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(used by permission from ACI’s Concrete Craftsman Series “Concrete Fundamentals”)

Freshly mixed concrete is made of cement, water, and aggregates such as sand and gravel. Frequently, it also contains one or more admixtures and supplementary cementitious materials (SCMs). The quality of these ingredients, their proportions, and the way they are mixed all affect the strength of the concrete. Typically a fresh concrete mixture should be plastic or semi-fluid, and capable of being shaped like modeling clay in the hand.

Let’s take a look at some of the more common types of cement used in concrete.

Portland cements are hydraulic cements, which means they set and harden by reacting chemically with water, and they are able to do so under water. During the reaction, which is called hydration, they give off heat as they form a stone-like mass that binds the aggregate particles together. Most of the concrete’s hydration and strength gain take place in the first month (typically referred to as 28 days). After that there may be slow gains in strength over long periods, sometimes 50 years or more. In massive structures such as dams and large piers, and in hot weather, the heat that is generated can cause cracking and strength loss at times. However, in most concrete work, particularly in cold weather, the heat helps concrete to harden and gain strength faster.

Portland cement was patented in 1824 by Joseph Aspdin, a mason in England. He named it “portland” because concrete made with it was similar in color to natural limestone from the Isle of Portland. Although Aspdin was the first to patent a formula for cement, natural cements produced by heating natural minerals had been used for centuries. The Greeks and Romans used lime mortars that were given hydraulic properties by the addition of volcanic ash and other natural pozzolans. The first recorded shipments of portland cement to the U.S. came from Europe in 1868, and it was first manufactured in the U.S. in 1871 (Design and Control of Concrete Mixtures 1).

To make portland cement, finely ground raw materials such as limestone, clay, cement rock, and iron ore are blended by either a wet or dry process to produce a mixture with desired chemical composition. The raw mix is heated in a kiln to 2600 to 3000°F (1400 to 1650 °C). In the kiln it changes chemically into pellets of cement clinker. The clinker is cooled and ground to the fineness of face powder with a small amount of gypsum added to regulate the setting time. The resulting cement is not a single chemical, but is a complex mix of chemical compounds that participate in the hydration process.

ASTM Cl50 /C150M, “Standard Specification for Portland Cement,” defines the principal types of portland cement used in the U.S. :

A general-purpose cement used where special properties of the other types are not required. Widely used in slabs-on-ground, reinforced concrete buildings, bridges, and elsewhere that concrete is not exposed to aggressive environments or to objectionable temperature rise due to heat of hydration.

Used where moderate sulfate exposure is required to be resisted, as in drainage structures where sulfate in groundwater is not unusually severe. Usually generates heat of hydration more slowly than Type I. Gains strength more slowly than Types I and III, but eventually catches up (about 56 days) when concrete is properly cured.

Develops strength much sooner than Type I would have at 28 days, usually in a week or less. Similar to Type I, but more finely ground so that it develops strength faster. Useful when forms need to be removed early, as for example, in precast plants or when a structure will be put into service quickly.

Develops strength at slower rate than other types and releases less heat as it hydrates. Used in massive structures such as gravity dams and mat foundations where the rate and amount of heat generated during hardening is required to be minimized. Type IV cement is no longer manufactured in the U. S. because SCMs offer a less expensive way to control temperature rise.

Used only in concrete exposed to severe sulfate action, principally where soils or ground waters have a high sulfate content. Sulfate attacks on concrete can cause the concrete to crack and break up unless the concrete is made sulfate-resistant.

ASTM C150/C150M also provides for three types of air entraining cements – Types IA, IIA, and IIIA – which are similar to Types I, II, and III described previously, except that they are manufactured with small amounts of air-entraining materials that improve the resistance of concrete to freezing and-thawing cycles. Most concrete producers believe it is more effective to add air-entraining admixtures during the concrete mixing process rather than to use special cements so there is limited demand for air-entraining cements.

Two cements that produce a moderate heat of hydration, Type Il(MH): “For general use, more especially when moderate heat of hydration and moderate sulfate resistance are desired,” and Type Il(MH)A, “Air-entraining cement for the same uses as Type II(MH), where air-entrainment is desired,” are also described in ASTM C150/C150M.

Type I portland cement is usually carried in stock and is supplied when the cement type is not specified. Type II is also widely available, particularly in areas with saltwater exposure or high sulfate content in the soil. Together Types I and II make up 90 percent of the cement shipped from U.S. plants. Type III and white cement are available in the larger cities, and they represent about 4 percent of cement shipments.

