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Transverse cracking is a major distress in asphalt pavements in north-western Oklahoma. Assessment of probable causes of such distresses is helpful to the design of new pavements and maintenance and rehabilitation of existing pavements. In this study, probable causes of transverse cracking were identified using field investigation and a parametric study using AASHTOWare Pavement ME Design. Specifically, non-destructive and destructive tests were performed on two flexible pavement sections, namely US 270 and US 287 in Oklahoma. Also, soil samples and asphalt cores were collected for laboratory testing. The Ground Penetrating Radar results revealed that the disturbance zone was confined within the pavement structure and cracks were generated at the surface and propagated downward at both sites. The Dynamic Cone Penetration and Falling Weight Deflectometer test results indicated that both pavement sections were structurally adequate to support the current level of traffic for 10 years or more, with proper maintenance. The cracking resistance of the asphalt cores collected from both pavement sections was ranked as poor based on the Illinois Flexibility Index Test. The field and laboratory investigations indicated that stiffer and brittle asphalt mixes at both sites resulting from aging during the long service life were primarily responsible for the transverse cracking observed in the field. Also, a large number of thermal cycles with significant difference between low and high temperature, observed from the weather data, was a likely contributing factor. In addition to field and laboratory investigations, a parametric study was conducted using the AASHTOWare Pavement ME Design. The influence of the changes in pavement structural components, material properties and the average hourly temperature on transverse cracking was examined. Binder grade and pavement thickness were found to be the most influential factors. A hybrid approach involving field and laboratory testing and a parametric study using the AASHTOWare Pavement ME Design was found to be a useful tool for assessment of probable causes of transverse cracking in asphalt pavements.

Reflective cracking potential in hot mix asphalt (HMA) overlays on Portland cement concrete (PCC) pavement depends on the condition of PCC pavement in terms of slab stability at discontinuities (cracks and joints) and asphalt material characteristics in terms of their ability to resist reflective cracking. To develop a more comprehensive HMA overlay on PCC pavement program that minimizes reflective cracking potential and thus improves HMA overlay performance, TxDOT employed evaluation tools for both continuous deflection measurement of PCC slabs and overlay mix material characteristics. Rolling Dynamic Deflectometers (RDD) evaluate deflections on pavement surface continuously, providing valuable information on the stability of concrete slabs and load transfer efficiencies at discontinuities such as cracks and joints. Overlay testers (OT) evaluate the capacity of asphalt mixtures to resist reflective cracking. Since the performance of HMA overlay on PCC pavement depends on the extent of reflective cracking, design criteria should be developed for both slab stability and asphalt material properties. To that end, RDD and OT were utilized for the evaluations of HMA overlay on PCC pavements in four projects in Texas: (1) IH20, (2) SH225, (3) SH12, and (4) US96, with the objective of developing design criteria. This paper documents the efforts made to evaluate the PCC pavement condition before overlay, overlay material properties, and long-term performance of the four sections. CAM and SMA mixtures have been used successfully to retard reflective cracking, as they have exceeded eight years of life expectancy. Threshold values were validated for slab stability and asphalt materials, and applied for the designs of three rehabilitation projects.

Many miles of CRCP and JCP in Texas suffer distresses due to longitudinal joint separation and slab faulting. The absence or ineffectiveness of tie bars causes larger deflections of concrete slabs and pumping, ultimately resulting in lane separation, cracking and faulting of slabs. In addition to full depth repair, slot stitching, stapling, and cross stitching have been used by districts to repair longitudinal cracks and longitudinal joint separations. Field results indicated that districts have successful experiences with slot stitching and stapling to restore load transfer along longitudinal joint and provide horizontal anchorage to prevent further lane separations. Longitudinal joints that had been repaired with slot stitching did not appear to have suffered any further separation or major faulting. Houston district has utilized stapling in many projects. Some of the stapling projects last for more than 8 years. Condition survey results indicated that the performances vary significantly when different slot filler (or elastomeric) materials were used in stapling projects. Few areas showed poor performance as the filler materials had cracked, spalled, and de-bonded from the wall of the slot. In some areas, chunks of the filler material had come out of the stapling joints. The cross stitching may be used to repair cracks/separations that are fairly tight. For wider cracks/joint separations and/or faulted slabs, cross stitching is not suitable. Slot stitching with Class P concrete filler material is the most cost effective approach to repair wide longitudinal joint separations. The cost would be double if full depth repair was used instead of slot stitching to repair the wide longitudinal joint separations.

