Premature Distress Research Articles

The Study on the Asphalt Pavement with Composite Base

Semi-rigid layer is widely used as the base in China. However, the structure has resulted in many premature distresses in asphalt concrete layer. In order to overcome the problem, the composite base is introduced which is composed by both flexible and chemically stabilized material. The internal stresses are calculated by linear multilayer elastic theory and then, a comparison of the stresses of asphalt pavement with semi-rigid base and composite base is provided. The result shows that the composite base composed by all, consisting of the asphalt treated layer, graded crushed stone and cement treated layer is more suitable structure to resist cracking and the structure also has good adaptability to heavy load.

Premature Birth, Respiratory Distress, Intracerebral Hemorrhage, and Silvery-gray Hair

Premature Birth, Respiratory Distress, Intracerebral Hemorrhage, and Silvery-gray Hair

Thermography-Driven Distress Prediction from Hot Mix Asphalt Road Paving Construction

This research was conducted to assess the effects of temperature segregation in hot-mix asphalt (HMA) paving construction on pavement distress in the early stages of its life cycle. Several paving projects across Nebraska were visited in which sensory devices were used to test how density, moisture content within the asphalt, material surface temperature, internal temperature, wind speed, haul time, and equipment type, contribute to temperature differential. Areas of high temperature differential were identified using an infrared thermal camera. A nonnuclear density device was also used to record how lower temperature asphalt density correlates with a more consistent hot area. The location was marked digitally with a handheld global positioning system to locate points of interest for future site revisits to verify research findings. The research findings indicate that among the investigated variables, truck types and density are highly correlated with temperature differential. Additionally, analysis of data from revisits after one or two freeze-thaw seasons shows that higher temperature differential is significantly correlated with premature distress of paved HMA roads while they are still in new condition. This finding suggests that higher temperature segregation created from paving construction in the zone of freeze-thaw cycles promotes visible surface distress in the very early stage of the pavement life cycle.

Use of Structural Asset Management to Evaluate Road Substructure Drainage Systems

Over the past three decades, many areas in western Canada have experienced increasing volumes of heavy commercial vehicles, primarily related to resource-based economic development. Combinations of changing moisture conditions, marginal granular materials, and heavy loadings often lead to premature road structure distress, failure, or both. In particular, slow-moving and turning truck traffic can significantly increase the applied stress states and moisture-pumping effects within the road structure, both at the surface and deep within the road structure. Strengthening a road structure to sustain severe heavy truck loadings often requires installing substructure drainage systems before placing the structural strengthening system. However, explicitly measuring the initial design requirements and the life-cycle performance of substructure drainage systems, as well as the impact of drainage systems on structural integrity, is difficult with traditional empirical model–based road structural evaluation and design methods. The use of a mechanistic model–based structural asset management approach to evaluate the performance of existing substructure drainage systems and to engineer the requirements of new drainage systems across three case studies is summarized. The findings of these case studies indicate that falling weight deflectometer and ground-penetrating radar are effective mechanistic model–based methods of structural assessment. They accurately quantify the spatial limits, the end-product structural asset value, and the performance of in-service drainage systems.

Mechanical behavior of concretes damaged by alkali-silica reaction

Alkali-silica reaction (ASR) can induce the premature distress and loss in serviceability of concrete structures. The internal crack pattern produced by ASR affects both transport and mechanical properties. Usually linear expansions are considered as indicative of the grade of damage into the material (internal crack pattern), nevertheless as diverse types of ASR have been recognized (rapid or slow reactive aggregates, fine or coarse aggregates) the effects on strength and rheological properties could be different for a same expansion. This paper compares the mechanical response of a reference concrete (without reactive aggregates) and concretes prepared with three different types of reactive aggregates, with the same mixture proportions. The first concrete incorporated 10% of a highly reactive siliceous orthoquartzite as a part of the coarse aggregate, the second included a highly reactive sand, and the third prepared with a slow reactive granitic migmatite as coarse aggregate. Concretes were moist cured at 38 °C. When linear expansions ranging between 0.11 and 0.18% took place, the stress strain behavior in compression and the load-displacement response in flexure were measured. The same tests were performed on reference concrete at different ages, between 75 and 745 days. Microscopic observations were performed on polished and thin sections in order to analyze concrete microstructure. It appears that the failure mechanism of concrete in compression is clearly affected by ASR, the shape of the stress–strain curves reflects the presence of internal fissures, showing that the capability of controlling crack propagation decreases. Differences in the crack pattern are also reflected in the shape of the load-deflection curves in tension, damaged concretes show an increased non-linearity and a more gradual softening. However, it was found that the modifications in the mechanical properties cannot be directly associated with a level of expansion, as the behavior depends on the component materials and mechanisms involved in the reaction.

