The request for an opinion from the Superior Council of Public Works
The MASTER Association has reported a recurring problem to the Superior Council of Public Works: the management of amnesty practices. In particular, a clarification was requested on the acceptance, by the Civil Engineering offices, of samples of materials (such as concrete and steel bars with improved adhesion) whose correct traceability is based on simple sworn statement from the owner of the propertypursuant to theart. 47 of Presidential Decree n. 445/2000.
The question mainly concerns theextension of the static suitability certificate in amnesty practiceswhich are regulated byart. 35 of law 47/85. However, the request for clarification led to a broader analysistouching on general aspects of the 2018 NTCs relating to the use of samples of materials not correctly traced.
The importance of material traceability
One of the key points raised in the Council opinion concerns the sample traceability. The 2018 NTC and other technical standards closely correlate theeffectiveness of controls on materials to the correct identification and traceability of specimens (concrete samples, steel bars, profiles, etc.).
In the absence of traceability, the laboratory responsible for carrying out the tests must issue a report clearly indicating the lack of identification. This report must contain a statement explaining the results obtained cannot be included in the statistical set provided for acceptance checks.
What to do if tests are performed late
Another topic addressed concerns tests carried out late compared to the date of sampling. The 2018 NTCs (par. 11.2.5.3) establish that the compression tests on concrete samples they must be carried out within the 45th day from the collection date. If this deadline is not respected, it is mandatory to resort to further investigations and assessmentsincluding on-site sampling.
The compression tests, in these cases, must be carried out according to the UNI EN 12390-3:2009 standards, and the new samples must be foreseen in the specific investigation plan of the work. This plan, therefore, must be drawn up in such a way as to take into account the actual conditions encountered on siteintegrating initial checks when necessary.
Knowledge levels and number of withdrawals
For buildings that have not been subject to building amnesty and for which no structural project has been filed (as required by theart. 65 of Presidential Decree 380/2001), the opinion refers to Chapter 8 of the 2018 NTC, which deals with existing buildings. In particular, the Tables C8.5.IV and C8.5.V, which indicate i levels of knowledge required depending on theinformation available and the correspondents permitted analysis methods.
These tables also provide guidelines for determining the minimum number of withdrawals to be performed for each primary structural element in order to reach a pre-established level of knowledge. It is clear, therefore, that the minimum number of withdrawals must be established on the basis of investigation plan specific on the structural elements of the work, which must take into account both the actual operating conditions and the corresponding level of knowledge and the consistency of the crack pattern and of characterization and quantification of material degradation.
In conclusion
The opinion concludes by confirming the need to rigorously apply the provisions of the NTC 2018 regarding the control of materials and the verification of the static suitability of the structures. It is reiterated that, in the case of late or untraceable samples, it is essential to proceed with further investigations and that the regulatory indications clearly establish the methods for carrying out the tests and the minimum number of checks to be carried out.
Finally, the Superior Council of Public Works invites the questioner to disseminate these indications as widely as possible among its members, so that technicians can correctly apply the rules regarding checks on materials and static suitability.