Type IT is the three-component member of the ASTM C595 blended-cement family, defined as a hydraulic cement produced by intergrinding, blending, or both, of portland cement with two distinct supplementary constituents [S2][S4].
Total supplementary cementitious material (SCM) content runs from 6% to 95% by mass, with each SCM individually held to a 6-95% window, and designation suffixes list the components in descending order by mass, e.g. Type IT(S20)(P10) for 20% slag plus 10% pozzolan [S2][S8].
How Type IT Is Built: Composition Rules
Type IT is the only C595 category built around exactly two SCMs blended with portland cement clinker, gypsum, and allowed processing or functional additions [S2][S4]. The two SCMs are drawn from the same ingredient list used by Type IP, Type IS, and Type IL: slag (S), pozzolan (P), and limestone (L). Each constituent is restricted to 6-95% by mass of the finished cement, and the combined SCM fraction must likewise stay inside that 6-95% envelope [S2][S8].
For Type IT(S≥70) the standard allows hydrated lime in the formulation, and the limestone component, when used as one of the two SCMs, is capped at 15% by mass to stay consistent with the Type IL cap that the same standard sets for binary limestone blends [S2]. Designation formatting is mechanical: list the larger mass fraction first, parenthesise the constituent code, then the smaller, so Type IT(P15)(S5) means 15% pozzolan plus 5% slag with the balance portland cement clinker and gypsum [S8].
Type IT vs IP vs IS vs IL: A Decision-Criteria Comparison
Across the C595 binary and ternary families, the right call depends on four selection levers: SCM chemistry, SCM mass range, the durability lever being targeted, and whether a third constituent is needed to hit a performance window [S2][S4][S6].
Type IP caps pozzolan at 40% by mass and is the default binary for alkali-silica reaction (ASR) mitigation and long-term strength gain, particularly in mass concrete where low heat is wanted. Type IS pushes slag up to 95% by mass, with slag ≥70% qualifying as the high-slag variant permitted to include hydrated lime; this is the binary for sulfate-rich exposure and chloride-screening reinforced concrete [S2][S4]. Type IL holds limestone at >5% and ≤15% by mass, the binary route to lower embodied carbon without changing the SCM strategy [S2][S4].
Type IT is the option when one SCM is not enough: a slag-fly ash combination will simultaneously target late strength (slag) and ASR/heat mitigation (pozzolan), and a ternary limestone-pozzolan or limestone-slag blend lets a producer tune the limestone up to 15% while pulling a second lever such as sulfate resistance or workability [S2][S6]. For deeper carbon reduction beyond Type IL's 15% limestone ceiling, see special cement for binders that push further by dropping clinker share, and compare with cement for the baseline portland framing.
Designation Suffix Coding: Reading the Stencil
The suffix block is the part specifiers most often misread. The base label IT is followed by parenthesised constituent codes in descending mass order, and the convention is unambiguous: larger first, smaller second, never alphabetical [S2][S8].
The mass balance closes out with portland cement clinker plus the gypsum or calcium sulfate addition that the standard permits across the whole C595 family.
Production Method: Intergrind, Blend, or Both
ASTM C595 lets the producer pick the manufacturing route that gives an intimate, uniform blend, which in practice means three plant options: full intergrinding of clinker, gypsum, and both SCMs in a single mill pass; separate grinding of each component followed by mechanical blending in a finished-cement silo; or a hybrid where clinker and gypsum are interground and the second SCM is post-blended [S2][S4].
The production-route flexibility matters because slag and limestone have very different grindabilities: slag is harder and benefits from separate grinding to a finer specific surface, while limestone is softer and can often be co-ground without penalty. Prosoco's industry write-up on the C595 family notes that Type 1L and other C-595 blended cements can contain 15-50% raw, uncooked limestone when treated as a Type IT(L)-designated ternary, well above the 5-15% Type IL window when paired with a second SCM [S5]. For concrete-level performance, the cement and concrete interaction ultimately drives strength gain, and SCM synergy in a ternary typically outperforms either binary used alone at equivalent total replacement.
Performance, Sustainability, and the EPD Anchor
The Portland Cement Association industry-average Environmental Product Declaration (EPD 193) for blended hydraulic cement under ASTM C595, ASTM C1157, AASHTO M 240, and CSA A3001 is the reference document for U.S. Type IT carbon footprint work, with the current validity window running from 2021-03-12 through 2027-07-31 per the revised July 2026 issue [S2]. The EPD was computed with the GCCA Industry EPD Tool v4.1 and verified against ISO 21930:2017 and ISO 14025:2006 [S2].
Type IT does not carry its own performance subclass inside C595; instead, ternary cements are typically ordered against the same C595 strength and optional physical requirement tables (e.g. moderate sulfate resistance, low heat of hydration) as their binary cousins, and the SCM package is what delivers the property. The Heidelberg Materials product literature for its blended-cement portfolio treats Type IT as the 'highest-performance' member of the C595 family specifically because of the dual-SCM synergy versus Type IP or Type IS used alone [S6]. The O'Quinn et al. (2025) study on blending portland-limestone cement with supplementary cementitious materials confirms the U.S. context: Type IL up to 15% limestone is a starting point, and ternary blends that add a pozzolan or slag on top of the IL base pull the binder's carbon profile further down while restoring early-age strength loss [S9].
Where Type IT Fits and Where It Doesn't
Type IT is the right call when a single SCM cannot hit all of the durability, strength, and carbon targets on the project, e.g. a mass-concrete pour that needs both low heat (pozzolan) and sulfate resistance (slag) at a low clinker factor, or a high-performance slab that needs ASR mitigation (pozzolan) plus workability and finishability (limestone) without exceeding the 15% limestone cap that constrains Type IL [S2][S6][S9].
Type IT is not the right call when one SCM already covers the durability lever in question, when the producer's mill cannot deliver a uniform three-component blend at the required specific surface, or when the specifier needs a single-letter code for simplicity on a low-risk pour. In those cases Type IP, Type IS, or Type IL are the cleaner spec, and the binary path avoids the additional QC load that a ternary blend places on plant labs [S2][S4][S7].
Procurement, EPD, and Traceability
Specifying Type IT on a U.S. project is straightforward: name the standard (ASTM C595/C595M), name the designation with full suffix coding (e.g. Type IT(S35)(P15)), state the optional C595 performance suffix if needed (e.g. MS for moderate sulfate resistance, LH for low heat), and require the mill certificate to show constituent percentages and conformity to the C595 chemical and physical tables [S2][S4][S7]. For embodied-carbon reporting, the PCA EPD 193 (valid through 2027-07-31) is the industry-average anchor; project-specific Type IT EPDs exist from individual producers and should be used where a self-declared product-specific declaration is required by the specifier [S2].
The traceability chain that supports a Type IT submittal is, in order: C595/C595M as the product standard, ASTM C219 as the terminology standard, C595 chemical and physical requirement tables for the type-and-optional-performance suffix, mill certificate for batch composition, and either EPD 193 or a product-specific EPD for the carbon disclosure. Two trackable signals to watch: any revision to C595's ternary-blend table in the next ASTM C01 ballot cycle, and any update to the GCCA EPD tool that shifts the industry-average carbon factor for Type IT. For spec context on a related standard family, the ASTM A820 steel-fiber classification article shows how ASTM handles multi-suffix designation coding for an unrelated product family.