High performance concrete with Czech metakaolin: Experimental analysis of strength, toughness and durability characteristics

Although the capability of metakaolin as pozzolanic material to improve mechanical and durability properties of concrete if used as partial replacement of Portland cement is well noted in concrete science, its utilization in building industry was limited to date, mainly due to its high price dictated by the low production amounts. However, with the current shortage of silica fume and high-quality slag in some countries the attitude of concrete producers to metakaolin may change in the near future. This change of mind can be facilitated by providing a more comprehensive view of the properties of composite materials with metakaolin, thus contributing to wider realization of the benefits of metakaolin in concrete. In this paper, an extensive set of parameters of high performance concrete (HPC) with metakaolin including basic physical characteristics, mechanical and fracture-mechanical properties, durability characteristics, hydric and thermal properties and chloride binding characteristics is measured. The experimental results show that the replacement of Portland cement by 10% of metakaolin as an optimal amount leads in most cases either to improvements or at least does not significantly impair substantial properties of the analyzed HPC. Basic physical properties and heat transport and storage properties are very similar to common HPC, mechanical and fracture-mechanical properties after 28 days are slightly worse but later improved, water- and water vapor transport parameters are substantially reduced, frost resistance is better, resistance against de-icing salts is slightly worse but still meets very well the required criteria. The chemical resistance of concrete with 10% of metakaolin instead of Portland cement in distilled water and HCl is found better than for Portland cement concrete, in MgCl2 it is slightly worse, and in NH4Cl, Na2SO4 and CO2 almost the same, carbonation is reduced, and chloride binding capacity is increased.