“…From Figure 12 d, the thickness of the penetration layer increased with w (CaO)/ w (Al 2 O 3 ) in the slag. The thickness of penetration can be expressed by Lucas–Washburn's equation, as shown in Equation (1) [ 23,24 ] . where l is the thickness (m), r is the pore size of the substrate (m), θ is the contact angle (deg), η is the slag viscosity (Pa s), γ is the surface tension (N m −1 ), and t is the dissolution time (s).…”