Self-Compacting Concrete (SCC) is a type of concrete that can flow and compact under its own weight without the need for external vibration or compaction. To achieve the desired consistency and flowability of SCC, it is crucial to carefully consider the ratios of aggregates, cement, water, and specific additives used in its formulation. The objective of this study is to enhance the performance of high-strength concrete by partially replacing cement with fly ash at 35% and 40%, and adding 1% polycarboxylate additive by weight of cement, aiming for concrete with a strength of 50 MPa. The research employed an experimental method using cylindrical test specimens measuring 15 cm × 30 cm, with 12 specimens for each variation tested at ages of 18 h, 7, 14, and 28 days. The test results showed that the compressive strength of normal concrete at 28 days was 48.7 MPa. Concrete with 35% fly ash and 1% polycarboxylate had a compressive strength of 65.9 MPa, and concrete with 40% fly ash and 1% polycarboxylate achieved a compressive strength of 66.8 MPa. This represents an increase in compressive strength of 26.1% and 27.1% compared to normal concrete, respectively. The slump value for normal concrete was 40 mm, whereas the slump for concrete with 35% fly ash was 72 mm, and for concrete with 40% fly ash was 74 mm, meeting the design target of 25–100 mm.