to become a 52 common practice in North America in the last 15 to 20 years (Tayabji & Buch 2012). During this 53 time, various departments of transportation across the United States and Canada have used them 54 in different ways to address different circumstances. Generally, PCPs are used in applications 55 where scheduling or location restrictions preclude the use of conventional cast-in-place concrete. 56 By curing concrete in off-site locations, a project schedule’s critical path can be shortened. There 57 are also typically benefits associated with the quality control aspects of factory production in 58 comparison with field construction. 59

One common practice is the use of PCPs for intermediate, full-depth repairs of concrete 60 pavements (Buch et al. 2003; Tayabji 2016). In this practice, the damaged areas of concrete are 61 removed and then replaced with a PCP that fits the dimensions of the concrete removal. The PCP 62 is connected to the adjacent existing concrete using dowels and rapid-setting grout. Continuous 63 PCP installations are another common practice, in which several PCPs are placed adjacently to 64 form a continuous lane. These PCPs are often connected using dowels and grout, but can also use 65 post-tensioning strands running through adjacent panels to improve performance. PCPs can also 66 be used to address application-specific needs, including high-traffic intersections and bus bays 67 (Tayabji & Tyson 2017). 68

A consistent requirement for all applications using PCPs, is uniform support beneath 69 panels. Non-uniform support can produce point loads or un-supported spans beneath the slabs, 70 which can result in premature cracking, loss of load transfer, and joint faulting. Constructing and 71 maintaining proper load transfer characteristics across joints is another important characteristic 72 of PCPs. Poor load transfer can also result in joint faulting which can cause panel degradation 73 and ride quality issues (Tayabji & Buch 2012). 74

The Ministry of Transportation of Ontario (MTO) in Canada has observed rutting issues 75 with several high-volume asphalt highways under its jurisdiction. The rutting has been observed 76 to re-occur 3-5 years after mill-and-replace asphalt rehabilitation operations are completed, 77 which indicates that the rutting issue stems from deep-seated issues in the pavement structure 78 that are not addressed by milling and replacing the surface asphalt. Addressing these issues 79 directly would require significant construction operations including excavation and 80 reconstruction. 81

Ontario has some of the busiest highways in North America, which are located in the 82 Greater Toronto Area. The average annual daily traffic (AADT) was measured in 2016 to be 83 greater than 100,000 in many areas with the busiest sections having over 400,000 vehicles/day 84 (Ministry of Transportation of Ontario: Highway Standards Branch 2016). Under these traffic 85 conditions, on-road construction operations can cause significant user-costs. Therefore, the MTO 86 will generally specify that any construction operations on these high-volume highways should 87 take place between the hours of 10 pm and 6 am, when traffic volumes are at their lowest point 88 in a given day. At the end of this overnight construction period (6 am) traffic flow must be fully 89 reinstated to avoid daytime delays. 90

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The construction schedule restraints and deep-seated nature of the observed rutting 91 combine to make a difficult situation for rehabilitation. It presents a situation wherein the MTO 92 must close portions of the highway for extended periods of time in order to address the pavement 93 issues, or use accelerated construction techniques capable of addressing the issue during the short 94 construction periods. Of these two options, the MTO has expressed a preference for finding an 95 accelerated construction technique to avoid incurring user costs. 96

In order to pursue this preference, a project team was put together to investigate the 97 feasibility of using precast concrete inlay panels (PCIP) to rehabilitate Ontario’s high-volume 98 asphalt highways. This team included members of the MTO, Cement Association of Canada, 99 Fort Miller, Golder Associates, and the University of Waterloo. The use of a stiffer paving 100 material in concrete was intended to provide wider dispersion of traffic loads in the lower levels 101 of the pavement structure, thereby alleviating the concerns that have resulted in deep-seated 102 rutting. Precast panels were considered to adhere to the typical short construction window, and 103 due to MTO’s positive experience with the technology in the past (Lane & Kazmierowski 2010). 104

A design was produced for a 100 m trial section, wherein the surface layer of asphalt was 105 removed from a lane of an asphalt highway and replaced with precast panels. The design 106 included three different base preparation techniques which would result in three different support 107 conditions. Briefly, the support conditions included: 108

