Theses and Dissertations - Department of Civil, Construction & Environmental Engineering

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Browsing Theses and Dissertations - Department of Civil, Construction & Environmental Engineering by Author "Allison, Paul Galon"

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    Assessment of bamboo culm ash for use as as an additive in concrete
    (University of Alabama Libraries, 2015) Soleimanzadeh, Sara; Giannini, Eric R.; University of Alabama Tuscaloosa
    Each year tens of millions of tons of bamboo are utilized commercially, generating a vast amount of waste. One solution is to calcine this waste and use it as additive in concrete to keep it out of landfills and save money on waste disposal. This research project identifies (1) the optimal calcination condition of bamboo culm ash (BCAsh) and (2) the effect of various cement replacement levels on mortar properties. After considering the amount of energy consumed and the carbon content, burning at 700 °C [1292 °F] for 1.5 h was selected as the optimum condition. Cement replacement levels between 0.5 and 5% were investigated by evaluating the effects on heat of hydration and compressive strength of four mixes of BCAsh mortar. While the BCAsh reduced the strength of the mortar only slightly, it did show a considerable retarding effect on mortar hydration.
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    In-situ production of calcium carbonate nanoparticles in fresh concrete using pre-carbonation method
    (University of Alabama Libraries, 2017) Qian, Xin; Wang, Jialai; University of Alabama Tuscaloosa
    To reduce the carbon footprint of ordinary Portland cement (OPC)-based concrete, a novel technique, pre-carbonation process, has been developed to produce CaCO3 nanoparticles in fresh concrete. In this technique, gaseous CO2 is first absorbed into a slurry of calcium-rich minerals which is then blended with other ingredients to produce mortar/concrete. The objective of this work is to obtain an in-depth understanding of the underlying scientific mechanisms associated with the enhancement of strength and durability of the concrete induced by the new method. A comprehensive research plan has been carried out to study the carbonated slaked lime slurry and the effect of carbonated slaked lime slurry on the performance of OPC-based concrete, and to evaluate the potentials of the pre-carbonation method. Experimental studies show that carbonating the calcium-rich mineral slurry with CO2 can produce CaCO3 nanoparticles and Ca(HCO3)2 in the slurry, and these carbonation products were dictated by four parameters of the pre-carbonation method: the duration and temperature of the carbonation, the concentration of the calcium source slurry, and the stirring method of the calcium source slurry during the carbonation. The mechanical properties and durability of the mortar/concrete made with the carbonated slurry were significantly improved, which can be attributed to major mechanisms induced by the pre-carbonation method: promoted hydration of the cement and denser microstructure of the mortar/concrete. Calorimetry testing showed that the hydration of OPC was greatly improved by the pre-carbonation because of the extra heterogenous nucleation sites provided by the CaCO3 nanoparticles. XRD and TGA results revealed that more ettringite was produced in the mortar/concrete with pre-carbonated slaked lime slurry. The overall volume of the hydration products of the cement was increased by the pre-carbonation, leading to denser microstructure of the mortar/concrete. It has been found that the pre-carbonation can be used to the OPC-supplementary cementitious materials (SCMs) blended cement mortar/concrete, as evidenced by the improved mechanical properties achieved by these mortars produced by using the pre-carbonation method. A preliminary study was also conducted to examine whether other calcium-rich minerals, such as Class C fly ash and limestone, can be used as calcium source in the pre-carbonation method.