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• Utilizing lime mud as a filler can lead to the production of high-strength materials. • Lime mud can enhance material hydration by creating more nucleation sites. • The use of lime mud can refine pores and decrease pore structure. • Lime mud can be used in large replacement ratios, which can improve the sustainability of the mixture. Lime mud (LM) is a solid industrial byproduct with high alkalinity and calcium carbonate (CaCO 3) content produced by the paper industry. LM has been used and investigated as a supplementary cementitious material (SCM). However, using LM with a high replacement ratio causes agglomeration, which reduces the material's strength and has a detrimental effect on other properties. In addition to agglomeration, LM is unreactive; thus, in this work, a high replacement ratio (70%) of sand with raw LM was investigated in a mortar mixture containing silica fume (SF), considering the fast SF hydration properties of cement in a high alkaline environment, and river sand is used to reduce the agglomeration of LM. The effects of the replacement were then evaluated using compressive strength, X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM). The hydration kinetics were investigated using isothermal calorimetry. The experimental results showed that combining SF with a high replacement ratio (70%) of LM improves compressive strength and flexural strength by 16% and 59.7%, respectively. This is due to the filler nature of LM, which refines the pore structure. Furthermore, the highly alkaline environment provided by LM increased the secondary hydration of SF with cement, which also improved the strength. [ABSTRACT FROM AUTHOR]