Concrete Structure Inspection

According to NP EN 206-1 and EN 13670, concrete must comply with the specified strength class (e.g. C25/30, C30/37). Conformity is assessed on standardised specimens (cubes or cylinders) tested at 28 days according to EN 12390-3. The delivery ticket must state the strength class, exposure class and consistency class.

1. Check that delivery tickets show the correct strength class (e.g. C25/30) as per the structural design

2. Confirm that test specimens (cubes/cylinders) were cast during concreting according to EN 12390-1

3. Review the 28-day test results — the mean strength must exceed fck + margin according to NP EN 206-1 Table 14

4. Verify that the exposure class matches the environmental conditions (classes XC, XD, XS, XF, XA)

5. Check the consistency class (S1–S5 slump or F1–F6 flow) upon delivery

- Concrete delivered with incorrect strength class

- Test specimens not collected or improperly cured

- Water added on site reducing the strength class

- Exposure class not matching actual conditions (e.g. XF class in freeze-thaw zones)

According to NP EN 1992-1-1 Section 4.4.1, the minimum nominal cover (cnom) depends on the exposure class, structural class and bar diameter. Typical cnom ranges from 25 mm (XC1) to 55 mm (XS3). Reinforcement must be placed in accordance with the design drawings, with tolerances according to EN 13670 Table 11.

1. Measure concrete cover with a covermeter — must meet the design cnom (typically 25–55 mm)

2. Verify that bar diameters match the structural drawings

3. Check bar spacing against the design — use a tape measure between bars

4. Verify that anchorage lengths meet requirements (per NP EN 1992-1-1 Section 8.7, typically 40–60 bar diameters)

5. Confirm that spacers maintain the correct cover during concreting

- Insufficient cover leading to corrosion risk

- Incorrect bar diameters or missing bars

- Inadequate anchorage lengths at critical sections

- Spacers displaced during concreting

According to EN 13670 Section 8, formwork must be sufficiently rigid to maintain shape during concreting. Surface finish classes range from F1 (basic) to F5 (special). Tolerances for completed elements are given in EN 13670 Table 10 — e.g. columns: verticality +/-h/300 (min. 15 mm), beams: +/-L/500.

1. Check dimensional accuracy of completed elements against EN 13670 Table 10

2. Confirm column verticality with plumb line or level — tolerance +/-h/300

3. Inspect the surface for honeycombing, blowholes or cold joints

4. Assess the surface finish class against the specification

5. Check that formwork ties and embedded items are properly sealed or removed

- Honeycombing due to insufficient vibration or overly dry mix

- Cold joints from delays in concreting

- Formwork deformation under hydrostatic pressure

- Formwork tie holes not properly sealed

According to EN 13670 Section 8.5, concrete must be cured for a minimum period depending on the ambient temperature and cement type. For CEM I at 15 degrees C, the minimum curing is 3 days for exposure class XC1, and 7 days for XC2–XC4. Early-age thermal cracking must be controlled according to NP EN 1992-1-1 Section 7.3. In Portugal, special attention must be paid to high summer temperatures which accelerate moisture loss.

1. Check that the curing method (wet curing, curing compound or membrane) is being applied

2. Confirm that curing started immediately after finishing (within approx. 1 hour)

3. Confirm that curing duration matches the exposure class and ambient temperature

4. In cold weather (<5 degrees C), check that thermal protection or heating measures are in place

5. Check for early-age thermal cracking in thick sections

- No curing — rapid surface drying causes shrinkage cracking

- Curing discontinued prematurely

- Cold weather concreting without protection (frost damage)

- Thermal cracking in thick pours (>500 mm) without cooling measures