Improving sulfate attack resistance of concrete by using calcined Mg-Al-CO3 LDHs: Adsorption behavior and mechanism

In this work, the impact of layered double hydroxides (LDHs) on sulfate attack resistance of concrete was explored. Replacement level of cement by calcined Mg-Al-CO3 LDHs was 2%. Mechanism of ion exchange and memory effects of LDHs has been revealed from structure evolution and adsorption behavior aspects of LDHs in aqueous solution. The efficiency of calcined LDHs in sulfate attack resistance was also assessed in terms of microstructure and compressive strength loss of concrete. The experimental results show that structure regeneration of calcined LDHs can be achieved based on memory effect and ion adsorption after mixing with solution. Calcined LDHs presents high sulfate ion adsorption capacity ascribes to the availability of large amounts of vacancy between the layers. The optimal dosage of calcined LDHs for achieving high uptake efficiency of sulfate ion surpasses 3.0 g/L. Langmuir isotherm suits more to describe the adsorption of sulfate ion on calcined LDHs compared with Freundlich model. Thermodynamic parameters calculation indicates the endothermic behavior (the maximum value is obtained at 40 degrees C) and spontaneous nature of sulfate ion adsorption on the calcined LDHs. Calcined LDHs exhibits improving effect on pore refinement. Calcined LDHs improves concrete strength and therefore enhances sulfate attack resistance especially at longer exposure days. (C) 2019 Elsevier Ltd. All rights reserved.