Method and limits

Nurse-Saul computes the temperature–time factor M = Σ(T − T₀)·Δt in °C·hours, with T₀ the datum temperature below which strength gain is taken as zero (−10 °C is the usual default). Arrhenius instead gives equivalent age at 20 °C, t_e = Σ exp(−(E/R)(1/(T+273) − 1/293))·Δt, which represents temperature sensitivity better at the extremes but needs an activation energy term for your binder. Strength is then read from the logarithmic calibration you supply.

The maturity method is only as good as its calibration. ASTM C1074 requires the strength–maturity relationship to be established for the specific mix, from at least 15 cylinders across several ages, before site use — and re-established when the mix, cement source or admixture changes. The default coefficients here will not match your concrete.

Maturity estimates the strength of concrete that experienced the logged temperature history at the sensor. It says nothing about concrete elsewhere in the pour, and thin or exposed sections at an edge or soffit will be colder and weaker than a sensor at mid-depth. Maturity does not replace the cube or cylinder results required for acceptance; it supports a striking decision between them. Treat the time-to-strike figure as an extrapolation at the current temperature trend, not a commitment.