Three premature failures (related to weak, moisture-susceptible aggregate base) were investigated and the results are presented in the paper. Falling Weight Deflectometer (FWD) tests were conducted to determine the structural load bearing capacity. Laboratory tests were performed to evaluate the aggregate base’s susceptibility to moisture. One successful project that used crushed aggregate base as an interlayer to mitigate reflective cracking was studied. The crushed aggregate base interlayer performed well while other treatments failed. The weak and moisture-susceptible aggregate base, in conjunction with a thin, porous and brittle surface AC, caused premature failures for the three studied projects. It was theorized that the weak base deformed under the traffic load, and this cracked the brittle/thin surface mix. FWD test results for all three projects yielded much higher deflections than the target design deflections, indicating insufficient load bearing capacity. Two key factors for minimizing premature failures are: (1) prevention of water infiltration into the base through good surface mix, and (2) building a base that is moisture resistant. The strategy of using a crushed aggregate base as an interlayer has been utilized on other projects with success, provided it meets two key requirements: (1) Class 1 Texas Triaxial class, after 10 days capillarity and (2) the 10-day final dielectric should not exceed 13.

The placement of an asphalt overlay is the most common method to rehabilitate existing concrete pavements. Reflective cracking, however, has been a serious problem with asphalt overlays for a long time. To prevent reflective cracking, it is critical to evaluate existing concrete pavements and identify the joints/cracks with poor load-transfer efficiency (LTE) before placing an asphalt overlay. The most common equipment for this evaluation is a falling weight deflectometer (FWD). However, FWD testing is conducted only at discrete points and is time consuming. It is desirable to use the rolling dynamic deflectometer (RDD) that can continuously characterize each slab and all joints and cracks (e.g., LTE). The RDD was developed in the 1990s at the Center for Transportation Research in Austin, Texas. The RDD is one of the few operational rolling deflection systems that provide continuous data to make project level decisions on rehabilitating concrete pavements. In contrast to the FWD, no RDD data analysis software is available. This paper discusses RDD data interpretation and its application on evaluating existing concrete pavement for asphalt overlays. First of all, some basics of RDD deflection data interpretation are discussed. Several common patterns within the RDD data are identified, and associated interpretation and limited verification are presented in this paper. The RDD deflection data measured before an asphalt overlay on Interstate Highway-20, Texas, and the observed asphalt overlay performance (in terms of reflective cracking) are then presented, and the relationship between RDD deflection and reflective cracking rate is further investigated. Finally, guidelines for evaluating existing concrete pavements using RDD are proposed.

Density criterion for base materials is the most common practice in quality control and quality assurance for pavement construction. However, cases in which the base material has met the density requirement but turned out to be the cause of a premature failure exist. It means meeting the density requirements would not prevent the premature failures from occurring. Field studies indicated that these base materials are found to be either too weak to provide sufficient base support or too brittle, which causes cracks in base layers which in turn leads to secondary damage in other pavement layers. This paper documents the pavement layer moduli obtained from eight forensic investigations spanning 10 years. Falling-weight deflectometer and dynamic cone penetration tests were conducted to determine the layer moduli on sections that were either too weak or too brittle. In some cases, laboratory tests were performed to evaluate the base materials’ reactions to the stabilizers (lime or cement) and base susceptibili...

A forensic study was conducted to investigate the premature cracking distress on an ongoing construction project on State Highway (SH) 24. Transverse cracks occurred at approximately every 9–15 m (30–50 ft) along the 9.6 km (5.9 mi) project. The field tests involved both destructive tests, including trenching and coring, and nondestructive tests, including falling weight deflectometer (FWD) and ground-penetrating radar (GPR) tests. The laboratory tests mainly included cement-treated base material and asphalt mixture material series tests. By integrating all the test results, it was concluded that the premature cracking was originating from the cement-treated base (CTB). Although CTB is not a new concept in pavement construction, stabilization of base materials is a complex process, which, if not handled properly, may lead to premature failures. The two primary factors that contributed to the premature failure are (1) an excessive amount of cement in the CTB, and (2) a high moisture content when the CTB wa...

