Cement supply is a staple of New Zealand’s construction industry. In 2014, over one million tonnes was supplied to the construction and infrastructure sectors.
The structure of the cement industry has changed considerably with cement imports increasingly commonplace. This shift will continue as Holcim (NZ) Ltd move to an import model in 2016.
New Zealand’s cement Standard, NZS 3122 Specification for Portland and Blended Cements (General and Special Purpose), has recently been subject to amendment, with the updated version published in December 2014. Whilst NZS 3122 has served the industry well, the amendments further strengthen the requirements for this important construction material.
The Standards committee, consisting of representatives from the cement and concrete industry together with representatives from IPENZ and the University of Canterbury, incorporated into the latest edition requirements for sampling and testing, and a provision to restrict the total alkali content of the cement.
These new provisions, together with their rationale, are described below.
Total Alkali Content
In NZS 3122 Table 1, the first amendment introduces a total alkali content requirement expressed as sodium (Na2O) equivalent for type GP (General Purpose) and HE (High Early strength) cement.
Aggregates susceptible to the potentially deleterious effects of Alkali Silica Reaction (ASR) exist in certain parts of New Zealand. Whilst provisions for minimising the risk of ASR are given in the CCANZ publication TR3 Alkali Silica Reaction: Minimising the Risk of Damage to Concrete: Guidance Notes and Recommended Practice, one such provision is to limit the maximum total concrete alkali content when potentially reactive aggregates are employed. The amendment to NZS 3122 limits the alkali content to 0.6% or less which will assist in achieving the limit on concrete alkali content. Importantly however, it does not replace the need to include the alkali from other sources such as admixtures, and it is imperative that the recommended procedures in the aforementioned TR3 are still followed (as indeed they need to be when General Blended, Low Heat and Shrinkage Limited cement types are used).
Interestingly, where there is specific prior agreement and notification of the purchaser or cement user, the cement manufacturer or supplier may supply cement which exceeds this maximum alkali limit. Whilst this may seem counter-intuitive, it should be remembered that where aggregates which are deemed to be non-reactive are used, no precautions are necessary in terms of ASR. Non-reactive aggregates are commonplace in New Zealand.
Under the new amendment, the supplier must report the alkali content to two decimal places, and the highest single value that is acceptable is 0.64%.
Sampling and Testing
Sampling and testing frequencies are now introduced in NZS 3122 Appendix E. There were no provisions in the previous version, although it should be stressed that the two cement companies, Golden Bay Cement and Holcim (NZ) Ltd, which have historically supplied the lion’s share of New Zealand cement, have always tested and reported routinely.
Furthermore, it is a new requirement that all cement sampling be undertaken at the point of entry into New Zealand prior to distribution to the New Zealand market. This ensures complete traceability between the cement consignment and its certification. It is also a requirement that any cement supplied out of sample date shall be subject to re-sample and re-test by the supplier. Again this tightens up the previous requirements.
Appendix E also gives minimum sampling and testing frequencies for ‘proven’ and ‘unproven’ sources. A source is proven where there is at least six months of data obtained in accordance with NZS 3122. All testing has to be undertaken by a laboratory independently accredited by a member of the International Laboratory Accreditation Cooperation, such as NATA or IANZ. Unsurprisingly, sampling and testing frequencies are significantly more onerous for unproven sources.
As in previous versions of NZS 3122, cement properties are classified as ‘specified’ or ‘reportable’. Of the eight reportable properties, the supplier will report test results as nominated by the purchaser or user. The supplier does not have to report the reportable properties unless requested.
At a time of dynamic changes in New Zealand’s cement industry it is pleasing to see that the cement Standard has kept pace to help maintain confidence in this vital construction material.