Effect of dosage of sodium carbonate on the strength and drying shrinkage of sodium hydroxide based alkali-activated slag paste.

This study investigated the properties of alkali-activated slag (AAS) pastes with NaOH and a blend of NaOH and Na 2 CO 3 as the alkaline activator. The effects of five different Na 2 CO 3 to NaOH molar ratios (0:10, 0.9:10, 2.5:10, 5.7:10 and 15:10) and three different Na 2 O contents (4%, 6% and 8%) in the alkaline activator on the setting time, mechanical performance and drying shrinkage were tested. The water to slag ratio was 0.35 by weight. The results showed that both the Na 2 CO 3 to NaOH molar ratios and Na 2 O contents are major factors influencing the fresh and hardened pastes. Higher Na 2 CO 3 to NaOH molar ratios yielded a longer setting time and higher compressive strength. The Na 2 O content of 6% was more sensitive to the properties compared with 4% and 8% Na 2 O. When the Na 2 O content was 4%, the drying shrinkage increased as the Na 2 CO 3 to NaOH molar ratio increased; however, when the Na 2 O content increased to 6% and 8%, the drying shrinkage decreased as the Na 2 CO 3 to NaOH molar ratio increased. The main hydration products were C-S-H(I), hydrotalcite, calcite and gaylussite. There was a strong relationship between the drying shrinkage and pore structures of AAS. Consequently, the Na 2 CO 3 to NaOH molar ratio of 15:10 and Na 2 O content of 6% can be regarded as the optimum mix proportion. [ABSTRACT FROM AUTHOR]