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In Texas, many miles of plain jointed concrete pavement (JCP) were constructed without proper load transfer devices such as dowels. After a number of years of service, some JCP sections without dowels showed distresses in the form of faulting at transverse joints. Some of the sections were designed in accordance with the AASHTO 1986 Guide, which required 50–75 mm thicker slabs in exchange for not using dowels. This pavement design did not work, with faulting at transverse joints that cause poor ride. Dowel bar retrofit (DBR) was performed on four projects to restore the pavement condition. Overall, DBR restored load transfer efficiency and resulted in improvement of ride quality. Even where the subbase stiffness is 5–10 times less than the minimum value required for proper performance of JCPs, properly installed DBR effectively restored pavement condition with minimum faulting after decades of service. Therefore, it indicated that DBR is able to minimize the faulting even where there is poor base/subgrade...

After only 2 months in service, the frontage road of US 290 developed a series of depressions that caused a very poor ride. The main cause of the premature failure was attributed to disintegration of the cement treated base (CTB) layer. This was attributed to two primary factors: (1) a very coarse gradation of the aggregate used in the CTB layer which produced a mix that was prone to segregation during placement; and (2) the CTB layer was placed in two lifts, which were not well bonded together. Another contributing factor was the lack of bond between the CTB and the hot mix asphalt (HMA) surface layer. Secondary factors include high air voids in the HMA layer and low HMA layer thickness. The material, when prepared carefully in the lab at the design cement content, passed the strength requirement of 2.07 MPa. But this coarse mix appears to have been difficult to place correctly in the field. The coarsely graded aggregate used on this project appears to be prone to segregation, either during placement or compaction. The ground penetration radar results (with confirmation by core samples) indicated that most of the problems were at the bottom of the upper CTB lift. The CTB was placed in two lifts and very poor condition was found between the two CTB layers. This problem was coupled with a thin, porous, and poorly bonded HMA layer that permitted moisture to enter the CTB layer. Similar failures have also been reported recently on other CTB projects in Houston.

This paper presents three field projects to illustrate the integrated approach to forensic investigations of roadway pavement failures used widely in Texas. In each case, the combined ground-penetrating radar (GPR) and falling weight deflectometer (FWD) data were extremely useful for identifying contributing factors, such as stripping in the hot mix or localized areas of wet or weak base. Dynamic cone penetration (DCP) is used for validating problems with base and subbase layers. Laboratory tests are often required to complete the investigation, especially if the repair strategy calls for in-place recycling of the existing structure. The extent of stripping and high porosity that caused delamination for Projects 1 and 2 was detected by GPR and verified by core samples. GPR, FWD, DCP, and field soil samples all showed indications that the existing base on Project 1 was wet and the stiffness was only about one-third that of a typical flexible base in Texas. FWD data demonstrate that the pavement structures for Projects 1 and 2 were inadequate, so a rehabilitation strategy was selected that included structural strengthening. In Project 3, GPR, lab density, and permeability tests indicate that the dramatic pavement failures were attributable to moisture entering the base through a poorly compacted asphalt concrete layer and poor longitudinal joints. The base material was found to be highly susceptible to moisture and did not meet the Texas Department of Transportation's compressive strength requirements when subjected to capillary soaking. The repetitive triaxial test results revealed that the stiffness and load-carrying capability became inadequate when the base materials were exposed to moisture. The pavement structure had been totally replaced in 2004.

Results from closely controlled full-scale Accelerated Pavement Testing (APT) were employed to establish a rutting prediction model using the “Find Laws” data mining technique. Seven test pavements (264 records) from the Cold Regions Research and Engineering Laboratory's (CRREL's) Heavy Vehicle Simulator (HVS) and one test pavement including 8 records from the Texas Department of Transportation's (TxDOT's) Mobile Load Simulator (MLS) were included in the model development. For model verification purposes, additional test pavements and 35 records from CRREL's HVS were utilized. Find Laws was applied successfully to develop a rutting prediction equation that uses wheel load, load repetitions and the pavement Structural Number (SN) as inputs. CRREL's HVS test pavements had wheel loads of 20kN to 103.5kN, while TxDOT's MLS test pavement had only one wheel load of 37.8kN. The overall R 2 for the 272 records is 0.6745. To compute the Load Damage Exponents (LDE), rutting for SN from 2 to 7 under wheel l...

