چكيده به لاتين
In recent years, the use of pozzolans of silica fume (SF) and metakaolin (MK) in self-compacting concrete structures exposed to aggressive environments has been increasing. So totally assessment of durability especially bar corrosion resistance of concretes is essential. Concrete durability is influenced by processes, in which particles such as ions or molecules enter and pass through pores within liquids, while gases fill the voids. Due to its effects on durability performance of cementitious materials, porestructure such as pore size distribution is the key in explaining the moisture and ionic transport phenomenon. It is known that pozzolanic materials improve water and chloride permeability by change in microstructure of concrete. There is the lack of comprehensive study on chemeical and physical properties which affect on durability of pozzolanic concretes. The aim of this paper is to investigate the effect of physical microstructure and chemical properties of concrete and more effective durability mechanisms on chloride transport and bar corrosion.
Based on the outlined objectives in this study, 8 mixes were designed. Three mixes were designed whitout any pozzolans in water to cement ratio of 0.35, 0.45 and 0.55(R1, R2, R3). Three mixes incorporating 8% silica fume as partially cement substitution where designed with water to cementitious materials ratio of 0.35, 0.45 and 0.55 (SF1, SF2, SF3). Two mixes containing metakaolin were considered with 20% metakaolin as partially cement substitution and water to cementitious materials ratio of 0.45. One of MK mixes had 20% metakaolin and 8% silica fume (MK+SF). All mixes were preapered with total cementitious material content of 450 kg/m3.
The physical microstructure of concretes including total porosity, pore size distribution, pore tourtousity and pore connectivity of concretes were investigated. The chemical properties of concretes including K+ and Na+ content and ions electrical conductivity were measured. The mechanical and durability properties of concretes were studied. The relation between the chemical and physical microstructure properties with durability and mechanical properties showed, the volume of coarse capillary pores, mean pore size (d50) and pore connectivity were more effective factors on water permeability and compressive strength. Results of chemical properties of concretes indicated that metakaolin and silica fume decreses K+ and Na+ content and electrical resistivity of ions. Based on the experimental results of pozzolanic concretes, it is shown that a reduction in pore connectivity has a higher impact on the electrical reistivity and chloride migration coefficient than a reduction in the pore size distribution. But reduction in pore sizes is more effective than porosity reduction in reducing Chloride migration coefficient in normal concretes (whitout any pozzolans). The results revealed that K+ and Na+ content in concretes is more effective on bar corrosion rate than physical microstructure. The concrete with 20% metakaolin and 8% silica fume had best corrosion performance. This concrete did not have the lowest porosity and water permeability.
