F. S. Khalid, Z. Zaki , S. M. Saadin , S. Shahidan , J.M. Irwan , M.H. Wan Ibrahim , N.S Ghadzali , N. A. A. Guntor. “Effect of Water to Cement Ratio and Replacement Percentage of Recycled Concrete Aggregate on the Concrete Strength”. International Journal of Advanced Science and Technology, Vol. 29, no. 6s, Apr. 2020, pp. 1625 -35, http://sersc.org/journals/index.php/IJAST/article/view/9312.