Premature Pavement Failure Research Articles

Predict the Service Life of Pavement: Evaluate Moisture Sensitivity and Oxidative Aging of Asphalt

Copyright: © 2012 Lu Y. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Pavements are subject to different stresses during their service life. Correctly predicting the service life provides decisive information to pavement design and rehabilitation. A properly designed pavement material will perform adequately during its design life, and normally the distresses will not exceed the allowable limits. However, premature pavement failure may often appear due to several degradation factors. Moisture sensitivity and asphalt aging properties are two main factors that contribute to the pavement service life reduction. In this editorial, the author will give some comments on the current research status about these two phenomena.

Computationally efficient surrogate response models for mechanistic–empirical pavement analysis and design

This paper proposes the use of neural network- (NN-) based pavement structural analysis tools as surrogates for the flexible pavement response analysis in the new mechanistic empirical pavement design guide (MEPDG) developed for the American State Highway and Transportation Officials (AASHTO). Some of the recent successful applications of NN-based structural analysis models for predicting critical flexible pavement responses and nonlinear pavement layer moduli from falling weight deflectometer (FWD) deflection basins are highlighted. Because NNs excel at mapping in higher-order spaces, such models can go beyond the existing univariate relationships between pavement structural responses and performance (such as the subgrade strain criteria for considering flexible pavement rutting). The NN-based rapid prediction models could easily be incorporated into the newer versions of the MEPDG, which will continue to be updated. This can lead to better performance prediction and also reduce the risk of premature pavement failure.

Looking to the future: the next-generation hot mix asphalt dynamic modulus prediction models

This paper describes an innovative approach related to the development of a new hot mix asphalt (HMA) dynamic modulus (|E *|) prediction model by employing the artificial neural networks (ANNs) methodology. Many studies have been conducted over the last 50 years related to the development of HMA |E *| prediction models based on the regression analysis of laboratory measurements. The current study is an attempt to replace the regression analysis with the ANNs that have proved useful for solving certain types of problems that are too complex, poorly understood or resource intensive to tackle using more traditional numerical and statistical methods. The ANN |E *| prediction models were developed using the latest comprehensive |E *| database that is available to the researchers (from the NCHRP Report 547) containing 7400 data points from 346 HMA mixtures. The ANN model predictions were compared with the 1999 version of the Witczak |E *| prediction model, which is included in the mechanistic–empirical pavement design guide (MEPDG) and the new revised version as well. The sensitivity of input variables to the ANN model predictions were also examined and discussed. The ANN |E *| models show significantly higher prediction accuracy compared with the existing regression models and could easily be incorporated into the MEPDG. This approach may lead to more accurate characterisation of the HMA dynamic modulus resulting in better performance prediction, thereby reducing the risk of premature pavement failure.

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 1.2miles 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.

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.

Predicting stripping and moisture induced damage of asphalt concrete prepared with polymer modified bitumen and hydrated lime

Many highway agencies have been experiencing premature failures that decrease the performance and service life of pavements. One of the major causes of premature pavement failure is the moisture damage of the asphalt concrete layer. Many variables affect the amount of water damage in the asphalt concrete layer such as the type of aggregate, bitumen, mixture design and construction, level of traffic, environment, and the additive properties that are introduced to the bitumen, aggregate or bitumen–aggregate mixture. This study is aimed to determine the effect of additives such as hydrated lime as well as elastomeric (SBS) and plastomeric (EVA) polymer modified bitumen (PMB) on the stripping potential and moisture susceptibility characteristics of hot mix asphalt (HMA) containing different types of aggregate (basalt–limestone aggregate mixture and limestone aggregate). The stripping properties and moisture susceptibility characteristics of the samples have been evaluated by means of captured images and the Nicholson stripping test (ASTM D 1664) as well as the modified Lottman test (AASHTO T 283), respectively. The results indicated that hydrated lime addition and polymer modification increased the resistance of asphalt mixtures to the detrimental effect of water. Moreover, it was found out that samples prepared with SBS PMB exhibited more resistance to water damage compared to samples prepared with EVA PMB.

Forensic Case Studies on Low-Volume Roads in Texas

Three forensic investigations were conducted to determine the causes of premature pavement failure. Specific causes for both longitudinal and transverse cracking, fatigue cracking, and sulfate-induced soil heave problems were identified and verified through a series of nondestructive field and laboratory evaluation tests. Conclusions were made, and recommendations are proposed to the districts to help them select a strategic rehabilitation plan to prevent the same problems from recurring. In Case I, the transverse cracking was believed to be due to either the shrinkage cracks of the very stiff treated caliche base or the shrinkage cracks in the lime-treated subgrade. The longitudinal edge cracks were attributed to edge shrinkage cracking due to wetting and drying cycles and heavy agricultural vehicles traveling along the pavement edge. The major cause for severe fatigue cracking in Case II was identified to be the very open structure of a lightweight seal coat beneath the hot-mix asphalt surface combined with weak support of the subgrade. A lack of sufficient support for the pavement under loading facilitated its fatigue failure. On the basis of Case III, stabilization of high-sulfate-bearing soil with calcium-based stabilizers alone is not recommended because of high swell potential and low residual unconfined compressive strength. The combination of lime and fly ash proved to be the best stabilizer for the soil with high sulfate content, provided that special precautions are taken during the mix design and construction process.

