Field and Lab Investigations of Prematurely Cracking Pavements

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..     

Forensic Study of Warranty Project on US82

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.     

Results from a Forensic Investigation of a Failed Cement Treated Base

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.     

Investigation of a Pavement Premature Failure on a Weak and Moisture Susceptible Base

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.     

Characterization of Emulsion Wax Curing Agent as Bond-Breaker Medium in Jointed Concrete Pavement

Bond-breaker media have been used with success to reduce and minimize undesirable cracks reflecting from cement-treated or lean-concrete subbases (LCSs). The common bond-breaking media include (1) emulsion slurry seal; (2) 30 to 60-mm-thin asphalt concrete; (3) one or two applications of wax-based curing compounds; (4) one or two layers of polyethylene sheets; and (5) geotextile. The cost differences among different bond-breaking media are significant for a highway project over 200 km long. Different types of tests (British pendulum friction, push off, pullout, and torsion) were performed to determine the cost-effectiveness of bond-breaking media. It was found that the bond stress had been reduced by approximately 90% when either emulsion wax curing compound (EWCC) or emulsion slurry seal was used. The results from the British pendulum, push-off, pullout, torsion, and cost analyses indicate that EWCC is the most cost-effective bond-breaker medium. Based on the observations from the laboratory testing and field trial section, the EWCC application rate was selected at 0.4?L/m2. As evident from the push-off and torsion test results, the effectiveness of the EWCC as a bond-breaker medium decreased with time. Thus, a second application of EWCC is required if the LCS base has been exposed to the environment for more than 14 days. The 216-km project was successfully constructed with EWCC. It resulted in a more than $7 million savings by using EWCC instead of emulsion slurry seal. No distress or cracking has been observed after the section was opened to traffic for more than 1 year.     

Field Investigations of Cracking on Concrete Pavements

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).     

Roadway Heaving Caused by High Organic Matter

A forensic study was conducted to investigate the premature pavement failure of heaving and cracking on the north bound lane of SH6 and to determine (1) the causes of the heaving and cracking; (2) the severity and extent of the problem; and (3) a prevention strategy. Ground penetration radar (GPR), falling weight deflectometer (FWD), dynamic cone penetrometer (DCP), and soil boring and laboratory tests were conducted. Soil maps provided by the Natural Resource Conservation Service (NRCS) and the electrical resistivity tomography (ERT) were utilized to locate areas that may have similar problems for the ongoing project. It was concluded that the heaving was caused by high organic content in soils. The low pH of the lime treated subgrade layer indicated that the lime stabilization was ineffective. This was due to the high concentration of organic matter. FWD and DCP results indicated that the heaved/cracked areas are losing structural load support. Approximately 84% of the bumps/dips detected by the profiler were also detected by the GPR. Based on the GPR results, it was estimated that about 1.2?miles of the roadway may have potential heaving in the future. Although it is not a standard practice to determine the organic content of soil for new construction, it is critical to determine the organic matter through soil boring and laboratory testing in the suspicious areas. It was found that the soil maps provided by the NRCS yielded a reasonable estimate, and can be used as a screening tool. All five locations (O1 to O5) identified by ERT were verified by boring and laboratory tests to have high organic content (1.9–3.3%). Boring results indicated that ERT was able to map the soil strata and could differentiate between sandy and clay soil types. Although ERT was able to identify the anomalies with high organic contents, and the results were confirmed by boring and laboratory testing, additional work is needed to refine the procedure.     

Characterization of Microstructures across the Heat-Affected Zone of the Modified 9Cr-1Mo Weld Joint to Understand Its Role in Promoting Type IV Cracking

In the postweld heat-treated (PWHT) fusion welded modified 9Cr-1Mo steel joint, a soft zone was identified at the outer edge of the heat-affected zone (HAZ) of the base metal adjacent to the deposited weld metal. Hardness and tensile tests were performed on the base metal subjected to soaking for 5 minutes at temperatures below Ac₁ to above Ac₃ and tempering at the PWHT condition. These tests indicated that the soft zone in the weld joint corresponds to the intercritical region of HAZ. Creep tests were conducted on the base metal and cross weld joint. At relatively lower stresses and higher test temperatures, the weld joint possessed lower creep rupture life than the base metal, and the difference in creep rupture life increased with the decrease in stress and increase in temperature. Preferential accumulation of creep deformation coupled with extensive creep cavitation in the intercritical region of HAZ led to the premature failure of the weld joint in the intercritical region of the HAZ, commonly known as type IV cracking. The microstructures across the HAZ of the weld joint have been characterized to understand the role of microstructure in promoting type IV cracking. Strength reduction in the intercritical HAZ of the joint resulted from the combined effects of coarsening of dislocation substructures and precipitates. Constrained deformation of the soft intercritical HAZ sandwich between relatively stronger constitutes of the joint induced creep cavitation in the soft zone resulting in premature failure.     

