Grantee Research Project Results
Final Report: Recycled Glass: Cement/Fly Ash Substitute in CLSM
EPA Grant Number: SU839469Title: Recycled Glass: Cement/Fly Ash Substitute in CLSM
Investigators: Solanki, Pranshoo , Jin, Guang , Bierma, Tom
Institution: Illinois State University
EPA Project Officer: Callan, Richard
Phase: I
Project Period: December 1, 2018 through November 30, 2019 (Extended to June 1, 2020)
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition Focusing on People, Prosperity and the Planet (2018) RFA Text | Recipients Lists
Research Category: P3 Awards , P3 Challenge Area - Air Quality
Objective:
Glass is often a byproduct of many municipal recycling programs. However, glass collected through the local single-stream recycling system represents a significant financial burden on the program due to lack of a market for mixed glass. Therefore, the primary objective of this project was to evaluate the feasibility of recycling glass powder (RGP) as a fly ash (FA) substitute in Controlled Low-Strength Materials (CLSM), also called as flowable fill. Following were the specific objectives:
1) Determine the quantitative relationship between the flow consistency of flowable fill and a) percent RGP substitution, b) finer RGP percentage 1,2, and c) coarser RGP percentage.
2) Determine the quantitative relationship between the penetration resistance of flowable fill and
a) percent RGP substitution, b) finer glass percentage1,2, and c) coarser glass percentage.
3) Determine the quantitative relationship between the 28-day compressive strength and stress-strain response of flowable fill and a) percent RGP substitution, b) finer RGP percentage, and c) coarser RGP percentage.
4) Characterize the changes in the microstructure of flowable fill due a) percent RGP substitution, b) finer RGP percentage, and c) coarser RGP percentage.
5) Determine the extent to which glass-based CLSM could potentially benefit a rural community. Finer RGP is greater than 90% passing through US Sieve No. 325 (< 0.044 mm, i.e., 44 µm); Finer RGP percentage is determined by weight of finer glass powder divided by total weight of cement to be partially substituted with glass powder; Coarser RGP is 0.21 to 0.60 mm powder with minimum fineness of 98% passing US Sieve No. 30 (< 0.600 mm, i.e., 600 µm)
Summary/Accomplishments (Outputs/Outcomes):
This study was undertaken to evaluate the feasibility of RGP as a FA substitute in flowable fill. A total of two types of RGPs, namely, finer (FG) and coarser (CG) glass powders, were used in different proportions for substituting with FA. Overall, a total of ten mortar mixtures and ten flowable fill mixtures were prepared by using different proportions of FA, FG and CG powders. The mortar mixtures were used to prepare cubes which were tested for 7-day compressive strength for determining the strength activity index (SAI). On the other hand, flowable fill mixtures were tested for flow consistency, penetration resistance, 28-day compressive strength, and stress-strain response. Further, casted cylindrical specimens for 28-day compressive strength were also weighed before strength testing for determining wet density and oven-dried after strength testing for determining moisture content. Further, microstructural study techniques, namely, SEM and EDS, were also used for characterizing the changes in the microstructure of flowable fill due to RGP substitution.
Conclusions:
Based on the study presented in this paper the following conclusions can be derived:
1. Single-stream waste glass could be cleaned and crushed to obtain desired gradation. However, crushing single-stream waste glass is labor intensive and milling equipment is recommended for crushing.
2. The substitution of cement with RGP in mortar mixtures was found to decrease the 7-day compressive strength. However, substitution of cement with CG reduced compressive strength of specimens more than the corresponding specimens prepared by substituting cement with FG powder.
3. The strength activity index values indicated that FG content up to 20% of cement can be allowed in concrete. Further, a constant decrease in the compressive strength of mortar mixtures with the increase in FG content was also observed.
4. Based on flow consistency results, RGP has the potential to be a suitable substitute of FA in flowable fill. However, flow consistency was found to decrease with increase in percent RGP substitution. Further, increase in the finer and coarser portion of the glass were found to improve and deteriorate flow consistency of the flowable fill mixtures, respectively.
5. The penetration resistance was found to depend on the percent RGP substitution and relative proportion of finer and coarser glass content in the flowable fill mixtures. Further, penetration resistance followed the trend of moisture content of casted specimens.
6. Overall, the compressive strength results show that RGP has the potential to be a suitable replacement of FA in flowable fill. The degree of improvement or deterioration in compressive strength was found to depend on combined influence of density and pozzolanic properties of RGP in flowable fill mixtures. Further, density and pozzolanic properties were found to depend on the percent RGP substitution as well as relative proportion of finer and coarser glass content in the flowable fill mixture.
7. Compressive strength was found to improve with increase in the finer portion of RGP. The FG percentage of 50% or more is recommended to achieve strength greater than control specimens. Substitution of FA with 100% FG produced maximum strength of flowable fill specimens.
8. All flowable fill specimens showed strain softening behavior. Overall, replacing FA with RGP made specimens brittle which could be attributed to more irregular and elongated particles of glass compared to fly ash.
9. Microstructural analyses found that cement and fly ash particles served as nucleation sites for the growth of the hydration production in flowable fill. Further, microstructure revealed formation of ettringite and C-S-H as major hydration products in the flowable fill specimens. These hydration products were found to bind aggregates, FA and RGP particles and thus improved compressive strength.
10. While many aspects of the local markets such as those in Durango and Normal/Bloomington are supportive of diverting recycled glass to substitute for fly ash in CLSM, the cost of glass milling and the limited use of CLSM locally make such diversion uneconomical at the present time. Developments that could alter this situation include lower-cost glass milling technology, alternative methods for harnessing the pozzolanic properties of glass (such as conversion to sodium silicate without milling) or altering state specifications for higher-volume concrete materials to include recycled glass.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
| Other project views: | All 2 publications | 1 publications in selected types | All 1 journal articles |
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Solanki P, Bierma T, Jin G. Properties of flowable fill produced by substituting fly ash with recycled glass powder. Construction and Building Materials 2020;265:120330. |
SU839469 (Final) |
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Supplemental Keywords:
flowable fill, fly ash, glass, compressive strength, flow, stress-strain, strength activity index, microstructure, single-stream waste, recyclingRelevant Websites:
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Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.