Before partial-depth repair using proper materials was implemented, Houston District of Texas Department of Transportation had to repair spalls and punchout constantly in the Continuously Reinforced Concrete Pavement (CRCP) pavements on US290 and SH6. The full-depth repair to address the cracking on US75 did not work well. Spalls, wide, cracks and punchouts due to mid-depth horizontal cracks represent functional and structural distresses in Portland cement concrete pavement. Traditionally, these distresses were repaired by partial-depth repair (PDR). The performance of PDR varies substantially. Two types of polymeric patch materials were used to repair the distresses. Material A is polyurethane-based and Material B is epoxy-based. Material A was used to repair spalls in CRCP. It provided quite satisfactory performance for more than 9 years. Material B was used to repair cracks in jointed concrete pavement and CRCP. Its performance was satisfactory when applied to stable slabs and the loose concrete was completely removed. Compared to full-depth repair (FDR), PDRs utilizing polymeric patch materials are much more cost-effective, and PDR takes much less time than FDR. It is believed that both chip-and-patch and saw-and-patch methods would work as long as the delaminated areas are completely removed and the concrete slabs are stable (e.g. no settlement or movement under moving trucks).

To prevent premature failures of rehabilitated concrete pavements, transportation authorities need tools to characterize the prerehab pavement condition of its load carrying capacity, and to determine the resistance of the overlay material to underlying crack/joint movements. Two quantitative methods, the rolling dynamic deflectometer (RDD) and overlay tester (OT), along with field performance data were employed in rehabilitation studies involving reflective cracks. The RDD is able to continuously assess vertical differential movements at joints/cracks that represent the potential for reflective cracks on existing pavements. The OT has the ability to determine the resistance of the overlay material to underlying crack/joint movements. The RDD W1−W3 deflections were used to determine areas that have a high potential for reflective cracking due to poor load transfer across joints and cracks. This paper documents results from the RDD and OT on the following five rehabilitation projects: (1) SH225; (2) US96; ...

An investigation was conducted to determine the root cause of the premature pavement failure. The premature pavement failure occurred in the form of rutting and alligator cracking. Although the affected portion was repaired by removing and replacing the top 75-mm asphalt concrete (AC), the repaired AC experienced recurring rutting and alligator cracking in a few weeks. Through extensive field and lab testing, it was found that the weak base is the root cause of the premature failure and the brittleness of the AC is secondary. However, both the base and AC were built according to plan and met the current material and field density requirements. It was concluded that density alone for construction quality control is not sufficient, as it was not able to protect against premature failures from occurring. Although there are many different ways to minimize premature failures, an immediate action is to include proof rolling in construction quality control. Proof rolling has been used with success to ensure proper compaction and to locate unstable areas, as the stability is greatly influenced by the degree of densification achieved during compaction.

Spalls and wide cracks represent functional and structural distresses in portland cement concrete pavement. Traditionally, these distresses were repaired by partial depth repair (PDR). The performance of PDR varies substantially. Two types of polymeric patch materials, Material-A and Material-B, were used to repair spalls and cracks. Material-A was used to repair spalls in continuously reinforced concrete pavement. It provided quite satisfactory performance for more than 6 years. Material-B was used to repair cracks in jointed concrete pavement. Its performance was satisfactory when applied to stable slabs. Compared with full-depth repair (FDR), PDRs utilizing polymeric patch materials is much more cost effective, and PDR takes much less time than FDR. It was found that chip-and-patch method would work as well as saw-and-patch method as long as the repair limits include all the delaminated areas.

As agencies continue looking for cost-effective methods to rehabilitate deteriorated jointed concrete pavement (JCP), rubblization using a resonant breaker has been experimented by the Shanghai Municipal Roadway Authority (SMRA). It was demonstrated that rubblization using a resonant breaker offers a viable option for the SMRA because the rubblized pavement sections have been performing very well with no visible distress. Based on field observation for a typical hot mix asphalt concrete (HMAC) overlay on a nonrubblized JCP, it was found the treatment normally would have reflective cracking for the same overlay thickness in the first three years. Besides the cost advantage over the reconstruction, a resonant breaker also had yielded the minimum disturbance during the rubblization. It was observed that it was very effective to use water during compaction on a rubblized JCP surface to improve compaction efficiency and to control dust. Furthermore, there is no need to apply a prime coat before the HMAC overlay, as there was no detrimental effect that could be identified. The average rubblized JCP moduli were found to be 1,323 to 1,375 MPa, which are within the range reported in the literature. It was believed that there were high possibilities to increase rubblized JCP moduli without sacrificing the performance by increasing the particle size, because a reduction of 200 mm of HMAC was observed when rubblized JCP increased from 345 to 3,445 MPa at a subgrade modulus of 138 MPa and traffic of 30 million ESAL. However, further research is needed to optimize the rubblized JCP moduli in an attempt to reduce overlay thickness without creating reflective cracking.

