PENGARUH RENDAMAN AIR LAUT PASANG (ROB) TERHADAP KINERJA LATASTON (HRS-WC) BERDASARKAN UJI MARSHALL DAN UJI DURABILITAS MODIFIKASI

Abstract

ABSTRACT Most of roads in Indonesia, particularly that located on the seashore areas, such as Semarang, are usually flooded by highly acid seawater tide (‘rob’). In recent years, the area of Semarang, which are flooded by ‘rob’ is widen. Some of the flexible pavement roads, which are flooded by the ‘rob’, were damaged. Regarding to these phenomena, it is essential to conduct a study on the effects of seawater tide (‘rob’) to the performance of hot asphalt mixture – the latest specification of lataston HRS-WC (2001). Analysis of the sample material, the amount of both aggregate and asphalt, as well as the gradation of HRS-WC mixture meet the requirement of latest specification. Marshall method was applied at the first step to find the Optimum Asphalt Content (OAC). The second step was aimed to find the value of Marshall at standard condition (2 x 75 blows), and the value of refusal density (2 x 400 blows) which was aimed to discover VIM, VMA, VFA, density, stability, flow, MQ, and the IRS of standard immersion. The modification of immersion was applied to find the first value of durability index (r,R) and the value of second durability index (Sa, SA). Four samples of water, those were water taken from laboratory, ‘rob’ water from LIK Semarang, from Ronggowarsito street, and from Mpu Tantular street, were used in the immersion test. The samples of water were checked their colour, smell, pH, level of chloride, level of sulphate, total value of alkalinity and the total value of acidity. The first step found that the OAC value varied from 7% to 7.5% and the OAC 7.25% was selected as the sample material. The second term research showed that there was a correlation between Marshall value and the immersion time, the result of void analysis met the requirement at standard density level (2x75 blows). At refusal density level (2x400 blows), the VIM values of the four samples of rob water did not meet the requirement at 24 hour of immersion. The value of stability test, flow and MQ, at standard condition and at refusal condition for all immersion time and total acid meet the required standard. IRS value at standard and refusal condition for immersion time and total acid value meet the required standard at 72 hours of immersion. Meanwhile, at the immersion time of 120 hours and 168 hours, the IRS value did not meet the required value, as the asphalt capability to maintain cohesion and adhesion between aggregate was weakened. Modification of immersion test discovered Durability I Index, where immersion time caused the increasing of index score (r and R) at both standard condition and refusal density condition. This indicates that the HRS-WC losses its power. Modification of immersion also discovered Durability II index, where immersion time leads index score of residual stability (Sa) to decrease at both standard and refusal density condition. This result indicates that the duration level of the HRS-WC is getting low. This also shows that the longer time HRS-WC immersed in rob water and the higher the acid level of the rob water resulted in decreasing density level of the mixture and decreasing the capability of asphalt in maintaining cohesion and adhesion of aggregate.