OPC vs PPC vs PSC: What's the Difference?

OPC, PPC, and PSC are three Indian cement industry types that differ in clinker content and the supplementary cementitious material (SCM) blended with it. OPC is roughly 95% clinker, PPC blends 15-35% fly ash, and PSC blends 25-70% ground granulated blast-furnace slag (GGBS). They conform to IS 269:2015, IS 1489 (Part 1):2015, and IS 455:2015 respectively, and they differ measurably in early strength, heat of hydration, and CO₂ footprint.

The three cements at a glance

OPC has the highest early strength and the highest CO₂ footprint. PPC and PSC have lower clinker fractions, lower heat of hydration, and lower CO₂ per tonne, with comparable long-term strength.

Property	OPC	PPC	PSC
Clinker content	~95%	65-85%	30-75%
SCM type	None	Fly ash (Class F)	GGBS (slag)
SCM range	0%	15-35%	25-70%
BIS standard	IS 269:2015 [^1]	IS 1489 Part 1:2015 [^2]	IS 455:2015 [^3]
Grade nomenclature	33 / 43 / 53 (MPa, 28-day)	No grade	No grade
Heat of hydration	High	Moderate	Low
Approx. CO₂ footprint	893-940 kg CO₂/t [^4]	~25% below OPC [^4]	~41% below OPC [^4]
Typical use	Precast, prestressed, fast-track	Mass concrete, RCC, marine	Mass concrete, marine, sulphate soils

OPC (Ordinary Portland Cement)

OPC, governed by IS 269:2015, is ~95% clinker plus ~5% gypsum, with no SCM; it is graded 33, 43, or 53 based on minimum 28-day compressive strength in MPa. [^1] OPC's defining property is high early strength; the trade-off is high heat of hydration and the highest CO₂ footprint of the three.

PPC (Portland Pozzolana Cement)

PPC, governed by IS 1489 Part 1:2015, blends 15-35% fly ash with clinker and gypsum and is the dominant cement type in the Indian market. [^2] The fly ash is a Class F pozzolan recovered from coal-fired power plant flue gas. PPC gains strength more slowly than OPC in the first 7-28 days but typically matches it by 90 days, with better long-term durability against sulphate and chloride attack. A study across five Indian zones found PPC CO₂ emissions average about 25% lower than OPC. [^4]

PSC (Portland Slag Cement)

PSC, governed by IS 455:2015, blends 25-70% GGBS with clinker and gypsum and offers among the lowest CO₂ footprints of the three. [^3] GGBS is a co-product of iron-making; rapidly water-quenched blast-furnace slag is ground to cement fineness. Unlike fly ash, GGBS is latent-hydraulic (it hydrates directly once alkali-activated), giving PSC very low heat of hydration and high resistance to sulphate and chloride. The same five-zone Indian study found PSC CO₂ emissions average about 41% lower than OPC. [^4]

The decarbonisation angle

PPC and PSC have lower clinker factors than OPC, and clinker production accounts for most of cement's CO₂; shifting OPC volumes to blended cements is the single largest near-term decarbonisation lever for the Indian cement industry. India's national clinker factor has fallen from ~0.79 in the early 2000s to ~0.71-0.72 today, driven by the OPC-to-PPC shift, and PPC now accounts for roughly 65-70% of Indian cement production. [^5] Cembureau reports a similar trajectory in Europe, with the EU clinker factor around 0.74. [^6] Reducing false air losses in cement kilns is a complementary lever on whatever clinker still has to be produced; see also supplementary cementitious materials (planned) and the cement manufacturing process (planned).