ABSTRACT

In this project, the Effects of Salt Water on the Mechanical Properties of Concrete was determined. For Compressive strength test, total number of concrete cubes cast was seventy two, that is, thirty six cubes using salt water and thirty six cubes using fresh water. Similarly, total number of beams cast for flexural strength test was the same as compressive strength test. Also, total numbers of concrete cylindrical cubes cast for Split tensile strength were the same too. Three mix ratios used were (1:1.51:3.2), water cement ratio (0.47), (1:2.06:4), water cement ratio (0.58), and (1:3.3:5.3), water cement ratio (0.78) respectively. The concrete cubes, beams and cylinders were cured at 7, 14, 21 and 28 days hydration period respectively before crushing. The results of the average compressive strength of concrete obtained using fresh water of mix ratio (1:1.51:3.2), ranges from (43.26-47.90)N/mm² while that of its salt water ranges from (42.07-47.26)N/mm². The flexural strength of concrete obtained using fresh water of the same mix ratio ranges from (6.60-9.09)N/mm² while that of its salt water ranges from (5.98-8.08)N/mm². The split tensile strength of concrete obtained using fresh water of the same mix ratio ranges from (3.30–3.69)N/mm² while that of its salt water ranges from (3.24-3.64)N/mm². Similarly, result of the average compressive strength of concrete obtained using fresh water of mix ratio (1:2.06:4) ranges from (26.07-41.62)N/mm² while that of its salt water ranges from (25.92-38.96)N/mm². The flexural strength of concrete obtained using fresh water of the same mix ratio ranges from (6.55–8.24)N/mm² while that of its salt water ranges from (6.26-8.18)N/mm².  The split tensile strength of concrete obtained using fresh water of the same mix ratio ranges from (2.00–3.20)N/mm² while that of its salt water ranges from (2.00-3.00)N/mm². Again, result of the average compressive strength of concrete obtained using fresh water of mix ratio (1:3.3:5.3), ranges from (16.29-29.63)N/mm² while that of its salt water ranges from (16.15-27.71)N/mm². The flexural strength of concrete obtained using fresh water of the same mix ratio ranges from (6.18–9.07)N/mm² while that of its salt water ranges from (6.15-8.39)N/mm².  The split tensile strength of concrete obtained using fresh water of the same mix ratio ranges from (1.25–2.28)N/mm² while that of its salt water ranges from (1.24-2.13)N/mm². The initial and final setting time of cement using fresh water was 50 minutes and 586 minutes while that of salt water was 57 minutes and 607 minutes respectively. The water analysis result shows a high percentage content of salinity of 930mg/l as chlorine in salt water and 0.00mg/l in fresh water. The difference in the slump, compressive, flexural and split tensile strength of concrete for fresh and salt water was as a result of the salinity content of the salt water sample used. I conclude that salt water has slight effect on the concrete and will corrode reinforcement if used in the construction; hence, I recommend the use of super sulphate cement which is resistance to sulphate attack.