Asphalt-Supported: Asphalt is milled to a ±3 mm surface tolerance and PCIPs are placed 109 directly on milled surface. 110

Grade-Supported: After conventional milling, cement-treated bedding material is screeded 111 and compacted to meet ±3 mm tolerance surface upon which the PCIPs are placed. 112

Grout-Supported: After conventional milling, cast-in lifting inserts are used to lift the 113 PCIPs into position before rapid-setting grout is pumped beneath the slabs. 114

In each case, the slabs were designed to have grout pumped beneath them to fill any voids 115 and provide uniform support (Pickel et al. 2016). Figure 1 and Figure 2 show the longitudinal 116 and transverse cross-sections of the PCIP design as submitted to the MTO. 117

As shown, the precast panels are placed within the milled asphalt pavement, with asphalt 118 remaining beneath the milled surface as supporting material. 119

120

Figure 1: Longitudinal cross-section of PCIP design (The Fort Miller Company Inc. 2015) 121

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122

Figure 2: Transverse cross-section of PCIP design (The Fort Miller Company Inc. 2015) 123

The transverse joints incorporated The Fort Miller Company’s proprietary super-slab joint 124 details. These joints are largely defined by their inverted dovetail dowel slots which provide an 125 uninterrupted driving surface even before dowels have been grouted into place. 126

Dowel bar slots at transverse joints were filled with non-expansive grout to provide load 127 transfer and the same grout was also used to fill gaps between adjacent panels and between 128 panels and the adjacent asphalt pavement. Transverse joints were sealed using rubberized-asphalt 129 sealant. 130

The design was reviewed and accepted by the MTO and the trial section was planned for a 131 section of Highway 400 which was under an active resurfacing contract at the planned 132 construction date. The trial section was constructed during the week of September 19-23, 2016, 133 on Lane #3 of the northbound portion of Highway 400. The site was located approximately 50 134 km north of Toronto, Ontario. 135

OBJECTIVES 136

Precast panel pavements have been used successfully in the past; however, the inlay of 137 precast panels in an existing asphalt pavement structure is a new and novel application of the 138 technology. For this reason, the trial section described previously represents an important 139 opportunity to investigate this new application in order to understand how it behaves and 140 ultimately performs. This understanding will serve to explain the performance as it is observed 141 throughout the trial section’s lifespan. This information is important as a thorough understanding 142 of the PCIP performance and the factors that affected it will largely determine whether this 143 strategy is deemed to be feasible for full-scale application in the future. 144

Part of this broad investigation involved the placement of instrumentation at the interface 145 between the PCIP and the milled asphalt. The objective of this paper is to present a preliminary 146 summary of the information gathered from this instrumentation and their potential impacts to the 147 performance of the PCIP trial. This information relates to thermal and static loading, sub-surface 148 moisture levels, and temperature gradients throughout the PCIP. 149

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INSTRUMENTATION 150

Because of the novel nature of the application, gathering information on the performance 151 of the PCIP trial was identified as a priority. This information gathering consisted of two parts: 152 post-construction testing, and sub-surface instrumentation. 153

The post-construction testing is on-going, and includes various aspects including falling-154 weight deflectometer testing of joints, visual surveys, roughness measurements, and coring. The 155 results of these other testing methods will be outlined in separate papers. 156

The sub-surface instrumentation involved the collection of data from sensors installed 157 beneath the slabs during the construction operation. An instrumentation plan was submitted as 158 part of the design package which was produced for the MTO, and included the sensor types, 159 installation plans, and positions within the project extents. 160

Two types of sensors were installed as part of this project: earth-pressure cells (EPCs) and 161 moisture sensors. The sensors were installed at the PCIP-asphalt interface in order to provide 162 information relating to the support conditions beneath the slab. 163

Two clusters of sensors were installed for each support condition type. Each cluster of 164 sensors was located beneath the right wheelpath and included two EPCs (one 300 mm from the 165 leading edge and one beneath the centre of the slab being instrumented) and one moisture sensor. 166 In total, twelve (12) EPCs and six (6) moisture sensors were installed. Figure 3 illustrates the 167 layout of the site and the positions of the six instrument clusters within the project extents. 168

