Análisis de la influencia de la adición de biosólidos calcinados en la resistencia a la compresión de un mortero

Abstract

The feasibility of using biosolids from a wastewater treatment plant (WWTP) as a cementitious supplement and incinerated at 850°C is being studied. Two types of ash were prepared, differentiated by their calcination time: BC1 (biosolids calcined for sixty minutes) and BC3 (biosolids calcined for one hundred and eighty minutes). Both were included in place of 5%, 10%, 15%, 20%, 25%, and 30% of the cement mix, generating series of 50 mm cubic specimens that were cured for a period of 28 days. The compressive strength test results show two ideal situations: 1. BC3 at 5%, which improves the compressive strength to 186 kg/cm² (+52% compared to the control), and 2. BC1 at 30%, reaching a strength of 218 kg/cm² (+79% compared to the control). The multiscale SEM-EDS study (200→2 µm) revealed that the 3-hour ash, which is rich in reactive Ca-Si-Al oxides, consumes portlandite and produces dense C-S-H/C-A-S-H gels, which obscure the transition area between the paste and the aggregate. In contrast, the 1-hour ash, with residual carbon, also functions as an internal curing agent and as a filler by filling capillaries at high dosages. EDS spectra confirmed that the best-performing mixtures had a Ca/Si ratio between 1.2 and 1.5, as well as the presence of carbon-aluminates and ettringite that strengthen the matrix.