Building highway embankments of fly/bottom ash mixtures

Ahmed Mahmoud Kamal Karim, Purdue University

Abstract

As part of a national effort for conserving natural resources and recycling non-hazardous waste materials, this research focused on analyzing the feasibility of using large volumes of mixtures of bottom ash and Class F fly ash in highway embankments. Most of these materials are currently disposed as waste, although several studies show that they can be used without significant adverse effects on the environment when appropriate procedures are developed and followed in their utilization. However, fly/bottom ash proportion is not uniform at disposal sites due to the current disposal practices. Due to the lack of knowledge about the effect of changing the fly/bottom ash proportion on the compaction and stress-strain behavior of the mixtures, a detailed investigation was needed. Large representative samples were extracted from disposal sites of two major power plants in Indiana. One disposes the bottom ash and Class F fly ash separately, hence explicit mixtures were possible, whereas the other disposes them together at a common discharge location and hence implicit mixtures were formed. Compaction and CID triaxial compression tests were performed on a wide range of explicit and implicit mixtures of bottom ash and Class F fly ash. Grain size analysis, specific gravity, minimum and maximum density tests were also performed. Close microscopic examination showed that a fly ash content of 25% was sufficient to mask most of the bottom ash particles and fill the inter-particles voids. The concept of relative compaction combined with a family of compaction curves, based on the standard Proctor energy, may be used for controlling compaction of the majority of mixtures. At low fly ash content, the friction angle of dense samples changes slightly as the fly ash increases from 0 to 25% then drops significantly as the fly ash increases to 50%. For dense and loose samples, the friction angle changes slightly as the fly ash increases beyond 50%. Samples compacted at relative compaction of 95% (ASTM 698) displayed adequately dilative or slightly contractive volumetric behavior under deviatoric stresses. Highway embankments can provide a final destination for the ash mixtures which can be consumed in construction instead of natural soils.

Degree

Ph.D.

Advisors

Lovell, Purdue University.

Subject Area

Civil engineering

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