Effect of Rubber Sludge on the Physical and Mechanical Properties of Low Calcium Fly Ash-Based Geopolymer - T. Hoe-Woon; H. Cheng-Yong; N. Qi-Hwa; M.M.A.B. Abdullah; L. Jia-Ni; O. Shee-Ween; O. Wan-En; H. Yong-Jie (Archives of Metallurgy and Materials)