Plastic is one of the most frequently utilized materials on the world. At the same time, most of this plastic will turn into waste. The recycling processes are not enough, and creating new uses for this plastic waste is an optimum solution. The current research utilized a three-phase bubble column reactor in the PET depolymerization process. Depolymerized PET (DPET) powder was utilized for replacing sand with four different percentages of DPET of 1, 3, 6, and 9% to improve several physical characteristics of cement mortar composites. According to the results, the use of a three-phase bubble column reactor in the depolymerization of waste PET reduced the processing time to less than one hour. The thermal conductivity and the density of the mortar decreased when replacing the sand with DPET powder. This effect rises with an increase in the DPET content. The results also demonstrate that the mortar with 9% DPET particles was 15.45 percent lighter than that without DPET particles. The thermal conductivity of the mortar with 9% DPET was 18.27 percent lower than the mortar without DPET particles.