Washout resistance of self-protected underwater concrete in freshwater and seawater

In this paper, the washout resistance of an innovative self-protected underwater concrete (SPUC) was tested under the influence of an underwater protective agent (UPA) in freshwater and seawater during the static case of water flow. The pervious methods of underwater concrete have been carried performed by incorporating the anti-washout admixtures (AWAs) into the proportions of concrete mix in order to make the mixture coherent during the placing of underwater concrete, but the UPA technique depends on changing the characteristics of the water to make it suitable for receiving fresh self-compacted concrete (SCC) without leakage into water. An experimental program consisted of 20 mixes was conducted by using 4 tests: non-dispersion test (US Army Corp CRD C61), slump, and slump flow (SF), and pH value test to investigate the behavior of concrete during placing the concrete underwater. These experiments were implemented based on five parameters: UPA concentration, W/C ratio, superplasticizer (SP) content, fine aggregate (FA) ratio, and water environment. Test results showed that the washout was decreased by increasing the UPA concentration. Mass losses also were increased by increasing the W/C ratio or SP and decreased by increasing the fine aggregate ratio. Besides, seawater showed higher resistance to washout than freshwater. On the other hand, the pH test was shown to be compatible with the results of the CRD C61 test. However, freshwater specimens achieved higher pH values than seawater because freshwater was more alkaline. Furthermore, the relationship between D loss of mass and D pH tests was induced between UPA and UPA-free. Finally, it was concluded that the recommendations relating to the SPUC proportions should be concluded in the technical guideline on SPUC. (c) 2021 Elsevier Ltd. All rights reserved.