This study is undertaken to explore the relationship between the reaction products and the drying shrinkage of alkali-activated slag (AAS) with the varying hydroxide dosage. AAS pastes were firstly produced with either Al(OH)3 or Mg(OH)2 to investigate the effects of hydroxide on the composition of reaction products and the drying shrinkage of AAS. Secondly, the main reaction products formed in AAS pastes, viz. C4AH13, M4AH10, C-S-H, C-A-S-H and C-M-S-H, were synthesized individually. Synthetic products were then taken to cast the respective paste sample to examine the performance against the drying exposure. The results show that adding Mg(OH)2 indeed improved the shrinkage resistance of AAS. This is primarily connected to the increased crystalline phases, namely the hydrotalcite-like phases and the unreacted Mg(OH)2. Whereas adding Al(OH)3 did not relieve the drying shrinkage of AAS as the interlayer spacing of C-A-S-H was enlarged, which in turn allowed for more shrinkage. Further, the investigation of individual synthetic products illustrates that their drying shrinkage scales satisfied the following order: C4AH13 < M4AH10 < C-M-S-H < C-S-H < C-A-S-H. Moreover, the shrinkage scale of C-S-H was found to evolve as the Ca/Si ratio decreased.@en

New self-healing agents that can chemically bind seawater ions invading cracked cementitious materials were proposed. The potential of self-healing and binding of seawater ions were investigated by thermodynamic modeling. It was found that CaO-NaAlO₂ and CaO-metakaolin agents can have Cl⁻, SO₄²⁻ and Mg²⁺ chemically bound by reacting with sea water to form Friedel's salt, Kuzel's salt, ettringite and hydrotalcite. The removal of Cl⁻ from seawater firstly increased and then decreased with the increase of Ca/Al molar ratio in both agents, while the removal of Mg²⁺ and SO₄²⁻ were hardly influenced and approximated 100%. Because NaAlO₂ dissolves and releases Al(OH)₄⁻ rapidly, precipitates binding Cl⁻, SO₄²⁻ and Mg²⁺ were formed fast. In comparison, the reaction of metakaolin binding aggressive ions occurred after 3 days. Because of the faster reaction and the capacity to make [Cl⁻]/[OH⁻] lower in the solution, CaO-NaAlO₂ would be more efficient for self-healing and mitigating reinforcement corrossion than CaO-metakaolin.

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