Increased economic growth in the city of Parepare with the presence of buildings around the estuary. In general, the composition of concrete making materials is taken from good materials. The problem encountered in the field is that the quality of concrete in construction decreases due to brackish water, causing structural elements in the construction to become porous. Meanwhile, preventive measures are rarely or never taken. As a result, the construction life is very short. Brackish water is one of the causes of structural failure. This is due to the content of sulfate and chloride ions in water containing salt/salts that react with chemical elements in reinforcing steel resulting in corrosion of the reinforcement. The purpose of the study was to analyse the compressive strength of concrete with a mixture of clean water against the percentage of brackish water with a maintenance age of 7, 14, 21, and 28 days. The results showed that brackish water had an impact on reducing the compressive strength of concrete due to the high chemical content in brackish water such as Sulfate (SO²¯) of 52.5 in brackish water in Kenjeran and 62.5 in brackish water in mangrove. Dissolved Solids (TDS) of 15188 mg/l in kenjeran brackish water and 3436 mg/l in mangrove brackish water. Organic Content (KMnO) of 8.05 mg/l in kenjeran brackish water and 6.69 mg/l in mangrove brackish water is too high, so the chemical content contained in brackish water can damage the compounds in the cement content and decrease the strength of the materials contained in the concrete. In this case it can result in concrete having a very low durability.

Bawasalo beach sand shows the potential of abundant material resources, but local people still face several considerations in the use of this material. The purpose of this research is to determine the characteristics and effect of the addition of bawa salo sand on compressive strength and split tensile strength. This research uses an experimental method carried out at the Structure and Materials Laboratory of Muhamadiyah University of Parepare using a sample of 27 cylinders with the compressive strength of the plan used is 25 Mpa. Based on the test results, the characteristics of Bawasalo beach sand have met the specifications to be used as fine aggregate for concrete mixtures. The results of normal concrete testing aged 7 days with an average of 17.41Mpa, at 28 days testing with an average of 27.77MPa, 50% variation aged 7 days with an average of 16.84MPa and 100% variation aged 7 days with an average of 13.16MPa and at 28 days testing with an average of 21.80MPa. Normal concrete testing aged 28 days 10.444 MPa, 50% variation with an average of 5.556 MPa and as for the 100% variation with an average of 3.889 MPa. Based on the results of research data analysis, compressive strength and split tensile strength decreased as the percentage of Bawasalo beach sand use increased.