Sugarcane bagasse ash (SCBA) is an agro-industrial byproduct with potential for use as a supplementary cementitious material (SCM) due to its pozzolanic properties, primarily attributed to its high silica and alumina contents. To confirm this pozzolanic potential, the reactivity of the ash must be assessed. Over the years, various methods have been developed to evaluate the chemical activity of SCMs. Recently, the R3 test was proposed as a rapid, relevant, and reliable method for determining the reactivity of these materials. However, as a relatively new technique, data on its application remain limited, especially for biomass ashes. In this context, this study aimed to apply the R3 test to evaluate the reactivity of different SCBAs and correlate the results with the conventional performance index method. Eight ashes were produced under laboratory-controlled conditions, and six residual ashes were collected from a sugar-ethanol mill, totaling fourteen ashes with different carbon and quartz contents. As expected, ashes with higher content of amorphous silica demonstrated greater pozzolanic activity. Carbon-rich ashes exhibited good pozzolanicity according to both performance index and R3 tests, whereas quartz contamination negatively affected reactivity due to its inert nature. Both bound water content and heat release measured in the R3 test showed strong correlations with performance index results (R2 > 0.90), supporting the suitability of the R3 test for assessing SCBA reactivity and suggesting its potential applicability to other biomass ashes. Based on these correlations, minimum requirements for bound water content and heat release have been proposed to classify reactive materials effectively.