ADVANTAGES:
Low Heat of Hydration: Due to the hydration, reaction in PPC takes place in two parts separated by a time difference. PPC as compared to OPC has a lower heat of hydration making it suitable for mass concrete structures, like dams, machine foundations etc where cracks in concrete are not desired.
Low Reactivity with Aggregates: The primary reaction that takes place with cement and aggregates is known as Alkali Aggregate Reactions, where in the alkali of cement combines with the reactive aggregate causing volumetric expansion. In case of PPC there is chemical fixation of free Calcium Hydroxide besides having low alkalis namely (Na+ & K+) ions. These cause less reactivity with reactive aggregates and make it suitable for use in areas where such reactive aggregates are found.
High Ultimate strength of concrete: In case of blended cement there is a dual reaction first between clinker and water and subsequently between blending agent (fly ash) & water. This leads to the additional gel formation and results in higher ultimate strength. This additional SPH (Solid products of hydration) fills up the pore spaces and leads to higher density of concrete there by higher ultimate strength.
Better Resistance to Sulphate attacks compared to OPC: High quality blended cement has C3A content ranging from 5% to 7% where as Sulphate resistance cement is defined as one as per ASTM –C-150 Type V, which has C3A less than 5%. The Sulphate resistance characteristics of PPC is further enhanced due to the low availability of Ca (OH)2. Thus blended cement has Sulphate resistance characteristics nearly as good as SRC, which is far better than OPC.
Excellent Resistance to Chloride attacks: Deterioration of concrete in moist and saline environment in tropical countries is generally caused by corrosion of reinforcement effected due to chloride penetration in concrete. Concrete in humid surroundings can dry out only to a depth of few millimeters which means that in such circumstances the penetration of chloride must take place by diffusion through water and not by capillary absorption. Due to the production of the additional SPH after the secondary reaction in PPC the permeability is reduced considerably, which thereby reduces the diffusivity of chloride ions.
Higher Geometrical Stability: The geometrical stability of cement mortar is primarily a function of balanced chemical composition & impermeability of the cement mortar. Since chemically PPC is less reactive to chlorides and Sulphate compared to OPC the volume change affected by reactions with these ions are reduced. Besides since the permeability of mortars made by PPC is much less the chance of reactive ions penetrating is further reduced. Hence PPC has a much better geometrical stability than OPC.
Cement and Construction Technology has progressed a lot in the last three decades. Its time now for the construction fraternity to adopt blended cement especially PPC as the general purpose structural cement. PPC not only gives strength but also assures durability, besides it is eco friendly too.