Admixtures in concrete
An admixture is a substance which can be added to concrete to achieve or modify its properties. Admixtures are added to the concrete, in addition to cement, water and aggregate, typically immediately before or during the mixing process.
Admixtures can be used to reduce the cost of building with concrete, or to ensure certain required properties or quality of the cured concrete. If problems arise with the concrete during the construction process, admixtures can be used as an emergency measure to try and prevent failure. In addition, some of the main functions of using admixtures include:
- Water-reducing: Can reduce the water content needed to reach a required slump by 5-10%.
- Retarding: Slow the setting rate of concrete, keeping it workable and are often used to counteract the accelerating effect of hot weather.
- Accelerating: Increase the rate of early-strength development and reduce the time required for curing.
- Superplasticizers/plasticizers: Can reduce water content by 12-30% to make a highly fluid but workable form of concrete known as flowing concrete.
- Corrosion-inhibiting: Used to slow the corrosion of reinforcing steel in the concrete. Often used in marine structures, bridges and others that will be exposed to chloride in high quantities.
- Air-entraining: Small bubbles of air formed uniformly through the concrete mix to increase cohesion and resistance to freeze-thaw degradation.
- Improving the curing of the concrete.
- Providing waterproofing properties.
- To improve hardness.
- Providing colour.
- Offsetting or reducing a chemical reaction.
- Aeration to reduce the weight.
- Offsetting or reducing shrinkage.
- Dispersing cement particles when mixed with water.
- Alkali-silica reactivity reduction.
Admixtures are usually provided in a liquid form. Some admixtures, such as pigments, pumping aids and expansive agents, are typically added manually from pre-measured containers as the amount used is very small.
[edit] Related articles on Designing Buildings Wiki
- Admixture, additive or agent.
- Aggregate.
- Alkali-activated binder.
- Bentonite.
- Binding agent.
- Concrete.
- Concrete masonry unit CMU.
- Concrete repair mortars.
- Concrete superplasticizer.
- Graphene-reinforced concrete.
- Gravel..
- Plasticiser.
- Portland cement.
- Reinforced concrete.
- Self-compacting concrete.
- Spalling.
- The properties of concrete.
- Types of concrete.
- Ultra high performance fibre concrete.
- Waterproofing admixture.
Featured articles and news
The UK's Modern Industrial Strategy: A 10 year plan
Previous consultation criticism, current key elements and general support with some persisting reservations.
Building Safety Regulator reforms
New roles, new staff and a new fast track service pave the way for a single construction regulator.
Architectural Technologist CPDs and Communications
CIAT CPD… and how you can do it!
Cooling centres and cool spaces
Managing extreme heat in cities by directing the public to places for heat stress relief and water sources.
Winter gardens: A brief history and warm variations
Extending the season with glass in different forms and terms.
Restoring Great Yarmouth's Winter Gardens
Transforming one of the least sustainable constructions imaginable.
Construction Skills Mission Board launch sector drive
Newly formed government and industry collaboration set strategy for recruiting an additional 100,000 construction workers a year.
New Architects Code comes into effect in September 2025
ARB Architects Code of Conduct and Practice available with ongoing consultation regarding guidance.
Welsh Skills Body (Medr) launches ambitious plan
The new skills body brings together funding and regulation of tertiary education and research for the devolved nation.
Paul Gandy FCIOB announced as next CIOB President
Former Tilbury Douglas CEO takes helm.
UK Infrastructure: A 10 Year Strategy. In brief with reactions
With the National Infrastructure and Service Transformation Authority (NISTA).
Ebenezer Howard: inventor of the garden city. Book review.
The Grenfell Tower fire, eight years on
A time to pause and reflect as Dubai tower block fire reported just before anniversary.
Airtightness Topic Guide BSRIA TG 27/2025
Explaining the basics of airtightness, what it is, why it's important, when it's required and how it's carried out.
Construction contract awards hit lowest point of 2025
Plummeting for second consecutive month, intensifying concerns for housing and infrastructure goals.
Understanding Mental Health in the Built Environment 2025
Examining the state of mental health in construction, shedding light on levels of stress, anxiety and depression.
The benefits of engaging with insulation manufacturers
When considering ground floor constructions.
Lighting Industry endorses Blueprint for Electrification
The Lighting Industry Association fully supports the ECA Blueprint as a timely, urgent call to action.