The utilization of marine resources in reinforced concrete is severely limited, due to the risk of steel corrosion caused by the introduced chloride. In order to reduce this risk, nano-Al2O3 (NA) was added into cement-based materials system by improving the chloride immobilization. The immobilized chloride ratio (ICR) of the system was evaluated, and the results indicated that the addition of NA could significantly enhance ICR. Based on the results from TG, XRD, 27Al NMR, MIP, 29Si NMR, and EDS, the mechanism behind was discussed from three aspects of chemical binding, migration resistance, and physical adsorption. The reasons for the increased ICR were as follows: a) chemical binding was promoted by increasing the amount of chloroaluminates; b) migration resistance was improved by refining the pore structure; c) physical adsorption, depending on the amount and the Ca/Si ratio of C-S-H gel, was reduced negligibly. These findings can provide guidance for the theoretical study of chloride immobilization and the application of marine resources.

Introduction

The utilization of marine resources, such as sea sand and coral sand, has great potential in marine concrete engineering, especially in reef construction in the distant sea. However, the direct use of these resources has been banned in reinforced concrete, due to the potential risk of steel bar corrosion induced by the diffused chloride ions. In order to resist this risk, corrosion inhibitors are usually used in concrete to produce a protective film on the surface of rebar [1–۳]. However, due to the existence of large amounts of internal free chloride ions, the risk of pitting corrosion is not completely eliminated by inhibitors. In this case, the chloride immobilization is considered to be another promising way [4,5]. The mechanism of chloride immobilization can be divided into three aspects: chemical binding, physical adsorption, and migration resistance [6,7]. Chemical binding is related to the chloride ions bound in Friedel’s salt (FS) or Kuzel’s salt (KS).