Lightweight concrete is categorized as a concrete that contains lightweight aggregate, and as defined in ASTM C-567 that its air-dry mass weighs not more than 1900 kg/m3 (Mulyono, 2004). In this study, rubber seeds are used as lightweight aggregates in concrete. The purpose of using rubber seed is to intensify its utilization as it is a massive by-product of plenteous rubber plantations that ar…