Category: Structure & materials
Prepared by Eng. Ahmed Fathy, Projects Manager ·
Definition
Admixtures are chemicals added in small doses during mixing to change concrete's properties, including plasticisers that improve workability without extra water, retarders that delay setting in hot weather, and permeability reducers for tanks and basements.
Why it matters on a project
In the Saudi summer concrete loses workability quickly, and retarders and plasticisers stop water being added on site, a practice that weakens concrete.
Measurement and pricing
Usually within the ready-mix price per the mix design, priced separately if special admixtures are required.
Common mistake
Adding water to the mixer on site to ease placing instead of using an approved plasticiser, lowering strength.
Frequently asked questions
Do admixtures weaken concrete?
No if approved and dosed correctly in the mix design; damage comes from added water, not admixtures.
Which admixture matters in summer?
A retarder and plasticiser, with pours in cooler hours and early curing.
Related terms
- Concrete grade (compressive strength)The characteristic compressive strength of concrete at 28 days, e.g. C30 or 300 kg/cm².
- Slump testA simple site test measuring the consistency and workability of fresh concrete.
- CuringKeeping concrete moist and at temperature after pouring so it reaches its design strength.
- Concrete cube testCubes taken during the pour and crushed to measure concrete strength.
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