Jul 11, 2025

Using the SRX6 Thermocouple Logger for Concrete Maturity Testing

Concrete maturity testing is a proven method for estimating the in-place strength of concrete using its temperature history. Rather than waiting a set number of days, engineers and construction crews can use real-time data to determine exactly when concrete is strong enough to move forward. The ACR SRX6 thermocouple logger supports this workflow with built-in maturity calculations, rugged design, and real-time alert capabilities—making it ideal for field use.

How Concrete Maturity Works

The maturity method is based on the principle that strength gain is a function of both time and temperature. Two standard equations are used in the industry:

Nurse-Saul Method – A linear method widely used in standard conditions
Arrhenius Method – A more advanced exponential model for non-linear curing, high-performance mixes, or extreme weather

Both are supported natively by the SRX6 logger and conform to ASTM C1074 guidelines.

📌 Sidebar: What Is the Datum Temperature?

The datum temperature (T₀) is the threshold below which concrete is assumed to gain no strength. In the Nurse-Saul equation, it is used as a reference point in calculating maturity:

M(t) = Σ (Tₐ - T₀) Δt

The SRX6 logger uses a fixed datum temperature of -10°C, which aligns with standard practice for ordinary Portland cement. This simplifies setup and ensures consistency across deployments.

Built-In Intelligence: Onboard Maturity Calculation

One key advantage of the SRX6 is that it calculates both Nurse-Saul and Arrhenius maturity values directly in the logger firmware. There’s no need for post-processing in software—the technician simply downloads the data, and both temperature and maturity are already calculated.

This approach ensures reliability and traceability, especially for validation and compliance documentation.

What Technicians See in the Field

When connecting the SRX6 to a computer using TrendReader TRX Pro software, the technician sees:

Time-stamped temperature readings for each thermocouple channel
Corresponding maturity values already calculated by the logger
Visual graphs of temperature and maturity over time

The technician compares these maturity readings against pre-established thresholds based on lab testing. For example, if a mix reaches 20 MPa at 1,200 °C·hr, the concrete is considered ready once the logged maturity value exceeds 1,200.

Real-Time Alerts with Two-Stage Alarming

SRX6 loggers also support a two-stage alarm system. Internally, LED indicators show when temperature or maturity thresholds are approaching or have been met. But for larger projects, the logger can also trigger external alarms—such as tower lights or beacons.

Stage 1 Alarm: Warns when maturity is nearing the critical threshold
Stage 2 Alarm: Signals that the concrete has reached the required maturity

This makes it easy for field crews to visually confirm concrete readiness without needing to check software or wait for verbal updates. The alarm interface can support 5–24V external signaling systems, and the thresholds are typically pre-configured based on the logger's setup.

Conclusion

The ACR SRX6 is more than a thermocouple logger—it’s a complete tool for modern concrete maturity management. With built-in calculations, reliable multi-channel logging, and visual alarming, it gives construction teams confidence and actionable data when it matters most.

References

ASTM C1074 – Standard Practice for Estimating Concrete Strength by the Maturity Method
ACI 228.1R – In-Place Methods to Estimate Concrete Strength
ACI 306R – Guide to Cold Weather Concreting
Edward G. Nawy – Concrete Construction Engineering Handbook, CRC Press
ASTM STP 169D – Significance of Tests and Properties of Concrete and Concrete-Making Materials

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Using the SRX6 Thermocouple Logger for Concrete Maturity Testing

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