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.

Diamond Grinding (DG) has been utilized by various districts to improve skid resistance (reduce accidents and fatalities) and improve ride quality (reduce International Roughness Index [IRI]), with the added benefit of reducing tire/pavement interface noise. The Department has used DG on both Jointed Concrete Pavement (JCP) and Continuously Reinforced Concrete Pavement (CRCP). This study performed crash accident analysis both before and after DG on a recent project section. After the completion of DG, the occurrences had reduced by approximately 62% and 46% for fatalities and incapacitating injuries, respectively. There was an average IRI reduction of approximately 44 in./mi. (0.70 m/km), or 40%, immediately after treatment. This study also analyzed eleven projects to derive a statewide trend on various surface characteristics of pavements due to DG, with the oldest section studied approximately 8 years after treatment. Immediately after DG, the average Skid Number (SN) increased 5.6, or by about 30%. Depending on the existing pavement conditions, the range of the increase in SN varies from 1–18. Similarly, there was an average IRI reduction of approximately 60 in./mi. (0.95 m/km) immediately after the DG, or about 40%. Depending on the existing pavement conditions, the range of IRI reduction varies from 20–122 in./mi. (0.32–1.94 m/km), or 17–57%. For deterioration rate under the effect of factors such as time and traffic, each year the SN decreases by approximately 2.0 and IRI increases by approximately 1.7 in./mi. (0.03 m/km).

The main objective of the forensic study was to identify the cause(s) of the pavement failure on a temporary detour of an interstate highway in Austin, Texas. Ground penetrating radar (GPR), falling weight deflectometer (FWD), coring, trenching, and comprehensive laboratory tests were performed. It was found that the main cause of the premature failure was attributed to material and construction practices. The base material used on this project did not meet the Triaxial class 1 requirement; it tested as a class 2.3 material. The base material was found to be highly moisture susceptible; it did not meet the Texas Department of Transportation's (TxDOT's) compressive strength requirements when subjected to capillary soaking. In addition, the repetitive triaxial test results revealed that the stiffness and load-carrying capability and resistance to permanent deformation became inadequate when the base material was exposed to moisture. It is believed that moisture entered this pavement primarily through poorly compacted AC layers and longitudinal joints. Cores taken in March 2004 from the original type B and C layers confirmed that the majority of cores have air voids exceeding 9%. The lower type B layer was also badly segregated and debonded from the upper type C layer at some locations. GPR results also indicated that the joints in the pavement were excessively porous. Further tests on the recovered binder for the type B layer indicated that the binder was prematurely aged, most probably from overheating during production.Key words: pavement failure, forensic, ground penetrating radar (GPR), falling weight deflectometer (FWD), laboratory testing.

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.

This paper focuses on the cause, possible solutions, and future prevention of pavement heave at a new construction project. We speculated that heaving on the east side of the project was caused by a reaction between the lime stabilizer and minerals in the soil. Because of a difference in soil chemistry, the west side of the project (which was still under construction) did not show evidence of heaving. A forensic investigation was initiated to test our hypothesis. The findings of the investigation concluded that the cause of the heaving on the east side of the road was related to the formation of the expansive mineral, ettringite. Ettringite formed due to the reaction of the lime stabilizer with seams of high sulfate soil on the east side. Laboratory testing did not find any effective stabilizer for the high-sulfate soils on the east side. Therefore, reconstruction would involve removing and replacing the treated layer with a select material that has less than 2,000 ppm sulfates. Test results indicate that there was no threat of sulfate heave on the west side. District personnel had performed the field conductivity tests to evaluate and monitor the concentration of the sulfate content on the remaining project. The treatment of 3%/72-h mellowing period/3% lime treatment was employed on the west side. The whole project has been completed for 1 year and no heave has been observed.

