Mitigation of High Alkalinity in Leachates of Aged Steel Slag

Steel slag, an abundant by-product of the steel-making industry, after it is aged, has a huge potential for use as an aggregate in road construction. However, the high pH of steel slag seepage (pH≥12) is a major impediment in its beneficial use. Analyses on aged steel slag samples demonstrated that the alkalinity producing capacity of aged steel slag samples strongly correlated to Ca(OH)2 dissolution and that prolonged aging periods have marginal effects on overall alkalinity. Treatment methods that included bitumen-coating, bathing in Al(III) solutions and addition of an alum-based drinking water treatment residual (WTR) were evaluated based on reduction in pH levels and leachate alkalinity. 10% (wt./wt.) alum-based drinking water treatment residual (WTR) addition to slag was determined to be the most successful mitigation method, providing 65−70% reduction in alkalinity both in batch-type and column leach tests, but final leachate pH was only 0.5−1 units lower and leachates were contaminated by dissolved Al(+III) (≥3−4 mM). Based on the interpretation of calculated saturation indices and SEM and EDX analyses, formation of calcium sulfoaluminate phases (i.e., ettringite and monosulfate) was suggested as the mechanism behind alkalinity mitigation upon WTR-modification. The residual alkalinity in WTR-amended slag leachates was able to be completely eliminated utilizing a biosolids compost with high base neutralization capacity. In column leach tests, effluent pH levels below 7 were maintained for 58−74 pore volumes worth of WTR-amended slag leachate using 0.13 kg compost (dry wt.) per 1 kg WTR-amended slag on average; also, dissolved Al(+III) was strongly retained on the compost.

DEVELOPMENT OF AN OFF-LINE RAINFLOW COUNTING ALGORITHM WITH TEMPORAL PARAMETERS AND DATA REDUCTION

Rainflow counting methods convert a complex load time history into a set of load reversals for use in fatigue damage modeling. Rainflow counting methods were originally developed to assess fatigue damage associated with mechanical cycling where creep of the material under load was not considered to be a significant contributor to failure. However, creep is a significant factor in some cyclic loading cases such as solder interconnects under temperature cycling. In this case, fatigue life models require the dwell time to account for stress relaxation and creep. This study develops a new version of the multi-parameter rainflow counting algorithm that provides a range-based dwell time estimation for use with time-dependent fatigue damage models. To show the applicability, the method is used to calculate the life of solder joints under a complex thermal cycling regime and is verified by experimental testing. An additional algorithm is developed in this study to provide data reduction in the results of the rainflow counting. This algorithm uses a damage model and a statistical test to determine which of the resultant cycles are statistically insignificant to a given confidence level. This makes the resulting data file to be smaller, and for a simplified load history to be reconstructed.

Mechanistic-based Design-Integrated Reliability Validation Framework for Mechanical Systems

Abstract: New product design challenges, related to customer needs, product usage and environments, face companies when they expand their product offerings to new markets; Some of the main challenges are: the lack of quantifiable information, product experience and field data. Designing reliable products under such challenges requires flexible reliability assessment processes that can capture the variables and parameters affecting the product overall reliability and allow different design scenarios to be assessed. These challenges also suggest a mechanistic (Physics of Failure-PoF) reliability approach would be a suitable framework to be used for reliability assessment. Mechanistic Reliability recognizes the primary factors affecting design reliability. This research views the designed entity as a “system of components required to deliver specific operations”; it addresses the above mentioned challenges by; Firstly: developing a design synthesis that allows a descriptive operations/ system components relationships to be realized; Secondly: developing component’s mathematical damage models that evaluate components Time to Failure (TTF) distributions given: 1) the descriptive design model, 2) customer usage knowledge and 3) design material properties; Lastly: developing a procedure that integrates components’ damage models to assess the mechanical system’s reliability over time. Analytical and numerical simulation models were developed to capture the relationships between operations and components, the mathematical damage models and the assessment of system’s reliability. The process was able to affect the design form during the conceptual design phase by providing stress goals to meet component’s reliability target. The process was able to numerically assess the reliability of a system based on component’s mechanistic TTF distributions, besides affecting the design of the component during the design embodiment phase. The process was used to assess the reliability of an internal combustion engine manifold during design phase; results were compared to reliability field data and found to produce conservative reliability results. The research focused on mechanical systems, affected by independent mechanical failure mechanisms that are influenced by the design process. Assembly and manufacturing stresses and defects’ influences are not a focus of this research.