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Project Abstract: Evidence in the literature indicates that the stiffness of the asphalt binder increases and ductility of the binder decreases with oxidative aging. Typically for unmodified asphalt binders an increase in stiffness or decrease in ductility is regarded as detrimental to the fatigue cracking or fracture resistance of the asphalt binder. However, fundamentally the stiffness of the binder and its strength are two different attributes that may not necessarily be related to each other. There is very little information in the literature that relates the fatigue cracking resistance or strength of the asphalt binder to the extent of oxidative aging. This information is not only important to assess the durability and cracking life of asphalt pavements but is also very important in the context of recycled asphalt pavements (RAP). The use of RAP not only reduces the waste produced from milling and removing asphalt pavement layers at the end of their service life, but also reduces the amount of asphalt required for construction of new roadways. In an effort to improve sustainable practices associated with pavement constructions, state DOTs have been gradually increasing the allowable percentage of RAP in new asphalt mixtures over the last two decades. However, the asphalt binder in RAP is highly oxidized and is deemed to susceptible to load related fatigue cracking. The focus of this study is to investigate the affect of asphalt binder oxidation on its fatigue cracking performance. To this end, fatigue cracking resistance of an asphalt binder will be measured at different levels of aging using an standardized glass bead composite. The glass bead composite simulates the stress state that asphalt binders experience in the field, while it excludes aggregate-asphalt binder interactions. Furthermore, this research investigates the effect of aging on fracture properties of an asphalt binder by conducting monotonic fracture tests using a poker chip test geometry. This study also investigates the effect rejuvenators on the fatigue performance of RAP. The findings from this study will provide a better understanding of the RAP long term performance, and also provides an analytic approach for choosing RAP mixture proportions.
Project Objectives: The main objective of this study is to evaluate the affect of aging and use of RAP on the fatigue cracking resistance of asphalt binders at an intermediate temperature. The PI has specialized in measuring the fatigue and healing properties of asphaltic materials using different experimental and analytical tools. To the best of the PIs knowledge there has not been any study to measure these properties at different levels of aging using and stress states similar to what asphalt binders experience in the field. In this study, we will use a standardized glass bead composite to measure the fatigue and healing properties of an asphalt binder at different levels of aging. The glass bead composite simulates the stress state that asphalt binders experience within HMA, while it excludes aggregate-asphalt binder interactions. To age asphalt binders in the laboratory in different levels, two different aging devices will be use: rolling thin film oven (RTFO), and pressure aging vessel (PAV). The RTFO simulates the short-term aging due to construction, and the PAV simulates the long-term aging due to construction and service. Furthermore, to simulate the extended aging, the PAV-aged asphalt binder will be further aged using PAV for the second and third times. Finally to simulate the HMA containing RAP, the RTFO-aged binder will be mixed with the double PAV-aged binder. After aging the binder and fabricating standardized glass bead composites, the mechanical (undamaged, fatigue, and healing) properties of the asphalt binder will be measured. This will include the mechanical properties of asphalt binder at different levels of aging and also mixtures with different percentage of RAP. To analyze the fatigue test results, we will use continuum damage mechanics. This study will also investigate the effect rejuvenators on the fatigue performance of RAP mixtures.
This study also quantifies the amount of aging, and seeks a correlation between amount of aging and the measured mechanical properties. Two-dimensional FTIR mapping will be used to quantify the amount of aging (by measuring the carbonyl area). The FTIR mapping will also provide a tool to examine the extent of co-mingling between the virgin binder (here RTFO-aged) and RAP binder (here double PAV-aged).
Task 3. Quantifying the extent of oxidation (FTIR)This study quantifies the amount of aging after each RTFO or PAV aging. Two-dimensional FTIR mapping will be used to quantify the amount of aging (by measuring the carbonyl area). This data will be later used to find a correlation between the amount of aging and the measured mechanical properties. The FTIR mapping will also provide a tool to examine the extent of co-mingling between the virgin binder (here RTFO-aged) and RAP binder (here double PAV-aged).
