Concrete vs. Cement – Understanding the Key Differences

Concrete and cement are not the same thing, and mixing the two up is a common source of confusion on a job site. Cement is one ingredient in concrete, alongside aggregate and water.

This article covers what separates the two, the types of Portland cement and what each is used for, and why the distinction matters when you are trying to keep moisture from ruining a floor.

• Cement Is Simply an Ingredient of Concrete
• Portland Cement
• Drying vs. Curing
• Water’s Okay… to a Point
• Moisture Measurement
• The Preemption of “Hurry up!”

In construction, concrete slab moisture problems result from many possible mistakes. One is a common misunderstanding of the difference between concrete and cement.

Cement Is Simply an Ingredient of Concrete

The most basic concept to understand is that cement, by itself, will not produce concrete. Concrete is formed by mixing cement, aggregate, and water. The term “concrete technology” characterizes the myriad ingredient proportions which blend into a concrete mix. Each of the three ingredients performs specific roles.

Cement reacts chemically (called hydration) when mixed with water and forms a paste. Aggregates come in coarse or fine grains and can originate as gravel, stone or crushed concrete. Paste and aggregate draw together the thick liquid form of what will harden into a concrete slab.

Portland Cement

Portland cement is considered one of the hydraulic types of cement because it will harden regardless of surrounding moisture conditions. (The binding chemical reactions will take place even under water.) There are ten different forms of Portland hydraulic cement, and each one has specific applications.

Type I and Type IA: general-purpose cement suitable for all uses where the special properties of other types are not required.

Type II and Type IIA: contain no more than 8% tricalcium aluminate (C3A) for moderate sulfate resistance.

Type II(MH) and Type II(MH)A: Type II(MH) cement has a moderate heat of hydration characteristic (the sum of C3S+4.75 C3A <100%), and moderate sulfate resistance (a maximum C3A content of 8%).

Type III and Type IIIA: chemically and physically similar to Type I, they are ground more finely to produce higher early strengths.

Type IV: used in massive concrete structures which require minimum rates and amounts of heat generated by hydration. It develops strength more slowly than other cement types.

Type V: contains no more than 5% C3A for high sulfate resistance.

Two key properties underlie concrete mixes that owners want: strength and durability. The engineered properties of a calcium-silicate-hydrate (C-S-H) gel are the most important influence on the setting, hardening, and strength of concrete. At the microscopic level, C-S-H structure determines the concrete’s durability over time.

Drying vs. Curing

One of the building industry’s biggest problems is our expectation for concrete to hurry up and dry so we can get on with construction. It’s like telling a child to hurry up and learn. Problems ensue.

Because of the different types of cement mixtures possible to form concrete, concrete quality control is all about moisture measurement of the water vapor within the slab.

While the new floor is curing and drying (two different processes), contractors measure moisture content as relative humidity (RH) by placing probes inside drilled holes in the slab.

Each probe has a sensor which feeds RH data to a hand-held meter. RH is displayed by percentage, and RH can vary in different locations and depths of any concrete slab. Concrete slab moisture problems occur when the slab’s RH has not reached the levels necessary for the chosen flooring or finish application.

Wagner Meters has developed the Rapid RH^®: an RH test method that accurately and cost-effectively assesses concrete moisture conditions. Once probes are inserted, they must equilibrate with the slab’s conditions before the testing begins.

The Rapid RH Smart Sensor stays in the hole once it is placed, so it remains equilibrated with the slab and can be read again at any time without starting over. A reading taken about an hour after installation is generally within 3–5% RH of the final 24-hour reading, which is enough to plan against, though ASTM F2170 compliance still requires the 24-hour reading. That lets building professionals watch how a slab is drying rather than wait on a single reading.

The concrete slab has been poured. Cement is chemically reacting with water, a process called hydration, and the resulting paste is bonding with aggregate in the mixture. Done well, concrete production goes a long way toward resolving many potential concrete slab moisture problems.

Water’s Okay… to a Point

The presence of water in concrete is as natural as the presence of kids in a playground. In fact, moisture remains in concrete slabs even after reaching their dry state. Concrete continues to exude water vapor in low relative humidity (RH) ambient conditions, and absorb it when ambient RH is high.

Moisture migration will be an ongoing reality until the slab is sealed. It’s after a slab is sealed that moisture mitigation can become problematic.

However, one must abandon the idea that water in concrete is inherently bad; its presence does not necessarily indicate an onset of concrete slab moisture problems.

Moisture Measurement

Water is nature’s liquid influence on slabs. Concrete slab moisture problems result when the moisture conditions in the slab have not been measured accurately before the finish or flooring application is installed, or when moisture is allowed to enter a finished slab through groundwater wicking or seepage from another source.

Fortunately, concrete moisture measurement is a matter of simple metric assessment. Technology inspired Wagner Meters to develop its Rapid RH: a cost-effective and reliable way to accurately measure slab moisture content during concrete installation. The Rapid RH measures the RH of moisture at all levels of a slab.

Installers place in situ probes (containing Smart Sensors) into the slab at 40% of the slab depth, the level whose reading best represents the slab’s condition once flooring is installed.

(ASTM F2170 requires 24 hours of equilibration before a documented reading.) This supports quality control.

The Preemption of “Hurry up!”

Construction is a tightly timed and rigorously budgeted endeavor. Time is seen as the ultimately unjustifiable building expense. However, Rapid RH is one tool which offers options.

If a Rapid RH moisture measurement shows uneven levels of concrete readiness, installers can dehumidify the wetter sections of the slab surface or they can apply concrete surface membranes. However, savvy building professionals can preempt those options in two ways.

First, ensure proper mix specifications, starting with 0.5 w/c ratio and a lightly troweled surface. Second, get the building enclosed as quickly as possible to allow the concrete more consistent conditions.

Rapid RH moisture measurement gives building professionals a way to find those problems before they happen.

Are you looking for a concrete calculator to estimate how many cubic feet and cubic yards of concrete you will need to fill your space? Try out our concrete calculator.

Last updated on September 21st, 2026