Concrete admixtures are chemical substances added to concrete before or during mixing to modify its properties for specific applications. Whilst cement, water, and aggregates form the base of every mix, admixtures are the specialist ingredients that transform standard concrete into precisely engineered, high-performance material.
These additions typically represent less than 5% of the total mix by weight — yet their impact on concrete performance can be dramatic. Small quantities of the right admixture can change workability, setting time, durability, and long-term strength in ways that make previously impossible projects routine.
What Are Plasticisers and Superplasticisers in Concrete?
One of concrete's fundamental challenges is achieving proper workability without compromising strength. Adding extra water makes concrete easier to place, but creates a weaker, more porous final product. Plasticisers solve this problem.
A plasticiser works like a lubricant between cement particles, allowing them to flow past each other more easily without additional water. The result is concrete that remains workable and easy to place whilst maintaining the low water-to-cement ratio essential for maximum strength and durability.
Superplasticisers take this further — enabling dramatic workability improvements or significant water reduction for ultra-high-strength applications. This is why commercial concrete for demanding structural applications typically includes superplasticisers as standard.
What Are Concrete Accelerators and Retarders?
Set-modifying admixtures give contractors control over timing — one of the most critical variables in any concrete pour.
Accelerators speed up the chemical reactions responsible for setting and strength gain. In the UK's climate, cold temperatures dramatically slow hydration, leaving fresh concrete vulnerable to frost damage. Accelerators counteract this, enabling construction to continue safely through autumn and winter. Our guide to pouring concrete in cold weather explains when accelerators are essential.
Retarders slow the chemical reactions, extending working time in hot weather or for complex pours where extended handling is required. See our guidance on concrete in hot weather for practical advice.
How Do Air-Entraining Admixtures Protect Against UK Freeze-Thaw Damage?
Air-entraining agents create billions of microscopic air bubbles throughout the concrete matrix. These tiny voids act as relief valves when water freezes and expands inside the concrete.
Without these voids, repeated freeze-thaw cycles gradually destroy concrete through internal pressure — creating the surface scaling and cracking common on UK driveways and paths after a hard winter. Air entrainment is why Procon 24/7 specifies air-entrained mixes as standard for all exterior domestic concrete applications including driveways, paths, and patios.
What Other Specialist Admixtures Are Available?
The admixture family extends beyond these core categories:
- Fibre admixtures: Add tensile strength and crack resistance — see our fibre-reinforced concrete service for details
- Waterproofing admixtures: Reduce permeability for basements, retaining walls, and below-ground applications, and work alongside the surface treatments in our guide to waterproofing concrete blocks
- Pigment admixtures: Create coloured concrete for decorative applications
- Shrinkage-reducing admixtures: Minimise volume changes during curing to reduce cracking
At Procon 24/7, our volumetric concrete service allows admixtures to be specified and adjusted on-site — meaning the exact right mix is produced at the moment of pouring, not an hour earlier at a batching plant.
Frequently Asked Questions About Concrete Admixtures
Are concrete admixtures expensive?
Admixtures typically add 2–8% to concrete material costs. They almost always provide far greater value through improved performance, reduced labour, or extended service life. The cost of the right admixture is usually negligible compared to the cost of the problem it prevents.
Can admixtures fix bad concrete after it's mixed?
Most admixtures must be added during mixing to be effective. Some surface treatments can address specific problems in hardened concrete, but prevention during the mixing stage is always preferable and more economical.
Are there safety concerns with concrete admixtures?
Modern admixtures meet strict safety standards and undergo rigorous testing. Standard construction site PPE is required during mixing, but the finished concrete poses no health risk when admixtures are used correctly.
Do all Procon 24/7 concrete mixes include admixtures?
Our standard mixes include air-entraining admixtures as standard for all exterior applications. Accelerators, retarders, fibre reinforcement, and waterproofing admixtures can all be specified when ordering. Use our concrete calculator for volumes, then call our team to discuss specification requirements.
