Construction documents often specify a cement type based on the required performance of the concrete or the placement conditions. Certain cement manufacturing plants only produce certain types of portland cement. What are the differences in these cement types and how are they tested, produced, and identified in practice?
In the most general sense, portland cement is produced by heating sources of lime, iron, silica, and alumina to clinkering temperature (2,500 to 2,800 degrees Fahrenheit) in a rotating kiln, then grinding the clinker to a fine powder. The heating that occurs in the kiln transforms the raw materials into new chemical compounds. Therefore, the chemical composition of the cement is defined by the mass percentages and composition of the raw sources of lime, iron, silica, and alumina as well as the temperature and duration of heating. It is this variation in raw materials source and the plant-specific characteristics, as well as the finishing processes (i.e. grinding and possible blending with gypsum, limestone, or supplementary cementing materials), that define the cement produced.
To ensure a level of consistency between cement-producing plants, certain chemical and physical limits are placed on cements. These chemical limits are defined by a variety of standards and specifications. For instance, portland cements and blended hydraulic cements for concrete in the U.S. conform to the American Society for Testing and Materials (ASTM) C150 (Standard Specification for Portland Cement), C595 (Standard Specification for Blended Hydraulic Cement) or C1157 (Performance Specification for Hydraulic Cements).
Some state agencies refer to very similar specifications: AASHTO M 85 for portland cement and M 240 for blended cements. These specifications refer to standard test methods to assure that the testing is performed in the same manner. For example, ASTM C109 (Standard Test Method for Compressive Strength for Hydraulic Cement Mortars using 2-inch Cube Specimens), describes in detail how to fabricate and test mortar cubes for compressive strength testing in a standardized fashion.
In the US, three separate standards may apply depending on the category of cement. For portland cement types, ASTM C150 describes:
Cement Type Description
Type I Normal
Type II Moderate Sulfate Resistance
Type II (MH) Moderate Heat of Hydration (and Moderate Sulfate Resistance)
Type III High Early Strength
Type IV Low Heat Hydration
Type V High Sulfate Resistance
For blended hydraulic cements – specified by ASTM C595 – the following nomenclature is used:
Cement Type Description
Type IL Portland-Limestone Cement
Type IS Portland-Slag Cement
Type IP Portland-Pozzonlan Cement
Type IT Ternary Blended Cement
In addition, some blended cements have special performance properties verified by additional testing. These are designated by letters in parentheses following the cement type. For example Type IP(MS) is a portland-pozzolan cement with moderate sulfate resistance properties. Other special properties are designated by (HS), for high sulfate resistance; (A), for air-entraining cements; (MH) for moderate heat of hydration; and (LH) for low heat of hydration. Refer to ASTM C595 for more detail.
However, with an interest in the industry for performance-based specifications, ASTM C1157 describes cements by their performance attributes:
Cement Type Description
Type GU General Use
Type HE High Early-Strength
Type MS Moderate Sulfate Resistance
Type HS High Sulfate Resistance
Type MH Moderate Heat of Hydration
Type LH Low Heat of Hydration
Note: For a thorough review of US cement types and their characteristics see PCA’s Design and Control of Concrete Mixtures, EB001 or Effect of Cement Characteristics on Concrete Properties, EB226.
Physical and Chemical Performance Requirements
Chemical tests verify the content and composition of cement,while physical testing demonstrates physical criteria.
In C150/M 85 and C595/M 240, both chemical and physical properties are limited. In C1157, the limits are almost entirely physical requirements.
Chemical testing includes oxide analyses (SiO2, CaO, Al2O3, Fe2O3, etc.) to allow the cement phase composition to be calculated. Type II cements are limited in C150/M 85 to a maximum of 8 percent by mass of tricalcium aluminate (a cement phase, often abbreviated C3A), which impacts a cement’s sulfate resistance. Certain oxides are also themselves limited by specifications: For example, the magnesia (MgO) content which is limited to 6 percent maximum by weight for portland cements, because it can impact soundness at higher levels.
Typical physical requirements for cements are: air content, fineness, expansion, strength, heat of hydration, and setting time. Most of these physical tests are carried out using mortar or paste created from the cement. This testing confirms that a cement has the ability to perform well in concrete; however, the performance of concrete in the field is determined by all of the concrete ingredients, their quantity, as well as the environment, and the handling and placing procedures used.
Although the process for cement manufacture is relatively similar across North America and much of the globe, the reference to cement specifications can be different depending on the jurisdiction. In addition, test methods can vary as well, so that compressive strength requirements (for example) in Europe don’t ‘translate’ directly to those in North America. When ordering concrete for construction projects, work with a local concrete producer to verify that cement meeting the requirements for the project environment and application is used, and one that meets the appropriate cement specification.