Development of <i>Sargassum</i> spp. ash as filler material on cement composites with low carbon dioxide production

The use of Sargassum spp. biomass presents an opportunity for the construction sector. This proposal is significant since traditional sources for cement production are becoming increasingly scarce and exploring environmentally friendly alternatives, such as the incorporation of waste materials, is therefore necessary. The use of Sargassum spp. ash (SSA) as a filler material is proposed. Two pretreatments were implemented and the material was calcined at 600, 700 or 800°C. Tests for physical–chemical characterisation and pozzolanic activity were conducted. In addition, compressive strength tests of cement-based pastes with 1, 3 and 5% (by weight) replacements of Portland cement by SSA were carried out after 7 days of curing. The results showed no significant differences between the SSAs with thermal (A1H) and sodium (A2Na) pretreatments. The concentration of heavy metals was also found to be below the permissible limits, meaning that the material does not represent a health problem for users. Additionally, although A1H600 (ash calcined at 600°C) and A2Na800 (ash calcined at 800°C) presented significant pozzolanic activity, SSA cannot be considered as a pozzolanic material. Furthermore, ash replacements of 1% and 3% in A1H600 increased the compressive strength by, respectively, 2.06% and 1.08% after 7 days of curing. The filler effect of SSA on cement-based composites was confirmed.