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Title:Quantification of bond strength between cementitious materials and microbially-induced calcium carbonate precipitates
Author(s):Stynoski, Peter B
Director of Research:Mondal, Paramita
Doctoral Committee Chair(s):Mondal, Paramita
Doctoral Committee Member(s):Lange, David; Popovics, John; Marsh, Charles
Department / Program:Civil & Environmental Engineering
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):microbially-induced calcium carbonate precipitation (MICP)
Two-Parameter Fracture Model (TPFM)
nanoscratch
healing efficiency
resonant frequency
cement mortar repair
Abstract:Researchers have recently demonstrated the capabilities of microbially-induced calcium carbonate precipitation to fill and seal cracks in cementitious materials. However, the mechanical strength of microbially-induced crack healing is seldom investigated, especially at the fundamental level. In an effort to aid future development of structural repairs using this technique, the research discussed herein examines the suitability of several test methods to quantify the mechanical bond between calcium carbonate bio-deposits and cementitious substrates. Tests are performed at laboratory- and nano-scale to study both realistic cracks and isolated interfaces created under ideal conditions. Resonant frequency and mechanical bending tests were performed on notched, damaged, and treated Portland cement mortar beams. Sporosarcina pasteurii in nutrient media was applied to cracked beams in two different environmental conditions. Several experimental control treatments lacking bacteria were applied to additional sets of beams. Furthermore, bio-deposits were grown on prepared surfaces of cement paste in order to analyze an isolated interface using nanoscratch tests. A low-viscosity epoxy repair system was studied alongside the bio-deposits at both scales to provide a benchmark for comparison. Due to the challenges encountered when analyzing nanoscratch test results for a porous, discretely crystalline coating, data analysis methods for nanoscratch experiments were first established using a simplified model system of calcium-silicate-hydrate corrosion products on soda-lime glass substrates. Over the course of a 28-day treatment period, mortar beams in nearly all treatment conditions recovered to 95-105% of their pre-cracked resonant frequency, though the rate of recovery varied. Beams healed autogenously through hydration of remaining cement, without addition of external water, recovered to only about 85% of their original resonant frequency. In mechanical testing, only the set of beams healed by epoxy was capable of recovering significant load-carrying capacity. Other treated beams exhibited marginal improvements in fracture toughness recovery, but again lagged far behind the epoxy-based repair used for comparison in this study. On the other hand, the stiffness recovery under nearly all treatment conditions was competitive with the epoxy investigated here. These results indicate that the bacteria-based treatment could produce a repair that is weak in tension on the laboratory scale, but that bridges cracks well enough to increase overall stiffness. Initial nanoscratch experiments studying the model system of corrosion products on glass were indeed capable of quantifying an empirically observed distinction in bond strengths. When isolating the interfacial mechanical bond on this smaller scale, we find that a bio-deposit coating on cement paste fails at similar critical loads as an epoxy coating. Therefore, while the beam tests on the laboratory scale indicate a weak bond, it is possible for nano-scale tests which better isolate the interface between bio-deposits and cementitious materials to measure a fundamental bond strength which approaches that of a conventional epoxy repair.
Issue Date:2015-12-03
Type:Thesis
URI:http://hdl.handle.net/2142/89041
Rights Information:Copyright 2015 Peter B. Stynoski
Date Available in IDEALS:2016-03-02
Date Deposited:2015-12


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