Effect of Temperature on the Hydration of Cement

Effect of Temperature on the Hydration of Cement
Temperature is one of the most influential external factors governing the hydration of cement. The rate of hydration, the nature and morphology of hydration products, the pore structure of the hardened paste, and ultimately the strength development of concrete are all significantly affected by the temperature at which hydration occurs. Understanding these effects is essential for concrete practice, particularly in extreme weather conditions, mass concrete construction, and oil well cementing applications.
General Effect on Hydration Kinetics
The hydration of cement is a chemical process that, like most chemical reactions, is highly temperature-dependent. The rate of concrete hydration is logically higher in warm than in cold weather . Increased temperature promotes the dissolution of anhydrous clinker phases, leading to faster formation of hydration products. At 50 °C, for example, portlandite, C-S-H, and ettringite have already precipitated after just 3 hours of hydration, whereas at 5 °C the dissolution of clinkers is considerably slower .
Calorimetric studies across a temperature range of 15 °C to 95 °C have shown that the apparent activation energy (Ea) of cement hydration decreases significantly with increasing temperature . The temperature dependence of Ea can be mathematically simplified as a step function, where Ea remains a nonzero constant below a critical temperature (Tcr) and reduces to zero above that temperature . This means that at higher curing temperatures, the hydration reaction becomes less sensitive to further temperature increases.
In practical terms, the dormant period—the interval during which cement paste remains workable—is shortened at high ambient temperatures. Setting time decreases as temperature rises above approximately 25 °C . This explains why concrete sets more rapidly in hot weather and more slowly in cold weather.
Effect on Hydration Products and Microstructure
Temperature does not merely accelerate hydration; it fundamentally alters the microstructure and phase assemblage of the hardened cement paste. The most notable effects occur at elevated temperatures.
At higher temperatures (40 °C and above), several microstructural changes have been observed. The formation of denser C-S-H occurs, along with a more heterogeneous distribution of hydration products . The initially fast hydration causes more rapid precipitation of hydration products during the first hours and days, leading to the build-up of a dense inner shell around clinker particles . This rapid precipitation prevents the hydration products from diffusing away from the cement grains and precipitating evenly into the interstitial space, resulting in a coarser porosity and less uniform distribution .
Research using transmission electron microscopy has shown that C-S-H formed at 80 °C has significantly smaller globules—around 3 to 4 nm—compared to C-S-H formed at 20 °C . The C-S-H particles in high-temperature systems are approximately half the size of those forming at lower temperatures.
The composition of the hydrate assemblage also shifts with temperature. At 50 °C, calcium monosulphoaluminate forms at the expense of ettringite . The amount of ettringite decreases, and the ettringite crystals that do form are very short needles rather than the longer, more fibrous morphology observed at lower temperatures . Additionally, curing at high temperature and with low water-cement ratio reduces the gel pore volume and increases the density of C-S-H .
The Strength Paradox: Early Gain versus Late Loss
One of the most important and well-documented phenomena in cement hydration is the temperature-strength paradox. Increased temperature leads to a fast hydration and high early compressive strength . However, at later stages, the strength of cements hydrated at increased temperature is reduced compared to those hydrated at room temperature .
This paradox arises from the microstructural changes described above. The rapid initial hydration produces a less robust physical structure of hydration products. The uneven distribution and higher porosity that result from rapid precipitation adversely affect later-age strength . As one study noted, rapid initial hydration affects strength after about the 7th day because the physical structure of the products formed is less robust, and it retards hydration at later ages .
Quantitative data illustrate this clearly. In one investigation, mortars cured for 7 and 28 days at 20 °C were stronger than material cured at higher temperatures, while mortars cured for only 3 days at 40 °C were stronger than samples cured at ambient temperature . This confirms that the early strength advantage of elevated temperature curing is reversed at later ages.

    Date: 2026-09-16 00:00:00.000000