Low temperature production and carbonation of calcium silicate to improve the cement industry

The objective of this dissertation was to develop an in-situ measurement method for low temperature carbonation (40°C) and novel routes for production of wollastonite (CaSiO3) to improve the cement industry. Carbonation of CaSiO3 as a low-carbon, non-hydraulic cement that reacts with CO2 is a commercially viable technology used to reduce the CO2 emissions attributed to concrete production. Unlike hydraulic cement that strengthens by reaction with H2O, non-hydraulic cement strengthens from CO2 uptake and only uses H2O as a medium for the CaSiO3 carbonation reaction. Growing interest for CaSiO3 cement requires a method to investigate carbonation variables with particular emphasis on the role of H2O in carbonation. An in-situ technique for carbonation and drying quantification of wet-cast CaSiO3 pastes was established using thermogravimetic analysis with mass spectrometry (TGA-MS). While steam production is necessary to elevate humidity and prevent rapid drying in higher temperature carbonation conditions, this measurement method showed that carbonation of CaSiO3 at 40°C can utilize dry, flowing CO2. A method to mathematically deconvolute CO2 mass uptake and H2O mass loss was developed. The effect of pore size reduction and sample densification caused by CaSiO3 carbonation in CO2 had a significant effect on the drying behavior of the cement paste compared to inert drying in N2. Since this measurement was based on mass and humidity, this method should easily scale to large concrete samples. Development of novel, low temperature CaSiO3 production routes was facilitated by Hydrothermal Vapor Synthesis (HVS), a recently discovered technique to crystallize inorganic oxides. HVS is low-pressure variation of hydrothermal solution synthesis that employs an unsaturated steam reaction medium below the water vapor-liquid equilibrium (VLE) pressure. In this dissertation, HVS chemistry was examined by comparing results from thermodynamic modeling and experimental data. Synthesis of CaSiO3 from abundant minerals other than limestone was demonstrated and the HVS reaction mechanism was postulated. By understanding the thermodynamic barriers of gas-evolving HVS reactions, a semi-batch process was designed to scale CaSiO3 production to >500 g/L/d. Furthermore, this dissertation examines the use of HVS as a pre-treatment process for reducing the energy of hydraulic Portland cement production. In summary, this work indicates HVS could significantly contribute to decreasing the cost, energy consumption, and CO2 emissions inherent to the production of non-hydraulic or hydraulic cement.Ph.D.Includes bibliographical referencesby Ryan Scott Anderso