The Kabul Serena hotel Project:
The setting of concrete is a chemical reaction of cement and water and accelerates due to temperature. As the temperature decreases, the rate of chemical reaction decreases, and the setting process becomes slower.
In standard practice, the initial setting time of concrete is a minimum of 30 minutes, and the final setting time is 600 minutes. But in cold countries where the ambient temperature goes below zero degrees Celsius, concrete does not set at all.
In cold weather concreting, water undergoes freezing and hence cannot take part in the chemical reaction with cement and, therefore, cannot develop compressive strength due to lack of hydration.
Plasticizers are used to reduce the water-cement ratio, whereas anti-freeze admixtures are used to prevent ice formation.
Sometimes locally chloride-based materials are used for anti-freezing, like sodium chloride. These materials should be strictly prohibited as they may lead to the corrosion of the reinforcement within the concrete.
The Application:
Strength of Concrete:
The strength of concrete is the function of hydration of cement. The hydration process occurs in the presence of water and if water is in ice form, hydration will not happen.
The lesser the water-cement ratio, the more the strength.
The above will work only if plasticizers and water does not convert into ice form.
Options available:
- To heat the aggregate
- To heat the water
- To carry out concreting in heated chambers
- Place concrete in heated conditions. Continue heating till the concrete sets.
All the above is possible, however, at a very heavy expense; hence practically becomes cost prohibitive
Innovative Solution:
Hence a high-performance anti-freeze chloride-free admixture (sp. gravity 1.22) was used.
This admixture prevents ice formation, allowing the water to be available for hydration reaction and permitting the concrete to gain strength.
Sunanda Global had introduced plasticizers also to ensure less water and required pumpability.
A pictorial use of anti-freezing admixture for concreting in subzero temperatures at Kabul Serena Hotel
Conclusion:
The entire project was completed in subzero conditions; hence, the hotel was in service as planned.
