Concrete is an essential element in the construction sector, and it functions as a raw material for the construction of infrastructure development. Concrete is trendy for construction, such as roads, bridges, buildings, etc., because concrete can withstand compressive forces well. The increase in concrete use is directly proportional to the increase in production needs for concrete production itself. Various innovations in making concrete are currently being carried out to obtain a good design for the composition of the materials that make up concrete to produce concrete with high compressive strength, for example, using inorganic waste such as PET plastic waste and paper waste.
PET (Polyethylene Terephthalate) plastic has the characteristics of being stiff, light, strong, durable, and thick, can be formed easily when heated, and has good resistance to tearing and abrasion, so it is very suitable for compression strength testing (Apriliya et al., 2021). The MPET plastic used is a packaged beverage bottle. Research conducted by Yudhis shows that adding PET plastic fiber to concrete can increase compressive strength by 23.67%. Paper is made from organic fibers, which can be converted into a material that can improve the characteristics of concrete in terms of being cost-effective, light, and strong and having resistance to changing temperatures (Israini & Rahman, 2018). The paper used is HVS paper, which is no longer used and is processed into pulp to make it easier to mix the ingredients.
Paper is used in everyday life by almost all humans. Increasing paper production will impact environmental sustainability (Astuti, 2018). The Paper on The Rocks states that the percentage of deforestation is equivalent to the destruction of 4.1 million hectares of forest every year. World Wild Life states that more than 40 percent of all global wood is used in the paper industry. Paper waste is relatively large, amounting to 7,458,000 in 2019 (KLHK, 2021). Not all of the paper that has been used is recycled by factories or the public. The useless paper will pile up at the final disposal sites (TPA).
Therefore, researchers researched a mixture of paper concrete and PET plastic in making k-125 concrete. K-125 concrete is low-strength concrete that has a compressive strength below 20 MPa. This research was created to develop previous research by Vladimir (2023). In his research, PET plastic waste and paper were combined into a lightweight concrete mixture with 0.2% PET plastic in the coarse aggregate and 4% paper in the fine aggregate. This research produces lightweight concrete that meets SNI 7394-2008 standards. However, this research needed more ineffectiveness because the percentage of paper and plastic used was only one variation each so that the resulting compressive strength could have been better. Based on this, concrete compressive strength tests were carried out using paper waste as a substitute for fine aggregate and PET plastic as a substitute for coarse aggregate in k-125 quality concrete. Variations were added to the substitute materials (PET plastic and paper) so that the optimum compressive strength of the concrete can be obtained and used in the construction of Lean Concrete and concrete floor slabs with quality according to SNI 03-2847-2002 standards.
This research shows that the optimum variation of concrete is concrete B, with a compressive strength of 10.68 MPa and an absorption value of 2.3% for Rp. 643,825.20/m3. It was concluded that concrete B meets the SNI 03-2847-2002 standard regarding K125 concrete so that concrete B can be applied as lean concrete, concrete floor slabs, and environmentally friendly concrete. The results of compressive strength and absorption tests on the addition of PET plastic and paper as aggregate substitutes in the K125 concrete mixture showed that the best value from the compressive strength test was in variation A with a compressive strength value of 138.25 kg/cm2, while the lowest value was in variation D with compressive strength value 106.19 kg/cm2. The best value for absorption is in variation D, with a water absorption value of 1.9%, while the lowest value is in variation A, with a water absorption value of 2.5%. Based on research and test results, it was found that the manufacturing cost for one normal concrete test object per m3 was Rp. 651,360.00 Meanwhile, the best concrete price is variation D with 1% PET plastic percentage and 4% paper with a production price of Rp. 642,914.40, resulting in a cost reduction of Rp. 8,445.60/m3.