QA vs QC in Construction: Who Checks What on Site

In construction, quality assurance is the system of plans and procedures that prevents defects, and quality control is the checking of the work that finds them. QA writes the rules before the work starts. QC inspects and tests the work as it happens. A civil site needs both, and the clearest way to see the difference is to follow one concrete pour and one compacted layer of soil from plan to result.

Facts about the ACI and ASTM pages were read on 1 November 2026. Test methods are named by number only, because editions change, and acceptance limits always come from the project specification.

Two jobs that are often confused

Quality assurance and quality control sound alike, and job titles blur them. The honest split is by timing. QA happens before and around the work: the project quality plan, the inspection and test plans, the method statements, the approval of materials and the control of documents. QC happens during and after: the slump test, the cube or cylinder sample, the inspection of reinforcement, the field density test.

A third piece closes the loop. When a check fails, a non-conformance report records what went wrong, why, and what will stop it happening again. That report is QA learning from QC.

The inspection and test plan is where they meet

An inspection and test plan, or ITP, lists each activity, the check to be made, the method or standard, the acceptance rule and the record. It also marks the type of check. A hold point means work stops until a named person signs the check. A witness point means the inspector may attend, and work may continue if they do not. A review point means a document is reviewed.

The ITP is a QA document, because someone writes it before the work. Yet every line in it is a QC check. That is why site teams talk about QA/QC as one job.

A worked example: one compacted layer

Here is a worked example of a QC result that decides whether the next layer can be placed. A sand cone test measures the in-place density of a compacted soil layer. The sand-cone method is described on the ASTM D1556 page. The inputs below are example values, and every step was computed in a script.

The jar of calibrated sand weighs 12,500 g before the test and 4,360 g after. The cone holds 1,720 g of sand. The sand's calibrated density is 1.45 g/cm3. The soil dug from the hole weighs 8,610 g wet, and its moisture content is 9.1 percent. The laboratory maximum dry density for this soil is 1.94 g/cm3.

1. Sand in the hole is 12,500 - 4,360 - 1,720 = 6,420 g.
2. The hole volume is 6,420 / 1.45 = 4,427.6 cm3.
3. The wet density is 8,610 / 4,427.6 = 1.945 g/cm3.
4. The dry density is 1.945 / (1 + 0.091) = 1.782 g/cm3.
5. Percent compaction is 1.782 / 1.94 = 91.9 percent.

Now compare with the specification. If it requires 95 percent, the target dry density is 0.95 x 1.94 = 1.843 g/cm3, and this layer falls short by 0.061 g/cm3. The QC engineer does not place the next layer. The contractor recompacts, and the test is repeated. If the specification asks for a different percentage, the answer changes, so read it first.

Concrete: the same split in action

For a concrete pour, QA produces the method statement, the approved mix and the ITP with its hold point before concreting. QC checks the delivery ticket, tests slump and temperature, and makes the cylinders or cubes. ACI describes its Concrete Field Testing Technician, Grade I programme as covering basic field tests on fresh concrete. These include sampling, temperature, slump, density, air content, and making and curing specimens.

The ASTM C39 page notes that compressive strength depends on how the specimens are prepared and cured. That is why QC cares about the way a cylinder is made and stored, and why QA writes a procedure for it.

What an ITP looks like in practice

A short extract shows how one document joins the two jobs. The rows below are examples for a concrete slab. Real ITPs cite the project's own specification and standards, so treat the wording as a pattern, not a template to copy.

Notice that the first row stops work until it is signed. That is the hold point doing its job. The other rows allow work to continue while a record is built.

Common failures and the system fix

QC finds the same few failures again and again. A slump that is out of tolerance often traces to water added on site. A low cylinder result may come from poor curing of the sample rather than poor concrete. A failed compaction test often follows a layer that was too thick or too wet.

QA turns each finding into a prevention. Water added on site leads to a rule that only the batching plant adjusts the mix. Poor sample curing leads to a procedure and a labelled curing tank. A thick layer leads to a maximum layer thickness in the method statement. Each fix lives in a document, so the next team inherits it.

Who does what on a project

On the contractor's side, a quality manager owns the system and site quality engineers carry out checks. On the consultant or client side, an inspector or resident engineer reviews and witnesses. Third-party laboratories often run the tests. The contractor still owns the quality of its work.

Titles vary by company, so read what a role does rather than what it is called. The same person may be called a QA/QC engineer, a quality engineer or a site inspector.

Records are the product

An inspector cannot see yesterday's pour, so the record is the only proof that a check took place. A good record names the activity, the location, the date, the method, the result, the limit and the person who signed. Photographs help, but they do not replace the written result.

Keep records in one place and give each a number. When a consultant asks for the cylinder results for a level, you should find them in a minute. That speed is a quality measure in itself.

Learn the site workflow free

The free Civil QA/QC Engineer: Concrete, Steel and Earthworks course follows one hospital project from the quality plan to handover. It has twelve study modules and a final assessment, with about 8.4 hours of video. Practise the sand cone arithmetic and the concrete result check in a spreadsheet as you go.

The civil quality course is a free course with a verifiable certificate of completion, and anyone can check a certificate on our verification page. It is not a testing technician certification, it gives no professional licence, and EDWartens is not affiliated with ASTM or ACI.

Keep a portfolio of records

Hiring teams like to see how you record work. Draft a one-page ITP for a slab pour, a sample non-conformance report and a results sheet for the layer above. Use a fictional project so you share nothing confidential. Our guide to building an engineering portfolio from course projects shows how to present them, and our post on electrical QA/QC engineers shows the same split on the electrical side.

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