XIII Conference on Durability of Building Materials and Components 752 DURABILITY AND MICROSTRUCTURE OF MORTAR WITH CALCINED MARL AS SUPPLEMENTARY CEMENTING MATERIAL Justnes, H. (1) and Østnor, T. A. (1) (1) SINTEF Building and Infrastructure, Trondheim, Norway – [email protected]; [email protected] ABSTRACT Mortars (sand:cement = 3:1 and w/c = 0.50) were made where Portland cement was replaced with 0, 20, 35, 50 and 65 vol% calcined marl. The compressive and flexural strengths were determined after 1, 3, 7, 28, 90, 365 and 730 days curing at 90% RH and 23C. The strength up to 28 days age was higher or equal to the reference for up to 50 vol% marl replacement of cement, while only 20 and 35 vol% replacements gave higher strength than reference at 90 days. The strength of mortar with 65 vol% calcined marl continued to increase until 2 years and approached the strength of mortars with 35 and 50 vol% cement replacements. The microstructure of the mortars was characterized by SEM after 90 days and 2 years curing, as well as capillary suction and saturation giving total volume of capillary pores and amount of macro pores. Electrical resistivity was also measured. Mortars of all compositions were tested for durability starting after 90 days curing with respect to chloride diffusion, expansion caused by sulphate attack (5% Na 2 SO 4 ) at both +5C and +20C, as well as carbonation (accelerated by 1% CO 2 and 60% RH). 1 INTRODUCTION Marl, or calcareous clay, is considered ”bad” clay for production of burnt clay products (e.g. bricks and light weight aggregate) since it is clay contaminated with substantial amounts of calcium carbonate that will form CaO after burning. This can lead to “pop outs” when calcium oxide reacts with water to calcium hydroxide during service. Calcined marl has been proven earlier by Justnes et al [1] to be an effective pozzolan in cementitious products. Thus, marl can be a large SCM resource that is not yet exploited to make blended cements or as mortar/concrete additive. Marl with 10-20% CaCO 3 , or rather calcareous mudstone, was calcined at 800°C leaving 20% of the original CaCO 3 intact. Calcined marl can be considered “industrial pozzolan” within the European cement standard (EN 197-1), and it may be feasible to make a pozzolanic cement with up to 55% clinker replacement (CEM IV/B) considering the 28 day strength and sufficient early strength documented in this paper. 2 MATERIALS AND EXPERIMENTS 2.1 Materials The marl was provided by Saint Gobain Weber who calcined it in a rotary kiln close to industrial conditions The calcined marl were ground to d 50 = 7 μm. Normal Portland cement (CEM I 42.5R according to NS-EN 197-1) produced by Norcem Brevik, Norway, was used
DURABILITY AND MICROSTRUCTURE OF MORTAR WITH CALCINED MARL AS SUPPLEMENTARY CEMENTING MATERIAL
May 20, 2023
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