Joint Deterioration in Concrete Pavements

Concrete pavements located in cold climates have been experiencing premature joint deterioration. Entrapment of moisture in the joints saturates the surrounding concrete, rendering it susceptible to freeze-thaw damage. To identify and to isolate the variables that might be causing this localized deterioration, concrete cores were obtained from deteriorated and non-deteriorated sections of US 35, SR 38 and SR 3 located near Indianapolis, Indiana and I-94 (located near Michigan City, Indiana). The visual evaluation of the condition of the pavement revealed that the drainage of the joints contributes significantly to their performance. Specifically, all deteriorated joint core holes drained poorly when compared to well performing joint core holes or mid panel joint core holes. Hardened air void parameters were determined following the procedure described in ASTM C457 and results for cores from deteriorated and non-deteriorated regions of the pavements were compared. The chemical and microstructural changes occurring in concrete were investigated using scanning electron microscope. Concrete panels with poor values of spacing factor and specific surface area were more prone to premature joint deterioration. Visual observation of coring sites on I-94 showed that unsealed joints performed better than sealed joints

Investigation of Use of Slag Aggregates and Slag Cements in Concrete Pavements to Reduce the Maintenance Cost

The air-cooled blast furnace slag (ACBFS), the by-product of the pig iron making process, is often used as coarse aggregate in portland cement concrete (PCC) pavements, especially in the areas located in the vicinity of the iron mills. The utilization of this by-product as an aggregate in concrete offers environmental and economic benefits in the form of elimination of waste, decrease in the disposal costs, and reduction in need for mining of the natural materials. However, concerns exist with relation of the influence of these aggregates on the long-term durability of pavement concretes, especially at locations exposed to freezing and thawing environment. The objective of this research was to evaluate the influence of using the ACBFS aggregate (slag aggregate) as a replacement for natural aggregates on the properties of pavement concrete designed to meet the standard specifications of the Indiana Department of Transportation. A total of eight different concrete mixtures, four containing air-cooled blast furnace slag (ACBFS) as coarse aggregate and additional four containing natural dolomite, were used in this study. These mixtures included plain concrete mixture (100% of Type I portland cement), two mixtures with binary binder systems (one containing 20 wt.% of Class C fly ash + 80 wt.% of Type I portland cement and the other containing 25 wt.% slag cement + 75 wt.% of Type I portland cement) and one mixture with a ternary binder system (23% slag cement + 17% of Class C fly ash + 60% of Type I portland cement). Specimens produced from each of these mixtures were ponded with each of the three different types of chloride based deicers (CaCl2, MgCl2 and NaCl) while being subjected to either freezing-thawing (FT) cycles or wetting-drying (WD) cycles. The mechanical and durability properties of these concretes were assessed by conducting series of tests prior and after the exposure to FT and WD cycles. In addition, changes in the overall physical appearance of the test specimens were also documented to aid in the evaluation of the effects of given exposure conditions on the deterioration process of concretes. In the case of a plain concrete, the analysis of the data collected during the study (i.e. the observed loss of strength, reduction in the dynamic modulus of elasticity, and physical changes in the appearance of the specimens) indicated that the calcium chloride (CaCl2) deicer caused the most severe distress, followed by the magnesium chloride (MgCl2). Specimens exposed to sodium chloride (NaCl) experienced the least damage and performed comparably to those exposed to distilled water (DST). The scanning electron microscopy studies of the microstructure revealed the presence of deposits of Friedel’s salt and zones of chloride rich C-S-H in all concretes used in this project, irrespective of the type of deicer the specimen was exposed to. The deposits of brucite (Mg(OH)2) and of magnesium-silicate hydrate (M-S-H) were found in specimens exposed to MgCl2 while calcium oxychloride was detected in concretes exposed to CaCl2 under FT conditions. The use of either Class C fly ash, slag cement or the combination of both as part of the binder was found to greatly increase the resistance of concrete to damaging effects of deicers

