Cement is a key ingredient in concrete and other construction materials, and over a dozen different cement types exist. Together, we’ll explore what cement is and how it’s different from concrete. Then, we’ll look at different cement types and how to make them. That’s a lot of ground to cover, so let’s get started!
Cement is a chemical binding agent that holds construction materials together. This fine powder is usually gray, but it also comes in red, brown, black, white, tan, and specialty colors.
English bricklayer Joseph Aspdin patented the first modern cement in 1824. He made it with clay and limestone from the Isle of Portland (hence its name, portland cement). Portland and other cement types serve many purposes, particularly in making concrete. And since concrete is one of the most fundamental building blocks of our modern society, that makes cement a pretty big deal!
People often interchange the terms cement and concrete, but they’re different. Cement is an ingredient in concrete, whereas concrete is the entire mixture that hardens into a rock-like substance. Concrete typically combines 10-15% cement, 15-20% water, and 65-75% aggregate.
Concrete may also contain pozzolans—materials that contain aluminum or silica. Pozzolans aren’t binding agents alone, but when they mix with water, they chemically react to make binding compounds.
Once the ingredients harden into concrete, they form a strong, durable, nearly impenetrable surface. Concrete’s strength and low cost make it popular for construction projects worldwide—and it’s all possible thanks to cement!
There are over a dozen different types of cement, but they all fit into two categories: hydraulic and non-hydraulic. We’ll talk about both. Then, we’ll explore some popular subtypes of cement that you can use.
Non-hydraulic cement requires dry conditions and carbon dioxide to set and harden, so it can take longer to cure than hydraulic cement. It’s not what you want to use if you’re building a bridge or drainage system, but it’s great for making bricks and mortar.
Hydraulic cement chemically reacts with water to set and harden. (Hydraulic comes from the word hydro, meaning water.) Hydraulic cement can harden in a wide range of moisture levels—such as water you add to it, groundwater, or complete submersion, depending on the type of cement you're using. The most common cement, portland cement, is hydraulic.
Portland cement comes in five main types. You can identify each one by its number or by a set of letters representing its use or characteristics.
Since it’s for general use, Type I portland cement is the most common. It works well for projects without many sulfates in the soil or high temperatures. You may hear people call it ordinary portland cement or OPC. Engineers grade OPC on its compressive strength, with grades 33, 43, and 53 being common. High-number grades are more finely-ground and produce stronger concrete.
Sulfates in groundwater and soil can cause temperature spikes that weaken concrete. So, Type II portland cement comes in moderately sulfate resistant (MS) and moderate heat of hydration (MH) varieties to help keep temperatures down as the concrete cures.
All portland cement takes around 28 days to reach full strength, and over half its strength develops in the first three days. However, Type III portland cement gets even stronger during the first three days of curing than Type I. (HE is short for high early strength.) That’s because it contains finer-ground particles. Water contacts more of the cement’s surface area, helping it hydrate, harden, and develop higher resistance sooner. Type III reaches around 70% strength in three days, whereas Type I reaches 60% strength in that time.
During construction, it’s important to keep concrete from building too much heat too fast; otherwise, heat could cause the concrete to cure improperly and fail later on. So, that’s where this low heat of hydration portland cement comes in. It’s less reactive than other cements to prevent cracking, although it may take longer to set.
When contractors use concrete in high-sulfate areas, they can use Type V (HS) portland cement because it’s highly sulfate resistant. To be effective, the high-sulfate area must also have low tricalcium aluminate content.
Air entraining is the process of adding microscopic air bubbles into cement. These air bubbles give concrete room to expand, shrink, and cope with moisture changes after it cures, making it more freeze-thaw resistant. The air bubbles in air-entrained cement are intentional and evenly dispersed. They won’t weaken concrete, whereas air bubbles that are entrapped in incorrectly poured concrete will fracture it.
Portland cement Types I, II, and III can come in air-entraining varieties called Type IA, IIA, and IIIA. (The names aren't rocket science—A stands for Air.)
Iron oxide and manganese oxide turn regular cement gray, so cement makers limit these minerals to produce white cement. White cement can be Type I or Type III portland cement, and it’s often the base for brightly colored decorative cements because it’s easier to dye than gray cement.
Most blended hydraulic cements mix Type I portland cement with other materials:
In addition to the standard variations on portland, you should know about these specialty cement types. Some still contain portland cement, while others do not. Let's check them out!
When you add calcium chloride to HE portland cement, you get extra-rapid hardening cement, which cures even faster. Other rapid-hardening cements contain calcium sulfoaluminate, or CSA. CSA cements are popular for jobs where you need concrete to set up fast to reduce downtime or please a picky client.
High-alumina cement has many nicknames: HAC, calcium aluminate cement, CAC, and refractory cement. Unlike silica-based portland cement, HAC is aluminum-based. It also contains melted bauxite and lime. HAC gained popularity in the mid-1900s for its high early compressive strength. However, it can be prone to weakness, structural failure, and chemical attack—so some countries are banning its use in new structures.
Concrete can shrink when it dries, causing structural unsoundness. Expansive cement does the opposite: it expands slightly as it cures to prevent cracks and failures. Expansive cement contains portland cement, an expanding agent made from a mix of burned minerals, and blast-furnace slag. The slag is a stabilizer that stops the cement from expanding too much.
The three main types of expansive cement are:
Hydrographic cement—also called hydrophobic or waterproof cement—contains portland cement and water-repellent chemicals like oleic or stearic acid. These chemicals help prevent water damage, making this cement good for underwater use.
Ancient people made cement from unexpected ingredients, like crushed clay pottery and volcanic ash. We’ve come a long way since then! Today, most cement begins its life as limestone or marl. (Some comes from clay and shells, too.)
Miners quarry these rocks and transport them to crushing plants, which break them into baseball-sized pieces. Secondary crushers or hammer mills smash them even smaller.
Plant operators add other materials such as lime, chalk, shale, slate, slag, silica, iron ore, calcium, aluminum, and fly ash. Most plants keep this mixture dry. But for a wet manufacturing process, they add water and stir the mixture in large slurry tanks.
The ground-up material passes through a preheater tower, which warms it with heat from the cement plant to start its chemical reaction before it enters the kiln. The kiln evenly heats the powder at 2,500°F to 2,800°F. This process releases gasses, letting the remaining materials become clinker.
Fun fact: Kilns can be more than 12 feet wide, and if you stood a big one on end, it could be as tall as a 40-story building.
Clinker emerges from the kiln looking like a red-hot lava flow, but it cools to a gray, marbly substance. Then, the cement plant grinds the clinker into fine powder—sometimes so fine it can pass through a sieve capable of holding water! They blend the ground clinker with gypsum, limestone, and other minerals to make cement. The materials and amounts they use help define the type of cement the plant produces.
Finally, some cement plants mix in other additives during grinding. These include mineral pigments to color cement for decoration and air-entrainment additives such as surface reactive agents (resins, soaps, and natural oils), certain salts, or gas-producing compounds like hydrogen peroxide, aluminum powder, or zinc powder.
Fun fact: According to the Portland Cement Association, one pound of cement can contain up to 150 billion grains of powder!1
During each manufacturing phase, cement plants check the cement’s chemical and physical properties to make sure it meets industry standards. (The ASTM and AASHTO set those standards in the U.S.)
Some cement tests measure:
These tests help engineers know how a given cement will perform in concrete, but remember that the quality and mix of other ingredients also help determine concrete’s performance.
There you have it! Next time somebody wants to start the ol’ cement-vs.-concrete debate, you can set them straight. And more importantly, you know the properties of different cement types so you can better understand how they may perform on your projects.
