Calculator inputs
Paste your temperature history as hour, temperature per line. Use hours since placement. Values can be comma or space separated.
Example data table
This sample resembles a warm early cure followed by cooling overnight.
| Hour since placement | Measured temperature (°C) | Notes |
|---|---|---|
| 0 | 20 | Fresh concrete placed |
| 4 | 28 | Heat of hydration rising |
| 8 | 32 | Peak temperature period |
| 12 | 30 | Beginning to cool |
| 24 | 25 | Overnight steady temperature |
Formula used
Nurse‑Saul maturity index
The maturity index combines time and temperature into one value:
M = Σ (T̄ − T0) · Δt
- T̄ is average concrete temperature for the interval (°C).
- T0 is datum temperature where hydration effectively stops (°C).
- Δt is time step length (hours).
Equivalent age (Arrhenius)
Equivalent age adjusts curing time to a reference temperature:
tₑ = Σ exp( −Ea/R · (1/Tk − 1/Trk) ) · Δt
- Ea is activation energy (J/mol), R is 8.314 J/mol·K.
- Tk and Trk are absolute temperatures (K).
- Use this when temperatures vary widely or for better mix specificity.
Strength estimation
Strength is estimated from maturity using a calibrated relationship:
- Log: S = A + B ln(M)
- Exponential: S = Su(1 − e^(−kM))
These parameters must be fitted with your cylinder break results for best accuracy.
How to use this calculator
- Record concrete temperature at consistent time intervals after placement.
- Paste the history as hour, temperature per line.
- Set the datum temperature T0 from your spec or testing.
- Optionally set Tr and Ea for equivalent age reporting.
- Choose a strength model and enter calibrated parameters for your mix.
- Press Calculate to view results above the form.
- Use the export buttons to save a CSV or PDF report.
Practical article
1) What concrete maturity means on site
Maturity combines curing time and temperature into one performance indicator. Because hydration is temperature dependent, two slabs of the same mix can reach different strengths at the same clock time. Using maturity helps crews plan finishing, saw-cut timing, form removal, and early loading with fewer conservative guesses.
2) Collecting reliable temperature history
Use embedded sensors, maturity meters, or well-insulated probes placed in representative locations. Record readings at consistent intervals, such as every 30 minutes to 2 hours. Shorter intervals improve accuracy when temperatures change quickly, especially in thin sections, cold weather, or when blankets are added or removed.
3) Choosing the datum temperature (T0)
The datum temperature is the baseline where hydration effectively slows to a stop for the selected method. Project specifications often state a value, but it can vary by cement type and admixtures. If T0 is set too high, maturity will be underestimated; too low, and maturity can be inflated.
4) Interpreting the Nurse‑Saul index
The Nurse‑Saul approach assumes a linear relationship between temperature and rate of strength gain within practical ranges. It is popular for daily site control because the calculation is straightforward. The output is reported as degree-hours or degree-days, which can be compared against validated break results.
5) Using equivalent age for variable curing
Equivalent age converts each time step into an “as if cured at reference temperature” duration using an Arrhenius factor. This method is useful when temperatures vary widely or when mixes are sensitive to temperature. Activation energy should be selected from testing or credible mix documentation.
6) Converting maturity to strength responsibly
Maturity alone does not equal strength; it needs calibration. Establish a strength–maturity curve by matching maturity values to cylinder or core results for the same mix. This calculator provides two common fitting options, allowing you to keep parameters stable and adjust them as more data is collected.
7) Decisions maturity supports in construction
Common decisions include stripping vertical forms, post-tensioning, opening pavements to traffic, early loading of slabs, and scheduling follow-on trades. When using maturity for critical actions, keep a margin of safety and follow the governing specification, especially for structural elements.
8) Data quality checks that prevent mistakes
Review your time steps for gaps, duplicated timestamps, or unrealistic spikes. Confirm sensor placement is not exposed to direct sunlight or air drafts. Use consistent units and verify the placement time is set to hour zero. Accurate inputs lead to actionable outputs and cleaner project records.
FAQs
1) Which method should I use for routine site tracking?
Nurse‑Saul is commonly used for routine tracking because it is simple and transparent. If your temperatures vary widely or your mix is temperature sensitive, equivalent age can provide more stable comparisons.
2) What time interval should I enter for readings?
Use the same interval you record in the field. One hour is a practical default. For thin sections, cold weather, or rapid temperature changes, shorter intervals improve accuracy and reduce averaging error.
3) Can I estimate strength without calibration tests?
You can calculate maturity without tests, but strength estimates require calibration to your mix. Use cylinder breaks or core results to fit the model parameters so predictions align with your actual materials and curing conditions.
4) Why does the calculator require a 0-hour entry?
Hour zero anchors the history to placement time and ensures each interval represents curing after placement. Without it, early curing may be missed, which can significantly affect maturity and equivalent age results.
5) What does activation energy affect in the results?
Activation energy controls how strongly temperature influences the equivalent-age factor. Higher values make hot curing count more, and cold curing count less. Use values supported by testing or reliable mix documentation.
6) How do I interpret negative maturity increments?
If the average interval temperature is below the datum temperature, the Nurse‑Saul increment becomes negative. This indicates minimal hydration for that step. Recheck your datum choice and verify sensor readings are realistic.
7) How can I share the results with inspectors?
Use the CSV export for spreadsheets and the PDF export for quick review. Include your sensor locations, mix ID, placement time, and calibration reference so reviewers can trace the maturity-to-strength relationship.
Use accurate inputs to plan pours and strip safely.