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
Download your free guide.
Four new types of prior approval for solar developments
Online Planning Portal application types from 5 September.
Election fails to spark construction industry revival
Contract awards and planning; post election.
Making diversity and inclusion easy for SMEs
The CIOB tool for companies with limited resources.
Sustainable Futures: Redefining Retrofit for Net Zero Living
BSRIA Briefing 2024, initial speakers announced.
Looking back at the UK's first Passivhaus leisure centre
Reflections on St Sidwell’s Point with CIAT.
A-Level results and electrical apprenticeships
Electrical Skills Index highlights areas with skills shortages.
One of the world's more unusual drive-throughs.
A quick introduction.
Hadrian's Wall Path and the national trails
The trails are heritage assets in their own right.
Articles on timely advice and hydraulic lime.
Building Designers Association of Australia
CIAT and BDAA sign Memorandum of Understanding.
Built Environment Inclusive partners issue statement committed to inclusion.
Building regulation requirements can have unintended consequences.
CIOB announces 2024/25 vice president
Sustainability champion Professor Saul Humphrey.
Accelerating towards a net-zero built environment.