School of Civil and Environmental Engineering

Ph.D. Thesis Defense Announcement

 The Re-Use and Beneficiation of Industrial Waste Products into New Sources of SCMs

By Daniel Benkeser

Advisor:

Dr. Kimberly Kurtis (CEE)

Committee Members:  Dr. Susan Burns (CEE), Dr. David Frost (CEE),
Dr. Fred Meyer (CEE), Dr. Carsten Sievers (ChBE)

Date and Time:  Friday, March 8th, 2-4 pm

Location: Mason Building Room 2119, Microsoft Teams

This research examines the re-use and beneficiation of industrial waste byproducts, primarily for use as supplementary cementitious materials (SCMs). Reducing cement clinker content in concrete is a significant strategy to meet the industry's de-carbonization goals. This combined with the decreasing supply of traditional SCMs, such as coal fly ash, is creating a need for new sources of SCMs at a scale consistent with the 20 billion tons of concrete produced annually. However, the appropriateness of potential sources of industrial waste must be assessed, as well as potential means to increase their reactivity with cement in concrete.  
 
The first half of this work primarily focuses on the potential re-use of two industrial sources: ponded coal combustion products (CCPs) and dredged river sediment. Potentially reactive phases, primarily fly ash for the CCP and kaolinite/diatoms for the calcined sediment, were identified allowing for the development of processes necessary to activate these phases. The reactivity of these SCMs was primarily determined via heat release and consumption of portlandite (Ca(OH)2) in blended cement pastes, and performance was primarily measured through comparisons to existing specifications (i.e., ASTM C618) for Class F fly ash and Class N Pozzolans. Results indicate that both sources are moderately reactive and demonstrate the ability to meet ASTM specifications, but that both exhibit some characteristics which limit their practical use, including their relatively low amorphous content (i.e., higher amount of non-reactive crystalline phases) and their effect in decreasing workability. 
 
The second half of this work, then, focuses on mitigation of these effects through the development and assessment of two beneficiation techniques - chemi-mechanical grinding and spray drying. Chemi-mechanical grinding in the presence of water was found to improve pozzolanic reactivity of reclaimed fly ashes through reductions in crystallinity and particle size along with increasing the number of terminal silanol groups in the particles, which act as reaction sites for the pozzolanic reaction. Spray drying improved the workability of natural pozzolans by spherulizing the clay particles, while maintaining their pozzolanic reactivity.
 
Based on these results, potential uses of large-scale industrial waste sources are recommended. Further, potential changes to existing standards are suggested to address the increasing needs of the cement and concrete industry for additional sources of SCMs.