Sanawang, W., Y. Chinnabut, S. Haruehansapong, W. Tangchirapat, and C. Jaturapitakkul. “Efficiency Factor of Palm Oil Fuel Ash in Concrete”. Science and Engineering Connect, vol. 45, no. 3, Sept. 2022, pp. 393-10, https://ph04.tci-thaijo.org/index.php/SEC/article/view/10314.