Measurements of moisture suction in hot mix asphalt mixes

The presence of moisture in hot mix asphalt (HMA) causes loss of strength and durability of the mix, which is referred to as moisture damage. This study deals with the development of experimental methods for measuring total suction in HMA, which can be defined as the free energy state of water in HMA mixes. The total suction is related to the ability of moisture to get into the mix under unsaturated conditions; it is also related to the ability of the mix to retain moisture. Soil suction has been studied extensively. However, suction in HMA as a porous material and its relationship to moisture damage have not been studied. The development of a procedure to measure the total suction in HMA mixes is the first objective of this research. The second objective is to relate suction measurements to physical and chemical properties of the mixtures. The objectives were achieved in two phases. In the first phase, the total suction was measured in HMA specimens with different types of aggregates (limestone and granite), and with different air void distributions and aggregate gradations. The results of this phase showed that the drying test using a 60 oC temperature-controlled room is the proper setup for measuring the total suction in HMA using thermocouple psychrometers. The characteristics of suction-moisture content curves were found to be related to the air void distribution in HMA. In the second phase, total suction was measured in sand asphalt specimens. These specimens had different combinations of aggregates and binders with different bond energies and exhibited different field performance in terms of resistance to moisture damage. The suction measurements in sand asphalt specimens were used to calculate the moisture diffusion coefficient. The results revealed that water diffused into sand asphalt specimens that are known to have poor resistance to moisture damage faster than those that are known to have good resistance to moisture damag

Compaction Effects on Uniformity, Moisture Diffusion, and Mechanical Properties of Asphalt Pavements

Field compaction of asphalt mixtures is an important process that influences performance of asphalt pavements; however there is very little effort devoted to evaluate the influence of compaction on the uniformity and properties of asphalt mixtures. The first part of this study evaluated relationships between different field compaction patterns and the uniformity of air void distribution in asphalt pavements. A number of projects with different asphalt mixture types were compacted, and cores were taken at different locations from these projects. The X-ray Computed Tomography (X-ray CT) system was used to capture the air void distributions in these cores. The analysis results have revealed that the uniformity of air void distribution is highly related to the compaction pattern and the sequence of different compaction equipment. More importantly, the efficiency of compaction (reducing air voids) at a point was found to be a function of the location of this point with respect to the compaction roller width. The results in this study supported the development of the "Compaction Index (CI)," which quantifies the degree of field compaction. The CI is a function of the number of passes at a point and the position of the point with respect to the compaction roller width. This index was found to correlate reasonably well with percent air voids in the pavement. The CI calculated from field compaction was also related to the slope of the compaction curve obtained from the Superpave gyratory compactor. This relationship offers the opportunity to predict field compactability based on laboratory measurements. The compaction of longitudinal joints was investigated, and recommendations were put forward to improve joint compaction. The air void distributions in gyratory specimens were related to the mixture mechanical properties measured using the Overlay and Hamburg tests. The second part of this study focused on studying the relationship between air void distribution and moisture diffusion. A laboratory test protocol was developed to measure the diffusion coefficient of asphalt mixtures. This important property has not measured before. The results revealed that the air void phase within the asphalt mixtures controls the rate of moisture diffusion. The measured diffusion coefficients correlated well with the percent and size of connected air voids. The measured diffusion coefficient is a necessary parameter in modeling moisture transport and predicting moisture damage in asphalt mixtures. The last part of this study investigated the resistance of asphalt mixtures with different percent air voids to moisture damage by using experimental methods and a fracture mechanics approach that accounts for fundamental material properties

State of the Art Study on Aging of Asphalt Mixtures and Use of Antioxidant Additives

The detrimental effects of hardening in asphalt pavements were first recognized by pioneering pavement engineers in the 1900s and have been studied extensively during the last 70 years. This hardening process, referred to as asphalt aging, is generally defined as change in the rheological properties of asphalt binders/mixtures due to changes in chemical composition during construction and its service life period. Aging causes the asphalt material to stiffen and embrittle, which affects the durability and leads to a high potential for cracking. This paper presents the state of the art on asphalt and asphalt mixture aging and use of antioxidant additives to retard the aging. A picture of complex molecular structure of asphalt and its changes due to atmospheric condition and various protocols used to simulate aging in laboratory environment are also discussed. Emphasis is given on recent studies on simulation of aging of asphalt mixtures as there has been limited research on mixtures compared to the asphalt binder. Finally, this paper presents the application of antiaging techniques and its mechanism, use of various types of antioxidant additives to retard aging of asphalt and, hence, improve the performance of asphalt pavements.This paper was made possible by the NPRP grant (NPRP 6-773-2-320) from the Qatar National Research Fund (a member of Qatar Foundation)

EFFECT OF COMPOST, BIO AND NPK FERTILIZATION ON ESSENTIAL OIL PRODUCTION OF YARROW FLOWERING TOPS, ACHILLEA MILLEFOLIUM, L.

