Pore Structure Indicators of Chloride Transport in Metakaolin and Silica Fume Self-Compacting Concrete

Abstract

The aim of this paper is to investigate the microstructure indicators and more effective durability mechanisms of SCCs (Self-Consolidating Concretes) containing supplementary cementitious material. The reference SCC mixture at constant water-to-cementitious material (W/CM) ratio of 0.45 and total cementitious material content of 450 kg/m3 was prepared. The other mixes containing binary (92% PC + 8% SF, 88% PC + 12% SF, and 80%PC + 20%MK) and ternary (72%PC + 8%SF + 20%MK) cementitious blends of metakaolin and silica fume were studied. The effect of using MK and SF in SCCs made with binary and ternary cementitious blends of metakaolin and silica fume and cement on chloride transport and electrical properties was investigated by measuring electrical resistivity parameters such as pore surface conductivity, pore solution conductivity, and tortuosity of pores as chemical and physical indicators of durability. Observations indicated a stronger relationship between the chloride migration coefficient and pore surface conductivity. A new parameter τσ s (multiplication of tortuosity and pore surface conductivity), called pore chemi-physical factor, was introduced. Results indicate that the addition of pozzolanic materials such as silica fume and metakaolin leads to a remarkable increase in pore surface conductivity. The correlation coefficient between τσ s and the chloride migration coefficient was 0.97. So, if chloride ions are absorbed by pore surfaces, the chloride migration coefficient will decrease in greater tortuosity.