Admixtures
Chemicals dosed into the mix to change how it behaves — workability, set time, air content, durability.
How to choose within admixtures
Admixtures exist mostly to solve one problem: concrete needs to be workable enough to place and low enough in water to be strong, and those two pull against each other. Every gallon of water added on site to make a mix easier to move permanently lowers its strength. Water reducers and superplasticizers break that trade-off — they give flow without adding water.
The rest of the category is about conditions. Air-entraining admixtures (ASTM C260) create microscopic bubbles that give freezing water somewhere to expand, and they are not optional where ACI 318 assigns exposure class F1, F2 or F3. Accelerators and retarders shift set time for cold and hot weather respectively. Corrosion inhibitors and shrinkage-reducing admixtures address specific durability problems rather than placement.
Chemical admixtures are classified Types A through G under ASTM C494. Dosage is per the manufacturer data sheet and per cubic yard — overdosing a retarder can leave a slab unfinishable for a day.
What this category covers
- Water reducers and superplasticizers
- Air-entraining
- Accelerators
- Retarders
- Corrosion inhibitors
- Shrinkage-reducing
- Integral waterproofing
Standards that govern it
- ASTM C494/C494M — Standard Specification for Chemical Admixtures for Concrete
- ASTM C260/C260M — Standard Specification for Air-Entraining Admixtures for Concrete
- ACI 318 — Building Code Requirements for Structural Concrete and Commentary
Manufacturers in this category
Listed alphabetically, in no order of preference. This site does not test products and does not recommend one brand over another.