Cement: What It Is, What It Isn’t and How It Works

Cement is an ingredient of concrete. You can’t have one without the other – and we owe much of our world to this combination.

Whether it was on the original 1960s series on TV or on a nostalgic cable television network, it’s hard for any fan of “The Beverly Hillbillies” not to know what the Clampetts called their swimming pool. It was the “cement (see-ment) pond,” of course.

Cement was likely used in that and thousands of other backyard pools of the time. But in fact the material in its entirety is more properly called concrete.

The public very often uses these two words – cement and concrete – interchangeably, but any concrete driveway contractor knows there’s a difference. In fact cement is one component of concrete, the other parts being gravel and other coarse aggregates. We might think of all pavements that are lighter in color than asphalt as cement, but all of them are almost certainly concrete.

Importantly, cement (and concrete for that matter) can be made in different ways and with variations of ingredients as well. Used to create cement are lime or calcium oxide, which is derived from limestone, chalk, seashells, shale and calcareous rock.  These are variously combined with clay, iron ore, shale, silica sand, slag from blast furnaces and slate.

And just as important, there is no single “recipe” for making cement, as there are many different types of cement used for many different purposes. There are at least a dozen types of cement, ranging from the most-common Ordinary Portland Cement (OPC) to a Portland Pozzolana Cement (PPC), rapid hardening cement, low heat cement, expansive cement, hydrophobic cement and several more. OPC is used in most construction, PPC and others in water environments (marinas, dams), quick setting cement is for underwater construction such as bridge building, and low heat cement is used to build chemical plants and wind turbine plinths. 

To make concrete, the end product, cement is combined with water, sand and crushed stone aggregates. It is remarkably versatile, made possible by adjustments in other ingredients and the composition of the aggregate: concrete is as good a material for building highways and dams as it is to build skyscrapers, sidewalks, bridges and even homes.  Achieving the right mix of cement and the other ingredients is essential to achieving the desired surface texture, strength and resiliency (consider how heavy vehicles ply concrete surfaces on roads, warehouse access points, and areas under construction). 

More recently, cement and concrete have come under criticism because the amount of energy required to produce the material means it has a high carbon footprint. This starts with quarrying rock (where most ingredients originate), hauling heavy components long distances and high heat processes that involve the burning of fossil fuels. Sometime, installed projects the mass of the hardened material holds daytime heat into night in urban environments (the so-called “heat island effect”), causing greater use of air conditioning.

Working on this is the Concrete Sustainability Hub (CSH) at the Massachusetts Institute of Technology, an academic research center. Funded since 2009 by the concrete industry, which is looking to a time when carbon taxes might be enacted (which would send customers looking for alternatives), the CSH is examining everything from using less energy in cement and concrete manufacturing to improving pavement life cycles and increasing the albedo (reflectivity) effect, the last which reduces heat retention by building, wall and road surfaces.

The invention of cement and concrete long precedes The Beverly Hillbillies – the Romans built aqueducts and portions of the famous Coliseum of concrete – but that doesn’t mean it can’t still be improved upon to meet the needs of a modern world as well as the modern concrete contractor.