Portland Limestone Cement | Michigan Concrete

QUICK FACTS ABOUT BLENDED CEMENTS & TYPE IL (PLC)

Blended cements are hydraulic cements manufactured under ASTM C595 and may include portland-limestone cement (Type IL), slag cement blends, pozzolan blends, or ternary blends.
Type IL, often referred to as portland-limestone cement (PLC), is the most common blended cement currently used in North America.
Cement manufacturers formulate modern blended cements to perform similarly to traditional ASTM C150 Type I cement while reducing embodied carbon.
Type IL allows up to 15% interground limestone, compared to the 5% limestone traditionally permitted in ASTM C150 Type I cement.
Other ASTM C595 blended cements may incorporate slag, pozzolans, or combinations of supplementary cementitious materials (SCMs) to further reduce carbon intensity and improve durability.
Most Type IL cements provide an approximate 10% reduction in carbon emissions compared to conventional Type I cement. Some blended cement systems can reduce emissions even further depending on the mix design and SCM content.
ASTM C595 blended cements are designed to meet the same performance requirements as ASTM C150 cements when properly proportioned and cured.
Owner and engineer specifications should allow both ASTM C595 blended cements and traditional ASTM C150 cements unless project-specific performance requirements dictate otherwise.
Blended cements, particularly PLC, can be more sensitive to poor finishing practices, water addition, and curing conditions. Proper field practices are critical for consistent performance. (See Contractor Tips Below.)

FOR MORE INFORMATION ON BLENDED CEMENTS & PLC

UNDERSTANDING BLENDED CEMENTS

Blended cements are engineered to reduce the environmental impact of concrete while maintaining the strength, durability, and performance expected in modern construction. Produced under ASTM C595, blended cements combine portland cement clinker with materials such as limestone, slag, fly ash, natural pozzolans, or combinations of supplementary cementitious materials (SCMs).

Portland-limestone cement (PLC), designated as Type IL, is currently the most widely adopted blended cement because it provides a practical and immediate reduction in embodied carbon with minimal changes to production, batching, or construction practices. By increasing limestone content and reducing clinker content, PLC lowers carbon emissions associated with cement manufacturing by approximately 10%.

Other blended cement systems may incorporate slag cement, fly ash, calcined clays, or ternary blends to achieve additional sustainability benefits, improved sulfate resistance, reduced permeability, and enhanced long-term durability.

Concrete made with blended cements meets the same specifications and mix design standards as conventional portland cement concrete, but contractors, producers, and finishers may notice differences in handling characteristics. Workability, air entrainment, finishing response, and set times can be more sensitive to temperature, moisture conditions, and water content.

In hot weather, some blended cement mixes may set more rapidly. In cooler temperatures, hydration and finishing times may be delayed compared to traditional Type I mixtures. PLC mixtures in particular may feel “stickier” during placement and finishing, requiring adjustments in admixture dosage, finishing timing, and curing practices to maintain consistent quality.

Concrete is the most widely used construction material in the world and, after water, the most consumed material on the planet. Because the industry produces and places enormous volumes of concrete every year, even small reductions in cement-related carbon emissions create significant environmental benefits.

Blended cements represent one of the construction industry’s most practical pathways toward sustainability. Much like fly ash and slag cement have been successfully used for decades, modern blended cements allow producers and contractors to reduce embodied carbon without sacrificing performance when mixes are properly designed and constructed.

Blended cements remain fully compatible with supplementary cementitious materials (SCMs), allowing producers to further optimize concrete mixtures for durability, sustainability, and performance. When combined thoughtfully with fly ash, slag cement, silica fume, or other SCMs, blended cement systems can significantly lower the carbon footprint of concrete while still delivering the strength and service life owners expect.

Success with blended cements ultimately depends on understanding that sustainable concrete still requires sound construction practices. Proper batching, moisture control, placement, finishing, curing, and contractor education remain essential to achieving durable, high-quality concrete in the field.

BLENDED CEMENTS FIELD TIPS FOR CONTRACTORS

Curing Best Practices are ESSENTIAL

Start Early: Begin curing immediately after finishing. PLC is more sensitive to drying, so don’t delay.
Moisture Retention: Use curing compounds, wet burlap, or plastic sheeting to keep surfaces damp. Dry surfaces can lead to surface checking and reduced durability.
Extended Duration: Maintain curing for at least the full recommended period (often 7 days). Blended Cements/PLC may need longer moisture retention than Type I to achieve comparable performance.

Temperature Protection:

In hot weather: Prevent rapid evaporation with fog misting, evaporation retarders, or sunshades.
In cold weather: Insulate placements with blankets or heated enclosures. Avoid early form removal.
Edge & Surface Care: Pay special attention to exposed edges, which dry out fastest and are prone to scaling or crazing.

Evaporation Retarders:

Apply a spray-on evaporation retarder if wind, heat, or low humidity could cause crusting before final finishing.
Avoid Overworking: PLC mixes can feel stickier — minimize excessive troweling to prevent sealing in water or causing surface defects.
Finishing Aids help control surface moisture loss during finishing, reducing crusting, stickiness, and premature drying that can lead to defects.

Finishing Timing:

In hot conditions: Be ready to finish sooner — Blended Cements/PLC may set up faster.
In cold conditions: Expect slower set — finishing aids (like accelerators or heaters) may help keep things on schedule.
Clean Tools Often: PLC pastes can build up on trowels and screeds more than Type I. Keep tools wiped down for smoother finishing.
Compatibility Check: Make sure any evaporation retarders or finishing aids are tested with your supplier’s mix design. Some products perform differently depending on admixtures.
BOTTOM LINE: Think proactive moisture control and smart finishing aids. PLC will reward crews that cure early, cure long, and use evaporation control wisely.

ACCELERATED EARLY STRENGTH GAIN

Almost anywhere you use ordinary portland cement, you can use Blended Cements instead. In the U.S., Blended Cements/PLCs have an established track record for transportation infrastructure. Many states have been placing PLC concrete pavements for more than a decade – with good results. From highways to driveways, PLC performs just as well in heavy-duty pavements as it does for residential flatwork. And it’s appropriate for bridge applications, too, from top to bottom, everything from the deck down to the foundation, even including geotechnical work. For buildings, PLC concrete is a natural fit for structural members of any type or size, and it’s also great for exterior finishes and hardscaping. Architects and other designers who are tasked with meeting goals put forth by green rating systems or codes will find PLC an especially useful approach to help them achieve a lower carbon footprint for any project.

EASY TO USE

To help with the transition to more environmentally friendly concrete, cement manufacturers understand that the switch to PLC must be simple. By optimizing PLCs, they have made it easy for specifiers, producers, and installers to use them. PLC can be swapped in for portland cement at a 1:1 replacement level. This is a big help to ready-mix producers, who can continue operations using their well-established systems with a minimal amount of disruption. In most cases, all that is needed for maintaining fresh concrete behavior is the typical tweaking of proportions or admixtures, similar to changing from one source of cement to another. Anyone who knows how to work with cement and concrete knows how to work with PLC concrete.

PORTLAND LIMESTONE CEMENT/BLENDED CEMENTS