Distress Modes Research Articles

Effect of Aggregate Gradation on Rutting of Asphalt Pavements

Permanent deformation (i.e. rutting) of asphalt pavements is one of major types of distress modes experienced in the service life of pavements. Aggregates are one of the key building materials used in the construction industry and the largest portion of an asphalt pavement. Therefore, aggregate characteristics impressively affect the performance of asphalt pavements. Gradation is one of the important characteristics of aggregates affecting permanent deformation of hot mix asphalt. The objective of this research is to investigate the impact of aggregate gradation variations on rutting characteristics of asphalt concrete mixtures.

Investigating effects of ethylene vinyl acetate and gilsonite modifiers upon performance of base bitumen using Superpave tests methodology

In this research study, relative performance of a series of ethylene vinyl acetate (EVA) and gilsonite modified bitumens were evaluated in terms of three main distress modes of flexible pavement namely rutting, fatigue damage and low temperature cracking. Seven modified and unmodified bitumens were tested and characterized in accordance with the Superpave performance criteria. The experimental tests performed were dynamic shear rheometer (DSR), bending beam rheometer (BBR) and rotational viscosity (RV). DSR test results for rutting showed that addition of EVA and gilsonite increase the rutting parameter (G∗/Sin(δ)) of the modified bitumens relative to the base bitumen. DSR fatigue test results showed that addition of EVA decreases the fatigue parameter (G∗Sin(δ)) of modified bitumens while addition of gilsonite increases the fatigue parameter of modified bitumens. BBR test results showed that addition of EVA decreases the creep stiffness (S-value) of modified bitumens while addition of gilsonite increases the creep stiffness of modified bitumens. Moreover, the addition of 2% and 4% EVA increase the m-value of modified bitumens while addition of gilsonite decreases the m-value of modified bitumens.

Effects of interface condition characteristics on open-graded friction course top-down cracking performance

Top-down cracking is a distress mode that is of particular concern for pavements with Open-Graded Friction Course (OGFC) because open-graded mixture has considerably lower resistance to fracture (lower fracture energy limit and lower resistance to damage) than dense-graded mixture. This particular cracking phenomenon initiates on the pavement surface and propagates downward; so because the OGFC layer is thin, cracking performance relies on the properties and characteristics of three components near the pavement surface: OGFC, underlying structural layer, and the interface between. For this reason, to increase the durability of pavements surfaced with OGFC, it is significant to ensure a quality fracture resistant bond between OGFC and the structural layer. This research investigated top-down cracking performance of OGFC with different tack coats using a newly developed composite specimen interface cracking (CSIC) test. In addition, X-ray computed tomography (CT) was employed to analyze the interface characteristics between OGFC and dense-graded HMA. HMA fracture mechanics was employed to quantify the effect of polymer modified asphalt emulsion (PMAE) on pavement top-down cracking resistance enhancement. Results clearly indicated that PMAE-created bonded interface conditions greatly increased pavement top-down cracking resistance as compared with conventional tack coat.

Calibrating and Validating Overlay Tester–Based Fatigue Cracking Model with Data from National Center for Asphalt Technology

There is a national movement to develop mechanistic–empirical methods for the design of flexible pavements, for which fatigue cracking is a major distress mode. Fatigue cracking has been studied for several decades. Different types of fatigue cracking models have been proposed. After a review of existing fatigue cracking models in the literature, it was found that the overlay tester–based fatigue cracking model was a rational choice for predicting the development of fatigue cracking and for incorporation into the mechanistic–empirical design system. The main features of the overlay tester–based fatigue cracking model include incorporation of both crack initiation and crack propagation stages; involvement of fracture properties (i.e., A and n) of every asphalt layer, if the flexible pavement has multiple asphalt layers and each layer material is different; and use of the simple overlay tester for determining the fracture properties required for predicting both crack propagation and crack initiation. The proposed fatigue cracking model was preliminarily calibrated with material properties and fatigue cracking performance data from seven test sections evaluated in the 2006 test cycle at the National Center for Asphalt Technology's Pavement Test Track. Validation of the calibrated model was performed with performance data from the 2003 test sections at the National Center for Asphalt Technology Pavement Test Track. Thus far, satisfactory results have been obtained. However, further model validation and calibration with more field data, varied traffic load spectra, different environmental conditions, and different materials are still required.

