Characterization of thermally cured nanotubes-based geopolymer composites

Umara Nasir , Nejib Ghazouani , Mohd Ahmed

Abstract

This study examines the role of aluminosilicate nanotubes (ANTs) in improving the performance of thermally cured geopolymer concrete (GPC) prepared using Class F fly ash and metakaolin. The main objective is to enhance early-age strength, durability, and microstructural stability of GPC under high-temperature conditions relevant to geothermal environments. ANTs were incorporated at 0-3.0 wt% of binder, and specimens were cured at 80oC. A systematic experimental program was conducted, including tests on flowability, compressive and tensile strength (3 h to 28 days), drying shrinkage, water absorption, and pore structure. Microstructural and chemical analyses were performed using XRD, FTIR, SEM, and TGA/DTG. Statistical evaluation was carried out using ANOVA and Tukey's HSD test to confirm the significance of results. Results show that ANTs reduce workability due to increased water absorption. However, significant improvements in mechanical and durability properties were observed. The optimum dosage of 2.0 wt% ANTs increased 1-day compressive strength by 32.77% and enhanced early tensile strength by up to 191%. This mix also showed the lowest water absorption and drying shrinkage, along with a denser pore structure. Microstructural results confirmed improved gel formation and matrix compactness. Hence, the study demonstrates that controlled incorporation of ANTs, especially at 2.0 wt%, can effectively enhance the performance of thermally cured GPC. This approach offers a durable and sustainable solution for construction in high-temperature environments such as geothermal tunnels.

Key Words

compressive strength; drying shrinkage; geopolymer composites; nanotubes; scanning electron microscopy; thermal curing

Address

Umara Nasir — Department of Civil Engineering, University of Engineering and Technology Taxila, 47050, Pakistan
Nejib Ghazouani — Mining Research Center, Northern Border University, Arar, 73213, Saudi Arabia
Mohd Ahmed — Department of Civil Engineering, College of Engineering, King Khalid University, Abha 61421, Saudi Arabia; Center for Engineering and Technology Innovations, King Khalid University, Abha 61421, Saudi Arabia

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