169

Figure 3: Project instrumentation schematic 170

A 25 mm deep trench was cut and chipped into the milled asphalt’s surface in the sensor 171 locations. This provided space to install the sensors, and also included a trench through the 172 adjacent shoulder to run the instrumentation cabling. The sensors were seated and covered in 173 packed sand with the surface of the pressure cells at the elevation of the milled surface. The 174

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moisture sensor was located between the pressure cells, adjacent to the channel where cabling 175 was run to the side of the road. The cabling was run through a buried conduit to data-logger 176 housed in a cabinet located approximately 10 m from the edge of the shoulder. Figure 4 shows a 177 typical instrumentation cluster being installed on-site and the cabinet. 178

179

Figure 4: Instrumentation cluster installation (left), solar-powered data-logger cabinet (right) 180

The instrumentation was planned to provide information relating to the distribution of load 181 through the PCIP into the asphalt support layer and the presence of moisture at the PCIP-asphalt 182 interface. Locating the EPCs adjacent to a joint and at the centre point of the panels was intended 183 to provide any insight into the differential pressures associated with these locations. 184

Table 1 summarizes the two types of sensors which were employed as part of this project. 185

Table 1: Sensor Summary 186

Sensor Type Model Sensors Installed

Measurements Made Sampling Frequency (readings/hour)

Earth Pressure Cell (EPC)

LPTPC09-V 12 ⋅ VW Frequency (Hz)

⋅ Therm. Resistance (ohm)

4

Moisture Probe CS-655 6 ⋅ Volumetric Water Content (m3/m3)

⋅ Temperature (°C)

1

187

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Internal sensors within the PCIPs were initially considered in order to gauge strains 188 throughout the panel depth, but ultimately these were not used due to concerns with cabling 189 during panel casting, transportation, and placement, combined with uncertainty related to 190 positioning on the site. 191

METHODOLOGY 192

Moisture Sensors 193

The moisture sensors beneath the slabs were monitored in conjunction with local 194 precipitation information. The precipitation data was gathered from a weather station located 195 17.5 km north-west of the project site (44°14'02"N, 79°46'45"W) that provided daily cumulative 196 precipitation amounts (mm/day). This weather station was the closest location which provided 197 information relating to precipitation, and provides the best available data relating to site 198 precipitation events. Comparing precipitation data with sub-slab moisture provides information 199 into the permeability of the design. 200

Because the design includes concrete sitting in an asphalt “bath tub”, the ability of water to 201 get and stay beneath the slab is an important consideration in the performance of the PCIP 202 design, particularly in a climate susceptible to freeze/thaw cycling. 203

Earth Pressure Cells 204

Since shortly after construction, the EPCs have been collecting readings at 15 minute 205 intervals. This process collects daily pressure variations that can be tracked over the course of the 206 year. 207

Following the completion of construction, the MTO specified that falling-weight 208 deflectometer (FWD) testing be undertaken on the PCIPs to gauge the load transfer efficiency 209 across all of the inter-panel joints. During the lane closure for this testing on October 6 and 7, 210 2016, a fully-loaded gravel truck was brought to site in order to conduct static load testing on the 211 slabs. On each instrumented slab, the truck was parked in two positions to gauge the load 212 imparted from the slab to the asphalt support layer. Each position was maintained for 213 approximately five minutes and the sampling frequency on the EPCs was increased to 33 mHz. 214 The two positions and a photo of the truck in Position #2 are shown in Figure 5. 215

216

Figure 5: Loaded truck axle configurations for static testing 217

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Each EPC contains a 3kΩ thermistor in order to calculate the pressure readings based off 218 of the cell fluid’s viscosity characteristics. The temperature readings from these thermistors can 219 also be used to determine the temperature at the bottom of the PCIPs. These data can be used 220 with air temperature readings from local weather stations to determine a reasonable estimate of 221 the temperature differential across the concrete panels. It is understood that pavement surface 222 temperatures will generally be higher than air temperatures during sunny periods; however, no 223 thermistors were installed in the concrete surface to get a more precise surface temperature 224 value. 225

