ABSTRACT

Optimization of Fly Ash Composition on the Compressive Strength-to-Density Ratio of Lightweight Foamed Mortar as a Non-Structural Material

Lightweight foam mortar is a non-structural construction material characterized by its low density due to the use of a foam agent that produces air bubbles within the mixture. One approach to improving the quality of lightweight foam mortar is by utilizing fly ash as a partial replacement for cement, while also promoting the sustainable use of industrial waste. This study aimed to analyze the effect of fly ash substitution at 3%, 6%, and 9% on the compressive strength of lightweight foam mortar and to determine the optimum fly ash composition based on its effect on mortar density. An experimental method was employed using cylindrical specimens with a diameter of 10 cm and a height of 20 cm. The tests conducted included physical properties of materials, slump flow, density, Unconfined Compressive Strength (UCS), and moisture content. The mix design referred to the Circular Letter of the Minister of Public Works and Housing of the Republic of Indonesia Number 44/SE/M/2015 concerning the Mix Design Guidelines for Lightweight Foam Mortar for Road Construction. The results indicated that variations in fly ash content affected both the compressive strength and density of lightweight foam mortar. The compressive strength increased with curing age, with the highest value of 24.95 kg/cm² achieved by the 9% fly ash mixture at 14 days, while the lowest value of 17.10 kg/cm² was obtained from the control mixture at 3 days. The density test results showed that all mixtures were within the range of 1,000–1,400 kg/m³, classifying them as non-structural foam mortar. Overall, the use of up to 9% fly ash improved the compressive strength without causing significant changes in density, making it a potential alternative material for efficient and environmentally friendly non-structural lightweight foam mortar. Furthermore, this study supports the achievement of the Sustainable Development Goals (SDGs), particularly Goal 9 (Industry, Innovation and Infrastructure), by promoting innovative construction materials through the utilization of industrial waste as a partial cement replacement to support sustainable infrastructure development.

Keywords : Fly ash, lightweight foamed mortar, compressive strength, density, non-structural material.