Since reflective cracking is related to both the existing pavement condition and the overlay material, appropriate tools are needed to characterize both properties. The rolling dynamic deflectometer (RDD) was employed to measure the continuous deflection profiles that relate to vertical movements of the underlying joints and cracks. An overlay tester (OT) was utilized to characterize the asphalt mix’s ability to resist reflective cracking. The reported threshold values were employed in the study that include: (1) W1–W3=6.5 mils for composite pavement with old asphalt concrete (AC) overlay; (2) W1–W3=5.5 mils for exposed concrete pavement; and (3) 700 cycles of the OT were employed to evaluate six field rehabilitation projects (SH12, IH20, US96, SH73, SH225, and IH44). It was found that although there were severe transverse cracks and spalling on US96, all W1–W3 deflections were less than 5.5 mils , indicating low risk for reflective cracking. A stone-mastic asphalt (SMA) layer was placed 3 years ago and t...

This paper presents the results of several investigations to identify the underlying causes of longitudinal cracking problems in Portland cement concrete (PCC) pavement. Longitudinal cracking is not intended and detrimental to the long-term performance of PCC pavement. Longitudinal cracking problems in five projects were thoroughly investigated and the findings indicate that longitudinal cracking was caused by: (1) late or shallow saw cutting of longitudinal joints; (2) inadequate base support under the concrete slab; and (3) the use of high coefficient of thermal expansion (CTE) aggregates. When the longitudinal cracks were caused by late or shallow saw cutting of longitudinal joints, cracks developed at a very early stage. However, when there was adequate base support, the longitudinal cracks remained relatively tight even after decades of truck trafficking. Another cause of longitudinal cracking was inadequate base support, and cracking due to this mechanism normally progressed to rather wide cracks. Some cracks were as wide as 57 mm. Evaluations of base support by dynamic cone penetrometer in areas where longitudinal cracks were observed indicate quite weak subbase in both full-depth repaired areas and surrounding areas. This implies that the current requirements for the subbase preparation for the full-depth repair are not adequate. Another cause of longitudinal cracking was due to the use of high CTE aggregate in concrete. Large volume changes in concrete when coarse aggregate with high CTE is used could cause excessive stresses in concrete and result in longitudinal cracking. To prevent longitudinal cracking, attention should be exercised to the selection of concrete materials (concrete with low CTE) and the quality of the construction (timely and sufficient saw cutting and proper selection and compaction of subbase material).

The fundamental mechanisms leading to the development of reflective cracking are differential movements from the supporting pavement structure. In this study, the deflection profiles collected using the rolling dynamic deflectometer (RDD) were used to determine the threshold values for reflective cracking. This provides a quantitative method to determine the severity of the cracks (or joints), which controls the potential for reflective cracking. Three different deflection parameters were considered: (i) sensor 1 deflection (W1), (ii) differential deflection between sensor 1 and sensor 3 (W1-W3), and (iii) multiple of baseline deflection value. The reliability concept was also incorporated such that pavement engineers can select criteria (based on predefined confidence levels) to identify locations where reflective cracking is likely to take place. Threshold values were determined from a 4 year study conducted along US Interstate Highway 20 (IH-20), and case studies from overlay projects along State Highway 73 (SH-73) and US Highway 59 (US-59) were investigated to verify the proposed threshold values. Based on the findings in this study, the RDD can identify problematic areas but can also be used to optimize the rehabilitation strategy. As evident from the SH-73 and US-59 projects, the W1-W3 deflection and 2.5× baseline deflection are better criteria than W1 deflection alone.Key words: rolling dynamic deflectometer (RDD), reflective cracking, jointed concrete pavements, continuous deflection.

This paper describes a successful failure analysis to determine the causes of loss of backfill sand from a mechanically stabilized earth (MSE) wall, and cracks on the concrete approach slabs on top of it. The Texas Department of Transportation was concerned that the cracks on the approach slabs may be related to the excessive loss of backfill from behind the MSE walls, and that the embankment structure may be unsafe due to potential voids under the concrete slab. Several cubic meters of sugar sand had washed out of the wall and deposited adjacent to the paneled walls. A series of destructive and nondestructive tests were carried out to determine the causes of the problems. It was found that the cracking of the approach slab and the loss of backfill were unrelated. Suggestions for resolving both problems were made based on this study.