Utilizing Advanced Characterization Tools to Prevent Reflective Cracking

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; (3) SH12; (4) SH342; and (5) IH35W. Based on the available test results from these five projects, it was observed that the W1?W3 threshold values of 5.5 mils (0.140 mm) for exposed concrete pavement and 6.5 mils (0.165 mm) for composite pavement with existing hot mix asphalt overlay and an OT threshold value of 700 cycles correlated well with the field performance. Ignoring either of these critical factors may lead to premature reflective cracking.     

Successful Application of CLSM on a Weak Pavement Base/Subgrade for Heavy Truck Traffic

Lack of proper pavement base and subgrade compaction leads to premature failures that account for millions of dollars in damages. Controlled low-strength material (CLSM) concrete was introduced in this study as pavement base material near a manhole where proper compaction is unachievable. Rut-resistant stone matrix asphalt was placed on top of the CLSM as a wearing surface layer. Dynamic cone penetrometer (DCP) testing was used to monitor CLSM construction. One day after placing, the CLSM gained sufficient strength to support construction traffic. Further, DCP results indicated that the CLSM possessed uniform characteristics of concrete that could improve the load-bearing capacity and serviceability of the pavement near the manhole. After 18 months of heavy truck traffic, maximum rutting was 5?mm, well below the failure criteria of 12.5?mm. Based on cost and performance, CLSM concrete has the potential to improve problematic areas in pavement.     

Stress Corrosion Cracking Behavior of Multipass TIG-Welded AA2219 Aluminum Alloy in 3.5?wt?pct NaCl Solution

The stress corrosion cracking (SCC) behavior of the AA2219 aluminum alloy in the single-pass (SP) and multipass (MP) welded conditions was examined and compared with that of the base metal (BM) in 3.5?wt?pct NaCl solution using a slow-strain-rate technique (SSRT). The reduction in ductility was used as a parameter to evaluate the SCC susceptibility of both the BM and welded joints. The results showed that the ductility ratio (?? _NaCl/(?? _air) was 0.97 and 0.96, respectively, for the BM and MP welded joint, and the same was marginally reduced to 0.9 for the SP welded joint. The fractographic examination of the failed samples revealed a typical ductile cracking morphology for all the base and welded joints, indicating the good environmental cracking resistance of this alloy under all welded conditions. To understand the decrease in the ductility of the SP welded joint, preexposure SSRT followed by microstructural observations were made, which showed that the decrease in ductility ratio of the SP welded joint was caused by the electrochemical pitting that assisted the nucleation of cracks in the form of corrosion induced mechanical cracking rather than true SCC failure of the alloy. The microstructural examination and polarization tests demonstrated a clear grain boundary (GB) sensitization of the PMZ, resulting in severe galvanic corrosion of the SP weld joint, which initiated the necessary conditions for the localized corrosion and cracking along the PMZ. The absence of PMZ and a refined fusion zone (FZ) structure because of the lesser heat input and postweld heating effect improved the galvanic corrosion resistance of the MP welded joint greatly, and thus, failure occurred along the FZ.     

Field Performance of a Compacted Clay Landfill Final Cover at a Humid Site

A study was conducted in southern Georgia, USA, to evaluate how the hydraulic properties of the compacted clay barrier layer in a final landfill cover changed over a 4-year service life. The cover was part of a test section constructed in a large drainage lysimeter that allowed continuous monitoring of the water balance. Patterns in the drainage (i.e., flow from the bottom of the cover) record suggest that preferential flow paths developed in the clay barrier soon after construction, apparently in response to desiccation cracking. After four years, the clay barrier was excavated and examined for changes in soil structure and hydraulic conductivity. Tests were conducted in situ with a sealed double-ring infiltrometer and two-stage borehole permeameters and in the laboratory on hand-carved blocks taken during construction and after four years of service. The in situ and laboratory tests indicated that the hydraulic conductivity increased approximately three orders of magnitude (from ≈ 10?7?to? ≈ 10?4?cm?s?1) during the service life. A dye tracer test and soil structure analysis showed that extensive cracking and root development occurred throughout the entire depth of the barrier layer. Laboratory tests on undisturbed specimens of the clay barrier indicated that the hydraulic conductivity of damaged clay barriers can be underestimated significantly if small specimens (e.g., tube samples) are used for hydraulic conductivity assessment. The findings also indicate that clay barriers must be protected from desiccation and root intrusion if they are expected to function as intended, even at sites in warm, humid locations.     

