Grantee Research Project Results

2013 Progress Report: Sustainable Utilization of Coal Combustion Byproducts through the Production Of High Grade Minerals and Cement-less Green Concrete

EPA Grant Number: SU835349
Title: Sustainable Utilization of Coal Combustion Byproducts through the Production Of High Grade Minerals and Cement-less Green Concrete
Investigators: Mohanty, Manoj K. , Kolay, Prabir , Kumar, Sanjeev , Rimmer, Sue , Wiltowski, Tomasz , Yang, Xinbo , Matenda, Amanda Z , Ackah, Louis , Shin, Sanguok , Jha, Praveen , Heller, Tom , Gribble, Luke
Current Investigators: Mohanty, Manoj K. , Kolay, Prabir , Kumar, Sanjeev , Liu, Jia , Rimmer, Sue , Wiltowski, Tomasz
Institution: Southern Illinois University - Carbondale
EPA Project Officer: Hahn, Intaek
Phase: II
Project Period: August 15, 2012 through August 14, 2014 (Extended to August 14, 2015)
Project Period Covered by this Report: August 15, 2012 through August 14,2013
Project Amount: $89,943
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2012) Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Sustainable and Healthy Communities , P3 Challenge Area - Chemical Safety , P3 Awards , Sustainable and Healthy Communities

Objective:

1. To develop low-cost process flowsheets for extracting valuable metal oxides, such as Iron oxide and Aluminum Oxide from the waste products of combustion of high-sulfur coal typically found in the Illinois basin.
2. To develop a suitable process to utilize majority of the coal combustion residues as a useful product in the form of a geopolymer-based concrete without the use of any Portland cement.
3. To educate the present and future university students about the challenges behind the continued use of coal-based electricity and the commercialization potentials of various high-value end uses of coal combustion byproducts.

Progress Summary:

Flyash samples were collected in bulk (55 gallon barrels) from two different locations in Illinois, named as SIPC and CWLP. Some of the important findings of the geopolymer concrete work and magnetite preconcentration work done at the Southern Illinois University Carbondale using the two fly ash samples are summarized below:

• A simple and low cost process flowsheet has been developed using a combination of a density based separator and wet drum magnetic separator to extract high grade magnetite from flyash. The first step of the process was verified in a relatively large-scale using a 10 inch diameter water-only cyclone that concentrated magnetite from 8.32% in the fly ash feed to 29.87% in the cyclone underflow product. The next step will be to further concentrate the magnetite content to above 90% level.
• The geopolymer concrete test samples composed of coal fly ash, fine aggregate (top size of 4.76 mm), coarse aggregate (top size of 20 mm), alkaline liquid (mix of alkaline solution and silicate solution) and water in different portion of each composition.
• The fly ash to fine aggregate ratio of 1:1.5~2.5 and the fly ash to coarse aggregate ratio of 1: 3.0~3.3 have been mostly used to produce geopolymer concrete. While the ratio of fly ash to aggregates can be varied in the range without significantly affecting the performance of concrete, the alkaline liquid to fly ash ratio of 0.35 is more critical in geopolymer paste produced with SIPC and CLWP fly ash to achieve a comparable performance with conventional cement concrete.
• Based on preliminary studies conducted in the past, NaOH solution was selected to produce stronger specimens with a 16 molarity (16M) concentration. The alkaline liquid combined with Na2SiO3 solution provided fairly good compressive strength at the ratio of 1:1. To achieve a high compressive strength geopolymer concrete, NaOH solution concentration of 12M, 14M, 16M and 18M have been used to produce concrete with both fly ash samples. For SIPC fly ash, a set of comparative experiments have been conducted to determine the optimized concentration for alkaline solution.
• The Na2SiO3 solution used in the experiments was made of water soluble sodium silicate powder with ratio of Na2O: SiO2: H2O = 14.7%: 29.4%: 55.9%.
• The amount of added water during mixing has been determined by controlling the ratio of H2O/Na2O in fly ash, sodium hydroxide solution and sodium silicate solution. Extra water addition barely affects the chemical reaction occurring during the geopolymerization process; however additional water helps to produce workability during concrete mixing and molding steps. From experiments conducted with both SIPC and CWLP fly ash, it was found that that the amount of water in the geopolymer mixture at H2O/Na2O ratio of 10 is optimum from both strength and workability points.
• Plasticizer can be applied while the mixture contains less water. The amount of plasticizer can be 0~2% of the weight of fly ash. Past literature indicates, plasticizer can promote the workability without affecting the chemical reaction of geopolymer aggregation.
• After the geopolymer paste casted into cylindrical molds, one day rest time in room temperature before curing in the oven was proved to have positive effect.
• The curing time of 3 to 5 days and curing temperature of 75 to 90 Celsius degree in the thermal oven have been applied for the 4 inch diameter by 8 inch height cylinder geopolymer concrete blocks. Past literature indicates curing temperature has more significant effect than the curing time; same observations were also made during this study. However, over-curing could happen by curing under a very high temperature to create cracks and deformation in the concrete specimen.
• The highest geopolymer concrete compressive strength of 6720 psi (at 28^th day after curing) was produced with mixture of SIPC fly ash: fine aggregate:  coarse aggregate = 1: 2.5: 3.3. The alkaline liquid combined with 1:1 ratio sodium hydroxide solution to sodium silicate solution. A concentration of 18 M sodium hydroxide solution was used and the curing time was 5 days (120 hours) at curing temperature of 75 Celsius degree.
• Statistically designed experimental program will be conducted to further optimize operating variables to further improve the compressive strength in future.

Future Activities:

• Class F fly ash generated from the combustion of Illinois coal could serve as a good raw material for geopolymer concrete.
• Magnetite of high grade (Davis tube analysis of >96%) could be extracted from fly ash generated from the combustion of high sulfur coal found in the Midwestern US.

Journal Articles:

No journal articles submitted with this report: View all 4 publications for this project

Supplemental Keywords:

Green concrete, fly ash derived magnetite, geopolymer

Progress and Final Reports:

Original Abstract

2014 Progress Report

Final Report

P3 Phase I:

Sustainable Utilization of Coal Combustion Byproducts through the Production of High Grade Minerals and Cement-less Green Concrete  | Final Report