Characterizing the effects of Al(OH)3 and Mg(OH)2 on reaction products and drying shrinkage characteristics of alkali-activated slag

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. C 4 AH 13, M 4 AH 10 , 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: C 4 AH 13 < M 4 AH 10 < 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. • Adding Al(OH) 3 or Mg(OH) 2 affects composition of reaction products of AAS. • The resistance of AAS to drying shrinkage evolves as the dosed Mg(OH) 2 increases. • Shrinkage of main reaction products of AAS is tested via artificial synthesis technique. • C-A-S-H contributes most to the global shrinkage of AAS among reaction products.