Use of recycled aggregates in pumice-based geopolymer concretes
Journal of Building Engineering, cilt.130, 2026 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 130
- Basım Tarihi: 2026
- Doi Numarası: 10.1016/j.jobe.2026.117054
- Dergi Adı: Journal of Building Engineering
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Compendex, INSPEC
- Anahtar Kelimeler: Geopolymer, Mechanical properties, Microstructural properties, Natural aggregate, Pumice, recycled aggregate, Sustainability
- Van Yüzüncü Yıl Üniversitesi Adresli: Evet
Özet
In this study, the effect of recycled aggregate on the mechanical, physical, and microstructural properties of pumice-based geopolymer concrete was investigated in a comparative manner. Pumice powder was used as the binder, alkali activation was performed using a 12 M NaOH solution, and the specimens were produced in 40 × 40 × 160 mm prism molds and cured at 50 °C for 72 h. While the early-age compressive strengths of natural aggregate geopolymer concrete (NAGPC) specimens ranged from 8.93 to 27.62 MPa, these values increased to 14.96–35.30 MPa in recycled aggregate geopolymer concrete (RAGPC) specimens. In addition, the shorter setting completion time of RAGPC specimens, approximately 50 h compared with approximately 72 h for NAGPC specimens, suggests that the old mortar phase present on the surface of the recycled aggregate may accelerate the reaction kinetics. Physical tests revealed that RAGPC specimens exhibited higher water absorption rates and lower densities. These changes were attributed to the porous old mortar phase present on the surface of the recycled aggregate. However, the fact that RAGPC specimens exhibit higher compressive strength despite high water absorption values indicates that recycled aggregate should be considered not merely as a physical aggregate substitute but also as an active component from chemical and microstructural perspectives. Microstructural analyses have shown that the old mortar phase on the surface of recycled aggregate may contribute to the development of the interface transition zone by providing additional nucleation sites and calcium-rich regions. Mineralogical differences—such as the preservation of the amorphous aluminosilicate structure observed in RAGPC samples and the higher intensity of crystalline peaks—indicate that recycled aggregates may influence both the reaction development and the microstructure of pumice-based geopolymers. In conclusion, the findings suggest that recycled aggregates may contribute positively to the early-age strength development and setting behavior of pumice-based geopolymers. However, the results should be interpreted within the limitations of the comparative experimental design. This study provides preliminary evidence regarding the combined use of pumice and recycled aggregates and contributes to the understanding of aggregate-matrix interaction in sustainable geopolymer systems.