Browsing by Subject "Curing"
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Item Breaking and curing rates in asphalt emulsions(2012-12) Banerjee, Ambarish; Prozzi, Jorge Alberto; Bhasin, Amit; Korgel, Brian; Folliard, Kevin J.; Zhang, ZhanminThis PhD dissertation addresses a number of issues pertaining to the use and application of surface treatments using asphalt emulsions. The work conducted as part of this research study shows in detail the problems associated with the state-of-practice and how these issues can be addressed using a scientific and rational approach as opposed to the experience-based approach which is prevailing currently. The first objective of this research study focuses on developing a methodology to determine the total amount of evaporative water loss of an emulsion before the aggregates are placed. An algorithm is presented that can be used by field inspectors and practitioners for the optimal timing of chip placement. The second objective focuses on another key aspect associated with the constructability of surface treatments, i.e., the optimal time to open a new surface treatment to traffic. Laboratory tests were conducted on the emulsion and aggregates to measure the rate of moisture loss and the evolution of the rheological properties as function of time. This was related to the field measured evaporation rates to determine the minimum stiffness required for optimal performance of the chip seal towards adequate resistance to raveling. The final objective of this dissertation focuses on developing a theoretical understanding of the current flowing through a circuit when an emulsion separates into its constituent phases when placed in an electric field. The measured current depends on a set of material properties that include the emulsion’s viscosity, surface potential, and dielectric of the medium and the strength of the electric field. A theoretical formulation was developed that relates the current flowing through the circuit with the mobility of the charged particles and the bulk charge density. The proposed theory was further utilized in developing a test procedure to quantify the breaking characteristics of asphalt emulsions. Results demonstrated that the parameters obtained from these tests were repeatable and different for different types of asphalt emulsions. It was also noticed that for a given type of emulsion the test method is sensitive to factors such as water content and partial breaking due to mechanical agitation.Item Modeling the Effect of Curing on Early Age Distress Potential of Concrete Pavement(2014-04-11) Bari, Muhammad EhsanulUnderstanding the early age behavior of concrete is an important issue in construction of concrete structures since different factors during construction, such as design consideration, material usage, and environmental influence, can alter the original configuration of the structure intended by the engineers and hence the structure may experience and exhibit undesired consequences. The primary interest of this research was to model the behavior of concrete under environmental excitations, such as the variation of temperature and relative humidity, during the early age after concrete placement. Experimental test results were obtained and mathematical models were developed for this research. Modeling the effect of curing process in response to the relative humidity variation was one of the main objectives of this research. A mathematical model for back-calculating the diffusion coefficient of cured concrete from experimental test was proposed. This back-calculated diffusion coefficient of concrete was indicative of the effectiveness of curing application provided during construction. Corner deflection model for predicting lift-off displacement and climatic stress model for predicting crack formations were formulated in order to predict the distress behavior of concrete for a given design and construction scenario. Probabilistic models for lift-off displacement and cracking were formulated to predict the probabilities of such distresses. Material properties, such as strength, elastic modulus, creep, drying shrinkage, were obtained from experimental program and were used as input in these distress prediction models. In order to assess the effectiveness of different curing compounds, two indices, such as curing index and overall curing index, were proposed. These indices were able to distinguish the difference in performance among different curing compounds. For validating the proposed corner lift-off displacement model and climatic stress model, numerical simulations were performed and the obtained results were compared with the field observations. The probabilistic models for predicting lift-off displacement and cracking behavior were validated by comparing the numerical simulation results with the field observations at Houston Intercontinental, TX. The predictions from these models were found to be in close agreement with the experimental observations. Furthermore, in order to assess the impact of a given design and construction, analytical study was performed with these models. In the sensitivity analysis, parameters of interest were the geometry of the structure, the effect of curing application, and the influence of time as well as the season of construction on the distress potentials. Numerical simulations indicated that the curing application was able to lower the early age distress potentials. The thicker slabs/overlays versus the thinner ones exhibited differences in performance in terms of distress potentials. The analytical study also revealed that it was possible to vary the distress potentials by varying the time as well as the season of construction. Finally, a constructability index was proposed in order to assist in decision making with regard to different designs and construction scenarios with a view to minimize the distress potentials in concrete structure. The results indicated that the constructability index was able to capture and demonstrate the effect of different parameters mentioned above on the constructability of rigid pavement/overlay projects.Item Synthesis and cure characterization of high temperature polymers for aerospace applications(Texas A&M University, 2006-04-12) Li, YuntaoThe E-beam curable BMI resin systems and phenylethynyl terminated AFR-PEPA-4 oligomer together with an imide model compound N-phenyl-[4-(phenylethynyl) phthalimide] were synthesized and characterized. E-beam exposure cannot propagate the polymerization of BMI system until the temperature goes up to 100oC. However, a small amount of oligomers may be generated from solid-state cure reaction under low E-beam intensity radiation. Higher intensity E-beam at 40 kGy per pass can give above 75% reaction conversion of BMI with thermal cure mechanism involved. NVP is a good reactive diluent for BMI resin. The cure extents of BMI/NVP increase with the increase of the dosage and applied dosage per pass. The reaction rate is much higher at the beginning of the E-beam cure and slows down after 2 dose passes due to diffusion control. Free radical initiator dicumyl peroxide can accelerate the reaction rate at the beginning of E-beam cure reaction but doesn??t affect final cure conversion very much. According to the results from FT-IR, 200 kGy total dosage E- beam exposure at 10 kGy per pass can give 70% reaction conversion of BMI/NVP with the temperature rise no more than 50oC. The product has a Tg of 180oC. The predicted ultimate Tg of cured AFR-PEPA-4 polyimide is found to be 437.2oC by simulation of DSC Tg as a function of cure. The activation energy of thermal cure reaction of AFR-PEPA-4 oligomer is 142.6 ?? 10.0 kJ/mol with the kinetic order of 1 when the reaction conversion is less than 80%. The kinetics analysis of the thermal cure of N-phenyl-[4-(phenylethynyl) phthalimide] was determined by FT-IR spectroscopy by following the absorbance of the phenylethynyl triple bond and conjugated bonds. The thermal crosslinking of N-phenyl-[4-(phenylethynyl) phthalimide] through phenylethynyl addition reaction has a reaction order of 0.95 and an activation energy of 173.5 ?? 8.2 kJ/mol. The conjugated bond addition reactions have a lower reaction order of 0.94 and lower activation energy (102.7 ?? 15.9 kJ/mol). The cure reaction of N-phenyl-[4-(phenylethynyl) phthalimide] can be described as a fast first-order reaction stage followed by a slow second stage that is kinetically controlled by diffusion.