Activation of Binary Binder Containing Fly Ash and Portland Cement Using Red Mud as Alkali Source and Its Application in Controlled Low-Strength Materials

The feasibility of using red mud as an alkali source in alkali-activated fly ash and Portland cement (PC) based binary binder for controlled low-strength material (CLSM) is investigated. The alkalis in red mud are NaOH and Na2CO3. The inclusion of red mud increases the pH value of pore solutions in the mixtures by direct dissolution of NaOH and reaction of Na2CO3 with portlandite formed in PC hydration. The mixture with increased pH value accelerates the hydration of fly ash and PC based binary binder, contributing to the strength development of CLSM. The red mud also acts as a micro-filler that refines the pore structure and thus reduces the concentration of harmful pores (≥50 nm). The engineering performance is enhanced with inclusion of red mud, which is mainly attributed to the accelerated hydration of the binary binder and the refined pore structure.