COMPRESSIVE STRENGTH OF CONCRETE WITH SEAWATER AND POWDERED EGGSHELLS AS PARTIAL REPLACEMENT FOR CEMENT

In efforts to generate sustainable concrete, alternative mixing constituents are used. In this study, the use of powdered eggshells as partial cement replacement and seawater as freshwater replacement were explored. The experiment consisted of two phases. First phase was the investigation of 50-mm mortar cube specimens to determine the effect on the compressive strength of mortars with 5% cement replacement with powdered eggshells that were heated at varying temperatures and duration. In the preparation of powdered eggshells, the heating duration was varied at 3, 6, and 12 hours while the temperature was varied at 100 degrees C and 200 degrees C. Based on the compressive strength test results, it was determined that heating of powdered eggshells at 100 degrees C for 12 hours achieved the highest compressive strength. Results of Scanning Electronic Microscope (SEM) showed that there was formation of fiber-like structures for mixes with powdered eggshell. This is believed to be the cause of increase in strength. For the second phase, the better heating method of powdered eggshells that was determined from the first phase was adopted and was used as mixing guide for the cylindrical concrete specimens. The three water-cement ratios used in making the concrete cylinders were 0.4, 0.5 and 0.6. All water-cement ratios of concrete cylinders cured for 28 days exhibited increased compressive strength as powdered eggshells were added as partial cement replacement. It was also determined that the compressive strength further increased when both seawater and powdered eggshells were utilized in concrete. An increase up to 36.4% was observed.