Understanding the role of brownmilerite on corrosion resistance

With the ever-growing construction in artificial islands and infrastructure, the durability of concrete applied in the marine area has become a hot topic. Previous works have paid much attention on the erosion resistance of C-S-H gel and calcium aluminate. However, the erosion resistance performance of ferrite phases (Ca-2(AlxFe2-x)O-5, 0 < X < 1.33), which is one of the most important mineral phases of cement clinker, was usually ignored and underestimated, due to its complexity in composition and crystal structure. To fill this gap, C2F, C(6)AF(2), C(4)AF, and C(6)A(2)F solid solutions are investigated in this paper, to assess their resistance to chloride and sulfate attacks. Results indicate that Al/Fe ratio of ferrite phase controls the formation of AFt, which can lead to the morphology transformation from needle-and little rod-like into uniform long rod-like shapes, ascribed to the discrepancy in ions' dissolution, and the formation of covering layer controlling the AFt growth. In terms of the chloride binding capacity, the ferrite phases with low Al/Fe ratio showed better chloride binding capacity in low-concentration NaCl solutions, whereas the opposite trend was revealed for high-concentration NaCl solutions. This finding can be attributed to the discrepancy in pore structure and solubility of products. The results obtained in this study are considered instrumental in regulating the corrosion resistance of ferrite phases in clinker, providing a new method for assessing the durability of construction materials. (C) 2020 Elsevier Ltd. All rights reserved.