Concrete properties

Tracing some of the fresh and hardened concrete properties back to the influences of the cement can often answer both fundamental questions and more complex problems in concrete construction.

Admixture Compatibility. Admixtures are chemicals added to concrete in small quantities for a specific function (for example water-reducing, set-retarding, or set-accelerating). These chemicals affect the hydration and/or are adsorbed by the cement particles. Certain combinations of chemicals and cement properties may adversely affect the setting behavior and be deemed incompatible. Examining the chemistry of the hydration reactions and the components of the cement can give clues to the source of the incompatibility.

Strength Gain. The ultimate compressive strength and rate of strength development of concrete is strongly influenced by the chemical reactivity of the Portland cement. Varying hydration rates of the different cement compounds can help explain how the relative proportions of these compounds affect the rate of strength gain. For instance, the C₂S reacts slowly and contributes to long-term strength gain. C₃S, on the other hand, has a much faster hydration rate, and contributes to higher early-strength gain. Thus, cement with a higher proportion of C₃S – as is the case with most of today’s cements – will tend to have a higher early strength, and allow for early form removal or post-tensioning.

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