Date of Award

2017

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Civil and Environmental Engineering

First Advisor

Sumanta Das

Abstract

Iron Carbonate is a novel carbon-negative sustainable binder that is made from metallic iron powder waste and utilizes the chemistry of iron carbonation. To produce the binder, usually landfilled iron powder and other constituents (fly ash, limestone powder, metakaolin, sodium carbonate, sodium bicarbonate, powdered organic reducing agent, and water) are mixed together and exposed to a pressurized CO2 regime that leads to slow external diffusion. The carbonation of iron particles results in the formation of complex iron carbonates that have binding capabilities and mechanical properties similar or better compared to ordinary Portland cement (OPC)-based binders. The metallic particulate phase incorporated in the novel binders’ microstructure increases the toughness of Iron Carbonate because of the energy dissipation by plastic deformation of the unreacted and elongated iron particles which are strong and ductile. In addition, the matrix contains other additives including harder fly ash particles, softer limestone particles, and ductile clayey phases which significantly influence the overall fracture performance of the novel sustainable binder.

Understanding the behavior of Iron Carbonate at high strain rates is important for a wide range of both military and civilian applications. The material behavior under highly dynamic conditions is significantly different from the material response under quasi-static conditions. The split Hopkinson (Kolsky) pressure bar (SHPB) system is used to test dynamic compressive mechanical response and failure behavior of Iron Carbonate under high strain rates to establish exceptional dynamic load mitigation characteristics for the carbon-negative sustainable binder under extreme combined environments.

Dynamic tests are conducted on cylindrical Iron Carbonate specimens using a conventional SHPB set-up. The experimental arrangement includes a gas gun and three steel bars (a striker bar, an incident bar, and a transmitted bar), aligned along a single axis. The Iron Carbonate specimen is placed between the incident and transmitted bar and the striker projectile is fired toward the face of the incident bar. Due to the impact of the striker bar an incident pulse, a reflected pulse and a transmitted pulse are generated that build up the stress level in the specimen and compress it. Objective of the carried out dynamic compression tests on Iron Carbonate specimen is the determination of the stress equilibrium, true stress-strain plots and strain-rate.

Analysis of the obtained pulses revealed that the transmitted pulses of the tested Iron Carbonate specimens were of much smaller magnitude than the incident and reflected pulses. As a result, achievement of stress equilibrium and homogeneous deformation of the Iron Carbonate samples was prevented. The small amplitude of the transmitted pulses is due to the possibly low mechanical impedance of Iron Carbonate. Testing specimens made of material with low mechanical impedance allows the incident bar-specimen interface to nearly move freely under stress wave loading, so that most of the incident pulse is reflected backward into the incident bar. Only a small portion of the loading pulse is transmitted through the specimen into the transmission bar.

Therefore, the conventionally used experimental standard set-up of the SHPB system using steel bars has to be modified in order to determine accurate dynamic stress-strain responses for Iron Carbonate. To increase the magnitude of the transmitted pulses a softer material, such as aluminum, should be used as transmitted bar material instead of common steel. Furthermore, a hollow transmitted bar instead of a solid bar should be used. The lower Young’s modulus of an aluminum alloy and the smaller cross-section of the hollow bar increase the amplitude of the transmitted strain signals by at least an order of magnitude as compared to a conventional steel bar.

Available for download on Saturday, July 20, 2019

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