How to Effectively Monitor Thermal Performance of Concrete and Slurry on Large Projects
For large-scale infrastructure projects, such as data centers, electrical vaults, and underground duct banks, thermal resistivity of concrete and slurry backfill is critical. Improper heat dissipation can reduce cable ampacity, compromise equipment, and cause long-term reliability issues.
The most effective way to ensure thermal performance is through lab-based dry-out curve testing of concrete and slurry samples, collected at strategically timed intervals during the project.
Collecting Concrete and Slurry Cylinders
To accurately track thermal resistivity over the life of the project:
Cylinders of concrete or slurry should be collected at specific intervals, which are project-dependent.
Early intervals capture initial curing conditions, while later intervals account for drying and moisture changes that significantly impact thermal conductivity.
Proper labeling and storage of each cylinder ensure that subsequent lab testing accurately represents in-place material.
For example, in a data center duct bank installation, cylinders may be collected every 50-100 feet of conduit, or at each pour session, depending on project size and material consistency.
Dry-Out Curve Testing: Tracking Thermal Resistivity Over Time
Once cylinders are collected, dry-out curve testing provides a comprehensive profile of thermal resistivity as materials cure and dry:
Cylinders are measured for initial thermal resistivity immediately upon collection.
Samples are gradually dried under controlled lab conditions, simulating long-term moisture loss.
Thermal resistivity is measured at multiple moisture levels, producing a dry-out curve for each cylinder.
Engineers can model heat transfer performance in the field based on these curves, ensuring that concrete and slurry will dissipate heat effectively after curing.
Why this is critical:
Freshly poured concrete or slurry has high water content, giving artificially low resistivity readings.
In-situ measurements provide a snapshot that doesn’t reflect long-term performance.
Dry-out curves reveal the true thermal behavior over the lifetime of the material.
Project-Specific Intervals
The frequency of cylinder collection depends on:
Project size: Large data centers or multi-phase electrical infrastructure require more frequent sampling.
Pour schedules: Each batch of concrete or slurry may behave differently due to admixtures, water content, or temperature.
Critical zones: Areas with high cable density or sensitive equipment may need additional sampling to confirm thermal performance.
Using project-specific intervals ensures representative thermal data without unnecessary sampling, optimizing both cost and accuracy.
Advantages Over On-Site Testing
Avoids unreliable in-situ readings: On-site conductivity tests only reflect the current water content, not the cured thermal performance.
Captures curing and drying effects: Dry-out curves simulate the long-term change in resistivity, critical for cable ampacity and heat management.
Provides standardized, reproducible results: Lab testing ensures each cylinder is evaluated under consistent conditions.
Note: Unless a sleeve is inserted during pouring, attempting to test cured concrete or slurry in-situ requires drilling a hole for the probe, which can damage the slab or backfill, further emphasizing the superiority of cylinder collection and lab testing.
Applications for Data Centers and Electrical Infrastructure
Duct bank backfill: Ensures engineered slurry conducts heat efficiently around high-voltage cables.
Concrete vaults and pads: Confirms foundation slabs dissipate heat from transformers, UPS systems, or server racks.
Substations: Validates thermal performance of poured concrete encasements to prevent equipment overheating.
By using dry-out curve testing of collected cylinders at strategic intervals, engineers can verify thermal performance, optimize backfill mixes, and prevent costly operational issues.
Conclusion
For large projects requiring concrete and slurry backfill, the most reliable method to ensure thermal resistivity compliance is:
Collect cylinders at project-specific intervals.
Conduct dry-out curve testing on each cylinder.
Use results to model long-term heat dissipation in the field.
This approach is far more effective than on-site thermal testing and provides accurate, reproducible data to support safe and efficient design for data centers, duct banks, and critical electrical infrastructure.
Contact our lab today to integrate dry-out curve thermal testing for concrete and slurry into your project workflow.
