Beton banyak digunakan karena harganya lebih murah dan bahan baku pembuatan mudah dijumpai. Penelitian ini digunakan serat sabut kelapa dan juga Fly ash sebagai pengganti semen. Benda uji dibuat dengan cetakan silinder berdiameter 15 cm dan tinggi 30 cm. Direncanakan sesuai dengan SNI 7656-2012. Dengan 6 variasi yaitu beton normal, substitusi fly ash dengan variasi 0%, 5%, 10%, 15%, dan 20% dari berat semen serta variabel tetap yaitu serat sabut kelapa sebesar 1 % dari berat beton. Pengujian dilakukan pada umur beton 7 hari, 14 hari dan 28 hari untuk pengujian tekan dan 28 hari untuk pengujian kuat tarik belah dan absorpsi. Berdasarkan pengujian pada umur 28 hari didapat nilai kuat tekan rata-rata yaitu 25,1003 MPa, 23,9679 MPa, 24,0623 MPa, 24,7228 MPa, 26,2326 MPa dan 22,7412 MPa. Nilai kuat tarik belah sebesar 1,6749 MPa, 2,7837 MPa, 2,4534 MPa, 2,3355 MPa, 2,1939 MPa, dan 2,0288 MPa. Nilai absorpsinya yaitu 2,391%, 3,441%, 3,030%, 2,730%, 2,671%, 2,527%. Nilai kuat tekan optimum yaitu pada variasi fly ash 15% dan serat sabut kelapa 1%. Kuat tarik belah tertinggi diperoleh pada variasi fly ash 0% dan serat sabut kelapa 1%. Dan nilai absorpsi tertinggi didapatkan pada variasi fly ash 0% dan serat sabut kelapa 1%.

Concrete is widely used because it is cheaper and the raw materials for making it are easy to find. In this study, coconut fiber and fly ash were used as a substitute for cement. The test object was made with a cylindrical mold with a diameter of 15 cm and a height of 30 cm. Planned according to SNI 7656-2012. With 6 variations, namely normal concrete, substitution of fly ash with variations of 0%, 5%, 10%, 15%, and 20% of the cement weight and the fixed variable is coconut coir fiber by 1% of the weight of the concrete. The tests were carried out at the age of 7 days, 14 days and 28 days for compressive testing and 28 days for splitting tensile strength and absorption testing. Based on the test at the age of 28 days, the average compressive strength values were 25.1003 MPa, 23.9679 MPa, 24.0623 MPa, 24.7228 MPa, 26.2326 MPa and 22.7412 MPa. The split tensile strength values are 1.6749 MPa, 2.7837 MPa, 2.4534 MPa, 2.3355 MPa, 2.1939 MPa, and 2.0288 MPa. The absorption values are 2.391%, 3.441%, 3.030%, 2.730%, 2.671%, 2.527%. The optimum compressive strength value is in the variation of 15% fly ash and 1% coconut fiber. The highest split tensile strength was obtained at variations of 0% fly ash and 1% coconut fiber. And the highest absorption value was found in variations of 0% fly ash and 1% coconut fiber.