## 4 Conclusions  
This study identified that as the amount of waste that is the by-product of industrial development continues to increase, waste oil and waste rubber (waste engine oil and waste EPDM rubber), with environmental problems due to low recycling rates, could be used as waterproofing materials. This study also quantitatively presented the viscosity range of synthetic mixed rubber gel waterproofing materials, which utilized waste resources by mixture ratio based on the mixtures of waste oil and waste rubber. It was found that the process oil and synthetic rubber, the main raw materials of previous synthetic polymerized rubber gel waterproofing materials, could be replaced with waste oil and waste rubber to be used as waterproofing materials by comparing and analyzing the correlation between the viscosity and waterproofing performance. It is expected to be used later as the study data to revise the quality standard for the performance improvement of waterproofing materials [23] and to expand waste resources to waterproofing areas. Furthermore, our future studies will include chemical analyses, including the chemical structure and molecular weights of polymers using such analyzers as XPS, FT-IR, NMR, etc., and extend into copolymerization techniques [9] for copolymerization reactions and the chemical and functional composition of the resulting products. The main study results are summarized below:  
(1) After testing the viscosity of synthetic polymerized rubber gel waterproofing materials created by mixing and stirring other components based on the mixture ratio between waste oil and waste rubber, the results showed that the viscosity value was the highest when the mixture ratio between waste oil and waste rubber was in the range of 2:1. In the range of 5:1 and 6:1, the viscosity value was measured to be lower than the quality standard of 2,000,000 mPa-s, and the mixture ratio of waste oil and waste rubber to secure the proper viscosity of W-SPRG could be determined. (2) In the waterproofing performance tests of samples A, B, and C of W-SPRG, whose viscosity values were measured to be higher than the quality standard of 2,000,000 mPa-s, it was shown that sample C, whose viscosity value was lower than 3,000,000 mPa-s did not secure the proper performance in water permeability resistance, wet surface adhesion, structural behavior responsiveness, and temperature safety. Thus, it showed that sample C should have higher viscosity than minimum of 3,000,000 mPa-s in the high-temperature environment, repeated behavior, and wet surface conditions. (3) The comparison of the performance improvement between the synthetic polymerized rubber gel waterproofing materials(P-SPRG), whose main materials include the previous process oil and synthetic rubber, and synthetic polymerized rubber gel waterproofing materials(W-SPRG) based on a mixture of waste oil and waste rubber showed that W-SPRG had an improved performance in viscosity (205%), solid content (3.6%), underwa  
Figure 14: Comparison of improvement level of W-SPRG compared to P-SPRG. ter loss resistance (161.7%), wet surface adhesion (165.5%), and chemical resistance safety (138.5%). (4) It was identified that the previous process oil and synthetic rubber can be replaced with waste oil and waste rubber to be used as synthetic polymerized rubber gel waterproofing materials, and the waterproofing performance could be improved. It was also identified that it can contribute to reductions in cost and environmental contamination problems arising from the disposal and incineration of waste oil and waste rubber. S.-K.O., S.-T.P. and J.-Y.L. conceived and designed the experiments; S.-T.P. and J.-Y.L. performed the experiments; S.-T.P. and S.-K.O. analyzed the data; S.-T.P. and J.-Y.L. wrote the paper. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The authors declare no conflict of interest.