According to regulations, the following test blocks, test pieces and materials must be witnessed and submitted for inspection:

1. Concrete test blocks used for load-bearing structures;

2. Masonry mortar test blocks for load-bearing walls;

3. Steel bars and connecting joint test pieces for load-bearing structures;

4. Bricks for load-bearing walls and small concrete blocks;

5. Cement used for mixing concrete and masonry mortar;

6. Admixtures used in concrete for load-bearing structures;< /p>

7. Waterproof materials used underground, on roofs, and in toilets and bathrooms;

8. Materials or specimens used for road subgrade and surface layers;

9 , In municipal projects, materials or components that the owner or the project director of the supervision unit consider to be closely related to quality;

10. Other test blocks, test pieces and materials that must be witnessed for sampling and inspection according to national regulations.

The construction unit or the supervision unit of the project should submit the "Authorization Letter of Witness Unit and Witness Personnel" to the construction unit, project supervision quality supervision station and project inspection unit. The authorization letter should indicate the witness unit of the project and the name, certificate number, and witness number of no less than 2 persons. When an inspection unit accepts an entrusted inspection task, the inspection unit must fill in the entrustment form. The witness should present the "Witness Certificate" and sign the inspection entrustment form. All testing units must implement a password management system.

To sum up, when the sampling personnel of the construction enterprise collect and prepare samples on site, witnesses must be present to witness, and the samples should be monitored and taken together with the inspection personnel entrusted to submit them for inspection. Effective sample sealing measures or sending samples to testing units.

Legal basis:

Article 59 of the "Construction Law of the People's Republic of China"

Construction enterprises must comply with engineering design requirements, construction In accordance with technical standards and contract stipulations, building materials, building components and equipment shall be inspected and unqualified ones shall not be used.

Article 29 of the "Regulations on Quality Management of Construction Projects"

Construction units must carry out construction materials, building components and equipment in accordance with project design requirements, construction technical standards and contract stipulations. Inspection of commercial concrete shall be carried out, and the inspection shall be recorded in writing and signed by a designated person; if it has not been inspected or failed to pass the inspection, it shall not be used.