h i g h l i g h t sOlive-stone biomass ash (OBA) was successfully tested as activator. OBA has alkaline properties suitable for alkali activated materials (AAM). OBA was used as unique activator for blast furnace slag (BFS). The effectivity of OBA was higher than KOH and similar to NaOH. OBA reduces the consumption of commercial chemical reagents in AAM.

Alkali-activated cements (AACs) technology is being widely investigated as a replacement for ordinary Portland cement (OPC) for environmental benefits. Blast furnace slag (BFS) is one of the most well known precursors used in AACs, having comparable properties to those of traditional OPC-based materials. AACs require alkali solutions, which are commonly based on a combination of sodium or potassium hydroxides with sodium or potassium silicates in high concentration. These alkali solutions represent the use of chemical reagents, and thus can have major environmental, health and economic impacts. Olive-stone (also known as olive pits) biomass ash (OBA) is a residue mainly composed of calcium and potassium oxides. Rice husk ash (RHA) is a rich silica residue from the combustion of rice husk. The combination of both residues can produce a good activating reagent for BFS-based AACs. In the present work, 100% waste-based ternary alkali-activated mortars (TAAM) based on BFS activated by OBA and RHA were developed. The mortars were assessed in terms of their dosage, curing treatment and time evolution. Finally an ecofriendly 100% waste-based TAAM with 67.39 ± 0.44 MPa after 90 days of curing at 20ºC is obtained and a complete microstructural characterization shows a dense and compact matrix with binding gel products labelled as C(K)-S(A)-H and C(K)-S-H.

Chemistry is an essential science for understanding and developing construction materials.

The use of binders as an alternative to Portland cement has gained importance in recent years. Among them, geopolymeric binders, developed by the reaction between an aluminosilicate precursor and a high alkalinity solution, have become one of the most promising alternatives. The activating solution generally comprises waterglass and sodium hydroxide. Since waterglass is the most expensive material and has a high environmental impact, using alternative silica sources will lead to more sustainable binders. Previous studies have successfully used rice husk ash (RHA) as a silica source. This research aims to assess the possibility of using diatomaceous earth (or diatomite) as an alternative silica source, like the previous studies with RHA. Diatomite is a sedimentary rock with a high amorphous silica content formed by fossilized diatom remains. In this work, the geopolymer was obtained using a fluid cracking catalyst residue as the precursor and six different activating solution types prepared with commercial products, residual diatomite (from beer and wine industries) and RHA. The results open a new possible route for the reuse and recovery of diatomaceous earth residue, although the compressive strength results of the mortars were slightly lower than those for mortars prepared with RHA or commercial reagents.