Importance of Cation Species during Sulfate Resistance Tests for Alkali-Activated FA/GGBFS Blended Mortars.

Sanghwa Jung,Yeonung Jeong,Joo Hyung Kim,Yoonseok Chung,Youngkeun Cho

doi:10.3390/ma12213547

Abstract

In this study, the changes in mass, compressive strength, and length of blended mortars were analyzed to investigate their sulfate resistance according to the ground granulated blast furnace slag (GGBFS) blending ratio and type of sulfate solution applied. All alkali-activated mortars showed an excellent sulfate resistance when immersed in a sodium sulfate (Na2SO4) solution. However, when immersed in a magnesium sulfate (MgSO4) solution, different sulfate resistance results were obtained depending on the presence of GGBFS. The alkali-activated GGBFS blended mortars showed a tendency to increase in mass and length and decrease in compressive strength when immersed in a magnesium sulfate solution, whereas the alkali-activated FA mortars did not show any significant difference depending on the types of sulfate solution applied. The deterioration of alkali-activated GGBFS blended mortars in the immersion of a magnesium sulfate solution was confirmed through the decomposition of C–S–H, which is the reaction product from magnesium ions, and the formation of gypsum (CaSO4·2H2O) and brucite (Mg(OH)2).

Highlights

With the increased awareness of global climate change as a social issue beginning in the 2000s, an increasing need has developed for new materials that can replace ordinary Portland cement (OPC)and thereby reduce the amount of CO2 emissions during the cement manufacturing process [1,2,3,4].It is worth noting that quantified sustainability indexes have been developed for cementitious materials, such as empathetic added sustainability index (EASI) [5]
(2) The compressive strength of alkali-activated mortars showed a significant variation according to the cation accompanying the sulfate
During the immersion in a 10% MgSO4 solution, the alkali-activated, ground granulated blast-furnace slag (GGBFS) blended mortars show a significant decrease in compressive strength

Summary

Introduction

With the increased awareness of global climate change as a social issue beginning in the 2000s, an increasing need has developed for new materials that can replace ordinary Portland cement (OPC)and thereby reduce the amount of CO2 emissions during the cement manufacturing process [1,2,3,4].It is worth noting that quantified sustainability indexes have been developed for cementitious materials, such as empathetic added sustainability index (EASI) [5]. Materials 2019, 12, 3547 gels [alkali-A-S(-H)], which are regarded as a phase resembling that of nano-scale zeolite [4,19,20,21,22] Numerous chemicals such as caustic alkalis (MOH), both non-silicates (M2 CO3 , M3 PO4 , and M2 SO4 ) and silicates (M2 O·nSiO2 ), alkaline earth oxides (CaO and MgO), and alkaline earth hydroxides (Ca(OH) , Ba(OH) , and Ba(OH)2 ·8H2 O) have been used as activators, NaOH, Na2 CO3 , Na2 O·nSiO2 , and Na2 SO4 are the most widely available chemicals [12,18,23,24,25,26]. Some potassium compounds and/or blended alkali compounds including potassium chemicals have been used in laboratory studies and special applications such as structural plaster [27], but their potential applications are slightly limited owing to their high costs [23]

Methods

Results

Conclusion