Use of Coal Combustion Residues and Foundry Sands in Flowable Fill

Abstract

This study is directed towards remedying some of the deficiencies in the present state-of-the-art concerning the behavior and design of flowable fill. The focus is on the utilization of waste foundry sand (WFS) and class F fly ash. However, the study addresses a much broader perspective so that a unified and rational approach becomes available to understand and predict the behavior of flowable fill in general. The objective is also to answer some of the questions which need to be answered before flowable fill can be used in many geotechnical applications. The report is organized in ten chapters. Chapter 1 outlines the objectives. Chapter 2 reviews the developments, applications, and advantages of flowable fill in general. Statistical data on the production and consumption of coal combustion by-products both in the United States and the state of Indiana are provided. A broad picture of the foundry industry in the United States, and in the state of Indiana is provided. The process of WFS generation is described. The environmental concern with regard to the use of WFS is briefly discussed. Lastly, the economics are addressed. Chapter 3 presents the basic physical and chemical properties of the materials, namely, cement, sand, and fly ash, used in this research. Chapter 4 deals with flow behavior of dry sand and fresh flowable fill mix. Flow curves are developed which help understand the mechanics of flow. Chapter 5 discusses penetration resistance test results using mortar penetrometer. A soil pocket penetrometer is also used to estimate the unconfined compressive strength as the fresh flowable fill hardens. The effect of drainage is studied by introducing geotextile drainage layers. Penetration resistance is correlated with the unconfined compressive strength. Penetration resistance necessary for walkability is defined. Chapter 6 presents 28-day and 90-day unconfined compressive strength test results. The 28-day compressive strength is correlated with the water/cement ratio. A step by step mix design procedure is described. Chapter 7 discusses mercury intrusion porosimetry and permeability test results, and bioassay toxicity test results on expressed pore solutions from hardened flowable fill. Chapter 8 discusses results of consolidated drained and undrained triaxial tests at different confining pressures, and also the Brazilian Tensile Strength test results. Chapter 9 presents the results of accelerated strength testing using hot water bath. Chapter 10 summarizes and presents conclusions for the present work.