Concrete Pavement Joint Deterioration

Concrete pavements are an important part of our national infrastructure. In recent years the relatively small number of reported joints deteriorating prematurely in concrete pavements around Indiana has increased. Changes over the past 45 years in INDOT specification, pavement materials, designs and construction practices, and current de-icing materials were examined and related to the durability of concrete at the joints of existing pavements. A survey of concrete pavements across the state revealed that no pavements from the two southern districts less than 40 years old showed this distress except in more recently placed patches. Cores were retrieved from the joints and mid-panel of 11 pavement sections that represented different materials, ages, construction, deicer exposure, and different levels of deterioration, from non-deteriorated concrete to concrete with severe deterioration at the joints. The pavement base drained well at the mid-panel of most pavements but was reduced at the joints for over half the pavements with the most severe joint deterioration associated with the slowest drainage. None of the concrete had an air void system that met all the criteria recommended for FT durable concrete but was better at the mid-panel than at the joints. Infilling and lining of the entrained air voids with ettringite and some Friedel’s salt was more common near the joints and could account for the reduced air void system. The FT testing did not correlate directly with the air void parameters but generally mid-panel samples did test as more durable than joints. Evidence from the presence of unhydrated cement grains suggested that the concrete at the joint face was not fully cured. One pavement section that did not have fly ash had worse deterioration than the panels nearby that had fly ash and calcium hydrate was more noticeable in the concrete from joints with severe deterioration. Several variables were identified that influence the durability of the concrete at the joints and there may be other variables that were beyond the scope or capacity of this study. In summary this study identified the following variables likely influenced the durability of the concrete at the joints: the drainability of the base at the joints, original air void system, reduced air void parameters due to lining and infilling of the air voids with secondary minerals, poor hydration of the concrete at the joint face and increased moisture at the joint

Synthesis: Accelerating Implementation of Research Findings to Reduce Potential Concrete Pavement Joint Deterioration

Distress has recently been observed in the joints of some concrete pavements, primarily in the wet-freeze states. This distress often begins in longitudinal joints, followed by transverse joints and results in the significant loss of material from the joint area. Although it may only affect approximately 10% of the concrete pavements system-wide, it greatly reduces the service life and increases maintenance costs of the pavements it effects. Primary issues that emerged from studies on this phenomenon include the importance of the timing of joint sawing, the width of the joint opening, degree of concrete or joint sealing, drainage and degree of saturation of the concrete at the joint, quality of the air void system, role of deicing chemicals, quality of curing, and the degree of restraint at the joint. Although this broad collection of issues implies that we still lack complete understanding of all causes of joint deterioration, it also makes it pretty clear that the observed damage is a result of combination of several factors. This study synthesizes completed research related to concrete pavements joint deterioration and provides information to advance the knowledge and understanding of the variables involved in in this deterioration process and suggests the best practices that can lead to its reduction or mitigation

A multinuclear solid state NMR, density functional theory and X-Ray diffraction study of hydrogen bonding in Group I hydrogen dibenzoates

An NMR crystallographic approach incorporating multinuclear solid state NMR (SSNMR), X-ray structure determinations and density functional theory (DFT) are used to characterise the H bonding arrangements in benzoic acid (BZA) and the corresponding Group I alkali metal hydrogen dibenzoates (HD) systems. Since the XRD data often cannot precisely confirm the proton position within the hydrogen bond, the relationship between the experimental SSNMR parameters and the ability of gauge included plane augmented wave (GIPAW) DFT to predict them becomes a powerful constraint that can assist with further structure refinement. Both the 1H and 13C MAS NMR methods provide primary descriptions of the H bonding via accurate measurements of the 1H and 13C isotropic chemical shifts, and the individual 13C chemical shift tensor elements; these are unequivocally corroborated by DFT calculations, which together accurately describe the trend of the H bonding strength as the size of the monovalent cation changes. In addition, 17O MAS and DOR NMR form a powerful combination to characterise the O environments, with the DOR technique providing highly resolved 17O NMR data which helps verify unequivocally the number of inequivalent O positions for the conventional 17O MAS NMR to process. Further multinuclear MAS and static NMR studies involving the quadrupolar 7Li, 39K, 87Rb and 133Cs nuclei, and the associated DFT calculations, provide trends and a corroboration of the H bond geometry which assist in the understanding of these arrangements. Even though the crystallographic H positions in each H bonding arrangement reported from the single crystal X-ray studies are prone to uncertainty, the good corroboration between the measured and DFT calculated chemical shift and quadrupole tensor parameters for the Group I alkali species suggest that these reported H positions are reliable

