Concrete Surface Evaporation Rate Calculator

Concrete Evaporation Rate Calculator

Based on Menzel Formula (NRMCA Nomograph – SI Units)

Air Temperature (°C) Relative Humidity (%) Concrete Temperature (°C) Wind Speed Wind Speed Unit km/h m/s

Menzel Formula

$$ W = 0.315 (e_o - e_a)(0.253 + 0.060V) $$

Where:

• W = Evaporation rate (kg/m²/h)
• eₒ = Saturation vapor pressure at concrete temperature (kPa)
• eₐ = Actual vapor pressure in air (kPa)
• V = Wind speed (km/h)

Magnus Equation

$$ e_s = 0.61094 \times e^{\left(\frac{17.625T}{T+243.04}\right)} $$

Used for calculating saturation vapor pressure.

Risk Interpretation

Evaporation Rate	Risk Level	Interpretation
< 0.5 kg/m²/h	Low	Generally safe
0.5 – 1.0 kg/m²/h	Moderate	Preventive measures recommended
> 1.0 kg/m²/h	High	High risk of plastic shrinkage cracking

Why Evaporation Control is Important

When evaporation rate exceeds bleeding rate, concrete surface dries rapidly causing plastic shrinkage cracking, crazing, reduced durability and poor finishing quality.

• High wind speed can be more dangerous than high temperature
• Low relative humidity sharply increases evaporation
• Bridge decks and pavements are highly vulnerable
• Hot weather concreting requires immediate curing measures

Recommended Preventive Measures

1. Use fog misting or evaporation retardants
2. Provide windbreaks and sunshades
3. Reduce concrete temperature using chilled water or ice
4. Schedule concreting during cooler hours
5. Start curing immediately after finishing

NRMCA Nomograph References

References

• ACI 305R – Hot Weather Concreting
• NRMCA CIP-5 Plastic Shrinkage Cracking
• IS 7861 (Part 1) – Hot Weather Concreting
• Menzel Formula for Concrete Surface Evaporation

Prepared for professional civil engineering and construction site applications.

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