A high rate of evaporation from the concrete surface leads to quality, durability, and potential strength-related issues. Plastic shrinkage cracks are highly likely to occur if the evaporation rate is higher than 1 Kg/m2/hour. Therefore, appropriate actions to slow down evaporation are necessary if it exceeds 0.5 Kg/m2/hour.
It is found that the evaporation rate is highly sensitive to two variables, namely wind velocity, and concrete temperature. So, protective measures can be focused on avoiding wind effects and controlling the concrete pouring temperature.
Evaporation controlling strategies include the placement of shading, windbreaks, utilization of fogging, or application of evaporation reducers.Â
The evaporation rate is naturally lower in the shade than in places exposed to sun rays. If site conditions do not allow these methods, an evaporation reducer can be used to solve the problem. Windbreaks decrease wind velocity and hence the evaporation rate.Â
How to Minimize Rate of Evaporation from Concrete Surface?
1. Shades and Windbreaks
Shades and windbreaks are a good way to reduce a high evaporation rate from the concrete surface and subsequently yield higher quality concrete.
Nonetheless, the placement of shades and windbreaks is not always feasible on a construction site. In this case, other options should be considered to reduce the evaporation rate.
2. Fogging
Fogging is a concrete curing method in which water is forced through special nozzles to atomize it and create a fog-like mist. In this manner, the relative humidity above the concrete increases, reducing the evaporation rate.
Frequent fogging is required during windy days to keep the evaporation rate down. Adding water by fogging compensates for the moisture that prematurely evaporates from the concrete surface.
3. Evaporation Reducers
If the above strategies do not work, applying an evaporation reducer to the concrete surface after strike-off and between finishing operations can help prevent surface drying.
The evaporation reducers are produced from water and chemical compounds that create an oil-like coat over the concrete surface. In this way, the evaporation rate of bleeding water is decreased.Â
The evaporation reducer should not be worked into the concrete surface. This is because such a mixture has around 90% water content and can increase the water-cement ratio along the surface, endangering both the quality and durability of the concrete.
The effectiveness of the evaporation reducer depends on the frequency and time of application. It is recommended to consider a higher application rate of relatively weak compounds to reduce the detrimental effects of a high evaporation rate.
Generally, such materials should be utilized when the sheen on the concrete surface disappears. The supervisor should distinguish between the disappearance of the sheen that occurs when the bleeding stops and bleed water evaporates and the apparent loss of sheen that happens before bleeding stops under the condition where the evaporation rate exceeds the bleeding rate.
If the evaporation reducer is applied during the latter case, a thin layer of surface mortar delaminates due to the subsequent bleeding, which raises to the concrete surface.
FAQs
A high rate of evaporation from the concrete surface leads to quality, durability, and potential strength-related issues.
1. Windbreaks
2. Shading
3. Fogging
4. Evaporation reducer
Plastic shrinkage cracks are highly likely to occur if the evaporation rate is higher than 1 Kg/m2/hour.
Evaporation reducers are produced from water and chemical compounds that create an oil-like coat over the concrete surface. In this way, the evaporation rate of bleeding water is decreased.Â
An evaporation reducer should be utilized when the sheen on the concrete surface disappears.
The supervisor should distinguish between the disappearance of the sheen that occurs when the bleeding stops and bleed water evaporates and the apparent loss of sheen that happens before bleeding stops under the condition where the evaporation rate exceeds the bleeding rate.
If the evaporation reducer is applied before bleeding stops, a thin layer of surface mortar delaminates due to the subsequent bleeding, which raises to the concrete surface.
Fogging is a concrete curing method in which water is forced through special nozzles to atomize it and create a fog-like mist. In this manner, the relative humidity above the concrete increases, reducing the evaporation rate.Â
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