Integration of field and laboratory testing to determine the causes of a premature pavement failure

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.

Inverse Gas–Liquid Chromatography Study of Asphalt Composition and Oxidative Aging

The chemical composition of an asphalt binder significantly affects oxidative aging and interactions with both aggregate and binder modifiers. In turn, it may cause premature asphalt pavement failures through fatigue cracking, moisture damage, or other failure mechanisms. Analytical chemical procedures, such as ion exchange chromatography, are time-consuming and cost prohibitive as routine tests. Inverse gas–liquid chromatography (IGLC) is a relatively faster and simpler technique that provides the chemical composition and polarity characteristics of asphalt samples. In IGLC, asphalt is used as the liquid substrate on an inert support in a GLC column and is characterized by measuring the retention behavior of selected test compounds that possess different functional groups. The interaction behaviors between seven test compounds and 19 unaged and GLC column–aged asphalt samples were determined and compared with functional group concentrations presented in the asphalts and in a nonaqueous potentiometric titration study. It was found that the retention behaviors of the test compounds are strongly related to the types and concentrations of functional groups in the asphalt. For unaged asphalts, the retention behavior of strongly basic test compounds is highly correlated with the concentration of acidic functional groups in asphalts. The retention behavior of phenol with oxidatively aged asphalts is highly correlated with the concentration of sulfoxide, one of the major products of asphalt oxidation.

Inverse Gas–Liquid Chromatography Study of Asphalt Composition and Oxidative Aging

The chemical composition of an asphalt binder significantly affects oxidative aging and interactions with both aggregate and binder modifiers. In turn, it may cause premature asphalt pavement failures through fatigue cracking, moisture damage, or other failure mechanisms. Analytical chemical procedures, such as ion exchange chromatography, are time-consuming and cost prohibitive as routine tests. Inverse gas-liquid chromatography (IGLC) is a relatively faster and simpler technique that provides the chemical composition and polarity characteristics of asphalt samples. In IGLC, asphalt is used as the liquid substrate on an inert support in a GLC column and is characterized by measuring the retention behavior of selected test compounds that possess different functional groups. The interaction behaviors between seven test compounds and 19 unaged and GLC column-aged asphalt samples were determined and compared with functional group concentrations presented in the asphalts and in a nonaqueous potentiometric titration study. It was found that the retention behaviors of the test compounds are strongly related to the types and concentrations of functional groups in the asphalt. For unaged asphalts, the retention behavior of strongly basic test compounds is highly correlated with the concentration of acidic functional groups in asphalts. The retention behavior of phenol with oxidatively aged asphalts is highly correlated with the concentration of sulfoxide, one of the major products of asphalt oxidation.

Derivation of Equation for Cost of Premature Pavement Failure

With the continuing interest in performance-related specifications and the development of software packages to compute the appropriate level of payment associated with variable levels of quality, there is a need for a simple, easily understood method to validate the output of these computer programs. A standard validation procedure is to create realistic hypothetical cases that can be calculated readily by hand and then to compare the results with the output of the procedure under test. An equation is derived that can serve two extremely useful purposes: it can be used as a validation tool for software currently under development, or it can be used directly to establish pay schedules that award payment appropriate for the level of quality received.

Effects of Testing Time and Confining Pressure on Falling-Head Permeability Tests of Hot-Mix Asphalt Concrete

Superpave implementation has resulted in increased interest in the permeability of hot-mix asphalt concrete. Relatively open-graded Superpave mixes have given rise to concern about premature pavement failures due to increased water infiltration from the surface. Arkansas is investigating the use of a falling-head permeability test to evaluate Superpave mixes with respect to potential performance problems caused by increased permeability. The initial phase of the project concerns the development of laboratory testing procedures and equipment. Superpave field mixes from projects in Arkansas were sampled to investigate permeability testing parameters. In addition, compacted test specimens from a round-robin study of permeability were included in the testing matrix. For the Arkansas mixes, loose mix sampled at the hot-mix plant was compacted using the Superpave gyratory compactor. Field cores were also taken from completed pavement sections. Permeability tests were conducted on all samples to investigate the effect of testing time (15, 30, 45, and 60 min) and confining pressure (69 and 96.5 kPa) on the measured permeability values. Results of the testing suggest that neither the time interval used in measuring the head drop in a falling-head test nor the confining pressure used in the flexible wall testing apparatus significantly affects test results. These findings will greatly simplify testing methods and setup, making the test more attractive as a relatively routine tool for the mix design laboratory.