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Purpose – The research was carried out in order to study the composition of minerals, content of total-K, total-Ca, total-Mg, and exchangeable of K, Ca, Mg in volcanish ash from Sinabung volcano eruption.

Design/Methodology/Approach – The volcanic ash material in amount of 5 kg was collected from the depth of 0–20 cm and 21–41 cm. Mineral composition was determined by using line counting method; total contents of K, Ca, and Mg were measured by HCl 1N extraction, and exchangeable of K, Ca, and Mg was measured by NH₄OAc 1N pH 7.0 extraction.

Purpose – The results depicted in volcanic ash layer at the depth of 0–20 cm found some minerals such as plagioclase (34%), hypersthene (9%), augite (3%), hornblende/amphibole (5%), and volcanic glass (1%). These minerals were also found in different amounts at a depth of 21–41 cm. Hypersthene and amphibole were higher and augite was lower at a depth of 0–20 cm than 21–41 cm. The total content of K, Ca, and Mg was found to be 2.27%, 8.12%, and 2.28%, respectively, at a depth of 0–20 cm. The exchangeable of K, Ca, and Mg was found in an amount of 1.89 me/100 g, 20.71 me/100 g, and 1.62 me/100 g, respectively. The total content of K, Ca, and Mg was not available to plants but could potentially be as a source of plant nutrient after weathering while exchangeable form can be uptaken by plant directly.

Research Limitations/Implications – Based on the composition of the minerals, total, and exchangeable of K, Ca, and Mg that the material of volcanic ash, it could potentially be used as source of fertilizers.

Originality/Value – The composition of primary minerals contained in volcanic ash and to know the amount of elements K, Ca, and Mg-associated minerals either in total or exchange.

This study aims to investigate the properties of mortar made from a bottom ash substitute as a sustainable construction material. It is believed that the use of cement in concrete construction contributes to the release of carbon dioxide into the atmosphere, which has been a consistent increase in recent years. The utilization of bottom ash waste is expected to reduce pollution associated with cement production.

Bottom ash is used as replacement materials for cement and fine aggregate in the manufacture of mortar. Bottom ash substituted for cement of 10%, 20% and 30% of the total weight of the binder, whereas bottom ash substituted for the fine aggregate of 30%, 40% and 50% of the total weight of the sand. Binder properties were determined using scanning electron microscopy and energy dispersive X-ray. Meanwhile, the fresh properties (slump flow) and hardened properties were determined (compressive strength and mass density). In the hardened properties test, two types of curing were used: water and sealed curing.

The compressive strength of mortar decreased as the amount of bottom ash as cement replacement. However, the compressive strength increased when bottom ash was used as aggregate replacement. Additionally, bottom ash was sufficient as a substitute for fine aggregate than as a substitute for cement.

This research presents test results that are more straightforward to apply in the construction site.