R. . Karolina, M. A. Sofran, M. . Handana, Syahrizal, and R. I. . Siregar, “Geopolymer Concrete Made From Volcanic Ash of Mount Sinabung”, ijie, vol. 12, no. 1, pp. 315–320, Feb. 2020, Accessed: Jul. 18, 2024. [Online]. Available: https://publisher.uthm.edu.my/ojs/index.php/ijie/article/view/5732