Application of burnt clay shale as pozzolan addition to lime mortar

Burnt Czech clay shale of different grain fineness is applied as a new pozzolan addition to lime mortar. Experimental results show that the new lime–pozzolan mortars have significantly better mechanical properties and frost resistance than the reference lime mortar. The fineness of burnt Czech clay shale is a very important parameter affecting the properties of lime–pozzolan mortars; the best results are achieved with an average particle size of 4 μm. In a comparison with a lime–metakaolin mortar of the same composition, the frost resistance of the new lime–pozzolan mortars is significantly better, the mechanical, fracture-mechanical, hygric and thermal properties are either comparable or slightly better. Therefore, it can be concluded that the burnt Czech clay shale has a good potential to be used in lime–pozzolan mortars for renovation of historical buildings.