Natural material-based ash mortar composition

A mortar composition, comprising:

• a treated palm oil fuel ash as a binder, wherein the treated palm oil fuel ash is the only binder present;
• a fine aggregate;
• an alkali activator comprising an aqueous solution of sodium hydroxide and sodium silicate;
• and
• aluminum hydroxide as a strength enhancer which is the only strength enhancer present in the mortar composition,
• wherein the treated palm oil fuel ash is present in an amount of 20 to 30 wt. %, based on a total weight of the mortar composition,
• wherein the treated palm oil fuel ash comprises, as constituent oxides, 60 to 72 wt. % SiO2, 4 to 8 wt. % Al2O3, 3 to 7 wt. % Fe2O3, 3 to 8 wt. % CaO, 1 to 5 wt. % MgO, 3 to 7 wt. % K2O, 0.2 to 0.5 wt. % SO3, 0.1 to 0.25 wt. % Na2O, and 1 to 5 wt. % of P2O3, each based on a total weight of the treated palm oil fuel ash, and
• wherein the treated palm oil fuel ash has a median particle size (d50) of 0.5 to 2.0 μm.