Buildings with lightweight concrete are currently used as a solution for mass housing construction which is relatively cheaper, although it does not provide indoor thermal comfort due to the use of this building material. Lightweight concrete building materials are able to store heat for a long time, so that at night the heat is released indoors. The combination of building materials and PCM is an efficient way to increase the storage capacity of thermal energy in building components. The

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... e of this study was to determine the compressive strength of the concrete if the coarse aggregate (gravel) was replaced by part of the gravel material using the Phase Change Material of beeswax (beeswax) according to the required percentage starting from 0%, 5%, 10%, 15% and if the aggregate was fine. (Sand) is partially replaced aby using Rice husk ash with various variations starting from 0%, 5%, 10%, 15%. In addition, this utilization is a good alternative, because there will be a process of utilizing rice husk ash which was previously wasted while these items can be used or processed into additives to the concrete mixture.