Mode of delivery and postpartum emotional distress: a cohort study of 55 814 women

To assess the association between mode of delivery and maternal postpartum emotional distress. A prospective study of women from 30 weeks of gestation to 6 months postpartum. Pregnant women in Norway during the period 1998-2008. A total of 55,814 women from the Norwegian Mother and Child Cohort Study. Emotional distress was reported in a short form of the Hopkins Symptom Checklist-25 (SCL-8) at 30 weeks of gestation and at 6 months postpartum. Information on mode of delivery was obtained from the Medical Birth Registry of Norway. Changes in SCL-8 score from 30 weeks of gestation to 6 months postpartum and presence of emotional distress at 6 months postpartum. Women with instrumental vaginal, emergency caesarean or elective caesarean deliveries had similar changes in SCL-8 score between 30 weeks of gestation and 6 months postpartum, as compared with women with unassisted vaginal delivery (adjusted regression coefficient, 0.00, 95% CI -0.01 to 0.01; 0.01, 95% CI 0.00-0.02; and -0.01, 95% CI -0.02 to 0.00, respectively). The corresponding odds ratios (ORs) associated with the presence of emotional distress at 6 months postpartum (SCL-8 ≥ 2.0) were: OR 1.01, 95% CI 0.86-1.18; OR 1.13, 95% CI 0.97-1.32; and OR 0.96, 95% CI 0.79-1.16, respectively. These estimates were adjusted for emotional distress during pregnancy and other potential confounding factors. Emotional distress during pregnancy showed the strongest association with the presence of emotional distress at 6 months postpartum (adjusted OR 14.09, 95% CI 12.77-15.55). Mode of delivery was not associated with a change in SCL-8 score from 30 weeks of gestation to 6 months postpartum or with the presence of emotional distress postpartum.

Differences Between Women Who Pursued Genetic Testing for Hereditary Breast and Ovarian Cancer and Their At-Risk Relatives Who Did Not

To (a) examine differences in appraisals of hereditary breast and ovarian cancer (HBOC), psychological distress, family environment, and decisional conflict between women who pursued genetic testing and their at-risk relatives who did not, and (b) examine correlations among appraisals of HBOC, psychological distress, family environment, and decisional conflict regarding genetic testing in these two cohorts of women. Descriptive, cross-sectional cohort study. Two clinics affiliated with a major research university in the midwestern United States. 372 women aged 18 years and older. 200 pursued genetic testing for BRCA1 and BRCA2 mutations (probands) and 172 of their female relatives who had a greater than 10% prior probability of being a mutation carrier but had not pursued testing. After providing informed consent, probands and relatives were mailed self-administered questionnaires. Perceived risk, knowledge of HBOC risk factors and modes of gene inheritance, perceived severity, perceived controllability, psychological distress, family relationships, family communication, and decisional conflict about genetic testing. T tests revealed that probands perceived higher risk and had more psychological distress associated with breast cancer. Probands had more knowledge regarding risk factors and gene inheritance, and greater decisional conflict regarding genetic testing. Relatives reported higher perceived severity and controllability. No differences were observed in family relationships and family communication between probands and relatives. Pearson correlations revealed different patterns in knowledge, perceived controllability, family relationships, and decisional conflict between probands and relatives. Significant differences exist between women who pursue genetic testing and those who do not. The family environment influences adjustment to HBOC and decisions about genetic testing. Enhancing the family communication process about HBOC can provide informational and emotional support to high-risk women and promote decision making about genetic testing.

Effect of Thermal Stresses on Fatigue Behavior in Bituminous Mixes

Fatigue cracking in asphalt mixtures—a common, widely studied mode of distress in flexible pavements—necessitates major investments in pavement maintenance and rehabilitation. To date, research has focused on the response of bituminous mixes subjected to cyclic loading until failure. Moreover, low-temperature thermal stresses in bituminous mixes have been investigated in isolation to determine the effect of thermal gradients on materials. However, decreased temperature leads to a combined effect of fatigue distress and thermal stress. To provide insight into this phenomenon, an experimental study based on a new test procedure developed by the Road Research Laboratory of the Technical University of Catalonia, Spain, is presented. This method allows the simultaneous evaluation of the effect of thermal stresses and the fatigue response of asphalt mixtures.

Study on Joint Deflection of Existing Joint Plain Concrete Pavement upon Adoption of Hot Mixture Asphalt Overlay

When HMA (hot mixture asphalt) is used to remedy functional or structural deficiencies of existing JPCP (joint plain concrete pavement), reflection cracking is a major distress mode in HMA overlay. The basic mechanism of reflection cracking is the propagation of cracks through the overlay due to deflection difference in the joints vicinity of the existing pavements. In this paper the model of JPCP is created by three finite element method and the relationship between joint deflection difference and effects such as base modulus, elastic coefficient of spring elements is discussed. Based on the model of JPCP, the finite element model of asphalt overlay is created then and shear stress concentration phenomenon is found at the bottom of HMA where is just above the joint of JPCP. So, the rule of the shear stress at the bottom of HMA with deflection difference at the joint of JPCP is studied.

