After six centuries of inactivity, Mt. Pinatubo in Zambales has erupted in June 1991, spewing million cubic meters of lahar and burying the nearby towns of Pampanga, Tarlac and Zambales. Numerous researches have already been conducted utilizing lahar as an alternative construction material, focusing on industrial purposes. This study focuses on lahar as an alternative pavement material, specifically as a subbase course material. To determine the suitability of lahar as a subbase course material, various laboratory tests were performed on lahar samples collected from Porac, Pampanga. Considering the physical properties and chemical and mineralogical composition, a suitable stabilizer or treating agent for lahar was chosen. Stabilization of lahar consisted of mixing lahar with varying percentages of Portland cement, emulsified asphalt and moisture contents. Results showed that although lahar passed the 25% CBR requirement set by the Department of Public Works and Highways for road subbase courses, it cannot be recommended as an alternative subbase material because of its tendency to deform with the application of high loads. However, lahar stabilized with 2% Portland cement and 5% emulsified asphalt can be one option for road subbase courses, with a CBR value of 84.91%. This mix was observed to be much stronger and more stable than raw lahar.