Use of an Infrared Joint Heater to Improve Longitudinal Joint Performance in Hot Mix Asphalt Pavements

Longitudinal joint cracking is one of the most prevalent forms of distress in asphalt concrete pavements. The joint area does not achieve the same density as the mat due to an unconfined edge on the initial pass and a cold joint during the second pass. The lower density allows water to penetrate and the material cracks, usually within one?year of construction. There are many techniques for constructing longitudinal joints, one being to preheat the joint prior to paving the second lane. This paper describes a field study conducted in New Hampshire using an infrared joint heater. Thermocouples were embedded in the pavement to determine the extent of heat penetration from the infrared heaters. Cores were taken along the joint and in the travel lanes for both the control and test sections. Density and strength measurements were taken on the cores. Permeability measurements along the control and test joints were performed. A cracking survey performed one?year after construction showed that the section of pavement where the infrared heater was used had significantly less cracking than the control section.     

Longitudinal Cracking Distress on Continuously Reinforced Concrete Pavements in Illinois

The Illinois Department of Transportation (IDOT) initiated a failure investigation to determine the distress mechanisms causing premature longitudinal cracking on continuously reinforced concrete pavements (CRCP) on several Illinois interstates. The longitudinal cracking approximately followed the embedded reinforcement steel and occurred in both the driving and passing lanes. In this paper, the results from field visual surveys, coring, and petrographic analyses are reported along with a review of archival construction and material records of the distressed CRCP sections. A laboratory forensic study was also performed on several field extracted slabs. The results of the field and laboratory investigation show the cracking was not initiated by steel corrosion, deleterious reactions in the concrete materials, or an inadequate structural design. Rather, the cracking is related to settlement of the steel bars in the concrete. Settlement cracking is conventionally thought to occur only in concrete slabs and decks with plastic (high slump) concrete and small values of bar cover depth, while the studied CRCP sections have large values of cover depth and were cast with stiff (low slump) concrete. The settlement was likely caused by the relative settlement of heavy steel bars (22?mm diameter) within the lower density concrete during the original CRCP construction. The technique of placing the steel bars in the fresh concrete (called tube-feeding) further contributed to the development of this distress, and this practice is no longer employed by IDOT.     

Forensic Investigation of Ultra-Thin Whitetopping Failures in Taiwan

This paper addresses the causes of the premature failures observed on newly constructed ultra-thin whitetopping (UTW) sections. The key factors contributing to premature failure were high pouring temperature and an insufficient underlying asphalt layer. Severe cracking and deep rutting were observed on sections placed during the daytime when the weather was hot and dry. Pouring temperature was even more critical when river gravel aggregate was used because it has a high thermal coefficient of expansion. Also, a low water-cement ratio magnified the effect of thermal cracking at high pouring temperature. On the basis of field results, it was found that the use of high-strength concrete should be discouraged when the pour temperature is high, since high shrinkage and premature cracking can result. It was concluded that the deep rutting was caused by the pumping of fines from the underlying base layer, in locations where there was no erosion-resistant asphalt layer. Sections poured at temperatures below 30°C with 100?mm of underlying asphalt performed well, and those two criteria are recommended for future UTW application.     

Computational Constitutive Model for Predicting Nonlinear Viscoelastic Damage and Fracture Failure of Asphalt Concrete Mixtures

A computational constitutive model was developed to predict damage and fracture failure of asphalt concrete mixtures. Complex heterogeneity and inelastic mechanical behavior are addressed by the model by using finite-element methods and elastic–viscoelastic constitutive relations. Damage evolution due to progressive cracking is represented by randomly oriented interface fracture, which is governed by a newly developed nonlinear viscoelastic cohesive zone model. Computational simulations demonstrate that damage evolution and failure of asphalt concrete mixtures is dependent on the mechanical properties of the mixture. This approach is suitable for the relative evaluation of asphalt concrete mixtures by simply employing material properties and fracture properties of mixture components rather than by performing expensive laboratory tests recursively, which are typically required for continuum damage mechanics modeling.     

