Sammendrag
Marl, or calcareous clay, is considered ”bad” clay for production of burnt clay products since it is clay contaminated with substantial amounts of calcium carbonate. Calcined marl is proven to be an effective pozzolan in cementitious products and for this reason marl can be a large resource that is not yet exploited to make blended cements or as a mortar/concrete additive. Marl with 10-20% CaCO3 was calcined over a range of temperatures from 600 to 1000°C, and the optimum calcination temperature with respect to mortar strength seemed to be 800°C. The compressive strength of mortars was tested at equal water-to-cementitious material ratio when Ordinary Portland Cement (OPC) was replaced with calcined marl. Mortar with 20, 35 and 50% marl calcined at 800°C achieved 62, 64 and 55 MPa (equal to reference without cement replacement!) compressive strength, respectively, after 28 days curing at 20 ºC. The 1 day strength for mortar with 50% calcined marl replacing cement was sufficient for removing formwork in practical concreting (about 10 MPa).