Phase modification induced drying shrinkage reduction on Na2CO3 activated slag by incorporating Na2SO4

Abstract

This paper aims to study the phase modification, reaction kinetics, mechanical properties and drying shrinkage of sodium carbonate activated slag by incorporating sodium sulfate in the activator. The results show that the reaction process is firstly controlled by CO 3 2-anions, and later runs similar to that of sodium sulfate activation. Besides, the relatively unstable phase gaylussite, commonly found in the sodium carbonate activation, is not observed in the reaction products upon hybrid activation, and monosulfoaluminate rather than ettringite is identified, probably caused by the reduced aluminate-to-sulfate ratio and increased pH value. The drying shrinkage is considerably reduced by up to 41% when replacing 50 wt% sodium carbonate by sodium sulfate, most possibly attributed to the induced phase modification. Furthermore, the relationships between the phase modification and drying shrinkage, and the potentially involved chemical reaction are discussed.

Autogenous shrinkage of slag-fly ash blends activated with hybrid sodium silicate and sodium sulfate at different curing temperatures

“…This indicates that the compensation of autogenous shrinkage with formation of expansive phase ettringite is limited in the studied systems. This is in contrast to ordinary Portland cement [64,65] and sole sodium sulfate activated slag [22,21], where the formation of expansive ettringite can benefit the autogenous shrinkage at early hours. Also, no other crystalline sulfate phases are observed in the studied AASF systems.…”

Recent progress in low-carbon binders

“…The shrinkage properties of alkali-activated binders based on different blended precursors have also been reported [181,182]. Shrinkage-reducing admixtures [183][184][185][186] and super-absorbent polymers [187][188][189] have also shown some effectiveness in reducing drying shrinkage, as has the tailored design of blended activators [190]. While shrinkage control in AAMs does remain an area of open research, with many questions yet to be answered, the fact that this broad range of approaches have all shown some potential for success is a strong indication that this is not an intractable issue.…”