Concrete Additives: How To Maximise Concrete Performance

Concrete might seem like a relatively simple mixture of cement, aggregates and water, but it’s easy to adjust modern concrete to suit the demands of a particular project.

One way to design the perfect mix is to use concrete additives, which can change how fresh concrete behaves, influence setting times, and improve certain properties of the finished concrete.

From making concrete easier to place on site to improving performance in challenging weather conditions, concrete additives can play an important role in producing the right mix for the job.

So, what are concrete additives, what do they actually do and which types might be used in your concrete?

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What Are Concrete Additives?

Concrete additives are materials incorporated into a concrete mix to modify one or more of its properties.

The term is often used generally to describe concrete admixtures, which are typically added in relatively small quantities during mixing. Different admixtures can alter characteristics such as workability, setting time, water demand, permeability and durability.

The type and amount required will depend on the application and the performance expected from the finished concrete.

There isn’t one universal additive that makes every concrete mix “better”. The goal is to select a mix that provides the right properties for the job.

Why Are Additives Used in Concrete?

The basic ingredients of concrete can produce an extremely strong and durable construction material. However, different projects present different challenges.

Concrete poured into foundations may have different requirements than concrete used for a driveway, industrial floor, or heavily reinforced structure.

Weather can also make a difference. A pour in warm summer conditions may require different considerations than one in colder weather. Therefore, using suitable concrete additives can help tailor the behaviour of the concrete to these different circumstances.

Depending on the admixture and mix design, potential benefits include:

• Reduced permeability
• Improved workability
• Reduced water demand
• Faster or slower setting
• Easier placing and finishing
• Improved long-term durability
• Improved early strength development
• Improved resistance to certain environmental conditions

The Different Types of Concrete Additives

Some of the most commonly encountered concrete additives include the following.

Plasticisers And Superplasticisers

Plasticisers and superplasticisers are water-reducing admixtures that can improve the workability and fluidity of concrete without simply adding extra water to the mix. Too much water can negatively affect the quality and performance of the finished concrete.

Superplasticisers can produce high workability while allowing a relatively low water-to-cement ratio. This can make concrete easier to place around reinforcement or into areas where good flow is required.

Accelerators

Accelerating admixtures are helpful when faster setting or earlier strength development is required.

They can be useful where construction schedules require the concrete to develop strength more quickly or where environmental conditions would otherwise slow the process.

However, an accelerator doesn’t mean you can immediately load freshly placed concrete or ignore normal curing requirements. The concrete still needs to be correctly specified, placed, finished and cured.

Retarders

Retarders delay the setting process, giving the concrete more time to remain workable.

Retarders can be useful during warmer weather, when concrete may otherwise begin setting more quickly, which can later lead to cracking. They’re also useful for larger or more complicated pours where additional placing and finishing time is beneficial.

Retarders can also be useful when concrete has a longer journey between the batching plant and the site.

Air-Entraining Admixtures

Air-entraining admixtures introduce a controlled quantity of tiny air bubbles throughout the concrete, which can help improve resistance to freeze-thaw conditions.

When water freezes, it expands. Repeated freezing and thawing can therefore place considerable stress on concrete exposed to certain conditions. That isn’t the same as accidentally trapping large pockets of air in poorly compacted concrete. Air entrainment is a deliberately controlled part of the concrete mix design.

Need Expert Advice?

Speak to the team at Flowmix Tewkesbury, Gloucestershire or Aldridge, Walsall. We are happy to help with all your concrete requirements. Contact us by email or telephone.

Flowmix Tewkesbury: Tel: 01684 217888 Flowmix Walsall: Tel: 01922 741731

Water-Resisting Admixtures

Water-resisting or permeability-reducing admixtures can be used where reduced water penetration is required.

These concrete additives reduce water movement through hardened concrete and can be part of a broader approach to improving durability.

However, adding a water-resisting admixture doesn’t automatically make every concrete structure completely waterproof. Mix design, joints, cracks, detailing and the overall construction system can all affect water resistance.

Fibres

Fibres are helpful in particular applications. Different types of concrete fibres are available, including synthetic and steel fibres, and their purpose varies according to the mix and project.

Some fibres help control plastic shrinkage cracking, while others improve the concrete’s mechanical performance.

Fibres shouldn’t simply be regarded as an automatic replacement for conventional steel reinforcement. Whether reinforcement can be reduced or replaced depends on the project’s design and structural requirements.

Can Concrete Additives Make Concrete Stronger?

