Graduate Thesis Or Dissertation
 

Towards the Development of Performance-Based Concrete Mixtures Made with Modern Cementitious Materials Using Thermodynamic Modeling

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/qj72pg561

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  • This thesis builds on a modeling tool that has been developed to link thermodynamic modeling and concrete performance. This tool is intended to predict the performance for modern concrete mixtures made with ordinary portland cement (OPC), conventional and novel supplementary cementitious materials (SCMs), and limestone (Ls). The first part of this thesis provides improvements to the pozzolanic reactivity test (PRT) used to quantify the reactivity of SCMs. The PRT is performed by mixing the SCM with an excess of calcium hydroxide (CH) and 0.9N KOH and reacting the mixture at 50°C for 10-days. The cumulative heat released (Q) and the CH consumed by the SCM are measured, and the value of reactivity is calculated by comparing the measured Q and CH consumed to theoretical values of Q and CH consumed by pure SiO2 and Al2O3 (obtained from thermodynamic modeling). First, the PRT is simplified to determine the reactivity using the measured Q alone by demonstrating using thermodynamic modeling that the well-defined bounds on the chemical compositions of standardized SCMs result in these SCMs having a relatively constant Q/CH consumed response in the PRT. Next, thermodynamic models are used to calculate the Q and CH consumed by SCMs that are combinations of SiO2, Al2O3, and CaO, which improves the PRT as it enables the user to more accurately quantify the reactivity of aluminous SCMs and expands the scope of the PRT to hydraulic SCMs. The reaction of CaO has the highest Q in the PRT (=1189 J/g), and the combination of 37%SiO2+63%Al2O3 has the lowest Q (=647 J/g). The addition of sulfates and carbonates is not recommended as it changes the reaction of Al2O3 in the PRT and makes the quantification of reactivity more difficult. The second part of this thesis shows the development of a pore partitioning model for concrete (PPMC) to predict the performance of OPC+SCM systems. The porosity and pore volumes are predicted to be within 2% of experimental measures, and the formation factor to within 13% for OPC and within 23% for OPC+20% fly ash systems. These predicted properties are used to estimate the service life of concrete exposed to freeze-thaw cycles and can aid in mixture design, e.g., replacing 20% of OPC with fly ash (of reactivity 40%) requires increasing the air-entrainment by 1%. This thesis also examines the partial replacement of clinker with Ls when SCMs are used to lower the carbon footprint of concrete. Simulations showed that SiO2 in the SCM does not change the porosity significantly and Al2O3 in the SCM reacts synergistically with the Ls to form carboaluminates that fill space and lower the porosity. The use of cement with up to 15% Ls is encouraged when Al2O3-rich SCMs are used. This thesis is a step forward in providing the tools required to predict the performance of concrete made with OPC+SCM+Ls binders and aid in proportioning concrete mixtures to have a lower carbon footprint. The model is used to predict concrete strength and durability properties (such as formation factor, time to freeze-thaw damage, resistance to salt damage) across a range of water-to-binder ratios (w/b), SCM replacement levels, and air contents. Using these predictions, a range of w/b, SCM content, and air contents where the concrete meets a set of predefined target performances is obtained, which allows for the optimal design of a concrete mixture. Finally, it is shown that the PPMC can be used to aid in concrete mixture design. This framework was validated by designing mixtures for three different applications (a bridge deck, a Midwest pavement, a foundation) using four SCMs. Except for one SCM, which caused workability issues due to rapid setting, all mixtures designed to meet the performance targets met the targets.
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  • Pending Publication
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  • 2022-05-16 to 2022-12-17

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