The effects of compost (5, 7.5 and 10 ton/fed), NPK (50, 75 and 100%) and/or Effective micro-organisms/Minia Azotein fertilization on plant height, number and dry weight of flowering tops/plant and essential oil productivity (% and yield/plant) were investigated during 2012/2013 and 2013/2014 at the experimental farm, Fac. of Agric., Minia Univ. All treatments of compost significantly increased, plant height, number and dry weight of flowering tops/plant, as well as, essential oil percent and yield/plant. The high level of compost was more effective in this concern. The used of mineral NPK (100%) followed by 75% NPK + E.M. + M.A. treatments were the best results in increasing all previous characters. Generally supplying yarrow plants with compost at the rate of 10 ton/fed and fertilizing plants with NPK (100%) or reduce dose at (75% NPK) plus E.M. + M.A. gave overall the highest values of previous traits

Operational Safety of Gravel Roads in Rural and Tribal Communities: Vulnerability to Structural Failures and GeoHazards

Of the 4.1 million miles of federal and state highways in the U.S., 2.2 million miles (or 54%) are unpaved, gravel roads. In the Pacific Northwest and Alaska, unpaved gravel roads provide critical transportation access, with some communities relying on just a single highway for access into and out of town. In such cases, these highways become a critical component of the infrastructure, and there is a need to ensure that safe access is always available to the communities. The Idaho highway database has been used to identify unpaved, gravel roads in Idaho that are critical for access to rural communities. Once identified, information regarding their existing condition has been used to assess their vulnerability and other impacts. The results of this study are considered an initial evaluation that relies on information that is readily available in the database. The project outcomes include a comprehensive literature review of unpaved roads including data produced from field visits. In addition, a questionnaire survey was sent to local jurisdictions authorities for investigating locations, reasons of road closures, and population size of the affected communities. Finally, 37 responses have been received by the research team indicating five rural communities that have experienced closures and isolation. The reasons for the closure of the unpaved roads were due to the lack of funding for snow removal, excessive dirt, unstable gravel roads, tornados, and heavy rains. The location of those communities was spread across the state of Idaho with corresponding populations range from 25 to 8,500 people

Development of a Correlation between CoreLok and AASHTO T 85 Tests for Specific Gravity of Coarse Aggregates used in Idaho

UI-20-01Specific gravity and absorption values of coarse aggregates are typically measured in accordance with the AASHTO T 85 standard. The test requires considerable experience to recognize the stage when a soaked sample reaches the saturated surface dry (SSD) condition upon drying. The CoreLok device offers an alternative approach which can be completed in less than 45 minutes compared to the 24 hours required by the AASHTO procedure. This study investigated the results from AASHTO T 85 and CoreLok testing of coarse aggregates to develop a correlation between bulk (dry) specific gravity (Gsb) values measured using the two test procedures. Blended samples, consisting of coarse and fine aggregates, were also tested to evaluate the use of the CoreLok method to reliably determine Gsb values. After testing 15 coarse aggregates and 17 blended aggregates, this study developed three equations that may be used to modify the CoreLok Gsb results to more closely reflect Gsb values based on AASHTO T 85 tests. The recommended equation uses the CoreLok Gsb and the fine aggregate percentage to predict the equivalent AASHTO T 85 Gsb with an R2 = 0.967. Furthermore, five reclaimed asphalt pavement (RAP) materials were also tested to see if the Gsb of the uncoated aggregate could be determined using the CoreLok method. Preliminary results indicate that the CoreLok Gsb results can be reliably calculated if the effective and absorbed binder content is known, or presumed, based on experience

Development of Gyratory Stability Index to Evaluate Variation of RAP Content and Rutting Resistance of Asphalt Mixtures