Regulating and permitting superheavy loads is a part of the Department of Transportation's operation. Since the size and weight of the superheavy loads greatly exceeds that of ordinary trucks, pavement engineers face a challenge if they do not have an appropriate analysis procedure. This paper covers the general superheavy load programme in Texas as well as some analysis and field monitoring done between November 2001 and November 2002. The results presented here are those related to gross vehicle weight (GVWs) greater than 227,000 kg where pavement analysis is required. There have been 63 superheavy load moves evaluated during the year monitored. There were three superheavy load moves of over 454,000 kg on load-zoned roads (with a GVW restriction of 26,520 kg). No structure-related damages or rapid shear failure have been observed during the monitoring period. Only three cases of minor pavement damage were reported by the districts as a result of superheavy moves. Two cases were related to a fresh seal c...

Although the cost-effectiveness of preventive maintenance (PM) treatments for pavement is important, literature addressing this issue is limited. Even under the well-controlled FHWA long-term pavement performance (LTPP) study, incomplete data and sections exist. Criteria for selecting PM treatments often conflict and have to be compromised. The multiple criteria decision-making (MCDM) method is one of numerous approaches available for resolving variations of results. The technique for order preference by similarity to ideal solution (TOPSIS), an MCDM method, was used to analyze successfully all 14 specific pavement study (SPS)-3 sites in Texas. The distress score (DS), international roughness index (IRI), and treatment costs were used as criteria to determine the cost-effectiveness of various PM treatments (thin overlay, slurry seal, crack seal, and chip seal). With TOPSIS, the cost-effectiveness of these treatments can be quantified, with variations caused by subjective judgment thus minimized. When all criteria were considered, the most and least cost-effective methods were chip seal and slurry seal, respectively. When cost was not considered, the most and least effective methods were chip seal and crack seal, respectively. The chip seals performed the best. Chip seals had the most forgiving qualities of all the methods, and they yielded no reflection of the cracking that preceded the treatment applications. The evaluation based on TOPSIS provides a viable option for engineers determining the best PM treatments for pavement in need of maintenance.

The success of a rehabilitation project that involves replacement of the asphalt concrete (AC) overlay on a concrete pavement often depends on the assessment of the existing conditions and the repair of critically weak locations. In a case study, a rolling dynamic deflectometer (RDD) was used to collect continuous deflection profiles at different stages in such a project. The project, conducted by the Texas Department of Transportation, was located in the Atlanta District. The condition of the pavement was monitored with an RDD in each stage. The stages ranged from before milling of the original AC overlay to 22 months after the placement of a new overlay. The deflection profiles measured after milling were used to identify locations with a high potential for reflection cracking. After the new overlay was placed, profiling was repeated at three different times to ( a) monitor changes at locations of previously high deflections, ( b) evaluate the effectiveness of full-depth repairs, and ( c) group different AC test sections of the new overlay according to the condition of the underlying concrete pavement. It was found that the continuous deflection profiles obtained at the start of a rehabilitation project can be used to identify high-deflection locations that, if not repaired, will likely deteriorate rapidly after the new overlay is placed. The continuous deflection profile measured on the concrete pavement after milling was particularly helpful in identifying high-deflection locations that were irregularly spaced. Continuous deflection profiles, measured at various times after placement of the new overlay, effectively tracked the zones of deterioration.

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.

Extensive laboratory tests were conducted and the results were compared to the known field performance results of Specific Pavement Studies-1 (SPS-1) sections on US281. The objective was to establish which of the available laboratory test procedures could match the observed field performance. The laboratory tests included the diametral resilient modulus, Asphalt Pavement Analyzer (APA), Hamburg Wheel Tracking Test (HWTT), Repeated Simple Shear Test at Constant Height (RSST-CH), dynamic modulus test, and repeated load permanent deformation test. It was found that both RSST-CH and repeated load permanent deformation test could differentiate the performance of different sections, and the results matched closely with the field performance. The total permanent strain was also found to be a reasonable indicator of field rutting performance. For the wheel tracking tests, the APA performed better than HWTT, but both failed to differentiate some mixes. The moduli at high temperature, including dynamic modulus, axi...