Temperature differences can be considered as both positive and negative temperature 226 differentials. Positive temperature differentials indicate that the top surface of the PCIP is 227 warmer than the bottom surface and usually occur during the daytime. This situation corresponds 228 with downward slab curling. Negative temperature differentials indicate that the bottom of the 229 PCIP is warmer than the top, which corresponds to upward slab curling, and typically occurs 230 during nighttime. 231

Weather data was collected from the Atmospheric Environment Service located northwest 232 of King City, Ontario. This location is located adjacent to Highway 400, 17 km south of the 233 project site (43°57'50"N 79°34'26"W). This data source represents the closest approximation of 234 the weather conditions on site. 235

RESULTS 236

Moisture Sensors 237

Figure 6 shows moisture content readings and daily precipitation amounts from October 3, 238 2016 until November 7, 2016. While there were 6 instrument clusters, it can be seen that initially 239 only 5 were reading properly. It was found that environmental conditions affected the readings, 240 and very cold temperatures occasionally resulted in unusable readings. The volumetric water 241 content (VWC, %) for each instrument cluster is shown on Figure 6. As there were two clusters 242 per different support condition, VWC 1 and 2, 3 and 4, and 5 and 6, were located under asphalt-243 supported, grade-supported, and grout-supported panels, respectively. 244

Because the moisture sensors were located in a trench beneath the milled asphalt surface, it 245 is likely that these trenches collect water which infiltrates beneath the slab and the probes 246 provide falsely high readings. For this reason, the magnitudes of volumetric water content 247 readings do not reflect expected conditions in PCIP applications. 248

The early dates shown on the plot correspond to days following construction. October 3, 249 2016 was the date when the data logging equipment was first brought on-line following the trial 250 section construction. Very few, and minor precipitation events had taken place between the 251 completion of construction on September 23, 2016 and this date. The moisture contents during 252 this period represent the approximate moisture content of the bedding material as placed during 253 construction. 254

During precipitation events observed on October 8, 13, and 17, 2016 small increases in 255 moisture content of sensors 2, 3, and 5 indicated that some water was infiltrating the material 256 beneath the slab. On the rain event occurring between October 20 and 21, 2016, significant 257 increases in moisture content indicate changes in the water infiltration rates throughout the site. 258

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This change in infiltration rate could be attributed to environmental changes, such as 259 moisture and temperature, which affect the material volume changes of concrete and asphalt. 260 Immediately following the construction of the trial, it could be assumed that some bond was 261 formed between joint and edge grouting materials and the adjacent existing asphalt. If the 262 volumetric changes of these two materials were different enough, this may have instigated a loss 263 of bond between the PCIP and the adjacent asphalt, resulting in a seam through which water 264 could pass freely. 265

Beyond October 21, 2016, frequent precipitation events combined with an increased 266 infiltration rate resulted in an average moisture content beneath the slabs between 30% and 50%. 267 This condition was observed throughout the months of December, 2016 to March, 2017, though 268 it should be noted that the sensors provided no data throughout significant portions of this period. 269

The volumetric water contents measured at VWC 4 and 5 were seen to be consistently 270 higher than in other locations within the project. While these two sensors were located beneath 271 different support conditions, they were in consecutive instrument clusters. This may indicate site-272 specific factors resulting in higher moisture levels in this area, such as a relative low spot in the 273 site. 274

275

Figure 6: Volumetric water content October 3 – November 7, 2016 276

Following the winter period, it was found that the moisture contents beneath the slabs were 277 generally found to drop during periods between precipitation events. Figure 7 illustrates this 278 point in the period between April 25, 2017 and June 13, 2017. 279

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280

Figure 7: Volumetric water content April 25 to June 13, 2017 281

The moisture content of sensor #3 can be observed to have increased steadily from May 8, 282 2017 until May 19, 2017, with some daily fluctuations. This is despite almost no observed 283 precipitation in the area. While this may indicate a secondary moisture source beneath the slab, it 284 probably indicates that the readings from this sensor are no longer reliable. 285

None of the three support conditions studied performed substantially differently with 286 respect to sub-panel moisture penetration. This condition may change over time, but at this time 287 no moisture conclusions can be drawn regarding the relative performance of the different support 288 conditions. 289