UI-19-03ITD Research Report RP 175 developed an algorithm for determining a Gyratory Stability (GS) for asphalt mixtures based on the Servopac gyratory compactor. The GS describes the ability of asphalt mixtures to resist rutting, and it can be determined during the mix design stage using the gyratory compaction data. This study developed a modified algorithm for GS applicable to Pine Gyratory compactor model AFG2AS which is used by ITD districts. In addition, this study investigated the use of the GS, other gyratory compaction indices, and performance tests to detect the variations in mix composition. The researchers prepared and tested laboratory-mixed laboratory-compacted (LMLC) mixes and plant-mixed laboratory-compacted (PMLC) mixes obtained from new paving projects

Burnout among surgeons before and during the SARS-CoV-2 pandemic: an international survey

Background: SARS-CoV-2 pandemic has had many significant impacts within the surgical realm, and surgeons have been obligated to reconsider almost every aspect of daily clinical practice. Methods: This is a cross-sectional study reported in compliance with the CHERRIES guidelines and conducted through an online platform from June 14th to July 15th, 2020. The primary outcome was the burden of burnout during the pandemic indicated by the validated Shirom-Melamed Burnout Measure. Results: Nine hundred fifty-four surgeons completed the survey. The median length of practice was 10 years; 78.2% included were male with a median age of 37 years old, 39.5% were consultants, 68.9% were general surgeons, and 55.7% were affiliated with an academic institution. Overall, there was a significant increase in the mean burnout score during the pandemic; longer years of practice and older age were significantly associated with less burnout. There were significant reductions in the median number of outpatient visits, operated cases, on-call hours, emergency visits, and research work, so, 48.2% of respondents felt that the training resources were insufficient. The majority (81.3%) of respondents reported that their hospitals were included in the management of COVID-19, 66.5% felt their roles had been minimized; 41% were asked to assist in non-surgical medical practices, and 37.6% of respondents were included in COVID-19 management. Conclusions: There was a significant burnout among trainees. Almost all aspects of clinical and research activities were affected with a significant reduction in the volume of research, outpatient clinic visits, surgical procedures, on-call hours, and emergency cases hindering the training. Trial registration: The study was registered on clicaltrials.gov "NCT04433286" on 16/06/2020

Deterioration of Green Conflict Paint for Bicycle Facilities

Bicyclists depend on the visibility of the surrounding environment to maintain a safe travel path. Throughout the country, new types of bicycle infrastructure and pavement markings are being installed. This study used a new procedure to evaluate different pavement markings used in bike lanes. Three different paints were evaluated, including green waterborne paint, green liquid methacrylate paint, and white thermoplastic paint. The deterioration of these materials was tested under different conditions to simulate wear from motorized vehicles and street equipment. Surface polishing (i.e., repeated passing over the material) was examined under pneumatic tires, steel wheels, and steel scraper blades. Different characteristics were measured, including durability, retroreflectivity, color changes, and friction of the test materials. The results demonstrated that the procedure used in this study was able to evaluate different materials in a shorter time than field evaluation, which often can take years to complete. As expected, = retroreflectivity decreased with the number of polishing cycles. Overall, there was a significant decrease in percentage of retroreflectivity after 1,000 cycles for all testing conditions before retroreflectivity reached a terminal value. These results were consistent with field observations. A logarithmic model was found to describe the change in the retroreflectivity versus the number of loading cycles with high R2-values. The methacrylate paint experienced the lowest color loss, even after 100,000 cycles, irrespective of the exposure and the testing conditions. It is believed that the small reduction in color was due to the presence of chemicals coupled with the thicker paint of the methacrylate materials in comparison to the thickness of the waterborne materials. The durability results demonstrated that the waterborne markings peeled off the surface with increasing numbers of polishing cycles.US Department of Transportation Pacific Northwest Transportation Consortium University of Idah

Evaluation of Adhesion and Hysteresis Friction of Rubber–Pavement System

Tire-pavement friction is a key component in road safety. Adhesion and hysteresis are the two main mechanisms that affect the friction between rubber tires and pavements. This study experimentally examined the relationship between rubber–pavement adhesion and friction. The adhesive bond energy between rubber and pavement surfaces was calculated by measuring the surface energy components of rubber and aggregates. The friction was measured in the laboratory using a dynamic friction tester. The results revealed that there is a fair correlation between the adhesive bond energy and measured coefficient of friction. A rubber–pavement system with higher adhesion provided higher friction at low speed. In addition, the results demonstrated that there is a strong correlation between rubber–pavement friction and rubber properties. Softer rubber provided higher friction and vice versa. The results of this study provide an experimental verification of the relationship between adhesion and pavement surface friction. The adhesive bond energy and rubber rheological properties could be incorporated in computational models to study tire-pavement friction in different conditions (e.g., speed and temperature)