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Marija Krstic

The City College of New York, Ph.D.
EREF Scholar 2016

Recycled Glass as a Supplementary Cementitious Material in High Performance ConcreteProject Description:
The aim of this research is to use post-consumer recycled glass pozzolan (nanoparticles of ~12 microns) as cementitious material for concrete. Interestingly, concrete is the most used material in the world, second only to water. Conventional concrete is produced with Portland cement. The production of cement is energy intensive and has raised environmental concerns since one ton of cement produces an equal ton of CO2. In the USA about 90 million tons of cement are used annually, with 3 million tons used in New York. Most contemporary concrete applications for buildings and infrastructure use High-Performance Concrete mixes which are produced by replacing a percentage of cement with Supplementary Cementitious Materials (SCMs), consisting mainly of Fly-Ash and Slag. The addition of SCMs are necessary to achieve high strength, increased durability, and reduce permeability of deleterious substances such as salt solutions. The added benefit of SCMs is production of ‘Green Concrete” by reducing CO2.

The two most used SCMs are Fly-Ash and Slag. However, recently there were shortages in availability of both. Thus, in response to the urgent need for an effective and economical SCM to support concrete construction, this research is focused on a new glass pozzolan SCM from recycled post-consumer glass. Her research offers a tremendous opportunity to benefit both, the glass recycling industry and the concrete production industry in the USA and the world.

This research has shown so far that recycled post-consumer glass pozzolan is an exceptional SCM for concrete. This work has been motivated by the results obtained by a commercial product branded as Pozzotive developed by Urban Mining Northeast and used in concrete-block, cast-in-place and pre-stressed concretes. Due to lack of marketable and profitable applications, post-consumer glass is often simply land-filled, or if processed the cost is subsidized by municipalities.

Glass pozzolan is produced from post-consumer recycled colored glass, which currently has no value-added real market application except as filler material. In the USA about 12 million annual tons of glass are discarded (~30% recycled). In NYC 140,000 tons per year (~60% recycled). The Materials Recovery Facility in NYC managed by SIMS produces about 70,000 tons per year of crushed mix colored glass, which represents an exceptional sustainable resource for large-scale production of glass pozzolan. This work can lead to large-scale worldwide implementation of glass pozzolan industry with significant financial and ecological benefits to society.

This research is focused on development and characterization of concrete mixes with glass SCM. This work so far has included replacements of cement from 20% to 40%. The results are impressive, with excellent strength and durability characteristics surpassing comparable Fly-Ash and Slag formulations. On May 5, 2016, the prototype mix designs were used in sidewalk construction in NYC by the Department of Design and Construction (DDC). Future applications for three 27 story buildings are being planned by the nonprofit organization DURST. Also, Google in California and officials in Toronto-Canada have used these results and guidelines for trial sidewalk projects. Moreover, this work and test results have contributed to the ASTM acceptance of this product to qualify under the ASTM C-618 Specifications, which is essential for main stream acceptance and applications of glass pozzolan in the construction industry.

Marija Krstic is currently a Doctoral student and Research Assistant at the City College of New York. She received her BS and MS Civil Engineering degrees from Serbia, the University of Nis. Her specialty is on materials and structures. She has been at the City College of New York since 2012, obtaining first a Master’s Degree in Structural Engineering in 2014 and proceeding to work on her doctoral degree thereafter. She is an outstanding student with an excellent academic record, and she is making very good progress in her research. Recently, she successfully passed the Ph.D. Qualifying Exam and by the Fall Semester she will be ready to defend her Research Proposal. She works with the Building Product Ecosystems (BPE) Group whose major activity is scaling industry acceptance and availability of recycled glass pozzolan as a supplementary cementitious material (SCM). Forward-thinking building owners, like Google and the Durst Organization follow her work on this topic. The City College of New York has recently highlighted the significance of the implementation of her research in the field, performed by the Department of Design and Construction of New York City.