Enhanced mechanical and self-healing properties of rice husk ash-incinerated sugarcane press mud biogeopolymer pastes

Abstract

This study examines the use of rice husk ash (RHA) and incinerated sugarcane press mud (ISPM) as precursors in the lime/pozzolan geopolymer system and the effect of the bacterium Lysinibacillus sp. WH on the mechanical properties and microstructures. The RHA-to-ISPM ratio was varied, and the geopolymer pastes were cured at ambient temperature. The results show that an increase of ISPM content up to 5% improves strength and reduces water absorption and voids, while higher ISPM levels beyond 5% degrade the quality of geopolymer paste. An increase in ISPM content reduces setting times due to an increase amount of calcium in the pastes. Notably, the addition of bacteria resulting in a reduction of setting times has been proved for the first time in this work. Moreover, the addition of bacteria can enhance all mechanical properties and introduce self-healing abilities, with microcracks healing within < 20 days of treatment, regardless of mix proportions. Microstructural studies, using a scanning electron microscope (SEM), Fourier Transform Infrared Microscopy (FT-IR), X-ray diffraction (XRD), and Rietveld refinement analysis, reveal that bacteria increase cristobalite, and decrease quartz, thus resulting in strength enhancement of geopolymer pastes. Furthermore, this work is the first to provide evidence that bacteria tend to reduce the efflorescence formation as confirmed by a decrease in gaylussite. These findings pave ways to the production of more sustainable geopolymer systems via upcycling wastes and prolonging service life due to bacterial activity. Keywords Lime/pozzolan system, Rice husk ash, Press mud, Self-healing property, Geopolymer Cement is the most widely used binder for construction materials. Unfortunately, a large amount of CO 2 is released to the atmosphere in the cement production process, thereby becoming one of the major causes of global warming 1 . It is, therefore, necessary to research novel alternative binders in place of cement. An alkali activated binder or geopolymer has been discovered as a more environmentally friendly material due to its less CO 2 emission compared to Portland cement 2 . Geopolymer is an inorganic polymer synthesized by combining aluminosilicate materials with alkali solutions. A 3-dimension structure of geopolymer occurs through complex chemical processes including geopolymerization of alumino-silicate materials, dissolutions of precursor materials by alkali activator solutions, and polycondensation of the products 3 . Geopolymer can be produced from pozzolanic materials such as rice husk ash 4 , fly ash 5 , bottom ash 6 , and blast furnace slag 7 , which serve as silica (SiO 2 ) and alumina (Al 2 O 3 ) sources for geopolymerization. The alkali activator solution is commonly a mixture of sodium hydroxide and sodium silicate. In some cases, an optimum amount of calcium compounds can be added to improve reactivity of the pozzolan precursors, and thus improve compressive strength of geopolymer [8][9][10] .