Mechanical Performance of Palm Shell Ash-Based Geopolymer Mortar with Silica Fume as Cement Substitute

¹ Department of Civil Engineering, Universitas Teuku Umar, Meulaboh, Indonesia
² Department of Civil Engineering, Universitas Syiah Kuala, Banda Aceh, Indonesia
³ Department of Chemical Engineering, Universitas Syiah Kuala, Banda Aceh, Indonesia
⁴ Department of Information Technology, Universitas Teuku Umar, Meulaboh, Indonesia

Abstract

The increasing demand for cement in the construction industry has contributed significantly to environmental degradation and global carbon emissions due to the energy-intensive clinker production process. In response, this study investigates a sustainable alternative in the form of geopolymer mortar synthesized from palm shell ash (PSA) a waste material from the palm oil industry that is rich in silica and alumina as a partial or full replacement for Portland cement. The research aims to evaluate the influence of silica fume additions (0%, 5%, 10%, 15%, and 20%) on the mechanical properties of geopolymer mortar, particularly flexural strength and compressive strength. The geopolymer paste was activated using a combination of 10 M sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃), with the addition of 1% superplasticizer to enhance workability. A total of 45 prism-shaped specimens (4×4×16 cm) were cast and tested at three curing ages: 3, 7, and 28 days, under standard laboratory conditions. The results demonstrate a clear positive correlation between the increase in silica fume content and the development of mechanical strength over time. At 28 days, the flexural strength reached a maximum of 10.69 MPa, while the compressive strength peaked at 52.87 MPa with 20% silica fume. This improvement is attributed to the enhanced polymerization reaction and the pozzolanic contribution of silica fume, which refines the pore structure and increases matrix density. The study concludes that palm shell ash, when combined with silica fume and alkaline activation, shows significant potential as an eco-friendly binder for use in geopolymer mortars. These findings support the material's viability as a sustainable cement substitute, offering both environmental benefits and satisfactory mechanical performance for use in green construction applications.