CHEMICAL ATTACK ON HARDENED PASTES OF BLENDED CEMENTS .1. ATTACK OF CHLORIDE SOLUTIONS

It is well known that chlorides constitute a danger for reinforcing steel embeded in concrete as they promote corrosion. The chloride ion takes part in chemical reaction similar to those involving sulphate ion and yields chloroaluminate hydrate. The corrosive action of the chloroaluminate is due to softening of the concrete. The aim of the present work is to study the aggressive attack of some chloride solutions on blended cement pastes. Blended cements were prepared from portland cement clinker, granulated slag and cement kiln dust. The results revealed that the cement kiln dust is not suitable for making blended cement. On the other hand, granulated slag can be mixed with portland cement (15\% slag) to make blended cement with good resistivity to aggressive attack of chlorides compared to sulphate resisting cement. Also, samples immersed in 4\% NaCl give higher values of strength than those immersed in fresh water, 4\% MgCl2, 2\% MgCl2 + 2\% NaCl or sea water at early ages of hydration. On the other hand, sea water is the more aggressive media on the blended cement pastes up to one year curing.