Kyle A. Riding

The Impact of Hydrothermal and Dilute Acid Pretreatments and Inorganic Metals on Thermal Decomposition of Agricultural Residues and Agricultural Residue Ash Properties

The impacts of hydrothermal and dilute acid pretreatments and alkali and alkaline earth metals (AAEMs) on the thermal degradation of biomass were studied. Besides, the influence of these pretreatments on the biomass ash properties was investigated. The influence of pretreatments on the biomass thermal degradation was manifested in the removal of potassium out of the biomass. The presence of potassium in the biomass catalyzed cellulose thermal degradation and increased the char percentage at temperatures higher than 380xa0°C. Pretreatments were effective at removing the potassium from biomass and dramatically reduced the char percentage at temperatures higher than 380xa0°C. It was found that the best burning temperature for biomass ash production was 500xa0°C because at this temperature the thermal degradation of biomass was completed under pure combustion. It was shown that when burning biomass in oxygen-limited environments, removing AAEMs, particularly potassium, will improve the quality of ash as a potential candidate for supplementary cementitious materials for concrete application.

Environmental and Track Factors That Contribute to Abrasion Damage

Sites with known occurrences of mud pumping or other track concerns were investigated to determine the prevalence of concrete bottom tie abrasion and environmental and track conditions that could contribute to its occurrence. Field investigations showed that it occurs in diverse geographic locations around the U.S. and is a source of continued maintenance concern for railroads. Water appeared to be a significant factor involved in concrete bottom tie abrasion. Ballast fouling, center-binding cracking, rail surface profile variations, and large track movement during loading was seen in locations with concrete bottom tie abrasion. Bumps or track stiffness changes were often found at locations of abrasion damage. Specifically, some locations with known stiff track conditions exhibited significant abrasion damage. INTRODUCTION Concrete railroad ties are being more frequently used in the railroad industry. Railroad ties are used to transmit loads from the train and rail to the subgrade and also to hold rail gage. Concrete ties are used in heavy-haul rail lines and high-speed rail lines because of their ability to carry large, repeated loads for a very long time. Concrete ties can last 50 years or longer when fabricated properly and the track is properly designed, built, and maintained. In order to achieve this life span, prestressed concrete tie thickness and prestressing forces are fabricated to resist design positive and negative bending moments. These design criteria are meant to prevent excessive deflections and gage widening during train loading and prevent ties from failing through breakage. If the tie section properties change during use, there is a potential for a loss in moment capacity, gage widening, tie breakage, and ultimately derailment [1]. Abrasion loss on the concrete tie sides and bottom could provide such a moment capacity reduction. On July 18, 2013, 10 cars on a northbound train on the Metro-North Hudson Line in the Bronx, NY containing municipal solid waste derailed, causing

Material Characteristics Evaluation of Existing Pre-Stressed Concrete Railroad Ties After Service Period

827,700 in damage [2] [3] [4]. At the location of derailment, the ballast was severely fouled with gray mud. The gray mud was mostly from ground up concrete fines from concrete ties that had lost section on the bottom. The ties also had center-binding cracking from high negative moments in the tie center that occurred or were

Risk of Thermal Cracking from Use of Lightweight Aggregate in Mass Concrete

As an important element in track, pre-stressed concrete railroad ties in the high-speed rail industry must meet the safety and performance specifications of high-speed trains. Systematic destructive and non-destructive evaluation of existing concrete ties can lead to a better understanding of the effect of prestressed concrete tie material design on performance and failure within their service life. It has been evident that environmental and climate conditions also have a significant impact on concrete railroad ties, causing various forms of deterioration such as abrasion and freeze-thaw damage. Understanding of the material characteristics that cause failure in different types of existing concrete railroad ties taken from different places is the main focus of this paper. Observing the current status and damages of railroad ties taken from track might give a correlation between the material characteristic and type of distress and cracking seen. Although it has been seen by previous works that effective factors such as air void system and material composition directly affect the performance of concrete ties such as freeze-thaw, material evaluation of existing ties after service life has not been addressed in previous publications. In this research, the authors have investigated the material characteristic such as aggregate and air-void system of existing pre-stressed concrete railroad ties taken from track. However, compressive and splitting tensile strength and fractured surface of samples cored from the ties were acquired. In order to obtain the strength of concrete materials of existing ties, six samples were cored from six different types of ties taken from tracks across the U.S., according to ASTM C42-16, and tested using ASTM C39 and ASTM C496 methods. However, the concrete air-void system (ASTM C457) was measured on saw-cut samples extracted from the ties to evaluate the influence air content and distribution on mechanical properties of the ties. Regarding the history and service life condition of the ties, it seems that material properties of the ties effectively alter the performance of the ties. Aggregate sources used at each location may have different properties such as texture, angularity, and mineralogy, contributing either propagation or resistance in splitting cracking in concrete. Furthermore, the polished surface of samples extracted from the ties show the uniformity and air void system in some ties which demonstrate their superiority in terms of resistance to freeze-thaw damage. Considering the results of this research, comprehensive evaluation of material characteristics might give a better view of existing concrete railroad ties situation, providing a worthwhile background for future tie design considerations.Copyright

Prediction Model for Concrete Behavior—Final Report

This paper describes the results of a numerical investigation of incorporating lightweight aggregate (LWA) in mass concrete structures. Numerical simulation was performed with ConcreteWorks software on three rectangular piers for normal weight concrete, internally cured concrete, sand–lightweight concrete, and all–lightweight concrete. Results show that temperature differences greater than 35°F may not necessarily introduce thermal cracking in mass concrete made with LWA. Maximum core temperatures and temperature differences increased with decreasing concrete density; however, the cracking risk of the mass concrete elements decreased as a greater quantity of LWA was used, regardless of element size. This trend occurred because other properties, such as coefficient of thermal expansion, creep, modulus of elasticity, tensile strength, and geometrical conditions, influenced the risk of thermal cracking. Additionally, the identification of the cross-section locations involved in measuring the critical temperature difference in a mass concrete structure are presented. The results of this work can be helpful in identifying critical stress locations in cross sections and assessing the cracking risk for mass concrete structures. A temperature and stress analysis is recommended before mass concrete construction involving LWA is begun.