The gray or tan color of ordinary portland cement depends mostly on the amount of iron in the cement. White cement, which differs from ordinary cements chiefly in color, is made to conform to ASTM Cl 50/1 SOM, usually Type I or Type III. White portland cement is made with selected raw materials containing very little iron or manganese oxides, which are the substances that give cement the typical gray color. White portland cement is used primarily for architectural purposes in both precast and cast-in-place concrete.

It is necessary for white concrete, and gives brighter, more intense colors for colored concrete in which pigments are added during the mixing. Colored cements are produced by intergrinding pigments with white clinker.

Only 6 percent of U. S. cement production goes into special hydraulic cements. Several of the more important types of special cement are briefly described.

Either ASTM C595/C595M, “Standard Specification for Blended Hydraulic Cements,” or ASTM Cll57 /Cll57M, “Standard Performance Specification for Hydraulic Cement,” is used to specify blended cements.

a.) Portland cement b.) Slag cement c.) Fly ash and other pozzolans d.) Hydrated lime e.) Ground limestone f.) Preblended combinations of(a) through (e)

These cements may have optional special properties designated by the additional notation, for example, MS for moderate sulfate resistance, HS for high sulfate resistance, MH for moderate heat of hydration, LH for low heat of hydration, and more.

Blended cements can be used in construction when specific properties of these types of cements are required. However, the concrete may not gain strength as fast as with ASTM Cl50 /Cl50M cements.

Masonry cements are hydraulic cements manufactured to meet ASTM C91/C91M, “Standard Specification for Masonry Cement,” requirements designed for use in mortar for masonry construction. They contain a variation of cement or hydraulic lime, usually in combination with other materials such as hydrated lime, limestone, chalk, slag, or clay. There are three types – M, N, and S – that are used with or without other cements to obtain workable, plastic masonry mortars. Masonry cements can be used for parging and plaster (stucco), but never for making concrete.

These hydraulic cements expand rather than shrink during early hydration after setting. Manufactured to meet ASTM C845 /C845M, “Standard Specification for Expansive Hydraulic Cement,” they are used most commonly to produce shrinkage-compensating concrete. There are three classifications-K, M and S. When the expansion is properly restrained, they are effective in making crack-free pavements and slabs, as well as plugging leaks in concrete and masonry walls. Expansive cements are not commonly manufactured; most concrete producers believe it is more economical to add an expansive admixture during the concrete mixing process rather than use a special expansive cement.

In addition, there are also oil-well, refractory, plastic, waterproof, and regulated-set cements, as well as others still under development. Refer to Design and Control of Concrete Mixtures for more information about blended cements.

This article is an excerpt from ACI‘s Concrete Craftsman Series “Concrete Fundamentals” and is used by permission. To purchase this series, or other ACI educational publications, go here.

Contents of this article are also covered in ACI’s Certificate Program Package titled “Fundamentals of Concrete Construction”

The last 10 years of Randy’s diverse 35 year career in communications have focused on the construction industry. The White Cap Resource Center is a product of his passion for developing relevant, informative content that gives pro contractors a competitive advantage.

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I live in Tucson and buckling sidewalks at the joints are a common sight here. What is the city and their vendors doing wrong? I would like to speak to this problem can anyone recommend a source where I can read up?

Great question. There is no simple answer, except, ALL concrete will eventually crack. The severity, and timing result from a combination of factors. Improper soil prep/compaction prior to pouring can cause cracks. improper curing can cause the concrete to be weaker. Freeze/thaw cycles, using the wrong mix design, joints that are too far apart, or joints that are too shallow for the slab can all cause cracking in the wrong places. Here’s a great article I found online that explains some of the basics. And we have additional articles on our site that deal with cracking and spalling concrete, and joint repair, etc. https://liftrightconcrete.com/why-do-you-have-concrete-sidewalk-cracks/ https://news.whitecap.com/six-ways-to-prevent-spalling/ https://news.whitecap.com/concrete-slab-repair/

Randy, you didn’t mention base soil as a factor. I live in High Desert in So. Cal., Mojave Desert, and our soil has large amounts of clay like soil, called Calechi here, and concrete on road medians crack and lift 4-6 inches after a wet period. Soil eventually dries and shrinks back but damage is done. Tucson may have soil issues?

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