A forensic study was conducted to identify the cause of the premature cracking on three recently completed projects that were built with the same design. Nondestructive [ground penetration radar, falling weight deflectometer (FWD), GeoGauge, and Portable FWD], nuclear density gauge, dynamic cone penetration, and extensive laboratory tests were performed. It was found that the initial stiffness of the treated base was found to be excessively high by FWD backcalculation. Some sections of the backcalculated base moduli were over 20.7 GPa. This indicates that the layer is excessively brittle for a base material, similar to lean concrete. Six specimens (that were made without a mellowing period) exhibited cracks. There was no cracking for six specimens that had two days of mellowing. It was concluded that the culprit of the transverse cracking in the main lanes was the shrinkage of lime treated base layers. The longitudinal cracks are related to the edge drying and the transverse cracks are related to the insufficient mellowing period. Based on the findings of this study, the District implemented a 2-day mellowing period for Quicklime treated caliche base. Three newly constructed pavements (age 8, 5, and 2 months) were surveyed. No cracking can be observed so far, and the District thinks the cracking problem has been mitigated by the 2-day mellowing period. Without the mellowing period, cracking had normally occurred 1 to 2 months after construction.

It is well known that fatigue cracking is not just a material problem; it also correlates highly with pavement structure and environmental and traffic conditions. This unique characteristic highlights the importance of a simple performance test (SPT) that can be used for daily hot-mix asphalt (HMA) mixture design and also for predicting fatigue cracking. This paper investigates the use of the Texas Transportation Institute's overlay tester (OT) as an SPT for fatigue cracking. Fatigue cracking occurs in two stages: crack initiation and crack propagation. However, as noted in this paper, crack initiation is theoretically related to crack propagation. Therefore, the OT that characterizes mainly crack propagation can be used for fatigue cracking. To validate experimentally the OT for fatigue cracking, the OT results were compared with laboratory bending beam fatigue test and field accelerated pavement fatigue test results from the FHWA's accelerated loading facility test site. Positive results were obtained. In addition, other requirements (e.g., cost-related) for being an SPT are discussed. On the basis of all findings, the OT meets most requirements for being an SPT for fatigue cracking. Potential application of the OT to HMA mixture design also is proposed.

This paper documents an investigation into the cause of structural distress (alligator cracking and deep rutting) found in a foamed-asphalt warranty project in Texas. This is a unique forensic study involving a warranty specification, where the contractor may or may not be liable for the cost of repairs, depending on the outcome of the study. Extensive field tests, including FWD, seismic, GPR, and DCP, were conducted. Laboratory tests were also done to determine gradation, moisture content, capillary action, and indirect tensile strength. Four trenches were opened to test each layer directly and to obtain samples for laboratory testing. Two of the trenches were located in distressed/failed areas, while two others were in intact areas. Based on this study, the forensic team concluded that the rutting and alligator cracking are associated with failure of the foamed asphalt base. Since the subgrade strength in the failed areas was similar to the intact areas, the subgrade strength could not have been the sole cause of the failure. The foamed asphalt base was found to be susceptible to moisture and exhibited a severe loss of strength when subjected to moisture. Thus, it is imperative to verify the moisture susceptibility during the design phase. Based on the findings of this study, the contractor did repair the failed section at his own expense.

Reflective cracking through jointed concrete pavement overlays has been a persistent problem. Several different rehabilitation strategies have been used in Texas. This paper is a summary of the performance of strategies used in the past 10 years. The performance of the crack-retarding grid has been disappointing as it has been related to several premature failures. Only one project has realized a benefit of the crack-retarding grid, where the reflective cracking was delayed by about 1 year. The writers believe the small openings in the crack-retarding grid and the lack of an effective bond may be the causes of the layer separation. A proprietary crack-retarding asphalt material has been performing well over two years of monitoring. In one experimental project, 100% of the cracks reflected through conventional overlay material in the first year. Both Petromat fabric underseal and crack-retarding asphalt material have been performing satisfactorily to retard reflective cracking. However, there is a large cost difference between these two treatments. Seven experimental treatments on a major section of US 59 were evaluated. The worst-performing section on the US 59 project was the break-and-seat method, which failed due to weak subgrade support. The weak subgrade is unable to support cracked concrete, which leads to a rocking action under traffic loads. It is concluded that for future projects, the break-and-seat method should not be applied on subgrade with a dynamic cone penetrometer penetration rate exceeding 25 mm per blow. A flexible base overlay with thin asphalt surfacing and the Arkansas (large stone) mix have performed well. Flexible base overlays were able to absorb the joint movement and eliminate the reflective cracking. The flexible base should be of top quality with very low moisture susceptibility. In Texas, this involves specifying a Texas triaxial Class 1 material with classification of "good" in suction/dielectric tests. It is also critical to provide an effective seal for the flexible base. A chip seal followed by a thin 75-mm hot mix layer is recommended.

