Enhancing the Strength of Volcanic Mud-based Class C Fly Ash Geopolymer Specimen by Limestone Inclusion

Volcanic mudflow disaster has brought negative impacts in the area around the mudflow. The contents of mud are predominantly silicate and aluminate, which are the primary constituent materials of fly ash-based geopolymer specimen. However, the main issue of fly ash-based geopolymer is the requirement of heat curing due to the low calcium in fly ash precursor. The aim of this research is to identify the effect of limestone inclusion on strength properties of volcanic mud-based class C fly ash geopolymer mortar. The volcanic mud was obtained from Sidoarjo mud in East Java Indonesia. The alkaline activator solution was prepared by mixing 10 Molar sodium hydroxide with sodium silicate with the ratio of 0.67. The compressive strength test was carried out at the age of 28 days. The specimens were cured at room temperature. The results show that the addition of 30% limestone in volcanic mud-based class C fly ash geopolymer specimen gives the highest strength at 28 days. It also improves the setting time rate due to the calcium addition. However, further addition of limestone tends to reduce the strength. This might attribute to the decrease of silicate and aluminate contents in geopolymer specimen along with the limestone addition.