Portland cement
is a common hydraulic material used in construction.
Hydraulic concrete, more properly called hydraulic cement, is a material that hardens when exposed to water but independent of the amount of water. Hydraulic cements can even harden under water, making them appropriate for use in wet areas and for completely or partly submerged structures. These types of cement work due to chemical reactions in the mix.
Portland Cement
This cement is the most common type of hydraulic cement and is used to make many kinds of concrete. Portland cement is made by heating limestone, clay and and small quantities of other ingredients to a high temperature. The material produced is then ground up and mixed with gypsum. When the Portland cement comes into contact with water, the calcium oxide in it absorbs carbon dioxide to create calcium carbonate. It doesn't matter how much water is in the mix, and Portland cement will set even underwater. Unlike other hydraulic cements, this material tends to shrink slightly as it cures.
Lime-Pozzolan Cement
According to the Journal Ceramics-Silikaty, this material has been in used since the Neolithic period and was common in Roman construction. Lime-pozzolan cement is made of fine, volcanic ash and agricultural lime. The chemical action of hardening is similar to that of Portland cement but takes much longer. Lime-pozzolan cements are also relatively weak initially and gain strength over time, becoming extremely durable. They are no longer commonly used because of the long time it takes for the cement or concrete to reach full strength. However, chemical additives can speed up the hardening process.
Slag-Lime Cement
Slag-lime cements are composed of agricultural lime and slag, the waste material from ore smelting. Manufacturers must use granulated slag, which has a glass appearance, since other types will not react effectively. The slag itself does not react hydraulically without the presence of an alkaline substance, such as lime. Once the lime has been added, the material works similarly to lime-pozzolan cements, including a longer hardening time and slow strengthening. Slag-lime cements aren't often used on their own but are a common ingredient in Portland cement blends.
Calcium Sulfoaluminate Cement
This cement is made from material that includes calcium sulfoaluminate, a material found in Israel, close to the Dead Sea. Calcium sulfoaluminate cements are expansive in contact with water and do not shrink like conventional Portland cement. They can be used to fill gaps effectively and repair leaks. This material requires lower kiln temperatures than Portland cement and can be made using less energy. However, producing calcium sulfoaluminate cement does release significantly more sulfur dioxide, a component of acid rain.