Estimation and Validation of Gaussian Process Surrogate Models for Sensitivity Analysis and Design Optimization

The Mechanistic–Empirical Pavement Design Guide (MEPDG) is a powerful predictor of pavement distress, but it is computationally expensive to evaluate. Analyses that require many MEPDG evaluations, such as sensitivity analysis and design optimization, become impractical because of the computational expense. These applications are important in achieving robust, reliable, and cost-effective pavement designs. This paper develops Gaussian process (GP) surrogate models that, with a trivial amount of computational expense, accurately approximate the results of the MEPDG for each relevant distress mode. The GP is validated in accordance with three model metrics: average predictive percent error, predictive coefficient of determination, and Bayes factor. The GP models are then exploited for sensitivity analysis and design optimization, making these tasks computationally affordable.

Bad obstetric history: A prospective study

Background: Death of an infant in utero or at birth has always been a devastating experience for the mother and of concern in clinical practice. Perinatal mortality remains a challenge in the care of pregnant women worldwide, particularly for those who had history of adverse outcome in previous pregnancies. To assess the risk factors and outcome of pregnancies in cases of bad obstetric history (BOH) and compare the results with control group, this study was undertaken. Methods: A prospective study from 2003 to 2007 was carried out in 79 pregnancies having BOH (history of unexplained stillbirth/neonatal death, three or more consecutive abortions etc). Test group was analyzed in terms of age, gravida, parity, risk factors and outcome in terms of preterm delivery, stillbirth, mode of delivery, birth weight, pregnancy complications and fetal distress. These parameters were compared with a systematic, randomly selected sample from rest of the deliveries. Necessary advice and treatment was given in cases of hypothyroidism, hypertension, antiphospholipid antibody (APLA) syndrome, gestational diabetes and other risk factors. Result: There was significantly higher incidence of malpresentations, hypertension, APLA, cervical incompetence, preterm deliveries and caesarean section in test group (p< 0.05). In this study, only 47 (59.49%) women out of 79 in BOH group were identified to have possible factor responsible for pregnancy losses. In 32 (40.51%), no probable causes could be identified. Nine (11.39%) patients were identified with more than one risk factor. Conclusion: APLA, hypertension, malpresentation, cervical incompetence, preterm deliveries and caesarean section were found significantly more in BOH group. In a large percentage of pregnancies with BOH, the risk factors for adverse outcome were not identified but pregnancy outcome was generally good in subsequent pregnancies with optimal antenatal care and advice.

Material Selection and Design for Moisture Damage of HMA Pavement

Moisture damage is a primary mode of distress occurring in hot mix asphalt (HMA) pavements. Usually, the acid aggregate like gneiss must use some anti-stripping additive to resist water damage. Hydrated lime is best known as an anti-stripping additive since 1910. The purpose of this paper is to look at some aspects of the effects of aggregate chemical properties and hydrated lime on the dynamic mechanics and stripping behavior of hot mix asphalt. Two types of aggregates evaluated in this study were limestone and gneiss. The effects of the aggregates type were evaluated on four different aggregate gradations which were composed with the two aggregates in different proportion. And the hydrated lime has been used for HMA pavements to mitigate moisture-related damage in gneiss asphalt mixture. Laboratory tests for different asphalt mixture include Marshall Test, Frozen-thaw Cycle Test, Dynamic Modulus Test (DMT) and Indirect Tensile Fatigue Test (ITFT). Testing data and analyses demonstrated that different aggregate gradations have different mechanical properties. Hydrate lime has greatly contributed to moisture damage resistance in acid aggregate gneiss and enhanced the dynamic modulus. The modified with hydrated lime mixture composed with coarse gneiss aggregate and fine limestone aggregate also has better performance of the mixture against rutting, fatigue and thermal cracking. It can be concluded from ITFT tests that the fatigue life (load cycle times) of additive hydrated lime asphalt concrete is more than neat ones. At last, we can conclude that the selection and design that modified with hydrated lime and fine limestone aggregate replace acid aggregate could create multiple benefits in asphalt mixtures.