A common rehabilitation strategy used for repairing aged concrete pavement is to place a hot-mix asphalt (HMA) overlay on the existing concrete pavement. However, reflection cracks are often found to propagate from the underlying cracks and joints through the HMA layer. As such, much reflection cracking is believed to be caused by differential vertical and horizontal movements in the concrete pavement. A common method of determining the differential vertical movements is by measuring the load transfer efficiency (LTE) at the joints by using nondestructive deflection testing devices. A study was conducted with a rolling dynamic deflectometer (RDD) to evaluate the movement of joints in concrete pavements. Evaluation of joint movements by RDD testing permits estimation of the LTE of each joint or transverse crack. On the basis of the assumption that reflection cracks are more likely to form at joints or cracks with low LTE than with high LTE, pavement engineers can use the results to identify areas with low LTE and perform necessary repairs at these locations to reduce the potential for creating reflection cracking. Field data collected before rehabilitation work on US-82 near Gainesville, Texas, are presented as a case study, and the benefits of continuous deflection profiling for use in the district’s rehabilitation strategy are discussed.

This forensic study is unique in that it involves a pavement warranty specification. Extensive field and laboratory testing was conducted to determine the cause(s) of longitudinal cracks observed on the surface. Four trenches were cut and removed to allow more testing on top of each pavement layer. The tests found that the stiffness of the foamed asphalt base is higher than that of a typical flexible base. However, the subgrade modulus is low compared with the average subgrade modulus in Texas. Water seeped into two trenches (dug into the road where there were surface cracks) within 20 min of digging. No water was observed in the other two trenches, where there were no surface cracks. The two trenches with surface cracks have lower base density and higher base moisture content than the two with no surface cracks. Based on observations of the trenching and coring operations, the same surface cracks have been detected in the base layer. Cracks up to 150 mm into the base layer have been observed. Although cracks have been observed in the base (and they can be related to lower stiffness and higher falling weight deflectometer deflections), it is difficult to determine if the cause of surface cracks is due to the base layer alone. It is difficult to prove if the layer is responsible for the failure, except by properties listed in the specification. One faulty pavement layer can easily cause the failure of other layers. For warranty purposes, layer-specific failure criteria should be clearly outlined. The base did not meet the gradation specification. The field material was substantially finer than specified. While some specifications may have been violated, there is little evidence to show that the cause of the longitudinal cracking is primarily related to the foamed-asphalt-stabilized base.

Current practices lack a standard procedure for evaluating the performance of trackless tack. The primary purpose of this study is to develop a procedure through literature search that incorporates the combined shear and tensile stress state that an interlayer tack coat experiences in between a hot-mix asphalt overlay and an existing pavement, using the crack mouth opening displacement (CMOD), a standard method to predict the fracture energy. Recent developments in fracture testing and numerical simulation techniques have provided stronger links between material fracture properties and field cracking performance of asphalt pavements. Using the fracture energy as a criterion, performance of various trackless tack materials can be compared. The higher fracture energy required to crack a material, the better performance the material will have. The fracture energy methodology can be applied to characterize the performance of trackless tack with confidence.

Repeated falling weight deflectometer (FWD) tests were conducted at three sites. The tests were conducted at regular intervals for 2 to 3 consecutive days per location, and also done during different seasons in order that the widest possible range of temperatures could be obtained. The influence of cracks on temperature correction was also investigated. Temperature correction equations for deflection and moduli were developed so that users could be allowed to input their own reference temperatures. For all test pads, only the W1 and W2 deflections were found to be significantly affected by temperature. Comparisons with other reported temperature correction equations showed close agreement for deflection, but not for moduli. Tests were also run on cracked locations. Temperature did not affect the response of the cracked pavement as much as it did the intact pavement. Due to the different temperature-dependent characteristics of intact and cracked locations, the equations developed from the intact locations may not be used on cracked locations.

