- The Credential at a Glance
- Exam Format and Scoring Rules
- The Four Standards on One Page
- C617: Capping Facts
- C1231: Unbonded Cap Facts
- C39: Compressive Strength Facts
- C78: Flexural Strength Facts
- Performance Exam Reminders
- Fees, Workbook and Scheduling
- Retakes, Deadlines and Recertification
- A Four-Week Plan Built Around the Standards
- Frequently Asked Questions
- The written exam is one hour, closed book, multiple choice, with roughly 35-40 questions across four standards.
- You need at least 60% on each standard and at least 70% overall to pass the written exam.
- The performance exam covers all four procedures on pass/fail checklists; a failed procedure earns one same-day second trial.
- Written and performance exams must both be passed within one year; certification then lasts five years.
The Credential at a Glance
Concrete Strength Testing Technician is an American Concrete Institute (ACI) certification for people who cap, test and report on concrete strength specimens. Examinations are delivered through ACI-approved Sponsoring Groups and resource centers, typically local chapters and industry associations. This page is a quick-reference sheet. If you want the full explanation of what the credential is and why employers ask for it, start with What Is CSTT Certification? and come back here for the facts you will want to review the night before your session.
One scoping note matters: this credential is separate from ACI's Field Testing Technician Grade I and from the combined Laboratory Testing Technician Level 1 certification. If a job posting or a chapter flyer names one of those, confirm that you are registering for the strength-testing program covered here.
Exam Format and Scoring Rules
There are two separate examinations, and you must pass both within one year of each other.
| Item | Written Examination | Performance Examination |
|---|---|---|
| Length / style | One hour, closed book, multiple choice | Closed book; you demonstrate procedures to an examiner |
| Content | Approximately 35-40 questions across the four standards | All four procedures assessed on pass/fail checklists |
| Passing standard | At least 60% on each standard AND at least 70% overall | Pass every checklist procedure |
| Calculator | Check with your examiner or sponsoring group | Simple, non-programmable calculators permitted |
| Failure rule | Retake the entire written component | Failed procedure gets a second same-day trial; after that, the whole performance component is retaken |
Why the question count is approximate
ACI's current program page describes approximately 40 questions with at least eight per standard, while Certification Program Policy CPP 620.2-19 describes approximately 35-40 questions with 8-10 per standard. Treat the number as a range. The dependable takeaway is that every standard gets a meaningful block of questions, so no standard can be ignored.
The Four Standards on One Page
The exam objectives are organized under four headings drawn from ACI's Job-Task Analysis, approved February 29, 2020 and editorially updated February 8, 2022. These headings are not four equally weighted domains; the written exam simply guarantees a minimum number of questions on each, and the performance exam checks all four procedures. For a deeper walk through each area, see CSTT Exam Domains 2026: Complete Guide to All 4 Content Areas.
| Standard | Subject | What it governs |
|---|---|---|
| ASTM C617/C617M | Capping Cylindrical Concrete Specimens | Bonded sulfur-mortar-style capping of cylinder ends |
| ASTM C1231/C1231M | Use of Unbonded Caps in Determination of Compressive Strength of Hardened Concrete Cylinders | Reusable pad systems with retaining rings |
| ASTM C39/C39M | Compressive Strength of Cylindrical Concrete Specimens | Loading cylinders to failure and calculating strength |
| ASTM C78/C78M | Flexural Strength of Concrete (Simple Beam with Third-Point Loading) | Breaking beams and calculating modulus of rupture |
The editions that matter are the ones ACI names as the current technical basis: C617/C617M-15, C1231/C1231M-15, C39/C39M-18 and C78/C78M-18. If your lab works from different editions, defer to the edition named in your workbook when answering exam questions.
C617: Capping Facts
ASTM C617/C617M: Capping Cylindrical Concrete Specimens
This standard is about making the bearing surfaces of a cylinder plane and perpendicular to the axis so load is distributed evenly. Expect questions on why capping exists and what makes a cap defective.
- Understand the purpose: uneven end surfaces cause stress concentrations and artificially low strength results.
