Technical Information

Cement

Cement

Why is it called "Portland" Cement?

Joseph Aspdin, an English mason who patented the product in 1824, named it portland cement because it produced a concrete that resembled the color of the natural limestone quarried on the Isle of Portland, a peninsula in the English Channel.

World of Cements

There are many different properties and applications of cements for use in concrete including; portland, blended, and hydraulic cements.

• Types of Portland Cement

Portland cements are hydraulic cements composed primarily of hydraulic calcium silicates.

• Types of Blended Cements

Blended hydraulic cements are produced by intimately and uniformly intergrinding or blending two or more types of fine materials. The primary materials are portland cement, ground granulated blast furnace slag, fly ash, silica fume, calcined clay, other pozzolans, hydrated lime, and pre-blended combinations of these materials.

• Types of Hydraulic Cements

All portland and blended cements are hydraulic cements. "Hydraulic cement" is merely a broader term. ASTM C1157, Performance Specification for Hydraulic Cements, is a performance specification that includes portland cement, modified portland cement, and blended cements.

Cement for Concrete

When a cement is specified for a project, consideration should be given to the types of material available in that location. The specification should be flexible, allowing either portland or blended cements. Consideration should always be given to the use of locally available pozzolans and slag cements, provided the desired concrete properties can be achieved. Ideally, the specification should allow any cement that meets the performance requirements of the project. Cements with special or unique properties should not be required unless absolutely necessary.

Effect of Cement Characteristics on Concrete Properties

Cement, together with water, creates the paste that binds aggregate together to form concrete. Concrete quality depends upon the quantity and quality of the aggregate and the paste, as well as the bond between the two. Therefore, the properties of concrete are influenced by the properties of cement. Whether it is the clinker composition, the fineness of the individual cement grains, or the amount with which it is used in the concrete, the type and proportion of cement affect both the fresh and hardened properties of concrete. An understanding of cement characteristics can provide insight to many of the issues arising in concrete construction.

Impact of Hot Cement on Concrete Mix

Hot cement describes clinker that has, through the process of grinding, gained additional energy stored in the form of heat. Once the clinker is ground, this “hot cement” is stockpiled in storage silos where the elevated temperature, especially in warm climates, is not readily abated.

Many attribute slump loss, strength reduction, or other concrete-related problems to the temperature of the cement upon batching. However, research has shown that cement’s ultimate effect on the concrete mixture’s temperature is quite minimal.

The Power of Microscopy

With only a basic assemblage of equipment, microscopical analysis can be easily performed on portland cement clinker to determine phase identities, sizes, conditions, and mutual relationships. Study of a polished section or thin section of clinker quickly reveals several details of crystal size, morphology, abundance, and distribution, leading almost intuitively to interpretations relating these data to certain features of the raw material and burning conditions. For example, if nests of tightly packed belite crystals form in silica-rich areas of the clinker, then coarse quartz grains may be in the raw feed. Alite crystal sizes of 10 to 15 micrometers may indicate an undesirably rapid rate of temperature rise in the clinker as it passes through the kiln. Large clusters of free lime suggest coarse limestone particles.

Some of the many aspects of portland cement production in which microscopy can play an analytical and quality-control role include:

Analysis of Raw Materials

• Quarry rock analysis
• Raw mix analysis

Clinker and Cement Examination

• Phase changes and concentration
• Temperature profile
• Grinding and storage
• Prediction of cement performance

Analysis of Other Materials

• Dust mineralogy and chemistry
• Coal
• Constitution of coal ash and slag
• Gypsum and other sulfates
• Metallography

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