A frequent question from contractors is: “How long do we have to work with this concrete before it hardens?” The window of time during which concrete can be easily placed, compacted, and finished without losing its structural strength is known as its period of workability.
The Normal Window
Under standard ambient conditions (around 20°C to 25°C), fresh concrete generally maintains good workability for 1.5 to 2 hours after the water first makes contact with the cement. After this window closes, the chemical process of hydration accelerates, and the concrete transitions from a plastic state to a rigid solid.
Factors Influencing Workability Lifespan
- Cement Type: Rapid hardening cements reduce workability time significantly, while low heat options extend it.
- Ambient Temperature: High ambient temperatures speed up the chemical reaction, drastically shortening your working window. Cold weather slows down the reaction, keeping the concrete workable for longer but delaying strength development.
- Travel Distance: Long transit times consume a significant portion of the concrete’s natural open window before the truck even reaches the site.
Extending Workability with Retarding Admixtures
To combat long transit distances or extreme heat, RMC plants mix in chemical retarders. These admixtures temporarily slow down the initial hydration process, extending the concrete’s workability window by anywhere from 1 to 4 additional hours without compromising the final 28 day structural strength.
📍 Company Details
Address: Addis Ababa, Ethiopia
Subcity: Kirkos Sub City
Head Office: Kazanchis, Addis Ababa
Batching Plants: Bole Michael & Bole Bulbula
TIN Number: 0090355672
📞 Contact Information
Phone: 251 90 605 0505 / +251 90 880 5555
Email: bamamixplc@gmail.com
