Abstract— The load capacity of a material as a road foundation expressed in CBR values. The low CBR value became a problem in many countries for road construction. Buton Island in Southeast Sulawesi, Indonesia, has large amount about 627 million metric tons of asphalt deposit in many forms. In Indonesia, natural asphalt derived from Buton Island was called Asbuton (Asphalt Buton). The Asbuton deposit divided to several type. One of the types is overboulder which about 30% of total deposit of asbuton. Overboulder occurred naturally when limestone reacts with bitumen in top soil layer of asbuton itself, made it a waste material which could be used as stabilizer material, due to its lime content with low bitumen content at about below 2%. Recently in Indonesia, asbuton in general started to be studied for either stabilization and asphalt content extraction. In this research, overboulder is used as replacement material for road foundation layer, stabilized with 3%, 5%, 7% and 10% cement based on the dry density of the overboulder to gain higher bearing capacity. The tests are carried out using CBR specimens with curing time of 7 and 28 days. The test results showed that the addition of cement significantly affected the CBR value. The addition of 10% cement increases the CBR value of the overboulder by 6.8 times, which equals to 82.5% after 28 days of curing time. This CBR value is greater than the addition of 3%, 5% and 7% cement. With this result, overboulder can be used as replacement material for pavement foundation layer which has a high CBR value. And by using local content, there is a chance for advantages both technically and financially for upcoming development, especially in Southeast Sulawesi.
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