Diffusion of various ions from sea water into polymer modified cement paste.

Durability of cement pastes, mortars and concrete structures, has received considerable attention in recent years and particularly diffusion of chlorides and sulphates. The diffusion of calcium, chloride, magnesium, potassium, sodium and sulphate ions from ASTM sea water into cement paste with and without polymers was studied using ordinary and sulphate resisting Portland cements, commencing twenty four hours after casting the specimens. The results showed that polymers reduced the diffusion of various ions. The rate of diffusion depended on the type of polymer, concentration of polymer and type of cement. A surface layer formed on the side of the specimen in contact with sea water was identified as magnesium hydroxide. Differential Thermal Analysis (DTA) experiments carried out on the specimen after diffusion showed two main peaks the first due to the loss of water from the C-S-H gel (100-120 degreesC), the second due to the loss of water from calcium hydroxide (400-500 degreesC) and in some cases, an additional third peak (300-330 degreesC) was observed. This was identified as due to the formation of chloroaluminates. (A)