The role of calcium chloride in concrete
Calcium chloride compound is used as an accelerator in the hydration process of cement, which leads to rapid formation of concrete and high strength concrete. The maximum permissible addition of calcium chloride is 2% in the form of flaking.
Methods of adding calcium chloride
Calcium chloride is available as granules, other granules, flakes, or as a solution. The regular exfoliation form contains at least 77 percent calcium chloride, granules and other granular forms with a minimum of 94 percent. Since all forms of calcium chloride are soluble in water, it is recommended to use it in solution form.
It should be noted that the solution does not come into direct contact with cement, as this leads to a rapid group of cement. Therefore it is recommended to dilute it in water and mix with aggregate.
The effect of calcium chloride on the properties of concrete
Effect on the physical properties
Timekeeping: Since calcium chloride is widely used as a concrete accelerator, it greatly reduces the initial and final preparation time of concrete. It is widely used in low temperatures as it allows for faster acceleration and early use of tiles. But the use of this accelerator is not recommended in hot weather because it determines concrete very quickly, which makes it difficult to lay and finish concrete.
CSA A266.2-1973 and ASTM C494-1971 standards require that with calcium chloride, the initial preparation time should occur at least an hour before, but no more than 3 hours [CSA] or 3½ hours [ASTM]) in relation to Concrete signal.
Water cement ratio: Calcium chloride does not significantly reduce the water needed to produce a specific slump and this agent is not expected to play any dominant role in cementing concrete. Since it is an accelerator, it may tend to cause early stiffness and thus reduce bleeding.
Air Entrainment: The use of calcium chloride in concrete does not lead to air leakage, but when used with air blocking agents, it facilitates the production of more air content in a smaller amount of air blocking agent.
Freezing and thawing: Concrete containing calcium chloride quickly hardens and develops early resistance to damage by freezing and thawing. This may be important in the winter of concrete when the material is exposed to early application of defrosting salts. In later ages.
Succulent concrete containing calcium chloride may be less resistant to frost attack.
Dry shrinkage: Calcium chloride is known to increase drying shrinkage, the size depends on the amount of added calcium chloride, the type of cement, the processing period, and environmental conditions.
Inflorescence: Because calcium chloride is used in concrete, white deposits form on the treated concrete surface in some cases. But under normal exposure conditions, it attracts water and is not likely to cause flowering as other salts do.
These white deposits are not soluble in water, so dilute hydrochloric acid is used to remove it.
Influencing chemical properties
Sulfate attack: Calcium chloride has a deteriorating effect on concrete when exposed to sulfate solutions. Sulfate reacts with calcium and aluminum ions in the cement paste to form calcium sulfate and calcium sulfate aluminate hydrate, which causes the concrete to malfunction. If calcium chloride is present, there is evidence of reduced sulfate attack resistance.
Water temperature: The water temperature is faster, and the hydration process is faster in the presence of calcium chloride, especially in the first 10 to 12 hours.
The total amount developed has not changed much, but its early development may be useful for pouring concrete in the winter.
Macro alkali reaction: When high alkali cement is used with certain types of aggregates, the deterioration of concrete occurs due to aggregate swelling.
Calcium chloride in concrete has been known to aggravate an alkaline total reaction. If calcium chloride should be used in such cases, the expansion may be controlled with low alkali cement, pozzolan, or non-reactive aggregate.
Rebar Corrosion: In concrete containing calcium chloride, this stable film that protects steel from the external environment cannot be maintained with equal efficiency and there is a possibility of corrosion.
Calcium chloride is forbidden for prestressed concrete since the wear rate is due more to the wiring surface area being large and the differences in stress being greater. Calcium chloride is not supported by steam treated concrete
Influence on mechanical behavior
Since calcium chloride is used as an accelerator in concrete, it increases the rate of hardening of concrete. ASTM C-494 requires an increase of at least 125 percent on control concrete in 3 days, but in 6 months or one year the condition is only 90 percent of the control sample.
Compared with conventional concrete and calcium chloride concrete, strength gains may vary between 30 and 100 percent in the first three days. Amounts of calcium chloride that exceed acceptable standards cause fewer strengths. The same amount of chloride strength increases for a richer mixture.
The effect of calcium chloride on the rate of increase in strength is especially important at lower temperatures.
Flexural strength does not increase as much as the compressive strength with the addition of calcium chloride. ASTM C-494 requires that the flexural strength at 3 days be at least 110 percent of the control sample. After longer periods of processing, the bending strength of the concrete containing calcium chloride may be lower than that in the control sample.
Shrinkage and infiltration:
Adding calcium chloride to the concrete increases the contraction of the concrete, which in turn increases the creep in the concrete.
Advantages of using calcium chloride:
- High starting strength
- Reduces production time
- Reduces scratches or voids.
- Improved operability
- Useful when using it with fly ash.