PORE-SIZE DISTRIBUTION OF OPC AND SRPC MORTARS IN PRESENCE OF CHLORIDES

The pore structure of chloride-free ordinary portland cement(OPC) and sulphate resistant portland cement(SRPC) mortars are compared with the corresponding mortars with NaCl and CaCl2 added during mixing. In both OPC and SRPC mortars the addition of chlorides reduced the total accessible pore volumes compared to the corresponding chloride-free mortars. Also, in the presence of chlorides, the number of coarse pores were increased. These changes in the pore structure are believed to be due to dense calcium silicate hydrate(C-S-H) gel morphology formed in the presence of chlorides. The SRPC showed greater changes in pore structures than the OPC with equivalent amounts of chlorides added. This may be due to the lower chloride binding capacity of the SRPC and hence the higher availability of free chlorides to modify the gel morphology.