Filler has an important role in the HRS-WC mixture besides aggregates and asphalt due to its functions to fill the void in the asphalt mixture so that it could produce more friction resistance and high interlocking aggregate. The use of filler in the mixture is limited in number because too much filler will lead to the stiffer and easily cracked mixture. On the contrary, the lower values could lead to the easily deformed and too flexible mixture. Previous researchers have studied the use of the waste of crude palm oil (CPO) ash as a filler. This research aims to study the performance of the HRS-WC mixture using CPO ash as a filler. The asphalt content used was 5.9%; 6.33%; 6.75%; 7.18% and 7.6%, while the proportion of CPO ash waste is 0%, 25%, 50%, 75% and 100%. The mixture gradation is made using a gap-graded and half gap-graded mixture. The results showed that the stability is higher when 25% of CPO ash proportion is used, but it is decreased again when the proportion is larger than 25%. The use of a small asphalt content will increase the value of VIM. The flow value decreases when 32% of CPO ash proportion is used and increases again over the use of 32%. The use of a large amount of CPO ash filler in the mixture will increase VMA. While the VFB will decrease if the larger amount of CPO ash is used. The immersion index of the mixture can still be maintained even when the use of CPO ash is increased. The use of CPO ash as a substitute for filler in the HRS mixture - WC must be balanced with the increasing of asphalt mixture.

The purpose of this study was to analyze the effect of adding ash from palm oil waste as a substitute for filler material from cement on the immersion index of the HRS-WC mixture using semi-gap gradations. The bitumen content used was 5.9%; 6.4%; 6.9%; 7.4% and 7.9%. Meanwhile, the proportion of oil palm ash waste to cement is 0%: 100%, 25%: 75%, 50%: 50%, 75%: 25% and 100%: 0%. The test results show the effect of adding CPO filler content on asphalt content, the higher the percentage of addition of asphalt content, the number of cavities in the mixture, the smaller the cavities in the aggregate and the more cavities filled with asphalt, up to the addition of 50% CPO content, then 50% CPO increase up to 100% reduced asphalt tar voids. The Marshall Immersion test obtained the immersion index for the Lataston HRS-WC mixture with a semi-gap gradation using CPO Waste Ash as a cement substitute material, it is susceptible to water, this is because even though the mixed cavity is filled with CPO Waste Ash, but effective asphalt which also functions to waterproof the mixture will have reduced. So that if you use CPO waste ash as a substitute for cement filler, the use of asphalt content must also be large (added). The semi-gap gradation in the Lataston HRS-WC mixture also affects the level of water tightness, where the semi-gap gradation will form a denser mixture so that it becomes more waterproof.