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The average concrete temperature over the elapsed curing period, in °C.
For a simple estimate, average your logged temperature readings over the period — a full maturity study integrates continuously logged sensor data instead.
The total elapsed curing time, in hours.
168 hours = 7 days.
The temperature below which the mix gains no useful strength. ASTM C1074 recommends 0°C.
The datum is the intercept of the strength-gain rate against temperature, and it belongs to the mixture rather than to the method: ASTM C1074 recommends 0°C (32°F) for Type I cement without admixtures cured between 0 and 40°C, and Annex A1 sets out how to measure it for anything else — a mix with an accelerator or a Type III cement will not sit at 0. You will also meet −10°C (14°F) in older references, which is Saul's original 1951 value; it is not what C1074 recommends, and because it adds 10 degrees to every hour it reports roughly 50% more maturity at normal curing temperatures.
Maturity index
3,360 °C-hours
This uses a single average temperature for simplicity — a real maturity study integrates continuously logged temperature data over time, which is more accurate when temperature varies significantly during curing (e.g. cold nights, hot days). The datum belongs to your mixture: 0°C is ASTM C1074's recommendation for plain Type I cement, and Annex A1 sets out how to measure it for anything else.
- Elapsed time
- 7 days
- Datum temperature used (°C)
- 0 °C
- Temperature above datum (Δ°C)
- 20 Δ°C
They open the calculator with your figures already in it
Concrete Maturity Method Calculator (Nurse-Saul): 3,360 °C-hours — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- ASTM C1074 Nurse-Saul maturity function: M(t) = Σ(T − T0) × Δt, where T is the concrete temperature, T0 is the datum temperature and Δt is the elapsed time interval. C1074 recommends T0 = 0°C (32°F) for Type I cement without admixtures cured between 0 and 40°C, and gives Annex A1 for determining it experimentally for any other mixture
- ASTM C1074: the increment (T − T0) is taken as zero for any interval in which the concrete is at or below the datum temperature
Inputs used
- Average Concrete Temperature
- 68 °F
- Elapsed Curing Time
- 168
- Datum Temperature (T0)
- 32 °F
Intermediate steps
- Elapsed time
- 7 days
- Datum temperature used (°C)
- 0 °C
- Temperature above datum (Δ°C)
- 20 Δ°C
Confidence note: This uses a single average temperature for simplicity — a real maturity study integrates continuously logged temperature data over time, which is more accurate when temperature varies significantly during curing (e.g. cold nights, hot days). The datum belongs to your mixture: 0°C is ASTM C1074's recommendation for plain Type I cement, and Annex A1 sets out how to measure it for anything else.
What this calculation does not cover
- A maturity index is not a strength. Until a strength-maturity relationship has been developed for the mix actually supplied — cylinders from that mix, broken at several ages against their own logged maturity — this number cannot be read as an in-place compressive strength, and on its own it does not release formwork, tendons, sawcutting or traffic.
- Nurse-Saul sums temperature over successive intervals; this takes one average for the whole period instead. Cold nights, the hydration peak and any spell the concrete spent below the datum are all flattened into a single figure, so the wider the temperature swing over the period the further this sits from what an embedded logger would report.
- It covers one temperature, not a position in the pour. Corners, edges, thin sections and the top surface run colder than the core and reach a given maturity later, and a striking decision belongs to the coldest critical location rather than to an average of the element.
- The datum is taken exactly as entered — nothing here checks it against your cement, admixtures or supplementary cementitious materials. The Nurse-Saul function is also linear in temperature, so it does not capture the reduced ultimate strength of concrete cured hot: a warm pour can accumulate maturity quickly and still fall short at later ages, which is what the Arrhenius equivalent-age methods exist to address.
- At or below the datum the index reports zero. That is the method's bookkeeping convention, not a verdict on the concrete: it says nothing about whether a pour that got cold or froze has been damaged, and it does not cover cold-weather protection requirements.
- The index is reported in °C-hours whichever measurement system you are reading the site in, and the two temperature rows beneath it are shown in Celsius terms for the same reason: the figure is only meaningful against the strength-maturity curve it is compared to, and that curve carries the units its own cylinders were logged in. Enter your temperatures in whichever units you measured — those fields convert — but if your calibration curve is in °F-hours, multiply this figure by 1.8 before reading a strength off it.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-05 · in the site-wide review of 2026-09-06 · v1.1.1
Regulatory standards & verification citations2
- ASTM C1074 Nurse-Saul maturity function: M(t) = Σ(T − T0) × Δt, where T is the concrete temperature, T0 is the datum temperature and Δt is the elapsed time interval. C1074 recommends T0 = 0°C (32°F) for Type I cement without admixtures cured between 0 and 40°C, and gives Annex A1 for determining it experimentally for any other mixture
- ASTM C1074: the increment (T − T0) is taken as zero for any interval in which the concrete is at or below the datum temperature
Which documents these citations point at
Standards referenced: ASTM C1074 (ASTM International, United States).
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