Iron Sulfide Minerals in Concrete Aggregates

Open Access
- Author:
- Piasente, Jonathon
- Graduate Program:
- Civil Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 10, 2020
- Committee Members:
- Aleksandra Z Radlinska, Thesis Advisor/Co-Advisor
Shelley Marie Stoffels, Program Head/Chair
Gordon Patrick Warn, Committee Member
Farshad Rajabipour, Committee Member - Keywords:
- Concrete
Aggregates
Iron Sulfide
Expansion
Deleterious
Oxidation
Secondary Mineral Formation
Reactive Aggregates
Problematic Aggregates
Pyrrhotite
Pyrite - Abstract:
- Aggregates account for a significant volume fraction of concrete, but it is often presumed that they will behave as inert material. If left unchecked, the aggregate composition can lead to undesired reactivity and subsequent devastating damage of structures. Standard approaches to assessing the quality of concrete aggregates fail to address the issue of iron sulfide inclusions. While the particular conditions a structural element will be subjected to are often considered beforehand, the effects those conditions will have on a relatively small amount of iron sulfides present in the aggregate are not well understood. Minerals such as pyrite and pyrrhotite can result in deleterious reactions that can compromise the integrity of a structure. Other reactive substances found in aggregate sources have been well studied, but the problem of iron sulfides has gained serious attention in recent years due to substantial damages in residential construction documented in Connecticut and Quebec. Other instances of similar damage have been suggested throughout the 20th century, but the full complexity of the problem is still poorly understood. Most concrete structures do not contain aggregates with reactive iron sulfides, but the structures where contaminated aggregates were used often exhibit expansive damage so severe that immediate intervention is mandatory. A concentrated effort to identify and understand the reasons behind the deleterious reactions is required. To fulfill this effort, various exposure conditions were utilized to promote the deleterious reactions documented in the literature. Mortar and concrete samples with variable dimensions and geometry were stored in the exposure conditions and measurements (unconfined compressive strength, length change and mass change) were continuously conducted. The objective of this thesis is to experimentally determine the factors (relative humidity (RH), oxygen content, temperature, water to cement ratio (W/C), freeze and thaw cycling and waterproofing application) that are significantly tied to iron sulfide mineral oxidation, and the subsequent chemical reactions, in cementitious media. One of the studies presented in this thesis indicates that waterproofing sealant is effective in reducing the expansion of mortar samples subjected to a novel rapid freeze and thaw procedure. A screening design considering multiple factors hypothesized to be contributing to iron sulfide reactivity shows that temperature and RH are statistically significant factors for length change and that RH is statistically significant for mass change.