The Temperature Effect on the Reflective Cracking of Asphalt Overlays

ABSTRACT This paper presents a study about the influence of temperature on the reflective cracking in a flexible road pavement through the evaluation of the asphalt overlay damage associated to traffic and temperature variations throughout a year. This study was developed from a numerical simulation of the asphalt overlay behaviour based on a three-dimensional finite-element analysis, considering the simultaneous loading of traffic and temperature variations. A mechanistic-based overlay design method was used to predict the reflective cracking overlay life. Climatic temperature variations in pavements lead to an increase of the reflective cracking phenomenon, due to the stress and strain states created by temperature, resulting in the premature distress of the asphalt overlay. This study also intends to establish a comparison between the expected performance of asphalt rubber hot mixes and conventional asphalt overlays.

Use of Slab Curvature and ProVAL to Identify the Cause of Premature Distresses

It has been argued that dynamic traffic loading due to the presence of a nonflat pavement shape may result in accelerated deterioration of the pavement because of higher stresses in the slab from restrained curling–warping movement. Slab curvature, though imperceptible to the naked eye, usually develops on the riding surfaces of the individual slab segments after construction. Select case studies on high- and low-altitude Bolivian concrete highways illustrate the magnitude of curvatures that are generated. The Butterworth high-pass and spectral density analysis tools in the ProVAL software are used to identify the pavement slab curvature in these projects. A mechanistic analysis is used to ascertain the causes of the observed longitudinal cracking. By resorting to a newly developed curvature index, the second-generation curvature index, the equivalent temperature gradient that corresponds to the fitted curvature was included in a finite element method analysis to determine stresses in the slabs. It is concluded that the curved shape of the slabs resulting from permanent curling–warping coupled with traffic loading is inducing excessive stresses and causing the observed cracking distress in one of the evaluated highways.

Subsurface Drainage and Premature Distresses in Concrete Pavement

Field and laboratory forensic investigations were used to identify the failure mechanism of a jointed plain concrete pavement with a subsurface drainage system in Virginia. Similar to many states' practice, this subsurface drainage system consists of open-graded drainage layer and edge drains to provide positive drainage for the pavement. The investigation included a review of construction practices and pavement performance records, a visual distress survey, nondestructive testing using a falling weight deflectometer, roughness measurements using a profiler, coring and boring for materials testing, observation wells, subgrade soil classification, mineralogy, determination of concrete compressive strength, edge drain camera inspection, and slab removal. On the basis of the investigation, it was concluded that lack of positive drainage along with heavily loaded truck traffic resulted in premature failure. The water entering the pavement because of poor joint sealing was trapped in the open-graded drainage layer; this led to severe faulting, midslab cracks, pumping, and eventual failure of the pavement.

Development and evaluation of a field permeameter as a longitudinal joint quality indicator

Intrusion of water through longitudinal joints can cause premature distress in hot mix asphalt (HMA) pavements. Similar to mat permeability, joint permeability is a critical factor governing the performance of HMA pavements. Hence, joint permeability should be used as a measure of quality of joint construction. In this ongoing study, a simple and effective permeameter has been developed, and used in a rational method to evaluate the permeability of longitudinal joints, relative to the permeability of the adjacent mat. The permeameter consists of three standpipes, which can be used for measuring the flow of water through a joint and through the mat on either side of the joint. Results from testing on several projects show that this permeameter can be used successfully to determine permeability of joints. The testing performed in this study shows that joints have significantly higher permeability compared to adjacent mats, different types of joints have different permeabilities and that treatment of joints with sealers and using improved joint construction techniques such as joint heater can reduce the permeability significantly. More testing of joints is being carried out, with the objective of developing specific criteria for using the joint permeameter for quality control of construction of longitudinal joints.