Economic Model of a Birth Cohort Screening Program for Hepatitis C Virus

Recent research has identified high hepatitis C virus (HCV) prevalence among older U.S. residents who contracted HCV decades ago and may no longer be recognized as high risk. We assessed the cost-effectiveness of screening 100% of U.S. residents born 1946-1970 over 5 years (birth-cohort screening), compared with current risk-based screening, by projecting costs and outcomes of screening over the remaining lifetime of this birth cohort. A Markov model of the natural history of HCV was developed using data synthesized from surveillance data, published literature, expert opinion, and other secondary sources. We assumed eligible patients were treated with pegylated interferon plus ribavirin, with genotype 1 patients receiving a direct-acting antiviral in combination. The target population is U.S. residents born 1946-1970 with no previous HCV diagnosis. Among the estimated 102 million (1.6 million chronically HCV infected) eligible for screening, birth-cohort screening leads to 84,000 fewer cases of decompensated cirrhosis, 46,000 fewer cases of hepatocellular carcinoma, 10,000 fewer liver transplants, and 78,000 fewer HCV-related deaths. Birth-cohort screening leads to higher overall costs than risk-based screening ($80.4 billion versus$53.7 billion), but yields lower costs related to advanced liver disease ($31.2 billion versus$39.8 billion); birth-cohort screening produces an incremental costeffectiveness ratio (ICER) of $37,700 per quality-adjusted life year gained versus riskbased screening. Sensitivity analyses showed that reducing the time horizon during which health and economic consequences are evaluated increases the ICER; similarly, decreasing the treatment rates and efficacy increases the ICER. Model results were relatively insensitive to other inputs. Conclusion: Birth-cohort screening for HCV is likely to provide important health benefits by reducing lifetime cases of advanced liver disease and HCV-related deaths and is cost-effective at conventional willingness-topay thresholds. (HEPATOLOGY 2012;55:1344-1355 H epatitis C virus (HCV) is the most common blood-borne viral infection in the United States, 1 affecting an estimated 3.6 million U.S. residents. 2 The majority of infected individuals develop chronic hepatitis; persistent liver injury leads to cirrhosis in 5$5 billion per year, 4 with projected HCV-related societal costs for the years 2010-2019 estimated to total $54.2 billion. 5 For the last decade, the standard of care for treating HCV has been the combination of pegylated interferon (Peg-IFN) and ribavirin (RBV), 6 which successfully eradicates virus (sustained virologic response; SVR) in 40%-80% of treated patients

Concurrent La and A-site Vacancy Doping Modulates the Thermoelectric Response of SrTiO3. Experimental and Computational Evidence

To help understand the factors controlling the performance of one of the most promising n-type oxide thermoelectric SrTiO3, we need to explore structural control at the atomic level. In Sr1–xLa2x/3TiO3 ceramics (0.0 ≤ x ≤ 0.9), we determined that the thermal conductivity can be reduced and controlled through an interplay of La-substitution and A-site vacancies and the formation of a layered structure. The decrease in thermal conductivity with La and A-site vacancy substitution dominates the trend in the overall thermoelectric response. The maximum dimensionless figure of merit is 0.27 at 1070 K for composition x = 0.50 where half of the A-sites are occupied with La and vacancies. Atomic resolution Z-contrast imaging and atomic scale chemical analysis show that as the La content increases, A-site vacancies initially distribute randomly (x < 0.3), then cluster (x ≈ 0.5), and finally form layers (x = 0.9). The layering is accompanied by a structural phase transformation from cubic to orthorhombic and the formation of 90° rotational twins and antiphase boundaries, leading to the formation of localized supercells. The distribution of La and A-site vacancies contributes to a nonuniform distribution of atomic scale features. This combination induces temperature stable behavior in the material and reduces thermal conductivity, an important route to enhancement of the thermoelectric performance. A computational study confirmed that the thermal conductivity of SrTiO3 is lowered by the introduction of La and A-site vacancies as shown by the experiments. The modeling supports that a critical mass of A-site vacancies is needed to reduce thermal conductivity and that the arrangement of La, Sr, and A-site vacancies has a significant impact on thermal conductivity only at high La concentration