Fourteen Texas SPS-3 test sites were studied to determine the effectiveness of preventative maintenance treatments. These sections were built on four highway classifications (IH, US, SH, and FM) in different climates and with different levels of traffic and subgrade support. Almost all 14 SPS-3 sites were given preventative maintenance treatments (thin overlay, slurry seal, crack seal, and chip seal) in Fall 1990. The distress score concept used by the Texas Department of Transportation (TxDOT) was adopted in this study to judge the effectiveness of preventative maintenance treatments. TxDOT has used this concept since the early 1980s, though the utility factors have been revised few times. The distress score quantifies the visible surface wear due to traffic and environmental influences. Only very few sections experienced premature failures on the SPS-3 sites in Texas. In many cases, superior underlying pavement conditions have been found. The chip seal has the most sites in which it is rated the best pe...

The Specific Pavement Study1 pavement test section on US281 in south Texas comprise the largest Strategic Highway Research Program experimental site in the United States. The project was opened to ...

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.

The main goal of a pavement maintenance program is to provide timely maintenance and promote cost-effectiveness in the pavement life cycle. The success of a maintenance program relies on accurate information on the relative performance of treatment methods. LTPP's SPS-3 test sections were built in 1990 to address the cost-effectiveness of various maintenance treatments such as a thin overlay, slurry seal, crack seal, and chip seal. Two SPS-3 sites on US175 and US62 were selected to evaluate the cost-effectiveness of these four treatments. TxDOT's distress collection and rating systems were applied to judge the effectiveness of these four treatments. Both the TxDOT system and the historical distress data were used in this study. Distress data collection criteria are slightly different between TxDOT and LTPP, which result in different distress scores. Based on TxDOT distress survey results from Summer 2000, it was found that the ride and distress scores yield a similar trend, in that the best performer is a...

This study involves the application of an Falling weight deflectometer (FWD) (JILS-20) on numerous test sections in Taiwan. The goal is to develop a temperature correction equation and to establish a structural evaluation system, Structural strength index (SSI), for rapid and reliable assessment of pavement structural conditions. The SSI evaluation system will assist transportation authorities in prioritizing routine preventive maintenance and rehabilitation needs. Temperature correction factors were established based on the 1176 FWD tests on two specific built test sections. Thus, the effects of traffic load on pavement sections can be eliminated. Comparisons of temperature correction factors with other studies were performed. Though, it is interesting to find that in those studies temperature correction factors for deflection were developed under different climatic conditions and pavement structures, the temperature correction factors differ, in average, by only 13%. Three significant indicators for upp...

This paper presents the results of comprehensive laboratory characterization of the premature rutted specific pavement studies-1 (SPS-1) sections on US281 in south Texas. It was soon found that it was the undocumented change in aggregate type from the limestone to gravel screenings and too much asphalt binder that caused the deeply premature rutting. As a follow-up study, the extensive laboratory tests on those cores were further conducted to establish which of the available laboratory test procedures could match the observed field performance. It was determined that both uniaxial Repeated Simple Shear Test at Constant Height and repeated load test could correctly rank the rutting performance of asphalt mixes. For the wheel tracking tests, the Asphalt Pavement Analyzer performed better than Hamburg Wheel Tracking Test, but both failed to differentiate between the bad and good mixes in this case. The moduli at high temperature, including axial dynamic modulus, axial resilient modulus, and shear re...

