Beton (concrete) merupakan bahan yang paling penting dan paling banyak digunakan dalam dunia konstruksi, baik berupa gedung, jembatan, maupun jalan. Campuran beton terdiri dari semen, pasir, kerikil, air dan bahan tambah lainnya dengan perbandingan tertentu. Pada penelitian ini pembuatan beton menggunakan limbah geothermal sebagai pengganti sebagian semen, bottom ash sebagai bahan pengganti sebagian agregat halus (pasir), dan penambahan additive admixture yaitu superplastisizer. Bahan pengganti tersebut bertujuan mengurangi produksi limbah yang dihasilkan oleh pembangkit listrik, serta berinovasi dalam pembuatan beton dengan komposisi beton yang ramah lingkungan yang memenuhi persyaratan. Komposisi beton variasi yang dibuat meliputi limbah geothermal 20% terhadap berat semen, bottom ash 10%, 20%, 30% terhadap berat pasir, dan penambahan superplastisizer 2% terhadap berat air dan dilakukan pengujian kuat tekan, kuat tarik, dan absorpsi yang kemudian hasil tersebut dibandingkan dengan beton normal. Pengujian kuat tekan dilakukan pada umur beton 7 hari, 14 hari, dan 28 hari, sedangkan kuat tarik belah dan absorpsi dilakukan pada saat umur 28 hari. Berdasarkan hasil pengujian diketahui bahwa kuat tekan paling tinggi untuk sampel beton dengan variasi campuran limbah geothermal 20 + bottom ash 10% + superplastisizer 2%, menghasilkan kuat tekan sebesar 28,969 MPa pada saat umur 28 hari. Jika dibandingkan dengan beton variasi normal yang mempunyai kuat tekan sebesar 27,271 MPa, memperoleh kenaikan sebesar 6,226% dengan selisih 1,698 Mpa. Sampel beton variasi dengan campuran limbah geothermal 20% + bottom ash 10% + superplasticizer 2% mempunyai kuat tarik belah yang paling tinggi dibandingkan beton variasi lainya yakni sebesar 1,603 MPa pada saat umur 28 hari. Hasil absorpsi paling tinggi diketahui dari variasi dengan komposisi limbah geothermal 20% + bottom ash 30% + superplastisizer 2% sebesar 1,712%.

Concrete (concrete) is the most important material and most widely used in the world of construction, both in the form of buildings, bridges, and roads. Concrete mixture consists of cement, sand, gravel, water and other added ingredients with certain comparisons. In this study, the manufacture of concrete uses geothermal waste as a substitute for some cement, bottom ash as a substitute for some fine aggregate (sand), and the addition of additive admixture, namely superplasticizer. The substitute material aims to reduce the production of waste produced by the power plant, and to innovate in making concrete with an environmentally friendly concrete composition that meets the requirements. The composition of the concrete variation made includes 20% geothermal waste on the weight of cement, bottom ash 10%, 20%, 30% on the weight of sand, and the addition of 2% superplasticizer on the weight of the water and testing the compressive strength, tensile strength, and absorption then yield compared to normal concrete. Testing of compressive strength was carried out at the age of concrete 7 days, 14 days and 28 days, while tensile strength and absorption were carried out at the age of 28 days. Based on the test results it is known that the highest compressive strength for concrete samples with variations in the mixture of 20 geothermal waste + 10% bottom ash + 2% superplasticizer, produces compressive strength of 28.969 MPa at the age of 28 days. When compared with normal variation concrete which has a compressive strength of 27,271 MPa, it gets an increase of 6,226% with a difference of 1,698 Mpa. Concrete variation samples with a mixture of 20% geothermal waste + 10% bottom ash + 2% superplasticizer have the highest tensile strength compared to other variation concrete which is equal to 1,603 MPa at 28 days. The highest absorption results are known from variations with the composition of 20% geothermal waste + 30% bottom ash + 2% superplasticizer at 1,712%.