Thermodynamic Modeling of Hydraulic Phases Evolution in CO2 Injected Concrete

Abstract

As the second largest industrial emitter of carbon dioxide, the concrete industry is expected to continuously grow due to increasing population rates causing a demand for concrete-based structures. The high emissions rates from ordinary Portland cement (OPC) production have caused the concrete industry to look for new technologies and cement alternatives to reduce emissions, one of these technologies being carbon capture and injection. With the potential to reduce emissions by 47% by 2050 as well as to improve strength properties in concrete, carbon capture at cement plants presents a viable option for reducing production emissions. However, current studies have found that there are limitations to the amount of CO2 that can be injected into fresh concrete before CO2 has a weakening effect. This poses a limitation on the potential benefit of CO2 injection, and therefore this thesis is focused on using thermodynamic modeling to examine the development of individual phase formation that occurs during hydration of CO2 injected concrete, using the modeling software GEMS. A variation of CO2 was added to OPC paste as well as blended OPC paste to determine how phase formation varied with added CO2 and how these variations could be causing larger doses of CO2 to detract from potential strength benefits seen experimentally in from low CO2 doses. The thermodynamic modeling included assessment of final phase formation for blended OPC pastes involving fly ash and slag, as well as time evolution simulations for OPC paste and alite hydration. The optimum dose of CO2 was found to be 1% by weight of cement powder since solid phase formation increased, specifically the amount of calcium-silicate-hydrate (C-S-H) gel, and porosity decreased. The addition of large qualities of CO2 produced caused a large production of calcite at the expense of portlandite formation leading to increased solid phases formation whose benefits were counteracted by a large increase in porosity. CO2 addition to blended PCs was found to be beneficial in final phase formation until portlandite was depleted from the samples. These results provide a good indication of what hydrates could be contributing to added benefits or drawbacks of CO2 injection to cement strength, however, physical tests should be conducted to examine how differentiation in hydrates affect actual strength.