Metakaolin concrete: Carbonation and chloride behavior

Abstract

The purpose of this paper is to present the results obtained in an experimental study that analyzed the performance of different concrete mixes. These mixes were produced with 90% of ordinary Portland cement (OPC) and the other 10% with the additions of metakaolin (MK) and silica fume (SF). Four types of MK were tested; two of these were produced by a thermal treatment on Colombian kaolin. The others two were imported from the international commercial market. The factors evaluated in all the concrete mixes were the following: compressive strength, water absorption and total volume of permeable porosity, capillary absorption, carbonation depth and chloride penetration. The concrete samples were submitted into an accelerated carbonation process inside a climatic chamber (30º C, 70% H.R. and 2.25% CO2 ). At 28 days of curing the carbonation depths for the blended concrete mixtures were greater than the one obtained in the OPC concrete without addition. With a prolonged curing age in all samples, with or without mineral additions, tend to slow the carbonation rate in the concrete. The resistance of the concrete to the chloride penetration was evaluated according to ASTM standard C1202. This study proved that blended concrete specimens have a lower capillary absorption and a higher chloride penetration resistance once these were compared with OPC concrete specimens without addition.