Construction materials and quality control
Construction materials and quality control
This domain tests material selection, acceptance testing and site quality control: cement type, aggregate grading, water/cement ratio, concrete strength class, slump, cube sampling, reinforcing steel and thermal insulation. Quality control is evidence-based: test results, certificates and traceability, not visual impression alone.
Core rules
- Concrete strength is specified as a characteristic 28-day cube or cylinder strength; the water/cement ratio and curing temperature control gain.
- Sample fresh concrete representatively, record slump and temperature, and make cubes from the same batch. Acceptance uses groups of results and specified criteria, not one favourable cube.
- Reinforcing steel must match the specified grade and diameter; check mill certificates, surface condition and correct lap lengths.
- Insulation performance depends on dry installation and continuous layers; compressed or wet insulation loses thermal resistance.
- Store cement dry and use it within its shelf life; retest if storage is doubtful.
Worked example A 150 mm concrete cube fails at 540 kN. Area = 150×150 = 22,500 mm². Compressive strength = 540,000 N ÷ 22,500 mm² = 24.0 N/mm². If three cubes from the batch give 23.5, 24.0 and 24.5 N/mm², the mean is 24.0 N/mm². The individual 24.0 MPa result is not automatically the characteristic strength: acceptance requires the specified group criteria and the specified curing age. If the specified class is C25/30 at 28 days, this batch needs review, not automatic rejection on one cube.
Traps that cost marks
- Treating a single cube result as the characteristic strength.
- Testing cubes cured in the wrong conditions or tested at the wrong age.
- Accepting rebar by diameter alone without grade or certificate.
- Ignoring wet insulation or poor compaction behind it.