ABSTRACT Various studies in the field of concrete were carried out in an effort to improve the quality of concrete, material technology and implementation techniques obtained from the results of these studies to answer the higher demand for the use of concrete and overcome the disturbances that often occur in the implementation of work in the field. The purpose of this study was to determine the effect of sand replacement on the compressive strength quality of concrete. The composition of sand replacement with Boiler Ash is 0%, 15%, 25%, 50% and 100% of the weight of the sand, and the cement water factor is determined the same for all variations of the mixture, which is 0.34. The sample used is the standard specimen of paving block with a thickness of 8 cm, a cube of 15x15x15 cm and a planned concrete quality of 20 MPa. The number of samples was 30 samples, namely 15 samples in the form of paving blocks and 15 samples in the form of cubes consisting of 5 variations and each variation of 3 samples. Samples were tested at the age of 14, and 28 days, prior to treatment before testing. From the research, it was found that the highest concrete compressive strength at 28 days of concrete (cube specimens) in a stable condition, the compressive strength of the concrete was found in the concrete mixture for replacing sand with 15% Boiler Ash, which was 25 MPa and the lowest concrete compressive strength was in the concrete mixture. with 100% Boiler Ash which is equal to 9 MPa.Keywords : Concrete, Boiler Ash, Concrete Compressive Strengt
