The sugar cane bagasse ash (SCBA) studied presented a high percentage of crystallized material
(mainly quartz, also calcite) and a high proportion of organic matter (ca. 25%). Despite this, the
amount of soluble material in alkaline conditions suggested that it could be an interesting waste
material for producing alkali-activated binders. Alkali-activated binders based on slag/SCBA blends
were prepared and their microstructure, their physico-chemical properties and their mechanical
strength development were assessed. Sodium hydroxide and a waterglass mixture were selected for
activating BFS/SCBA samples: 5 mol kg
−1
of sodium cation and a SiO2/Na2O molar ratio of 1.46.
Mineral BFS/SCBA mixtures were dosed in the following proportions by weight: 100/0, 85/15, 75/25
and 60/40. Studies on pastes and mortars cured for 3–7 days at 65 °C demonstrated that there was an
important reaction degree of SCBA particles in the formation of gel matrices, and a good contribution
on compressive strength was measured: SCBA containing mortars with 42–54 MPa after 3 days of
curing at 65 °C were obtained. The development of BFS/SCBA blends alkali-activated matrices cured
at 20 °C was better than at 65 °C: the H2O/OH groups in the gel formed were strongly bonded according
to the thermogravimetric analysis. Moreover, mortars yielded high strengths after long curing times (90
and 270 days): compressive strengths in the 55–65 MPa range were obtained. In the same way, the
porous structure of mortars was enhanced for mixtures cured at 20 °C, yielding a reduction in total
porosity to 7.5%–10%, clearly lower than those found for mortars cured at 65 °C (9.5%–12.5%). In
general terms, this study demonstrates the feasibility of the use of slag/SCBA blends in alkali-activated
systems, and these types of mixtures could form part of an alternative approach to reusing ashes
obtained in the sugar cane industry.