Mechanical properties of alkali-activated materials based on blast furnace slag and calcium sulphate dihdyrate

Abstract

Alkali-activated materials (AAMs) are currently under research for providing opportunities for re-use of industrial residue streams in the construction sector. The valorisation of industrial residues into sustainable building materials has become an important feature for reducing the need of disposal and avoid the scarcity of primary resources. The use of ordinary Portland cement (OPC) as primary construction material has also been questioned extensively due to its environmental impact, i.e. CO2 emission during production. The aforementioned issues have prompted various researches in an attempt to develop AAMs as sustainable alternative binders. The most popular industrial solid residues used in making AAMs are: ground granulated blast furnace slag (GGBFS), steel slag, phosphorus slag, fly ash, bauxite residue, among others. In some cases (phospho-)gypsum and flue gas desulfurisation gypsum are also used. This wide range of solid residues provides a wealth of potential precursors for AAMs. GGBFS, produced during iron production, is an excellent raw material for making high-strength building materials for civil engineering applications. The slag’s main components are CaO, SiO2, and Al2O3, available in a glassy state. GGBFS is used in a wide range of applications, in which some of these contain a significant amount of sulphate (e.g. flue gas desulfurisation gypsum). For this reason, GGBFS-based AAMs serve here as a test matrix in order to allow the incorporation of sulphate-rich residues. Alkali silicate based activator is the most used activating solution for GGBFS based AAMs. The modulus (MS) of the activator solution (molar ratio SiO2/Na2O) is an important parameter for mechanical strength and is usually optimal between a ratio of 1 to 2. It is the aim of this paper to investigate the influence of curing regimes on the mechanical properties of AAMs, focussing solely on pastes based on GGBFS and calcium sulphate dihydrate.