wet areas like dikes or dams.
Yes. Type IV Portland cement is generally known for its low heat of hydration. This cement is used for very large concrete structures, such as dams, which have a low surface to volume ratio. This type of cement has not been made for many years, because Portland-pozzolan cements and ground granulated blast furnace slag addition offer a cheaper and more reliable alternative. These classes differ from the ASTM classes. I - Portland cement: Comprising Portland cement and up to 5% of minor additional constituents. II - Portland-composite cement: Portland cement and up to 35% of other single constituents. III - Blastfurnace cement: Portland cement and higher percentages of blastfurnace slag. IV - Pozzolanic cement: Portland cement and up to 55% of pozzolanic constituents. V - Composite cement: Portland cement, blastfurnace slag and pozzolana or fly ash. Read the links below for more details.
Thomas hit the second part of the question, but not the first part. For a VERY simple comparison: Portland Cement (PC) is a complex mixture of anhydrous calcium, silica, lime, etc. that hydrates (not dries) with water to form CSH (calcium-silicate-hydrates), the basic crystalline structure of cement/concrete. Pozzolans are not PC, but are simply forms of amorphous silica which can react with the byproducts of the hydration of PC to form more CSH. Typical pozzolans are fly ash, ground-granulated-blast-furnace slag (GGBFS), silica fume, etc. They do not begin reaction (or contribution to the hydrated cement crystalline structure) until later in the process... from about 7 to 14 days of hydration. Therefore, while a concrete mixture heavy in proportion of pozzolans will usually have a finer crystalline structure and higher 28 or 56 day strength, it usually lags in early strength gain up to 7 days and will exhibit a lower heat of hydration due to lower PC content.
