Method Development for Transmission Electron Microscopy of Carbon Nanotubes and for Distributed Sensing With Triboluminescent Materials in the Premise of Sustainable Infrastructure

Cement is one of the largest contributors to the carbon footprint with approximately 3-5% share of global CO2 emission. Cement production is increasing with the increase in global population and their need for added accommodation. Moreover, the relatively short lifespan of already constructed cementitious infrastructure further inflates the demand of cement and continues to increase its carbon footprint. Thus a need for higher material strength and proactive structural health monitoring can allow for a significant reduction in overall cement usage as well as the carbon emission associated with it. The overall goal of this thesis is to develop novel techniques for evaluation of material compatibilitybetween carbonaceous nanomaterial and cementitious matricesand for distributed sensing employing fracto-luminescent materials. The developed techniques will likely allow for improvement in durability and health monitoring of cementitious composites and thus will likely contribute toward a sustainable use of cementitious material. The first half of the thesis focuses on development of a sample-preparation technique for transmission electron microscopy (TEM) of graphitic nano-reinforced cementitious (GNRC) composites. A unique colloidal suspension protocol was developed where cement materials with embedded single-walled and multiwalled carbon nanotubes (SWNTs and MWNTs) were systematically prepared and characterized. SWNT and MWNT aqueous suspensions were prepared using an acid etching technique. The suspension properties were characterized with Raman spectroscopy and time-resolved dynamic light scattering measurements. The water containing functionalized SWNTs and MWNTs were incorporated in the mix design to prepare the cement paste. Compatibility between functionalized nano-reinforcements and the cementitious matrix at the nanoscale was evaluated using high resolution TEM imaging. Preferential association of the functionalized SWNTs and MWNTs within the cement matrix was found and such novel colloidal protocol for image GNRC composites can be effectively used for characterizing such compatibility. The latter half of the thesis presents a simple however robust method for material testing in the field of damage sensing in cement mortar surfaces. Manganese-doped zinc sulfide (ZnS:Mn) triboluminescent (TL) material was used to coat 2 × 2 mortar cubes. The cubes were then tested under compression loading and crack propagation was imaged with a DSLR camera. Loading rate and concentration of TL material was systematically varied and luminescence emanating from the coated surfaces was quantified with a novel image processing technique. The image analysis technique included an image processing step where total luminescence/pixel along the cracks was quantified. Overall increase of the luminescence occurs with both increase in TL concentration and rate of loading. Quantification of crack in cement based materials through this novel technique will be useful and reliable for damage sensing in both real-systems and laboratory scale material characterization. This thesis has contributed through developing a TEM imaging technique, which is a first-of-a-kind technique, and can evaluate material compatibility of SWNTs and MWNTs with complex cement crystals. This method has potential for mechanistic understanding of nano-scale reinforcement of cementitious materials. The quantitative image analysis method developed here employing TL coatings also lays foundation for material testing in the field of distributed damage sensing and monitoring of cementitious surfaces