Concrete Evaporation Rate Calculator

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function calculateEvaporationRate() { var temperature = parseFloat(document.getElementById("temperature").value); var relativeHumidity = parseFloat(document.getElementById("relativeHumidity").value); var windSpeed = parseFloat(document.getElementById("windSpeed").value); var concreteSurfaceArea = parseFloat(document.getElementById("concreteSurfaceArea").value); var resultDiv = document.getElementById("result"); resultDiv.innerHTML = ""; // Clear previous results if (isNaN(temperature) || isNaN(relativeHumidity) || isNaN(windSpeed) || isNaN(concreteSurfaceArea)) { resultDiv.innerHTML = "Please enter valid numbers for all fields."; return; } if (relativeHumidity 100) { resultDiv.innerHTML = "Relative humidity must be between 0 and 100%."; return; } if (temperature 100) { // Realistic range for concrete applications resultDiv.innerHTML = "Temperature should be within a realistic range for concrete applications."; return; } if (windSpeed < 0) { resultDiv.innerHTML = "Wind speed cannot be negative."; return; } if (concreteSurfaceArea <= 0) { resultDiv.innerHTML = "Concrete surface area must be a positive value."; return; } // Simplified model for concrete evaporation rate (kg/m²/h) // This is a highly simplified model and real-world calculations might involve more complex factors. // Key factors influencing evaporation: temperature, humidity, wind speed, and surface area. // Saturation vapor pressure (es) in kPa using the Goff-Gratch equation approximation var es = 0.6108 * Math.exp((17.27 * temperature) / (temperature + 237.3)); // Actual vapor pressure (ea) in kPa var ea = es * (relativeHumidity / 100); // Vapor pressure deficit (VPD) in kPa var vpd = es – ea; // Evaporation rate (E) in kg/m²/h // A common empirical formula relates E to VPD and wind speed. // This is a simplified form; more complex formulas exist. // Wind speed multiplier is often simplified as a linear or square root relationship. // Here, we use a simple linear relationship for wind speed, adjusted for units. var evaporationRatePerSqMeter = 0.0025 * vpd * (1 + 0.5 * windSpeed); // Empirical constant and wind speed factor var totalEvaporationRate = evaporationRatePerSqMeter * concreteSurfaceArea; // Convert to liters/hour (assuming density of water is ~1000 kg/m³ and 1 m³ = 1000 L) // Since the rate is kg/m²/h, multiplying by m² gives kg/h. // 1 kg of water is approximately 1 liter. var totalEvaporationRateLitersPerHour = totalEvaporationRate; resultDiv.innerHTML = "

Estimated Evaporation Rate:

" + "Saturation Vapor Pressure: " + es.toFixed(3) + " kPa" + "Actual Vapor Pressure: " + ea.toFixed(3) + " kPa" + "Vapor Pressure Deficit: " + vpd.toFixed(3) + " kPa" + "Evaporation Rate per m²: " + evaporationRatePerSqMeter.toFixed(6) + " kg/m²/h" + "Total Evaporation Rate: " + totalEvaporationRate.toFixed(4) + " kg/h" + "Total Evaporation Rate: " + totalEvaporationRateLitersPerHour.toFixed(4) + " L/h"; }

Understanding Concrete Evaporation Rate

Controlling the rate of evaporation from fresh concrete is crucial for achieving durable and high-quality concrete structures. Evaporation affects the surface properties, leading to potential issues like plastic shrinkage cracking, reduced surface strength, and poor aesthetics. This calculator provides an estimate of the evaporation rate based on key environmental factors.

Factors Influencing Evaporation:

  • Temperature: Higher temperatures increase the kinetic energy of water molecules, leading to a higher potential for evaporation.
  • Relative Humidity: This is the amount of water vapor in the air relative to the maximum it can hold at a given temperature. Low humidity creates a larger "vapor pressure deficit," driving more water to evaporate from the concrete surface.
  • Wind Speed: Moving air carries away moist air from the concrete surface, constantly replacing it with drier air. This increases the rate of evaporation. Higher wind speeds result in faster evaporation.
  • Concrete Surface Area: A larger exposed surface area of concrete will naturally lead to a higher total amount of water evaporating.
  • Solar Radiation: While not directly included in this simplified calculator, direct sunlight significantly heats the concrete surface, increasing evaporation.
  • Mix Design: The water-cement ratio and the presence of admixtures can influence the rate at which water is available at the surface to evaporate.

Why Control Evaporation?

Plastic Shrinkage Cracking: If water evaporates from the concrete surface faster than bleed water can rise to the surface, the surface layer shrinks. If this shrinkage is restrained by the underlying concrete, plastic shrinkage cracks form. These cracks occur while the concrete is still plastic (unhardened).

Surface Strength and Durability: Rapid drying can lead to a weaker, more porous surface layer, making it more susceptible to abrasion, freeze-thaw damage, and chemical attack.

Finishing Issues: Excessive evaporation can make finishing difficult, as the surface may dry out too quickly for proper troweling or finishing operations.

Using the Calculator:

Enter the ambient temperature in degrees Celsius, the relative humidity as a percentage, the wind speed in meters per second, and the exposed surface area of the concrete in square meters. The calculator will then estimate the total evaporation rate in kilograms per hour and liters per hour, providing valuable insight into the drying conditions.

Note: This calculator uses a simplified empirical formula. Real-world evaporation rates can be influenced by many other factors, including solar radiation, the amount of bleed water available, and concrete mix properties. For critical applications, consult ACI guidelines and more advanced modeling tools.

Example Calculation:

Consider a scenario on a warm, breezy day:

  • Temperature: 30°C
  • Relative Humidity: 50%
  • Wind Speed: 3 m/s
  • Concrete Surface Area: 20 m²

Inputting these values into the calculator will provide an estimated evaporation rate under these conditions, helping to determine if protective measures like fogging, windbreaks, or evaporation retarders are necessary.

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