Amid growing awareness of the importance of sustainability, the construction industry has begun to explore more environmentally friendly alternatives. One such innovation is the use of geopolymers—alternative materials that can replace Portland cement, which has long been used in various building projects. The main advantage of geopolymers lies in their lower CO₂ emissions during production, making them a more eco-friendly choice. One promising source of geopolymer raw materials currently under investigation is volcanic ash from Mount Sinabung. This ash, rich in aluminosilicate compounds, presents significant potential for use in geopolymer mortar, marking a breakthrough in the pursuit of greener construction materials.

 

Using volcanic ash as a geopolymer raw material is not merely an attempt to reduce reliance on traditional building materials such as cement. This perspective stems from research conducted by Rahmi Karolina and Johannes Tarigan from Universitas Sumatera Utara (Indonesia), M. A. Megat Johari from Universiti Sains Malaysia, M. J. A. Mijarsh from Al-Merghab University (Libya), and Harianto Hardjasaputra from Universitas Pembangunan Jaya (Indonesia).

 

“Volcanic ash contains the chemical compounds necessary for the geopolymerization process, enabling it to play a crucial role in developing materials that are not only eco-friendly but also strong and durable. Furthermore, the ash is readily available in the vicinity of Mount Sinabung, making it a highly promising local resource,” explained Rahmi Karolina.

 

To produce optimal geopolymer mortar, the researchers combined volcanic ash from Mount Sinabung with sodium silicate (Na₂SiO₃), sodium hydroxide (NaOH), and sand. The synthesis process involved adjusting several variables, such as the percentage of volcanic ash, concentrations of sodium silicate and sodium hydroxide, and the water-to-binder ratio. To identify the optimal formulation, the researchers used the Taguchi method, a statistical approach that helps optimize multiple factors. The curing process was conducted at 75°C for 48 hours, followed by storage at 28°C and 75% relative humidity. The result was a geopolymer mortar that was not only strong but also significantly more sustainable.

 

According to Rahmi Karolina, the geopolymer mortar produced with the optimal mix achieved a compressive strength of up to 79.62 MPa after only three days of curing. This optimal mix consisted of 20% volcanic ash, 1% sodium silicate, and 10M sodium hydroxide, with carefully calibrated ratios of sodium silicate to sodium hydroxide and water to binder. This success demonstrates that volcanic ash from Mount Sinabung can be effectively utilized to produce materials with high structural strength. In addition, scanning electron microscope (SEM) analysis revealed a dense microstructure with very low porosity, which is a key indicator of material durability. X-ray diffraction (XRD) analysis confirmed the formation of N-A-S-H and C-S-H gels—compounds known for their excellent strengthening properties.

This achievement offers not only improvements in construction quality but also significant environmental benefits. The use of volcanic ash in geopolymer production helps reduce dependence on traditional cement, which is known for its substantial carbon dioxide emissions.

 

“By partially or entirely replacing cement with volcanic ash, we can create materials that are more environmentally friendly and sustainable. Moreover, utilizing volcanic ash helps minimize natural resource waste while adding value to materials that were previously considered waste,” said Rahmi Karolina.

 

The potential of Mount Sinabung volcanic ash-based geopolymers presents major opportunities for both local construction projects in volcanic regions and broader global applications in sustainable construction. The abundant availability of this ash provides a practical and environmentally friendly solution for developing high-quality and durable building materials. Thus, this research not only demonstrates the successful production of high-performance geopolymer mortar but also offers new hope for a greener and more sustainable future in construction.

 

Rahmi Karolina emphasized that the use of volcanic ash-based geopolymers holds great potential for wider application—not only in disaster-prone infrastructure projects but also globally. With continued research and development, this material could potentially replace traditional cement in many construction scenarios, delivering both local economic benefits and positive impacts on global sustainability.

 

With innovations like these, the construction industry can move toward a more environmentally responsible future while maintaining strength and durability in building performance. Volcanic ash from Mount Sinabung may be just one example of the many untapped natural resources around us. With further exploration and research, these resources could offer practical solutions to some of our most pressing challenges in addressing climate change and sustainability.