Some concrete additives, such as water-reducing admixtures, can improve strength, but the relationship isn’t as simple as adding a product to a mix and automatically creating stronger concrete.

Concrete needs sufficient water for workability, but excess water can weaken the hardened concrete. A water-reducing admixture can achieve suitable workability at a lower water-to-cement ratio.

Best Concrete Additives to Use in Cold Weather

Cold temperatures can slow concrete setting and early strength development.

Depending on the project, you may incorporate an accelerating admixture to increase the rate of setting or early strength development.

Concrete poured during cold weather still needs appropriate protection and curing. An accelerator isn’t a substitute for sensible cold-weather concreting practices.

For concrete exposed to repeated freezing and thawing during its service life, air entrainment may also be specified, depending on the exposure conditions. UK guidance under BS 8500 includes requirements relating to freeze-thaw exposure and air-entrained concrete.

Best Concrete Additives for Hot Weather

Higher temperatures can reduce concrete workability and speed up setting, potentially making placing and finishing more difficult.

Retarding admixtures can extend working time where appropriate. Water-reducing admixtures can also help maintain the required workability without simply adding more water to the concrete.

Planning is particularly important during hot-weather pours, particularly as we’re now experiencing multiple heatwaves during the summer months.

Do Concrete Additives Make Concrete Waterproof?

This is a common misconception.

Certain concrete additives can reduce permeability or improve resistance to water penetration, but that isn’t the same as guaranteeing that an entire structure will be waterproof.

The performance of concrete exposed to water depends on several factors, including concrete specification, water-to-cement ratio, compaction, curing, construction joints, cracking, structural design and waterproofing systems and detailing.

✅ Order ready-mix or volumetric concrete today
✅ Free, fast quote within 24 hours
✅ Call, message or complete our simple online form

Flowmix Tewkesbury: Tel: 01684 217888 Flowmix Walsall: Tel: 01922 741731

Concrete Additives and Durability

One of the biggest advantages of modern concrete additives is their ability to help optimise concrete for the conditions it will face throughout its service life.

Reducing permeability, improving the effectiveness of the cementitious component and helping concrete withstand harsh environments can all contribute to durability.

Choosing concrete shouldn’t therefore be based on compressive strength alone.

Concrete Additives and the Environmental Impact of Concrete?

Modern admixtures can help producers optimise mix designs and use cementitious materials more efficiently. For example, water-reducing admixtures can improve workability while reducing water demand rather than requiring additional cement to achieve particular performance characteristics.

It’s worth distinguishing these cementitious additions from chemical admixtures. Materials such as GGBS and fly ash can replace a proportion of Portland cement in suitable concrete mixes. In contrast, chemical admixtures are generally used in much smaller quantities to alter particular properties of the concrete.

How to Choose the Right Concrete Additives

Rather than deciding that you need a particular additive before ordering, it is often more useful to consider what you need the concrete to achieve.

For example:

• Is access to the pour difficult?
• What will the concrete be used for?
• Is early strength development important?
• Does the concrete need particularly good workability?
• Will it be placed during unusually warm or cold conditions?
• Will the finished concrete be exposed to water, frost or other challenging environmental conditions?

These factors can help determine the best concrete specification and whether concrete additives or particular admixtures are beneficial.

For structural or specialist applications, the concrete should always meet the relevant project specification and engineering requirements.

Ordering the Right Concrete Mix

Ordering concrete involves more than choosing a strength grade. The intended application, quantity required, site access, placement method, and required performance can all influence which mix is most suitable.

The Flowmix team can help you choose an appropriate concrete mix for your project and discuss any specific requirements before delivery.

Whether you’re pouring foundations, a driveway, a floor, a slab or another concrete project, giving us as much information as possible when ordering helps us provide the right concrete for the job.

How Flowmix Can Help with Your Project

Flowmix has two plants, Gloucester and Walsall. We provide the following services (with time slots):

✅ Ready-mix concrete, mix on-site (volumetric concrete)
✅ Traditional and liquid screed.
✅ Concrete line pump Hire to reduce manual labour and associated costs, increase efficiency, reduce wastage and clean up.
✅ Interlocking concrete blocks for temporary or permanent barriers.
✅ Mini-Mix loads up to 4 cubic metres.

Flowmix holds the BSA-approved Ready Mix Concrete Kitemark KM683844, a certification that “confirms a product or service’s claim has been independently and repeatedly tested by experts” (source BSI).

Flowmix Tewkesbury: Tel: 01684 217888 Flowmix Walsall: Tel: 01922 741731

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