The Effect of Seawater on The Strength, Microstructure and Elemental Distribution of Fly Ash/ Kaolin Based Underwater Geopolymer

Concrete in seawater is subjected to various aggressive constituents in seawater commonly sulphate, chloride and carbonate. This paper investigates the potential effects towards mechanical and physical properties of geopolymer when used as underwater concreting material. Besides identifying the microstructure using Scanning Electron Microscopy (SEM), the sample is also characterized using Synchrotron based micro X-Ray Fluorescence (µ-XRF) to identify the elemental distribution that had occurred in the underwater geopolymer. Other essential properties for concrete such as compressive strength, water absorption and density were also determined. The compressive strength result indicates a slightly lower strength for underwater geopolymer (31.40 MPa) compared to normal geopolymer (35.91 MPa). Relevant to the strength, the water absorption and density also shows a slight difference between the geopolymer samples. The µ-XRF analysis shows the presence of chlorine (Cl) element only for underwater geopolymer which indicates that the are chloride penetration for underwater geopolymer. Additionally, other element distribution such as Silica (Si), Aluminum (Al) and Calcium (Ca) shows a different value when comparing normal geopolymer and underwater geopolymer. Despite the difference in elemental distribution between sample, geopolymer is proven to have the potential to be used as underwater material since it is able to retain at least 70% strength of the control sample.