Calcium Chloride in Concrete
In order to speed up the hydration process of cement and produce concrete with a high initial strength, calcium chlorides are employed as an accelerator. The maximum amount of calcium chloride that can be added in the form of flake is 2%.
Techniques for Including Chloride in Water
It is possible to get calcium chloride in the form of flakes, solution, or pellets or other granules. A minimum of 77 percent calcium chloride is present in conventional flake form, and a minimum of 94 percent is present in pellet and other granular forms. It is advised to utilize calcium chloride in solution since all forms of the mineral are soluble in water.
It is important to avoid getting the solution in direct touch with the cement as this can cause the cement to set quickly. Therefore, it is advised to mix it with aggregate after diluting it in water.
Calcium Chloride’s Impact on Concrete’s Properties
1. Impact on Physical Characteristics
(i) Establishing a Time
Since calcium chloride is primarily utilized in concrete as an accelerator, it dramatically shortens the concrete’s initial and final setting times.Because it allows for early usage of slabs and faster completion, it is primarily utilized in colder climates. However, because this accelerator sets concrete quickly and makes finishing and placing the concrete more difficult, it is not advised to use it in hot weather.
According to CSA A266.2-1973 and ASTM C494-1971 regulations, the initial setting time for calcium chloride must happen at least one hour earlier than the reference concrete (but not more than three hours or three and a half hours, respectively).
(ii) Compost to Water Ratio
The amount of water needed to achieve a given slump is not greatly reduced by calcium chloride, therefore this aspect is not anticipated to be particularly important for reinforcing concrete. Because it is an accelerator, bleeding may be lessened by its tendency to cause early stiffness.
(iii) Entrainment in the Air
Although calcium chloride does not entrain air, it can help produce higher air content with less air entraining agent when used in conjunction with other air entraining agents.
(iv) Chilling and Warming
Calcium chloride-containing concrete hardens quickly and becomes resistant to freezing and thawing damage early on. This could be significant during the winter months when de-icing salts can be applied early to the material. The calcium chloride-containing mature concrete may become less resistant to frost damage as it ages.
(v) Dehydration
It is well known that adding calcium chloride can cause drying shrinkage; the degree of this increase varies based on the type of cement, amount added, curing time, and ambient factors.
(vi) Luminescence
In certain cases, the use of calcium chloride in concrete causes a white deposit to appear on the surface of the cured concrete. However, it draws water when exposed normally and is unlikely to induce efflorescence, unlike other salts. Since these white deposits are insoluble in water, they must be removed using diluted hydrochloric acid.
2. Impact on Chemical Characteristics
(i) Attack with Sulfur
Concrete exposed to sulphate solutions experiences degradation due to calcium chloride. The reason for the disruption of the concrete is caused by the sulphates reacting with the calcium and aluminum ions in the cement paste to generate calcium sulfate and calcium sulphoaluminate hydrates. There is evidence that resistance to sulfate attack is decreased in the presence of calcium chloride.
(ii) Hydration Heat
In the presence of calcium chloride, heat of hydration occurs more quickly and the hydration process proceeds more quickly, especially during the first 10 to 12 hours. Although not much has changed in terms of total developed, its early development could be helpful for winter concreting.
(iii) Aggregate-Alkali Reaction
Aggregate swelling causes concrete deterioration when high alkali cement is used with specific kinds of aggregates. It is well known that the alkali-aggregate reaction is exacerbated by the calcium chloride found in concrete. If calcium chloride is required in these circumstances, expansion may be managed by using non-reactive aggregate, pozzolan, or low alkali cement
(iv) Steel Reinforcement Corrosion
This stable coating that shields the steel from the environment cannot be maintained as effectively in concrete containing calcium chloride, and corrosion is a possibility.
since of the huge surface area of the wires and the bigger stress variations, calcium chloride is not allowed for prestressed concretes since it increases the rate of corrosion. It is not recommended to use calcium chloride for steam-cured concrete.
3. Impact on Automated Behavior
(i) Strength of Compression
The concrete hardens more quickly because calcium chloride is employed as an accelerator in it. According to ASTM C-494, there must be a minimum of 125% rise over the control concrete after three days; however, after six months or a year, the requirement drops to 90% of the control specimen.
The strength gain in the first three days can range from 30 to 100% when compared to both calcium chloride concrete and regular concrete. Lower strengths are the result of calcium chloride concentrations over recommended limits. Richer blends exhibit greater strength gains for the same amount of chloride.
At lower temperatures, the impact of calcium chloride on the percentage increase in strength is very noteworthy.
(ii) Strength in flexion
When calcium chloride is added, compressive strength increases more than flexural strength. Flexural strength at three days must be at least 110% of the control specimen, according to ASTM C-494. The flexural strength of calcium chloride-containing concrete may even be reduced after longer curing times than that of the control specimen.
(iii) Swelling and Swelling
When calcium chloride is added to concrete, the concrete shrinks more, which causes more creep to occur.
Using calcium chloride in concrete.
- High initial Strength
- Shorter last set duration
- Less bleeding
- Increased viability
- Quick form work completion
- Economic effectiveness
- Helpful when used with fly ash.