Extending the Fatigue Life of Riveted Coped Stringer Connections

Fatigue cracking occurs at the copes of stringer–floorbeam connections of older, riveted steel bridges. Some cracks are quite long and raise serious questions regarding the remaining fatigue life of the subject bridges. Damage limitation methods (DLMs) have been used to increase the fatigue life of these stringers, but the effectiveness of the DLMs for these riveted connections had never been evaluated by tests. Therefore, tests were conducted to evaluate the fatigue life of coped, riveted stringer–floorbeam connections, and the effectiveness of DLMs. Fatigue cracks in the coped stringer–floorbeam connection were initially developed to establish crack initiation requirements and the rate and extent of crack growth. Once a significant crack was noted, one of several DLMs was applied, and the specimens were retested to determine the effectiveness of the DLM in controlling cracking. These DLMs included the drilled hole, the inserted bolt and the removed rivet methods. The relative effectiveness of the methods is described, and a design procedure is proposed for improving their performance.     

Forensic Investigation of Ultrathin Whitetopping Pavements in Florida

Developed in the early 1990s, ultrathin whitetopping (UTW) is a relatively new technique for asphalt pavement rehabilitation. To evaluate the applicability of UTW pavement in Florida, in 1997, the Florida Department of Transportation (FDOT) constructed an experimental UTW pavement in a weigh station along I-10, located in north Florida. The performance of these test sections, however, was less than ideal, with the observation of some early cracking on the concrete surface, which developed into severe cracking with time. Therefore, a forensic investigation was conducted to determine the causes of the problems in these UTW sections, so that lessons could be learned from this experimental project, the use of UTW under Florida’s conditions could be adequately assessed, and UTW technology could be properly applied in the future. The scope of work consisted of field evaluation, laboratory testing, and pavement design evaluation. Field evaluation included a pavement condition survey, pavement temperature measurement, nondestructive load testing using a falling weight deflectometer, and slab thickness determination. Laboratory tests were performed to determine concrete and asphalt material properties. Other design and traffic data were also acquired from FDOT. Data collected from the field evaluation and laboratory testing were used in conjunction with a mechanistic UTW pavement design/evaluation procedure to determine the possible causes for premature failure. From this comprehensive evaluation, the primary cause for the failure was found to be inadequate UTW pavement design. The inadequacy of the combination of thickness and slab dimensions contributed to the early cracking of the UTW pavement.     

Structural Analyses and Assessment of Historical Kamanl? Mosque in Izmir, Turkey

Historical structures are one of the most precious pieces of cultural accumulation. In this study, an interdisciplinary work was conducted to assess the structural condition of a historical masonry structure, Urla Kamanl? Mosque in ?zmir, Turkey. The structure is a member of group of structures, Yah?i Bey Complex, which includes a Turkish bath, a tomb, two fountains, and a primary school. The structure dates back to early 14th century to mid-15th century. History investigation, measurement survey, long-term settlement, and moisture observations were conducted. Nondestructive and destructive material tests were performed on stone, brick, and mortar. 3D finite-element model of the structure was used to investigate the critical locations of the structure under its self-weight, seismic load, and settlement load. Linear elastic and nonlinear settlement analyses were conducted to investigate the reason for massive cracks challenging the structural integrity.     

Deformation and fracture of miniature tensile bars with resistance-spot-weld microstructures

Plastic deformation of miniature tensile bars generated from dual-phase steel weld microstructures (i.e., fusion zone, heat-affected zone, and base material) was investigated up to final rupture failure. Uniaxial tensile true stress-strain curves beyond diffuse necking were obtained with a novel strain-mapping technique based on digital image correlation (DIC). Key microstructural features (including defects) in each of these three metallurgical zones were examined to explore the material influence on the plastic deformation and failure behavior. For weld fusion zones with minimal defects, diffuse necking was found to begin at 6 pct strain and continue up to 55 to 80 pct strain. The flow stresses of the weld fusion zones were at least twice those of the base material, and fracture strains exceeded 100 pct for both materials. The heat-affected zones exhibited a range of complex deformation behaviors, as expected from their microstructural variety. Only those fusion zones with substantial defects (e.g., shrinkage voids, cracks, and contaminants) failed prematurely by edge cracking, as signaled by their highly irregular strain maps.