Generally, all support condition types exhibited sharp increases in volumetric water 290 content following precipitation events followed by slow decreases. This seems to indicate that 291 water is draining from sub-slab area or evaporating from the original infiltration points, instead 292 of remaining pooled beneath the slabs; the exit point for this water is not clear. Therefore, water 293 located beneath the panels is a design consideration. This is especially relevant considering the 294 PCIP is placed within a largely impermeable asphalt structure. Based on these findings it is 295 recommended that a drainage detail be considered for any future applications of this 296 rehabilitation technique. 297

Earth Pressure Cells 298

The static load testing on October 6 and 7, 2016 provided insight into the relative pressures 299 imparted by the PCIP onto the supporting asphalt. The twelve total EPC sensors were paired 300 within their instrument cluster: pairs 1/2 and 3/4, 5/6 and 7/8, 9/10 and 11/12, were located 301 beneath asphalt-supported, grade-supported, and grout-supported panels, respectively. Following 302 the static testing, it was found that sensor pairings 1/2, 3/4, 7/8, and 9/10 were producing 303

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readings based on significant slab loading. From these findings it was determined that sensor 304 pairings 5/6 and 11/12 were not producing reliable results. One sensor in each of these pairings, 305 was displaying pressure data while the second was not. For this reason, these sensor pairs were 306 disregarded for other comparisons. 307

Figure 8 illustrates the typical response under the testing conditions described previously. 308 The pressure readings were set to zero before the loads were applied to better show the effects of 309 loading. 310

311

Figure 8: Static load test results for slab instrumented with EPC 9/10 312

Under load Position #1 (rear axle group spanning joint) approximately 13 kPa pressure was 313 observed in the EPC 9 located adjacent to the joint, with very little pressure observed in the EPC 314 10 at the centre. When the rear axle group was positioned centrally on the instrumented slab 315 (Position #2), the centre EPC 10 read approximately two times the joint EPC 9, but well less than 316 the joint EPC 9 had read under Position #1. 317

Comparing the measured pressures under the two loading configurations may provide 318 insight into the slab behaviour. In each case, one EPC is between the axles and one is outside of 319 the axles. When the joint is loaded (Position #1), high pressures are measured between the axles 320 but almost none are seen at the mid-slab, indicating that loads are largely supported by the 321 materials directly beneath the joints. However, when the centre of the slab is loaded (Position 322 #2), increased pressures are measured at both sensors, indicating a distribution of the load across 323 the full slab. 324

Position #1 Position #2

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The pressure readings in each case are a function of the panel’s downward deflection under 325 load. As the slab deflects downward, the pressure cell is engaged. Therefore, the relative pressure 326 readings under load Position #1 and Position #2 indicate that larger slab deflections are occurring 327 at joints than at mid-panel under the same load. This larger deflection is also localized around the 328 joint as the mid-panel pressure cell is not engaged under the Position #1 load. The differences 329 between the deflection results are illustrated in Figure 9. The deflected and original shape is 330 shown for each load position. The deflections shown in the figure are exaggerated for illustration 331 and are not to scale, but the relative magnitude of the deflections at the centre and joint locations 332 are to scale. 333

334

Figure 9: Displacement shape under static load positions (not to scale) 335

In typical concrete pavements, high deflections beneath joints could eventually result in 336 pumping of base material in that area; however, the asphalt support layer should not generally be 337 susceptible to this. 338

Falling weight deflectometer testing was undertaken following construction to gauge the 339 performance of the joints. A falling weight was dropped adjacent to each joint in strategic 340 locations and the deflection on either side of the joint was measured. The detailed results of this 341 testing will be included in a separate paper, but some general results provide insight into the 342 joints following construction. The load transfer efficiency (LTE) is one of the values which is 343 obtained using this data. This measure represents the ratio of the deflections on either side of a 344 joint or crack when only one side is loaded. The ratio is the measured deflection of the unloaded 345 side divided by the measured deflection of the loaded side. The MTO specifies a minimum LTE 346 value of 70% to indicate an acceptable joint. The average LTE for the site was 81.3%, indicating 347 that most joints were transferring load across joints acceptably. The relative deflection of the two 348 sides of the joint can provide more meaningful insight into the behaviour of a joint than a ratio of 349 deflections. To determine this value, the difference between the deflections on either side of the 350 joint was found and divided by the magnitude of the applied load. On average, the joints were 351

found to have a relative deflection of 0.42 µm/kN, which is a very small relative deflection. 352

