What is ASTM G187 Testing?
ASTM G187 is a standard test to measure the electrical resistivity of soil and water-based electrolytes to evaluate their corrosiveness to buried and submerged metallic materials. The test uses a four-electrode soil box, and it converts measured electrolyte resistance to resistivity, typically reported in ohm-centimeters. ASTM G187 is frequently used to assess corrosion in underground pipelines, tanks, cables, grounding systems, and other metallic structures installed in the ground. A lower resistivity value is a more conductive condition, and may lead to increased corrosion.
What Was the Client Looking to Evaluate?
The client approached Matestlab Inc. for urgent testing of a sand aggregate/cushion material to determine whether it met their specified material requirements.
The initial scope encompassed ASTM C33/C33M, ASTM C1218/C1218M, ASTM D4972, ASTM G187, and ASTM C88 testing. The client specified the following compliance thresholds:
- Fine sand aggregate conforming to ASTM C33/C33M, with modified maximum passing thresholds reduced to 5% for the 150 µm sieve and 15% for the 300 µm sieve.
- Water-soluble chloride content not exceeding 300 ppm per ASTM C1218/C1218M.
- Water-soluble sulfate content not exceeding 150 ppm per ASTM C1580.
- pH greater than 7.0 per ASTM D4972.
- Minimum electrical resistivity of 13,780 ohm-inch per ASTM G187.
- Magnesium sulfate solution required for ASTM C88 soundness testing.
To meet the client’s urgent timeline, Matestlab collaborated closely with laboratory analysts and client representatives to review standards, resolve technical constraints, and define an optimized testing strategy.
What Were the Testing Challenges?
Challenge 1: Reviewing the Applicability of Requested Standards
Technical review revealed that ASTM C33/C33M is a material specification standard, not an individual test method. Compliance testing had to be structured around the specific test methods referenced within the specification.
Challenge 2: Identifying the Most Critical Property for Initial Screening
Based on the client’s previous experience with the material, electrical resistivity was considered the property most likely to cause the material to fail the specification. To optimize schedule and budget, the client prioritized ASTM G187 testing as a preliminary screening step prior to authorizing full multi-parameter testing.
Challenge 3: Determining the Applicability of ASTM C1218/C1218M
During testing design, analysts identified that ASTM C1218/C1218M was unsuitable for the submitted homogeneous sand aggregate sample. The team selected and validated an appropriate alternative method for water-soluble chloride determination.
Challenge 4: Evolving Testing Requirements
As evaluation progressed, the client requested additional analyses, including magnesium sulfate content and ASTM C1580 sulfate testing. Matestlab seamlessly integrated these additions into the scope without compromising project deadlines.
The Customized Testing Approach by Matestlab
1. Phase I – Initial Material Screening via ASTM G187
The client submitted an initial sample volume of approximately one gallon, satisfying the sample requirements for ASTM G187. Because electrical resistivity was a critical parameter, testing was expedited to quickly verify material suitability.
The ASTM G187 test results successfully met the client’s specification threshold, prompting authorization to proceed with Phase II characterization under an expanded work scope.
2. Phase II – Comprehensive Material Characterization
For comprehensive evaluation, the client submitted a bulk sample of approximately 5 gallons.
The Phase II program initially comprised:
- ASTM C88 – Soundness of aggregates using magnesium sulfate over 5 cycles, including grain-size determination.
- ASTM C1218/C1218M – Water-soluble chloride evaluation.
- ASTM D4972 – Soil pH determination.
- ASTM C1580 – Water-soluble sulfate in soil.
- ASTM D6913 – Sieve analysis of soils.
3. Alternative Approach for Chloride Analysis
Following standard suitability assessment, laboratory analysts confirmed that ASTM C1218/C1218M was inappropriate for the provided homogeneous sand aggregate.
Matestlab team collaborated with analytical staff to select an effective alternative for water-soluble chloride content. Based on sample characteristics, ASTM D512, Method B (Silver Nitrate Titration) was adopted.
The client confirmed sample homogeneity and verified that depth-specific profiling was unnecessary. The testing scope was updated accordingly.
4. Expanded Testing Requirements
The client subsequently requested magnesium sulfate content determination and formally added ASTM C1580 to the active test scope.
The final executed testing program consisted of:
- ASTM C88 – Soundness testing over 5 cycles using magnesium sulfate, including grain-size determination.
- ASTM D512, Method B – Water-soluble chloride determination via silver nitrate titration.
- ASTM C1580 – Water-soluble sulfate content in soil.
- ASTM D4972 – Soil pH measurement.
- ASTM D6913 – Particle size distribution (sieve analysis).
For the sieve analysis, handling procedures accounted for applicable bulk sample surcharges for test samples exceeding 20 lb.
A Balanced Testing Plan
To meet project urgency, the team managed testing execution through proactive, real-time communication among the client, analytical staff, and project managers. Rather than withholding findings until the project’s completion, the team issued preliminary data as individual analyses were completed. The team proactively addressed technical inquiries regarding standard applicability, analytical method selection, chemical evaluations, and project specification thresholds.
What Were the Analysis Results and Interpretation?
The initial ASTM G187 electrical resistivity testing met the client’s specified requirement, allowing the client to proceed with the comprehensive testing program. The sieve analysis was subsequently completed, and the results were shared with the client. The final report was updated to include the client’s detailed acceptance criteria alongside the measured test results. This side-by-side comparison provided the client with clear verification of material compliance against specified parameters.
Discussion and Conclusions
The project successfully transitioned from urgent preliminary screening via ASTM G187 to a thorough characterization of the sand aggregate material. Project execution demonstrated strong adaptability in modifying test scopes, validating standard applicability, establishing alternative analytical methods for chloride testing, and managing concurrent testing tracks under tight schedules. Through close coordination between the client, laboratory, and Matestlab project team, the testing scope was successfully adapted, and results were provided progressively to support the client’s evaluation.
FAQ
What does electrical resistivity indicate about sand aggregate?
Electrical resistivity indicates how readily electrical current can pass through the material under specified conditions. It can help evaluate the potential corrosivity of the environment around buried or submerged metallic structures.
Why is sieve analysis important for sand aggregate?
Sieve analysis determines the particle-size distribution of the aggregate and helps verify whether the material meets specified grading requirements. This is particularly important when the client has defined maximum percentages passing specific sieve sizes.