Permanent Deformation Characterization of Bituminous Mixtures using Laboratory Tests

ABSTRACT The permanent deformation of bituminous mixture is one of the most important distress modes observed in in-service pavements. This distress can be estimated through laboratory tests where the most common include the Wheel-Tracking Test, the Cyclic Compression Test (Uniaxial and Triaxial) and the Repeated Simple Shear Test at Constant Height (RSST-CH). The study of the reliability and accuracy of each test in predicting permanent deformation behaviour is of great importance. In this work, these tests were used to assess a typical Portuguese mixture. The results showed that all tests accurately predict permanent deformation behaviour, mainly for the mixture tested in this work. Good correlations were obtained between the different test results, making it possible to define the simpler and cheaper tests as more useful in practice.

RESILIENT BEHAVIOUR OF ASPHALT CONCRETE UNDER REPEATED LOADING & EFFECTS OF TEMPERATURE

In this paper resilient behavior of asphalt concrete mixes were studied by varying temperature & time of loading to understand the pavement behavior under Pakistani climatic conditions & to address the problem according to mode of distress. The common cause of pavement distress in Pakistan is rutting, which initiates due to uncontrolled axle load & large variation in temperature. Indirect Tensile and creep tests were carried out using Universal Testing Machine (UTM 5P) on the cores taken from Islamabad-Peshawar Motorway Section (M1), IJP Principal road dual carriage way (Links Islamabad to Grand Trunk Road) & mixes prepared in the laboratory. Both sections had been opened for traffic on 2 nd , November, 2004. Polymer Modified Bitumen (PMB) has been used on M1 and is a unique opportunity to compare the behavior of in situ Asphalt Concrete mixes with & without PMB under same temperature & loading conditions. The results of laboratory tests on asphalt concrete cores (from M1 & IJP road) under the influence of load, environmental and mix variables are presented in this paper.

Effect of Factors Affecting Fracture Energy of Asphalt Concrete at Low Temperature

ABSTRACT Low temperature cracking is considered one of the primary distress modes of asphalt pavements built in northern climates. The detrimental effects of low-temperature cracking of asphalt pavements have motivated new work in fracture testing of hot-mix asphalt (HMA). A comprehensive study was conducted to investigate the effect of various factors on the fracture resistance of asphalt mixtures at low temperatures. The Semi-Circular Bending (SCB) and Disc-Shaped Compact Tension Test (DCT) fracture tests were performed at three low temperatures to measure the fracture energy for 28 asphalt mixtures, which represent a combination of factors including binder type, binder modifier, aggregate type, asphalt content and air voids. In this study, the analysis from the experimental data indicates that fracture energy is strongly dependent upon temperature and significantly affected by type of aggregate and binder modifier. The results of the analysis show the significance of air voids in the SCB test, but no statistical difference was found for the DCT test data. The analysis also illustrates that richer mixtures, ones with more asphalt than the design optimum, are not necessarily more crack resistant.

Permanent Deformation Characterization of Bituminous Mixtures using Laboratory Tests

ABSTRACT The permanent deformation of bituminous mixture is one of the most important distress modes observed in in-service pavements. This distress can be estimated through laboratory tests where the most common include the Wheel-Tracking Test, the Cyclic Compression Test (Uniaxial and Triaxial) and the Repeated Simple Shear Test at Constant Height (RSST-CH). The study of the reliability and accuracy of each test in predicting permanent deformation behaviour is of great importance. In this work, these tests were used to assess a typical Portuguese mixture. The results showed that all tests accurately predict permanent deformation behaviour, mainly for the mixture tested in this work. Good correlations were obtained between the different test results, making it possible to define the simpler and cheaper tests as more useful in practice.

Accumulated strain in polymer-modified asphalts

One of the distress modes of asphalt pavements is the rutting that occurs at high operating temperatures, and it is believed that the accumulated strain in asphalt binder is mainly responsible for the rutting. The asphalt industry has tried to use the parameter 1/J″ as the specification parameter for the determination of the susceptibility of asphalt pavements to rutting. It was, however, recognized that this parameter is not suitable for polymer-modified asphalts, and currently, the repeated creep and recovery test (dynamic creep test) is studied as a new specification tool. In this paper, we study the general response of binders to a train of shear-stress pulses with a constant rest time between the pulses. We have found that the viscous approximation of the creep compliance function yields a suitable description of the test when the creep recovery is very weak. To extend the description to cases with significant recovery, an alternative model is proposed. Using the simple approximation of the continuous retardation spectrum, L, by the reduced loss compliance, L is modeled by a gamma-type distribution function. With this form of the shear compliance function, one can successfully describe the dynamic creep test in various polymer-modified asphalts.

