Ask any engineer or ready-mix producer what drives concrete performance, and the water-to-cement ratio (w/c) will be near the top of the list. It’s one of the most influential variables in concrete design. Lowering the w/c ratio consistently improves strength, reduces permeability, increases durability, and supports longer service life in demanding environments.
But there’s a catch.
As the w/c ratio drops, the concrete loses access to the internal water it needs for complete hydration. The cement continues trying to react, but the pores dry out early. This leads to self-desiccation, autogenous shrinkage, and the buildup of internal stresses—problems that can trigger early-age cracking, curling, and reduced durability.
This paradox has challenged designers for decades:
The same low w/c mix intended to increase performance can underperform if it isn’t cured properly from within the slab.
This is where the practice of internal curing becomes especially important. Internal curing technologies—including nano-silica admixtures such as E5® Internal Cure—are designed to help low w/c mixes maintain the internal moisture they need for deeper hydration and more uniform volume stability.
Modern performance-based specifications often target w/c ratios at or below 0.45 for applications such as:
Industrial floors
Parking decks
Bridge decks
Post-tensioned slabs
Infrastructure with chloride exposure
These mixes deliver:
Higher compressive strength
Lower permeability
Superior long-term durability
However, reduced water availability comes with consequences.
As cement hydrates, it consumes mixing water. In low w/c mixes, that water is consumed early, causing the internal relative humidity to drop quickly.
Even without external drying, the cement paste shrinks due to internal water consumption. This shrinkage begins at early ages and continues as hydration progresses.
Internal shrinkage generates tensile stresses, particularly at joints and edges. This can lead to cracking and upward warping of slab corners.
Without additional moisture, unhydrated cement remains in the matrix—reducing density, durability, and long-term strength potential.
Traditional curing methods attempt to combat moisture loss at the surface. But in low w/c concrete, the surface is not the problem—the core is. External water cannot penetrate through the dense capillary network quickly enough to supply the internal hydration needs.
This is why the industry increasingly uses internal curing technologies to fully realize the potential of low w/c concrete.
Internal curing provides an engineered supply of moisture inside the concrete, making it available exactly when hydration demands it. Instead of relying on sprayed water or curing membranes, the moisture is distributed throughout the slab from the beginning.
Internal curing admixtures—such as nano-silica–based E5® Internal Cure—help manage both the “water of transport” and the “water of convenience” in the mix.
Maintain internal relative humidity
Reduce early-age shrinkage
Hydrate deeper into the microstructure
Improve density and reduce permeability
Lower the risk of volume change and curling
This allows low w/c mixes to hydrate as designed, without the internal moisture deficits that traditionally limit their performance.
Internal curing offers several critical performance advantages, especially when designing for strength and durability.
Internal curing admixtures help slow internal moisture loss, supporting the continuation of hydration throughout the paste—not just at the surface. This deeper hydration contributes to:
Increased density
Reduced porosity
More stable long-term performance
E5® Internal Cure, for example, is engineered to retain moisture that would otherwise escape early in the hydration process.
Autogenous shrinkage is one of the most overlooked contributors to cracking in low w/c concrete. Anything that reduces internal shrinkage also reduces stress and the risk of early-age cracking, joint separation, and curling.
Internal curing helps by:
Maintaining internal RH
Reducing capillary tension
Supporting uniform volume change
When cement hydrates more fully, the resulting cement paste is:
Stronger
Denser
More resistant to water and chloride intrusion
This translates into better long-term performance, especially in structures where permeability and corrosion resistance are critical.
Traditional curing methods often rely on labor-intensive steps such as blankets, ponding, or curing compounds. Internal curing significantly reduces reliance on these methods.
Some internal curing admixtures—such as E5® Internal Cure—are tested and qualify as curing compounds under ASTM C156, allowing them to replace surface curing in many specifications.
This simplifies field practices and makes curing more consistent across variable site conditions.
When internal curing is incorporated into a low w/c mix, the concrete is better positioned to deliver its intended performance:
More hydration = more reacted cement = more strength.
A denser microstructure improves resistance to water, chemicals, and chloride intrusion.
Uniform moisture reduces internal stresses that distort slab geometry.
Minimized shrinkage leads to fewer long-term deformation issues.
With internal curing, engineers no longer have to choose between “high strength” and “low shrinkage.” The mix can achieve both.
Internal curing doesn’t just improve performance—it also simplifies construction.
Internal curing reduces or eliminates the need for wet curing in many applications.
In flooring applications, removing curing compounds is one of the biggest sources of delays. Internal curing avoids that entirely.
Reduced curling = preserved flatness.
This is especially valuable for warehouses, industrial floors, and slabs with high wheel loads.
Because internal curing admixtures are added at the batch plant, they become part of the mix design and are not dependent on site conditions or field labor.
This standardization supports more reliable performance across multiple projects and ready-mix suppliers.
Low w/c concrete has limited internal moisture for hydration. Internal curing helps prevent self-desiccation and micro-cracking, enabling the mix to achieve its design strength and durability.
No. You still design your mix for structural and durability requirements. Internal curing simply helps the mix reach its full potential by supporting the hydration process.
Yes. More complete hydration results in a denser matrix, lower permeability, and greater resistance to chemical and environmental attack.
Yes. SCM-rich mixes often benefit even more because their slower hydration rates require sustained internal moisture over time.
The water-to-cement ratio is one of the most powerful tools in concrete design—but lowering it without addressing internal moisture leads to predictable challenges: self-desiccation, autogenous shrinkage, cracking, and curling.
Internal curing provides a practical, science-based solution by supplying moisture from within the slab. This allows low w/c mixes to hydrate more completely, reduce shrinkage, and deliver the strength and durability they were designed for.
Internal curing admixtures—such as nano-silica products like E5® Internal Cure—make it easier to unlock the full performance of modern high-strength mixes while simplifying the curing process.
For an in-depth look at internal curing strategies, moisture control, and high-performance mix optimization, explore:
Inside, you’ll learn how to:
Incorporate internal curing into low w/c mix designs
Reduce shrinkage and cracking while improving long-term strength
Streamline curing and moisture mitigation practices
Use internal curing to improve the performance and predictability of high-strength concrete