SUMMARY
Abstrak Penelitian ini bertujuan untuk mengetahui pengaruh penggantian sebagian semen dengan fly ash dan penambahan serat plastik PET pada Self Compacting Concrete (SCC) terhadap karakteristik beton segar, kuat tekan beton, kecepatan rambat gelombang ultrasonik (UPV), dan modulus elastisitas dinamik. Penelitian ini termasuk dalam penelitian eksperimental yang dilakukan di laboratorium. Penambahan serat PET diberikan sebesar 0%; 0,25%; 0,50%; dan 0,75% berdasarkan volume fraction matriks beton. Sedangkan penggantian parsial semen dengan fly ash dilakukan sebesar 0% dan 15%. Terdapat delapan varian dalam penelitian ini. Masing-masing varian terdiri dari lima benda uji silinder berukuran 150×300 mm. Sehingga total terdapat 40 benda uji. Pengujian kuat tekan dan cepat rambat gelombang dilakukan saat benda uji berumur 56 hari. Pengukuran UPV dilakukan sebanyak lima titik setiap benda uji. Hasil penelitian menunjukkan bahwa kualitas campuran beton segar mengalami penurunan seiring dengan penambahan serat PET secara bertahap. Pada pengujian beton kondisi mengeras, penambahan serat PET cenderung menyebabkan penurunan kuat tekan, kecepatan gelombang ultrasonik, dan modulus elastisitas dinamik. Persentase penambahan serat PET pada campuran beton tanpa fly ash yaitu sebesar 0,50%, sedangkan pada campuran dengan subtitusi semen dengan 15% fly ash yaitu sebesar 0,25%. Kata kunci: Ultrasonic pulse velocity, kuat tekan, self compacting concrete, fly ash, serat plastik PETAbstractThis study aims to determine the effect of partial replacement of cement with fly ash and the addition of PET plastic fibers to Self Compacting Concrete (SCC) on the characteristics of fresh concrete, compressive strength of concrete, Ultrasonic Pulse Velocity (UPV), and dynamic modulus of elasticity. This research classified as experimental research conducted in the laboratory. The addition of PET fiber is given at 0%; 0.25%; 0.50%; and 0.75% based on the volume fraction of the concrete matrix. While the partial replacement of cement with fly ash was carried out at 0% and 15%. There are eight variants in this study. Each variant consists of five cylindrical specimens 150×300 mm. So in total there are 40 specimens. Tests for compressive strength and UPV were carried out when the specimens were 56 days old. UPV measurements were carried out at five points for each specimens. The results showed that the quality of the fresh concrete mix decreased with the gradual addition of PET fiber. In testing the hardened condition of concrete, the addition of PET fibers tends to cause a decrease in compressive strength, ultrasonic wave speed, and dynamic elastic modulus. The percentage of addition of PET fiber to the concrete mixture without fly ash was 0.50%, whereas in the mixture with cement substitution with 15% fly ash, it was 0.25%. Keywords: Ultrasonic pulse velocity, compressive strength, self compacting concrete, fly ash, PET plastic fiber