ANALYSIS OF THE INFLUENCE OF ALKALI ACTIVATOR TO-FLY ASH MASS RATIO AND Na2SiO3-TO-NaOH MASS RATIO ON THE COMPRESSIVE STRENGTH OF FLY ASH BASED GEOPOLYMER MORTAR FORM SOUTH SUMATERA

ANALISIS PENGARUH VARIASI RASIO MASSA ALKALI AKTIVATOR/FLY ASH DAN RASIO MASSA Na2SiO3/NaOH TERHADAP KUAT TEKAN MORTAR GEOPOLIMER BERBASIS FLY ASH DARI WILAYAH SUMATERA SELATAN

Abstract

Geopolymer mortar is an environmentally friendly material innovation with the potential
to replace conventional mortar, as it does not use cement as a binder but instead utilizes
industrial waste such as fly ash. This study aims to analyze the effects of varying the mass
ratio of alkali activator to fly ash (AA:FA) and the mass ratio of sodium silicate to sodium
hydroxide (Na₂SiO₃/NaOH) on the compressive strength of geopolymer mortar using fly
ash from two sources in South Sumatra: PT Pupuk Sriwidjaja (PUSRI) and PT Bukit Asam
Tbk (PTBA). Compressive strength tests were conducted at 3, 7, and 28 days of curing.
Additionally, the characteristics of the fly ash were evaluated using X-ray Fluorescence
(XRF), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) to determine
its chemical composition, reactivity, and particle morphology. The results indicate that
both the AA:FA and Na₂SiO₃/NaOH ratios significantly affect the compressive strength of
the mortar. The optimum compressive strength was achieved at an AA:FA ratio of 0.6,
resulting in 47.25 MPa for fly ash from PUSRI, and at an AA:FA ratio of 1.3 with 7.28
MPa for fly ash from PTBA. Regarding the Na₂SiO₃/NaOH ratio, the optimal value was
found at 2.5:1 for both fly ash sources, producing a compressive strength of 43.28 MPa for
mortar with PUSRI fly ash and 6.02 MPa for mortar with PTBA fly ash.