A tack coat provides necessary bonding between pavement layers to ensure that they behave as a single system to withstand traffic and environmental stresses. Poor bonding at the interface leads to slippage failures. Even if the tack is applied correctly to the surface, the material is often picked up and contaminated by construction traffic. This study conducted a literature search to examine the major trends shaping the future and the trends' interrelationships with pavement engineering. It is believed that this will promote a framework for a research program that will address long-range strategic issues facing the pavement engineering community. Thus, transportation agencies will be better prepared to respond to new and emerging challenges. Many different transportation authorities reported the successes of utilizing trackless tacks. One of the emerging technologies on trackless tacks is utilizing nanotechnology to provide modification to the traditional tack through adding additive called nanomaterial. Although limited results are available, it appears that nanotechnology has high potential to be used in trackless tacks.

This study performed crash accident analysis both before and after diamond grinding (DG) on a recent project section. After the completion of DG, the average crash occurrence was reduced by 15%, and there was an average international roughness index (IRI) reduction of approximately 40% immediately after treatment. Eleven projects were evaluated to derive a statewide trend on various surface characteristics of pavements due to DG, with the oldest section studied approximately 8 years after treatment. Immediately after DG, the average skid number increased by about 30%. Similarly, there was an average IRI reduction of approximately 40% immediately after the DG. Depending on the existing pavement conditions, the range of IRI reduction varies from 17 to 57%.

Nanotechnology is the term used to cover the design, construction, and utilization of structures with at least one dimension measured in nanometers. Initially developed in the fields of physics and chemistry, nanotechnology has established itself as an inter-disciplinary science. However, for the technology to have practical effect in the advancement of humanity, it needs to be applied in areas such as the engineering fields. This paper focuses specifically on current and potential developments in the field of pavement engineering where the unique properties of nanomaterials may be used for the betterment of this field, based on identified needs and challenges in pavement engineering. It is demonstrated that there are several areas where nanotechnology can complement pavement engineering, first, through the development of improved materials to be used in pavement constructions and second, through the use of characterization methods to improve the understanding of the materials. Examples of current and planned research in these areas are cited and discussed. Finally, current challenges in exploiting the unique properties of nanomaterials in pavement engineering are indicated and discussed.

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.

Selected papers from the proceedings of the Geo-Hubei 2014 International Conference on Sustainable Civil Infrastructure, held in Yichang, Hubei, China, July 20-22, 2014. Sponsored by the China Three Gorges University, the Committee on Sustainability of ASCE, and the Geo-Institute of ASCE.

The main objective of the most recent Mobile Load Simulator (MLS) test program was to conduct a comparative study of two rehabilitation processes, Rehabs A and B, constructed on the south- and northbound lanes of US281 near Jacksboro, Tex., in 1995 and 1996, respectively. The underlying pavements have composite asphalt layers with the first construction done in 1957. Performance was evaluated in terms of surface rutting, loss of stiffness in pavement layers, and permanent deformation in the layers. Tools used during the study included an on-site weather station, nondestructive testing equipment (FWD, SPA, PSPA, SASW), and in situ instrumentation (MDD). The findings of this study provided conclusive results on the relative performance of the two rehab strategies. Rehab A performed well with its sound underlying structure. The Dallas District has elected to use this recycling process based, in part, on the results of the MLS tests in Jacksboro. The study serves as an example of how the MLS program has yield...

The dynamic cone penetrometer (DCP) is one of the lowest-cost alternatives for characterization of pavement layer qualities. In addition, it is fairly easy to collect and analyze data with the DCP. The DCP is not popular in the pavement engineering community, partly because of the lack of a solid correlation between DCP results and modulus values. More than 60 DCP tests have been conducted on two test pavements used for accelerated pavement testing to assess the validities of empirical equations proposed in previous literature to compute layer moduli from data obtained with the DCP. The effect of the test procedure on the DCP test values was studied, and the moduli obtained with the DCP were compared with those obtained by falling weight deflectometer (FWD)-multidepth deflectometer (MDD) and laboratory tests. It was found that the values obtained with the DCP are dependent on the test procedure, which affects the results by at least 10 percent. If there is an asphalt concrete layer, it is preferable to conduct DCP tests through a drilled hole. A sample size of 6 is recommended for routine characterization of base and subgrade layers, because this number would achieve 95 percent confidence and an error of estimate of less than 20 percent. The moduli obtained by using the DCP and the adopted equations yielded results compatible with those obtained from FWD-MDD tests. Those equations have been recommended to the Texas Department of Transportation for further evaluation and use in routine analysis. The laboratory-determined subgrade moduli were only slightly higher than those from DCP and FWD-MDD tests. No correction factor is required for the moduli backcalculated from FWD data to match the moduli obtained in the laboratory.

