Sulfate Attack Mechanisms in Geopolymers: Measurements and Modeling at the Nanoscale

Princeton University, Princeton NJ

Investigators

Abstract

One of the main contributors to anthropogenic carbon dioxide emissions is ordinary Portland cement production, accounting for approximately 8 percent of total emissions. With Portland cement production forecast to double in the next 30 years it is imperative that low-carbon alternatives are successfully implemented in industry. Geopolymer cements have emerged as viable alternatives to Portland cement-based systems, however, there is the explicit need to be able to accurately predict the long-term durability performance of these cements for the successful implementation in the built environment. Nevertheless, as is the case for conventional cement systems, the exact chemical and physical processes controlling durability are not fully understood. Degradation of concrete exposed to sulfates is a serious durability concern for both conventional concrete and sustainable alternatives. Hence, the development of sulfate resistant concrete is extremely important for a wide range of infrastructure applications including sewer pipes, storm-water drainage systems, coastal structures and foundations. The outcome of this project will be the creation of sustainable cements with superior resistance to sulfate attack, which will benefit society by reducing costs associated with repair and maintenance of concrete structures exposed to sulfates. This project will investigate the atomic structure and morphology of sustainable geopolymer cements to improve our understanding of (i) cement formation mechanisms and (ii) chemical degradation processes caused by sulfate attack. The objective is firstly to discover the atomic processes that occur during formation of fly ash-slag-metakaolin geopolymer cement mixes by creating a geopolymer-specific atomistic modeling methodology utilizing quantum chemistry and molecular dynamics. Key characterization techniques will be employed to ensure experimental validity of the model, specifically in situ atomic analysis techniques at synchrotron and neutron user facilities, and Fourier-transform infrared spectroscopy. The structural models will be used to identify the key chemical mechanisms controlling geopolymer cement formation together with the influence of precursor chemistry on these mechanisms. The second objective of this project is to uncover and control the atomistic degradation mechanisms that occur during exposure to sulfate solutions. By exploiting the stability of the atomic structures most resilient to sulfate attack, mix designs will be engineered with improved sulfate resistance characteristics at the atomic level. The modeling methodology developed during the first part of the project will be extended to enable simulation of the chemical processes that occur when different sulfate salts are exposed to the geopolymer cement surfaces. In situ degradation experiments will be conducted to provide experimental validation of the models.