Guide for Investigating and Remediating Distress in Flexible Pavements: California Department of Transportation's New Procedure

In 2001, the California Department of Transportation (Caltrans) initiated a 3-year, $7 million project with MACTEC, Inc. The project included on-call flexible pavement consulting services to Caltrans in the areas of new products, asphalt rubber, modified binders, moisture sensitivity, failure investigations, independent quality assurance, training, laboratory testing, pavement maintenance, pavement rehabilitation, and asphalt recycling. One of the key tasks of the project was to develop a comprehensive guide and a detailed procedure to investigate flexible pavement distresses and develop cost-effective remedies and repair strategies. The emphasis of the procedure is on addressing premature distress and certain problems that might arise during pavement construction. The guide contains two manuals: (a) an office manual that describes the types of flexible pavement distress, identifies the factors that affect distress and performance, and provides tools that can be used to characterize distress condition, determine likely causes, and generate a corrective solution and (b) a field manual for use in the field by experienced engineers familiar with the new tools and requiring little instruction on its application. The principles presented in the guide are based on modern pavement engineering technology and are applicable to the practices of many federal, state, and local agencies. The process presented in the guide is summarized, and several of the new tools that have applicability to other agencies are described.

Active Crack Control for Continuously Reinforced Concrete Pavements

Continuously reinforced concrete pavements (CRCP) traditionally have been allowed to crack naturally. This type of passive crack control has resulted in nonuniform crack spacing, which has led to premature distress development. Although the accuracy of the mean crack spacing prediction has greatly improved, punchout and spalling distresses on CRCP have been found to occur primarily at locations of small crack spacing, divided cracks, cluster cracks, and Y-cracks. The findings of previous research results on active crack control for CRCP in Texas are presented, along with the results from recent full-scale test sections constructed at the University of Illinois. The active crack control process used two systems: automated tape insertion and early entry saw cut. Active crack control was found to eliminate crack meandering, Y-cracks, divided cracks, and cluster cracking. The active crack control sections also propagated 90% of the cracks in the first month after construction, whereas the passive crack sections took 18 months to reach a similar number of cracks. Both active and passive cracks propagated only in the winter months. Crack opening measurements showed that active crack control resulted in slightly smaller movements relative to the natural crack sections. By using active crack control on CRCP, more uniform, straighter, and early-age transverse cracks result, which will increase the expected service life of CRCP.

Evaluation of Premature Deterioration of Concrete Bridge Barriers by Petrographic Examination

Many of the current-generation concrete bridge barriers used in Michigan have deteriorated at a rate greater than expected. For an assessment of the possible causes of this premature distress with the objective of alleviating future occurrences, sixteen core specimens from eight sites constructed between 1983 and 2001 were evaluated. The evaluation included visual inspection, stereo and petrographic optical microscopy, and scanning electron microscopy. The major observations revealed through this analysis were that poor consolidation, marginal air-void systems, alkali-silica reaction associated with chert and siltstone in the fine aggregate, corrosion of reinforcing steel, and possibly frost susceptibility of fine siltstone aggregates were responsible for the deterioration. These results provide the basis for improving the quality of such barriers in future construction.

Pavement Evaluation and Rehabilitation Design Methodology Currently Used on Low-Volume Roads in Southern Africa

A pavement evaluation and rehabilitation design methodology is currently employed in southern Africa on relatively light pavement structures used for low-volume roads. The pavements normally consist of natural gravel materials in most layers and thin bituminous surfacings. When nearing the end of their design lives, they exhibit distresses ranging from minor deformation through aging of the surface to structural cracking and potholes. Rehabilitation options normally involve light stone seals or other inexpensive and cost-effective treatments. The phases of investigation for pavement evaluation and rehabilitation designs start with desk study to establish the history of the road and its past performance from pavement management system outputs. Detailed visual evaluations are then conducted of road features and extent of various forms of distress. These data are presented followed by a decision-making process to select areas for more detailed testing. All the information is used to determine the causes of distress and likely rehabilitation alternatives. Further destructive and nondestructive testing is carried out to predict performance of rehabilitation designs and equivalent annual cost comparisons. Rehabilitation design is also done with use of the dynamic cone penetrometer. Decision criteria are set for use of tests undertaken in the assessments, and test results are evaluated. This procedure normally results in a wide range of rehabilitation options, from application of a diluted emulsion as a surface rejuvenator to more extensive patching and resealing to major rehabilitation and overlays. This process effectively produces cost-effective solutions that maximize limited budgets. It is essential that the road authority be prepared to share the risks of the low-cost options with the designer. In this way benefits of low-cost solutions are realized, whereas, in a limited number of instances, premature distress may have to be repaired under routine maintenance.

