The Use of Sargassum spp. Ashes Like a Raw Material for Mortar Production: Composite Performance and Environmental Outlook

The accumulation of brown algae from the genus Sargassum has been increasing over the years in coastal regions of the Caribbean, Africa, Brazil, and Mexico. This causes harmful effects to the ecosystem, human health, the economy, and the climate due to gas emissions from its decomposition process. There is the possibility of this biomass being reused in civil construction, and some studies have been carried out on its application to common Portland cement mortar. As such, the objective of this study is to evaluate the potential of sargassum ash as a mineral addition to partially replace fine aggregates in Portland cement mortar. Characterization of the raw materials was carried out through X-ray fluorescence spectroscopy, loss on ignition, particle size distribution, Brunauer-Emmett-Teller (BET) analysis, real density, X-ray diffraction, scanning electron microscopy, and dispersion spectroscopy of electrons. The mortars were prepared by partially replacing the fine aggregate (sand) with sargassum ash at 0%, 5%, 10%, and 20%. Mortar performance was evaluated through water absorption, apparent porosity, apparent specific mass, and compressive strength 7, 28, and 63 days after curing. Lastly, a life cycle assessment was conducted in accordance with ISO standards 14040:2006 and 14044:2006. The results showed that replacing sand with sargassum ash increases water absorption and apparent porosity, and decreases the apparent specific mass and compressive strength as replacement increases. Nevertheless, the compressive strength results after 63 days for 5 and 10% replacement did not differ statistically from reference values. The life cycle assessment indicated that mortars with partial replacement of sand by sargassum ash show positive environmental impacts when compared to reference values for most categories, regardless of the scenario analyzed, especially for mortar with 10% replacement. As such, the use of sargassum ash at 10% does not alter the mortar's compressive strength values after 63 days, but does reduce its environmental impact. The application of this biomass in civil construction materials provides a destination for this algae, and that can be a solution to mitigate the social, environmental, and economic problems it has been causing.