Calcium sulfoaluminate cement (CSA) is a potential low-carbon binder that
has a markedly less alkaline matrix environment compared to traditional
Portland cement. Investigations on its long-term chemical compatibility with
different reinforcements (i.e. glass fibre and steel rebar) are necessary
before widespread adoption could occur. In this project, studies mainly focus
on the microstructural evolution at interfacial zones over time, which has a
significant impact on the durability properties of reinforced concretes.
Glass fibre reinforced composites made with two matrix formulations (OPC,
and OPC plus calcium sulfoaluminate based matrices) aged for 10 years at
25℃ and steel reinforced CSA concretes aged for 28 days and 1.5 years are
studied. Optical transmitted microscopy and SEM/EDX on the thin section
petrographic specimens of composites are employed to give a
straightforward interfacial zone characterization.
The results suggest that CSA cement is highly compatible with the
embedded glass fibre and steel reinforcement in the long term. Aged GRC
composite modified by calcium sulfoaluminate cement shows greatly
retained toughness, accompanied by considerably flexible interfacial and
interfilamentary areas around the glass fibres. This is in contrary to the aged
OPC/GRC, which demonstrates significantly brittle behaviour with
substantial densification of C-S-H/CH intermixture occurring around glass
fibres. In the steel reinforced CSA concrete, elemental mappings clearly
show that there is a non-continuous aluminium-rich layer at the
steel/concrete interface; and the aluminium gel is slightly consumed over
time by chemical reactions
