What are the different types of admixtures used in concrete?
Concrete is the backbone of modern construction, used in everything from high-rise buildings and bridges to house foundations and driveways. Its popularity stems from its strength, durability, and versatility. But achieving optimal performance from concrete isn’t always straightforward. Factors like temperature, humidity, setting time, and workability can all affect the quality and finish of the final structure. This is where admixtures come into play.
Admixtures are specially formulated additives that are introduced into the concrete mix either before or during the mixing process. They’re designed to enhance specific properties of the concrete without altering its core composition. Whether you need faster curing times, increased resistance to harsh weather, or improved flow for complex formwork, the right admixture can make a big difference in your project’s outcome.
So, what are the different types of admixtures used in concrete, and why are admixtures used in concrete in the first place?
In this guide, we’ll answer those questions, and explain how each type plays a role in boosting performance, durability, and workability, while also helping you choose the right product for your site conditions and structural needs.
What are concrete admixtures?
Concrete admixtures are specialist materials added to a concrete mix either before or during the mixing process. Their role is to modify the behaviour of the concrete in fresh or hardened states, whether that's to accelerate curing, improve flow, reduce shrinkage, or increase long-term durability. In short, admixtures are essential tools for achieving precise, high-performance results in both standard and specialist applications.
So, why are admixtures used in concrete exactly? These additives are designed to solve specific challenges that concrete might face on-site. For instance, in hot weather, concrete can set too quickly, making it difficult to work with or finish properly. A retarding admixture slows this process down, giving contractors more time to place and finish the mix. On the other hand, cold weather may require a set accelerator to ensure concrete reaches sufficient strength quickly enough to avoid frost damage.
They can also be used to enhance workability without increasing water content, crucial for avoiding strength loss. Others reduce permeability, improve resistance to chemicals, or allow concrete to maintain integrity under freeze-thaw conditions.
From commercial slabs and foundations to precast elements and intricate formwork, admixtures allow concrete to be tailored to the unique demands of the job. This not only improves construction outcomes but also helps meet environmental, technical, and cost requirements.
Ultimately, concrete admixtures are one of the most essential elements of modern construction. Whether you're looking to improve strength, durability, finish, or efficiency, the right admixture makes all the difference. You can explore our full range of concrete admixtures here and find the solution that matches your project's needs.
What are the admixtures used in concrete?
Admixtures are engineered to tackle specific performance challenges in concrete, whether related to workability, durability, setting time, shrinkage, or environmental resistance. Selecting the right admixture can transform the way concrete behaves on-site, resulting in stronger, longer-lasting structures and more efficient construction processes.
Here’s a detailed look at the most widely used types of concrete admixtures, their functions, and practical use cases.
1. Water-reducing admixtures
Water-reducing admixtures lower the water-to-cement ratio in a mix without affecting its workability. This is important because while water improves flow, too much of it can weaken the concrete and increase the risk of cracking or shrinkage.
By reducing water content by 5–15%, these admixtures increase compressive strength, reduce permeability, and enhance finishability. They're especially useful in high-strength concrete or mixes where durability is a key concern.
Use case: In commercial slabs and structural elements where strength is critical, such as high-rise buildings or bridge decks, water-reducing admixtures help deliver the performance needed without compromising consistency.
2. Plasticisers and superplasticisers
Plasticisers (also known as normal water reducers) and superplasticisers (high-range water reducers) dramatically improve the workability of concrete. These additives enable the concrete to flow freely, making them ideal for pouring into intricate moulds, around dense reinforcement, or for pumpable mixes—without the need for extra water.
Superplasticisers can reduce water content by up to 30%, producing highly workable, fluid concrete that doesn’t segregate. Improved surface quality and finishability are added benefits.
Use case: Heavily reinforced foundations, architectural formwork with detailed finishes, or precast concrete where a smooth, compact mix is vital. Our range of grout and concrete admixtures includes industry-grade plasticisers suited for both commercial and infrastructure use.
3. Accelerators
Accelerating admixtures speed up the hydration process of cement, enabling the concrete to set and gain early strength more quickly. This is particularly valuable in cold weather, where low temperatures naturally slow curing, risking frost damage or project delays.
Faster turnaround of formwork or traffic loads is also possible, which is ideal for time-sensitive builds. Calcium chloride is a common accelerator (though not suitable for reinforced concrete), while non-chloride alternatives are preferred when corrosion risk is a concern.
Use case: Winter concreting, precast production lines, or fast-track commercial builds where early load-bearing strength is needed.
4. Retarders
Retarding admixtures do the opposite—they slow down the setting time of concrete. This extended working time provides greater flexibility, especially when pouring in hot climates where rapid setting can be a challenge.
They’re also useful for preventing cold joints in large pours involving multiple batches, helping to maintain uniformity and bond strength across layers.