Relatively large deflections of adjacent slabs under load Position #1 can result in high 353 flexural stresses in the dowels and grout in the joint. Each slab will have opposite slopes at the 354 joint under that condition, placing the dowel between the slab under a significant moment 355 couple. This can result in high bearing stresses between the dowel and the surrounding grout. 356

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The pressure difference between the two EPCs in each working instrument cluster was 357 tracked throughout the course of the study period. The difference in temperature between the air 358 and the average EPC was also tracked during this time. Both sets of data are displayed in Figure 359 10, which shows these data types between the dates of October 15, 2016 and October 21, 2016. 360 Each pairing shows the relative change in sub-panel pressure between a given panel’s front joint 361 and mid-slab locations. 362

This plot shows that during the period between October 18, 2016 and October 20, 2016, 363 the system underwent rapid temperature changes. Throughout the course of those two days, the 364

air temperature above the surface of the PCIP system went from approximately 6°C warmer to 365

8°C cooler twice, indicating two reversals from positive temperature gradient to negative 366 temperature gradient and back again. During this period, the differences between the joint EPC 367 readings minus the centre EPC readings were seen to fluctuate. Since changes in these readings 368 are largely due to small slab deflections, changes in the difference between joint pressure and 369 mid-panel pressure indicate the occurrence of minor slab curling. The joint and edge stresses 370 related to curling could result in cracking of the joint and edge grouts. This may be the factor 371 which resulted in higher sub-slab moisture contents after October 20, 2016 noted previously. 372

If this is the case, it indicates that a flexible sealant may be required at all edges and joints. 373 Flexible sealant was only applied at transverse joints to account for temperature-induced changes 374 in joint width. This material should be able to maintain its bond to both concrete and asphalt to 375 reduce the amount of water which can penetrate beneath the PCIP. A drainage detail into the 376 adjacent shoulder may also be a beneficial consideration where the situation allows for it. 377

Curling can be exacerbated by the presence of water beneath the concrete slab, particularly 378 in the case of a negative temperature differential between the top and bottom of the slab (Delatte, 379 2014). When this is considered in relation to the moisture sensor data presented previously, it 380 indicates that the conditions of the PCIP slab may be conducive to slab curling, further 381 reinforcing the need for sub-slab moisture control. 382

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383

Figure 10: Instrument cluster pressure differences and temperature differential (Oct 2016) 384

Figure 11 and Figure 12 show the pressure and temperature differences for a period of 385

warm weather (daily highs approximately 25°C) and a period of cold weather (daily highs 386

approximately -6°C), respectively. 387

During the warm period, the temperature differential fluctuates from positive to negative 388 on a daily basis. Each functioning pair of sensors can be observed to fluctuate similarly as a 389 result of this temperature change. With average daily temperature difference fluctuations of 390

12.7°C, the average magnitude of these daily pressure fluctuations were 1.8, 0.9, 3.5, and 0.8 391 kPa, respectively. 392

During the cold period, a similar daily pattern in the temperature differential is observed; 393 however, it remains generally negative, meaning that the surface temperature is generally colder 394 than the temperature beneath the panels. The average daily temperature difference fluctuation of 395

8.1°C, resulting in daily pressure fluctuations of 1.3, 1.0, 3.8, and 0.5 kPa, for each of the EPC 396 pairs, respectively. 397

The pressure difference ranges seen in both cases are very similar, indicating that the 398 curling pressures in both situations are similar. Because of asphalt’s viscoelastic behaviour, the 399 supporting layer beneath the PCIP will be stiffer in cold temperatures. When a concrete 400 pavement is supported by a stiffer material, curling and warping stresses within the concrete are 401 magnified. Therefore, despite similar curling pressures between seasons, the curling stresses may 402 be magnified in colder months. 403

