PROYECTO EJECUTIVO:
2.6 RECEPCIÓN DE LOS TRABAJOS
The method of determining the volume of concrete supplied is related to the mass of concrete delivered divided by the average mass per cubic metre of the concrete. Testing for volume is not usually carried out unless it is specified. NZS 3104 allows a tolerance of 2% on under supply for the volume delivered. The Standard notes that if the volume of concrete is to be measured at any time then the method of determining the mass of supplied concrete will need to be specified.
Concern is frequently expressed because on site the ordered volume does not fill the forms the volume of which, it is assumed, is known. The reasons why this may occur include: spillage and wastage on site, variation in dimensions of the
Chapter 7 Supply of Concrete
Guide to Concrete Construction 7.6
forms as constructed and deflection of forms, and the compaction of concrete.
7.2.5 Slump
Where a strength grade concrete is specified, NZS 3104 requires that a slump test be carried out on each strength sample. Generally, additional slump tests will need to be performed if water is added to the concrete after discharge from the mixer has commenced. Slump tests will have to be performed if slump is one of the specified parameters.
Where the slump of the sample, as determined in accordance with NZS 3112, is not within the limits shown in Table 7.2, a repeat test may be made from the same sample, or from a fresh sample taken and tested immediately.
Table 7.2 Permissible tolerances on slump (Table 2.6 in NZS 3104) Tolerance Target slump (mm) Representative Sample (mm) Snatch Sample (mm) 60 or less ±20 ±20 70 - 110 ±20 ±30 120 and above ±30 ±40
7.2.6 Supervision
The mix designs and quality control are supervised by the plant engineer who must be a Chartered Professional Engineer or Registered Engineering Associate experienced in these functions. If not resident at the plant he must visit often enough to fully discharge these responsibilities. In his absence 'the person in continuous control', usually the plant manager or supervisor, has responsibility for quality matters.
NZS 3104 places much emphasis on the monitoring role of the supervision. Routine tests are required to be under the continuous review of the supervisor and evaluated by the engineer. Other control tests are to be reported to the engineer at least monthly, except that non-complying results are to be reported Immediately
7.3
CONTROL AND ASSURANCE
TESTS
NZS 3104 sets out or refers to testing methods, testing frequencies and criteria to be achieved in respect of the following:
Slump test.
Yield test.
Air content test.
Performance test for mixers and truck mixers.
Strength tests for proof of control.
Evaluation of strength test results.The specifier's control of the concrete production varies with the type of concrete specified i.e. Normal or Special.
If Normal concrete is specified the specifier relies on the testing being carried out by the supplier in order to comply with NZS 3104. This is why it is important that the specifier has confidence that the supplier's quality control programme has been independently checked by an organisation like the NZRMCA Plant Audit Scheme.
However with Special concrete, the specifier needs to discuss the testing regime that is needed for the specific project. Usually the specifier will require testing from the specified project under construction. Often these Special concretes will not have sufficient test results for full statistical analysis which is why additional testing is likely to be required. The testing may not always be for compressive strength buy may be for other properties such as abrasion resistance, marine durability, permeability etc.
For extra information see Chapter 20.
7.4 AUDIT CERTIFICATION
NZS 3104 sets out the requirement for an independent audit of the quality control measures being undertaken by the plant.
This can be done by an independent Auditing Engineer or in the case of the majority of members of the New Zealand Ready Mixed Concrete Association (NZRMCA), by an independent committee of professional engineers. This committee includes members representing IPENZ and the New Zealand Concrete Society. The current membership can be checked by reference to www.cca.org.nz.
Each year the statistics of plant performance are sent to the Plant Engineer/Plant Supervisor for review. Every second year the plant is physically inspected for compliance.
If the Plant Audit Committee is satisfied that the information demonstrates compliance with NZS 3104, then the Audit Certificate will be issued. The Certificate is valid for 12 months only. An up to
Chapter 7 Supply of Concrete
date list of Audited Plants is held and can be checked by reference to www.cca.org.nz.
The Committee can withhold a certificate, require a special inspection which may or may not be pre- notified and issue an Interim Certificate which is valid for three months only.
During the course of the year, quarterly statistics of testing are required to be submitted which again
can result in Plants defaulting on testing frequency to be removed from the list of Audited Plants. The NZRMCA Audit Scheme is itself independently audited each year by Bureau Veritas Quality International (BVQI) for compliance with ISO 9001.
Figure 7.2 shows the Certificate of Audit displayed
by an Audit Certified Plant in the NZRMCA scheme.
Chapter 8 Handling and Placing
Chapter 8 Handling and Placing