TY - JOUR
T1 - Mechanical performance and micro-structure of bentonite-fly ash and bentonite-sand mixes for landfill liner application
AU - Gupt, Chandra Bhanu
AU - Bordoloi, Sanandam
AU - Sahoo, Rakesh Kumar
AU - Sekharan, Sreedeep
N1 - Funding Information:
The authors acknowledge the Department of Science and Technology, India, for funding the current research work vide Project No. SR/S3/MERC/0040/2011. The authors further thank the Central Instrument Facility (CIF), Centre for the Environment, Environmental Engineering Department at the Indian Institute of Technology Guwahati for providing the necessary support for the completion of this work.
Funding Information:
The authors acknowledge the Department of Science and Technology , India, for funding the current research work vide Project No. SR/S3/MERC/0040/2011 . The authors further thank the Central Instrument Facility (CIF), Centre for the Environment, Environmental Engineering Department at the Indian Institute of Technology Guwahati for providing the necessary support for the completion of this work.
Publisher Copyright:
© 2021 Elsevier Ltd
PY - 2021/4/10
Y1 - 2021/4/10
N2 - Low permeability (10−9 m/s) and adequate unconfined compressive strength (UCS = 200 kPa) forms the basis of using compacted bentonite (B) clay in landfill liner. However, B induces cracks or swells upon excessive drying and wetting events, respectively. To overcome failure of liner layer, B is amended with cohesionless sand (S), despite S being costly and ecologically unsustainable. In the recent past, fly ash (FA) a by-product from thermal power plants, has been explored as a suitable additive material in landfill liner, in line with the adoption of cleaner usage of waste material in construction. The objective of this study was to investigate the mechanical performance of both B-FA and B–S mixes along with the related changes in microstructure and physio-chemistry. 180 sets of UCS tests were conducted on 4 B-FA mixes (including class C and F) and B–S mixes at different compaction state and additive rate. Unlike B–S mixes, all B-FA mixes showed an increase in UCS with respect to B regardless of compaction state and additive rate. Detailed microstructure and physio-chemical characterization for B–FAs revealed the relative abundance in the formation of calcium aluminosilicate hydrate, and ettringite minerals after curing as compared to B–S mixes. In fact, Class C FA exhibited the largest UCS even at high moisture content, which can be attributed to higher formation of minerals upon curing. All B-FA mixes showed UCS greater than the minimum limit for liner application regardless of the compaction state. All B–S mixes did not adhere to the minimum UCS criterion at higher moisture content. FA additive at 50% showcased the highest increase in strength improvement factor (10 out of 12 cases), while for B–S mixes, this factor decreased with an increase in additive rate. Based on the measured data, two new linear relationships of UCS with pH and electrical conductivity (both indicative of reaction) of the mixes were observed. The relationship with respect to pH was more pronounced at higher moisture content as pH indicates the existence of CaO minerals.
AB - Low permeability (10−9 m/s) and adequate unconfined compressive strength (UCS = 200 kPa) forms the basis of using compacted bentonite (B) clay in landfill liner. However, B induces cracks or swells upon excessive drying and wetting events, respectively. To overcome failure of liner layer, B is amended with cohesionless sand (S), despite S being costly and ecologically unsustainable. In the recent past, fly ash (FA) a by-product from thermal power plants, has been explored as a suitable additive material in landfill liner, in line with the adoption of cleaner usage of waste material in construction. The objective of this study was to investigate the mechanical performance of both B-FA and B–S mixes along with the related changes in microstructure and physio-chemistry. 180 sets of UCS tests were conducted on 4 B-FA mixes (including class C and F) and B–S mixes at different compaction state and additive rate. Unlike B–S mixes, all B-FA mixes showed an increase in UCS with respect to B regardless of compaction state and additive rate. Detailed microstructure and physio-chemical characterization for B–FAs revealed the relative abundance in the formation of calcium aluminosilicate hydrate, and ettringite minerals after curing as compared to B–S mixes. In fact, Class C FA exhibited the largest UCS even at high moisture content, which can be attributed to higher formation of minerals upon curing. All B-FA mixes showed UCS greater than the minimum limit for liner application regardless of the compaction state. All B–S mixes did not adhere to the minimum UCS criterion at higher moisture content. FA additive at 50% showcased the highest increase in strength improvement factor (10 out of 12 cases), while for B–S mixes, this factor decreased with an increase in additive rate. Based on the measured data, two new linear relationships of UCS with pH and electrical conductivity (both indicative of reaction) of the mixes were observed. The relationship with respect to pH was more pronounced at higher moisture content as pH indicates the existence of CaO minerals.
KW - Bentonite
KW - Compressive strength
KW - Fly ash
KW - Landfill liner
KW - Microstructure
UR - http://www.scopus.com/inward/record.url?scp=85100039850&partnerID=8YFLogxK
U2 - 10.1016/j.jclepro.2021.126033
DO - 10.1016/j.jclepro.2021.126033
M3 - Article
AN - SCOPUS:85100039850
SN - 0959-6526
VL - 292
JO - Journal of Cleaner Production
JF - Journal of Cleaner Production
M1 - 126033
ER -