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404

Figure 11: Instrument cluster pressure differences and temperature differential (June 2017) 405

406

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407

408

Figure 12: Instrument cluster pressure differences and temperature differential (February 2018) 409

410

Figure 13 shows the distributions of the daily maximum daytime and nighttime 411 temperature differentials between the top and bottom of slabs, as considered based on EPC 412 thermistor readings and local air temperature readings. This distribution considers the period 413 between October 3, 2016 and October 3, 2017. It should be noted that in some instances, the 414 maximum daytime differential is a negative value. This indicates that during that 24 hour period, 415 the surface of the PCIP was not warmer than the base. Similarly, the maximum nighttime 416 temperature differential was often positive. 417

The distribution is considered in terms of 1°C increment. The distributions of both daily 418 maximum daytime and nighttime differentials are approximately normally distributed. During 419 the time period the average daily maximum daytime and nighttime temperature differentials were 420

1.2°C and -6.6°C. Assuming a normal distribution, only approximately 7% of the days will have 421

a maximum nighttime differential below -12.3°C or a maximum daytime temperature differential 422

greater than 8.1°C. 423

The largest observed daytime differential during this period was 15.5°C while the largest 424

nighttime differential was -16.7°C. Based on an assumption of a spring constant of 135 MPa/m 425 (Delatte 2014) and the PCIP design characteristics, these differentials could result in slab edge 426 temperature stresses of approximately 2.3 MPa. This can represent a significant stress, 427 particularly when combined with the effects of traffic loading, and should be considered in future 428 designs of the PCIP. 429

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430

Figure 13: Daily maximum and minimum temperature differentials, October 3, 2016 – October 3, 2017 431

Reviewing the environmental and sub-surface data, it was found that during the analysis 432 period, the air temperature underwent 67 cycles between above and below the freezing point 433

(0°C), or freeze-thaw cycles. Because of the insulating effects of the PCIP, only 23 freeze-thaw 434 cycles were observed below the PCIP. 435

The presence of moisture beneath the slabs combined with freeze-thaw conditions indicates 436 that any support or grout material beneath the PCIP should be designed for these aggressive 437 conditions. 438

CONCLUSIONS AND RECOMMENDATIONS 439

The Ministry of Transportation of Ontario (MTO) is interested in developing a fast 440 rehabilitation technique for the repair of high-volume asphalt highways. For this reason, the 441 precast concrete inlay panel (PCIP) rehabilitation strategy was designed and a trial section was 442 constructed on Highway 400, north of Toronto, Ontario. Since the purpose of the trial section 443 was to gather information to determine the feasibility of this rehabilitation design, 444 instrumentation was installed beneath the PCIP during the construction phase. 445

The instrumentation included six clusters, each of which consisted of two earth pressure 446 cells (EPCs) and one moisture sensor. The sensors have been monitored since October 3, 2016, 447 and this process is on-going. 448

Preliminary results indicate that as environmental temperatures began to drop at the end of 449 October, a change may have occurred that resulted in increased moisture infiltration rates 450 beneath the slabs. Beyond this point, significant amounts of moisture were observed beneath the 451 slabs for most of the winter season. Since the end of April 2017, sub-slab moisture contents have 452 consistently dropped to relatively low levels following the increases associated with precipitation 453 events. This indicates that moisture is exiting the area beneath the PCIPs effectively, despite the 454 impermeable nature of the asphalt support layer. The presence of moisture beneath the slabs 455

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indicates that the bond between edge grouts and existing asphalt is allowing for the passage of 456 water. A flexible sealant material should be considered at all joints and edges of the PCIP design. 457

Under static load testing using a fully loaded gravel truck, the functionality of the sensors 458 was tested. All but two EPCs were found to be functioning, resulting in four functioning EPC 459 pairs. Two load positions were observed for each instrumented slab: one with the tandem axle 460 spanning the joint and one with the axle tandem axle centred on the slab. Under these conditions, 461 it was found that the supporting material beneath the joint experiences loads from traffic as much 462 as twice those experienced under the centre of the slab. This confirms the joint load transfer 463 efficiency measured through FWD testing. Higher deflections at joints can place the dowels and 464 their surrounding grout under stress due to the moment caused by opposite slopes of adjacent 465 slabs. 466

