Input Data
Calculate Heat of Hydration
Enter consistent project data. The measured temperature rise is optional and helps compare observed storage with theoretical heat.
Example Data
Sample Calculation Inputs
| Input | Example Value | Unit | Purpose |
|---|---|---|---|
| Cement mass | 350 | kg | Mass of cement in the placement. |
| Ultimate heat of hydration | 500 | kJ/kg | Potential heat per kilogram of cement. |
| Degree of hydration | 60 | % | Estimated reaction completion at the chosen age. |
| Concrete mass | 2,400 | kg | Total concrete mass receiving the heat. |
| Specific heat capacity | 0.88 | kJ/kg°C | Heat required to raise concrete temperature. |
| Curing duration | 72 | hours | Time used for the average heat rate. |
Formula Used
Heat Release and Temperature Rise Equations
Q is total released heat in kJ. Mcement is cement mass in kg. Hu is ultimate heat of hydration in kJ/kg. α is the hydration fraction.
ΔTad is the ideal adiabatic temperature rise. Mconcrete is total concrete mass. cp is concrete specific heat capacity.
Pavg is average heat release rate in kW. t is curing duration in hours. The optional stored heat comparison uses Qstored = Mconcrete × cp × ΔTmeasured.
Calculator Guide
How to Use This Calculator
- Enter the cement mass for the complete concrete placement.
- Enter a tested or specified ultimate heat of hydration value.
- Select the degree of hydration expected at the chosen curing age.
- Enter total concrete mass and specific heat capacity.
- Add the time period used to calculate average heat release.
- Enter initial concrete and ambient temperatures for peak screening.
- Optionally add a measured core rise from installed sensors.
- Select Calculate Heat. Review the result panel above the form.
- Export the data or print the result for project records.
Concrete Hydration Heat Explained
Why Temperature Control Matters
Concrete gains heat when cement reacts with water. This reaction is called hydration. The heat supports strength development. It can also create temperature gradients. Large gradients may cause thermal cracking. The risk rises in thick walls, raft foundations, dams, bridge piers, and heavily reinforced members.
Heat Changes Over Time
Fresh concrete does not release heat at one constant rate. Early reactions can be rapid. Later reactions continue more slowly. Cement chemistry, cement content, fineness, supplementary materials, water content, temperature, and curing conditions all matter. A rich mix usually produces more heat. A cooler mix usually reacts more slowly.
Using the Estimate
The calculator estimates released heat from cement mass, heat of hydration, and degree of hydration. It then estimates an adiabatic temperature rise. Adiabatic means no heat escapes. Real placements lose heat to forms, soil, air, and reinforcing steel. Therefore, field temperatures may be lower. However, the adiabatic result is useful for screening potential thermal risk.
Choose Reliable Inputs
Use tested mix data whenever possible. Portland cement mixtures can have different heat values. Slag, fly ash, limestone, and silica fume can also change the heat pattern. The degree of hydration is an estimate. It describes how much of the available reaction has occurred by the selected age. Match the selected duration with this estimate.
Understand Thermal Storage
Concrete mass and specific heat capacity affect temperature rise. More concrete mass can absorb more heat. A higher specific heat capacity also reduces the calculated rise. These inputs should represent the entire placement. Include aggregate, paste, water, and embedded material only when they meaningfully store heat.
Compare With Field Monitoring
The measured temperature-rise field is optional. Enter a monitored internal rise when available. The calculator compares measured stored heat with the theoretical release. This comparison is a simplified retained-heat indicator. It does not replace thermal modeling. Temperature sensors remain important for critical work.
Control the Placement
Plan placement before concrete arrives. Review maximum placement temperature. Consider lift height, pour sequence, form insulation, aggregate cooling, chilled water, and pipe cooling. Avoid sudden cooling after peak temperature. Gradual cooling limits surface-to-core differences. Protect the surface from wind and cold exposure.
Record Each Scenario
Use results as an engineering estimate. Verify material properties with supplier reports or laboratory tests. Check project specifications and local requirements. Consult a qualified engineer for mass concrete work. They can select monitoring locations, acceptance limits, and curing actions. Good thermal control protects durability, appearance, and long-term structural performance.
Input units must remain consistent. Use kilograms for cement and concrete mass. Use kilojoules per kilogram for heat values. Use degrees Celsius for temperature rise. The numerical size of a Celsius rise equals a Kelvin rise. Do not enter Fahrenheit without converting it first.
Run several scenarios. Test a high cement content case. Test a hot-weather case with greater hydration. Test a cooler mix with supplementary cementitious materials. Compare the results. This exposes combinations that need more controls.
Document each assumption alongside the calculation output. Clear records support reviews, troubleshooting, quality control, and future mix improvements.
Frequently Asked Questions
Concrete Heat of Hydration FAQs
1. What is heat of hydration?
Heat of hydration is thermal energy released when cement reacts with water. The reaction helps concrete gain strength. It can also raise internal temperature, especially in large placements.
2. Why does mass concrete need thermal control?
Mass concrete holds heat because its core cools slowly. A hot core and cool surface can create tensile stress. That stress can lead to thermal cracking.
3. What is an adiabatic temperature rise?
It is the temperature increase calculated when no heat escapes from the concrete. It is an idealized limit. Actual placements lose heat through boundaries and cooling systems.
4. Which heat of hydration value should I enter?
Use laboratory data, supplier data, or an approved project value for the selected binder. The value should match the cementitious system and the intended curing period.
5. Does the calculator include heat from all cementitious materials?
It uses the heat value you enter. Combine or adjust values when your mix includes slag, fly ash, silica fume, or other cementitious materials.
6. What does degree of hydration mean?
Degree of hydration is the percentage of available cement reaction completed by a selected time. It increases as curing continues, but the rate slows over time.
7. Why is concrete specific heat capacity needed?
Specific heat capacity describes how much heat concrete absorbs for each degree of temperature rise. It links released hydration heat to an estimated temperature increase.
8. Can I use Fahrenheit values?
Use Celsius values in this calculator. Convert Fahrenheit temperatures before entry. Temperature differences in Celsius and Kelvin have the same numerical size.
9. Why can measured temperatures differ from the estimate?
Real conditions include heat loss, mix variability, sensor location, weather, formwork, insulation, placement geometry, and active cooling. The calculator is a screening tool.
10. Does this replace a thermal model?
No. Critical mass concrete work may require detailed thermal modeling, sensor plans, acceptance limits, and engineer review. Use this calculator for fast preliminary estimates.
11. What should I do after calculating the result?
Use findings to plan monitoring, curing, and placement controls.