Results obtained with the rut bar were compared with those obtained with other devices, and it was determined why the rut-bar measurements are different from field observations. Also, because it would be beneficial if the cause of the rutting could be identified from the shapes of the profiles collected by next-generation rut-bar vehicles, it was determined whether this is possible. Trenching data were collected for 10 different pavements located in Texas. Rut depths were measured with several devices before a trench was cut across the traffic lane. Careful measurement of each pavement layer was done to determine the amount of rutting in each layer. Although there may be 50 mm of rutting as measured with a straightedge, the rut bar sometimes measured no rutting. The rut bar yielded zero rut depth in 10 percent of cases in which ruts were deeper than 16 mm. This is mainly due to limitations of the current rut-bar setup, specifically, the sensor spacing and rut-bar length. A profile alone is still not adequate to determine the layer in which rutting occurred. Material-related problems such as bleeding yielded wide-basin rutting that appears to be base or sub-grade rutting, as observed from the profile alone. The profile has been found to be inadequate for determination of the major source of rutting except when there is a clear dual-wheel rut. This is a good indication that rutting is isolated to the asphalt concrete surface layer. The sensor spacing recommended for routine data collection is 100 mm. Analysis of the data shows that this spacing is 95 percent accurate and capable of capturing dual-tire ruts.

The mechanistic system rutting model VESYS3AM was used to predict the rutting performance of three full-scale accelerated pavement test pads. Since the VESYS3AM system rutting model is not formulated to calculate layer rutting, a method was devised to extract the information by manipulating the layer input rutting parameters. Two MDDs were installed into each MLS test pad to determine layer deformation under a uniformly applied set of loads. For simplicity, all comparisons were made for a two-layer system; that is, an AC layer and a subsystem. The layer deformations from the MDDs were used to calibrate the VESYS3AM model parameters α and µ. The study represents a laboratory and Field determination of material properties, which could be used to model rutting if they were reproduced in other pavements. The predictions from the VESYS3AM system model matched field rutting performance data. Also, the layer rutting contributions were computed, and these compared favorably to MDD measurements.

The Texas Department of Transportation (TxDOT), in partnership with the Center for Transportation Research, has implemented the Texas mobile load simulator (TxMLS) as a tool for accelerated testing of in-service pavements. Although the TxMLS has been used successfully to test in-service pavements in the Yoakum and Fort Worth districts, the fact that only one TxMLS machine exists limits the number of accelerated pavement tests (APT) that can be performed. Therefore, TxDOT is evaluating a modification of the rolling dynamic deflectometer (RDD) for use as a super-accelerated pavement tester. In this application, the truck-mounted dynamic loading system is operated in a stationary mode, with the loading rollers and rolling sensors of the RDD removed from operation. The servohydraulic actuator is used for application of harmonic loading to a wheel footprint on the pavement surface. Hundreds of thousands of load repetitions are applied in a matter of hours; hence the designation as super-accelerated testing. This stationary dynamic deflectometer (SDD) is being studied as a possible tool for use in expanding TxDOT’s APT program. The SDD may allow TxDOT to increase, in a cost-effective manner, the number of accelerated tests that can be performed. Preliminary tests have been performed with the TxMLS and SDD on two different pavement recycling strategies constructed on the northbound and southbound lanes of US-281 in the Fort Worth District. That the same conclusion was reached about the relative performance of the test sections with both machines indicates the potential usefulness of the SDD.

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.