Task 4. Fatigue test using a standardized compositeAfter aging the binder, the mechanical properties (viscoelastic and fatigue cracking resistance) of the asphalt binder will be measured at an intermediate temperature. This will include the mechanical properties of asphalt binder at different levels of aging and also mixtures with different percentage of RAP. To measure the fatigue and healing properties of an asphalt binder, we will fabricate standardized asphalt binder-glass bead composite. The glass bead composite simulates the stress state that asphalt binders experience in mixtures, while it excludes aggregate-asphalt binder interactions. Then, we will use a dynamic shear rheometer (DSR) to apply cyclic loads in shear, and to measure fatigue-cracking resistance of the asphalt binder. The test results will be analyzed using continuum damage mechanics. This will allow testing materials at different stress or strain levels, and comparing their performance under a similar loading condition.
Implementation of Research Outcomes:The use of reclaimed asphalt pavement (RAP) in asphalt mixes has significantly increased over the last few years. However, the long-term impact of using high percentages of RAP is not clear. Also, mixes with RAP are often regarded as prone to fatigue cracking. The results from this study indicate that it is possible to carefully design mixes with high RAP content without compromising on durability.
Test method developed: The research study has led to the development of a test method to evaluate fatigue cracking resistance of asphalt binders in a more realistic manner. The information has been shared with other Universities and personnel from the TxDOT. Future work using this test method is anticipated.
Impacts/Benefits of Implementation:One of the findings from this study is that the use of reclaimed asphalt pavement in new mixes does not necessarily negatively impact the fatigue cracking resistance of an asphalt mixture. To this end, we believe that this research is a small but critical step to educate pavement engineers on the appropriate design and use of materials.
Abstract:Austenitic stainless steels are extensively used in mechanical engineering. The machined surface integrity has an essential influence on the stress corrosion cracking (SCC) performance of stainless steels. In this paper, the effects of multi-pass turning on the SCC susceptibility of AISI 304 austenitic stainless steel were investigated by correlating the SCC crack density to the machining-induced surface characteristics in terms of roughness, micro-hardness, and residual stress. In the multi-pass turning, the surface roughness and residual stress were the least after the double pass turning, and the surface micro-hardness was the maximum after the triple-pass turning. The SCC susceptibility was evaluated after SCC tests in boiling MgCl2 solution. The results showed that the weakest SCC sensitivity was observed in double-pass turning 304 stainless steel, while the most susceptible SCC was found in triple-pass turning. Compared with the double-pass turning, the increase in SCC sensitivity of triple-pass turning was attributed to the larger roughness, higher micro-hardness and greater residual tensile stresses.Keywords: multi-pass turning; austenitic stainless steel; roughness; micro-hardness; residual stress; stress corrosion cracking
A first-time exhibitor at NPE, Kaplan Technology Products, Inc. showed off its new FastMeasure product which can "turn your vehicle into a giant measuring wheel." FastMeasure was developed for the paving industry and mounts in trucks, cars, on crack routers, and on concrete saws. Once mounted, the FastMeasure measures the distance the vehicle travels, which helps save time on measuring and estimating. Also on display (and able to be taken for a brief test ride) was the FastMeasure Scooter, which featured the measuring device attached to a motorized scooter as another lightweight option to measure and lay out patching and paving work.
Technical Coatings Inc. showcased its one-of-a-kind high build liquid thermoplastic Plastech at the show. This cold-applied thermoplastic can be applied with a conventional sprayer or airless machines and has a fast dry and cure time. Technical Coatings pitches Plastech as tough and abrasion resistant, with low VOC and high solids, and up to 120-mil buildup. They say it has excellent bead retention, has water and solvent base, and is great for nighttime reflectivity. Other products drawing interest at the Technical Coatings booth included Dura Stripe Aerosol Paint, Sharp Stripe machines, Aerosol Layout Chalk, Stampcrete asphalt and concrete overlays, and Supreme Curb Paint.
WEP Asphalt introduced to visitors at its booth the WEP Wizard crack cleaning tool, which WEP Wizard says was developed for contractors looking for a new way to clean cracks. They say the WEP Wizard is designed to help relieve physical stress and reduce hours spent on crack cleaning. The tool can be used on both concrete and asphalt commercial parking lots and residential driveways. Contractors can buy just the WEP Wizard or the tool and a complete tool kit, which includes a hose reel and 100-foot 3/8-inch hose, a steel skid platform, and an air compressor. 2b1af7f3a8