Currently, significant quantities of recycled glass containers are stockpiled due to prohibitive transportation costs between collection points and glass melting facilities. The objective of this research is to utilize this waste material as a replacement of eco-negative portland cement in high-performance and environmentally efficient concrete materials. The research (1) performs a multi-scale investigation of the reactivity of soda-lime glass in alkaline-calcium environments to significantly enhance the pozzolanic reactivity of glass using optimized chemical and physical treatments; (2) explores the link between pozzolanic and alkali-silica reactions and the role of calcium in altering these reactions; and (3) conducts comprehensive environmental and economical life-cycle assessments to allow quantitative comparisons of the cost and eco-impact of glass-based concretes with those of conventional portland cement and fly ash concretes. This collaborative effort between Penn State and Carnegie Mellon universities leads to a new approach in integrating detailed environmental and economic analysis with design and engineering of green materials to determine the best choices for material processing and proportioning while ensuring the sustainability of new products and technologies.
The research findings will have broader impacts on improving the durability and eco-efficiency of concrete infrastructure by more effective use of pozzolanic materials and advancing the knowledge on the mechanism of alkali-silica reaction and its mitigation techniques (which will be applicable to natural reactive aggregates). Integration of research and education is accomplished by (a) development of course modules (disseminated through the online library of Center for Sustainable Engineering) for civil engineers on applying environmental life cycle assessment methods, as well as designing and testing non-portland cement concretes; and (b) organizing a summer camp to attract prospective female students to education and careers in civil engineering through a project-based learning experience.
Intellectual Merit: The goal of this project was to engineer high performance, inexpensive and ecologically efficient concretes by utilizing a widely available waste material, soda-lime glass powder which is a byproduct of recycling glass containers, as a substitution for portland cement in concrete. The major obstacles were slow dissolution and reactivity of glass (which would lead to concretes with low strength) and a risk of alkali-silica reaction (leading to cracking and short life of concrete). The project proposed to use alkali-activation (i.e., admixing alkaline chemicals in concrete) and heat curing to boost the reactivity of glass, and to analyze the risk of alkali-silica reaction (ASR) in such concretes. Towards these objectives, the mechanisms and rate of dissolution and reactivity of silicate glass in an alkaline environment (representing the pore solution in portland cement or alkali activated concretes) were comprehensively characterized. The effects of temperature, glass composition, and pore solution composition (alkalinity and calcium content) were quantified. The results provide important new understanding on how silicates dissolve and precipitate at high pH, and on factors that promote the beneficial pozzolanic and geopolymeric reactions and those that prevent deleterious ASR. Also, the stoichiometry of the pozzolanic reaction of soda-lime glass was accurately quantified, which allow for correct proportioning of glass powder in portland cement (PC) and lime-based concretes. For the first time, in this project, three types of alkali-activated PC-free concrete binders were developed: a lime-glass binder with moderate compressive strength (19MPa at 3 days) and blast furnace slag-glass or fly ash-glass binders with excellent compressive strengths (e.g., 43MPa at 1 day). Environmental life-cycle assessment (LCA) and life-cycle cost (LCC) methods showed that these new glass-based concretes could be environmentally and economically advantageous to traditional portland cement concretes. Glass powder can be used in combination with portland cement in non-activated concretes. Alkali activation of PC-glass concretes was found to be ineffective due to negative impact of high alkalinity on cement hydration. Glass powder, when proportioned correctly, was found not to cause ASR damage. In addition, accelerated ASR tests (e.g., ASTM C1567) suggested that glass powder could serve as an effective pozzolan in PC-concretes to mitigate ASR caused by reactive aggregates. However, more reliable long-term ASR tests (e.g., ASTM C1293) showed that the high sodium content of soda-lime glass powder serves to maintain high alkalinity of concrete pore solution, which sustains ASR. As such, glass powder may not be an effective ASR mitigator. Broader Impacts: The results of this research help in constructing and maintaining a more sustainable and resilient concrete infrastructure that is safer, greener, cheaper (to build, maintain, and operate), and better in serving the public. For example, the improved durability and reduced repair needs for highway infrastructure allows for safer travels, and faster and cheaper transport of goods and services with less interruption. Replacement of portland cement with industrial waste materials reduces energy use and emission of greenhouse gasses that contribute to climate change. In addition to benefits to concrete materials (including applications in energy, petroleum and natural gas engineering), the project findings benefit a wide spectrum of technologies that deal with glass and ceramic products. The improved understanding of durability of silicate glass is valuable to technologies for containment of nuclear waste materials inside glass matrices. Four Ph.D., one Masters, and four undergraduate (REU) students were trained in this project. Among them, one Ph.D., one Masters, and two REU students are female. In addition to the state-of-the-art research training, the graduate students have received training in principles of pedagogy and effective instruction and have been mentored in teaching undergraduate courses. The REU students were given valuable opportunities to work with PIs, graduate students and other scientists, to attract them to research and technology development and become the next generation of U.S. scientists and engineers. Two of the four REU students have subsequently enrolled in graduate degrees in civil engineering. A new undergraduate course was developed (CE437: Engineering Materials for Sustainability), which integrates sustainability into civil/structural engineering and design. This course adds positively to civil engineering curriculum by enabling students to learn about and practice life-cycle assessment methods and green design strategies through real-life numerical problems and computer simulations. In addition, an outreach activity (Expanding Your Horizons: Career Day for Girls) was organized on Penn State campus, during which, 110 middle school female students attended a civil engineering/concrete workshop along with 4 other science and engineering workshops. The goals of this activity were to increase young women’s interest in science, technology, engineering, and mathematics (STEM) through immersive, hands-on experiences; fostering awareness of career opportunities in scientific and technical fields; and providing young women with positive role models who are active in STEM studies and careers. The findings from this project have been disseminated in nine journal and four conference papers, three Ph.D. dissertations, and twelve conference presentations.