Using Pavement Distress Data to Assess Impact of Construction on Pavement Performance

Most state highway agencies specify incentives, disincentives, or acceptance criteria based on one or more attributes that can be measured during or immediately after construction (smoothness, early completion of construction, and nuclear density). In many scenarios in which contractors were awarded incentives, the pavement showed premature distress after construction. Furthermore, the magnitude of the incentive or disincentive is typically determined on the basis of intuition and past practice, without assessing the effect of the incentive’s attribute on pavement performance. In a study sponsored by the Michigan Department of Transportation (MDOT) and conducted by the Pavement Research Center of Excellence at Michigan State University, the impact of segregation on pavement performance was assessed, and an expedient test to detect segregation was developed so that MDOT could establish incentives, disincentives, or acceptance criteria. The study included 17 segregated pavement projects and 2 nonsegregated projects. Two types of segregation-related distress were observed: raveling, which was observed on 11 projects, and cracking, which was observed on 7 projects. Three projects showed both raveling and cracking. For each project, the raveled areas and the length of the cracks were measured over time, and their rates of growth were assessed. On the basis of the results, the reductions in the pavement service life due to raveling and cracking were estimated. It is shown that areas with heavy and medium degrees of segregation experience on average 73 and 56 percent reduction in pavement service life, respectively, due to raveling and 46 percent due to segregation-related cracks.

A REVIEW ON ABSORPTION OF ASPHALT INTO POROUS AGGREGATES I PHYSICOCHEMICAL MECHANISMS AND VARIABLES AFFECTING ABSORPTION

ABSTRACT Absorption is the process in which asphalt flows into a porous aggregate, under the driving force of capillary pressure. Asphalt absorption is of interest because it represents an economic loss of effective binder, and because it may change the properties of the resulting asphalt film and lead to premature pavement distress. Incorrect air voids estimation may also result from failure to properly account for asphalt absorption in pavement design. The present review of asphalt absorption is divided into two parts. In part I of the review we have examined the literature over the past 70 years to determine the practical consequences of asphalt absorption, its fundamental physicochemical mechanims, and the influence of asphalt and aggregate properties on the process. Our review shows a need for additional fundamental research if the complex absorption phenomena is to be adequately understood and modeled.

ABSORPTION OF ASPHALT INTO POROUS AGGREGATES: TEST OF A SIMPLE PHYSICOCHEMICAL MODEL

ABSTRACT Absorption is the process in which asphalt flows into a porous aggregate, under the driving force of capillary pressure. Asphalt absorption is of interest because it represents an economic loss of effective binder, and because it may change the properties of the resulting asphalt film and lead to premature pavement distress. Incorrect air voids estimation may also result from failure to properly account for asphalt absorption in pavement design. The objective of this research was to determine the temporal dependence of absorption upon asphalt and aggregate properties and to test a rational model for this dependence. Absorption data were obtained for several model liquids and asphalts with synthetic alumina aggregates and a natural limestone aggregate. The data were used to test a simple absorption model incorporating the effects of asphalt and aggregate properties into a single dimensionless time variable. While quantitative agreement was not obtained in all aspects of the model, certain predicti...

