What is Cement?
If we’re going to discuss cement testing equipment, we should be clear what we mean by “cement.” A single definition is hard to pin down, and cement can’t be characterized as just one material.
In a general definition, hydraulic cement is a powder, that when mixed with water, undergoes a chemical reaction called hydration. The cement paste hardens and gains strength as it cures over time. Portland cement is the most common type of hydraulic cement and forms the basis of most cementitious materials used for concrete, mortar, and grout.
Note: What is the difference between Mortar and Grout?
- Mortar is a compound made with hydraulic cement, sand, water, and lime, used to bond brick or block masonry units together. Mortar consistency must be thick enough to stay on the masonry surfaces during placement and maintain correct joint thickness under load until cured.
- Grout often has a similar composition to mortar but can be made with many different ingredients that control its consistency and flow. Grout has a higher viscosity, allowing it to flow into the voids and recesses between structural surfaces or preplaced aggregate.
History of Cement
The history of cement is complex and anything but linear. We know that ancient Egyptians used super-heated (calcined) gypsum as a cement long before Greeks and Romans combined calcined limestone and sand to create a different version. Romans were the first to discover that adding finely-ground volcanic pozzolanic materials would enhance the strength of their concrete mixes.
Aspdin's Beehive Kiln, Photo Credit: Dartford museum
Modern Cement Development
The development of modern cements is rooted in the United Kingdom beginning in the 1750s. Many individuals, ranging from engineers and researchers to brick masons and tinkerers, slowly developed and improved formulations over the next century. Their compounds were varied combinations of heated lime or ground limestone mixed with clays, shales, slates, or chalk. Between 1824 and 1853, Joseph Aspdin of Leeds and his son William developed the most successful formulation and process. Equally as crucial as refinements in chemical composition were the introduction in the 1860s of rotary kilns in the United States and Germany. These new devices allowed virtually continuous production of a much higher-grade cement product.
Production of Cement
The manufacture of hydraulic cements begins by compounding carefully controlled portions of limestone, shale, clay, and iron ore. Blended cements may also add slags or pozzolan materials. A sloped rotary kiln, which can be 10 to 15 feet in diameter and up to 300 feet long, heats the raw compound. Materials are heated to between 2,700° and 3,000°F (1,480° to 1,600°C) while rotating along toward the lower end. The calcining process creates new chemical compounds and results in marble-sized pellets called “clinker,” which are then finely ground to produce the cement powder. The producer may add Gypsum or lime during grinding.
Cement Types and Specifications
Three major specifications define hydraulic cements and their usage:
ASTM C150/AASHTO M 85 for Portland cement is a prescriptive specification and lists both the chemical composition required and the physical tests needed to characterize the material. ASTM C150 defines ten types of Portland cement, based on five basic formulations:
- Type I: A general-purpose cement, used mostly in the production of Portland cement concrete.
- Type II: Cement with moderate sulfate resistance for concrete in direct contact with soils or groundwater. Most cement sold in North America will meet either Type I or Type II specifications.
- Type III: Similar to Type I, but ground to a smaller particle size during production. Develops strength more quickly and is known as “high-early” cement.
- Type IV: The lower heat of hydration and a slower rate of strength development controls internal temperatures on mass pours. Blended cements that are less expensive and more reliable have mostly replaced Type IV cement.
- Type V: This type resists sulfate attack in applications where sulfate soils and groundwater would cause permanent damage to ordinary cement. Cements blended with blast furnace slag and fly-ash are more effective and less expensive to produce than Type V cement.
Air entraining compounds added to Types I, II, and III during production produces Types IA, IIA, and IIIA cements. Separate air-entraining admixtures dosed directly into ready mix concrete batches have mostly replaced these modified cement types.
The fineness of Type II cement can be manipulated during the grinding phase to reduce the heat of hydration, desirable in mass pours such as dams or bridge abutments. A material with larger individual particles has reduced surface area and, subsequently, a slower rate of hydration. Custom grinding adds both Type ll(MH) and Type ll(MH)A cements to the list.
ASTM C595/AASHTO M 240 is another prescriptive specification, but this one details the composition and tests required for blended hydraulic cements with Portland cement as the main ingredient. Additional materials are mixed in that reduce cost, alter set times or control other characteristics of the Portland cement commonly include Slags from blast furnace operations or pozzolans like coal ash and silica fume from coal-fired electricity production.
ASTM C595 covers blended cements. As noted above, these compounds use other cementitious materials to modify the characteristics of plain Portland cement. The blends can enhance workability, prevent alkali/aggregate reactions, reduce water demand, and more. The usage of coal ash from coal-fired electrical plants reduces the environmental impact of these waste materials. There are four main categories of blended hydraulic cements:
- Type IS: Portland-Slag Cement contains 25% to 70% blast furnace slag products by weight.
- Type IP: Portland-Pozzolan cement Includes coal ash and silica fume waste materials.
- Type IL: Portland-Limestone Cement has added calcium carbonate and gypsum and reduces the amount of carbon dioxide released during production.
- Type IT: Ternary Blended cements add two types of additional cement materials instead of just one to basic Portland cement to produce desired qualities.
Letter suffixes designate additional features and ingredients, as noted in the specification. For example, Type IP(MS) is a Portland-pozzolan cement with moderate sulfate resistance. (HS) indicates high sulfate resistance, and (MH) is for moderate heat of hydration.
ASTM C1157 is a performance-based specification for hydraulic cements. It places no restrictions on the chemical composition of the materials, but only requires adequate performance in a series of physical tests. ASTM C1157 is a performance specification that categorizes hydraulic cements by their performance attributes instead of their content. There are no requirements for chemical composition. Type designations for these cements are straightforward:
- Type GU: General Use, when particular types are not required
- 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
Cement Test Methods & Testing Equipment List
While the list below is not comprehensive, it shows the most common testing equipment used for the physical testing of cement. Each of the three main specifications for hydraulic cements references some or all these devices. Also, their use is incorporated into other ASTM/AASHTO test methods for cement as noted.
Fineness of Cement
Consistency Test of Cement
Setting Time of Cement
Length Change/Soundness of Cement
Air Content of Cement
Specific Gravity/Density of Cement
References and Useful Links
- Portland Cement Association offers an explanation of cement types, applications and nomenclature in this article, and thorough reviews and characteristics in two popular publications:
- Design and Control of Concrete Mixtures
- Effects of Cement Characteristics on Concrete Properties
- Significance of Tests and Properties of Concrete and Concrete-Making Materials, ASTM Publication STP169D, Lamond JF, Pielert JH, 2006. The chapters in Part V, Other Concrete Making Materials, are particularly useful for cement testing.
We hope this blog post has helped you select the right cement testing equipment needed for your lab. Please contact the testing experts at Gilson to discuss your application.