The temperature differentials across the PCIPs were approximated using air temperature as 467 a surface temperature. The maximum daily daytime and nighttime temperature differentials were 468

found to be approximately normally distributed, with average values of 1.2°C and -6.6°C, 469

respectively. The largest negative temperature differential was found to be -16.7°C while the 470

largest positive temperature differential was found to be 17.2°C. These values can contribute to 471 significant curling stresses at the slab edges, and should be considered in conjunction with traffic 472 loads in PCIP designs. 473

During the period of study, 67 freeze-thaw cycles were observed in the air temperature on 474 site, while only 23 cycles were observed beneath the PCIP. Considering that moisture was found 475 to be present beneath the slabs, freeze-thaw resistant grouts and bedding materials are a 476 necessary design feature of PCIP rehabilitation design. 477

The preliminary results do not differentiate any of the support conditions considered in 478 terms of early-age performance. Each support condition provides similar load transfer, moisture-479 penetration susceptibility, and relative joint vs mid-panel pressures. These values will be tracked 480 throughout the trial section’s service life to determine the relative performance of the support 481 conditions which could inform agencies when selecting the best PCIP strategy. 482

ACKNOWLEDGEMENTS 483

The authors would like to thank the following people for their contributions throughout this 484 project: Peter Smith of the Fort Miller Company, Tom Kazmierowski of Golder Associates, and 485 Mark Snyder. 486

Funding for this research was provided in part by the MTO Highway Infrastructure 487 Innovation Funding Program, the Cement Association of Canada, the Natural Sciences and 488 Engineering Research Council of Canada (NSERC), and the Norman McLeod Chair. 489

490

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REFERENCES 491

Buch, N., Barnhart, V. & Kowli, R., 2003. Precast Concrete Slabs as Full-Depth Repairs. 492 Transportation Research Record, Volume 1823, pp. 55-63. 493

Campbell Scientific, 2017. Soil Water Content Reflectometer 12 cm. [Online] 494 Available at: https://www.campbellsci.ca/cs655 495 [Accessed 26 June 2017]. 496

Delatte, N. J., 2014. Concrete Pavement Design, Construction, and Performance: Second 497 Edition. Boca Raton, FL: CRC Press. 498

Lane, B. & Kazmierowski, T., 2010. Performance of Precast Pavement Repairs on an Urban 499 Freeway in Toronto. Edmonton, Alberta, s.n. 500

Ministry of Transportation of Ontario: Highway Standards Branch, 2016. Traffic Volumes. 501 [Online] Available at: http://www.raqsb.mto.gov.on.ca/techpubs/TrafficVolumes.nsf/ 502 fa027808647879788525708a004b5df8/f51986ea499a13b08525745f006dd30b/$FILE/Prov503 incial%20Highways%20Traffic%20Volumes%202016%20AADT%20Only.pdf 504

Pickel, D. et al., 2016. Using Precast Concrete Inlay Panels for Rut Repair on High Volume 505 Flexible Pavements, San Antonio, TX: International Conference on Concrete Pavements. 506

Rollings, R. S. & Chou, Y. T., 1981. Precast Concrete Pavements, Vicksburg, Miss.: U.S. Army 507 Engineer Waterways Experiment Station. 508

Tayabji, S., 2016. FHWA Project R05 IAP Funded Project Case Study: Hawaii Interstate H1 509 Precast Concrete Pavement Demonstration Project , Washington, D.C.: Federal Highway 510 Administration. 511

Tayabji, S. & Buch, N., 2012. Precast Concrete Pavement Technology Project R05 – Modular 512 Pavement Technology , s.l.: The Strategic Highway Research Program 2 Transportation 513 Research Board of The National Academies. 514

Tayabji, S. & Tyson, S., 2017. Precast Concrete Pavement Implementation. Concrete 515 International, April, pp. 41-46. 516

The Fort Miller Company Inc., 2015. Super Slab Detailed Drawings, Schuylerville, NY: Fort 517 Miller Co. Inc.. 518

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