Influência da cinza do bagaço de cana-de-açúcar na microestrutura de compostos cimentícios com cura em autoclave

Abstract

Autoclave curing accelerates cement hydration, increases mechanical strength, and enables rapid demolding. In this type of curing, it is common to use an external silicon source to enhance microstructure development; therefore, sugarcane bagasse ash (SCBA) was used. This research aimed to evaluate the influence of SCBA on the microstructure of cementitious composites subjected to autoclave curing. The study was divided into two steps: analysis of the heterogeneity of four types of SCBA, and evaluation of their influence on the microstructure and compressive strength of cementitious composites. In the first stage, two ashes were obtained from bagasse combustion, and two others were re-burned in the laboratory from ashes collected in decantation basins, aiming to reduce organic matter content. SCBA samples were characterized in terms of loss on ignition, chemical composition, morphology, particle size distribution, and reactivity (Lúxan test). Similar behavior was observed between the bagasse-derived ashes and between the decanted ashes. The SCBA from bagasse showed higher reactivity, but the mass loss (>90%) made its use impractical. Thus, the SCBA from the boilers was used to produce mortars with a 1:3 mix ratio (binder:sand), in which the binder consisted of 0%, 10%, 20%, and 30% SCBA as a partial replacement of cement by mass. The water-to-binder ratio was 0.5, and two curing methods were applied: water curing in a saturated calcium hydroxide solution and autoclave curing. Samples were analyzed for microstructure, porosity, water absorption, and compressive strength. Water curing resulted in higher mechanical strength due to lower porosity. SCBA-containing samples showed approximately 20% lower compressive strength compared to the reference, with no significant variation among different SCBA contents. Under autoclave curing, only the 30% replacement level prevented the formation of the α-C2SH phase, enabling the development of tobermorite and xonotlite. However, the increased porosity led to lower strength. It was concluded that water curing provided better performance than autoclave curing.