This paper presents the test results from full-scale accelerated pavement testing with the Texas Mobile Load Simulator. Data from in-situ instrumentation and nondestructive testing were collected and analyzed at different loading stages to assess material property changes under accelerated loading. Forensic studies were performed at the end of trafficking to assist in explaining the performance of the pavement. Two trenches were made to study material characteristics in the longitudinal and transverse directions. It was found that at the early stage of trafficking the test pad responded to falling weight deflectometer (FWD) load linearly, not only over the whole pavement system but also within individual layers. Before mobile load simulator testing, FWD data indicated the weakest area exists at the left wheel path (LWP) of 7.5-m line (7.5L). Later, this weak area was confirmed to have the highest rutting and the most intensive cracking. The dynamic cone penetration results showed that the base at this location was at its weakest. Also, at 7.5L, the dry density was lowest, approximately 7% lower with a moisture content approximately 8% higher than the adjacent area. The LWP had higher FWD deflections than the right wheel path (RWP), and consequently the LWP manifested more rutting. This proved to be primarily due to differences in moisture content. This was probably because more water infiltrated in this area during rain due to manifestation of more extensive cracking during early phases of trafficking. The maximum surface deflection values increased as trafficking increased in the left and right wheel paths due to pavement deterioration, while deflection for the center remained constant because of the lack of traffic loading. The LWP had more rutting than the RWP and this correlated with the measured FWD deflections prior to trafficking. The W1 values increased as trafficking increased for the LWP and RWP due to pavement deterioration. The majority (greater than 60%) of rutting was from the 300-mm uncrushed river gravel base.

Several strategies have been used for the repair of jointed concrete pavements. The primary goal of such repairs is to minimize and delay the reflective cracks through a subsequent overlay. Fiber reinforced patching binder, with or without geo-textile mats, has been used on the joints with varied success. This paper outlines four joint repair strategies, along with technical data on the patch materials and techniques. Performance was measured over the course of 7 years (many seasons and much traffic) following the final overlay of each section. The performance of each pavement is reported in terms of reflected cracks and International Roughness Index (IRI). Ride quality (RQ) is moderate to good, and there is little evidence of reflected cracks coming through. It was believed that fiber reinforced polymer patching binder is a viable option for minimizing and delaying reflective cracks. Performance history indicates that milling off prior asphalt concrete overlays is not necessary and does not improve the long-term performance.

A forensic investigation was conducted to determine the underlying cause of a premature pavement failure. The premature pavement failure was occurred in the form of rutting and alligator cracking. Through extensive field and lab testing, it was found that the moisture susceptible base is the primary cause of the premature failure and the porous asphalt concrete (AC) being the secondary cause. It is noted that the base layer was built according to plan and met the current material and field density requirements. As part of the field investigation, ground penetration radar (GPR) was utilized to survey the entire area. AC cores were taken to correlate the dielectric measurements from GPR with the lab measured density to generate the density/air-void map. More than 50 cores were taken to accurately determine the air void content. The results indicate that the air void exceeds 10% and did not meet the specification requirements. Based on the lab results, there are 36% of the cores fall into the category of either penalty or remove and replace. It was concluded that material requirements which are only based on the field density and moisture content are inadequate to control the construction quality, as it was not able to protect against premature failures illustrated in this paper from occurring. Even though it is tedious to conduct the moisture susceptibility tests to determine strengths at different moisture levels, it is a viable tool to minimize the premature pavement failures.

The Rolling Dynamic Deflectometer (RDD) is a nondestructive testing device that is used to evaluate the structural conditions of pavement systems. Unlike discrete deflection measurements such as the Falling Weight Deflectometer and Dynaflect, the RDD provides continuous deflection profiles that enable 100% coverage along the testing lane. The continuous deflection profiles have been used to delineate poorly performing areas to be repaired, develop input for pavement forensic studies, select rehabilitation treatments, and monitor pavement deterioration rates. In this paper, the patterns in RDD deflection data which represent four different structural conditions (with respect to joint load transfer and slab support) in jointed concrete pavements (JCP) are presented and discussed. Then, results from RDD tests used in three project-level studies are presented. The first project involved a continuously reinforced concrete pavement (CRCP) with an asphalt overlay. RDD measurements were used to measure the relative improvement due to the overlay rehabilitation and also monitor the pavement deterioration rate with time. The second project involved a JCP with longitudinal cracking. RDD deflection profiles were used to delineate poorly performing areas due to poor slab-support conditions and identify potential locations of reflective cracking. The third project involved a JCP with faulting. RDD deflection profiles were used to identify locations that needed either dowel-bar retrofit or full-depth repair.

