Mechanical properties, durability and microstructures of calcined layered double hydroxide mortar in marine environment

In marine environments, concrete structures such as underwater tunnel segments face aggressive conditions. Enhancing concrete's resistance to ionic attack is crucial for ensuring the durability of marine concrete structures. This study investigates the effects of calcined layered double hydroxide (CLDH) on the hydration process, pore structure, and mechanical properties of mortars through various tests, including isothermal calorimetry, mercury intrusion porosimetry, and compressive and flexural strength assessments. Additionally, chloride adsorption equilibrium isotherms, rapid chloride ion migration coefficients, sulfate dry and wet cycles, and accelerated carbonation tests were conducted to examine the chloride adsorption behavior and durability of CLDH mortars. The results show that incorporating CLDH increases peak intensity, shortens the induction phase, and activates the hydration process. Furthermore, CLDH enhances the microstructure by increasing the proportion of less harmful and harmful pores while reducing the percentage of more harmful pores. The compressive and flexural strengths initially rise and then decline with varying CLDH dosages. At a 2% CLDH concentration, compressive and flexural strengths improve by 8.7% and 18.1%, respectively. Due to its excellent ion adsorption capacity, CLDH significantly reduces chloride ion diffusion coefficients, corrosion resistance coefficients, and carbonation depths, thereby enhancing the durability of mortars.