- Know the cap qualities the standard cares about: flatness, perpendicularity to the cylinder axis, thickness and adequate strength relative to the concrete.
- Review timing relationships between capping and testing, including cure or set time before loading.
- Be able to identify visual cap defects such as voids, cracks or debonding and know that a questionable cap is a reason for corrective action.
- Know which cylinder ends require capping and how ends outside tolerance should be handled.
On the performance side, capping is hands-on. Examiners watch your preparation of the cylinder end, handling of the capping apparatus and checks of the finished surface. Memorize the sequence so your hands do it correctly under pressure.
C1231: Unbonded Cap Facts
ASTM C1231/C1231M: Unbonded Caps
Unbonded capping uses reusable pads held in rigid retainers rather than a bonded cap material. The exam rewards knowing the limits and conditions of the system, not only the assembly steps.
- Know the components: elastomeric pads, metal retainers and how they seat on the cylinder.
- Know the conditions under which pad use is allowed, including limits tied to the strength level of the concrete being tested.
- Understand pad qualification and when pads must be inspected or discarded, including wear, cracking and deformation.
- Understand centering and alignment, since misaligned retainers can invalidate a test.
- Be able to contrast the unbonded approach with bonded capping in terms of speed, reuse and limitations.
A common misconception is that unbonded caps are simply an easier version of capping. They are a different system with their own qualification and use conditions, and exam questions often target exactly those conditions.
C39: Compressive Strength Facts
C39 is the centerpiece of cylinder testing and the standard most candidates associate with the credential. Expect both conceptual and calculation questions. Our difficulty guide explains why this standard tends to feel most demanding.
ASTM C39/C39M: Compressive Strength of Cylindrical Specimens
Know the testing machine, the specimen requirements, the loading procedure and the reporting items.
- Specimen measurement: diameter and length, and how measured diameter feeds the area calculation.
- Length-to-diameter considerations and when a correction factor is needed.
- Loading rate: understand the stress-rate approach and why a controlled rate matters to the result.
- Bearing blocks and platens: seating, cleanliness and condition requirements.
- Fracture patterns: recognize the standard cone-type break and identify atypical fractures that signal a problem with capping, alignment or the specimen.
- Calculation: maximum load divided by cross-sectional area, reported to the precision the standard specifies.
- Report contents: identification, dimensions, age, load, strength, fracture type and any defects noted.
- Moisture condition at test: know what the standard expects of the specimen at the time of loading.
C78: Flexural Strength Facts
Flexural strength is where candidates who trained mostly on cylinders get surprised. The geometry, loading arrangement and formulas are different, and the standard's title tells you the setup: a simple beam with third-point loading.
ASTM C78/C78M: Flexural Strength (Third-Point Loading)
Know why third-point loading is used, how the apparatus is arranged and where the beam fails relative to the loading points.
- Apparatus: support and loading blocks, span arrangement and how the blocks contact the beam.
- Specimen preparation: beam orientation during testing, with the tested surfaces being the sides as molded, and the importance of smooth, plane contact surfaces.
- Loading rate and how it is controlled during the test.
- Fracture location: a fracture within the middle third of the span uses the standard modulus of rupture calculation; know what the standard says about fractures outside that region.
- Calculation: modulus of rupture from load, span length and measured average width and depth.
- Measurement requirements: how and where width and depth are measured after failure.
- Report items: specimen identification, dimensions, load, fracture location and calculated modulus of rupture.
The most frequent point of confusion is the fracture-location rule, because the calculation or validity of the result depends on where the break occurred. Memorize it cold.
Performance Exam Reminders
The performance exam is closed book and assesses all four procedures using pass/fail checklists. That wording matters: an examiner is checking whether each required step is performed correctly, not grading your overall impression.
- Narrate your checks mentally. Know why each step exists, not just the order.
- Treat measurements as graded steps. Taking and recording dimensions correctly is part of the procedure, not preamble.
- Inspect before you proceed. Checking equipment condition, pad condition or cap quality is typically a checklist item.
- Use the second trial wisely. A failed procedure permits one second same-day trial, so settle yourself, review the missed step and reattempt deliberately.
