Several types of cement varying in mineralogical compositions, fineness, rate of hardening, strength, development and amount of heat generated during setting and hardening are available. These variables are taken into account during the manufacturing process. Blended cement contains Portland cement and admixtures such as - fly ash, calcined clay, puzzling and granulated blast furnace slag to improve impermeability or corrosion resistance of concrete against sea and sulphate water.  Cement is supplied in bags and steel drums for bulk uses.  Cement deteriorates in quality on long storage, particularly in damp condition or when exposed to air. Common Types of cement used in construction are: