Concrete Structure Inspection

In accordance with EN 206, EN 13670 and NF EN 206/CN (French National Annex), the concrete must conform to the specified strength class (e.g. C25/30, C30/37). Conformity is assessed on standardised cube or cylinder specimens tested at 28 days per EN 12390-3. The delivery note must state the strength class, exposure class and consistency class. DTU 21 specifies site conformity control procedures.

1. Check that delivery notes indicate the correct strength class (e.g. C25/30) matching the structural design

2. Ensure that test specimens (cubes/cylinders) were taken during casting per EN 12390-1

3. Review 28-day test results — mean strength must exceed fck + margin per EN 206 Table 14

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

5. Check consistency class (S1-S5 slump or F1-F6 flow) at delivery

- Concrete delivered with incorrect strength class

- Test specimens not taken or improperly cured

- Water added on site reducing the strength class

- Exposure class not suited to actual conditions (e.g. XF class absent in freeze-thaw zone)

In accordance with 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 execution drawings with tolerances per EN 13670 Table 11. DTU 21 supplements these requirements with specific provisions for the French market.

1. Measure concrete cover with a covermeter — must comply with the designed cnom (typically 25-55 mm)

2. Verify that bar diameters match the structural drawings

3. Check bar spacing in accordance with design — measure with tape between bars

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

5. Ensure spacers and chairs maintain correct cover during casting

- Insufficient cover leading to corrosion risk

- Incorrect bar diameters or missing bars

- Lap lengths too short in critical sections

- Spacers displaced during concrete casting

In accordance with EN 13670 Section 8 and DTU 21, formwork must be sufficiently rigid to maintain its shape during concreting. Surface finish classes range from F1 (basic) to F5 (special). Tolerances for finished elements are given in EN 13670 Table 10 — e.g. columns: plumbness +/-h/300 (min. 15 mm), beams: +/-L/500. DTU 21 defines surface finish classes specific to the French context (ordinary, standard, high quality).

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

2. Verify column plumbness with plumb bob or spirit level — tolerance +/-h/300

3. Inspect surfaces for honeycombing, blow holes or cold joints

4. Assess the surface finish class achieved against project specifications

5. Verify that formwork tie rods and inserts are correctly filled or removed

- Honeycombing due to poor vibration or overly dry concrete mix

- Cold joints from interrupted casting

- Formwork deformation under hydrostatic pressure of fresh concrete

- Formwork tie holes not properly filled

In accordance with EN 13670 Section 8.5 and DTU 21, concrete must be protected and cured for a minimum duration depending on ambient temperature and cement type. For CEM I at 15 degrees C, the minimum curing duration is 3 days for exposure class XC1, and 7 days for XC2-XC4. Early-age thermal cracking must be controlled per EN 1992-1-1 Section 7.3.

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

2. Ensure curing commenced immediately after finishing (within approximately 1 hour)

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

4. In cold weather (< 5 degrees C), verify that insulation or heating measures are in place

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

- No curing applied — rapid surface drying causes shrinkage cracking

- Curing interrupted too early

- Concreting in cold weather without protection (frost damage)

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