- Know what a second failure costs. A later re-examination covers the entire failed component, not just the one procedure.
Key Takeaway
Rehearse physical procedures aloud with real equipment where you can. Reading C39 and C78 tells you what is required; only repetition builds the fluency a checklist-graded practical rewards.
Fees, Workbook and Scheduling
ACI does not publish one national tariff for exam sessions, because sponsoring groups set local prices and bundles. The figures below are verified local 2026 examples, not national rates, and were checked October 5, 2026. For a fuller breakdown, see CSTT Certification Cost 2026.
| Sponsor (2026 example) | Offering | Price |
|---|---|---|
| Las Vegas Chapter | Certification or recertification, including workbook, review and both exams (excludes optional training) | USD 475 member / USD 550 non-member |
| Las Vegas Chapter | Optional training | USD 225 member / USD 300 non-member |
| Las Vegas Chapter | Failed-component retest | USD 235 member / USD 290 non-member |
| Ohio Concrete | Full exam only | USD 330 Ohio Concrete member / USD 490 non-member |
| Ohio Concrete | Review, workbook and exams | USD 450 member / USD 700 non-member |
The workbook
The current study workbook is CP-19, 25th Edition (2022). ACI also accepts the 23rd and 24th editions because their technical basis is identical, so a used older copy is acceptable. The 25th-edition workbook is listed at USD 71 for ACI members and USD 136 for non-members, and it excludes the ASTM standards themselves. ACI notes first-printing errata, but the linked errata document requires sign-in, so check it if you own a first printing. ACI also sells a separate on-demand preparation course, but it does not award certification.
Scheduling
Sessions are scheduled by sponsoring groups, so availability depends on where you live. The Las Vegas Chapter, for example, lists an October 24, 2026 session. Because the one-year window starts running once you take your first exam component, plan both exams close together. More on timing is in CSTT Exam Dates 2026.
Retakes, Deadlines and Recertification
- One-year window: Written and performance examinations must both be passed within one year.
- Failed written exam: Re-examination covers the entire written component.
- Failed performance exam: A failed procedure earns a second same-day trial; subsequent re-examination covers the entire performance component.
- Window expires: If one year passes before both are completed, both components must be retaken.
- Certification term: Five years.
- Recertification: Passing both examinations again.
Because recertification means retaking both exams rather than submitting continuing-education credits, treat your first certification as the start of a five-year skills cycle. Keep your workbook and notes; you will want them again.
A Four-Week Plan Built Around the Standards
This is the only scheduling section in this cheat sheet. For the longer methodology, see the CSTT Study Guide. The sequence below follows the standards because capping knowledge feeds directly into compressive testing.
Capping Foundations (C617 and C1231)
- Learn cap requirements and defects, then pad and retainer rules.
- Build a bonded-versus-unbonded comparison from memory.
Compressive Strength (C39)
- Drill measurement, area, loading-rate and fracture-pattern questions.
- Run calculations with a simple calculator.
Flexural Strength (C78)
- Memorize apparatus layout and the fracture-location rule.
- Practice the modulus of rupture calculation until automatic.
Integration and Practicals
- Take timed mixed question sets and check each standard against the 60% floor.
- Rehearse each procedure end to end against a checklist.
When you take timed sets, score each standard separately. A single combined percentage can hide the weak area that would actually fail you. Try our free CSTT practice tests and review misses by standard rather than by total score.
Frequently Asked Questions
ACI's program page describes approximately 40 questions with at least eight per standard, while the certification policy describes approximately 35-40 with 8-10 per standard. Treat the count as an approximate range rather than a fixed number.
You need at least 60% on each of the four standards and at least 70% overall. Missing either threshold means a failed written exam, regardless of how strong your other results are.
No. There is no specific education or work-experience prerequisite. Eligibility details are covered in CSTT Requirements 2026, and career context is in CSTT jobs.
A failed procedure permits a second same-day trial. If you still do not pass, you must later re-examine the entire performance component, and both exams must be completed within the one-year window.
Five years. Recertification requires passing both the written and performance examinations again. To judge whether the investment pays off, see Is the CSTT Certification Worth It? and the CSTT Salary Guide.