Portland Cement

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that are not fully understood, hydration comes to a stop. This quiescent, or dormant, period is extremely important in the placement of concrete. Without a dormant period there would be no cement trucks, pouring would have to be done immediately upon mixing.
Following the dormant period (which can last several hours), the cement begins to harden, as CH and C-S-H are produced. This is the cementitious material that binds cement and concrete together. As hydration proceeds, water and cement are continuously consumed. Fortunately, the C-S-H and CH products occupy almost the same volume as the original cement and water; volume is approximately conserved, and shrinkage is manageable.
Although the formulas above treat C-S-H as a specific stoichiometry, with the formula C3S2H3, it does not at all form an ordered structure of uniform composition. C-S-H is actually an amorphous gel with a highly variable stoichiometry. The ratio of C to S, for example, can range from 1:1 to 2:1, ...

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Society for Testing and Materials (ASTM): I. Ordinary, II. Modified. III. High early strength, IV. Low heat, and V. sulfate-resistant. In other countries Type II is omitted, and Type III is called rapid-hardening. Type V is known in some European countries as Ferrari cement.


ASTM type and name Characteristics Applications
I. Ordinary No special requirements General construction (e.g. sidewalks)
II. Modified Moderate sulfate resistance, moderate heat hydration Draining systems, sea walls, floor slabs, foundations
III. High early strength Higher strength soon after pouring Cold weather constructions
IV. Low Heat Low heat hydration Massive structures (e.g. dam)
V. Sulfate ...

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