Application of bacterial endospores in cement pastes containing wastes from sugar industry as binary and ternary binders: Mechanical, self-healing properties and microstructural analysis

• IBFC and ISPM are used as binary and ternary binders with cement for the first time. • Endospores slightly enhance strength, but largely reduce water absorption and void. • Binary binders show self-healing ability, while ternary binders do not. • Endospores accelerate cement hydration and self-healing time. This study examines the use of incinerated sugarcane black filter cake (IBFC) and incinerated sugarcane press mud (ISPM) as binary and tertiary binders with cement ranging up to 20 % by weight of cement. Compressive strength, water absorption, and void of the cement composites were investigated. Endospores of a calcifying bacterium Lysinibacillus sp. WH were added to enhance the mechanical properties and introduce self-healing ability to the materials. Moreover, microstructure analysis using X-ray diffraction (XRD) followed by Rietveld-refinement analysis and Thermogravimetric-Derivative thermogravimetry (TG-DTG) were conducted to study the effects of endospores on cement hydration. Scanning electron microscope (SEM) was also used to visualize microstructures. The results show that the incorporation of endospores slightly affects compressive strength of all mixes, while it can significantly reduce water absorption and void. XRD-Rietveld analysis indicates that an increase of IBFC to 15 % and 20 % causes an increase in alite. Moreover, a larger amount of portlandite is observable in endospore-added mixes compared to the controls, suggesting a higher degree of cement hydration. TG-DTG results show a tendency of more calcite accumulation in the endospore-added mixes than the ones without. Self-healing study suggests that the incorporation of endospores accelerates crack healing in all mixes within 4 days of treatment. The findings thus provide an insight into a promising way to upcycle waste from sugar industry, IBFC and IWFC specifically, in construction materials.