Let's Talk Concrete

Concrete’s versatility, durability, and economy have made it the world’s most used construction material. The U.S. uses about 260 million cubic meters (340 million cubic yards) of ready-mixed concrete each year. It is used in highways, streets, parking lots, parking garages, bridges, high-rise buildings, dams, homes, floors, sidewalks, driveways, and numerous other applications.

Specifying Cement for Use in Concrete

There are many different properties and applications of cements for use in concrete including; portland, blended, and hydraulic cements. To help determine which cement is most appropriate for your construction needs and to optimize mixture performance and economy it is important to know what is available… we’ve come along way from Joseph Aspdin’s patent in 1824!

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 ground-granulated blast furnace slag, 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.

If no special properties are required

The specification should permit the use of Types I and II portland cement, blended cements, or any cement meeting the requirements of a type GU hydraulic cement. The use of pozzolans or slags should be permitted wherever possible. It may not be possible to use significant levels of pozzolans or slag (or Types S or P blended cements), in many applications because these concretes tend to set, harden, and gain strength at a slower rate, especially in cold weather.

Heat of hydration requirements –

Where moderate heat of hydration is required, Type II portland cement meeting the moderate heat option can be used, as well as a blended cement with the MH suffix, or any hydraulic cement meeting the requirements of Type MH. The temperature requirements of the concrete may also be met using other cements such as a Type I portland cement in combination with sufficient amounts of pozzolan or slag.

Low heat of hydration requirements can be met with a Type IV portland cement (although generally not produced in the U.S.). A portland-pozzolan cement meeting the low-heat option (Type P(LH) cement), or any hydraulic cement meeting the requirements of Type LH will also provide a low heat of hydration. Low heat can also be achieved by using suitable supplementary cement materials.

For more details about selecting the right cement type to prevent thermal stresses, see Portland Cement, Concrete, and Heat of Hydration (PL972).

Where sulfate resistance is required –

Moderate sulfate resistance can be provided by the appropriate portland or blended cement or by any hydraulic cement meeting the requirements of Type MS. The sulfate resistance of concrete can also be improved by the appropriate use of pozzolans or slag.

High sulfate resistance can be achieved with a Type V portland cement or any hydraulic cement meeting the requirements of Type HS. Many blended Type IS or IP blended cements will meet the requirements for high sulfate resistance, but there is no specific classification for these cements in ASTM C595. Sulfate- resistant concrete may also be met by using other cements such as a Type I portland cement in combination with sufficient amounts of appropriate pozzolans or slag.

High early strength requirements-

High early strength requirements can be met by either a Type III portland cement or a Type HE hydraulic cement. Blended cements containing highly reactive pozzolans such as silica fume may also meet the requirements for high early strength, although there is no specific classification for such a cement in ASTM C595.

Resistance to ASR-

When a potentially reactive aggregate is being used some level of protection against damaging ASR expansion may be achieved by specifying either the low-alkali option for portland cement, the option for low-reactivity with pyrex glass for blended cements, or by specifying any type of hydraulic cement that meets option R (which is also based on a performance test using pyrex glass). Resistance to ASR may also be conferred on a concrete by incorporating sufficient amounts of appropriate pozzolans or slag.

Some types of portland cement may not be readily available in all areas. Type I portland cement is usually furnished when a specific cement type is not specified. Type II cement is usually available, especially in areas of the country where moderate sulfate resistance is needed. Cement Types I and II represent about 90% of the cement produced. Some cements are designated as both Type I and II (Type I/II), meaning that they meet specification requirements for both types. Type III cement and white cement are usually available in larger metropolitan areas. Type IV cement is manufactured only when specified for particular projects (massive structures like dams), and therefore is usually not readily available. Type V cement is available only in particular regions where it is needed to resist high sulfate environments.

Blended cements are available in many regions of the United States but certain types may not be available in some areas. The properties conferred on concrete through the use of blended cements can usually be attained by combining normal portland cement with appropriate levels and types of supplementary cementing materials at the mixer.

When cements with special properties are not available, adjustments to the proportions and types of material in the concrete mixture can usually be made to attain the desired properties using available materials.

(Reprinted Courtesy of the Portland Cement Association)

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Comments

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[Hauu Ward]

Wel that was informative and accurate, but not much use to the average joe on How to and DIY. When you use concrete for any purpose, remember the material has a working time limit and get it right the first time. Mistakes are permanent or very expensive to redo.

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Love the information. Consider future posts on clean up of sites containing high volume of cement and other sharp jagged or corrosive materials.

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