The accuracy of falling weight deflectometer (FWD) back-calculated moduli depends heavily on knowledge of bedrock depth. The bedrock depth can be obtained from coring, boring, and seismic refraction tests, but these operations are not practical. Determining the bedrock depth from FWD data is the easiest and least expensive way. This paper documents the effects of bedrock depth on FWD responses and makes comparisons between predicted bedrock depth and field measurements. Modified algorithms that better fit the field measurements are proposed. It was found that bedrock depth has a great influence on outer FWD sensor (r3 to r6) readings. Deeper bedrock resulted in a higher percentage of increase in r3 to r6 readings in response to increased load. When the r4 reading is less than 25.4 μm for any drop height, it is very likely that the bedrock is within 1.52 m of the surface. The time-deflection history patterns were drastically different between shallow and deep bedrock. When there is no free oscillation after the first deflection peak in a time-deflection history, shallow bedrock (within 1.52 m) is indicated. A modified equation (Equation 2) using the peak deflections provides an accuracy within 30 percent. It is recommended that these equations be used on a pavement where there is no severe surface distress. Another modified equation (Equation 6) using time-deflection history data yields an accuracy within 20 percent but cannot be used when there is no clear indication of free oscillation.

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.

A test pad was closely monitored for a 6-month period, with 640,000 axle load repetitions applied to the test pavement. The load was applied by the Texas Mobile Load Simulator, a full-scale accelerated loading device. Pavement performance data, such as rutting and cracking, were collected at intervals of 0; 2,500; 5,000; 10,000; 20,000; 40,000; 80,000; 160,000; 320,000; and 640,000 axle repetitions. Falling weight deflectometer (FWD) tests were performed at these same data collection intervals to characterize the structural capacity of the pavement system. Although there is a trend indicating that locations with higher FWD deflection result in higher rutting, a unique relation to predict rutting accurately from the surface deflection alone was not found in the study. The back-calculated asphalt concrete pavement moduli were reduced by 50 percent of the original value at the end of 320,000 repetitions. However, the test was not terminated until 640,000 repetitions, when moduli were reduced to 40 percent of the original values. Both FWD deflection and percent of cracked area share the same trend; the left wheelpath had higher initial FWD deflections and later yielded a higher percentage of cracked area. Approximately 50 percent of the wheelpath area was cracked at the end of 80,000 repetitions, as measured by counting the number of cracked squares on a 100 mm by 100 mm grid. However, most of the cracks were hairline cracks. The percentage of cracked area is strongly related to the grid size used. A grid size of 100 mm by 100 mm has been recommended by other researchers and was adopted in this study. Eighty-five percent and 90 percent of the area in the wheelpaths was cracked at the end of 320,000 and 640,000 repetitions, respectively. These numbers are higher than those adopted by the Asphalt Institute, which defines failure as 45 percent cracking in the wheelpath.

The seismic pavement analyzer (SPA) combines several wave propagation techniques in a single unit and can rapidly perform nondestructive tests to determine the condition of pavement. The modulus of each layer of pavements is a major parameter estimated with the SPA. The SPA and its portable version, the PSPA, have been used with the field operation of the Texas mobile load simulator (TxMLS) to detect the variation in properties of different layers with the number of axle loads applied to the pavement. The theoretical background related to the methods used with the SPA and PSPA is discussed. Results from tests of the SPA and PSPA at a TxMLS testing site are presented. The variation in moduli as a function of the deterioration of pavement is detected. The results have been compared with those obtained from direct seismic measurements made on the top of each layer to evaluate the accuracy of the devices. In general, a good agreement was achieved.

