Microstructure, Quasi-Static, And High-Strain Rate Dynamic Characterization Of Metakaolin And Fly Ash Based Geopolymers For Structural Applications
Geopolymers are a class of rapid setting cementing systems that have been used as mortar or additives in concrete mixes to improve properties. Several types of geopolymer systems such as metakaolin and fly ash based geopolymers are widely used, and are available in different mixture proportions [1, 2]. Metakaolin (Al2Si2O7), a dehydroxylated form of Kaolinite (Al2Si2O5(OH)4) clay readily available from many sources, provides several benefits whenadded to a concrete mix design or used as a mortar system, including durability, freeze/thaw, acid resistance, and high temperature resistance [3]. Class F fly ash-based mortar geopolymers provide added fire retardation, reduces crack formation, etc., when added to a concrete mix or used as a mortar system. This thesis compares the quasi-static and dynamic properties of both a pure metakaolin geopolymer and a fly ash based geopolymer material system that utilizes siliceous sand as fine aggregate. Microstructural characterization studies included Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), and Thermal Gravimetric Analysis (TGA). The mechanical properties were evaluated from nanoindentation and monotonic experiments. Spatially correlated nanoindentation and EDS provided mechanical property information (modulus and hardness) and elemental data of individual phases in the samples. Metakaolin and fly ash based geopolymers are two fundamental alternative cementitious binder materials that can be used to produce sustainable mortars and concretes. While there is limited information related to the quasi-static properties of these materials, no information exists related to their high strain rate mechanical behavior. A Split-Hopkinson Pressure Bar (SHPB) was utilized to determine the high-strain rate compressive properties of both pure Metakaolin and Class F fly ash geopolymers with sand as fine aggregate. SHPB compressive data for Metakaolin and Class F Fly ash-based mortar along with a Portland cement-based mortar for comparison are presented. Punch-shear response of the candidate material systems under low-velocity impact is also presented.
Fly Ash, Geopolymer, High Strain Rate Dynamic, Metakaolin, Microstructure, Quasi-Static, Mechanical Engineering
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