Reaction Kinetics, Microstructural Features and Mechanical Properties of CO2 Activated Low-Lime Calcium Silicate Binders

Warda Ashraf, Purdue University

Abstract

Relatively high CO2 footprint (5 to 8% of global CO2 emission) of ordinary portland cement (OPC) is mainly due to the following two factors: a) calcination of large quantities of limestone in order to produce high-lime calcium silicates (i.e. alite - Ca3SiO5 and belite - Ca2SiO4) which constitute the main components of the ordinary portland cement (OPC) and, (b) high production temperature (~1450 °C) required to form these calcium silicates (thus requiring high amounts of energy derived from burning of fossil fuels). The ability to utilize calcium silicates with lower calcium-silica ratio (such as rankinite- Ca3Si2O7) and wollastonite – CaSiO3) as the primary compounds of the cement would lead to substantial reduction of its CO2 footprint as these compounds will require less limestone and could be produced at lower temperatures. The reason such low-lime calcium silicates are preferentially excluded from the composition of the typical OPC is that they are non-hydraulic (i.e. are practically non-reactive in the presence of water). However, some of the recent studies showed that the reactivity of these low-lime calcium silicates can be substantially enhanced in the presence of CO2. This opens-up the possibility of utilizing these low-lime calcium silicates as CO2 activated binders, thus offering viable (and more sustainable) alternative to OPC. In order to successfully develop this new binder type as a practical replacement for the OPC, a fundamental, in-depth understanding of the variables controlling the reactivity of these materials along with the understanding of the properties and characteristics of the reaction products is required. This dissertation presents a comprehensive investigation of the novel, CO2 activated binders with a broader aim to contribute in the further development and long term successful application of similar alternative cementitious materials. The specific focus of this study was in the following areas: (a) effects of CO2 on the reactivity of pure calcium silicates, (b) carbonation reaction kinetics of pure calcium silicates and industrial grade low-lime calcium silicate cement (CSC) (c) chemical composition, molecular arrangements, and elastic/viscoelastic properties of the carbonation products of pure calcium silicate phases and CSC, and (d) The macroscale mechanical properties of carbonated matrixes. (Abstract shortened by ProQuest.)

Degree

Ph.D.

Advisors

Olek, Purdue University.

Subject Area

Civil engineering|Materials science

COinS