Cement Additives & Concrete Admixtures: Explaining the Difference
Cement Additives and Concrete Admixtures Disambiguation
If you’re new to the world of cement additives and concrete admixtures, there are certain differences between the two that you should understand. The fundamental difference to understand is that cement is an ingredient in concrete, and it can contain “cement additives.” Concrete contains cement, sand, aggregate, and water, and it may contain various “concrete admixtures” that enhance its properties during mixing.
Here we’ll further break down cement additives and concrete admixtures to help you determine which to use for a given application and location.
There are certain elements that go into cement manufacturing, including the following:
Cement is an ingredient of concrete comprising multiple ingredients of its own. These ingredients include a mixture of silicon, calcium, iron, and aluminum, among others. Some of the additional ingredients that make up cement might include limestone, chalk, shells, or mile along with slate, clay, silica sand, shale, and iron ore.
Manufacturers of Portland cement also produce cement clinker, which is an intermediary solid material that helps bind cement products. It consists of four primary minerals, including belite, alite, calcium silicates, calcium aluminoferrite, and tricalcium aluminate. Manufacturing clinker entails heating clay and limestone materials to produce the necessary minerals.
To improve cement surfaces, applications may also use grinding processes. Specifically, grinding is a type of mechanical treatment process that involves using equipment such as Husqvarna HTC grinders to even out cement surfaces, producing a consistent and smooth surface. Grinding can help remove paint, dirt, or mastic from cement surfaces, help rebuild them, and prepare them for tile and other flooring installations.
Types of Cement
Depending on the needs of each application, multiple types of cement are available. These include Ordinary Portland Cement (OPC), Portland Pozzolana Cement (PPC), rapid hardening cement, low heat cement, high alumina cement, and sulfate resisting cement, along with others. Each type requires a unique manufacturing process and materials that enhance various properties.
For example, high alumina cement uses the same manufacturing process as OPC, but with added lime and bauxite as well as clinker. This cement also requires a minimum alumina content of 32%, and it’s ideal for use in applications with high temperatures.
In some cases, pozzolans may serve as an alternative to cement in concrete, or they may replace the clinker used in cement. Pozzolans are aluminous and siliceous construction materials that offer numerous benefits when added to cement, including improved chemical resistance, higher compressive strength, and the inhibition of alkali-silica reactions that might otherwise damage cement installations.
Cement may also incorporate different additives if it requires certain enhancements. Some of these cement additives include:
- Grinding aids — These additives come with several key benefits, including saved electrical energy, boosted productivity, and increased fineness.
- Strength enhancers — Cement may also use certain strength enhancers that increase its mechanical strength, often through chemical activation that maintains the integrity of the cement’s structure and surface.
- Performance enhancers — Supplementary cementitious materials (SCM) sometimes function as additives replacing clinker, with options such as natural pozzolans, blast furnace slag, and others available.
When making concrete, multiple factors contribute to its construction:
Concrete consists of a mix of cement, aggregates, and water. The specific formula is around 10-15% Portland cement, 15-20% water, and 65-75% aggregates. The aggregates in concrete may consist of gravel, stone, sand, or other materials.
Mixing for Application
The ideal cement mix ratio for most applications is 1:2:4, which refers to one part cement, two parts sand, and four parts coarse aggregates. This mixture works well across most applications, but the ratio may vary depending on the properties required of the concrete mixture.
The ratio of cement, sand, and aggregates will change, for example, if you require added compressive strength, consistency, flowability, or other properties.
The slump of concrete refers to its consistency before it sets. The higher the slump, the more the fluidity of the concrete. You can test slump by seeing how much of a concrete mixture “slumps” while standing. The ratio of water to cement and/or the use of various concrete admixtures will affect the slump, which has a range of S1 to S5, with S1 being the driest and S5 being the wettest, the latter of which has a high water-to-cement ratio.
Different applications and locations may require the use of concrete admixtures to enhance the properties of concrete during the mixing process. For example, the following applications will have different needs when it comes to compressive strength, workability, and other properties:
- Structural support
- Earth retention
- Building construction
- Swimming pools
The location where these installations are will also dictate which admixtures to use, with factors such as weather, remoteness, and land and soil consistency all influencing concrete mixtures.
To increase compressive strength, you might use the following concrete admixtures:
- Microsilica admixtures — Admixtures containing condensed silica fume (microsilica) are ideal for applications requiring added compressive strength.
- Superplasticizers — Another type of admixture that can help improve compressive strength is a superplasticizer, which produces higher compressive strength when hardened. The reason for this is their ability to increase the cement-to-water ratio, allowing for improved performance.
Admixtures that improve flexural strength for applications include:
- Microsilica admixtures — In addition to compressive strength, microsilica admixtures can boost flexural strength, preventing concrete from breaking when bent.
- Fly ash — This additive, especially when mixed with silica fume, can further improve flexural strength in concrete. Fly ash contains carbon-burned fragments and has many potential applications.
Your application may also require admixtures that optimize durability in certain environments. Factors to consider could include permeability, shrinkage, cracking, freeze/thaw, delaminating and spalling, corrosion, and abrasion resistance.
For example, air-entrained admixtures form microscopic chambers in concrete that allow for the expansion of water, protecting concrete during freeze-thaw cycles. Meanwhile, silica fume is also helpful in maximizing overall durability in concrete mixtures.
Some applications may also need admixtures to increase workability. Jobs might require certain set times based on the distance to the job site, temperatures, and hot or dry climates. Additionally, applications may need optimal pumping and flowability, or carving and finishing of shotcrete.
Air-entrained admixtures are also great for increasing workability, while superplasticizers provide a great combination of pumpability and workability.
Find the Solutions You Need for Your Application
Knowing the differences between cement additives and concrete admixtures, along with the various types you can use to enhance various properties, will help you make the right selection for your unique application. You can choose which additives to include in concrete mixtures, which may then contribute to concrete mixtures with certain property-enhancing concrete admixtures. Together, the right combinations of cement and concrete will give all types of structures the reinforcement they need to last and withstand many conditions.
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