Canterbury Today (Nov / Dec 12) Quality Assurance in Ready Mixed Concrete

04 Dec 2012

Rob Gaimster
Cement & Concrete Association of New Zealand (CCANZ)

With a period of intense construction anticipated across residential, commercial and civil sectors in Canterbury over the coming years it is crucial that building materials and products can be relied upon.

As the shadow of leaky buildings still looms over the wider construction industry issues of material and product performance must be addressed to ensure confidence amongst architects, designers, engineers, builders and their clients.

In terms of quality, New Zealand consumers of ready mixed concrete can take comfort in the knowledge that concrete produced and supplied by a plant certified under the world-class New Zealand Ready Mixed Concrete Association (NZRMCA) Plant Audit Scheme meets high quality standards.

The NZRMCA was formed nearly half a century ago in 1963, and continues to grow in size.  Today, 46 companies now control around 185 ready mixed concrete plants throughout New Zealand.  Quality control was the prime reason for the formation of the NZRMCA, and in turn the creation of the Audit Scheme.

For a time the Ministry of Works ran a similar scheme, however when the iconic Government department was dismantled in the 1980s the Audit Scheme remained the only scheme in operation.

The Audit Scheme is available to NZRMCA members, and most avail themselves of the opportunity. The Audit Scheme is audited to ISO 9001 by Bureau Veritas Quality International (BVQI). Full details of the scheme are set up on an independent website:

The Audit Scheme operates to audit NZRMCA member’s ready mixed concrete plants as defined in NZS3104 Concrete Production. The Audit Scheme is of great convenience to the specifiers and purchasers of concrete. It provides a rigorous audit of the quality systems in place at a ready mixed concrete plant.

When using concrete from non- Audit Scheme plants, the purchaser is responsible for the implementation of the audit process required by NZS3104 to ensure compliance with NZ Building Code.

The Audit Scheme Plant Audit Committee comprises five or more Professional Engineers and Registered Engineering Associates from organisations such as IPENZ, all with extensive experience in concrete production.

The establishment and monitoring of the production of a ready mixed plant are requirements for the supply of structural concrete for compliance with NZS3109 Concrete Construction and NZS3104, and in turn the NZ Building Code.

NZS3104 is the standard used by the Plant Audit Committee to audit a ready mixed plant. Compliance with NZS3104 also requires compliance with a number of other Standards, such as NZS3112 Methods of Test for Concrete.

Plants report quality performance data to the Plant Audit Committee annually and are subject to a detailed annual review of data, together with an onsite audit every second year. Site audits may also be carried out at any time.

Among performance criteria audited are:
• Mean concrete strengths and coefficients of variation
• Aggregate quality by testing and monitoring
• Weigh scale calibration and accuracy
• Mixer efficiency tests
• Laboratory equipment calibration
• Production and testing record keeping
• Technician training
• Plant operator performance
• Effectiveness of plant engineer’s monitoring of quality controls

In addition to the above, the frequency of testing within each quarter must be submitted to the Plant Audit Committee. Failure to maintain testing requirements can result in the withdrawal of an Audit Certificate. Performance standards of all plants in the scheme are under regular review. Certificates of Audit are issued for a period not exceeding 12 months. The current status of plants is updated on the PAS website.

Where plants fail to meet the criteria, their Audit Certificate is removed and noted on the plant list. It is necessary for such plants to resubmit to an initial reassessment with at least 30 results indicating compliance with NZS3104.

Members of the NZRMCA are free to elect to use another authority to classify their plants, and award an Audit Certificate. Other such authorities work outside the jurisdiction and ISO Certification of the NZRMCA Audit Scheme.

The benefits of concrete are well documented. It doesn’t rot for example, is inherently fire resistant, is largely maintenance free, extremely durable and in passive solar design affords a significant degree of thermal comfort.

When concrete’s unique attributes are coupled with a world-class product assurance scheme, such as the Audit Scheme, consumers of New Zealand’s ready mixed concrete can take great confidence in their building material.

Article appeared in Canterbury Today magazine (Nov / Dec 2012).