Calcium chloride is an accelerator for concrete and is produced at the rate of 9 billion cubic yards per year. Calcium chloride increases the setting time of concrete by 30-50%. This effect is mostly seen in mixtures with a higher ratio of cement to sand and in cold weather. Also, calcium chloride plays a role in the cement hydration process, which leads to quick setting of concrete and obtaining concrete with high initial strength. In the continuation of this article, Chemygostar Company has given you complete explanations about the role of calcium chloride and the use of calcium chloride in cement and concrete. Stay with Chemygostar until the end of this article.
Addition of calcium chloride
In the previous articles, we have learned about the different forms of calcium chloride. All forms of calcium chloride can be used in cement and concrete. It is preferred to use liquid calcium chloride in concrete formulation, but solid products are also used. Flake type of this product dissolves faster than pellet product in cement. At the time of use, care should be taken that calcium chloride does not come into contact with cement, because it leads to its quick setting, so it is recommended to dilute it with water first and then add it to cement.
Effects of calcium chloride on the physical properties of concrete
Setting Time
Calcium chloride reduces the initial and final setting time. Calcium chloride is mostly used in lower temperatures, but it is not recommended to use calcium chloride in hot weather, because it will increase setting time very quickly, which will eventually make it more difficult to use concrete and place concrete in the desired location. There are standards in this field that state that if calcium chloride is used, the initial setting time should be reduced by at least one hour compared to the reference cement.
Water cement ratio
Calcium chloride does not significantly reduce the water-cement ratio and does not seem to play a dominant role in strengthening concrete.
Freezing and melting
Calcium chloride cements increase the initial resistance against damage caused by freezing because they harden quickly. Special concretes at low temperature can be prepared with a mixture of calcium chloride, different clays and other additives so that this problem no longer exists.
Dry shrinkage
Depending on the amount of calcium chloride added, environmental conditions, setting time, and type of cement, dry shrinkage increases.
Dandruff and flaking
Due to the use of calcium chloride in concrete, white scale on the surface of concrete. Because these white scales are not soluble in water, hydrochloric acid (HCl) should be used. Calcium chloride does not reduce scaling, but it reduces the deterioration time of concretes that have not had a proper drying period.
Effects of calcium chloride on the chemical properties of concrete
Sulphate attacks
Calcium chloride has a negative effect on concrete; when concrete is exposed to sulfate, the sulfate reacts with aluminum and calcium ions to form calcium sulfate and calcium sulphoaluminate hydrates.
Alkaline reactions
When cements with high alkalinity are used together with certain types of aggregates, concrete deterioration occurs due to the expansion or swelling of the aggregates. It has been found that calcium chloride in concretes aggravates the alkaline reaction. If calcium chloride is used in such situations, expansion may be controlled by using low-alkali cement, pozzolan, or a non-reactive aggregate.
Steel corrosion enhancer
In concrete containing calcium chloride, there is a stable layer that protects the steel from the external environment, but this layer cannot be maintained with the same efficiency and there is a potential for corrosion in this area. It is forbidden to use calcium chloride for pre-stressed concretes.
The effects of calcium chloride on the mechanical behavior of concrete
Compressive strength
Since calcium chloride is used as an accelerator in concrete, it increases the rate of hardening of concrete. There are standards that require an increase of at least 125% of the control concrete in 3 days, but only 90% of the control sample is required in 6 months or one year. Compared to normal concrete and calcium chloride concrete, the increase in strength may vary between 30% and 100% in the first three days. Amounts of calcium chloride more than accepted standards reduce the strength of concrete.
Flexural strength
Flexural strength does not increase as much as compressive strength by adding calcium chloride. Adding calcium chloride in concrete increases the shrinkage of concrete.
Important points when using calcium chloride in concrete:
- The total amount of calcium chloride should not be more than 2%.
- Calcium chloride can be added to the sand as a solution or as part of the mixing water.
- If calcium chloride is used as part of the mixing water, the total amount of mixing water should be reduced.
- It is usually recommended to add calcium chloride to water and then use it in cement and concrete.
- Never use hot or warm water to dissolve calcium chloride.
Conclusion
In this article, we learned about the advantages of calcium chloride (CaCl2), such as high initial strength, reduction of final setting time, Reduced bleeding, and improvement of efficiency. Chemygostar Aran Company is known as a producer of calcium chloride. If you want to buy this product, please don’t hesitate to contact us.