Use case: Mass pours, bridge decks, foundations, or remote site pours where the concrete may travel long distances before placement.
5. Air-entraining agents
Air-entraining admixtures introduce tiny, uniformly distributed air bubbles into the concrete. These microscopic voids improve the material’s resistance to freeze-thaw cycles, as they create space for water to expand when frozen—minimising internal pressure and preventing cracking or spalling.
Such admixtures also enhance workability and reduce segregation and bleeding, making them highly effective in outdoor applications exposed to fluctuating or low temperatures.
Use case: Pavements, driveways, airport runways, or bridge decks—any external structure exposed to cycles of freezing and thawing.
6. Shrinkage-reducing admixtures (SRAs)
Drying shrinkage is a major cause of cracking in concrete, particularly in slabs, floors, and large pours. Cracking can also result from thermal movement, restrained shrinkage, poor curing practices, or external loading during early strength development. These factors generate internal stresses that exceed the concrete’s tensile strength, leading to visible surface defects or structural weaknesses.
SRAs are formulated to reduce the shrinkage that occurs as water evaporates during curing. In turn, this helps prevent surface cracking and other structural issues. By modifying the surface tension of pore water, these admixtures lower drying stresses and minimise the risk of curling in slab-on-grade installations.
Use case: Industrial floors, multibay slabs, screeds, or exposed concrete surfaces where dimensional stability and crack prevention are essential.
7. Corrosion inhibitors
Corrosion inhibitors are critical in reinforced concrete exposed to chlorides (such as saltwater or de-icing salts). These admixtures help protect embedded steel by forming a protective barrier or altering the electrochemical environment to reduce the likelihood of rust.
Corroded reinforcement can expand and crack the surrounding concrete, ultimately compromising structural integrity. Inhibitors are essential for extending service life in environments where corrosion risk is high.
Use case: Marine structures, coastal defences, multi-storey car parks, bridges, or tunnels exposed to chloride-rich conditions.
8. Grouting admixtures
Grouting admixtures are specialised formulations used to improve the flow, consistency, and stability of grout mixes. They reduce segregation and bleeding while enhancing early and final strength—particularly valuable in precision grouting where complete void filling is essential.
For example, when anchoring heavy machinery to a concrete foundation, it’s crucial that the grout fills every gap under the baseplate without shrinking or cracking—this is where grouting admixtures ensure a stable, long-lasting bond.
Formulations may include plasticisers, anti-shrink agents, or expanding agents depending on the application.
Use case: Precision anchoring of machinery, cable duct grouting, void filling beneath baseplates, or structural repairs involving pressure grouting or pumpable systems.
Understanding what admixtures are in concrete and how each type performs is key to choosing the right solution for your project. Whether you need better workability, quicker setting times, enhanced durability, or protection against environmental exposure, there’s an admixture to meet your needs.
Choosing the right admixture
Selecting the right admixture is essential for achieving reliable, high-performance results in any concrete application. With such a wide range of products available, the ideal choice will depend on several key factors, including the nature of the project, environmental conditions, time constraints, and specific performance goals.
1. Nature of the project
The type of structure you're building will influence which admixture is most suitable. For example, precast elements or high-strength columns may benefit from water-reducing admixtures to increase strength without compromising workability. Complex or heavily reinforced formwork is better suited to superplasticisers, which improve flow without adding excess water.
2. Environmental conditions
Weather plays a major role in how concrete performs. In cold climates, accelerators help speed up setting and early strength gain, reducing the risk of frost damage. In contrast, hot or arid conditions may call for retarders to slow down curing, giving contractors more time to place and finish the concrete effectively.
3. Time constraints
Fast-track projects with tight deadlines often require admixtures that shorten curing times or allow for quicker reuse of formwork. Accelerators are ideal in this scenario, helping you stay on schedule without compromising strength or quality.
4. Performance goals & durability
If your concrete will be exposed to aggressive environments—such as freeze-thaw cycles, chlorides, or chemical attack—durability is key. In such cases, air-entraining agents, corrosion inhibitors, or waterproofing admixtures can enhance resilience and extend service life.
Find the right admixture for your next project
At Complete Construction Products, we offer a comprehensive selection of high-quality admixtures trusted by contractors, builders, and concrete suppliers across the UK. From fast-setting options to advanced additives for strength, flow, or durability, we’ve got the right solution for any job.
Our technical experts are also on hand to provide practical guidance—whether you’re looking to meet British Standards, tackle a challenging site, or simply improve consistency in your concrete mix.
So, what are the different types of admixtures used in concrete, and how do you choose the right one? It all comes down to understanding your site conditions and performance needs. Browse our full admixtures range or get in touch with our team to find the best fit for your project.