The pavement behavior under 630,000 axle repetitions from the Texas Mobile Load Simulator (TxMLS) was studied. During the course of TxMLS testing, nondestructive testing and in situ instrumentation (pressure cell, strain gauge, and multidepth deflectometers) were applied to monitor and assess the pavement condition. In addition, pavement distress data, such as measurements of permanent deformation, rutting, and cracking, were collected and analyzed. At the end of 630,000 axle repetitions, the maximum permanent deformation was approximately 22 mm. A forensic study was then performed by cutting a 1.8-m by 3-m trench in the middle of the test pad and three nuclear density gauge (NDG) tests were performed on top of each layer to determine the densities and moisture contents. It was found that the lime-treated gravel base (LTB) layer contributed the most to rutting. The axle-load applications increased the density of the LTB layer in the pit area, which caused the pavement structure to settle and consolidate. The highest rate of rutting was observed at the early stages of loading, between 10,000 and 20,000 axle repetitions. The higher deflections on the left wheelpath as observed from falling weight deflectometer data were probably due to the higher moisture content and the instrumented pit. NDG data showed that the LTB, lime-stabilized subgrade (LTS), and subgrade in the left wheelpath all had higher moisture contents than those in the right wheelpath.

Permitting superheavy loads may increase the rate of pavement damage and the cost of maintenance. An analysis of a proposed superheavy load route (FM519) to evaluate the potential pavement damage caused by a planned superheavy load move is presented. Falling weight deflection (FWD) tests and backcalculations of layer moduli were performed on the FM519. FWD tests and backcalculation of layer moduli were performed on the pavement before and after the superheavy load was moved. ELSYM5 and BISAR were used to evaluate the pavement responses using the backcalculated layer moduli from FWD data. The predictions of surface deflections from ELSYM5 and BISAR were close to (within 10 percent of) the measured deflections from FWD tests. The FWD data and analyses show that the existing pavement structure is adequate for the planned superheavy load move. Finally, the permit was issued with the condition that the transport vehicle should be kept within the travel lanes and away from the shoulder whenever possible. FWD tests were conducted after the superheavy load move and comparisons with before superheavy load move were made. T-tests were performed to check for significant difference at the 95 percent confidence level. T-tests showed that there is no significant difference between before and after superheavy load move. Also, no significant distresses due to this superheavy load were observed after the move, and the pavement condition is consistent with the analysis performed to issue the permit.

A series of exploratory tests was performed on six of the most commonly encountered aggregates that are used as subbases/bases of roadways in Oklahoma. The purpose was to assess the effect of gradation, compaction method, specimen size, and testing procedures on the resilient modulus values. Values reported by various agencies were compared to values obtained in the study. Statistical correlations were established between resilient modulus and the California bearing ratio as well as between resilient modulus and cohesion and friction angle. Investigators observed that the influence of gradation and compaction method on resilient modulus values were less significant than the effects of the stress state. A satisfactory correlation existed between resilient modulus values and the cohesion and friction angle. American Association of State Highway and Transportation Officials testing methods were used.

Longitudinal joint separations are often observed in concrete pavements. An innovative repair procedure was developed in this study for slot stitching in faulted or separated longitudinal joints. It involves with three stages: (1) low pressure grout to restore support under slabs that exhibited signs of pumping and faulting (2) the slot stitching method of retrofitting tie bars, to restore lateral restraint and load transfer across longitudinal joints, and (3) latex modified concrete overlay to restore proper elevation to slabs that had faulted. This paper discusses the results and lesson learned from the first implementation project on US Highway 75 near Sherman, Texas.

The nondestructive mapping of anomalies and voids under roadway pavements is critical to highway authorities because of the potential safety hazards caused by the loss of support. A 400 MHz Ground Coupled Penetrating Radar (GCPR) was utilized in this study to characterize subsurface voids. To enhance the understanding of the data collection and interpretation, different thicknesses of calibration concrete slabs with different depths of voids were designed and constructed. In addition, a field study using the GCPR was also conducted on US-290 with visible settlement. The extents of the anomalies in the horizontal and vertical directions were accurately identified from the GCPR images. Coring was performed to verify the extent of the subsurface void conditions. Fortunately, the voids near the drainpipes were detected by GCPR in time. Otherwise, the void would have been progressed in size, and that could have led to a severe hazard to the general public. This study has successfully demonstrated that the GCPR is able to identify anomalies and voids. Engineers can utilize the information from GCPR to undertake remedial actions with confidence.

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.