Grantee Research Project Results

2014 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 , Farbakhs, Faraz , Peiravi, Meisam , Sinha, Swara
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, 2013 through August 14,2014
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 Awards , P3 Challenge Area - Sustainable and Healthy Communities , P3 Challenge Area - Chemical Safety , 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:

Fly ash 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 (iron oxide) concentration work done during the 2^nd project year (August 15, 2023 to August 14, 2014) using the two fly ash samples are summarized below:

• From the sample characterization, both SIPC and CWLP fly ash samples are qualified as ASTM Class F type fly ash by examining Calcium content of close to or below 5 %. Particle size analysis indicated that 86 % of CWLP fly ash was finer 45 um while SIPC fly ash had 91% of -45 micron size fraction. The Loss on Ignition (LOI) values examined for both SIPC and CWLP fly ash were 5.34% and 1.72%, respectively. The above-mentioned properties contribute in making the fly ash samples favorable for Geopolymer concrete production.
• To optimize the strength of geopolymer concrete, a series of parametric studies were designed and conducted with both SIPC and CWLP fly ash type. The parameters targeted were Hydroxide type, Hydroxide Concentration, Silicate to Hydroxide ratio, Water to Na2O ratio, Curing Time and Curing Temperature.
• The fractional factorial test was designed to investigate the effect of parameters on Geopolymer concrete strength. Mortar samples with dimensions of 2x2x2 inches were made with SIPC fly ash. The mortar specimen with the highest compressive strength which reached 5063 psi at day 60 had NaOH concentration of 16 Molars, the silicate to hydroxide ratio of 1:1, and were cured for 2 days at 90 °Celsius. The fractional factorial design test program indicated the concentration of hydroxide, curing time and temperature as the the significant parameters with respect to the compressive strength of the specimen.
• A full factorial design test was developed to determine the best possible combinations of hydroxide and silicate for the activator alkaline solution. The potassium hydroxide and silicate were involved to compare with the sodium hydroxide and silicate alkaline solution. In this test, the hydroxide concentration of 16 molar, 3 days curing and 70 °C curing temperature remained constant. It was observed that for both CWLP and SIPC fly ash, the mixture of NaOH and NaSiO₃ combination yield higher strength. Therefore, NaOH and NaSiO₃ were used as the alkali/silicate combination for all the subsequent tests.
• The optimal mixture design for SIPC geopolymer concrete was with 18 molar NaOH concentration and alkali to silicate ratio of 1:1. The compressive strength peaked at 6720 psi after 28 days of curing; it stabilized at 6530 psi after 60 days of curing. With the same mixture condition, the CWLP fly ash reacted differently. The hydroxide to silicate ratio of 1:2 was more favorable for CWLP geopolymer concrete.
• A Box-Behnken test program was designed following the factorial design for the CWLP gepolymer, to determine the best process parameter vaues to achieve the maximum possible compressive strength of geopolymer concrete. The NaOH solution concentration, curing temperature and curing time were the three significant factors, and the three responses were the compressive strength at 7^th day and 28^th day after curing as well as the split tensile strength at 28^th day after curing. The levels for NaOH solution concentrations that were tested included 12, 14 and 16 Molars. For curing time, 1, 3 and 5 days were chosen as variables.  Curing temperature was varied in the range of 50 to 90 degrees Celsius.
• Based on the Box-Behnken design test results, it was concluded that the alkali concentration and curing temperature are significant parameters affecting both compressive and tensile strengths of the CWLP fly ash-based geopolymer concrete. Lower alkali concentration and lower curing temperature resulted in high compressive strength of CWLP geopolymer concrete. The compressive strength of the CWLP fly ash based geopolymer increased with a decrease in alkali concentration, a trend that is exactly opposite to that observed with SIPC fly ash based geopolymer concrete.
• The highest strength of CWLP concrete was achieved with 12 molar NaOH concentration and cured for 3 days under 50 °C. The compressive strength and tensile strength reached 4613 psi and 388 psi at the 28^th day after curing. Although this compressive strength is not high as high as SIPC�s, it certainly compares very favorably with the strength (~4000psi) of conventional OPC concrete.
• The tensile strength refers to the greatest stress a material can tolerate when being stretched or pulled before failing or cracking. The tensile strength for the optimal SIPC concrete was examined to be 405 psi. High strength Geopolymer concrete sample were concluded to achieve higher tensile strength than the OPC counterpart.
• Slump Test was conducted to measure the workability of fresh concrete. The slump height of 4 inches is preferred in OPC concrete industry. For CWLP geopolymer concrete mix, 3.7 inch, 4.0 inch and 4.1 inch drop were measured from the concrete paste of 12M, 14M and 16M alkali solution, respectively. However, for the optimal SIPC mix which gave the highest strength, the slump height was above 5 inches. This slightly larger slump height occurred apparently due to the high concentration of NaOH that required the addition of more amount of water to the mix.
• Freeze-Thaw Tests were conducted on Geopolymer concrete with the optimal mixture of both SIPC and CWLP concrete. After 12 freezing and cooling cycles, there was over 5% mass loss on the Geopolymer concrete samples made with SIPC fly ash. The weight of CWLP based geopolymer concrete on the other hand increased by about 1 % of mass on average apparently due to water absorption in pores.
• An economic analysis was conducted to compare the cost of geopolymer concrete versus the OPC concrete. As detailed in the following table, the cost of Geopolymer concrete is compares very favorably with that of the OPC concrete cost. The costs/cubic yard in respectively order are $106.50 and $108.90.

Future Activities:

• Geopolymer concrete specimen produced using two different F-class fly ash samples provided compressive strength up to 6500 psi. The minimum strength achieved of about 4600 psi is better than that of the conventional cement concrete.
• The cost of geopolymer concrete compared very favorably with that of the OPC concrete. The respective cost figures on kg basis were $2.07 and $2.11; the respective costs/cubic yard were $106.50 and $108.90.

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

2013 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