Temperature tells you one thing about curing concrete. Electrical resistivity tells you another. Here is how resistivity works, the standards behind it, and why a second independent signal matters for high-stakes precast and prestressed pours.
Electrical resistivity in concrete measures how strongly the hardening concrete resists an electrical current. As cement hydrates and the pore network refines, resistivity rises, giving a direct, independent indicator of strength gain and, at later ages, durability. Paired with the temperature-based maturity method (ASTM C1074), it is a second strength signal that catches what temperature alone can miss.
Fresh concrete is full of water carrying dissolved ions, so it conducts electricity easily and its resistivity is low. As cement hydrates, it consumes water and fills the pore network with hydration products. The pores become finer, more tortuous, and less connected. Current has a harder path to follow, so resistivity climbs. That climb is a continuous, physical record of how the microstructure is developing inside the pour.
Resistivity is reported in kilohm-centimeters (kohm-cm). Two standards define how to measure it. AASHTO T-358 is the surface resistivity test, applied with a four-probe (Wenner) array. ASTM C1876 is the bulk electrical resistivity test, measured through the full specimen. Both translate a reading into information about the concrete's pore structure.
The maturity method is the workhorse of in-place strength estimation, and it is accurate when the mix matches its calibration. But it rests on a single input. Maturity converts the temperature-time history into a strength estimate using a curve calibrated for one specific mix. If the real concrete drifts away from that calibration, the temperature record gives no warning.
Three common drifts: a cement source or w/c ratio that changed since calibration, a chemical admixture behaving differently than expected, or unusually wet aggregate that shifts the real water content. In each case the maturity estimate can read normal while the actual strength gain is not. Temperature alone cannot see the difference.
Electrical resistivity comes from a different physical basis, so it provides an independent check. When the two signals agree, confidence is high. When they diverge, that is an early flag worth investigating before a release or strip decision rides on it.
| Approach | What it measures | What it can miss |
|---|---|---|
| Maturity (temperature only) | Temperature-time history, converted to strength through a mix-specific calibration (ASTM C1074) | Calibration drift, admixture surprises, wet aggregate. The estimate can read normal while real strength differs |
| Resistivity + maturity (two-signal) | Temperature-time plus a direct physical reading of the pore structure (AASHTO T-358, ASTM C1876) | Far less. The second signal flags the cases temperature alone hides, and adds a durability indicator |
The same pore refinement that raises resistivity also makes concrete harder for chloride ions to penetrate. That is why AASHTO T-358 frames surface resistivity as an indication of the concrete's ability to resist chloride-ion penetration. A higher later-age resistivity points to a denser, more durable concrete.
For bridge girders, marine structures, and infrastructure with long service-life requirements, that durability signal is valuable on its own. A sensor that already reads resistivity for strength verification gives the durability indicator at no extra step.
Precast and prestressed plants make high-stakes calls fast. Transfer-strength release, form stripping, and shipping all happen on a tight 12 to 24 hour cycle, and each one rides on knowing the concrete actually reached strength. A single estimate that quietly drifted is a real risk on that timeline.
A second independent signal turns that risk down. When resistivity and maturity agree, the plant can detension and turn the bed with confidence. When they diverge, the QC manager has a reason to pause and check before the strands are cut. That confidence is what lets a plant run a tighter cycle without taking on more risk.
Most embedded concrete sensors measure temperature only and compute maturity from it. SensyCast measures temperature and electrical resistivity in the same device, following ASTM C1074 for maturity, AASHTO T-358 and ASTM C1876 for resistivity. The two readings stream together to SensyHub, so the strength estimate and its independent check sit side by side on the same pour.
This two-signal measurement is the core hardware difference between SensyCast and the temperature-only sensors that make up most of the market. It is the one capability a temperature-only product cannot match without new hardware.
A measure of how strongly hardening concrete resists an electrical current through its pore solution. As cement hydrates and the pore network refines, resistivity rises, giving an independent indicator of strength gain and, at later ages, durability. It is reported in kilohm-centimeters (kohm-cm).
Maturity (ASTM C1074) estimates strength from temperature applied to a mix-specific calibration, so it depends on one input. Resistivity measures a physical property of the concrete directly. Because the two come from independent bases, resistivity can confirm or flag the maturity estimate.
AASHTO T-358 (surface resistivity, four-probe Wenner array) and ASTM C1876 (bulk electrical resistivity). Both relate a reading to the concrete's pore structure and, at later ages, its durability.
Temperature-based maturity rests on one input and a calibration that can drift. A changed cement source, an admixture behaving differently, or wet aggregate can move real strength away from the estimate with no warning from temperature. Resistivity is an independent second signal that catches those cases.
Yes. At later ages, resistivity correlates with resistance to chloride-ion penetration, a key durability indicator for bridge, marine, and infrastructure concrete. A denser, more refined pore structure both raises resistivity and resists chloride ingress.
SensyCast reads temperature and electrical resistivity from inside the pour, so your strength estimate comes with its own independent check.
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