For many small construction materials testing labs, accreditation is what opens the door to public work and larger clients. It is also the moment when a lab's records get read by someone who was not there when the tests were run. Assessors do not just look at the result. They look at whether the lab can show how it got it: which equipment, which technician, which version of the data, who reviewed it. This guide explains the main frameworks in plain terms and focuses on the records that make an assessment smoother.
What is AASHTO re:source accreditation?
AASHTO re:source runs the AASHTO Accreditation Program, which, according to its website, covers more than 2,100 accredited labs. For many US construction materials labs, this is the accreditation that clients and agencies ask about.
AASHTO R18 covers quality systems for construction materials testing laboratories: how a lab organizes its people, equipment, procedures and records so results are consistent. ISO/IEC 17025 is the general international standard for the competence of testing and calibration laboratories, across all fields, not only construction materials.
The details, scopes and current requirements of each come from the programs and standards themselves. Read the current documents and your program's requirements rather than relying on summaries, including this one.
Why does a CMT lab get accredited?
Accreditation is independent evidence that a lab can perform specific tests competently and consistently. It is test-specific: a lab is accredited for the tests on its scope, not for testing in general. For a small lab, that means choosing a scope you can support with trained people, maintained equipment and written procedures.
What records does an accredited lab need to keep?
Traceability. Every result should trace back to the sample, the date, the technician, the procedure and the equipment used. If a sieve analysis result is questioned, you should be able to show the original masses, the balance used and who ran it.
Raw data, not just results. Keep the masses, diameters, loads, counts and readings that produced each number, so a result can be recalculated by someone else.
Equipment status. A list of equipment with identifiers and calibration or verification due dates. The question is always whether that machine was in calibration on the day it was used.
Review and approval. A record of who reviewed a report and when. A reviewed result should not change silently afterward.
Changes and corrections. When a report is corrected, issue a revision with a reason and keep the original. An assessor wants to see that history, not a clean file with no trail.
Report content. Lab reports commonly state that results relate only to the items tested. That sentence reflects a real limit: a cylinder, a Proctor sample or a sieve split describes that specimen, not an entire placement or stockpile.
How does a small lab prepare for accreditation?
Decide the scope. Write procedures that match how your lab actually runs each test. Train and document the competence of each technician. Set up equipment records and a calibration schedule. Run proficiency samples where your program requires them. Do an internal audit before the assessor does. Then fix what you find, and keep records of the fixes too.
Why do calculations need the same scrutiny as procedures?
Spreadsheets are where silent errors live: a formula overwritten in one cell, a range that skips a row, a rounding step in the wrong place. Whatever tool you use, be able to show the formula, the inputs and the rounding rule. Sieve analysis is a good example because every row depends on the one above it; an error in one cumulative value carries all the way down to the fineness modulus. The formulas are simple: % retained = mass retained ÷ total dry mass × 100; cumulative % retained is the running sum; % passing = 100 − cumulative. Fineness modulus = the sum of cumulative % retained on No. 100, 50, 30, 16, 8, 4, 3/8 in, 3/4 in, 1-1/2 in and larger sieves in the 2:1 series, divided by 100.
What formulas are used?
- 01% retained = mass retained ÷ total dry mass × 100
- 02Cumulative % retained = running sum; % passing = 100 − cumulative
- 03FM = Σ cumulative % retained on No. 100, 50, 30, 16, 8, 4, 3/8 in, 3/4 in, 1-1/2 in and larger (2:1 series) ÷ 100
What does a worked example look like?
Inputs
A fine aggregate sieve record a reviewer might recheck: total dry mass 500 g. Retained: 3/8 in 0 g, No. 4 10 g, No. 8 65 g, No. 16 100 g, No. 30 125 g, No. 50 110 g, No. 100 65 g, pan 25 g.
Result
Cumulative % retained on No. 4 / 8 / 16 / 30 / 50 / 100: 2.0 / 15.0 / 35.0 / 60.0 / 82.0 / 95.0. Percent passing the No. 4: 98.0 %; passing the No. 100: 5.0 %. Fineness modulus 2.89. Keeping the raw masses on file is what lets anyone reproduce these numbers.
