Road is an important structure to enable and facilitate people to move from one location to another. Based on Public Works Department of Malaysia's (PWD) Specification for Road Works (JKR/SPJ/2014), the conventional materials for subbase are sand, laterite, crushed aggregate and cement stabilized. Overdependence on these conventional materials has kept the road construction cost getting higher. Therefore, suitable ways for low cost road need to be proposed by fully utilizing the waste materials like agricultural waste for the engineering purposes. An attempt is made to implement the rice husk ash (RHA) as fully or partially replacement to sand for subbase layer due to the depletion of the natural materials. On the other hand, the massive expansion of rice planting in Malaysia requires hectares of land to dispose the RHA which also may lead to the environmental hazards. A series of laboratory testing of unsoaked and soaked (4 days) CBR have been performed in order to evaluate the best percentage mixture of sand and RHA that fulfilled the JKR specification for subbase layer. Several mixtures of 100% sand, (90% - 10%), (80% - 20%) and (60% - 40%) of sand and RHA have been tested throughout this study. The laboratory result shows, the optimum percentage of RHA in road subbase is 10%. The addition of 10% RHA to the sand were improved the CBR value for unsoaked and soaked conditions. From the results, the best percentage mixture which potentially considered to be used for subbase is (90% - 10%) of sand and RHA.
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