Binary and Ternary Shale Binders with High Replacement Levels

Abstract

This paper investigates mortars with fifty percent cement replacement of supplementary cementitious materials in binary and ternary blends, according to DS/EN 197-5: 2021. A new standard that allows for up to 50% of cement replacement levels than previously. Different aspects ranging from rheology, mechanical properties, and mineralogical changes were measured. The selected shale was ground in a laboratory disk mill, blended and tested in binary blends (only shale), and together with limestone filler as ternary blends. As expected, the mechanical properties of these mortars are lower than the mortar made only with Portland cement. The binary binder, with 50% cement replacement by calcined shale alone, developed larger compressive strengths and larger reductions in portlandite than the ternary binder, due to the additional pozzolanic reactions. The replacement of one-third of the shale by limestone filler, with a total cement replacement of 50%, had the lowest compressive strength values but less superplasticizer demand for the target workability. This allows, when judged by the rheology and mechanical properties alone, a mixture of both SCMs might be beneficial, for example where no risk of corrosion would be expected (X0, XC1). Furthermore, one might consider the optimization of the relation between the calcined shale and limestone where CO₂ emissions are being reduced.