Calculated by the same tested functions as the ProofGrit free calculators.
How should a lab check its own calculations?
Pick a few recent reports each month and recalculate them by hand or with an independent tool: a sieve analysis, a cylinder set, a nuclear density day. Check that the rounding on the report follows the lab's written rule and that pass or fail was decided on the displayed value.
Write down what you checked and what you found. A short, honest internal check log is exactly the kind of evidence an assessor can follow, and it catches spreadsheet formula drift before a client does.
What are common accreditation mistakes?
Keeping only final results.
Equipment lists that do not match the identifiers written on data sheets.
Corrections made by overwriting.
Procedures that describe an ideal process nobody follows.
Reviews that happen but are never recorded.
Which standards and programs relate to lab accreditation?
AASHTO R18 (quality systems for construction materials labs), ISO/IEC 17025 (testing and calibration labs) and the AASHTO Accreditation Program run by AASHTO re:source. Your scope then lists the specific test methods, such as ASTM C39, D698 or D6938, that the lab is accredited to run. The standards index lists every method explained on this site.
See the standards index for every standard covered on this site.
| Item | AASHTO Accreditation Program | AASHTO R18 | ISO/IEC 17025 |
|---|---|---|---|
| What it is | An accreditation program | A quality system standard | A general competence standard |
| Run or published by | AASHTO re:source | AASHTO | ISO and IEC |
| Field | Construction materials testing | Construction materials testing labs | All testing and calibration labs |
Frequently asked questions
Is AASHTO accreditation the same as ISO/IEC 17025?
No. ISO/IEC 17025 is a general standard for testing and calibration labs. The AASHTO Accreditation Program, run by AASHTO re:source, is specific to construction materials testing. Check each program's current requirements.
What is AASHTO R18?
A standard covering quality systems for construction materials testing laboratories: how people, equipment, procedures and records are organized.
Does software make a lab accredited?
No. Accreditation comes from an assessment of the lab. Good records make the assessment easier, but they do not replace procedures, training or proficiency testing.
Why do reports say results relate only to the items tested?
Because a specimen describes itself, not the whole placement or stockpile it came from. The statement is common on lab reports.
How should corrections be handled?
Issue a revision with a stated reason and keep the original, so the change history is visible.
How ProofGrit helps
The ProofGrit free calculators show every formula and intermediate value, so you can check a spreadsheet or a hand calculation against a second, transparent source. The sieve analysis calculator, for example, lists % retained, cumulative and % passing for each sieve. The tools run in your browser and keep no records, so your lab's own record system remains the record of truth.
Related guides and tools
- ASTM C39: compressive strength of concrete cylindersHow a cylinder break works, how strength is calculated from two diameters and the maximum load, when the L/D correction applies, and what to check.
- Nuclear density test: field compaction with ASTM D6938How the nuclear gauge test works, the dry density and percent compaction math, the daily standard count check, and the mistakes that cause retests.
- Fresh concrete tests: slump, air, temperature and unit weightA plain-English tour of fresh concrete tests: sampling, slump, air content, temperature and unit weight, and why the field sheet matters later.
- CMT technician: role, training and certificationsWhat a construction materials testing technician does, how method-specific training supports reliable records, and where ACI and NICET programs fit.
- Sieve analysis calculatorPercent retained, cumulative retained and percent passing for each sieve, a log-scale gradation chart and fineness modulus.
- Concrete strength calculatorCylinder strength from two diameters and the maximum load, with L/D correction and the set average.
- Nuclear density calculatorDry density, percent compaction, moisture status and the daily standard count check for nuclear gauge tests.
- Standards indexEvery ASTM, AASHTO and ACI standard explained on this site.
- All lab operations guidesBrowse the full guide library by topic.
Sources and further reading
- AASHTO re:sourceAASHTO re:source
- AASHTO Store (AASHTO standards, including R18, T 99 and T 180)AASHTO
- ASTM InternationalASTM International
- American Concrete InstituteACI
Standards are summarized in our own words. Read the current edition from the publisher before you test.
This guide is a plain-English summary. Always follow the current standard and your project specifications.