Asphalt mixes often have many ingredients that can interact with each other. When put into service, where there are multiple environmental effects, there are many interactions that need mixture testing. This paper’s objective was to evaluate laboratory conditioning protocols coupled with subsequent property measurements for their ability to detect damage of asphalt mixtures in the southeastern U.S. climate (or similar climates). The investigation’s focus is the property measurements themselves, and in particular how a given test can simultaneously assess multiple types of damage (i.e. oxidation, moisture damage, and freeze-thaw damage). While in service, mixtures can be damaged in multiple manners so laboratory conditioning protocols that expose specimens to multiple types of damage are needed as are test(s) that can detect these damages in a manner that can help assess performance during service. Four plant produced mixtures with all virgin ingredients were evaluated at intermediate temperatures with mixture and binder tests. The mixtures were well suited for such a comparison because they consisted of all virgin binder. Indirect tensile (IDT) strength did not relate to Cantabro Mass Loss (CML) or binder test results, which was concerning. Even more concerning was IDT’s inability to respond to laboratory conditioning protocols that considered multiple environmental effects (i.e., oxidation, moisture, and freeze-thaw). CML results related to binder properties and were able to reasonably detect multiple types of environmental effects. As such, Cantabro testing is recommended over tensile strength for intermediate temperature mixture property assessments related to non-load associated environmental effects.
Aluminum composites are preferred in many kinds of applications such as aviation, space, automotive, and marine, owing to their outstanding properties, high strength, and corrosion resistance. The main objective of the current study is to evaluate the mechanical properties of aluminum alloy 6061/titanium dioxide (micro-TiO2) microcomposite synthesized using the stir casting method. The effects of changes in stir casting parameters, such as stirring speed and tiring durations, were studied. Al6061 matrix was reinforced with micro-TiO2 particles with weight fractions of 1, 2, 3, 4, and 5 wt.%. Microstructural and chemical analyses were conducted to explore microstructural transformation resulting from the presence of the TiO2 microparticles. The mechanical characteristics were evaluated, and the results showed a considerable enhancement in the mechanical strength and hardness resulting from the incorporation of micro-TiO2 into Al606. The additions of 2 wt.% and 5 wt.% of micro-TiO2 recorded the highest ultimate tensile strength and hardness, respectively.
This article demonstrates the need to laboratory condition asphalt mixtures to simulate combined environmental effects and then to test unconditioned and conditioned specimens in a manner that damage from these environmental effects can be accumulated. The current state-of-the-art for evaluating asphalt mixtures for use on projects relies on either single-mechanism laboratory conditioning such as oxidation in AASHTO R30, or test methods that cannot accumulate combined effects such as indirect tensile strength in AASHTO T283. This article evaluated hundreds of laboratory-conditioned and field-aged specimens in a hot and no-freeze climate to demonstrate a laboratory conditioning protocol that was able to simulate at least 4 years of field aging, whereas conventional single-mechanism protocols were not. Temperature and moisture conditions within asphalt mixtures were measured over time and used as part of the assessment. The conditioning protocol that showed the most promise consisted of combined exposure to oxidation, moisture, and freeze–thaw mechanisms. The specific combined-effects conditioning protocol used here was 5 days of oxidation at 85°C, 14 days of moisture while submerged in 64°C water, and one freeze–thaw cycle. Other combined-effects protocols could be more suitable for other environments or situations; the main point of this article is that inclusion of oxidation, moisture, and freeze–thaw conditioning into one protocol is promising. The environmental conditions and mechanical property test data presented here suggest the asphalt industry needs to be harsher on mixes during laboratory evaluations, and that combined environmental effects conditioning should be given implementation consideration.
In recent years, the asphalt industry has been increasingly evaluating mixture testing for a variety of purposes. This article assesses the Micro-Deval (MD) test for its ability to evaluate compacted dense-graded asphalt mixtures. Historically, the MD test has been used to evaluate durability characteristics of loose aggregates, so this investigation deviates from the equipment’s intended purpose. MD testing was performed in traditional manners (i.e., submerged in water), as well as absent water. The investigation benchmarked MD testing against Cantabro mass loss and the Illinois Flexibility Index Test with an emphasis on use of the protocols during mixture production. Four evaluation criteria were used for assessment (level of rationality of test results, equipment cost, noise during testing, and time to achieve test results). Results of this investigation were that the MD testing protocol was not optimally suited for assessing compacted dense-graded asphalt. Wet MD tests (traditional test manner) were highly variable and provided no appealing test outputs. Operationally, the MD test was one of the noisier tests evaluated; it required an intermediate amount of time to conduct a test but had the lowest equipment cost. With all factors considered, the other tests considered are believed to be more promising than the MD for assessing dense-graded asphalt.
Any construction must be designed and built after the subsurface soil has been determined. The subsurface qualities of the soil are rendered by expensive, time-consuming, and risky operations, which on the other hand, raise the project's capital expenditure while also getting the engineering properties of distinct soil materials. Standard sampling techniques for boreholes are used for the assessment of the engineering properties of soil. But it is pretty costly, intrusive, and takes too much time. Therefore, a different method of determining the subsurface soil parameters is required. An alternate strategy for borehole sampling is to use geo-electrical techniques, such as electrical resistivity (ER). This research aims to ascertain the relationship between the electrical resistivity of various soils and their engineering characteristics. Without using the borehole sample method, appropriate correlations will aid in determining the subsurface soil parameters. Good correlations are obtained for the relationship of electrical resistivity against friction angle, cohesion and moisture content with an R2 value of 0.79, 0.41 and 0.66, respectively. The correlation of resistivity with unit weight showed a weak relationship due to typical soil behavior.
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