Alterations in Circulating Human Chorionic Gonadotropin Freeα-Subunit in Insulin-Dependent Diabetic Pregnancy: Correlation with Maternal Characteristics*

Circulating concentrations of hCG free alpha-subunit (alpha hCG) increase throughout pregnancy. To address the hypothesis that maternal plasma alpha hCG may reflect placental dysfunction and/or adverse perinatal outcome during insulin-dependent diabetic pregnancy, alpha hCG was measured serially throughout gestation, beginning before week 12, with a specific RIA using a monoclonal antibody in 54 insulin-dependent diabetic (randomly assigned to strict and customary glycemic control) and 25 nondiabetic pregnancies. alpha hCG was significantly lower in pregnant insulin-dependent diabetic subjects than in nondiabetics subjects until 24 weeks gestation, after which it was higher until delivery. Plasma alpha hCG stabilized in nondiabetics at 32 weeks, whereas it continued to increase in diabetics until delivery, at which time it was 37% greater than that in nondiabetics (mean +/- SE, 1441 +/- 90 vs. 1052 +/- 78 micrograms/L; P less than 0.002). Values in diabetic subjects assigned to strict control were intermediate between those in diabetic subjects assigned to customary control and nondiabetic subjects. alpha hCG was greater in diabetic subjects with pregestational hypertension or microvascular disease, but not in those with pregnancy-induced hypertension. These findings were independent of the assigned goals of glycemic control. alpha hCG was not correlated with the duration of diabetes or related to premature delivery, fetal distress, birth asphyxia, or macrosomia. Thus, alpha hCG is increased during the third trimester of the type I diabetic pregnancy and is associated with preexisting hypertension and maternal microangiopathy, but is not a predictor of adverse perinatal outcome. Excessive alpha hCG secretion in diabetes may share pathophysiological mechanisms in common with those underlying diabetic microangiopathy.

Intracranial hemorrhage in low-birth-weight twins during neonatal period.

Since twins have a higher incidence of premature birth, fetal distress, asphyxia and other pre- and intrapartum high-risk factors, it is reasonable to expect that they may be vulnerable to intracranial hemorrhage. Forty-seven pairs of low-birth-weight twins were studied during the newborn period by serial cranial ultrasound. The comparisons of groups, based on birth order, relative size of the neonates, and the mode of delivery, showed no significant differences in the incidence of intracranial hemorrhage between first and second twins, smaller and larger twins, or vaginal and cesarean delivery. However, the comparison based on the presentation of the infant revealed a significantly higher number of intracranial hemorrhages within the first week of life in the breech group than in the cephalic presentation group. The adverse effect of breech presentation on intracranial hemorrhage did not appear to be mediated by the well recognized risk factors such as lower gestational age, lower Apgar scores, and higher incidence of respiratory distress syndrome and assisted ventilation. Since most of the twins with ICH had breech presentation and were delivered by cesarean section, this mode of delivery does not seem to protect the twins with breech presentation from intracranial hemorrhage.

Bile acids in maternal serum, umbilical cord serum and amniotic fluid of healthy women, women with pruritus and patients with intrahepatic cholestasis of pregnancy

SummaryCholic acid (CA), chenodeoxycholic acid (CDCA) and deoxycholic acid (DCA) concentrations were measured by radio-immunoassays in control subjects, in women with pruritus in pregnancy without an apparent liver disorder and in patients with intrahepatic cholestasis of pregnancy. In controls and in women with pruritus, primary bile acid (CA and CDCA) levels were higher (P < 0•01) in fetal cord serum than in maternal serum. In patients with intrahepatic cholestasis of pregnancy, CA and CDCA levels were 2-10 times higher in all compartments than in controls, except for the levels of CDCA in the amniotic fluid, which did not differ. In patients with cholestasis of pregnancy, there were more cases of fetal distress, earlier delivery times (P <0•01) and lower Apgar scores than in the controls, but no direct correlations were found between the bile acid concentrations in any of the compartments and premature delivery, fetal distress or excessive blood loss at the confinement. Only very high levels of primary...

Effect of terbutaline on the human fetal placental circulation.

The effect of terbutaline, a beta2-adrenoceptor stimulator, on the vascular resistance of isolated human placenta was examined. Terbutaline produced no change in basal placental vascular resistance, but when the placental vessels were constricted with angiotensin, terbutaline produced a graded decrease in vascular resistance. The vasodilating effect of a high dose of terbutaline was smaller than the effect 20 microgram of isoprenaline and the effect was significantly blocked by propranolol, a beta-adrenoceptor antagonist. The results suggest that the vasodilating effect of terbutaline on the fetal placental circulation can play a role in the improvement of fetal condition during treatment of premature labour and intrapartum fetal distress.