Seiring dengan kemajuan dan perkembangan yang terjadi dalam bidang konstruksi, beton merupakan salah satu pilihan bahan bangunan untuk konstruksi. Beton memiliki nilai kuat tekan dan kuat tarik berbanding terbalik. Dari berbagai penelitian dan percobaan yang dilakukan adalah untuk meningkatkan kualitas beton. Penelitian ini bertujuan untuk mengetahui pengaruh penambahan serabut kelapa terhadap kuat tekan dan kuat lentur beton mutu K-250. Penambahan serabut kelapa kedalam adukan beton adalah dengan panjang serat ± 10 cm. Variasi penambahan serabut kelapa adalah 0%, 1%, 2%, 3%, 4%, dan 5% dari berat semen. Benda uji yang digunakan adalah silinder dan balok. Perancangan beton normal menggunakan metode SNI. Hasil penelitian kuat tekan dengan penambahan serabut kelapa kedalam adukkan beton menunjukkan bahwa kuat tekan mengalami peningkatan dan penurunan dari nilai kuat tekan beton normal, nilai kuat tekan maksimum terdapat pada penambahan AA 2% sebesar 24,35 MPa dengan persentase peningkatan kuat tekan sebesar 14,41% dari kuat tekan beton normal. Nilai kuat tekan minimum terdapat pada penambahan serabut kelapa AA 5% sebesar 11,26 MPa dengan persentase penurunan sebesar 45,99% dari kuat tekan beton normal. Hasil pengujian Kuat lentur dengan penambahan serabut kelapa menunjukkan bahwa kuat lentur mengalami peningkatan dari nilai kuat lentur beton normal, nilai kuat lentur yang paling optimal terdapat pada penambahan serat AA 1% sebesar 5,47 MPa dengan persentase peningkatan kuat lentur beton sebesar 23,58%. Hasil pengujian benda uji balok dengan penambahan serabut kelapa menunjukkan bahwa retak pada ? bentang tengah maka retak dinamakan retak lentur.

With the improvement and development in construction aspect, concrete is one of building materials for construction. Concrete has a compressive strength value and tensile strength is inversely proportional. Based on the research was done is to improve concrete quality. The research aims to determine the effect of adding coconut fiber on the compressive strength and flexural strength of concrete characteristic K-250. The addition of coconut fibers into concrete mixture is with the fiber length ± 10 cm. The adding variation of coconut fiber is 0%, 1%, 2%, 3%, 4% and 5% by weight of cement. Specimens used were cylinders and beams. Mix design of normal concrete using SNI method. The results of compressive strength research by the addition of coconut fiber into the concrete mixture showed that compressive strength increased and decreased by the compressive strength of normal concrete, the maximum value of compressive strength of AA 2% as much as 24.35 MPa with a compressive strength percentage increase as much as 14.41% of the normal concrete compressive strength. The minimum compressive strength value found in the addition of coconut fiber AA 5% as much as 11.26 MPa with a percentage of compressive strength decrease as much as 45.99% of the normal concrete compressive strength. Flexural strength test results with the addition of coconut fibers showed that the flexural strength had increase of normal concrete flexural strength, flexural strength values of the most optimal fiber contained in the addition of AA 1% as much as 5.47 MPa with the percentage increase in flexural strength of concrete equal to 23.58%. The results of the testing beam specimens with the addition of coconut fibers showed that the cracks in ? the spans middle of the crack called crack flexural.