Longitudinal cracking and longitudinal joint separations are commonly observed distresses in concrete pavements. The Texas Department of Transportation instituted a research project to determine the causes and to recommend repair methods. Repair methods that are generally recommended to repair cracks and joints are (1) cross stitching; (2) slot stitching; and (3) stapling. Finite element modeling was performed to determine the stress distribution in the concrete for each method when a truck tire load was placed on one side of the joint. Assuming no interlock between joint faces, the slot stitching model produced the lowest stress and cross stitching produced the highest stress, when the load was placed on the upper end of the diagonal bar. Cross stitching is recommended for repairing narrow cracks and slot stitching is recommended for wider cracks and joints.

Maintenance and rehabilitation (MR (2) in terms of resisting reflective cracking 1 unit thick of 35 % RAP is equivalent to 0.26 unit thick virgin mixture; (3) with the 40 % reflective cracking rate criterion, the life for virgin AC with a 125 mm overlay is 65 % longer than that for a 50 mm overlay; (4) in terms of pavement performance, no significant difference exists between 50 mm milling and non-milling if the milling does not remove existing cracks completely; (5) the maximum rut depth of 12.7 mm among the test sections indicates that the mixture is rut-resistant, and the existing pavement with lime-treated base and subbase beneath the overlay provides sound foundation; and (6) the overlay tester can be a viable and simple measure to evaluate the asphalt mixtures’ reflective cracking resistance.

This paper presents the results of seven field investigations (US59, IH20, SH342, US75, US90, MLK Blvd., and US96) to identify the underlying causes of settling and irregular cracking in Portland cement concrete (PCC) pavement. Settling and cracking are not intended, and they are detrimental to the long-term performance of PCC pavement. The falling weight deflectometer and dynamic cone penetrometer were utilized to characterize the load transfer efficiency (LTE) and base support conditions. It was found that when there is adequate base support (e.g., a modulus>345 MPa), the irregular cracks remain tight even after decades of truck trafficking, as evident in the IH20 and MLK projects. Irregular cracks on these projects were caused by late or too-shallow saw cutting. In areas that had 50 % lower base moduli, the cracks typically grew to about 57 mm. The subsidence and settling on US59 and US75 were observed in the areas with LTE in the range of 40 %. Tie bars were found to be ruptured in those areas. When LTE exceeds 80 %, the tie bar was intact and no settling was observed. The maximum deflections were approximately eight to ten times higher in the area with settling than the area without settling. It is because the low load transfer efficacy would lead to higher deflection under truck trafficking. The high deflection would initiate pumping and then settling. Despite severe spalling observed before the overlay on US96, the stone-mastic asphalt overlay is now 5 years old, and no visible cracks can be observed. This is because of the high LTE (exceeding 85 %) and sufficient base support (modulus exceeding 1378 MPa). The results from the seven projects investigated indicate that base support and LTE play a critical role in concrete pavement performance. To minimize the cracking and settling, it is preferable to have a base modulus and LTE exceeding 345 MPa and 80 %, respectively.

A forensic study was performed using a rolling dynamic deflectometer (RDD) and overlay tester (OT) to investigate the reflective cracks on SH87. Comparative tests were performed on the BU90 that has no cracks. The test results show that BU90 has lower density and lower asphalt content than SH87. This means the hot-mix asphalt (HMA) on BU90 has less resistance to reflective cracking than SH87. The OT confirmed that the cycles to failure are less for BU90 than for SH87. Thus, in terms of individual layer properties, the wearing surface and crack-retarding layer on SH87 has a greater crack resistance than that on BU90 and the asphalt mixes were not the principal reason for the cracking. The three main contributing factors for the reflective cracking on SH87 are: (1) thinner HMA, (2) higher joint movements, and (3) poor bonding between layers. Based on the reliability concept, at 90 % confidence level, the threshold W1–W3 deflection values were found to be 4.4 mils and it is much less than 6.5 mils developed from the IH20 project that has 100 mm of HMA as opposed to 64 mm for the SH87 project. It reaffirms that thicker HMA takes longer to have reflective cracking and it also needs a higher threshold W1–W3 deflection value. Thus, the thicker HMA overlay on BU90 (183 mm) would delay the reflective cracks. The methodology presented demonstrates RDD and OT’s abilities to characterize the reflective cracking potential and the proposed threshold value provides a good foundation for further refinement when additional data are available.