Siregar, Shinta Marito, Syahrul Humaidi, Nurdin Bukit, and Erna Frida. “Palm Oil Fuel Ash and Fly Ash for a Partial Replacement of Cement in High-Quality, Environmentally Friendly Mortar As a Solution to Industrial Waste”. Science and Technology Indonesia 9, no. 1 (January 22, 2024): 59–68. Accessed May 1, 2026. https://www.sciencetechindonesia.com/index.php/jsti/article/view/834.