A Yield Strength Model for Partially Saturated Unbound Granular Material

ABSTRACT The predominant mode of distress for unbound pavement layers is the permanent deformation of the layer either through gradual deformation or rapid shear failure. Both these forms of permanent deformation have been linked to the shear strength of the material by researchers. Conventionally, the shear strength of the material is characterised with the Mohr-Coulomb shear strength parameters of the material. This paper presents an alternative model to describe the yield strength of the material incorporating the effects of density and degree of saturation. The model includes the influence of the suction pressure resulting from matric suction in partially saturated material on the yield strength and has been calibrated with a high degree of accuracy using conventional tri-axial test results for a number of road-building materials ranging from fine sand to crushed stone.

A Yield Strength Model for Partially Saturated Unbound Granular Material

ABSTRACT The predominant mode of distress for unbound pavement layers is the permanent deformation of the layer either through gradual deformation or rapid shear failure. Both these forms of permanent deformation have been linked to the shear strength of the material by researchers. Conventionally, the shear strength of the material is characterised with the Mohr-Coulomb shear strength parameters of the material. This paper presents an alternative model to describe the yield strength of the material incorporating the effects of density and degree of saturation. The model includes the influence of the suction pressure resulting from matric suction in partially saturated material on the yield strength and has been calibrated with a high degree of accuracy using conventional tri-axial test results for a number of road-building materials ranging from fine sand to crushed stone.

Assessment and upgrading of in-service heavy duty pavements to long life

The context of long-life pavements (LLP) is winning specific international interest the last years; especially in regards to the upgrading of existing pavements to LLP, which constitutes the main focus of the present research study. For this reason, a detailed assessment of the in situ condition of a heavy-duty highway pavement was performed, based on a comprehensive long-term monitoring approach of its structural performance. The main distress mode of the investigated pavement was cracking in the pavement surface. It is shown that the originally designed pavement could be classified as an upgradeable long lasting one and transferred into a context of a full long-life pavement.

Study on the Modeling Method Suitable for Pavement Rutting

A paved road surface is in contact with a vehicle directly through its tire therefore its condition is closely associated with vehicle running 1) . It also greatly affects road user’s ride quality, safety and the living environment of roadside resident. Therefore, it is important to keeping track of the conditions and evaluate the conditions of the paved road surface, then make the suitable maintenance at the appropriate time according to the evaluation 2) . A major distress mode of the paved road is caused by road surface characteristics, such as rutting (pavement rutting), roughness and crack. Rutting and roughness are a special concern because these will affect road user and roadside resident directly. A longitudinal profile such as roughness has associated with elements which are related to the road user’s rating 3) . On the other hand, for the problems of a transverse profile such as the rutting, although there are the attempts being made to evaluate the rutting which affects the vehicle stability and controllability 3) , it has not yet reached to establish the evaluation index with the road user’s point of view. In Japan today, rut depth as an index for maintenance of the rutting has some disadvantages 2) . For instance, the index has problems the measurement method and definition of the rut depth differs from one administrator to another and it is does not reflect the road user’s point of view. There are two experimental approaches to estimate the road profile which affects vehicle behavior and road users. One approach is to use the actual vehicle with real road conditions. And the other is to use the simulation based on the vehicle dynamics (vehicle dynamics simulation). Recently vehicle dynamics simulation have developed and its achievements have become a center of attraction because it can do experiments to diagnose the road profile safely, rapidly and efficiently with same driving situation 3)-6) . The experiment for the rutting evaluation with the simulation has studied to concentrate on the vehicle dynamics 3) . However, the rut shape which is the object of investigation, especially the rutting caused by flowing which depends on heavy traffic, did not take into account the actual shape at the existing road, although it approximated only depression in the wheel path. Against this background, for the purpose of quantitative grasp of the rut shape, we developed the geometrical models of the rutting (the pavement rutting models) which simplified and approximated by use of comparatively easy functions and which have a moderate flexibility. The developed models were verified in respect of the adaptability of these shapes for actual road profile data and the applicability for the simulation method of the vehicle dynamics. The actual road profile is using part of the data which is obtained from the second Permanent International Association of Road Congress – World Road Association (PIARC) International Experiment to Harmonize Longitudinal and Transverse Profile Measure and Reporting procedure (EVEN Project) 1) . While there are various types of vehicle dynamics models or simulation Abstract: In case of fitting geometric model of pavement rutting to the real data, the model of a high order function has the well advantage of fitness. However, it also has the disadvantage of versatility. In this study, we developed the pavement rutting models with quadratic function and spline function for quantification of pavement rutting characteristics on road surface. The two developed models are verified in respect of the adaptability of these shapes and the accommodation for the simulation method of the vehicle dynamics using the road profile data of the PIARC EVEN experiment in 1998. As a result, it is indicated that the spline function is applicable for representing pavement rutting characteristics.