Alkali leaching features of 3-year-old alkali activated fly ash-slag-silica fume: For a better understanding of stability

Alkali-activated material (AAM) is regarded as a promising greener cement that is attracting worldwide attention. This paper reports an investigation on the leaching behaviour of a series of 3-year-old AAMs that are manufactured from fly ash-slag-silica fume. The leaching percentages of sodium from the binders consist of 45–60% fly ash, 30–40% slag and 0–15% silica fume keep increasing slightly in contact with water and reach to the maximum of 30–40%, depending on the mixture composition. The variation of the relative contents of slag and silica fume in the studied range could change the early age strength development but does not alter the leaching behaviour of sodium from the matured AAMs. The relationships between leaching sodium and nonstructural water and overall Al [4] concentration are not clear. As is expected, leaching makes more nano-sized pores permeable and coarsen, however, does not lead to continuous increase of porosity or phase change. The proved stability of this type of AAMs increases the confidence for future application.