portland cement

ASTM C 150 defines portland cement as "hydraulic cement (cement that not only hardens by reacting with water but also forms a water-resistant product) produced by pulverizing clinkers consisting essentially of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulfate as an inter ground addition." Clinkers are nodules (diameters, 0.2-1.0 inch [5-25 mm]) of a sintered material that is produced when a raw mixture of predetermined composition is heated to high temperature. The low cost and widespread availability of the limestone, shales, and other naturally occurring materials make portland cement one of the lowest-cost materials widely used over the last century throughout the world. Concrete becomes one of the most versatile construction materials available in the world.The manufacture and composition of portland cements, hydration processes, and chemical and physical properties have been repeatedly studied and researched, with innumerable reports and papers written on all aspects of these properties.
The composition of portland cements is what distinguishes one type of cement from another. ASTM C 150 and AASHTO M 85 present the standard chemical requirements for each type. The phase compositions in portland cement are denoted by ASTM as tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), and tetracalcium aluminoferrite (C4AF). However, it should be noted that these compositions would occur at a phase equilibrium of all components in the mix and do not reflect effects of burn temperatures, quenching, oxygen availability, and other real-world kiln conditions. The actual components are often complex chemical crystalline and amorphous structures, denoted by cement chemists as "elite" (C3S), "belite" (C2S), and various forms of aluminates. The behavior of each type of cement depends on the content of these components. Characterization of these compounds, their hydration, and their influence on the behavior of cements are presented in full detail in many texts. Some of the most complete references dealing with the chemistry of cement include those written by Bogue (1955), Taylor (1964), and Lea (1970). Different analytical techniques such as x-ray diffraction and analytical electron microscopy are used by researchers in order to understand fully the reaction of cement with water (hydration process) and to improve its properties.