The anorthite formation is minimized in low- and ultralow-cement castables due to the overall lower CaO content and by the use of reactive alumina in the formulation that will combine with someof the silica to form mullite.
Cement-free castables do not experience anorthite formation (unless a lime-containing compound is used to “set” the system).
The silica fume in these systems reacts with the reactive alumina and forms mullite
as the stable bond phase at elevated temperature (23).
Typical strength curves for commercially available low-cement (LC), ultralow-cement (ULC), and cementless (NC) castables is illustrated in Figures 5 and 6.