different cement dealers are suggesting me to go for portland slag cement as i

Sulphate Resisting Portland Cement is a type of Portland cement in which the amount of Tricalcium aluminate (C3A) is restricted to lower than 5 % and (2 C3A + C4AF) is lower than 25%. SRC can be used for structural concrete wherever OPC or PPC or Slag Cement is usable under normal conditions. The use of SRC is particularly beneficial in such conditions where the concrete is exposed to the risk of deterioration due to sulphate attack. The use of SRC is recommended for following applications:

+  Foundations, piles.
+  Basements and underground structures.
+  Sewage and Water treatment plants.
+  Chemical, Fertilizers and Sugar factories.
+  Food processing industries and Petrochemical projects.
+  Coastal works.
+  Also for normal construction works where OPC is used.
+  Construction of building along the coastal area within 50 km from sea.